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Mahesh.s -
Posted 5 days Ago

My T'

  My T'"/est|

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Sreedevi.s -
Posted 6 days Ago

Interview: Jolanta Skeivelienė, Head of the Railway Industry Department, Blue Bridge Code

Jolanta Skeivelienė, Head of the Railway Industry Department at Blue Bridge Code, explains how the CargoRail solution can help rail freight operators simplify their processes, avoid errors and save time. What are the main reasons a rail freight operator should consider digitalising its processes? Digitalisation is a good habit, like diet or exercise. It helps an organisation stay fit and strong and outrun its competitors. But as with any practice, it can be overused and not deliver the desired results. That is why we see ourselves as partners to help organisations grow and adapt to changing business conditions. In implementing CargoRail, we usually follow these steps to ensure railway operators obtain value from digitalisation : 1. Implementing basic operations This is a vital, but often overlooked, step which includes key data and change management processes. It can take months, sometimes more than a year even, for the people in an organisation to get used to a new way of working, reporting, and managing. We work together closely with everyone involved to ensure an organisation is ready to proceed. Advertorial Interview: Jolanta Skeivelienė, Head of the Railway Industry Department, Blue Bridge Code Jolanta Skeivelienė, Head of the Railway Industry Department at Blue Bridge Code, explains how the CargoRail solution can help rail freight operators simplify their processes, avoid errors and save time. What are the main reasons a rail freight operator should consider digitalising its processes? Digitalisation is a good habit, like diet or exercise. It helps an organisation stay fit and strong and outrun its competitors. But as with any practice, it can be overused and not deliver the desired results. That is why we see ourselves as partners to help organisations grow and adapt to changing business conditions. In implementing CargoRail, we usually follow these steps to ensure railway operators obtain value from digitalisation : 1. Implementing basic operations This is a vital, but often overlooked, step which includes key data and change management processes. It can take months, sometimes more than a year even, for the people in an organisation to get used to a new way of working, reporting, and managing. We work together closely with everyone involved to ensure an organisation is ready to proceed. After this step, an organisation can operate faster, with fewer errors and greater efficiency, and the workplace is decentralised (work from anywhere is possible). Onboarding of new employees is faster and more efficient as well. New speakers join Digital Rail Revolution - 15-16 September. Join Global Railway Review’s two-day online event that gives you unparalleled access to the latest information, vision and innovation within the rapidly evolving digital rail industry. We currently have a fantastic super early bird price* on offer – so make sure that you register your place today and join your industry peers to discuss the biggest issues and topics facing railways today. If you work for a rail infrastructure manager, train operating company, public transport authority, transit agency, local authority, industry association or you are a government official, then you can attend this online event for free. Check out our speaker line-up! Don’t delay and make sure you register your place today! *Super early bird discount expires on 4th August 2021. 2. Automation and reporting This is the cherry on the cake. Once the client trusts its data and CargoRail as a solution, we start rolling out automated processes. They reduce the amount of work needed and ensure data quality. The role of the client’s employees changes from execution to monitoring and correction. At this stage, less work is required of the back office and the quality of work increases. Automated mechanisms mean fewer employees are needed to do the same work. Overall, processes become easier to control and predict. At the same time, integrations with third parties, such as other countries’ customs agencies, optimise our client’s work and that of their clients and partners. 3. Measuring and adjusting When the client is ready to move to the next stage, we agree on the goals and the processes to achieve them. We usually work together to find solutions for specific business situations and implement them through software and process changes. Then we use analytics tools to measure success and improve or fine-tune the solution At this point, the client can tackle new opportunities faster than competitors and is focused on new horizons, not past problems. How can the CargoRail solution help the rail freight sector adapt to changes due to the coronavirus pandemic? It helps in many ways, but I would point out three in particular. First of all, because of how CargoRail works and is accessible via web browser, all roles can be carried out without close contact. So CargoRail makes it possible to work in a safe and mobile way without losing effectiveness. Secondly, management and the back office can monitor and assist field operations thanks to near real-time data availability. And thirdly, data integration and analysis capabilities enable smooth processes and improvement programmes even in the middle of a pandemic.  

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Deepu Dharmarajan -
Posted 89 days Ago

TRAIN DESCRIBERS

  CONTENTS 1. Introduction 2. Berth to Berth Train Describers 3. Facilities and Terminology of a Train Describer 4. Train Describer Planning and Design 5. Train Describer Stepping Tables 6. Processing Systems 7. Display Systems 8. Signalling Inputs 9. Peripheral and Ancillary Systems 1.  INTRODUCTION As well as knowing of the existence  of  a train  within  his control  area, the signalman  needs to know something about its identity. The type or class of train  and,  when  necessary,  the route to be taken at the next junction,  is  adequate  information  in  mechanically  signalled areas (where the area of control is very  localised).  Train  movements  are generally  recorded in the Train Register, which also provides a permanent record  as  a  reminder  to  the  signalman and to aid investigation of any incident. The train register, the block bell and a working timetable are usually adequate  for a small  signal box. With power operated signalling and automatic signals it became  possible  for several trains to be in the sections between signal  boxes,  creating  the  possibility  of confusion. More information was required. Magazine type train describers were introduced. They operated by transmitting a series of pulses, similar to an impulse dialling telephone, along just one or two line pairs. The display gave a brief description of the  trains  approaching  on  each  line and  the  last  train  departed on each line. Up to three approaching trains could be displayed and  further  stored  if necessary. The form of the display was an illuminated light against a fixed description label. 2. BERTH TO BERTH TRAIN DESCRIBERS The limit was eventually reached where the description of trains approaching became insufficient. Trains would remain on the signalman's panel for considerable  time.  Several trains could be under the control of one signalman. It was therefore necessary to provide a description of each train as it progressed through the control area. An alphanumeric display associated with each signal on the panel generally provides sufficiently detailed information. The characters may be used to indicate the class, route and sequential number of each train. Must railways haYc a st;md:nd fmm:11 for tuin idrntific1tilln The BR. s·stcm consists of Train describers may be restricted to displaying train  numbers  only  in a valid format or may be capable of displaying any combination of characters. Together with the 4-character berth display system came the automatic stepping of the description along the control panel, controlled by the passage of the train. The basic train describer system therefore consists of the following:-   A facility to store the train description or identity in a standard alphanumeric format. Each store, usually referred  to  as  a  berth  or  address  is  normally  associated  with a particular signal section. Each address may be empty or may hold a   A means of moving train descriptions  from  berth to berth in step with the movement  of   A means of displaying the descriptions held in some or all of the berths. This  may either be on the signalman'panel or on a separate   A typical train describer  display  for a single berth would  appear as below when incorporated  in the signalman's panel. The transfer of a train description from one berth to another is known  as a STEP.  This  is usually initiated by the passage of the train. To ensure that the signalm211 is awa;e of a train which has not had a description allocated, a train without  a description  when  it moves  from one signal to another will  be  allocated  a  not  described  special  description  (N.D.S.D.).  This is often displayed as "****" or"*---".   If the train  description  is stored  but  is not  required  to be displayed,  the berth  used  for  this  is known as a blind bet1h or blind store.   Cum crsc.:ly, some sign:il :,,cct1u1h :ouch 1 SlJ.tiun pLlliurms may oltcn be ;_i_Jluc:HcJ r:hHc.: th:rn one berth if two trains regubrl y use the platform at the same time. 1.             FACILffiES AND TERMINOLOGY OF A TRAIN DESCRIBER   To provide the operators with useful information,  the signal  engineer  must  define precisely the manner in which the data (train descriptions)  are to be handled.  To enable  that definition to be precise and unambiguous, train describer terminology  has been standardised.  Some of  the common terms are defined below.   3.1     Signal Boxes   A signal box large enough to require its own train describer system will be described as the main box.   It will normally send and receive trains and  train  descriptions  to/from  other  signal  boxes with their own train describer systems. Each of these is referred to as an adjacent box.   Due to the limited amount of traffic or small area  of  control,  train  describer  working  may not be required throughout a railway. Block  bells or other similar methods  may  be adequate. A signalbox at which  this  transition  occurs  is known  as a  fringe  box. This  box  will  have a display of trains approaching from the Main Box and be able to send descriptions of trains proceeding towards the Main Box using equipment which is part of the Main Box Train D,escriber system.   Within the area controlled by the Main Box local control facilities may be  retained  for shunting in depots and yards or supervision of level crossings. These are referred to  as shunting boxes or crossing boxes and generally have similar facilities to a Fringe Box. ,,   The transfer of train descriptions from one box to another will be by transmission from the originating box and reception at the second box. This may  occur between  a main  box and any other box with which it communicates.   Types of Berth   Most berths are associated with a signal and will hold and display a single description. The description will step in and out of the berth with the passage  of  the train  past  each signal. Most train describer systems will require a few specialised berths which operate in a slightly different manner. These are described below.   Ripple Berths   Certain signal sections may be designed to permit more than one train in the section. An example is a station platform where  two  trains  are joined.  Consequently,  extra  berths  may be provided up to the number of trains allowed in the section. The berths are  known  as RIPPLE BERTHS and a train description will automatically  occupy  the  foremost  vacant berth. Ripple berth situations may include Blind Berths. Simple Ripple Berth Situation Any description arriving in BOOS is required to move forward to A005 if the latter is clear, otherwise it should move forward when A005 becomes clear.   Where there is a series of automatic signals on a section of plain line,  it  may  not  be  considered necessary to  have  a  train  describer  display  for  every  signal.  The simplest  way of reducing  the number  of displays  is to have a series of ripple  berths with only the first one  or two actually displayed. It is usual for the last automatic  signal  to be excluded  from  the above arrangement to give a better indication of trains approaching the controlled signal.   Series of Ripple Berths for Automatic Section Shuttle Berths   Where a signal section is bidirectional and more than one train could occupy  the section (e.g. station platforms), multiple berths will be provided. These are known as shuttle or p'ush-drag berths. The method of operation varies between the two types of  berth according to the particular local requirement. Although each berth is associated with  a signal, each may be used for movements in either direction according to circumstances.   Typical Shuttle Berths Shuttle berths  behave  in a simibr  manner  to Ripple  berths,  but on  bidirectional  lines.  When a description steps into 0006 from 0001, it  will  immediately  shuttle  forward  if  0003  is  empty.   When a train is present  in  the  platform  with  its description  held  in 0003  berth,  and  a route is set for the train to proceed from  6 signal  it  is  necessary  to shuttle  the  description  back from 0003 to 0006 so as to be in  the  correct  berth  for  the step 0006  to 0002  to occur  when the train proceeds.   Also if a description of one train is held in 0003 when a second train is signalled into  the platform at  that end from 8 signal, the .first  description  must shuttle  back from  0003 to 0006  in order to make room for the second description to step from 0008 to 0003. Push - Drag Berths   The example uses the same layout and arrangement  of  berths  as for  the  previous  example. The  stepping  logic  is slightly  different.                                                                    ·   For trains  running  in the down  direction  from  1 signal  the description  will  step from 0001  to 0006 as normal. If 3 signal is at red the description will stay in 0006.   If however 3 signal  is already  showing  a proceed  aspect  the step into 0006 will immediately be followed by a step from 0006 to 0003.   If 3 signal is cleared after the description has entered  0006,  then  the  description  1s DRAGGED into 0003.   If a second train is signalled into the platform from 1 signal, and the first description has remained in 0006, then setting the second route from 1 will cause the first description to be PUSHED into 0003.   Arrangement of Push-Drag berths Operator's Control Unit   Apart from simply observing the train descriptions provided by the train describer, the signalman must be able to insert, amend and delete train descriptions. He may also be provided with certain additional facilities (e.g. to find the location of a particular train).   On train describer systems incorporated in the signalman's control panel,  the  operator's control unit (OCU) is the means for the signalman to communicate with the train describer. This generally consists of  at  least  three  displays,  an  alphanumeric  keyboard  and  a  number of function  keys.          ·   Typical Operator Control Unit Layout for Control Panel Main Functions   By using the  alphanumeric  key  pad,  the  signalman  is  able  to  SET  UP  information  into  the train  describer.  He  enters  the  signal  address  berth.  which  will  normally   be   the   sigr:al number. He CJn then:- If a train description is also entered immediately after setting up the signal address the signalman may:- OCU Indications and Alarms   If a train moves within the train describer area without an associated  description,  it is known as not described and, as such, causes the signalman  to  receive  a  not  described  alann (NDA). This comprises a brief audible alarm, together  with a flashing  indication which  may be acknowledged by pressing the NDA button.   In addition to the visual and  audible  alarms,  the berth  address  for  the Not  Described  train is displayed in the OCU Alarm Address berth.  This  information  will also  be cleared  when the alarm is acknowledged.   Other alarms may  be provided,  including  the indication  of  the failure of  the equipment  or  of a transmission to or from another signal box.   Fringe boxes may have the facility to change the transmitted description after its initial transmission. If this happens, the signalman will receive an  alarm  which  will  normally require acknowledgement.                      Use of Visual Display Units   Early train describer display systems provided panel displays only. The interface with the signalman was via an OCU as described  above.  More recent installations  incorporate VDUs  in addition to or in place of the conventional panel displays and OCU. The most common formats are as follows:-   Use of VDU in place of OCU. A standard VDU and keyboard may be considerably more versatile than the specialised OCU. As well as  being  used  for  input  and alarms, the signalman may be able to call up various area maps showing the train describer berths over a specific area of the   Use of VDU in place of panel indications. This arrangement is useful where a train describer is to be added to an existing installation. It avoids expensive  panel alterations and a large number of hard wired displays.  On  large panels,  it may  be more difficult to relate the train identities on the VDU  to the movement  of trains on the   This method of display can, of course, be used where the signalling is not operated from a control panel. Small train describer installations have been  successfully installed in signal boxes operated from lever frames. Additional VDUs for staff other than signalmen. Signal box supervisors, station staff and train announcers may all benefit from the information available in the train describer. Various area maps may be called up to provide relevant train running information. Input facilities are usually removed from such additional   Use of VDU for signalling control. To avoid the initial high cost of a panel and the difficulty of subsequent alterations, VDUs are increasingly being used as  a replacement for the custom built control panel. Depending on traffic  requirements, route setting information is entered via the keyboard, a mouse or a trackerball. The standard VDU graphics provide for the equivalent of all normal panel indications. Provided the display system has access to both signalling and  train  describer  data, both can be incorporated in a single   It is usual to provide both overview maps,  with  limited  signalling  data  displayed, and detailed maps showing complete indications for a  smaller  area. The signalman may have more than one VDU available.     1.             TRAIN DESCRIBER PLANNING AND DESIGN   The design of a train describer system will generally follow the main steps listed below.   Firstly, the general type of system must be decided. This will depend on the extent of area controlled, the density of train service,  other  interfaces  which  will  be required  and whether or not the existing signalling and/or control panel will be replaced at the same time. The incorporation of individual displays in an existing control panel can be  very  expensive. Usually, the best opportunity to install individual displays is when the  panel  is  fust constructed.   VDU based control and display systems can (at  least  in  theory)  accommodate  train describers within the signalman's display, provided they can  access  the  relevant  train describer data in a compatible format.   Assuming  the  area  of  coverage  is  to  be  a  complete  signal  box  area,  the   facilities  at   fringe boxes and links to adjacent boxes must be  determined.  Simple  fringe  boxes  may  only require simple input and output facilities. Others  may  require  some  stepping  within  their own area.   It is also possible to provide a distributed train describer system covering several smaller installations although the signalling inputs and the data links can prove quite complex. Having decided the type of system, the next step is to produce a block schematic. This will show all berths and all possible steps between them. It is a useful intermediate step in the  design process and enables the logic of the train describer to be discussed with  non­ engineering staff. Although the block schematic defines all berths and  steps,  we must still add  the stepping  logic. This is produced in tabular form, similar to signalling control tables, and  defines precisely the conditions required for steps to occur. The stepping conditions will  allow  the  designer  to define  the signalling  inputs  required.  It is important that the list of signalling inputs is complete.  These  will  have  to be allocated either to physical input circuits to the train describer equipment or, more usually in modem systems, to individual data bits in a TDM link, the data entering the train describer in serial form. It is also important to check that the signalling data is actually available at the correct physical input point!   We now return to our stepping tables to prepare the train  describer  data  ready  for compilation. In fact, it is now possible to prepare stepping tables in a format which  can  be  read directly by the train describer's data compiler.   The remaining task is now to define the available output formats. In the case of individual displays, each will require a physical output and a circuit from the equipment cubicle to the control panel. For VDU based systems, the maps will have to  be  drawn.  The  graphics package usually includes a library of standard characters to depict signals, various configurations of track layout elements and, of course, the train describer berths. The production of maps may be achieved by defining a text file or possibly by an interactive process.     4.1    Block Schematics   Block Schematics are used to show what facilities are to be provided by a train describer system. They are prepared from the signalling plan, generally agreed with the operating representatives, and used as a basis for stepping control tables etc. They frequently form a useful starting point for dealing with alleged faults, especially stepping faults.   The original BR train describer specification, BR800, defines the symbols used for train describer  schematics. The principal symbols are depicted on the following page. An example  is also shown of how the signalling plan can be converted to a block schematic.   The two ends of the station have heen drawn in different styles. One  in  the  form  of  a simplified  track  layout.  the   other   shuwing   ;m   indi  idu;il   line   for   each   step   or   pair   of   steps. BR Spcc.800 docs not define any preference between the two and practice may vary. The provision of a distinct line for each step does however permit the designer to check  that all steps have been listed on the stepping tables.   Each berth must be allocated a unique identity or address. This will be used by the train describer processor to manipulate the data. Usually the signal number  may  be  used  (often with leading zeros added).  Two  or  more  berths  associated  with  the same signal  will  have to be given different identities. This can normally be achieved by replacing the leading zero with an alphabetic character. It is also possible to  allocate  more  than  one  address  to  the same berth. This is useful on reversible lines to avoid confusing the signalman when  he is trying to enter a description. Train Describer Block Schematic Symbols Example of Block Schematic Production Track Layout Stepping Conditions   A step will always requires a TRIGGER, a change in  the  state  of  a signalling  input,  and may require one or more CONDITIONS, which must exist before the step is triggered.   Whether the step actually takes place however depends on the contents of the "FROM" and "TO" berths when the step is initiated. BRS00 uses the following rules:- Rule 1 covers the normal stepping function. Rule 2 assumes that if two trains JOill, the description of the second train will be carried forward. Alternatively, if a description  has been left in a berth for any reason, the next train will carry  its own  description  forward. This will also occur if either or both displays contain text (3, 9 & 10). If atrain carries a NDSD with it, rule 4 allows it to pick up a valid description  inserted  ahead. Rule 5 applies to the movement of a train without a description. NDSD is inserted and the alarm raised. Rules 6 & 7 ensure that a non described  train does  not overwrite  the existing contents of  the TO berth. 8a or 8b should be chosen as appropriate to determine whether or not text will step to an empty berth with the passage of a train.   4.3       The Basic Step lf signal 1 is an automatic signal, the step from berth 0001 to berth 0003 will take place when B Track Circuit becomes occupied. B T.C. occupied is therefore the TRIGGER  for the system. There is no condition.   TRIGGER        B Track Circuit Occupied.   STEP                000 I to OOOJ.   The system normally requires the trigger  to  be  present  for  one  second  before  the  step occurs, and to be absent for  three  seCDnds  before  the system  resets  and  allows  the step  to be repeated.     If signal 1 is a controlled signJI the description should only step if the  route  is set  and  the signal is clear. This information of route set or signal  clear  (usually  only  one  input  is  used, not both) will be available  from  the  interlocking.  These  will  be  included  in  the control  of the step as CONDITIONS, which must be present before the trigger  can  cause  the step  to occur.   CO:--:DITJON : 1 Route Set or 1 Signal Clear. TRJGGER                      : B Track Circuit occupied. STEP    : 0001 to 0003. Step Where Choice of Route Exists The train describer now requires  information  about  which  route  the  train  will  be  taking. This can be obtained in one of  several  ways  according  to  the availability  of  relay  contacts, the type of interlocking and/or the designer's preference.   CONDITION I (B) Route Set TRIGGER                        B Track Occupied STEP                   0001 to 0003   CONDITION : I Route Set (any route) and 101 N TRIGGER : B Track Occupied STEP         : 0001 to 0003     CONDITION : 1 Signal off and 101 N TRIGGER : B Track Occupied STEP         : 0001 to 0003   Where there are many routes from a signal in  a complex  track  layout  there  will  be  several sets of facing points. In this case it will generally be simpler to use a "route set" condition. If trailing points exist in the route they  are  not  included  in stepping  conditions  since  they give no choice. of route.                    Clear Out Conditions   When a train description is no longer  required,  (e.g.  train  entering  siding  or  train  leaving area of control) it is CLEARED OUT from the panel. The CLEAR OUT (CO) function is sometimes referred to as AUTOMATIC  CLEAR  OUT (ACO).  An  automatic clear  out can be considered to be a step from a berth to nowhere, and as such it  will  be  initiated  by conditions and a trigger.   Shunting Movements Usually, a train proceeding on a shunt class  route  into  sidings  will  have  its  description cleared out from the train  describer.  Thus  a  train  arriving  at  3 signal  and  proceeding  into the sidings will have its description cleared out. Similarly, a train arriving  at  4 signal  and setting back into the sidings using 301 signal will have its description cleared out.   There may be some movements where steps are provided for shunting movements. It is  important to obtain an accurate specification of  the  operators'  requirements  for  any  such steps. They can only be provided where the  train  movements  remain  within  the confines  of the signalled and track circuited lines. Overloading of Permissive Sections   A problem arises if the signalman sends another train into a pemuss1ve  section  (using ripple, shuttle or push-drag berths)  when  all  the available  T  D berths  are full since  there is nowhere for the incoming description to go. There are two common solutions to the problem. Either may be adopted for a particular situation. The choice will depend on the operating conditions - whether trains always continue in the same direction or reverse, whether trains are joined or divided etc. The train describer may either:-   Allow    the  incoming   description to overwrite the rearmost description in the permissive section.   or   Clear out the incoming description. Other applications for Clear Out conditions   Clear out conditions may also be applied in situations such as terminal platforms last berth on a panel ground frames TRAIN DESCRIBER STEPPING TABLES   There are many different styles of presentation. These have generally evolved  to  suit  the design of the interface with the signalling  equipment.  The  following  example  allows  the table to be followed easily  but  may  not  be representative of  current  practice,  either on  BR or elsewhere.   The choice of whether to use signal cleared or route set inputs depends on the information available which in tum will depend on the  type  of  interlocking  and  the form  of  the  data link. In the example below, steps from junction signals are conditional on signal cleared and point positions rather  than  identifying  routes  set. This  would  be  the  normal  situation  with a serial TDM link because the signalman's indications would not relate to individual routes. PROCESSING SYSTEMS   The fundamental function of a train describer is to  store  train  descriptions  in  individual berths and step those description from one berth to the next in response to trigger and conditions.   The earliest forms of berth to berth train describers were electromechanical using relay sets and uniselectors. Although a few examples remain in use today, this type of train describer is no longer manufactured.   During the mid 1960s electronically controlled train describers were introduced. These were designed as hard-wired logic systems, with solid state circuits performing the functions. With this type of train describer the relay sets of the electromechanical type are replaced with electronics - one "electronic store" per panel display. All stepping logic was wired into the system.   Computers were used initially to monitor the system and  provide  some  ancillary  facilities such as interrogation and train reporting.   Today, the non-safety nature of the train describer together with the low cost of the modest processing power required to perform the basic stepping and display functions has led to virtually all train describer installations being processor based.   Small systems can be produced to run on little more than a standard  desktop  computer although large control centres would  require  something  larger. This  has radically  changed  the economics of train  describer  provision.  Small  installations  with  perhaps  20-30  berths are now available at very low cost.   Each system will generally run on standard software  with  the  site  configuration  being defined in data for the stepping controls and display maps.   Computer based train describers possess  the following  advantages over previous generations of T.D.:   Standard hardware can be used for any  train  describer,  the  particular  local  berths and step arrangements can be specified in the software (program and/or data).   Modifications to the train describer caused by track layout alterations become easier since they only require software   The computer has the facility to  interrogate  all  berths,  looking  for a particular  train in response to a request from the signalman,  or  from  an  external  system.  This enables the Train Describer to become a source of train running information. 1.              DISPIAY SYSTEMS   Development   Various methods have been used for the display of train descriptions  on  the  Signalman's panel.   Early systems used a back projection system with separate lamps behind a stencil for each character, projected on to a screen. An alternative was an electromechanical moving stencil (generally restricted to a range of 10 characters per display). Both systems required frequent maintenance and would not meet the reliability requirements of a modern railway.   Miniature cathode ray tubes were the next development. Each  tube is mounted  in the panel  and fed with appropriate signals from character generation circuits. These have been very widely used, mainly as 2" x l" rectangular tubes,  but  occasionally  as  1"  diameter  round tubes.   Their main disadvantages were:-   They required a very high voltage supply (approx 2KV) which poses obvious safety problems in the confines of a signalling panel.   The power supply units used to derive the high voltage tended  to  produce  a lot of heat.   The C.R.T.'s fade with age and usage so it is virtually impossible to maintain all displays on a panel at a uniform brightness and character   The displays are difficult to mount and relatively   For the above reasons, light emitting diode displays soon became the most popular form of display where it was required to incorporate TD. displays in a  conventional  panel.  They usually consist of a 7 x 5 d1t matrix of LEDs for e:1ch uf the four TD. characters. The following advantages arc ascribed in the LED display:-   Use low voltage and have low power   Provide a display of constant uniform   Compact and easy to mount. 7.2 Visual Display Units (V.D.U.'s)   Visual display units (v.d.u's) were initially used in panel boxes  to  display  a  simplified pictorial "map" of the track layout and train descriptions, for use mainly by regulators, train announcers, etc. It was soon realised that such displays could be of great use outside the confines of the signal box operating floor.   It is now becoming more general practice with new train describer systems in existing signalboxes to use this as the only means of display.   The full benefits of VDUs can be provided where these form an overall control and display system for the train describer and the signalling system as a substitute for the conventional panel.     1.        SIGNALLING  INPUTS   The signalling functions that will be used to condition and trigger  steps  are  generally presented to the train describer in individual input circuits  (i.e. parallel data) where derived from a local relay interlocking.   Some form of relay interface is normally used between a relay interlocking and the train describer system for separation of power supplies.  For  a  duplicate  train  describer  system, two input circuits will therefore be required, generally fed over  contacts  of  the  same signalling input relay.   Where data is from a remote interlocking, a serial input sub-system driven by the  remote control system is provided. These are rarely duplicated.     2.             PERIPHERAL AND ANCILLIARY SYSTEMS   The modern train describer syslL'm conuins cxtcnsi·e data regarding the running of trains within the control area monitored. In addition it presents a useful display medium for train running dat from other sources.  The following  sub-systems  may  therefore  be found  as part of or communicating with the train describer in a modem signalling control centre:-   It will directly operate panel displays, visual display units and a technicians fault reporting printer.   It will receive inputs from O.C.U. key pads and signalling functions. It will be  required  to  communicate  with  adjacent  train  describers  and  with  fringe  boxes. It   may   provide    information    to   Automatic    Route   Setting   equipment    and  Passenger Information  Systems.  These  sub-systems  will  generally  be  driven  by  their  own computers rather than form part of the train describer system. Some of  these  other  sub-systems  are briefly described below.             Automatic Train Reporting (A.T.R.)   It has been customary to provide a record of train running for future reference in case it is necessary that incidents need investigation. This was originally done by the signalman, with assistance in busy signal boxes. Automatic Train Reporting uses the data available from the train describer to record the times of trains passing certain signals and relieves the  signalman of the responsibility.   A.T.R. information may be provided in  a transient  form  using  a VDU  or as a hard  copy  using a printer. It can be made available to Signalmen, Regulators,  Control  and  other  operating supervisors according to their needs.   Whereas earlier A.T.R. facilities were controlled by the train  describer  directly,  it  is  now more common to provide a separate computer  sytem  for  this,  and  other  information  facilities.   The basic format for A.T.R. is:-  Automatic Train Reporting By Exception (A.T.R.E.)   In a busy area an A.T.R. system  will  produce  an  extensive  record  of  train  movements during a normal day. However, it is of little interest to record the trains that run to time. Regulators and, timetable planners want to know which trains run late so that they can make short and long term adjustments respectively.   If the A.T.R. computer can be provided with the expected passing times for trains, it can compare actual passing times and only log those which are not in agreement. The Master Timetable System computer provides such information though it must be up dated daily to account for irregular train movements.   A realistic tolerance before or after the booked time must be allowed in  the  comparison between booked and actual times before a report is made. Two minutes is normal. Thus the report is considerably reduced in length and contains only those trains that need attention.                      Train Running System on T.O.P.S. (f.R.U.S.T.)   BR operates a system called TOPS (Total Operations Processing System) to monitor rolling stock movements. When first introduced, all stock movement data was  input  manually. Provided the consist of a particular train is known, the location  of  each  vehicle  can  be updated by way of train movements information.   Train running information from the train describer is passed to the TOPS network for comparison with the timings  held  by TOPS, and so that  the train's location  within TOPS can be kept up-to-date. The information is available  immediately  at  teleprinter  or  TOPS terminals, and is stored to allow for statistical analysis of train performance. Automatic Speed Measurement   The A.T.R.. system can  be  used  to register  a  train  speed  in  addition  to its passing  time  at a signal. It is achieved by  measuring  the time taken from stepping  the train description  into the berth to stepping it out again. The distance between triggering points is known and the system divides it by the time to calculate the average  speed  of  the  train  over  one section. This speed, and the maximum permitted speed, will be displayed as part of the passing time report.   e.g.  11.00        AH0120        1T15        70MPH, 80MPH    Hot Axle Box Reports   Hot Axle Box Detector Information has usually been presented in separate display units mounted adjacent to the control panel. The necessary information can be input to the A.T.R. system and displayed either on a VDU screen or as a report associated with the next signal passed.   Passenger Information Systems   Platform indicators and passenger announcements may be operated automatically. The A.T.R. or a dedicated sytem will be used to recognise a train description and display the  relevant information on the correct platforms as the  train  approaches  stations.  The information format for the public  varies  widely  and,  therefore,  the  system  programs  must be designed around the needs of the area served.   Announcements are triggered in a similar way as the train approaches stations.   It should be remembered however that the train describer  information  is  not  always  sufficient for full passenger information to be given in adequate  time. The  main  problems are:-   Frequent changes of platform, often at short   Routes not set early enough to provide passengers with sufficient   Control area does not cover a large enough approach area. Data has then to be obtained from adjacent systems.                  Automatic Route Setting   A signalman is required to set routes such that trains run to schedule. He does this  by comparing the actual position of a train with its  scheduled  position  and  may  amend  his action for several trains should one be 0!-1t of schedule. A computer based Automatic Route Setting sytem has been developed which takes current train  positions  from  the  train  describer, scheduled positions from the Master Timetable  system  and  then  optimises  the route setting to most effectively attempt to meet the scheduled requirements.   The programme for this requires to account for connections that should be  kept  and conflictions that may occur.     Train Radio   A secure radio link between the signalman and each train driver is a requirement  for Driver Only Operation of passenger trains. This requires that each locomotive  is provided  with a radio, uniquely coded with that loco's  stock  number  (eg.  47.001).  The  train  describer  is used to correlate the train description with the locomotive  stock  number,  so  that  the signalman can call trains by referring to their description on the panel.   At the start of each journey the driver sets up the signal position of  his  train  on  a  thumb-wheel switch, which is encoded and transmitted  along  with  the loco  stock  number. The train describer is then interrogated for the description at that address. Any calls the signalman makes to that description will then automatically be converted to a call to  the relevant locomotive, and similarly calls from the driver  will  be  identified  by  the  relevant train description.   At the end of the journey the train describer will automatically  remove  the  correlation between the loco number and train description.    

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Deepu Dharmarajan -
Posted 89 days Ago

RECENT DEVELOPMENTS IN SIGNALLING

  CONTENTS 1. Introduction 2. Interlockings 3. The Operator Interface 4. Train Detection 5. Train Operation 6. Infrastructure 7. The Signal Engineer's Work 1. INTRODUCTION There is no doubt that railway signalling continues to change at an ever increasing rate.  It is very difficult to predict the future but these notes will give an indication, often in the form of general headings rather than detailed descriptions, of devlopments which may occur in the next few years. These developments will have an impact on the manner in which the signal engineer performs his work. 2. INTERLOCKINGS This course has already covered the Solid State Interlocking. From an experimental prototype only a few years ago, SSI is now firmly established as a safe and cost-effective replacement for relay technology. Its many advantages include:- Lower interlocking hardware cost Can be housed in smaller buildings Lower cabling costs Much testing can be done off-site Built-in diagnostic equipment Although SSI is undergoing further development, the basic configuration and equipment standards will probably remain for several years to allow the cost advantages of volume production to be realised. Although some electronic interlocking systems are hardware based, it is likely that all future systems will be processor based. Areas for future development include:­ SSI interface with axle counters. Use of newer processors with greater processing power. Incorporation of ATP functions. Smaller low-cost systems for small interlockings. Remote control of relay interlockings which it is uneconomic to replace at present. 3. THE  OPERATOR  INTERFACE Traditionally the signalman has been in control of the movements of trains. Routes are set manually and decisions are made by the signalman and/or regulator/supervisor on priorities for dealing with trains running out of course. Meanwhile, there is an ever increasing demand for information on train running, to advise passengers and operating staff and to monitor performance. Manual methods no longer have the required capacity or speed to capture, process and distribute the volume of data required. We have therefore seen the introduction of Automatic Route Setting which will deal with routine movements and even make decisions on the routes  and  priorities of trains in the event of disturbance to normal running. This leaves the signalman free to deal with emergencies and other unusual situations. Information on train running is now widely distributed outside the controlling  signal box or control centre. Platform indicators and other passenger information displays are driven from the train describer equipment (with reference to a stored master timetable)  and Automatic Train Reporting is almost a standard feature. It is inevitable with the high cost of custom built control panels that the VDU  will  be used more extensively as the signalman's  main display. Although it can cover only a limited area on one screen, multiple screens take up no more  space than a comparable panel and can offer the signalman a wider range of views of the control area to meet different situations and preferences. Where a large scale overview is required, projection of the indication diagram  on to a screen is an acceptable alternative. An example of a modem system incorporating most of these features is BR's Integrated Electronic Control Centre (IECC). The use of VDUs allows industry  standard hardware to be used. Alarms and other operating information can be  included in the displays and a change to the track layout can be incorporated into the display simply by alteration to the stored data used by the graphics program. This provises the "signalman's workstation". The general structure of the IECC is depicted on the accompanying diagrams. Although the IECC is designed to work with SSI interlockings, it can also  interface with relay interlockings. It is built around two duplicated ring networks, a signalling network, dedicated to handling signalling data, and an information network to link all the operating information systems. The networks are  designed around the commercially available VME bus system. An IECC system monitor is connected to both networks to locate faults and, where permitted, change the status of the system. Automatic route setting is connected to both networks because it gains its information from the train describer and the timetable processor as well as the interlockings. It issues its commands to the interlockings.   The Gateway subsystem collects data from the signalling network for the use of the systems connected to the information network. Its main purpose is to reduce the volume of messages which would otherwise lead to congestion on the signalling network. It is essential that the signalling network remains lightly loaded to ensure a fast response. Most of the IECC hardware is standard for any installation. The configuration to a particular layout is mainly achieved by the data held within each subsystem. On B.R. five IECC installations are currently in use and a further three are  under construction. 4. TRAIN DETECTION The track circuit has for many years been the primary means of train detection. Due to ever increasing reliability demands, other methods may be considered:- Axle counters End of train detection systems Transponders, either on the train or track mounted Transmission based control systems where the train regularly reports its  progress along the track to a central processing system. 5. TRAIN OPERATION Automatic Train Operation and Automatic Train Protection have already been  covered in more detail elsewhere. However it may be of interest to discuss  possible future strategies in this area. Most ATO systems have been introduced on completely new railways or as part of a major modernisation. Usually all trains have identical characteristics and the service pattern is simple (all trains call at all stations). ATP has been superimposed on conventional signalling systems as a supervisory sub-system to aid the driver and monitor his performance. Although ensuring greater safety, it has stopped short of taking control from the driver due to the complexities of mixed traffic operation, numerous different stopping patterns and the impossibility of total implementation over a large railway system. A supervisory ATP system offers a partial solution to problems of safety by  permitting fitted traction units to operate over unfitted lines and vice versa while still deriving the benefits when ATP fitted traction units operate over fitted lines. Given sufficient investment, complex stopping patterns should be capable  of  solution. Provided the train is receiving regular messages regarding its location, station stop data can either be set up on the train at the start of the journey or transmitted to the train as it proceeds on its journey. It must be remembered that stopping at stations is a non-safety (although very important) function of an ATO system. When all traffic over a section of line is ATP fitted it should even be possible to dispense with lineside signals. With the increasing safeguards built into interlocking equipment, primarily to avoid signalman's error, it is inconsistent that the driver should be expected to observe lineside signals under all  conditions of visibility, often with no other safeguards. As a minimum, the signals could be brought into the cab but the ultimate aim is likely to be the direct control of the train by the signalling equipment. As an interim solution, while still working towards the long term objective of full ATP, simple systems can be overlaid on the existing signalling initially. The systems should be capable of upgrading to provide better facilities as traffic, commercial or safety requirements dictate. Systems should allow a progression from intermittent to semi-continuous to fully continuous ATP. 6. INFRASTRUCTURE On lines with very low levels of traffic, infrastructure costs can be a severe burden on the operating costs of the railway. Although the track must obviously be kept in place (in as simplified form as possible), significant savings can be obtained by reducing train control infrastructure, together with the related operating and maintenance staff. Possible areas for economy are:- "No signalman" operation of single lines; remote releasing of token instruments, self-normalising points at passing loops or train crew operated loops. Reduction or elimination of lineside signals. Radio or satellite based control systems. 7. THE SIGNAL ENGINEER'S WORK Apart from processor based signalling systems, the signal engineer, along with many other professions, can employ computers to make his work easier. Commercially available hardware continues to give increased performance at  a reducing price. The possibility of a workstation or terminal at everybody's  desk has already become a reality in some offices. Obviously, data preparation for SSI and IECC installations must be done using  specific software on a suitable design workstation. However, even for more traditional types of equipment, the computer can be used to advantage. Computer Aided Design is one of the most widespread applications. In its simplest form CAD can be used to draw a new diagram on a VDU  screen, store it on disk and produce a print or plot when required. The drawing is stored as "elements" (lines, circles and other shapes) having specific coordinates and/or defined by a mathematical expression on a matrix or grid. In this form we are simply replacing the traditional drawing tools with a screen and a keyboard. The main advantage of such drawings is that they are clear, legible and  dimensionally accurate (dimensions can be specified during the drawing  process)  and subsequent alterations are easier. Although a skilled operator may be able to produce a drawing slightly faster than with pencil and paper, the time savings are unlikely to be great. If we then consider that much of the design work is likely to be the alteration of existing diagrams rather than the production of new ones, the CAD system will not hold records of old drawings produced manually. Therefore, if  we insist  that all work is done using CAD, we have the additional task of redrawing existing diagrams. If we only use CAD for new drawings it will be many years before the system  holds a complete record of all installations. However, more powerful systems are available which not only draw diagrams  but can produce a database of equipment and other information associated  with each item depicted on a drawing or set of drawings. In addition an extensive library of "cells" - small parts of drawings (e.g. a relay contact) or complete standard drawings (e.g. a location track feed circuit) can be called up for incorporation into any drawing. As cells are added, so is the relevant information to the database. From this, it can deal with routine tasks such as contact, fuse and cable allocations. The use of a cell library can also have far greater benefits in terms of the checking effort required. Once the master of a standard circuit has been checked, each copy has, effectively, been checked. Only the variable information such as the function numbers need be added. Obviously the checker will still have to check that the correct circuit has been employed, but once he is satisfied of this, the detail can be taken as correct. However, the investment in hardware and the initial setting up effort must not be underestimated. Many man-years of work will be involved in producing a working system. Neither is this a "one-off" task. As technology changes, the  CAD system must be kept up to date to be capable of dealing with it  BR's  original CAD system did not, for example, have the ability to deal with SSI. Future developments are likely to be aimed at greater integration. If the signalling plan and control tables can be produced by computer and the SSI data has to 'be prepared by computer,  a logical development is to integrate  the steps leading from one to the other into a single continuous process. The  engineer of  the future may find that his main task is to specify the system by  means of the signalling plan and control tables. Once this is done, the remainder of the design process will follow automatically. Even with control  tables, over 80%  of the controls are standard and the data can be derived direct from the signalling plan. This may also create new problems of ensuring the integrity of  data  produced in this manner. Checking may consume a far greater proportion of the engineer's time and means will have to be provided to automate this also. This may well be an over-simplification . Ultimately, the engineer's job is to produce a safe and cost-effective system. and as one routine task is automated, there may well be several others demanding his personal attention. There is no doubt however that the nature of the job is changing significantly.

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Deepu Dharmarajan -
Posted 90 days Ago

PRINCIPLES OF TESTING

    CONTENTS 1. Introduction 2. Competence of Testing Staff 3. Documentation 4. Testing of Equipment Rooms and Location Cases 5. Testing of External & Lineside Equipment 6. Remote Control Systems 7. Control Panels 8. Power Supplies 9. Functional Test of System 10. Other Important Considerations 11. Maintenance Testing 12. Conclusions 1. INTRODUCTION These notes deal with the principles of testing a new or altered signalling  installation. It is not possible to cover in detail the testing of specific types of equipment. It must be stressed that these notes must not be taken as any form of testing instruction. The instructions and procedures issued by your own administration must be observed. 1.1 Why Do We Test? It is vitally important for the safety of the railway that a signalling installation operates correctly. Prior to installation, the signalling equipment  will  have  been  specified  and designed to sound signalling principles. At each stage the  specification  and  design  should have been checked. The installation should therefore be carried out  to  a  correct  and  consistent set of drawings. When installation is complete, a thorough test must be undertaken to ensure  that the equipment as installed is correct to the drawings and also that it  actually performs  to signalling principles and basic safety rules. It must be stressed that this is the last opportunity to uncover any errors in specification, design or installation before the equipment goes into service. The testing must therefore be done correctly and completely. 1.2 What is to be Tested? For a new installation, the answer to this question is simple - everything.  There   will also be interfaces to existing equipment. These too must be tested. For an existing installation which has been modified, it is not always so clear as to what requires testing. Obviously, all circuits and other equipment  which  are shown as altered on the drawings must be tested. However, it may be necessary to test some parts of the installation which remains unchanged. Although the work may have been confined to a small portion of the equipment, it may have been possible for an installer  to have interfered with working circuits which were not part of the equipment to be altered. This is a matter for the tester's skill and judgement. He must take into account the type of equipment and the environment in which the work is carried out. The limits of the testing should then be clearly defined in a testing plan. 1.3 Who Will Test? It is vital that all staff who undertake testing are competent to do the job. There  must also be one person in overall charge of testing who will define the tests  to be carried out in the form of a testing plan and ensure that the progress of testing is properly monitored and documented. The testing must be carried out independently of the design and installation. Persons who have participated in the design or installation process must never test their own work. It is generally acceptable for those who designed or installed the equipment to  be involved in an assisting capacity. Where testing is carried out by contractors or other external testers,  the standard of testing must be maintained. The employing company must be satisfied that such testers are of the required standard. The competence of testing staff will be covered in more detail in section 2 of these notes. 1.4 Where to Test? In many cases equipment can only be tested on site. This is particularly true of alterations. However, where new equipment is factory wired and delivered complete to site, it is very often easier to carry out some of the testing before it leaves the factory. The continuity of through lineside circuits may often be tested before the equipment is connected at either end. 1.5 When to Test? A basic rule which should always be followed is to test as much as possible before commisssioning. New installations may often be tested complete using suitable simulations for external equipment and interfaces to existing signalling. Even with alterations, it is generally possible to reduce the amount of testing at the commissioning by testing any complete new circuits beforehand. It is often desirable to take this into account at the design stage. It may be  better  overall to replace a circuit which would be extensively altered with a complete new circuit rather than cut into the existing circuit in several places. The testing workload on commissioning may then be substantially reduced. It should be remembered that testing staff are often under pressure at a  commissioning. Testing staff are always the last to finish and they may well have been delayed by earlier stages of the work taking longer than planned. However great the pressure to do so, equipment must never be handed over  to the operators until it has been fully tested. Testing as much as possible beforehand can help to reduce such pressures. 1.6 How to Test? - The Management of Testing This will be covered in detail in sections 3 onwards. A good tester is thorough  and methodical. He works efficiently but does not rush. Testing does not only  involve proving that what does happen should happen. It is much more important that the tester ensures that what should not happen does not happen. One person must be appointed in overall charge of testing. He should first of all prepare a testing strategy. This should be done at an early stage.  As the strategy adopted for testing and commissioning any project can have a significant bearing on costs, the testing strategy will need to be considered before financial authority is given for the project. The testing strategy should cover as a minimum the following matters:- What will be tested? How many staff, and with what specific skills, will be required to undertake all testing? How long will the testing take, both before and during commissioning? When will the equipment be available for testing and when is it required  to be in service? In what order should the tests be carried out? What additional resources (equipment, transport, staff etc.) will be required and for what period. This testing strategy must then be developed into a full testing plan detailing a programme of tests to be carried out (including those associated with the commissioning) and the individuals responsible, preparatory work required, possessions required, equipment, temporary work (simulations etc.), methods of working, methods of communication, and methods of recording. This plan must then be thoroughly discussed with all those involved. It must also be independently checked. Once it has been agreed and approved, the testing plan must be communicated to everybody involved in the testing and commissioning programme. 2. COMPETENCE OF TESTING STAFF To be effective, testing must be carried out by competent staff. It is therefore the responsibility of each railway administration to ensure that all staff who are entrusted with any part of the testing are competent to carry out their delegated tasks. There are generally two ways to deal with competence of testers. Informal. The duties of testing are included in the job specification and are implicit in taking up the post. The tester's ability will be known by his superior on appointment to the job and will be monitored by normal managerial processes. Suitable action must be taken by the manager (training, discipline, restriction of duties) if the tester is found to be deficient in any part of his work. Formal. Formal processes of ensuring competence of testing staff may involve periods of instruction and/or experience in an assisting role (or under supervision), will usually require some form of examination, and will enable individuals to be certified. This certification will be required either as a qualification for a particular post or to permit the individual to perform specific duties. A specific time limit on the certificate should be considered, after which retraining and/or re-examination will be required. British Rail originally adopted the informal approach. With the greater variety and complexity of equipment, faster changes in technology and the need to attain the highest standards of quality and safety, the emphasis has now changed to a much more formal system of training, examination and certification. Sufficient staff must be trained and certified to carry out the required amount of testing, ensuring that testing remains independent of the design, checking or installation. Larger companies can usually justify the employment of specialist testing staff. Even so, there will be peaks (e.g. major commissioning stages) which require additional resources. Suitable design staff may obviously be employed but it is important to ensure the independence of  all testing carried out by careful allocation of tasks. Smaller companies with limited numbers of staff will obviously require their staff to be more versatile. It is even more important in this case to ensure independence of testing. It  is a natural preference for railway companies to prefer to carry out their own final acceptance tests for equipment from external suppliers. However, if independence of testing cannot be ensured it may be better to employ suitably qualified  contractors  or consultants to undertake all or part of the testing. 3. DOCUMENTATION At each stage of testing it is important to document precisely what has been tested and by whom. Ideally a signature should be obtained from the person carrying out each part of the test although in practice it may not be possible to do this for some remote tests until some time after the test has been carried out. To aid the tester full use should be made of check lists and other similar reminders. The person in charge of testing should ensure that a single log book is provided in which to document all queries and faults found. It will be necessary to provide multiple copies of entries in the log book so that these can be passed on to designers, installers or contractors (as appropriate) to take any action necessary and then reported back to the testers after corrective action has been taken. Test certificates should be provided for each  part of  the work. These are then  summarised into the required parts, building up to a master test certificate to cover the complete project. All testers must adopt a standard method of marking  diagrams and control  tables so that there will be no ambiguity in the record of testing if one person  has to take over from another. These standards should be issued as standard instructions or incorporated into the testing plan. 4. TESTING OF EQUIPMENT ROOMS AND LOCATION CASES 4.1 General Inspection Before testing individual circuits, an inspection should be carried out to ensure that the correct equipment is in place and properly identified. This inspection should include the  following items:- Location cases are correctly labelled. All equipment is installed as specified on the drawings, to the correct  layout  and actually present. All equipment which is pin coded or otherwise uniquely configured to its mounting (e.g. signalling relays) is of the correct configuration. Cables and wires are of the correct size and type, correctly terminated  and  properly secured where appropriate. Equipment is undamaged. Where initial testing takes place off site, this  check to be carried out again when the location or other equipment is installed on site. 4.2 Wire Count The inspection above should have proved that the equipment is in place as  specified. The next group of tests must prove  that the circuits are wired as specified.  As well as proving that each circuit exists as shown in the wiring diagrams, it must be proved that there is no electrical connection between circuits. The presence of a wire forming part of a circuit can be proved by a continuity  test  (see  4.3.). The absence of any other wires will not necessarily be shown by a continuity test. By counting the number of wires on each terminating  point  of all affected items of equipment, the presence of unwanted connections between circuits can be proved. If all wires have been installed according to the diagram, the wire count will correspond to the contact or terminal analysis for each item of equipment in the circuit. Any unwanted  connection to another circuit will be evident by an additional wire or wires to those shown. All terminating points must be examined, not just those shown in the circuit  diagrams. This is to ensure that wires have not been connected to the wrong terminals. When carrying out a wire count, opportunity should also be taken to check  that each  wire is correctly terminated and secured and that there are no other superfluous metal items (e.g. offcuts of wire or washers) in the vicinity of any termination. 4.3 Continuity Test Using a bell or buzzer connected to a low voltage power supply, the continuity  of each wire in each circuit should be checked. Where practical (e.g.  new installations) all relays, fuses and links should be removed. On working installations, it may be necessary to test an unterminated wire. In this case the wire must be suitably labelled. On commissioning, it must be checked that the wire has been terminated on the correct terminal. 4.4 Circuit Test  (Strap & Function Test) Persons carrying out this test must have a knowledge of the function and operation of each circuit being tested. To ensure that any earth faults are  detected and eliminated, earth leakage detection is advisable on each leg of  the supply for the duration of the test, if this is not already incorporated in the permanent power supply. The object of this test is to ensure each circuit operates as intended.  Each  circuit  will normally have an end function (e.g. a relay) which operates when the circuit is fully connected. The equipment should be set up so as to operate  this function. The voltage  and polarity at the operating terminal (e.g. relay coil connection) should be observed using a meter or other suitable measuring instrument. Having proved that the circuit operates when it should, we  must now break  each switch, fuse, contact or link in the circuit, in turn, to prove that the relevant control is included. If there are controls in both legs of the circuit, each leg must be tested. The contact should be broken by energising or deenergising the relay  or  operating the switch (as appropriate) and the change in voltage noted. The broken contact should then be strapped out and the voltage observed to return to its original value. Where there are parallel branches of a circuit, all possible circuit paths must be completely tested. It is important that any straps used for such tests are not left behind after the testing is completed. To avoid this possibility, a set number of straps shall be provided, identified and numbered. Only these straps shall be used for circuit  testing and they shall all be accounted for at the end of each testing session. 4.5 Other Tests Other tests may also  be  required  to ensure  the correct  functioning  of  equipment. Included in these are:- Continuity, earth and insulation tests on all cables. Adjust and/or set all timers. Where seals are provided, these should be in place before testing is complete. Test all power supplies - see section 8 4.6 Other Precautions If a test panel or other temporary wiring is used to simulate external functions,  all circuits must be fully documented and must be re-tested after removal before an installation is fully brought into use. All redundant wiring to be removed must be distinctly identified (e.g. by tapes or labels of  a specific colour). It may be desirable not to remove the wiring until the testing is complete.  If this is the case, all removed wires must be completely insulated on disconnection until the wiring is removed. If possible,  redundant  wiring must  be removed before the equipment is brought into use, otherwise as soon as possible thereafter. 5. TESTING OF EXTERNAL & LINESIDE EQUIPMENT Section 4 has dealt with the general method of testing the controlling circuitry.  In addition, each item of external equipment must be tested to ensure its correct operation and that controls from and indications back to the interlocking function properly. The most common items of equipment are detailed below. Only general guidance can be given here. Additional tests may be necessary for specific types of equipment. In general it will be necessary to have one or more persons on the track to observe the  operation of the external equipment and its controlling relays and  circuits. Another person will be required to operate the signalman's controls and observe indications. Suitable communication must be provided. Alternatively, it may not be possible for various reasons to use the controls from the interlocking. In this case, a temporary feed must be provided at the location to enable all local circuitry to be tested. The through circuits must be tested at a later stage when they are available. If it is not possible to carry out a complete test this must be recorded on the testing documents to ensure the remainder is subsequently tested. 5.1 Power Operated Points A general inspection should be carried out to ensure that the points are correctly installed and labelled and that all cables are secured clear of moving equipment. The points should be operated by hand to ensure that they move freely, each switch rail fits correctly against its respective stock rail and there is adequate  clearance when the switch is open. A wire count should be carried out on all terminations. Before commencing the test, the tester on site and the tester at the control  panel should confer to check that the site tester is at the correct set of points  (name runing line and position relative to other equipment etc.). When describing the position of the points, the term "left (or right) hand switch closed" should be used rather than normal or reverse. The person at the control panel should then check correspondence with the controls and indications. Earth leakage detection should be operative during all electrical tests. Operate the points under power from the control panel to confirm detection at  the location and the signal box, the panel indications and all controlling relays  correspond with the position of the points. On 4-wire detection circuits the opposite circuit to that under test should be monitored to ensure that no irregular voltages appear during the operating cycle. For each position of the points break each detection contact of each end of the points to ensure that the detection relay deenergises and the panel indications extinguish. Any supplementary detectors must also be included in this test. Check that the clutch (where provided) slips at the correct current when an  obstruction is placed in the switches and that the cutout timer operates correctly. On multi-ended points check for correspondence. For example, if the points are normal, move each end to reverse in turn to ensure that detection is lost in each case. Check all possible permutations of normal and reverse to ensure that normal detection is only obtained when all ends are normal. Each supplementary detector, if provided, must be separately included in this test. Repeat for reverse detection. 5.2 Signals Firstly, visually check the signal to ensure that the profile of the signal is as shown on the signalling plan and agrees with all documented sighting requirements. The correct identification plate must be fitted and other items such as signal post telephones and emergency replacement switch (if provided) should be correctly fitted and labelled. If possible the signal post telephone should be in working order so that it can  be used for the test. Where the facility is provided, the signalman's telephone equipment should indicate the correct signal to which he is speaking. Check inside the signal head that the lamps are of the correct type, close-up segments are correctly positioned and filament changeover relays are present. Check for correct alignment and sighting of the signal. Carry out a wire count on all terminations. Check by operating the control relay(s) that the correct aspects and route indications are displayed. All routes must be tested. Check each main aspect  lamp in  turn  to ensure that only the main filament illuminates and that filament changeover relays and associated indications function correctly when the main filament fails. Lamp proving should continue to operate when the main filament fails. Check its correct operation by simulating failure of both filaments. Where junction or route indicators are lamp proved, test that the failure of the  required number of bulbs maintains a red aspect in the signal. Check for the correspondence of indications to the aspect(s) displayed for all  indicated signals. Where the signal is not indicated (automatic signals) test the  aspect lines to the signal in rear. 5.3 Automatic Warning System, Trainstops and ATP Systems On most British Rail main lines, the electro-magnetic Automatic Warning  System (AWS) is still fitted as standard. The following procedures apply to testing the track mounted equipment. Inspect the track mounted equipment for correct layout, height relative to the rail and distance from signal(s). Check that the internal links in electro-inductors are correctly connected for the supply voltage used. Test each permanent magnet and inductor with a strength and polarity meter. The electro-inductor should be tested for each aspect of the respective  signal(s) and should only be energised for a green signal. Suppressor inductors should respond to the controlling relay. Where other similar warning or automatic train protection equipment is provided, its correct operation in conjunction with the signals must be tested. For a trainstop, inspection should check that it is securely fixed to the sleepers in the correct position relative to the signal. Height relative to and distance from the running rail must be within tolerance. The arm must be checked in both raised and lowered positions. The arm should not be bent or otherwise damaged. Setting of indication contacts must be checked for tolerance. A wire count should be carried out on tail cable terminations. Depending on the type of trainstop, the lowering mechanism or circuit should  cut off and the holding device should operate at the end of travel when lowering. Disconnection of the operating circuit should result in the trainstop returning to the raised position. Normal and reverse indication circuits should be checked for correct operation  via the allocated contacts. The operation of the trainstop with the signal may  be checked at this stage or when performing the aspect sequence test. Energisation of the signal operating relay (HR or equivalent) should cause the trainstop to lower. The signal should remain at danger until the trainstop is fully lowered. Locking the trainstop arm down should prevent the signal in rear from clearing  when the signal is at stop. Unless the controls specify otherwise, the signal in rear should be able to show a caution aspect when the signal associated with the trainstop has cleared again. 5.4.   Track Circuits The full length of the track circuit must be examined to ensure that its limits agree with the bonding plan, all bonding (including traction  bonding)  is in  position and correctly secured to the rail and all block joints and track circuit interrupters (where specified) are present. Staggering of block joints, spacing of  adjacent block joints, clearance points and track circuit minimum and maximum lengths must conform to laid down requirements. The lineside/location equipment must be inspected to ensure that the correct equipment has been provided and that it is compatible with all adjoining and parallel track circuits. A wire count should be carried out at all disconnection and termination points. Check the required voltages/currents to ensure that the track circuit has been  correctly set up and test for correct operation by shunting the track circuit at several places, including all extremities. On jointless track circuits ensure that the actual limits of the track circuit are as specified. If all or part of the track circuit has excessively rusty rail surfaces, the drop  shunt test should be repeated after the rails have been cleaned sufficiently by passing trains. With all adjacent track circuits energised, disconnect the feed and check that the relay deenergises. This ensures that cables are not  transposed  and/or  voltages are reaching the track relay from adjacent feeds via the rails. Any residual voltage on the rails should be below a specified safe level which will not under any circumstances energise the relay. Check polarities for staggering with respect to adjacent tracks and test that the correct indications operate when the relay is deenergised.  All  sections of a  multi-section track circuit must be tested. 5.5 Level Crossing Equipment Check that the layout of the equipment corresponds to the drawings and all  equipment is of the correct type. Telephones where provided should be operational and give the correct indication to the signalman when in use. All indications (e.g. road signals, barriers, power supply) should be tested for correct operation. To test the operation of the crossing equipment, the same tests should be applied to the controlling equipment as those specified for locations and relay rooms (section 4). 6. REMOTE CONTROL SYSTEMS The main test of any remote control system is that each output responds to its associated input and does not respond to any other input. This is best done for TDM equipment by first checking at the inputs and outputs of the TDM equipment itself and then testing between the signalling input and the corresponding signalling output. For FDM systems, each receiver should respond only to its associated transmitter. Where several parallel systems are in operation tests should be made to ensure that crosstalk is within safe limits. Line voltage levels should be checked to the equipment specification.    Where automatic line or system changeover is provided, simulate a failure to ensure that the changeover operates correctly. Check that all system alarms  operate correctly. Check that the failure of a TDM system produces the correct warning indications on the control panel. If the remote control system performs any button or indication processing,  outputs should be tested individually to confirm that they are only produced by the correct combination and/or sequence of inputs. 7. CONTROL PANELS It is vitally important that the control panel (or VDU graphic display) represents accurately the layout of the track and signalling. It should be checked to both  the signalling plan and the panel drawing. Check that the correct relay(s) or remote control input(s) respond to buttons and switches. Check that incoming indication circuits illuminate the correct lamp(s) on the panel. Indications which are combined at the signal box (e.g. point indications in route lights and track indications over points) should be checked for correct operation. Check that the correct indications are shown under remote control failure conditions. 8. POWER SUPPLIES Before testing any power supplies ensure that the correct safety precautions  are taken for the highest voltage likely to be present. The main tests which could have serious implications for safety are the  polarity of each supply and the operation of earth leakage detection. Other tests are mainly concerned with the reliability of the supply and its  ability to carry out its required function. A wrongly rated fuse for example may not  cause a wrong side failure but could cause serious disruption if a cable burns out. Measure all voltages to ensure that  they are within 10% (or other specified  tolerance) of the required value. In particular check the voltage at the supply point under light load conditions and the voltage at the end of each feeder  under maximum load to ensure that these tolerances are not exceeded. Check all fuses are of the correct rating and that there is the correct fuse discrimination. Check the charging rate of trickle chargers. Where equipment is commissioned in stages, power supplies should always be re-tested whenever the addition or removal of equipment significantly alters the electrical load. Because of interaction between the various electrical loads and the distribution system, final adjustment of power supplies may not be possible until all other equipment has been connected. 9. FUNCTIONAL TEST OF SYSTEM Many separate parts of the signalling system will have been tested  beforehand. It  is important that, before any equipment is brought into use, the  signalling is tested as a complete working system. If it has not been possible to do so beforehand, each through circuit must be tested complete to ensure that all controls and  indications operate correctly to the correct function. The signalling must then be tested to ensure that it conforms to the control tables and to signalling principles. It is possible to carry out both these tests at the same time as described below. The aspect sequences between all signals must also be tested by observation of each signal. 9.1 Through Circuits All circuits, whether direct wire or via a remote control or data link must be tested to/from the controlled function. Where cables are terminated intermediately, the polarity is to be checked to confirm that there are no crosses in the circuit. Polarised circuits are to be tested to ensure that they only operate on the correct polarity of supply. 9.2 Control Tables Test This test ensures that the interlocking performs according to the control  tables. It must always be remembered that we are testing that unsafe situations will not occur rather than looking for the expected clearance of signals and movement of points. Therefore, as an example, when testing the controls on a signal, the route  should first be set and the signal cleared. Each individual control must then  be removed in tum to prove that the signal will return to danger each time. Similarly, route locking should be retested as the train clears each track circuit. A test panel, wired to a bank of switches to disconnect each incoming  indication circuit, is the normal means of testing that items such as track  circuits, point detection and lamp proving are included in the appropriate controls. It is vitally important that the test panel wiring itself is documented and tested on its installation and again on its removal. Generally, the tester in charge of this test will require an assistant to operate the various functions from the test panel, If a principles test (see  9.3) is carried out at the same time he must also have an assistant to mark off each item on the control table as it is tested. The main tests to be carried out are listed below although this is not an exhaustive list. Signals All points, tracks, ground frames, slots & releases included. Signal replacement conditions. Overlap controls - including swinging overlaps. Restricted aspect or signal does not clear if signal ahead not alight. Auto buttons, emergency replacement Trainstop/AWS suppression where provided Points Track locking. Locked by all required routes - tested individually. No preselection Route calling Each route calls all required points - test to all possible overlaps. Points held in opposite position prevent route from setting. Route holding   All points locked after route set. Route releasing Points may only be operated after route cancelled & train passed. Approach locking  Approach locked under correct conditions. All combinations of approach under comprehensive approach locking conditions. Release by passage of  train. Release by timer - timing correct.   No release if supply interrupted. Approach control Correct track occupied and time (if timed release). TPR used for approach control is in control of previous signal(s). Opposing locking Direct locking provided. Route locking released under correct conditions. Omitted only where specifically shown. Train operated route release (Automatic  normalisation)  Only operates after signal cleared Inhibited when train approaching Route can be cancelled manually Override controls   Correct signals replaced. Approach lock timed release as appropriate. Auto or selected routes operate correctly. Other miscellaneous items Ground frame releases Level crossings Alarms Block controls 9.3 Principles Test As previously stated, this can generally be carried out at the same time as the control tables test. The tester must request all controls from his knowledge of  signalling principles, not by reference to the control tables. He must not be led by the checker, who is recording the progress of the test on a copy of the control tables. The checker should only intervene if the controls have not been completely  tested. In this case the checker and tester must resolve any discrepancies before proceeding.  Remembering that any redesign must be independently checked and tested, testing staff should not become involved in the detail of any circuit alterations required as a result of incorrect controls discovered during testing. Where circuit alterations are necessary, all previous tests should be repeated on the affected circuits before continuation of the principles test. As well as tests between conflicting routes and points, the tester should also attempt to test  as many other routes and set up as many other independent conditions as possible during testing to prove the integrity of.the signalling. 9.4 Aspect Sequence Test Although the individual signals will have been tested to their controlling relays, this is a vital test which ensures the correctness of all circuits between signals  so that the correct aspect is displayed to the driver. The control tables may be used for this test  but it is often easier and more  efficient to use an aspect sequence chart. Signalling plans should not be used  alone unless they show complete and unambiguous aspect sequence information. All signals should be cleared to all possible aspects for each route. The aspects of all signals which are dependent on that aspect are to be observed and checked for correctness. Lamp proving controls should be tested. For automatic signals, the presence of all track circuit controls should also be tested. Trainstop proving controls should also be tested where appropriate. 10. OTHER IMPORTANT CONSIDERATIONS It has been stated previously but it will be repeated here that all redundant  and temporary test wiring is best removed before the signalling is brought into  service. If this cannot be done, wires to be removed must be insulated at both ends and suitably identified. The removal must take place as soon as possible after testing. The removal of temporary wiring will require a further possession. The circuits affected must be fully tested. Effective communication is vital to efficient testing. All instructions and messages must  be clear and concise. Standard forms of messages should be used where  possible.  Messages should be repeated where necessary. Where radio or telephone communication is used, each person must be clear whom he is speaking to. When requesting an action, confirmation that it has been done should be obtained before noting the results of any test. Consistent terminology should be used throughout Examples are:- Relays - "up" or "down", "normal" or "reverse". Points - "left hand switch closed" or "right hand switch closed" Signals - state lamps illuminated, not meaning of aspect  (e.g.  "yellow",not  caution  or "two green lights", not clear). Give number, letter or position for route, junction or turnout indicators. State whether or not marker lights are illuminated and if  the main signal red lamp(s) remain alight when the subsidiary signal is in use. Trainstop position (where fitted) should also be stated. Track circuits - "clear" or "occupied". There are many advantages to running a test train as an additional final test. Finally, however thorough the test there are likely to be some further  adjustments (e.g. power supply voltages, signal lamp voltages) necessary after commissioning. Remember that the equipment is now working and possessions will have to be requested and arranged. 11. MAINTENANCE TESTING All of the preceding paragraphs refer to the testing required for new and altered signalling installations. The high degree of testing is necessary because the equipment has not been used in service before or its controls have been altered. Testing is often necessary during maintenance activities, either as part of the routine replacement of equipment for servicing or during the rectification of a fault. In general the scope of testing under these circumstances is much  reduced. This can be justified provided the work comes within any of the following categories:- like for like replacement of equipment. The signalling controls and the function and arrangement of all circuits are unaltered. When the work is complete, existing wiring diagrams are still valid. Circuit diversion. Re-routing part of an existing circuit through another  identical item of equipment, e.g. bypassing a faulty cable core or relay contact. The function of the circuit is still identical. The form of the wiring diagrams is unaffected but allocations will change and suitable record must be made of the alteration, whether temporary or permanent. Temporary disconnection of a circuit and its subsequent reconnection in the same form, to enable engineering works to take place (e.g. the disconnection of track circuits or the removal and replacement of a trainstop while permanent way renewals are carried out). If the work affects the form or function of a circuit (e.g. track circuit bonding changes) tests must be carried out as for new work. Under the above conditions, a detailed test of all controls is not necessary because the majority of the circuits have not been altered. The purpose of testing under these conditions is to prove that the replacement equipment has been correctly connected and is in working order, a diverted circuit is connected in the same manner as the circuit replaced or disconnected equipment has been replaced in its original state. It is not possible to give comprehensive rules to cover all known situations but  the following principles should provide useful guidance. 11.1 Preparation and Planning Even with the smallest job, adequate preparation and planning can assist in the prompt execution of a job and its completion without any mistakes. It is often useful to identify the tasks involved and write them down as a check list. In effect, this is a simplified form of the test plan used for new works. If wiring is to be removed and later replaced, the wiring should first be checked to ensure that it corresponds to the wiring diagrams (e.g. by wire count) and any affected wires labelled. Before any work is started, replacement equipment should be inspected and, where possible tested, to ensure it is of the correct type and in full working order. Where more than one  item of equipment is involved, all equipment should be available at the site of work. Cable cores and other wiring to be used for diversion of circuits should be tested for continuity and insulation to earth. Contacts on relays should be checked that they are of the same configuration as the faulty contact (i.e. front or back). If a component or module to be replaced  has any variable settings,  a note should be made of the existing settings for later reference (e.g. track feed resistor/capacitor, power supply transformer tappings). This will aid setting up but does not avoid re-testing of circuit values and adjusting as appropriate. 11.2 Execution of Work Make the necessary arrangements for possession of the affected equipment  and ensure that the appropriate rules have been complied with before commencing work. Take the necessary steps to ensure staff safety by switching off power or disconnecting circuits as appropriate. As the work progresses, check that each step has been carried out before  proceeding to the next. Where wiring has to be replaced, check that the  termination point of each wire conforms with the labelling and carry out a wire  count when all wires have been replaced on their terminations. Depending on the type and scale of the work, it may be better to test in stages or to carry  out a single final test. Do not hand back equipment to service until testing is complete. 11.3 Testing on Completion Ensure that equipment is correctly fitted and secured. Carry out a wire count  on all terminations where wires have been removed and/or replaced. Carry out any earth or insulation tests according to the type of equipment. Perform any mechanical adjustments of equipment (e.g. point machines) before applying power. Test for the correct operation of the new or replacement item of equipment in the existing circuits. Full circuit tests should not need to be carried out on  parts of the circuit which have not been affected. Ensure that equipment is labelled correctly. 11.4 General Precautions Although it is important that persons do not test their own work, the strict requirements for independence of new works testing are not necessarily appropriate for maintenance testing. Much work, particularly fault rectification, will be done by a small team of perhaps  two or  three staff. One of these may need to perform lookout duties. It is therefore permissible in most cases for one person to direct and test the work provided he does not participate in the detail of the installation. It is essential when carrying out any work that complete current circuit  diagrams are available. If an alteration to equipment allocation is necessary, this should be noted on the wiring diagrams and (if permanent) arrangements made for the records to be amended. 12. CONCLUSIONS Following testing, the equipment is brought into use. It will now be used to  control real trains. Rigorous design, checking and installation procedures, together with the tester's skills must have eliminated any remaining errors in design and installation. The only acceptable level of accuracy is 100%. Testing is the last defence against any previous errors.  The safety of the railway depends on it.

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Deepu Dharmarajan -
Posted 90 days Ago

CHECKING PROCEDURES

  CONTENTS 1. The Purpose of Checking 2. What Should be Checked? 3. The Checking Process 4. Checking for a Typical Signalling Project 1. THE PURPOSE OF CHECKING 1.1 The Signalling Production Line  The following is a very simplified view of a signalling project from beginning to end. Note that checking does not appear as a specific item. This is because it should be built into each stage to ensure that it is being carried out correctly. This is part of the quality control of the whole project. It should be an integral part of every task. Each check should be recorded so that the next stage can use the results of the previous stage as a basis from which to work. 1.2 The Importance of Checking A signalling system is required to perform correctly to ensure the safety of the railway. Unfortunately the system is specified, designed installed and tested by humans. Humans despite their ability to process information better than any computer have a tendency to make mistakes occasionally. The purpose of checking is to ensure that these mistakes are detected and corrected before they are incorporated into a working system. 1.3 Checking Principles These notes cannot cover in detail how to check. That is a skill which the checker develops with experience. There are however some basic principles which should be observed. The producer should first check the work. Any responsible designer should not pass on his work knowing that there are errors present or assuming that another person will find any deficiencies. The designer should aim to get  his work right frrst time. Of course this will not always be possible but, if errors have been made, it is better for the producer to identify them for his own future reference. All formal checks should be independent.  Anybody,  particularly an  engineer can become so familiar with his work that he fails to detect simple  and obvious mistakes. Where checking is a mandatory part of any design process, this should be performed by somebody who has not been involved in the detail of the work. Be sure of your assumptions. Any drawing will make certain assumptions, about site information, equipment performance, materials or the user of a system. The checker should ensure that he is informed of all assumptions made and be prepared to challenge them if necessary. Record all checks as you go. If you get interrupted, it is possible to see where you need to resume. If somebody takes over from you, he will know what is left to be done. Most important, you have a record for future reference that the check has been carried out. Be sure you check enough. On a new installation, deciding what to check is  easy - everything is a new design so it all needs checking. Where alterations to working circuits are involved, this decision is not so easy. For a minor  alteration, there is no point in checking every circuit on every wiring diagram if 95% of them are unaltered.  However, deciding the boundaries of what should be checked requires great care. 2. WHAT SHOULD BE-CHECKED? These notes are mainly intended for those who will be involved in producing and checking drawings in various forms. These drawings will be used for:- Agreeing the specification for the system. Estimating and ordering of materials A contract with a supplier or installer Installation of the equipment Testing and commisioning Maintenance of the system, probably for a long period after it has been installed. Drawings retained as a record of a working system will be used as the starting point for any future alterations. It is just as important that these are correct as those drawings used for installation. Drawings used for any of  the  above functions, either directly or indirectly,  should always be independently checked. The checking should ensure that the drawings are consistent with all previously checked drawings for the same project or system. 3. THE CHECKING PROCESS  3.1 Who Should Check?  As mentioned earlier, the first check should be performed by the producer himself. In most cases this will be followed by a more formal check which should be independent of the producer. Many organisations have strict rules as to who should check certain types of  work, or the work of specific individuals. These notes do not set out to challenge those rules. If there are no clear rules on checking in your organisation, it would be desirable to establish some. The general principles must be that the checker will:- Be independent of the work which has been done. Nobody should be required to certify that their own work is totally correct. In general, though, it is acceptable for a person who is involved in the planning or management of a project to check elements of the detail provided he has not been involved in the production. Be qualified to check the work in question. He should obviously be capable of doing equivalent work himself. It is a matter for each organisation to decide whether and how to ensure, certify, and record  that an individual is capable of checking particular types of work. Have the authority, either directly or indirectly, to ensure that any errors found are corrected. Many organisations require that the checker is of equivalent or higher status than the producer. These principles can be applied whether persons are employed purely as  checkers or alternate between production and checking. 3.2 When Should Checking Be Done? In general, checking should be an integral part of each step in a project.  It should ideally be done as soon as possible after completion of one stage and  before the commencement of the next. Otherwise there is a risk of errors  being carried forward which will subsequently be more difficult to correct. Only in the case of very minor works should checking of the whole design  process be attempted in a single stage. 3.3 Where Should Checking Be Done? Most design work will be done in an office and there is no reason why the checking should not also be done in the same office. However, some checks  will require information from site. If these are not adequately documented in the office, a physical check of certain site details may be necessary. 4. CHECKING FOR A TYPICAL SIGNALLING PROJECT  As an example of the type of checks that should be made to ensure the accuracy of all documentation for a signalling project, the main types of drawings required for a new or altered route relay interlocking are listed below  together with the type of checks that should be made and the source of information against which the check can be made. It is important to note that this is not an exhaustive list. The student will no doubt think of other items to add. It should also be noted that many of the checks involve ensuring consistency between drawings. Others may require reference to external sources  of information. 4.1 Signalling Plan/Layout Check Source of Information Track layout correct Distances accurate Braking distances adequate Signal profiles correct Route information correct Track circuits correct Signal/point/T.C. numbering Headways adequate P.Way drawings, site surveys P.Way drawings, site surveys Braking charts/tables, gradient profiles Signalling principles Signalling principles Signalling principles Signalling principles Headway charts  4.2 Control Tables Check Source of Information All signals & points listed All controls included Converse controls shown Signalling plan Signalling principles,signalling plan Cross-check between control tables 4.3 Location Area Plan This is normally derived by adding information to a copy of the signalling plan. It should therefore be confirmed that the original signalling plan has been checked. Check Source of Information Each function (signals, points, track feeds and relays assigned to a location Location suitably sited By examination of plan Site survey 4.4 Interlocking Wiring Diagrams Some work can be saved here if the circuits have been drawn to standard masters, with only the individual function numbers/letters added to each sheet. Provided the master has been checked for correct circuit operation, only the existence of the correct circuits and the correct labelling need be checked. Check Source of Information All circuits drawn All controls included Correct circuit operation Equipment space allocated Relay contacts allocated Correct contact type used Fuses allocated Terminals allocated Wire count recorded Signalling principles, circuit knowledge, control tables Signalling plan, control tables Circuit knowledge Relay rack layout Relay contact analysis Contact analysis, relay specs Busbar allocation Terminal panel Relay contact analysis 4.5 Cable Schematic Check Source of Information All locations included Correct size & type of cables Location area plan Cable core allocation, power supplies 4.6 Cable Core Allocation Chart Check Source of Information All functions included Correct type of circuit Through spares reserved Circuit suitable for cable type Signalling plan, location area plan Signalling principles, loc & relay room  wiring By observation Knowledge of equipment 4.7 Location Wiring Diagrams (& Equipment Layout) Check Source of Information Equipment space allocated All functions included Terminations correct Circuits correct Loc. internal layout drawing Location area plan, cable core allocation Cable core allocation Signalling  principles 4.8 Track Circuit Bonding Plan Check Source of Information Position of block joints Clearance points Traction bonding continuity Min/max T.C. lengths Series bonding Feeds/relays shown Signalling plan, P.Way drawings Control tables By observation Signalling principles By observation Location area plan 4.9 Control Panel Faceplate Check Source of Information Correct layout Numbering Indications Button & switch types Track circuit colours Signalling plan Signalling plan Signalling principles Signalling principles By observation 4.10 Relay Rack Layout Check Source of Information All relays shown Relays correct type Wiring diagrams Signalling principles, relay specs 4.11 Terminal Panel Check Source of Information Circuits shown Functions allocated Wiring diagrams Cable core allocation 4.12 Power Supplies Check Source of Information All supplies shown Transformers etc. correct rating Fuse discrimination Fuse/busbar allocation Wiring diagrams Wiring diagrams (equipment count) Wiring diagrams Wiring diagrams 4.13 Relay Contact Analysis Check Source of Information All relays shown Correct contact arrangement Wire count shown Contacts allocated Relay rack layout Relay specs Wiring diagrams Wiring diagrams 4.14 Aspect Sequence Chart Check Source of Information All sequences shown All sequences correct Signalling plan Signalling plan, control tables 4.15 Other documents Other documents not included here may comprise:- Remote control schematics Remote control allocations & interfaces Level crossing layouts Train describer stepping controls Train describer interfaces On computer based systems such as SSI and most train describer systems, much of the information is computer generated data. Checking and testing SSI installations is a large enough topic for a course on its own. It is too specialised to be covered in detail here.  

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Deepu Dharmarajan -
Posted 91 days Ago

OTHER ELECTRONIC SYSTEMS

    CONTENTS 1. Introduction 2. Hot Axlebox Detectors 3. Closed Circuit Television 4. Axle Counters 5. Passenger Information Systems 1. INTRODUCTION For many years, the signal engineer has justifiably had a cautious approach to electronics. Electronic systems were introduced to enable communication over longer distances and non-vital data handling. They were not at first trusted with any of the safety functions of signalling. However, with the increase in  reliability of electronic components, a better understanding of fail safe circuit design and most recently the application of microprocessor technology, the use of electronics has become an essential part of signal engineering. Some applications, like track circuits, train describers and remote control systems, have been dealt with elsewhere in the course. This section is intended to give a brief appreciation and understanding of the application of other electronic systems so far not covered. Systems to be covered are those which form part of the operation of the railway, rather than those which come under the category of general communications and/or data processing systems. 2. HOT AXLEBOX DETECTORS 2.1 Background When signal boxes were located at frequent intervals along the line, one of the duties of the signalman would normally be to observe the train. If he observed any defect or irregularity, he could stop the train (or request the signalman at the next signalbox to do so) and arrange for it to be diverted to a siding and/or examined. As many lines are now centrally controlled there is less opportunity for trains to be observed. One of the most likely occurrences requiring a train to be stopped is an axle bearing running hot. This could potentially disable a vehicle and in the worst case lead to a derailment. Hot Axlebox Detectors (HABD's) are intended to detect such defects before they become dangerous. 2.2 Principles Different vehicles have different types of axle bearings which may have a wide variety of normal operating temperatures. Within this wide range, the equipment must be capable of detecting any overheating axlebox before it reaches a dangerous state. All hot bodies radiate infra-red heat. Therefore, detection of radiation at the appropriate wavelength  would appear to be the best means of detection. However there may be many other quite normal sources of heat, including the sun and parts of a locomotive, present at the same  time. In addition the temperature of a "hot" bearing will differ according to the ambient temperature. To be acceptable to the user, equipment must be reliable. Reliability of HABD equipment includes correctly detecting those axle bearings which are excessively hot while  minimising the number of false alarms. Regular false alarms will delay traffic and will eventually lead to the user ignoring the alarms which are given. These problems have been solved by the following means:- The amount of radiation received, which is an indication of the temperature of an axlebox at a fairly constant distance from the scanner, is compared  against an  absolute level - a temperature above which no normal axlebox is likely to run - and between the left and right axleboxes of the same axle. As both axleboxes are of the same design, a significant temperature difference indicates a possible defect. To eliminate the effects of extraneous heat radiation, the  scanner  is  precisely focussed on the trailing or rear side of each axlebox. The received radiation is then "gated" with the presence of a wheel on the rail. A transducer mounted on the rail detects the presence of the wheel  flange  by  a change in the magnetic circuit formed by the transducer, the rail and the steel flange. The received radiation is filtered to only accept the frequency range known to be produced by hot axleboxes. The design of the optics and the sensors  is a very complex and specialist area. Essentially, the heat sensing probe measures the radiation when an axlebox is directly in line with the scanner, compares the left and right hand readings with an absolute  maximum level and with each other and raises an alarm if the temperature is outside the expected range. The lineside equipment may be a considerable distance from the  control centre.  A transmission system is normally required to communicate between the lineside equipment and the signalman's display. A block schematic of a typical system is shown on the accompanying diagram. Original systems used analogue signal processing which required careful setting up and  frequent maintenance to ensure reliable operation. With the introduction of microprocessors, the data obtained from each passing train can be processed more  thoroughly and the equipment can within certain tolerances be self calibrating. As well as comparing both sides of each axle, the processor can store and compare the readings along the train. Based on the reasonable assumption that the number of hot axleboxes on any train will be very small, the processor can filter out the situations where one train appears to give a large number of alarms. Too many alarms generally  indicate  that the equipment is too sensitive. Hot Axlebox Detector Layout and Schematics 2.3 Signalman's Display The signalman does not need to know the state of every axlebox on the train, only those which are suspected to be defective. Additionally, if there is more than a small number, this information will be of little use when examining the train. Signalman's displays therefore generally show a maximum of three alarms giving the axle number and whether left or right axlebox. They may also count the total number of axles on a train. Originally, a separate display was provided. However it is easier for the signalman if HABD information is incorporated into his main operating area. It is therefore often included in train describer displays on a VDU. If he has a VDU based display system, the alarms could be reported on a general purpose alarms screen. Siting of HABD Equipment The careful choice of a site for a HABD installation can make it both more reliable in use and more effective in detecting hot axle boxes (thus minimising potential false alarms and disruptions to traffic); The main operational requirements are:- There should be a convenient loop or siding beyond the detector equipment where vehicles can be examined and/or detached. A signalman should be able to stop and/or reroute a train with a suspected hot axlebox as soon as possible after receiving the alarm but without changing a signal to a more restrictive aspect immediately in front of the driver. Equipment should be sited so that hot axleboxes can be detected and trains stopped before critical sections such as long tunnels, viaducts and single line sections. Trains should not normally brake over or just before the detector. The heat  produced could cause false alarms. The detector should be at a site where most  trains are running unrestricted at normal line speed. Trains should have run for a sufficient distance and at a sufficient speed for axleboxes to have reached their normal operating temperature before passing over the detector. It should be at a position which will be passed by the majority of traffic on the line. It may be necessary to reach a compromise between some of the above requirements.  On BR a spacing of 35 to 50 km. between detector sites is normally suitable. Obviously, the investment in HABD equipment has to be set against the likely number of hot axleboxes detected. This will increase with the frequency of traffic. HABD's are therefore  generally placed on busy main lines rather than infrequently used branch lines. The equipment will operate most reliably if it does not sense heat from sources other than hot axleboxes and its alignment with respect to passing vehicles can be precisely maintained. It should not be located where it can receive direct rays from the sun. It should also be mounted on straight, level, well maintained track which will minimise vibration from passing trains. Failure to observe these rules will probably result in an increase in false alarms and a reluctance of staff to act upon alarms received. 3. CLOSED CIRCUIT TELEVISION Closed circuit television (CCTV) is used in a railway environment for any of the following purposes. Many railways, especially urban and underground rapid transit systems employ CCTV for general surveillance, security and passenger control purposes. To monitor controlled level crossings (i.e. those which are  interlocked  with  the signals but remote from the controlling signal box). Where trains are operated by the driver only with no other train operating staff on board, it is vital for the driver/train operator to be able to see along the full length of the train to safely close the passenger doors. On straight platforms, this may not be a problem, but where the platform curves or is frequently very crowded, CCTV is used to allow the driver to observe the full length of the train. As the fast category may be found outside the railway environment, it will not be covered further here. 3.1 CCTV at Level Crossings 3.1.1 General Arrangement The signalman operates the barriers and road signals  remotely from a control panel Television monitors are used to select when to operate the barriers and to check that the crossing is clear before signals protecting the crossing can be cleared. Barriers are normally provided across the full width of the road and are fully interlocked with the protecting railway signals. Road signals are also provided. It is possible to take local control of the barriers and, once this has been done, the  signalman is unable to view the crossing or operate the barriers. Cameras at the crossing are duplicated for availability. They are mounted on a pole and  may be lowered independently for maintenance or repair. Both cameras are aligned for the same view of the crossing. The picture should cover to about 2 metres beyond the point at which road vehicles will stop. The picture should show the barriers when lowered and the whole of the level crossing area (which should fill at least 50% of the monitor screen area. Signalmans Control Panel for CCTV Supervision of Level Crossings The location of the cameras is selected to avoid bright lights entering the camera lenses. Sunlight, either direct or reflected from rails etc, and vehicle headlights can damage the cameras. For night viewing it is necessary to illuminate the crossing.  Suitable lighting poles are provided to give a uniform illumination of the whole crossing area. In the signalbox two monitors are provided per crossing. Generally a signalman will supervise a maximum of two remote crossings, although in some situations it is possible  to add a third. If a large number of crossings is monitored, it is more economic to provide spare portable monitors. A set of level crossing controls is provided for each crossing, which may be mounted in the signalman's control panel as the example shows. 3.1.2 Signalman's Controls Alarms are provided for the crossing equipment and the crossing power supply.  A failure will initiate an audible alarm and cause the appropriate lamp to flash. When acknowledged by pressing the button, the indication will be continuously illuminated. When the fault  is cleared the light will again flash, requiring a further acknowledgement, after which the lamp will be extinguished. A wiper is provided for each camera to clear rain and snow. An on/off switch  controls the wiper of the camera in use. The signalman may select camera 1 or 2 by a 3-position (centre off) rotary switch. He may select the required monitor by a similar switch. Although control of crossing illumination is generally automatic, a "day/night" switch will override the automatic controls to switch the crossing lights on and also open the camera  lens iris to admit maximum light. To maximise camera tube and monitor life, the picture is normally switched off. To display a picture before operating the barriers, the picture button must be pressed. The picture may also be turned off by pulling the button provided the crossing operating sequence has not commenced. Push buttons are provided to raise and lower the barriers. The lower button must be continuously depressed until the barriers are fully down. An alternative to this arrangement is to provide "raise",  "stop",  and  "lower"  buttons.  A  momentary operation of each  button is then required. For most movements the barriers may be raised automatically after the passage of  the train. The "auto raise" facility is controlled by a two position switch. Indications are provided for barriers fully up and fully down and for the road signals operating. After the barriers have lowered, the barriers down indication flashes until the "Crossing Clear" push button is pressed. It will then show a steady light. The crossing clear button must be operated by the signalman to enable the signals to clear. He must therefore observe that the crossing is actually clear  before pressing this button. It will also extinguish the picture if automatic raise has been selected. 3.1.3 Operating Sequence Assuming that a camera and a monitor have been selected but the picture is off, the normal operating sequence would be as follows:- Push and release Picture Picture will be displayed. Push and hold Lower button. The road  signals will commence operation and after the appropriate time the barriers will start to lower. The road signals are then indicated. When all the barriers are fully lowered, the barriers Down indicator flashes. The signalman may release the lower button. After checking on the monitor that the crossing is actually clear, depress the Crossing Clear button until Down indicator goes steady.  If the conditions are set for Automatic Raise , the picture switches off. If set for Manual Raise the picture remains on. Signal(s) will clear for routes over the crossing. These routes may be set before or after the barriers are lowered. If automatic raise is selected, the barriers will raise after the passage of the train(s). If manual raise is selected the barriers will remain down until the routes over the crossing are normal and the raise button is pressed. 3.1.4 The CCTV System The earliest CCTV systems installed on B.R. for  monitoring remote level crossings were base band systems i.e. the video signal was transmitted directly down the transmission line consisting of coaxial cable. This arrangement severely limited the distance between the  crossing and the  supervising signal box due to degradation of the video signal. A simplified diagram of such a system is illustrated on the following page and consists briefly of two cameras mounted on a pole to survey the crossing area, control circuitry situated by the crossing, a transmission system to link the remote crossing to the signal  box and monitoring equipment in the signal box. A camera column is provided at the crossing to accommodate the two cameras. The selected camera would normally be in the "Standby" mode until required (Working but not providing pictures). Each camera is mounted on a platform trolley on a pan and tilt head and can be lowered independently for maintenance purposes. The cameras are contained within Environmental Housings equipped with a  screen wiper and thermostatically  controlled heater. Additionally a motorised sun shutter is fitted which shields the lens  when the camera is not in use and an iris motor to control the lens aperture to its two settings  i.e.  f/5.6 during the day and f/1.4 for night. CCTV Supervision of Level Crossings The barrier apparatus case contains all the relay circuitry to control the cameras. Also contained are the two Camera Control Units (C.C.U.) which provide all power supplies and certain controls to the cameras. Each. C.C.U. is adjusted to control one particular camera. The "Video Relay and Test Unit" is an extra unit which is used to monitor the off-line camera for maintenance purposes. A special cable connects each camera to the location case and carries all video, control and power functions needed to operate the camera. Wherever electronic circuitry is connected to a cable running along the track, some protection is required against lightning strikes. In C.C.T.V. applications a surge protector module provides this protection. Most other circuits between the crossing location and signal box are sent through standard signalling multicore cables or via a remote control link. The crossing clear circuit is however a vital signalling function and must not be sent via a non-vital  remote  control system. The equipment is designed to require as little adjustment by the signalman as possible. Therefore the monitors are only provided with brightness and contrast controls to allow adjustment for ambient lighting conditions and personal preferences. 3.1.5 Transmission Systems To improve noise immunity over longer distances, most systems use a carrier system  rather than base band transmission. In this case, the video signal is modulated on to a carrier of 14.5 MHz then sent via a surge protector onto the cable. There are repeater stations which amplify the signal. At the signalbox the signal is demodulated and the video  signal is fed to one of the monitors. The system is designed so that an ordinary monitor can be used to check for the presence  and quality of the signal at each repeater. A video output is provided for this purpose. The attenuation of the cable used is specified as 10dB/km at 10MHz. The attenuation at 14.5 MHz is 12dB/km and higher frequencies are attenuated progressively more than the lower frequencies. The modulated video signal has a bandwidth of 9-20 MHz  and so the higher frequency components will thus be more attenuated than those at 10 MHz. To overcome this problem the modulator and line amplifiers incorporate a means of providing "Slope Correction". Even with the use of a carrier system, the repeated amplification of an analogue signal will introduce unacceptable levels of noise. A practical limit of length is reached at about 30km. To improve picture quality and noise immunity, the  equipment for modem crossings processes the video signal digitally, usually with fibre optic cable as the transmission medium. Provided the digital signal can be regenerated at regular intervals, there is no limit (in theory) to the distance of the level crossing from its control point. Even with a monochrome monitor, the bandwidth of the video signal is large. To reduce the transmission capacity used, slow scan techniques are used on some crossings. This is in effect the transmission of only those parts of the picture which change.  As most of the crossing view remains constant, this economises on transmission capacity. This does however affect the response speed when changes are  widespread over a large portion of the screen. Fortunately, at the time when this is likely to be most critical (with the barriers down) there should be minimal change to the content of the picture in the area covering the railway. CCTV for Driver Only Operation The potential staff savings from driver only operation (DOO)  are  significant. It is also  usually argued that the quality of on-board ticket examination and issuing can be improved if those responsible do not have to deal with operational safety matters and do not have to be allocated to work on  the  basis of one person per train (i.e. resources can be concentrated on those services where the commercial requirement is greatest). As a result, the driver is the only person responsible for the train's direct control and cannot be  expected to leave his cab on a regular basis. He must be able to perform all normal duties from his normal driving position. This will in general require:- A secure radio link for DOO drivers to use in place of signal post telephones. Means for station staff, where necessary, to convey clear messages to the driver regarding the closing of doors and/or clearance to start from the station. Where station staff are not available (or may not be available) to supervise all station stops, the driver must have a clear view of the full length of the train at each station. The third condition is difficult  to fulfil on many curved platforms and may require the use of closed circuit television. The  basic principles for the provision of CCTV equipment are as follows:- Monitors must be grouped together and clearly visible from the driving position at the normal stopping point of the train. Where different length  trains  are  operated, more than one set of monitors may be needed. Monitors must be visible during day and night and under all weather. This often requires the provision of hoods to minimise glare. The monitors  should also be angled down (unless in tunnel). Monitors should be mounted in a position which will minimise vandalism where this is likely to be a problem. Sufficient cameras should be provided  to give an adequate view of the full length of the train. Train length, picture resolution, size of monitor screen and environment will all need to be considered. On BR, certain problem platforms have required up to 5 cameras for 12 car trains. To avoid the need for an excessive array of monitors, split screen pictures should be used. Two views along the train can usually be accommodated side by side on a single monitor. The system should be switched to a standby mode when no train is in the platform to maximise camera and monitor life. Usually this can be accomplished by a simple track occupied input from the signalling. Maintenance arrangements must ensure a high availability of equipment and prompt attention to failures. Once a line is fully equipped, it is unlikely for there to be a surplus of station staff waiting to attend stations at which CCTV equipment has  failed. 4. AXLE COUNTERS 4.1 Introduction For many years, the normal means of train detection has been by track circuit. A  wide variety of track circuit equipment is available to cater for different types of  track and traction equipment. However, there remain some situations where the track circuit cannot be used or  is  unreliable in operation. Some of these situations are listed below:- Ballast Conditions. The ground conditions, or sometimes the structure upon which the track is laid, may be electrically unsuitable for a track circuit, e.g. track directly fixed to a steel bridge, use of steel sleepers, ground conditions varying between totally dry and waterlogged making satisfactory adjustment impossible. Length of Track Section. For very short track circuits, there is a minimum length below which some vehicles may not be detected. It may therefore be impossible to provide track circuits sufficiently short in length through some crossings (e.g. large angle between tracks of multiple track lines crossing each other). Conversely, there is also a maximum length over which any track circuit will operate. Multi- section track circuits can be very expensive to provide. Access to Line. A track circuited line wil need access at regular intervals for maintenance. In long tunnels and in areas where the terrain makes safe access difficult, it is undesirable to locate any equipment which requires regular maintenance. Power Supplies. On long sections of rural railway, it is expensive and therefore undesirable to provide lineside power supplies. Axle counters can assist in solving these problems 4.2 Principle of Operation As its name suggests, the axle counter operates by counting the number of axles entering and leaving a track section, as opposed to a track circuit which proves that an entire track section is clear of rail vehicles. Provided there is a reliable, fail safe communications link between the ends of the track section and the interlocking, its length may be as small or as large as required. It is not constrained by minimum vehicle lengths or the electrical characteristics of the trackbed. When the section is clear, the count of axles in the section must be zero. As a train runs  into the section, each axle is counted in and added to the total. When the train leaves  the section, each axle is counted out and subtracted from the total. A zero total is therefore equivalent to a track circuit clear, a nonzero total is equivalent to a track circuit occupied. The detection and counting equipment must be capable of bidirectional operation.  Even if this is not required for normal traffic, but the absence of this facility will prevent return to normal use without manual intervention after an emergency or irregular train movement. 4.3 General Description of Equipment The German manufacturer, SEL provides the majority of Axle Counter equipment. The following description relates to their systems. Axle Counter General Arrangement The equipment can be divided into three basic parts:- The trackside (including track mounted) equipment which detects the passage of the wheels of the train. This in tum controls a.c. signals to the interlocking or other suitable central location. A transmission link from the trackside to a suitable location or equipment. The equipment has the facility to transmit to two separate destinations to enable one set of track equipment to serve the boundary between track sections in different interlockings. The "indoor" equipment which processes the signals from the various trackside detection points and converts them into "track clear" or "track occupied" data in a form that can be used by the interlocking. It also monitors the trackside equipment for correct operation. 4.4 Wheel Detection Toe track mounted equipment must reliably detect the passage of each axle as it passes the detection point. It must be able to detect the direction of travel of  the train. It must operate over the full possible range of train speeds. An electromagnetic system is used. A detector consists of a transmitter on the outside of each rail and a receiver on the inner (running) edge of the rail. Two of these detectors are mounted in close proximity (170-200mm measured along the track). To detect the direction of movement, the two detectors are staggered. Toe stagger distance must be large enough to detect the direction of movement at high speed but small enough to ensure detection of only one axle at a time. Older systems were mounted one on each rail, newer systems are constructed so that all the track equipment can be mounted together on one rail, simplifying the cable connections. The distance is normally set at about 170mm. Both detectors can therefore be mounted in the same sleeper bay. Both the transmitter and receiver consist of coils wound on to a magnetic (ferrite) core. The transmitter coil is adjustable to suit different magnetic characteristict of various rail profiles. It is continuously fed with an a.c. signal. Rail Mounted Transmitter and Receiver Axle Counter Track Equipment Although the magnetic field surrounding the transmitter, receiver and rail is complex, the simplified diagram assumes two components of flux, ∅1,  and ∅2, linking the two coils.  With no wheel present ∅1, is greater than ∅2. The wheel and flange have a greater effect on ∅1, reducing it almost to the level of ∅2, in older systems and, due to differing frequencies used, below the level of ∅2, in more  recent systems. The induced voltage  therefore  reduces almost to zero (older systems) or reverses phase (newer systems). By  processing the outputs from the two receivers the number of axles passing the detection  point, and their direction, can be determined. Alongside the two rail mounted detectors is a junction box containing  the electronics and power supply. It is connected to the location or equipment room by a two core balanced cable (some four wire circuits were used in older systems). As the wheels pass over the detector, each receiver experiences a reduction or phase reversal of voltage in each receiver. On earlier systems the outputs were each amplified  and transmitted to the indoor equipment. Newer systems perform more processing at the trackside. The Tx/Rx board for Tx/Rx1 produces a continuous 30kHz signal. Tx2 & Rx2 operate at 29kHz. The receiver signal is then compared with the transmitted signal. As the wheel passes, the phase of the receiver  signal will reverse. This causes the d.c. output of each Tx/Rx  board to switch between a high voltage (logic 1 - no wheel present) to a low voltage (logic 0 -  wheel  present)  and back again. These two pulses are modulated on to 5060Hz and 4150Hz signals respectively. These are then transmitted together with a supervisory signal at  2530Hz  over  a single cable pair to the evaluator. Axle Counter Signal Waveforms Referring to the waveforms shown, if we assume that the track section is to the right of the detectors, a vehicle passing from left to right (into the track section will produce a pulse on  Rx1 first. A vehicle travelling from right to left will produce a pulse from Rx2 first. 4.5 Transmission This consists essentially of line matching at each end and a twisted cable pair between the trackside and the location or equipment room. The length of the transmission circuit is limited by the attenuation of the audio frequency signal which imposes a practical limit of about 20km. A lower transmission frequency can be  used  to  increase  this  distance  if required. If the d.c. supply to the junction box is fed via the transmission line (to avoid a separate power cable) the maximum circuit length for 0.9mm diameter conductors  is about 4km. It can therefore be seen that there is potential capability for axle couters to cover much longer track sections than track circuits. 4.6 Indoor Equipment To operate the equivalent of a track circuit, data is required from two (plain line) or more  (points & crossings) detection points. More complex track layouts can be provided for by the use of additional detectors. By provision of appropriate wiring between the inputs and counters, overlapping track sections could be catered for if required. the evaluator  requires an input for each detection point and a counter for each track section. The received a.c. voltages are filtered and amplified and converted to a d.c. pulse for counting. Axles can now be counted "in" and "out" with respect to a nominated reference direction (equivalent to up or down traffic). An "in" count  for  example  may  add to or subtract from the count for a section depending on whether the detector is at the up or down end. Pulse 1 is used as a gate pulse which must be present for any count to register. Pulse 2  counts in or out depending on whether the falling or rising edge falls within pulse 1. Each counter is a binary counter capable of counting up to 511, 1023 or more axles as appropriate to the traffic needs. If the count is zero, a "track clear"  output is produced, if non zero, a "track occupied" output is produced. On a plain line track section, in pulses from one input will add to the count while out  pulses from the same input will subtract from it. The converse will apply for the inputs from the other detector. To ensure fail safe operation the equipment also includes several checking and monitoring circuits at each stage of  the counting  process. There will not be opportunity to cover  these in detail. In essence, however, a correct count "in" or "out" will only be registered by the combined signals from both rails. Any irregular signal from one or the other of the detectors will invalidate the count, raise an alarm and show the equivalent of a "track occupied" indication. 4.7 Failure of Equipment The outputs from the counters are in the form of "track occupied" (count non-zero), "track  clear" and "alarm". To correctly give a track clear  indication to the interlocking,  the track clear output must be present and the other two absent. All  other  conditions  will produce  a track occupied indication to the interlocking. Circuits are provided to monitor all counts into a track section. Any failure in counting out will automatically result in a track occupied indication because the resultant axle total will not be zero. A significant change in the gain of any amplifiers in the system will result in the count  in not being valid, due to the change in received voltage. Any change in the frequency of the oscillators and/or filters will result in the absence of an input a.c. signal thus initiating an alarm. If a failure occurs, the counter can be reset to zero by the maintenance technician after remedial action has been taken. Great care must be taken to ensure that the section is clear of all trains when this is done. Axle counters can therefore be used as an effective substitute for track circuits where track circuits would be either impractical or unreliable. 5. Passenger Information Systems 5.1 Purpose of Passenger Information Systems Passengers must be reliably informed of the details of their intended train if we are to expect them to continue to use rail services. This involves presentation of some or all of the following information:- Platform and time of departure Calling points Facilities available or formation of train Any delays or disruption to normal service This  can  generally be presented by fixed information displays (e.g. departure posters),updated visual indications giving current arrival/departure information and loudspeaker announcements. The requirements will vary considerably according to the  type of station and train services operated. 5.2 Structure of Systems The simplest systems can be purely manual, an operator making announcements or setting up displays according to the timetable and information received on train running. It is possible to provide a much more accurate and reliable system if some of the tasks are automated. Whatever the type of system, it is likely to consist of the following. Data storage relating to the planned service, at its simplest a list of trains and their calling points, at its most complex a complete stored timetable. A facility to update this data for alterations to the train service. This may be a manual editing system or automatic updates from the train describer or a combination of both. A transmission or distribution system to transfer selected parts of the current train running data to the points at which it is to be displayed. A display system appropriate to the needs of the station. This may consist of individual platform displays or concentrated displays for the whole station. Train information may be complete or summary only. Indicators may be required at entry barriers, subways and footbridges, ticket and information offices and other locations 5.3 Data Storage and Communication For large terminal stations, a comprehensive system is likely to be needed to give passengers preliminary information on departures long before the train describer even knows of the existence of the train in its control area. Some form of stored timetable is essential. Operation of the system is usually by a combination of manual and automatic  input.  The user may be prompted to enter a train into the active system at a certain time  before departure. There will almost always be a need to handle short term amendments such  as platform changes. For smaller stations, the source of data could be from a stored timetable at a major centre, if necessary transmitted only on an instruction from the train describer. Human  intervention will be minimal unless the service is disrupted. On rapid transit systems where all trains follow an all stations stopping pattern to a small number of destinations, information on train destination may be all that is necessary. The train itself may be used to identify the destination at a fixed point on the line. This is transmitted forward to each station ahead of the train. 5.4 Display Systems The  following methods of display are in common use:- Flap indicators  -   clear, reliable  but inflexible to major changes service pattern. Large number of moving parts to be maintained. Dot matrix (electromechanical) - more flexible than flaps but a large increase in moving parts. Usually requires backlighting to give a sufficiently clear display. VDU - probably the most flexible but can be difficult to see at high ambient light levels. Dot matrix  (LED) - generally unsuitable for outdoor use but adequate for underground stations. Liquid Crystal - reliability now improving. Some contrast problems, generally solved by external or internal illumination. 5.5 Audio Systems Apart from the permanent train announcer which will probably still remain effective at large stations, better control of audio announcements can be achieved by recorded announcement systems and long line public address. Recorded announcement systems now tend to use digitally stored speech (using EPROMs) rather than the older analogue tape method which was prone to rapid  deterioration with regular use. Triggering of the announcements can be by station staff  or automatically with the approach of the train. Long line public address enables the announcement of train running information,. particularly for disruptions to service at unstaffed or partially staffed stations. They can be operated by the train announcer at the main control centre.  

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Deepu Dharmarajan -
Posted 92 days Ago

INTERFERENCE & IMMUNISATION

    CONTENTS Introduction Traction Systems D.C. Traction Systems Mixed Traction Systems Protection Against Other Forms of Interference Future Developments and Problems 1. INTRODUCTION Electric traction is increasingly being used as an economic means of operating a railway. Electric power is taken from the national or regional supplier. Due to the scale of production this can normally be produced at a lower price than with individual power units on each locomotive. Electric locomotives are much simpler and cheaper to control maintain and operate than their diesel equivalent. Electric traction brings with it a number of additional problems for the signal engineer. Signalling equipment, in most cases, operates at relatively low voltages and currents compared to locomotives and multiple units. Unavoidably, traction circuits run alongside and even share conductors with signalling circuits. Interference, usually through direct contact or induction must be anticipated and equipment protected from its effects. Even without electric traction, signalling equipment may still be subject to interference from adjacent power supply lines or lightning storms. Similar techniques are often employed to protect against the likely effects. The objectives of protection (or immunisation) can be summarised as:- Prevention of failures, particularly wrong-side failures. To ensure the safety of staff working on the equipment under normal operating conditions and, as far as possible, under traction fault conditions also. To prevent the effects of traction currents from damaging or destroying signalling equipment. 1.1 Electrification Systems The effects of electric traction and the precautions which must be taken will depend on the type of traction supply. The electrification system chosen for a railway will, in tum, depend on a number  of factors:- Type and frequency of traffic Availability of Power Supplies and the locations at which they can conveniently be brought to the lineside. Local geographical and climatic conditions Structural clearances (for overhead wires etc) The overall length of the line Whether the line to be electrified is an extension to an existing electrified line or a completely new traction system. As a result many different systems are in use. Once a system has been selected, it is very expensive to change due to the investment in traction units and power supplies. The systems can generally be divided into two groups:- A.C. systems, normally employing a high voltage (typically 25kV) with overhead current collection. D.C. systems, generally at much lower voltages (600 to 1500 volts). The method of current collection is either overhead (requiring a much heavier conductor than for a.c.) or third rail. Low voltage systems tend to be d.c. because this makes the traction equipment on the trains much simpler. Early electrification did not have the benefits of modern power semiconductors to control traction motors so the power was at a voltage which could be applied directly to the d.c. traction motors. The cost penalty is a large number of substations and heavy feeder cables. The use of a.c. traction permitted substations to be spaced considerably wider apart and the overhead conductor to be used as the main feeder. No separate feeder cable is necessary. The equipment on board the train is generally more complex. The high supply voltage must be transformed to a usable voltage and rectified to d.c. for the traction motors. Modern variable frequency a.c. drives have now made the induction motor a viable alternative to the series wound d.c. motor. 1.2 Modes of Interference In most cases one or both running rails are used for the return current path. To some extent earth currents will also be present. In all types of track circuits there is the risk of interference by direct contact, traction currents passing through the signalling equipment or between the signalling equipment and earth. There is a high risk that traction currents could cause wrong side failures. The incidence of right side failures could affect reliability to an unacceptable level. Other circuits are generally not in direct contact but there is still the possibility of induced interference. lrtsulation could also break down causing direct contact with the traction supply. Protection must also be provided against dangerously high voltages (either induced or through direct contact) which could injure or kill personnel working on signalling and communications equipment. 2. A.C. TRACTION SYSTEMS 2.1 Feeder Arrangements BR's 25KV 50 Hz AC. traction system is typical of those on many other  railways and is usually derived from the132 KV National Grid system. The  supplies are taken as single phase through 132/25 Kv transformers provided by the Supplier. The supplies are taken to feeder stations at usually the same phase. Adjacent feeder stations are not parallel (i.e. not necessarily from the same  phase and usually not from the same source. This enables the Electricity  Authority to balance the railway load between the 3 phases of its system. The distance between feeder stations is dependant on traffic and power requirements.  An electric locomotive accelerating with a full load may take  a  current of the order of 270 amps. Neutral sections are provided between feeder  stations to separate the supplies and track sectioning cabins (TSC) are located at  intermediate points and the boundaries of feeding sections to provide alternative feeding and track isolation facilities in the event of failures or isolation for maintenance. 2.2 Return Paths for Traction Current 2.2.1 Rail Return This is the simplest form of traction current return. In most cases, only  one running rail is used. On plain track this is normally the cess rail, but in complex  layouts the location of return rail changes in order to meet track circuit  requirements by cross-bonding. The problem with rail return is that the rail is not well insulated and return traction current will leak to earth over the  length  of  the return rail. This produces a large imbalance between the current in the overhead wire and that in the rail, which  dramatically increases the level of induced voltages in lineside cables (see later sections for details). 2.2.2 Return Conductor If the traction return path is well insulated, the current imbalance in the circuit is reduced, hence interference is minimised. A return conductor can therefore be provided to carry the traction return current. The current carried is in anti-phase to the current in the contact and catenary wires, and similar in magnitude,  therefore the net electro-magnetic inducing field is reduced. The reduction over rail return, where signalling  curcuits are placed in the optimum position for minimum interference, is of the order of 45%. 2.2.3 Booster Transformers Some of  the return current will still flow via earth instead of the return wire.  This will be in inverse proportion to their relative impedances between the train and  the substation. The cost of a conductor large enough to eliminate the earth currents would be prohibitive. To force the majority of  the return current into the return conductor, transformers are provided in the traction circuit as shown on the following page. Typical Arrangement of Booster Transformers The return conductors are bonded to the traction return rail midway between booster transformers. These are located at 2 miles, 3.2 Km intervals, the primary winding connected in series with the catenary and the secondary winding in series with the return conductor. The effect of the booster transformer is to produce a current in the return conductor which approximates to that in the catenary, but is 180- out of phase. Maximum suppression of induction is achieved with the traction load at the mid-point connector (95% reduction) and the minimum when at the booster transformers. This alone does not immunise signalling and communications circuits. As the two conductors are widely separated, induction will still occur whenever a signalling circuit is nearer to one conductor than the other. The relative positioning of the overhead conductors, the return conductor and the signalling cable route must be such as to place the cable route equidistant from the traction conductors. 2.3 Modes of Interference and Immunisation Techniques Of the three possible modes of interference, conduction, electrostatic induction and electromagnetic induction, induction is the dominant mode in a.c. traction areas. Conduction, by direct contact between the power line catenary and the rails,  equipment or cable conductors happens rarely. If unprotected, it is usually  fatal to personnel and equipment. The only safeguard is the provision of contact circuit breakers in the traction supply. Due to bonding of overhead structures direct to the traction return rail, the risk of  a traction fault raising the rail potential, and that of track circuit equipment,  to dangerous levels is small. Track circuits will however be subject to false operation due to the multiple return paths created by return conductors and earth bonding and extra precautions must be taken when setting up and adjusting track circuits to ensure safe operation. Due to the distance between the traction equipment and the signalling  equipment and the low supply frequency of 50Hz., electrostatic effect are usually negligible. Electromagnetic induction is caused in one conductor by current flowing in another. This action is similar to a transformer, the traction conductors being the primary winding and the signalling conductors the secondary. The voltage is induced along the conductor (not between the conductor and earth). The effect is maximised when conductors run parallel to each other. The induced voltage increases with length of conductor and decreases with separation of the conductors. As signal engineers we are concerned with the following aspects of a.c. induction into our lineside cables: AC. voltages produced under normal operating conditions that could  affect  line circuits and tail cable circuits and result in the malfunction, failure or damage to equipment and/or hazard to staff working on the equipment. Higher levels of voltage induced in our cables as a result of traction  system faults. Any increase of these effects due to disconnection, earthing  or other failures  within the signalling Dangerous levels of induced voltage are possible if the traction current rises rapidly (short circuit or traction flash over). Telecommunications circuits are susceptible to all normal levels of induced voltage on unprotected cables from the traction system. Therefore special measures have to be adopted to protect these systems from the 50 Hz base and odd harmonics of this frequency. 2.3.1 Positioning of Cable Route The simplest method to reduce the levels of induced voltage is the physical location of the cable route, as described earlier. The best position for the cable route is approximately equidistant from the two traction conductors (where booster  transformers and return conductors are provided). With the normal  B.R.  overhead line equipment, this is 9 ft (2.75m) from the centre of the nearest track, and 2 ft (0.61m) below running rail. This distance will obviously vary for different designs of overhead equipment, for multiple track lines where two or more return conductors are mounted together, and for lines without booster transformers and/or return conductors. On most circuits which form a loop (one conductor out and the other return), this provides an adequate level of protection for normal operation provided the signalling equipment is in full working order. Both conductors are subject to the same electromagnetic fields which tend to oppose each other. Under fault conditions (earth faults and/or disconnections) further protection will be required. 2.3.2 Electro-Magnetic Screening With any wire installed parallel to an A.C. electrified line, a reduction in interference is obtained by the screening effect of earthed conductors in its vicinity. This includes cable sheaths, metal pipes and running rails. All communications cables are provided with a screening sheath (usually  aluminium)  with up to a maximum of 4 steel tapes around the sheath.  These  are connected to a good earth of no more than 4 ohms located every 1000 m. Signalling cables run in the same cable routes as screened telecomms cable and  therefore benefit from the mutual screening effect between the cables. Where existing cables, not to electrification standards are to be retained, it may be possible to immunise them by a separate screening conductor. This is a large cross-section copper wire run along the length of the cable route and earthed as above. Cable sheaths should also be earthed. 2.3.3 Immunisation of Relays Relays for d.c. circuits can be designed to withstand substantial a.c. voltages without energisation. The relays have copper slugs fitted over the cores, near the pole pieces and  a magnetic shunt is fitted between the cores above the copper slugs. When a DC voltage is applied to the winding the DC flux is produced as normal and attracts the armature. Some of this flux is diverted via the magnetic shunt and therefore greater power has to be supplied. However, when an AC voltage is applied, the AC voltage has difficulty in establishing itself across the air gap due to the large copper slugs and it tends to short circuit the air gap via the magnetic shunt, thus the AC flux plays little part in the operation of the mechanism. The following diagram shows the principle. A.C. Immune Relay Construction 2.3.4 Choice of Operating Frequency Where d.c. circuits are not practical, equipment should be designed to operate at frequencies other than the mains frequency and its harmonics. Filters can be used to keep signalling and traction currents separate Although the mains frequency is normally very accurate, fluctuations can  occur  and  these must be allowed for in the design of systems. Fluctuations of  ±  0.5%  are  typical  so  the design may allow for 1% maximum error to give a degree of margin for error. It should therefore be evident that the available bandwidth between successive harmonics decreases by 2Hz each time and above 1kHz no bandwidth  is  available.  In  practice, harmonics of this order are very small and frequencies  above 1.5 kHz are successfully  used  for track circuits. For additional safety, two or more frequencies are used together so that traction faults could not generate both together. 2.4 Practical Immunisation of Signalling Equipment 2.4.1 Limits Appreciable earth currents may still flow for some distance away from electrified lines and protection must be extended sufficiently far for their effects to  become  negligible.  At  the limits of electrification, or where  a  non-electrified  line  leaves  the  electrified  lines, experience has shown that signalling equipment should be immunised for 880 yards (800m) from the electrified line. 2.4.2 Line Circuits These should be DC circuits using AC immunised line relays. The length of line must be limited to 2km to ensure that the induced voltage from the traction system does not exceed limits for electrical safety (maximum induced voltage of 110v). Circuits required to cover greater distances must be repeated  by means of a relay and new power supply. Where circuits run along  non-electrified branches,  they  must be cut 800m from the electrified line. Where circuits from the same supply feed in opposite directions,  care  must  be  taken  to  ensure that the total length of parallel circuits is less than 2km. All vital line circuits are double cut to reduce possible false operation  and  hazard  to staff where an earth fault is present. 2.4.3 Track Circuits The traction return current can ususally be carried satisfactorily by only  one of  the running rails. Single rail DC track circuits, immune to the highest AC voltage that  could  occur, are used. It has been found desirable to limit the track circuit length to a lower value than on non-electrified lines to prevent the combined effect of a return conductor and a broken rail providing an alternative path to the train shunt. The track feed set must be designed  to  prevent  a significant  DC  voltage  being  applied  to the rails as a result of rectification of AC from  the  traction  current.  The  track  relay  must also be immune to AC in the same manner as those used for line circuits. Reed track circuits operate  at frequencies  clear  of  50Hz  harmonics  and  may  also be  used in AC electrified areas as may most modulated audio frequency track  circuits  such  as  the TI21. When little used and therefore rusty rails require  track  circuiting  there  are  two solutions - a welded stainless steel strip on the top surface of the rail or a high  voltage impulsing type of track circuit. The Jeumont  track  circuit  is immune  to false  operation  by AC traction current,  but  its length  is severely  limited  in a.c. traction  areas. This may  not be a serious disadvantage, as it is mostly used for point and crossings into sidings and loops. 2.4.4 Signals Colour light signals use tungsten filament lamps, which operate readily on both AC and DC. Therefore the only method of  preventing  induced  AC lighting  the lamp is to limit the length of the circuit between control relays and lamps and employ as high a voltage as practical. The usual practice is to have a transformer for each aspect in the signal head to reduce the voltage to the 12 volts or less required to operate the lamp and supply llOV AC over  the contacts of the controlling relays. In this  case  the  maximum  parallelism  allowed  is  200 yards (183m), i.e. a signal head  must  be less than  200 yards  from  its controlling  relays.  If the overall maximum distance between signals fed from the same location  or  relay  room supply exceeds 200 yards, then an isolating transformer  is required  to feed  signals  on  one side of the location or relay room. By limiting the length of signal lamp circuits, it is unnecessary for them to be double cut. Shunt signals generally operate on 110 volt lamps so no transformer is necessary. Searchlight signal operating mechanisms  must  be immune  to false operation.  This immunity is achieved by the use of chokes mounted as close as possible to, and in series with, the d.c. searchlight mechanism. An a.c. searchlight signal could be operated at a different frequency (e.g. 83.3Hz) 2.4.5 Points Electric point machines are immunised by using permanent magnet machines. These ensure that, even if there is an AC voltage at the terminals, the motor's field will  remain  uni-directional and although there will be considerable vibration, there is no resultant  torque and therefore the motor will not move. Electro-Pneumatic point machine valves must be immune. These valves are immunised  in a similar manner to that outlined for relays. Electro-Hydraulic (clamp lock) point mechanisms were found to have inherent immunity and can be used with no special measures being taken. Mechanical Points should  have  insulation  inserted  in the point  rodding  at the ends adjacent to the lever frame and  the  points.  This  is to prevent  stray  voltages  causing  electric  shock  to personnel. Detection of all types of points is by polarised relays. These relays are fully immunised in the manner already described. 2.4.6 Level Crossings Where lifting barriers are used it is desirable to position the barrier so that, if it is knocked over no part of it shall come closer than 150 mm to the overhead line equipment. If other positioning requirements make this impossible,  then  the  barriers should be made of metal or have a continuous metallic strip of adequate section along its length. The barrier or metallic strip should be bonded to a traction return rail or cable. Control circuits must be immunised as already described. Where closed circuit television is used special precautions must be incorporated  into the design. 2.4.7 Remote Control Immunisation of remote control systems is dealt with in the separate notes covering remote control. This mainly involves line isolation at regular intervals. 2.4.8 Power Supplies Although the safety precautions in force for higher voltage power supplies  would cater for the possibility of induced voltages at the levels expected, care must be taken when working on supplies which are switched off to avoid the possibility of high induced voltages. As the cable may not be sectionalised in the same way as vital signalling circuits, dangerous voltages could occur on long power feeders. 3. D.C. TRACTION SYSTEMS Because of the low traction voltage, traction currents are high, typically, 2,000  -  3,000 amps per train during acceleration. Due to the large DC return  currents  present in the earth near to and in the return rail, there are problems caused by corrosion, and problems  caused when insulation, equipment and cables break down. A d.c. supply will normally produce no inductive interference effects other  than from switching transients and ripple at harmonics of the mains frequency from  an  unsmoothed power supply. The main hazard is from conduction (to which track circuits are particularly exposed) by direct contact or via earth faults. The main precautions therefore comprise operation of equipment from a.c.  supplies, effective insulation arrangements and earth leakage detection. 3.1 Limits Earth currents from d.c. supplies are much more troublesome than for a.c.  They may propagate over much longer distances and immunisation should be provided for at least 3km from a d.c. electrified line. 3.2 Line Circuits DC circuits are used which are not sectionalised other than for volt drop purposes. It might initially seem unwise to. use d.c. but the reasons for accepting d.c. line circuits on B.R. in most situations are as follows:- All cables have non-metallic sheaths and are therefore less likely to pick up DC potentials along their routing. All cables are tested to a rigid specification. Additional insulation is provided by terminating cables on non-metallic materials. All line circuits are double cut to ensure that an earth fault in one leg of the circuit cannot cause false operation. Additional earth leakage detection equipment is used. In most d.c. traction supplies there is a significant a.c. ripple from the rectifiers.  Use of a.c. circuits would not provide immunity from the effects of this ripple  3.3 Track Circuits AC track circuits use vane relays which have self  immunity to the effects of  DC.  Even where the traction supply may contain a.c., the two element vane  relay will only operate if the interference signal is at the correct phase relationship. The relay will not respond to higher harmonics unless these are contained in the correct proportions in the supply to both coils. Reed and TI21 track circuits and several other audio frequency track circuits  are also immune to the effects of DC. 3.4 Signals No special precautions are taken for signal lighting circuits. These are usually a.c. fed with signal head transformers. Search-light signals are operated by a.c. vane type mechanisms, which, like track relays, have self immunity to DC. 3.5 Points No special precautions are taken in the choice  of machine for the control of  points. Although a.c. machines might be considered to have better immunity, d.c. operation is normally acceptable at higher voltages (110-130 volts) together with adequate earth leakage detection. Clamp locks, having separate valve and motor circuits can only be falsely operated by two simultaneous faults. Detection of points may be achieved with a.c. circuits using vane type three position relays. Alternatively, 110 volts a.c. may be used from the detector to the location where each individual circuit is transformed and rectified to operate a 50 volt d.c. line relay. 3.6 Automatic Warning System The BR Automatic Warning system, using d.c. magnetic fields is particularly  susceptible to d.c. traction effects. The train equipment is designed to detect the magnetic fields produced by the track equipment. Unfortunately, currents in the rails, on the traction unit itself, and in cross-track feeders can cause similar fields. This  problem  is overcome by:- Mounting the receiver away from collector shoes, traction equipment and associated cables and screening it on all sides except directly below. Use of track equipment which produces a higher magnetic field streangth. 4. MIXED TRACTION SYSTEMS There are some areas where both traction systems are in use, either using the same tracks or an adjacent track. This means that the signalling system has to be immune to both  AC and DC traction supplies. Circuits used must operate  on a  frequency distinct from the mains frequency and its harmonics. 4.1. Limits Although the d.c. immunity is required for a greater distance,  it is normal  to dual  immunise for approximately 3km. 4.2 Line Circuits Circuits are usually d.c. with precautions taken as for a.c. and d.c. lines. 4.3 Track Circuits Formerly, the most popular method was to use a.c.  two-position vane relays  but operated from an independent power supply at a frequency different to the mains supply and its harmonics (normally 83.3 Hz for 50 Hz mains). The additional power supplies were a significant added cost. Modern audio frequency track circuits such as the TI21 are immune to both d.c. and a.c. traction. 4.4 Signals The circuits are identical to those used in AC traction areas.  Searchlight  signals are immunised by using an AC vane type mechanism with a maximum length of 60 yards (55 metres) for the feed circuit. If signals are more than 60  yards  apart on either side of the relay room or location an isolating transformer must provided in the feed circuits of all signals on one side of the relay room/location. 4.5 Points The methods of operating points are identical to those used in areas of AC traction. Detection of all types of point is either by a two element vane relay from an  independent supply at a separate frequency, or by a filtered circuit such as the GEC vital Reed system. Frequencies 477.5 Hz and 414.75 Hz (fype RR  4000)  have  been  allocated for use with point detection circuits on B.R. and are employed for Normal and Reverse detection respectively. 5. PROTECTION AGAINST OTHER FORMS OF INTERFERENCE Apart from traction, adjacent power supplies and lightning are the main sources of electrical disturbance. Power transmission lines generate the same type of interference as  a.c.  traction and protection is therefore similar. Lightning protection is a very specialised area and will only be covered in outline. A direct lightning strike produces voltages far higher than the worst traction  fault conditions. It is virtually impossible to provide effective protection. When  lightning finds a path to earth, it will however raise the voltage at the point at which it enters the earth. Currents will flow which, although of extremely short duration, can induce large voltages in adjacent equipment. The danger is that the voltages may be large enough to find a path through the signalling equipment or break down insulations in cables etc. Fortunately, protection can be provided against this effect by the provision of  surge arrestors. The most common type is a gas discharge tube which has three electrodes, one connected to each leg of a loop circuit. and the other to earth. For the  normal  operating voltages of the signalling circuit, it will appear as an open circuit.  When the voltages induced by lightning are sufficiently high, an arc will form in the gas discharge tube which will provide a low impedance, high current capacity path to earth for the duration of the lightning strike. When the current is insufficient to sustain the arc,  the surge  arrester  will revert to its open circuit state. Semiconductor devices are also available to operate in a similar manner.  Their switching time is much faster than a gas discharge tube, giving quicker protection, but their current capacity is much lower. They provide better protection against moderate strikes but may not be able to handle the current caused by severe strikes. Both types of device are also suitable for protecting vulnerable equipment  (e.g.  electronic track circuits) from traction fault conditions where required. 6. FUTURE DEVELOPMENTS AND PROBLEMS We have concentrated so far on interference caused by the supply. This is always at the mains frequency or harmonics of it and these frequencies can therefore be filtered or avoided as appropriate to the type of equipment. Electric traction units have in the past invariably employed d.c. traction  motors. These do not produce any different interference to that already produced by the power supply. Many railways are now employing traction units either with d.c. motors  and  variable frequency thyristor chopper controllers or more recently, ac. variable frequency induction motors. The control equipment for these types of traction unit can produce interference at many (often continuously variable) frequencies over a broad spectrum. It is impossible to detail specific problems but the signal engineer must be very careful in the future as new traction units are introduced that he is aware of  their possible effects on the signalling equipment.

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Deepu Dharmarajan -
Posted 121 days Ago

ROUTE RELAY INTERLOCKING

  CONTENTS 1. Introduction 2.Push Button Interlocking 3. Point Circuits 4. Route Locking 5. Signal Aspect Controls 6. Route Releasing 7. Overlaps 8. Preset Shunt Signals 1. INTRODUCTION 1.1 Development of Relay Interlocking Systems The earliest interlockings were mechanical, between the levers of a frame but, with the development of block systems and track circuits, electrical controls were added. Staffing levels could be reduced by displacing a number of small signalboxes by fewer, larger installations. Fully electrical interlocking systems became necessary to control power operated signalling equipment. Initially, miniature lever frames were used. There are however many advantages in using a control panel incorporating buttons and switches into a diagrammatic representation of the track layout. With panel operation, a totally relay based system was required. Many suppliers produced their own different systems which, although different in detail, followed similar principles of design and operation. The signalman's control device was usually a button or a switch. Unlike the lever, it was free to move at any time. The relays now provided the security of the interlocking system. Additional indications had to be provided to show the signalman the state of the interlocking. During a period of substantial investment in signalling modernisation in the 1970's, design, installation and testing resources were in short supply. B.R. invited major suppliers to offer standardised interlocking systems which could as far as possible be factory wired and automatically tested. The contractors met the need with modular or "geographical" systems. The two main systems adopted, the Westinghouse "Westpac" and the AEI (now GEC) systems underwent several stages of development and were widely used. These systems certainly provided for very quick installation but there were disadvantages. The most important was that each development of a system was incompatible with its predecessors. The two systems were very different in their design philosophy. Westinghouse adopted a "one set per function" approach which led to high levels of redundancy, whilst GEC provided several sets combined as necessary for the functions actually present. This approach increased substantially the quantity of inter-set wiring. Due to rising costs and problems of spares and modifications, geographical systems have fallen in popularity. SRA never adopted any form of geographical interlocking but has for some years purchased interlockings built to its own set of standard circuits. B.R. also developed a set of typical circuits for free-wired interlockings which in operation would appear similar to the geographical systems and adopt a high level of standardisation of circuit design. These were incorporated into a B.R. Specification (BR850) which is probably one of the most standardised, and probably the last, relay interlocking specification in widespread use. On B.R. the use of route relay interlocking systems has now been superseded by solid state interlocking for all new work. As most route relay interlocking systems follow similar design principles and methods of operation, the SRA circuits will be used throughout for reference.  1.2 Relay Types Various types of relay are used in the interlocking. As well as neutral relays, slow to operate, slow release and magnetically latched relays are used. It is important that the operation of each type is understood, and circuit symbols recognised, in order to follow the operation of the equipment. In particular, latched relays will remain in the last position they were moved to. 1.3 Diagrams All the circuit diagrams used for reference are based on the SRA standard circuits and the examples shown in the accompanying ST401 notes. 1.4 Variations In practice, different installations may vary slightly in detail of circuit design. For example, full overlap swinging facilities may not always be provided. It is important to understand the relationship between the control tables and the interlocking circuits. The circuits must always be designed to function in the manner described by the control tables. 1.5 Relay Names and Functions In the ' article' is a list of all relays, their names and functions in the interlocking. Control Panel Symbols  Article shows the detail of the panel push buttons. Of particular note to this course is the directional arrowhead on push buttons giving information about their use as the start (entrance) or finish (exit) of a route. The button surround may be of a different colour according to the button function (main or shunt) and direction of traffic (up or down). 2. PUSH BUTTON INTERLOCKING 2.1 Operation of Entrance-Exit (N-X) Panel The entrance-exit (N-X) push button panel is the standard  type used by B.R. and SRA, and widely used elsewhere. The method of operation to set a route is:- Press the entrance (start) button and release it. The button will flash to indicate it is the selected entrance. The next button pressed must be the exit or finish of the route, and provided the route selected is both valid and available, the route will be set and locked and white route lights will indicate the extent of the route set. The entrance button will display a steady white light. If an invalid exit or an unavailable route is selected, the route setting will be aborted. Because some buttons may function as both start and finish buttons, and since the start signal may have several valid routes, each with a different finish, a constraint is imposed that only one route may be selected at a time. Where this would be over restrictive, several independent push button interlockings will be provided, one (or more) for each signalman's control area. 2.2 Push Button Relays All push buttons on a panel have three positions, middle (denoted 'M' ), pushed (denoted 'F' - meaning "from" the operator) and pulled (denoted 'T' - "towards" the operator). The button is sprung to return to the middle position after it is either pushed or pulled. Depending on the exact function of the button, relays will be provided to repeat the relevant positions or combination of positions of the button. ST401/5 shows the most common circuit. The diagrams show these relays wired direct to the panel button. This is the normal arrangement for the local interlocking at the control centre. For other interlockings, a remote control link, normally TDM, is employed. 2.3 Push Button Checking Circuit At various stages in the route selection process, it is necessary to prove that only one button is being pressed. This is accomplished using the (R)PR circuit  2.4 Pressing the Commence Button The interlocking will store the signal selected as the start of the route by holding the appropriate CeR up  2.5 Pressing the Finish Button The finish of the route will be identified by one FnR energised. The combination of CeR and FnR uniquely identify the route  2.6 Push Button Circuit Normalisation Approximately 1 second is allowed before the push button circuits are normalised, to permit setting of another route. This prevents preselection by the selection of the commence and finish signals before the route is available.  2.7 Effect of Pressing the Wrong Type of Button Pressing a finish only button at the start of route setting will have no effect because the signal does not possess a CeR. The circuits will normalise as soon as the button is released. Pressing the incorrect finish button will result in no route being set as the FnR and the CeR previously selected will not both appear together in the same route setting circuit anywhere in the interlocking. 2.8 Indications Panel To assist the signalman indication lamps are provided to show "machine in use" or "machine finish" to advise him of the current state of route setting. On many BR interlockings, the technician is provided with the facility to hold the equivalent of the FnJP2R energised to assist fault finding. This enables him to test circuits which otherwise may only be energised very briefly. This facility must be used with great care, and with the agreement of the operator, as it will inhibit the setting of any other route in the interlocking. 2.9 Checking Route Availability & Validity The Commence and Finish selected by the signalman, stored as CeR and FnR, must now be checked for validity - physical route possible - and availability. Normal lock and reverse route relays are provided for each possible route in the interlocking. These circuits comprise two parts. To the right of the relays (in the negative feed) are the relay contacts which respond to the push button circuits. The validity of a route is proven by the presence of a circuit with the correct CeR and FnR combination. The availability of the route is checked via the positive feed where all locking is proved. An example of a route with points. The points must be in the required position (NLR or RLR up) or free to move (WZR up). Providing the route is available the NLR will unlatch and allow the RUR to pick and stick. This operation must complete within the 1 second before the push button circuits normalise. In the event of the route not being available at the time of selection, or within one second, the push button circuits will normalise. The selection is not stored until the route becomes available, but can only be acted on at the time of selection. 3. POINT CIRCUITS 3.1 Principles of point operation Points may be called to operate by one of two methods:- the setting of a route requiring the points to be moved by the use of route setting buttons, or - the operation of a point key (lever) on the panel. At the time of calling, the points must be free of locking in their present position. Points may be locked by route locking, track circuit occupation, the point key having been turned, or another route having been set. The points must be free at the time of selection, and the selection must not be stored until the points become free, (anti-preselection). In the event of a power failure the last legitimately selected position of the points should be held and, on restoration of the power, the points should not be called to another position due to the random recovery times of different relays within the interlocking. 3.2 Calling the Points A point Jock relay (NLR/RLR) circuit. It has two halves. Setting contacts are in the negative feed and locking contacts in the positive feed.   At any one time only one lock relay should be up corresponding to the position to which the points were last called. Unlike the route lock relays, both NLR and RLR are latched relays. There is no distinction in safety terms between the normal and reverse positions for points. Except in special circumstances, points controlled from a route setting panel are not returned to the normal position after use. 3.3 Locking Circuits The positive feed to the NLR/RLR circuit checks the availability of the points to be moved, either normal to reverse or reverse to normal. The feed to the WZR can be obtained from either the normal or reverse branch of the circuit, dependent only on the present state of the NLR and RLR. If WZR is able to energise it shows the points are free to move from their present position. 3.4 Calling the points by route setting Energisation of an RUR in the negative feed of the lock relay circuit will set the points provided the point key is central and the points are not locked by other routes, track locking or route locking. Energising the RUR will have proved that the points are in position or available (e.g. NLR or WZR up for a move to the normal position). Contacts of the RURs for each route shown in the control tables to set the points will be wired in parallel in the NLR or RLR negative feed. Conversely the NLRs for the same route must be included in series in the positive feed of the opposite lock relay. 3.5 Moving the points using the point key/lever Relays (N)R and (R)R repeat the panel key/lever in the normal and reverse positions respectively. They allow the points to be moved individually. It is important to note, WZR must be up at the time of setting with the point key or the points will not move, even if any locking is later removed. Therefore, when moving the point key from normal to reverse (or vice versa), it must be held momentarily in the centre position to allow the WZR to reoperate. 3.6 Points in Overlaps There are situations, generally where swinging overlaps are involved, in which the simple use of route RLRs to call the points is not sufficient. Relays NOLR and/or ROLR may be provided to give the required point setting commands  3.7 Point Operation & Detection The position of the NLR and RLR in the interlocking must be translated into a command to the points to move to or remain  in the corresponding  position. This is done by  means of a polarised circuit to the NWR & RWR at the location.  Once the points have moved to the correct position, a polarised detection feed comes back to energise NWKR or RWKR provided the detection corresponds to the position required by the interlocking (NLR/RLR).  The point operation circuit has the additional protection of the IR (isolating relay). This proves all signals reading over the points normal, all direct locking  tracks clear and no trains between the points and a protecting signal (unless moving away from the points.) The WTJR (where  provided)  disconnects  the circuit to the point contactors if the points have been running too long. This will avoid damaging the point motor or clutch if an obstruction in the points prevents them completing their movement. article shows typical circuits for point operation. 4. ROUTE LOCKING 4.1 Principles The control tables will often specify route locking to allow the route to be held  in front of a train whilst being released section by section behind the train. This  is effective  as soon as the route is set and releases only after the passage of the train (or if no train has entered the route after the signal approach locking is released). 4.2 USR Circuits The relays used to lock each part of the route are called USRs, Route Stick Relays, which are energised when that section is free of route locking in the direction specified, and de-energised when route locked. A typical USR circuit is shown. The presence of the JR contact in the circuit will depend  on whether  the  control tables specify a timed release. 5. SIGNAL ASPECT CONTROLS  5..1 Aspect Requirements Once any route has been set, it must be proved entirely, including any overlap before displaying an appropriate proceed aspect and relevant route information to the driver. This may include track circuits and/or points depending on the type and geography of the route. 5.2 UCR Circuits The UCR proves continuously that all conditions are present for the signal to clear. A UCR will generally be provided for each route. UCR circuits will generally contain the following controls:- A contact of the relevant RUR which only operates when the route is required to set. The SR, which allows the signal to clear for one movement only. Track circuits proved clear by TPRs. For main routes, the tracks will be proved clear to the end of the overlap. Where facing points exist in the overlap, tracks beyond the facing points will have NWKR or RWKR contacts in parallel to exclude tracks when the points are set away from them. Points set and locked, using NLKPR and RLKPR Also shown in the circuit examples are back contacts of the TZR (this will be present when automatic nomialisation is required) and down proving of any track circuit timers which will be used to release route locking associated with the route. 5.3 Different Types of Route Where controls are common between different types of route (e.g. 3(M)A and 3(S)A), part of the circuit can be common to both UCRs. In the example shown, the main route UCR will include track circuits but the shunt route will not. Such circuits can often be laid out in a geographical manner. The circuit designer should decide the most efficient layout by reference to the signalling plan and control tables. Where main and shunt routes exist from the same signal, the track circuits and overlap points will have to be separated out to appear in the (M)UCR circuit only. 5.4 Signal Operation The UCR is at the interlocking. This will be used to operate a circuit to the HR at the location, controlling the clearance of the signal. To prove that the signal has responded to the interlocking control, an NGPR (signal normal - at stop) and an RGKR (signal cleared) are fed from the signal location back to the interlocking. Proof of signal normal is vital in the approach lock release. Both relays are used to provide control panel indications. 5.5 Stick Relay The function of this relay is to maintain the signal at stop after the train has passed it. The signal will clear for one train movement only.  Once the train has occupied the first track in the route, the stick relay can only be reoperated by normalising and resetting the route. If automatic working is required, an (A)SR will be provided to maintain the SR circuit energised. 6. ROUTE RELEASING 6.1 Principles Route releasing comprises the following sequence of events:- Initialisation of route release - signalman pulls the signal button at the start of the If automatic normalisation is provided, this will be initiated by  the train passing the signal. Release of approach locking on the signal  -  the train is proved past the signal (this may occur before or after (a)), the train  has come to a stand  at the signal or there is no train approaching. Release of the route up to the rear of the train, if any, known as sectional route release. 6.2 Approach Lock Release As far as the circuits are concerned,  the first step must always be to operate  the ALSR. Three separate circuit paths are provided to pick the ALSR according to whether the train is entering the route, the train has come to a stand at the signal or there is no train approaching. The arrangement of this circuit will be determined by the "approach lock tracks" and "approach locking released by" sections of the control table. Once operated, the ALSR will remain up until the signal is ready to clear again for another movement. 6.3 Route Release Picking  the ALSR will allow the NLR to latch up provided  the route has actually been cancelled. This, in turn, will allow the USR (or the first  USR if there is more than one) to pick as soon as the tracks are clear. It can  therefore be seen that the route locking will always release behind the train. If  the route is cancelled with no train, the USRs will pick up immediately as all the tracks are clear. 7. OVERLAPS 7.1 Principles Interlocking circuits are considerably complicated by overlaps. The controls must be accurately specified in the control tables and then translated into additional calling and locking circuits. The circuits must ensure that any route requiring an overlap has that overlap (or an acceptable alternative) maintained as long as the route is set or there is a train in the route. 7.2 Points in the Overlap Trailing points are dealt with as for points in the route. The route RLR operating calls the points in exactly the same way as for points in the route, and the detection and locking (NLKPR) is checked in the aspect circuits as usual. Facing points in the overlap will remain free whilst an alternative overlap is available. The overlap may be swung by:- operation of the point key/lever (e.g.101 points), setting a forward route from the exit signal (e.g. 3(M)A when 101 lying normal), setting a route which conflicts with the present overlap (e.g. 5A when 101 lying normal). Facing points in the overlap which have only one acceptable position will be treated as for trailing points, being set, locked and detected. 7.3 Aspect Circuits The UCR circuit will include the additional point detection and track circuits in the overlap. For signals with facing points in the overlap, all valid overlaps will be included, with the necessary conditions of the position of the facing points. The facing points themselves will only be detected where they are set and locked to prevent a confliction with another route. 7.4 Route Locking of the Overlap Where an overlap is provided, route locking must extend to the overlap. Normally a timed release is necessary to prove the train has come to a stand and allow the overlap to release when no route has been set forward from the next signal. The USR will then include a TJR contact for the last track in the route in parallel with the TPR front contacts. 8. PRESET SHUNT SIGNALS Occasionally a preset (or facing) shunt signal is positioned within another route. It may either be operated on its own as a shunt signal or cleared by setting the main route (presetting). Once a train has entered the main route, the preset shunt must remain off until the train has passed it. The preset shunt may be replaced to danger in emergency but this will not permit any release of the main route beyond the preset shunt. The examples do not include a preset shunt signal. The main points to note are as follows:- Main routes which require the shunt signal to be preset will first prove that the corresponding routes from the shunt signal are not in use (and vice versa). Setting of the main route will initiate the presetting process The main signal will prove the shunt signal cleared in its UCR circuit. Pulling the signal button of the preset shunt will therefore return the main signal to stop. Route locking for the main route will be effective to the end of the route, not just to the preset shunt signal. Once the train has entered the main route, it cannot be partially released beyond the preset shunt. A train cannot therefore be re-routed by cancelling the preset route and resetting for another route. ROUTE CONTROL SYSTEM - CIRCUIT NOMENCLATURE CIRCUIT NOMENCLATURE Relay Name Meaning Function Located at Refer Handout ROUTE SETTING INTERLOCKING (F)R Button Pressed Repeats push button operation Interlocking 5 (FM)R Button Pulled (contacts brocken) (FM)R provided for emergency replacement of signal Usually non-vital relay 5 (R)PR Button Reverse (pressed) Repeat Relay Used in ring to ensure only 1 (one)button pressed at a time. Operates commence & finish relays Interlocking 5 CeR Commence Relays Defines & Initiates route to be set. Interlocking 5 FnR Finish Relays Defines end of route in conjunction with CeR sets route Interlocking 5 MuR Machine in Use Relay Operates when commence relay is up to make next button operation a finish. Interlocking 5 FnPR Finish Repeat Relay Initiates timing sequence to remove route call. Interlocking 5 FnJR Finish Timing Relay Provides timing sequence Interlocking 5 FnJPR Finish Timing Repeat Relay Initiated by finish function     FnJP2R Finish Timing Repeat (No.2) Relay "           "         " 5 (N)R Normalising Relay Normalises Route Interlocking 6 AUTO NORMALISING TZR Track (Special) Relay Guarantees integrity of Automatic normalising path Interlocking     CIRCUIT NOMENCLATURE Relay Name Meaning Function Located at Refer Handout ROUTE SETTING (Cont) RUR Reverse Relay Signals Picks when route is set. Calls points to correct position. Interlocking 8 NLR Normal Lock Relay Main interlocking relay. Indicates when route is normal Interlocking 8 IR Isolating Relay Cuts point motor circuite to ensure no movement due to leakage currents. Point Location 11 NLR Normal Lock Relay Main interlocking relay for points normal position Interlocking 9 RLR Reverse Lock Relay Main interlocking relay for points reverse position   9 WZR Points Free Relay Indicates its points are free & would respond to a call Interlocking 9 WJR Points Timer Relay Provides additional time delay before points become free to cover bobbing tracks Interlocking 9 NLKPR Points Normal & Locked Indicating Relay Checks that points are in the normal position & locked Interlocking 9 RLKPR Points Reverse & Locked Indicating Relay. Checks that points are in the reverse position & Locked Interlocking 9 NWKR Normal Points Indicating Relay Indicates normal point position Interlocking 12 RWKR Reverse Points Indicates reverse point position Indicating Relay Lockal Points 12 NKR Normal Indicating Relay Indicates points normal Local Points 12 RKR Reverse Indicating Relay Indicates points reverse Lockal Points 12 .   CIRCUIT NOMENCLATURE Relay Name Meaning Function Located at Refer Handout ROUTE SETTING (Cont) NWAR Normal Points available Relay Determines if points would go normal if other conditional locking released. Interlocking 21 RWAR Reverse Points available Relay Determines if points would go reverse if other conditional locking released. Interlocking 21 NOLR Normal Overlap Relay Selects normal overlap is clear Interlocking 9 ROLR Reverse Overlap Relay Selects reverse overlap is clear Interlocking 9 SIGNAL CONTROL SR Lever Stick Relay Prevents signals automatically releasing after trains. Interlocking 15 UCR Route Checking Relay Checks all tracks & points detection for signal controls Interlocking 16 LSpR Low  Speed Relay Operates low speed light Signal Location   HR Signal Caution Relay Operates signal lights to caution Signal Location 17 HDR Signal Medium Relay Operates signal lights to medium Signal Location   DR Signal Clear Relay Operates signal lights to clear Signal Location 17 ECR Lamp Checking Relay Proves lamp alight Signal Location 18 NGPR Signal Normal Repeat Relay Proves signal & trainstop is normal Interlocking 19 RGPR Signal Reverse Repeat Relay Indicates signal cleared Interlocking 19     CIRCUIT NOMENCLATURE Relay Name Meaning Function Located at Refer Handout TRAIN STOPS VNR Train Stop Normal Realy Proves Train Stop normal Signal Location   VRR Train Stop Reverse Relay Proves Train Stop reverse Signal Location   VCSR Train Stop Checking Stick Relay Proves train stop normalising after train passsage Signal Location   VR Trainstop Relay for contractor Operates train stop Signal Location   TRACK LOCKING ALSR Approach Lock Stick Relay Hold locking if signal placed normal in face of train Interlocking 14 ALSJR Approach Lock Timer Realy Times out approach locking Interlocking 14 USR Route Stick Relay Holds after train enters route Interlocking 13 TJR Timing Relay Track timing to release route locking or conditionally clear signals, depending on application Interlocking Signal Location   POJR Power off Timer Relay Disconnects quick release path in approach sticks & TZR to retain locking during power failure Interlocking 14 RELEASING SWITCHES NR Normal Relay Detects releasing switch normal Interlocking 20 NKR Normal Indicating Relay Detects releasing switch normal (for diagram) Interlocking 20 9. ROUTE CONTROL SYSTEM  9.1 INTRODUCTION In the route control system of signalling, a route is set and the signal leading over it cleared by the signalman operating two push buttons which are located on a control panel. The first button operated is at the commencement of the route and the second button at the finish of the route. The finish button is generally at the next signal applying to the direction of traffic being dealt with, but in the case of a route which leads into a section, siding or terminal road the finish button is located in the section, siding or terminal road. Providing all conflicting routes are normal the push button operations are registered and any points in the required route which are not in the correct position will operate, then providing the line is clear to the clearing point the signal will exhibit a proceed indication. If a conflicting route is set or a previous train is passing over points within the route and the points are out of position for the next movement, the button operation is not registered and it will be necessary for the signalman to again operate the buttons when the route is free. To clear the next signal the last button operated which represented the finish of the previous route is again operated and acts as a commence button for the next route. A second button is then operated to locate the finish point for this route. After the passage of a train, or if it is required to cancel the route, without the passage of a train, the commence button for the route must be pulled to restore the route to normal. A signal cannot clear for a second train unless the route is normalised and then set again. If a button has been pushed as a commence button and for any reason the route which was to have been set is not required the commence action may be cancelled by pulling that button. Only one button may be effectively pushed at a time and when operating a button as a finish button it should be depressed for approximately one second. 9.2 OPERATION The diagram below shows a typical control panel layout. Where a signal leads over more than one route, as in the case of No.2 signal, the various routes are designated A, B, C etc, reading from left to right Thus No.2(M)A route leads to the Down Main, No.2(M)B route leads to the Down Refuge. The method of clearing No.1 and No.2(M)A routes is set as follows:- Push button No. 1 and then button 2 to clear No.1(M) route. Push button No.2 again and then push button No.4 to set 5 points normal, if not already in that position, and clear No.2(M)A route. When a subsidiary calling-on or shunt signal is provided on the post of a running signal, a separate button is provided on the control panel adjacent to the running signal push button. Referring to the diagram below, a separate button is provided adjacent to No.2 button for use when a move is to take place from No.2 signal. To clear the calling-on indication the subsidiary button is pressed as a commence button and a finish button is selected as for a running movement. When a shunting signal exists within a route the action of setting that route will automatically clear the shunting signal. In the diagram below, No.7 is a shunting signal which is within No.2(M)A route. When No.2 running or subsidiary button is pushed as a commence button and then No.4 button is pushed as a finish button No.2 route sets. No.7 route will also set. No.2 route is cancelled by pulling No.2 running or calling-on button, and No.7 route is cancelled by pulling No.7 button. This is only true for older installations such as Campbelltown, but if wired to modern practice the cancelling of the route by pulling No.2 bunon, will cancel the whole route from No.2 to No.4 destinations, which includes No.7.     9.3 PUSH BUTTON INDICATIONS Button knobs are made of clear perspex and are arranged to show a white light. When a button has been pushed as a commence action, a flashing white light is exhibited until a finish button for a route originating at the commence button previously operated, has been pushed. The light in the commence button becomes steady white, providing, track and locking conditions are favourable and the normal route lock relay is de-energised. If the finish button operation is not successful the flashing light in the commence button knob is extinguished. When the route is to be cancelled the commence button for that route is pulled and if the cancelling action is complete the white button light is extinguished. If when the button is pulled the route cannot be cancelled due to approach or track locking, the button light will remain illuminated. If the approach or track locking is subsequently freed then the normalising action will become effective and the button light will be extinguished. If when an attempt has been made to cancel a route, and it is found  to be approach locked, and it is then desired to clear the route again, it will be necessary to push the commence and finish buttons again, for the route concerned. 9.4 PUSH BUTTON  INSCRIPTIONS ENGRAVED AND FILLED BLACK ENAMEL 9.5 CONTROL PANEL PUSH BUTTON CIRCUITS Panel buttons work in three positions, namely, normal, push and pull with spring return to the normal position. Each button is fitted with two contacts, one which is normally open and only made when the button is pushed, the other contact is opened when the button is pulled. PUSH BUTTON RELAYS Push button contacts can make in two positions as shown below:- The track diagram shown on Sheet 2, applies to the circuits shown in the following handouts. To set a route from No. 1 signal to No. 3 (M) Signal Button No. 1 (for commence) is pressed, energising 1(F)R relay. 9.6 ROUTE SETTING - NX 9.7 PUSH BUTTON REPEAT RELAYS The (R) PR provides the interlocking between buttons to ensure only one button operation is registered at a time. 1(F)R contacts make, energising 1(R)PR relay. This lifts 1(R)PR contacts cutting out all other (R)PR relays. Back contacts of all following. (R) PR relays are included in the negative side of each (R) PR  relay to prevent it picking up if its button is operated ((F) R energised)  whilst any following (R) PR is already energised. Thus ensuring only one button operation will be registered at a time. 9.8 COMMENCE RELAYS The CeR initiates the commence operation to set a route. 1(R)PR contact makes, energising 1CeR relay. 1 CeR stick contact is made and holds 1CeR relay energised when 1(R)PR drops out (ie when commence button No.1 is released) via 1(N)R & FnJP2R contacts. 1(N)R contact is a route cancelling contact which energises when a button is pulled and the FnJP2R contact (2nd repeat finish relay) forms part of the timing cycle circuit. These circuits will be covered at a later stage in this handout. As 3 button can be either a commence or finish button, 3FnR (Finish Relay) is proved de­ energised in its commence relay circuit 9.9 MACHINE IN USE The MUR sets circuit operation to ensure the next button operated initiates the finish operation for the route. 1CeR contact picks up and energises the MUR relay whose contact turns MUR indication light on (flashing red). The FnPR contact ensures that the MUR is held energised to prevent the MUR from dropping out if a finish button is held longer than one second this would change the button from finish to a commence function (See later). In the diagram above the MUKR is a repeat of the MUR and the FnPKR is a repeat of FnR shown on Sheet 7 of this handout. This gives a flashing red or green indication on the console which indicates to the signalman whether the machine is in use or finish. When FnJP2R relay drops out 1CeR relay de-energises, thus extinguishing the MUR light. (described in this article). To select destination (finish) in this case there is only one possible destination from Signal 1 which is No. 3 signal. Pressing button 3(M) for finish, energises 3(M) (F)R. The (FM)R relay provides for emergency replacement of a signal after the route has been set. 9.10 FINISH RELAYS The FnR initiates the finish operation to complete the route being set. When the 3(M) (R)PR energises, and because the MUR relay is already held up via No. 1 CeR as shown on Sheet 5 of this handout, 3 FnR relay energises for the period of time that the button is held in. As No. 3 button can be either a commence or finish button, both commence relay functions, 3 & 3 (S), are proved down in its finish relay circuit. This holds the FnR de-energised during the commence function when the MUR has picked up and while the (R) PR is still energised.   9.11 FINISH REPEAT RELAYS The FnPR (finish repeat relay) initiates the timing sequence for a route to set. When 3FnR contact makes, and energises the FnPR relay the timing cycle, of approximately one second commences and, in this period the route must be capable of setting. If the route is not capable of being set within one second of the signalman operating the finish button, the action is not registered and the entire operation for setting a route must be commenced again. The FnJP2R and the stick function of the FnPR maintain the FnPR energised if the finish button is released before the timing cycle is complete to allow the timing cycle, once commenced to oe completed. 9.12 PUSH BUTTON TIMING CYCLE The FnJR & FnJPR's (finish timing relays) provide the timing sequence initiated by the finish function. The FnPR energising starts the timing cycle through the slow to drop relays FnJR, FnJPR & FnJP2R. When the FnJP2R relay drops out a number of things occur: The CeR relay is dropped out via FnJP2R contact in the stick path circuit already shown in the article The MUR relay is dropped out via the CeR contact dropping out in circuit already shown in the article The FnPR relay drops out if the finish button is released in circuit already shown in the article, via the FnJP2R de-energised in its stick circuit. This timing sequence provides the non-storage feature of the system. (ie. routes cannot be pre­ selected until a train has vacated the route).   9.13 ROUTE SETTING                                           Having now dealt with the operation and circuits associated with the control panel switches, we will now cover the operation and / or function of each relay, for the setting of the points to the correct position, locking them, setting the required route, and clearing the appropriate signal leading over that route which will include route locking and approach locking etc.     9.14 ROUTE SETTING When a button is pushed to select the commencement of a route (R)PR energises & providing that no other button has been pushed a contact on the (R)PR closes the circuit for the 'commence relay' CeR, (Refer Sheet 4 of Handout 5). A front contact of the CeR then energises the 'machine in use' relay MUR (Sheet 5 of Handout 5). The MUR energised opens the pick up circuit for all CeR's & this determines that the next button to be pushed will function as a 'finish' button. The CeR for the button operated is held energised by a stick circuit which includes a front contact of the finish timing relay FnJR, back contacts of its own (N)R relay & its own front contact. When the next button is operated  to define the finish point of the route to be cleared, its  (R)PR is energised & because the MUR is up, the finish relay FnR (Sheet 7 of Handout 5) for that button will energise for the period of time that the button is held in. A circuit is provided for the MUR via a front contact of FnPR, the finish relay's repeat relay, to prevent the MUR from dropping out if a finish button is held for longer than one second. (This would change the button from a finish to a commence action). Contacts of the CeR & FnR relays in series are utilized in the negative side of the route NLR delatching coil, and drive the relay down this in turn closes the circuit for the route RUR and providing all locking and track circuit conditions are satisfactory the route will set and its signal clear. (This will be dealt in the article). The commence relay CeR and FnR (finish relay) remain energised for approximately one second after the finish relay has operated but long enough to allow the route NLR to delatch and the RUR  to energise.  This sequence provides  the non-storage feature of  the  controls.   That is, if the route is not capable of being set within one second of the signalman operating the finish button, his action is not registered & he must operate the buttons again when the route is free. The method of obtaining the one second timing period is as follows. When a finish relays FnR energises, its front contact completes the circuit to the finish repeat relay FnPR (described in this article) & a back contact of the FnPR opens the circuit to the finish timing relay (in the article). The three finish timing relays are slow release relays & approximately one second after the FnPR has energised the FnJP2R opens its front contact to break  the holding circuit for the commence relay network (CeR).(detailed in this article) A stick circuit is provided to hold FnPR energised until FnJP2R is de-energised.   This ensures that if the finish button is released before the timing cycle has been completed, the FnJP2R will still release & cancel out the CeR. When the commence relay releases & the finish button has been released the MUR releases, and with the timing relays energised  & all button relays are in their normal position  the  system is ready for another route to be set or for another attempt to be made to set the same route. 9.15 ROUTE NORMALISING The (N)R Relay controls the normalising of the appropriate route NLR, and when energised, drops the route reverse relay (RUR), and latches up the route normal relay (NLR). When No. 1 button is pulled, 1(N)R is energised and is held up by a  back contact of the route NLR  which is to be normalised, a back contact of 1 CeR and its own contact.  The stick circuit will maintain 1 (N)R energised  until the route NLR circuit is completed  by the signal returning to stop or the approach stick energising as the case may be. The push button can therefore be released immediately after it has been pulled. Once the route NLR has latched up, its circuit is opened by the (N)R relay dropping & it is held in the up position by its magnetic latch. The back contact of the CeR in the (N)R stick circuit  permits a  signal  to be recleared,  if required, after it has been cancelled but the route has not normalised due to approach locking. A back contact of the (N)R relay is wired in the stick circuit of the relative CeR relay & this allows a button which has been incorrectly pressed as a commence button to be cancelled by pulling the button. 9.16 POINT LEVERS Points levers are located as a separate group on the control panel and are provided to allow operation of the points without the necessity of setting a route. This type of operation may be required for maintenance purposes, under failure conditions or to hold a set of points in a particular position during route setting. The point levers are of the rotary switch type and operate in three positions, left, centre and right. For route setting the lever is placed in the centre position and when lever operation of the points is required the lever is placed in the left hand position for operation to normal and the right hand position for operation to reverse. The operation of the points lever is such that before the position of the points can be changed the point lever must be placed in the centre position while the points free light is exhibited and then the lever moved to the desired position. When moving the point lever from R to N or N to R a pause must be made in the centre position. The four lights associated with a points lever are shown below. The points free light is mounted above the centre position of the lever and exhibits a green light when conditions are such that the points will respond to lever movement or route setting. The points normal light is adjacent to the normal position of the lever and exhibits a white light when the points are in the normal position. The points reverse light is adjacent to the reverse position of the lever and exhibits a white light when the points are in the reverse position. The transit light is in the centre of the lever knob or mounted below lever knob and exhibits a flashing red light when the points are operating from one position to another. The lights associated with the points lever function under both lever control and route setting control. 9.17 ROUTE LOCK RELAYS Each route in the interlocking from signal to signal or from signal to section, siding or terminal road has a RUR to set points and clear the entering signal and a NLR which proves the route normal and is used in locking conflicting routes. The route lock relay circuits for No. 1 route are shown on Sheet 2 of this handout. The route RUR and NLR circuits are electrically interlocked with each other. Thus I NLR back contact is in series with 1 RUR operating coil and 1 RUR back contact is in series with1NLR operating coil. The NLR is a magnetically latched relay and remains latched in its last operated position. It has two coils, one to latch the relay up, and another to latch the relay down. The operation is described in this article The route NLR when latched up is used to release conflicting routes, and proves that:- the signal has returned to stop the signal is not approach locked the route RUR is de-energised & is therefore not capable of setting points or clearing the controlling signal. The route RUR when energised proves that the route NLR is latched down thereby checking that all conflicting routes and points are locked prior to the route setting. The interlocking between routes is carried out in the positive leg of the RUR relay in accordance with the locking table for the interlocking. If a route requires that certain other routes must be proved normal before that route can set, then normal contacts of the conflicting route NLR's are included in the positive side of the RUR for the route concerned. The interlocking between routes and points is also carried out in the positive leg where a contact of the points NLR or RLR is included, and qualified by a contact of the WZR for the points concerned if the points are out of position but are free to move. 9.18 ROUTE LOCK RELAYS (NLR/RUR) CIRCUIT OPERATION When the commence and finish push buttons have been operated to clear No 1 signal, 1 CeR and 3 FnR contacts will be up together as described in handout 5 sheet 1. This drives 1 NLR magnetically latched relay down and closes 1 NLR contacts. This action then completes the circuit for 1 RUR relay to energise via 1 CeR and 3 FnR contacts. Front contacts in the negative leg of 1 RUR circuit then close, and hold the relay energised via 1 (N) R and 1 (FM) R normalising contacts after 1 CeR and 3 FnR have dropped out at the completion of the timing cycle. The route will remain set until the commence button at No 1 signal is pulled, which will pick up 1 (N) R contact and open 1 (FM) R contact. If the ALSR relay is de-energised, ie, the route is approach locked, the route cannot be normalised to release the interlocking. However it may be re-cleared for the train to proceed. 10 ROUTE CONTROL SYSTEM - POINT LOCK RELAY 10.1 LOCK RELAYS The points normal lock relay (NLR) and points reverse lock relay (RLR), perform route and interlocking functions associated with the points, they also controls their operation. On operation of the control panel buttons to set a route, the RUR is energised, providing the interlocking is free. The RUR contacts then set all necessary point lock relays which in turn operate the points to line up the route. With point detection indicating that the points are in their correct position and providing that the track circuits concerned are clear the signal control relay energises via contacts of the RUR and button normalising relays. These relays are magnetically latched and remain in their last operated position. Therefore before picking up one relay, it is necessary to energise the release coil of the other. This is accomplished by wiring the negative side of each release coil to the negative side of the operating coil of the other lock relay. As each lock relay operating coil is wired through a back contact of the opposite lock relay, one lock relay is proved down before the other lock relay can energise. Therefore, before a points lock relay can be energised to drive the points to the next position, the lock relay for the existing position is proved down ensuring that all routes which lead over the points in their present position are normal before the points can move. In the positive leg of the points NLR and RLR is the interlocking function between the points, and signals which lead through the points. Route (track) locking over the points, including selective overlap (tracks which will allow the points to operate to the vacant overlap), and back contacts of the opposite points lock relay, and detector relay, to prove those functions de­ energised before the lock relay concerned will operate. In the negative side of the NLR circuit are RUR contacts of all routes which will set the points normal in series with a contact of the points (C) R (Lever Centre Relay) and in the RLR circuit, RUR contacts of all routes which will set the points reverse, together with a point (C) R contact.  An alternative path is also provided for use when the points are to be operated under lever control for both normal and reverse operation. CIRCUIT OPERATION When a call is placed on 101 points to operate reverse, e.g. 3(M)"A" route has been called, 3(M)"A" RUR will energise closing the negative leg for 101 NLR release coil and 101 RLR operating coil via the lever centre relay (C) R, to negative. Providing the points are free to operate, i.e. 101 WZR (points free relay) is energized, indicating that the interlocking is correct, and the track circuits through the reverse route are clear, 101 NLR will be driven down via front contacts of 3(M)"B" and 3(S)"B" NLR's, 3ATPPR and 3XTPPR tracks (interlocking and track locking for the reverse route) 101 NLR and 101 WZR and WJR. This action closes a back contact of 101 NLR in the positive leg of 101 RLR operating coil, proving the NLR has de-latched and allowing the RLR to energise (latch up). A front contact of 101 RLR now connects the WZR to 101 NLR circuit in readiness for the points when called to operate normal. 10.2 ROUTE CONTROL SYSTEM - POINT LOCK RELAYS (NLR/RLR Etc)                                                                                   10.3 POINTS FREE RELAY (WZR) The WZR or points free relay is a slow to release relay to prevent the RUR from dropping out during the operation of the points lock relays. It taps off the interlocking and track locking portions of both NLR and RLR. When the NLR is energised the WZR detects if the points are free to move reverse. When RLR is energised the WZR detects if the points are free to move normal. Thus the WZR relay when energised indicates if the points are free to operate to the next position. The WZR is used to convey this information to the route RUR circuits which are allowed to energise if the required point lock relay is energised or if it is free to be energised. A point timer relay (WJR) is provided to ensure that the tracks have been free for a length of time to cover "bobbing" tracks. The WJR is a slow pick-up relay, which together with the slow pick-up track repeat relays provides a two stage timing before the points are free. The WJR is tapped off the points lock relay circuit, and a contact of this relay cuts the WZR. The WJR is provided in the NLKPR and RLKPR circuits. (Detailed in this article). A contact of the WZR is also used to illuminate the points free light above the centre of the lever and indicates to the signalperson when the points lever may be operated to drive the points to the next position. The only interlocking information not conveyed by the WZR relay is the point to point locking and this is added to the points free light circuit. The WZR relay and WJR point timer relay in conjunction with the transient nature of the button controls provides for non-storage operation of the points under route setting conditions. If when the buttons are pushed to set up a route, the point lock relays are not in the correct position or free to be operated to that position as indicated by the WZR relays for the one second period during which the button relays are energised, it will be necessary to operate the buttons again when the route is free. If a train were passing over points within the route in question the security of the points is dependent entirely on the track relays remaining down whilst occupied by the train. Therefore, if the track relay should "bob" during the one second which the button relays are energised the points would commence to move under the train. To guard against this event, track repeat relays are made 4 seconds slow operating so that local tracks in the point circuit must be clear for 4 seconds before the points become free to operate to the next position. 10.4 LOCK AND DETECTOR REPEAT RELAYS (LKPR) The circuits for these two relays which tap off the points lock relay circuits are the points Normal and Reverse lock and detector repeat relays (NLKPR and RLKPR). Contacts of these relays are used in the signal control circuits to provide proof that the detection and lock relays are in their correct position and that the operation of a route RUR has locked out the points lock relay for the movement to the next position, before a signal can clear. The NLKPR taps off the normal lock relay circuit so that it includes all interlocking which prevents the points from driving normal. In the case of 101 points, 3(M)"A" and 3(S)"A" NLR's, proving that routes which require 101 points reverse are normal. It ensures that 101 NLR and 101 NWKR are normal. It also ensures that 101 ROLR, 101 RLKPR, 101 WZR and 101 WJR are de-energised by back proving contacts. The proving of 101 WZR de-energised is most important and its function is as follows. With 101 NLR energised (latched up), and 3(M)"A" route is called, the release coil of 3(M)"A" NLR is energised when the commence (CeR) and finish (FnR) button relays are operated and when 3(M)"A" NLR makes its back contact, 3(M)"A" RUR is energised. When 3(M)"A" NLR opens its front contact the circuit for 101 WZR and 101 NLR is opened and 101 WZR drop contact makes to allow 101 NLKPR to energise and complete No. 3 signal HR circuit. Therefore before No. 3 signal can clear proof is obtained that 101 RLR circuit is opened via 101 WZR de-energised and therefore 101 points cannot be operated to the reverse position. 101 RLKPR taps off 101 RLR circuit and performs similar functions to 101 NLKPR, being utilized in signal control circuits which lead over 101 points in the reverse position. OVERLAP RELAYS (NOLR and ROLR) Overlap relays automatically set facing points in the overlap of a signal to give a clear overlap for that signal. When a route which has facing points in its overlap is set and the points are lying so that the overlap over which the signal would clear is occupied, but an alternate overlap is clear and the points are free to operate to that overlap, the overlap relay OLR will energise and drive the points to that position. The controlling signal for the route then clears via the free overlap. The OLR relays are only energised during the one second period that the button relays are energised and thus comply with non-storage requirements. Protection against the OLR's causing the points to move if a track relay should bob under a train is obtained by wiring a contact of the relative point WZR relay in the OLR circuit, thereby ensuring that the points have been free for at least four seconds before they can be operated to another position. If the· points in the overlap of a route are not free to move to an unoccupied overlap when the route setting buttons are operated, the route RUR will energise providing its requirements are met but the OLR will not be energised. Because of the transient nature of the button controls it will be necessary to either re-operate the buttons when the points become free or to set the points to the required position by operating the point lever. 11. ROUTE CONTROL SYSTEM - MAGNETICALLY LATCHED RELAYS 11. 1 PRECAUTIONS TO BE TAKEN IN CHANGING MAGNETICALLY LATCHED RELAYS Magnetically latched relays remain in the position to which they were last operated and for this reason special precautions are required to ensure that a relay is down before it is plugged into service. Magnetically latched relays are used for the parent relay of the route, point and release lock relays and the procedure for changing these relays is as follows: 11.2 ROUTE NLR AND RLR RELAYS Prior to unplugging a route NLR or RLR relay the electrician must: Ensure that the signal to which the route lock relay applies is at stop, the route normalised, and that any train which is approaching the signal has been brought to a stand. The magnetically latched relay which is to be placed in service must then be plugged into magnetically latched relay test base and the indicator lamp observed to ensure that the relay is down. The relay to be withdrawn from service is then unplugged and the new relay is removed from the test base and plugged into service. NOTE After changing a route NLR relay both the route NLR and RLR relays may be down. This will be indicated by a steady white light in the button knob controlling the route and the button should be pulled to energise the NLR. 11.3 POINT NLR AND RLR RELAYS Prior to unplugging a point NLR or RLR relay the electrician must: (i) Ensure that no trains are standing on or passing over the points concerned. (ii) Ensure that all signals which protect the points concerned are at stop and that any trains which may be approaching those signals have been brought to a stand. The magnetically latched relay which is to be placed in service must then be plugged into the magnetically latched relay test base and the indicator lamp observed to ensure that the relay is down. The relay to be withdrawn from service is then unplugged and the new relay is removed from the test base and plugged into service. NOTE  After changing a point lock relay both point NLR and RLR relays may be down. This will be indicated by both point position lights extinguished, and the transit light flashing. Under these conditions it will be necessary to move the point lever to the centre position (to energise the point (C)R relay) and then to return the lever to its previous position and thereby energise the point lock relay for the position in which the points are laying. 11.4 RELEASE NLR OR RLR RELAYS Prior to unplugging a release NLR or RLR relay the electrician must: (i) Ensure that no trains are standing on, passing over or approaching the ground frame concerned. (ii) Ensure that all signals which protect the ground frame are at stop and that any trains which may be approaching those signals have been brought to a stand. The magnetically latched relay which is to be placed into service must then be plugged into the magnetically latched relay test base and the indicator lamp observed to ensure that the relay is down. The relay to be withdrawn from service is then unplugged and the new relay is removed from the test base and plugged into service. 11.5 LOCK OUT CONDITION OF POINT LOCK RELAYS Lock out exists when both the point NLR and RLR relays are down at the one time. It is so called because with both point lock relays down the points WZR relay is also down and hence it is not possible to energise a route RUR which is interlocked with the points and which, when energised would be able to close the circuit to one or other of the point lock relays. Lock out may occur during operation of the point lock relays if the lock relay circuit is interrupted after one point lock relay, either the N or R has been released but before the other point lock relay has had time to energise. During lock out the control panel indications are as follow:- Both point position lights are extinguished, the point free light is out and the transit light is flashing. Lock out may be corrected by the signalperson moving the point lever to the centre position, if it is not already in that position and then turning it to the normal or reverse position to correspond with the position of the points. Lock out can be caused as follows:- by operating the route setting buttons and then immediately cancelling the route. by simultaneous operation of the point levers which - lock one another lock one another due to conditional locking which is not conflicting at the moment of operating the levers but becomes conflicting as soon as the levers are operated. lock one another due to selective overlap holding which is not conflicting at the moment of operating the levers but becomes conflicting as soon as the levers are operated. iii. by changing a point lock relay which is in the 'Up' position with a relay which is in the 'Down'  position in accordance with the instructions for changing magnetically latched relays. 11.6 ROUTE CONTROL SYSTEM - POINTS CONTROL CIRCUIT   Points control is effected through the NLR and RLR. Contacts of the relevant lock relay operate the normal points contactor (NWR) or reverse points contactor (RWR). The points contactors can be of the type that are mechanically interlocked with each other and are installed in the points locations, or polarity sensitive relays installed in the points location or provided within the point machine and which will only energise if the polarity of the supply to the coils is correct. Relays installed in the points location are type QBCA1 and have two heavy duty front contacts that are capable of switching about 10 amps current to the point motor. Refering to the circuits above, each contactor is double switched by contacts of the points lock relay concerned. The points NLR when latched up will pick up the normal contactor and the points RLR when latched up, will pick up the reverse contactor. The opposing lock relay is proved down in the relevant contactor circuit in each case. This provides a measure of safety so that if both lock relays should be up at the same time or if either lock relay is unplugged both contactor coils are open circuited. At installations where mechanically interlocked contactors are installed, emergency switch machine contacts (ESML) are provided in each contactor circuit and when points are to be operated by hand crank both the NWR and RWR are open circuited. Contactors are checked energised in their relative detector circuits and when the contactor is de-energised the detector relay circuit is opened and it in turn drops the relative LKPR relay, contacts of which break the signal HR circuit and maintain protecting signals at stop. As the NLR's and RLR's are of the magnetically latched type, no special holding circuits are required for the contactors. The NWR's and RWR's are usually situated in the location, near to the point machine. When energised the motor will to run either normal (if NWR energised) or reverse (if RWR energised).  They are polarity sensitive relays, usualy QBCA1 and will only energise if polarity is correct. Positive to R1 and negative to R2 contact. These relays have two heavy duty front contact (detailed later) which are capable of switching about 10 amp current on and off to the point motor. They are energised by the NLR energised and RLR de-energised in the case of the NWR, and the NLR de-energised and RLR energised as in the case of the RWR. These contacts are double cut into the point relays, ie contacts in both positive and negative feeds. Each relay is also controlled by the opposite relay being de-energised, ie RWR proved down in NWR circuit and vica-versa. There are two contacts of each relay in the opposite circuit, ie: referring to the circuit diagram RWR A6/A5 and D6/D5 are in the NWR circuit. This is to prove that the whole relay is de­ energised as it is possible to have half the relay 'stuck-up' by failure of a set of contact strips. Relay rows A and B are operated by one strip from the armature and relay rows C and D from another. This then proves that the RWR is definitely de-energised before the NWR can pick and vice-versa. 12. ROUTE CONTROL SYSTEM - ISOLATING and PLUNGER LOCK RELAYS 12.1 ISOLATING RELAYS (IR) and PLUNGER LOCK RELAY (LWR) IR's (for electrical operated points) and LWR's (for E.P. points) prevent irregular operation of the points should the point lock relay, contactor or control valve be falsely energised whilst a train movement is taking place over the points. The IR associated with electrically operated points can be of the neutral contactor type or a polarity sensitive relay and is installed at the points so as to be physically remote from the points contactor to prevent manipulation, or in the points location where the points contactors are of the relay type and thus sealed, or located in the points machine. The LWR is associated with E.P. points and is normally located adjacent to the points. When energised the LWR unlocks the facing point lock via the plunger lock, and allows the points to move. The IR and LWR check that the home signals protecting the points are normal and not approach locked, and that tracks from the home signals to the points, and the local tracks over the points are clear before the points can be operated to the next position. When the points have reached the required position the IR or LWR is open circuited by either a switch machine contact where the contactor type is used, or the relevant local detector relay (NKR/RKR) energising where polarity sensitive relays are used, and proved de-energised in the detector relay circuit (NWKR or RWKR). Where polarity sensitive relays are used, for electrically operated points a contact of the ESML (Emergency Switch Machine Lock) is provided and when operated manually the isolating relay is open circuited. 13. ROUTE CONTROL SYSTEM - DETECTION CIRCUITS                13.1 DETECTOR RELAYS (LOCAL) NKR & RKR The NKR and RKR (Normal and Reverse indicating relays), are located locally at the points and prove that the points have corresponded to the lever movement and are locked.They are divide into (2) two basic circuit types, those for E.P. points and those associated with electrical operated points. Figure 1, shows a typical NKR and RKR circuite for E.P. points using polarity sensitive relays. The circuit ensures that before the NKR or RKR will energise that:- The points are locked , via indication box contacts The points are laying in the correct position, via detector contacts The correct points solenoid is energised, via a micro switch (only style "E" & "D" units) The opposing KR and WR are de-energised, via back contacts. Figure 2 shows a typical NKR and RKR circuit used for electrically operated points using polarity sensitive relays.The points are proved Normal or Reverse and locked before the corresponding detector contacts are allowed to make. The opposing KR is also proved de­ energised via back contacts.   13.2 DETECTOR RELAYS (NWKR & RWKR) The detector relay circuits (NWKR & RWKR) as well proving that the  points have corresponded to the lever and are locked (via NKR or RKR), also proves the following:- The opposing WKR de-energised, via a back contact.   The corresponding NLR or RLR energised,thereby ensuring all interlocking functions are correct. The LWR (E.P. points) or Isolating Relay (electrical points) de-energised via back contacts. This ensures that the points cannot be operated, except under normal operating conditions. For E.P. points that the Plunger Lock has returned to the normal position (locked), via plunger lock normal contacts. This ensures mechanically that the points will not move should the control valve be falsely energised, or "creep" open due to worn equipment. For electrically operated points, a contact of the ESML is included to ensure that while the ESML is withdrawn from the lock for emergency operation of points, both WKR's are de-energised, thereby ensuring that the signals protecting the points cannot be cleared, or the points operated from the control centre. With the points normal and called reverse, the points NLR is driven down and drops the normal detector (NWKR). A back contact of the NWKR closes the circuit for the points RLR, allowing the relay to latch up, providing that all interlocking functions are correct. This allows the points to then operate to the reverse position. USING POLARITY SENSITIVE DETECTION RELAYS (Electrical Points) USING POLARITY SENSITIVE DETECTION RELAYS (E.P) 14.ROUTE CONTROL SYSTEM - ROUTE STICK RELAY      14.1 ROUTE STICK RELAYS The route stick relay in route control systems of interlocking performs a similar function to those in conventional interlockings where it may be used to: maintain or hold the route locking to provide maintenance of selective overlap. hold the route locking where a train has passed an outer protecting signal which is interlocked with the points, and the signal normalised with a train occupying the track circuits ahead of that signal. qualify that portion of the route locking that would not be required where the route is signalled for both directions. The route stick relay is a normally energised relay with a stick function the relay being held energised by the signal concerned at Stop (ALSR Energised). The relay is de-energised when the signal is cleared and will remain de-energised with the track circuit ahead occupied although the route has been normalised. The USR is dropped by the ALSR down (signal cleared) and proved de-energised in the signal HR circuit. Under certain conditions the USR may be required to be timed out to release the locking, and where this is required a front contact of the track time limit concerned qualifies the stick function to allow the relay to energise at the completion of the timing cycle. An example of the function of a USR relay is shown in Handout 9 where 1 USR is used to hold the points lock relay de-energised for maintenance of selective overlap. ROUTE STICK (USR) 15. ROUTE CONTROL SYSTEM - APPROACH LOCKING 15.1 APPROACH LOCKING (REQUIREMENT) Approach Locking is achieved by means of an Approach Stick Relay (ALSR) and is provided on all controlled signals with the exception of certain starting signals. Its purpose is to hold the route locked, thus preventing the operation of points in the route and/or the setting of a conflicting route if the signal protecting the route has been returned to stop in the face of an approaching train. A route becomes approach locked once a driver has seen a 'proceed' indication or has seen an indication at a previous signal which would indicate to him that the next signal is displaying a 'proceed' indication. Where long sighting distances are involved, 600 metres is considered a suitable approach locking distance to the first warning signal. The approach stick relay is energised by front contracts of the NGPR i.e. signal at stop, and the approach track or tracks circuits to that signal unoccupied and will remain energised with the signal at stop via the stick path with the approach track occupied. The relay is de-energised when the signal for the route is cleared and will remain de-energised with the approach track occupied although the signal has been normalised. A front contact of the approach stick relay is included in the route NLR and prevents this relay from normalising (latching up) when approach locking occurs as described above, thus preventing release of the interlocking. When a route becomes approach locked it is impractical to hold the route locked indefinitely once the train has come to a stand. To overcome this and the need for the signal electrician to provide a 'release', a time release relay is provided (ALSJR). The relay commences its timing cycles once the signal has been returned to the stop position (NGPR) energised. A timing cycle of 120 seconds is provided for main line running signals, and is considered sufficient to ensure the train has come to a stand. For shunting signals a time limit of 60" is provided. A front contact of the time release relay is placed around the stick function of the ALSR and when energised allows the ALSR to energise. 15.2 APPROACH LOCKING (Operation) The circuit for 3 ALSR as shown in this handout, and its various circuit paths are as follows:- PATH No 1:- 3 ALSR will energise (approach locking not effective) if No 3 signal is at stop, (NGPR energised) and track circuits approaching No 3 signal (1A T and 1BT) energised, with the approach track to No 1 signal (54.5B) included if No 1 signal has not normalised (1 ALSR down). This arrangement satisfies the condition where a driver has seen an aspect at a previous signal which would indicate to him the next signal is displaying a proceed aspect. The two track occupation to release approach locking under normal running conditions is to overcome the problem of a track bobbing under a train thus releasing the locking. PATH No 2:- Allows for energisation of 3 ALSR when a train proceeds past No 3 signal in the normal manner and allows a release of approach locking should a long train be standing with its rear on the approach locking tracks. To guard against a release due to an intermittent failure of 3AT, either 3BT or 3XT must be shunted at the same time. To guard against a premature release due to a power failure and restoration, which will cause the track circuit PRs to drop and then pick up, a front contact of POJPR, a power off time delay relay, is included in the release path.The POJR, which is the parent relay for the POJPR, is wired directly across the AC supply and does not make its front contacts until 30 seconds after the supply is restored. PATH No 3:- The stick circuit holds the ALSR energised with the protecting signal (No 3) at stop and a train occupying the approach tracks. PATH No 4:- Energises the time release which allows the release of the approach locking when the signal has been cleared and then returned to stop with a train occupying the approach tracks. 16. ROUTE CONTROL SYSTEM - ROUTE CHECKING RELAY 16.1 LEVER STICK RELAYS (SR) The lever stick relay (SR) performs the same function as in a conventional interlocking. When a train passes a signal, the signalperson must pull the panel button to normalise the route before the signal can be cleared again. Referring to the circuit below, with the passage of a train passed No 1 Signal 1, SR is de-energised by IAT track dropping and will remain down after the train has vacated the track until No 1 panel button is pulled to energise 1(N)R relay, where a pick up circuit is established via 1AT and 1(N)R contacts. 1 SR is held energised via 1AT track contact and 1 SR stick contact when the route is set by the operation of the panel button. A front contact of 1 SR is included in No 1 signal control circuit (1 HR or 1 UCR if provided) and after the passage of a train past No 1 signal the SR contact prevents the signal from clearing again until the route is normalised and then re-set by the operation of the panel buttons. The (N)R contacts in parallel with the route NLR contacts allows re-energisation of the SR relay should power failure occur when a train is approaching the signal and the signal is showing a proceed indication, under which conditions the approach stick down would prevent energisation of the route NLR (approach locking) when the panel button was pulled and it would not be possible to energise the SR relay to re-clear the signal unless the timing period of the ALSR had elapsed. 1 Lever Stick (SR) 16.2 ROUTE CHECKING RELAYS (UCR) The route checking relay checks all tracks and points detection in the required route. Front contact of this relay are used to control the signal control circuit (HR) which leads over that route. The UCR relays are mounted in the main location and include all the functions normally placed in the HR circuits. In effect the UCR is an internal HR relay. The HR relays are located in the remote locations. The UCR drops the NGPR and then the USR and ALSR relays which are proved down in the outgoing HR circuit, in series with front contacts of the UCR. The UCR relays allow proving of internal relays. The diagram below shows the UCR circuit for No.1 signal where the route is proved set by the RUR being energised thereby ensuring that all interlocking is correct and all relevant track circuits, including selective overlaps are proved clear (energised). The diagram above shows the UCR circuit for No.3 signal which has four routes. 1 To Down Main Main Signal Route (M) B  2 To Down Main Subsidiary Signal Route (S) B  3 To Down Relief Main Signal Route(M) A  4 To Down Relief  Subsidiary Signal Route (S) A 17. ROUTE CONTROL SYSTEM - SIGNAL CONTROL RELAY 17.1 SIGNAL CONTROL RELAYS (HR) The HR (Signal Control) Relay operates the signal lights to show a proceed indication from the Stop position, and is located at the signal location. The HR circuit for 1 signal is shown above. The NGPR which proves the signal and trainstop, if provided, have returned to normal, is proved de-energised in the HR circuit via back contacts. The ALSR and ALSJR are proved de-energised and ensures that the approach locking requirement is effective. The USR where provided is back proved thereby ensuring that the route locking is effective. The UCR proves that all points are detected in the correct position and that the track circuits are unoccuppied for the route set. The circuit diagram above shows the HR circuits provided to signal the routes from No.3 signal, both running and subsidiary for main and branch lines. 17.2 SIGNAL CONTROL RELAYS (DR) The DR Relay when energised provides the full clear (green) indication in the signal. The relay is energised by a front contact of its own HR and the HR for the signal in advance. Where single light colourlight signalling is used, a front contact of the ECR for the signal in advance is included.This ensures that if a lamp fails in the signal in advance, the signal will only display a caution indication. The VRR of the signal in advance is also included when trainstops are provided. 18. ROUTE CONTROL SYSTEM - SIGNAL OPERATING CIRCUITS 18.1  No.1 SIGNAL OPERATING * If a trainstop was fitted to No.1 signal, 1A TPR would be replaced by a contact of 1 VRR. 18.2   No.3 SIGNAL OPERATING   19. No 3. SHUNT SIGNAL OPERATING 19. SIGNAL REPEAT RELAY The NGPR (Normal Signal Repeat Relay) proves that all signal control and operating functions, ie:- UCR's HR's and trainstop if provided, have returned to the normal position, signal showing stop indication. The NGPR conveys this information via a front contact to the ALSR for the necessary proving, and the stop indication for the signal repeater in the diagram. It is also proved de-energised in the signal HR circuit. The (RGKR) Reverse Signal Indicating Relay, indicates that the signal has been cleared and is energised by front contacts of the HR relay concerned. This relay provides the clear indication for the signal repeater in the diagram. 20. ROUTE CONTROL SYSTEM - RELEASING SWITCH   RELEASING SWITCHES Releasing Levers - Releasing levers are located adjacent to the point levers and control the operation of the various ground frame releasing switches. The releasing levers are of the rotary switch type, coloured blue and operate in two positions, left (normal) and right (reverse). To release a particular releasing switch, all conflicting functions must be normalised and then the releasing lever must be turned to the reverse position. After shunting operations, have been completed and the releasing switch has been restored to normal, the release normal light will be displayed and the lever must then be turned to the normal position. Two indication lights are associated with each releasing lever as follows:- Release Normal Light - The release normal light is adjacent to the normal position of the lever and exhibits a lunar white when the releasing switch is in the normal position. The lever must not be restored to normal until this light is displayed. Release Reverse Light  - The release reverse light is  adjacent to the reverse position of the lever and exhibits a lunar white light when the lever is placed in the reverse position provided that all conflicting functions are in their normal positions. If any conflicting points are not in the correct position when a releasing switch lever is turned from N to R but are otherwise free to be operated, the release reverse light will be illuminated and the points will be automatically set to the correct position. If the reverse light is not displayed when a releasing switch lever is turned to the reverse position, this would indicate that a conflicting function may be reversed. The lever then must be restored to the normal position and other functions checked before the releasing switch lever is again reversed. 21 ROUTE CONTROL SYSTEM - INTERLOCKING 21.1 INTERLOCKING The locking table below shows the Interlocking requirements for the track layout shown, and gives a complete list of routes, destinations, route and point locking, and point setting requirements. Against each route is listed every other route with which it conflicts, this form of table is used when carrying out the interlocking test for the installation. Because certain routes are released by points and other routes are locked by the same points the locking between those routes is actually applied via the points lock relays and the direct route to route locking is deleted. The only route locking remaining is the locking between routes which require points to be set in the same position, eg, back to back routes; directly opposing routes and, between a running route and a subsidiary route originating at the same point and leading to the same destination. This is shown in the "Requires Routes Normal" column. With interlocking between routes and points, the RUR can energise over the WZR when the points are out of position eg:, in 3A RUR circuit, shown on Sheet 2 of this Handout, 101 points are required to be reverse for that relay to energise, or if the points are out of position they must be proved free to operate to the reverse position as indicated by the WZR energised. With the exception of certain catchpoints, points are not driven back normal when a route which requires them reverse is normalised. Hence points stay in the position to which they were last operated. Route Requires Routes Normal Sets Locks and Detects Points Sets Only Points Sets Points In Sequence Normal Reverse Normal Reverse   1   (102w101N)1 (101w102R)2       3A     101       3B   101,102       102 Then 101N When 1 Rev DR Route DCC 5A     102   101 When 1 Rev DR Route DCC 101R Then 102R When 1 Rev DR Route DCC 5B 6,10 102         6 5B 102         10 5B 102           21.2 CONDTIONAL LOCKING Is provided where it is required that certain conditions must be met with regards to the position of points before a route will set. eg: as 101 points and 102 points are included in the overlap of No.1 route the points will be set when certain conditions apply to provide a safe clear overlap for that route. When No 1 route is set with 101 points normal and 102 points reverse, and with no route set through 102 points, those points will operate normal (1 route sets and locks 102 points normal with 101 points normal). If however 5A route is set, ie: 102 points reverse, or the points held reverse by its own control switch, 101 points will set reverse (1 route sets and locks 101 points reverse with 102 points reverse). Provision for this is included in the points lock relays circuit. Sheet 3 shows:- 1 Route sets and locks 102 points normal with 101 points normal. Sheet 4 shows :- 1 Route sets and locks 101 points reverse with 102 points reverse. 21.3  1 SETS AND LOCKS 102N WITH 101N   21.4  1 SETS AND LOCKS 101R WITH 102R 21.5 NORMAL AND REVERSE POINTS AVAILABLE RELAYS (NWAR-RWAR) Necessary when a route requires operation of two or more sets of points, one of which is locked and will remain locked until the other points have operated. The point available relay detects all the functions which lock the points are non-conflicting, or will become non-conflicting when the other point or points have been set by the route. Contacts of the point available relay are utilised to qualify the point WZR contact in the signal NLR circuit and so allow the signal NLR to drive down. The RUR then energises and operates the points in sequence to line up the route. The point available relays are proved de-energised in the relative point lock and detector repeat relays. The NWAR determines that the points are available to operate to the normal position and is proved down in the RLKPR. The RWAR determines that the points are available to operate to the reverse position and is proved down in the NLKPR. 21.6 SEQUENTIAL OPERATION OF POINTS The sequential operating requirements of points for the diagram shown in this article are listed in the route setting table. If 101 and 102 points were reverse and the points are called normal by:- No. 1 route reverse (1 NLR de-energised, 1 RUR energised) or A train has passed No. 1 signal and is occupying 1AT (1 USR de-energised) 102 points would first operate normal, then 101 points normal. When a route is set requiring both sets of points reverse, (eg. 5 A Route) and the above conditions apply, 102 points would be locked normal until 101 points have operated to the reverse position and removed the conflicting condition which would otherwise occur if 102 points were allowed to operate reverse before 101 points were reverse (ie. an unsafe condition would exist if 101 points were allowed to remain normal with 5 A Route set (102 points reverse) for a train to run past 3 signal at stop and into the path of a train travelling 5 A Route). The circuit arrangement can be seen by referring to Sheet 3 and 4, were the conflicting point lock relay is prevented from energising (latching up) with No.1 route reverse (1 NLR latched down) or occupied (1 USR de-energised) until the leading points have driven to the required position and locked. This being achieved by placing a front contact of the detector relay concerned for the leading points, to qualify the front contact of 1 NLR or 1 USR. 22. ROUTE CONTROL SYSTEM - DIAGRAM INDICATIONS 22.1 INDICATOR DIAGRAM An indicator diagram is provided and contains signal repeaters and track circuit indicators. Each signal symbol is fitted with a signal repeater which shows a red light when the signal is at stop and a green light when the signal is exhibiting a proceed indication. Each track section is fitted with a number of lamps which exhibit white lights when a route is set over the track, red lights when a train occupies the track and no light when the track is unoccupied and all routes over the track are normal. When points exist in a track circuit section, only those lamps for the portion of the track circuit section over which the train will actually pass are illuminated when a route is set or when occupied by the train. If points within a route are not in the correct position when the route is set, two lights in the track line at the points flash white until the points have been driven to the required position, when they become steady white. When a train enters a route, the signal repeater changes from green to red and the group of lamps associated with each track circuit section in the route will change from white to red as they are occupied by the train. As the rear of the train clears each track section the track lights change from red to white and will remain white until the route is normalised by the signalperson pulling the panel button. If the route is normalised before the train vacates a track section, the track light is extinguished when the train vacates the track section. If a train enters a track section without a route being cleared over that track section, as may occur when a train overruns a signal or is flagged past a signal under failure conditions, all lights in that track section show Red. 22.2 ROUTE SETTING NX-DIAGRAM INDICATIONS The FEKR relays switch the illumination of console buttons. The FEKR energises via the NLR and CeR pickup contacts when the route is initiated ie when a button is pressed as a commence. The FEK2R energises when a finish button has been selected and pressed and the route NLR is driven down (de-energised). ROUTE CONTROL SYSTEM - DIAGRAM INDICATIONS Referring to No.1 signal in the diagram above it can be seen that there are two feeds to each lamp one being a normal BX24 the other is a Flashing BX24. When the route is initiated by pressing a commence button, a Flashing BX24 is applied to the button lamp via the FEKR contact in the energised position. When the finish button is pressed the button illumination changes to a steady white light via a pickup contact of the FEK2R. Number 3 button has additional FEK2R contacts in parallel to provide for the alternative routes from that signal. ALSKR The ALSKR relay is used to indicate to the signalman when a signal is approach locked. Its application will be described already in the aticle. The ALSKR is a repeat of the ALSR (Approach Stick Relay). The GZKR is used to flash the first route light past a signal, and indicates to the signalman that a train has passed a signal and the signal button should be pulled to normalise the route. Its application is shown on sheet 7 of this handout. The GZKR is energised by the ALSR energised (signal at stop), and the SR (lever stick) down. Front contacts of this relay are connected to the Flashing 24 v diagram BUS and the back contacts to the steady 24v diagram BUS. 22.3 SIGNAL REPEATERS The RGKKR is a repeat of the RGPR (Reverse Signal Repeat Relay) and is energised by a front contact of this relay. When energised it will illuninate a green light in the diagram signal repeater. The Red indication will be illuminated in the signal repeater when the NGKR is energised and is a repeat of NGPR (Normal Signal Repeat Relay) shown earlier in this article. If the ALSKR is down (signal approach locked) a flashing feed will flash the Red signal indication on the diagram, to bring to the attention of the signalman that he is approach locked. If the ALSKR is energised (approach locking released) a steady Red light will appear in the diagram. 22.4 POINT LEVER LIGHTS Point lever lights are provided above the points lever and indicate the position the points are laying and whether the points are free to be operated. A flashing red transit light is provided in the points switch to indicate when the points are unlocked or in transit. It is operated by back contacts of both normal and reverse indicating detector relays de-energised. The WZKR is a repeat of the points free relay and when energised will illuminate a green light above the points lever indicating the points are free of route locking and can be operated. The white normal and reverse lights are provided either side of the points free light to indicate points position i.e. either normal or reverse. These lights are illuminated by their respective indicating detector relays energised (NWKKR or RWKKR). Track Route Relays (TUR) are required for every track which contains points, (eg 3AT Track) contacts of the TUR relay are used to provide red track lights should a train occupy a route past the signal  at stop. The group selection of track lights as selected by the position of the points, is eliminated and every track light for that track circuit shows red. (shown already  in the article)   The UR's UKR's, U2R's and U2KR's (Non Vital Route Stick and Repeat Relays) are used to illuminate the white route lights on the diagram. They illuminate when the route has been set, ie when commence and finish buttons have been pressed. This is straight forward when there is only one route from a signal as in the case of No. 1 signal, but when there are a number of routes from the signal as in the case of No.3 signal provision must be made to accommodate this. If the route is to be set in the direction of the Down Relief, only the white lights in that direction would be illuminated. This is achieved by 3(M) A or 3(S) A FEK2R's energising and picking up 3A UR and 3 A UKR. These relays will remain energised when 3 A track is occupied by the drop contact of 3ATKR and stick contact of 3 A UR. 3 A U2R  is then  energised  by a pickup contact  of 3 A UR and is held by the stick contact when 3X TRACK is occupied via the drop contact of 3XTKR. 3 B UR operates in the same manner except it illuminates the route lights in the other direction, along the Down Main. The stick function on the UR relays is provided when more than one track circuit exists in the route to the next signal, as in the case of 1, 3A and 3B routes. Its purpose is to prevent the loss of the white lights in track sections ahead of the train if the route is normalised after the train has passed the entering signal. E.G. In the case of No 1 signal, if the train has passed No 1 signal and is occupying 1 AT track and the route is normalised 1 FEK2R will be de­-energised, however, 1 UR will remain energised via the stick function of 1 UR circuit, allowing 1 BT track in the diagram to continue to exhibit white route lights until the train occupies that track circuit.(shown already  in the article)   22.5 LAMP NUMBERING As 53. 1AB and 54.5AB tracks are outside the area of control thus not affected by the selection of a route the only indication required are the Red lights which illuminate when the track circuits are occupied. The straight route from No. 1 to No.3 signals has both route (white) and track (red lights) indications. The first white route light past No. 1 signal has the ability to flash (GZKR). This is used to indicate to the signalman that a train has passed over the route and he should cancel the route by pulling No.1 button. It will be seen that the white route lights requires the track circuit clear 1ATKR energised whereas the red track light requires 1A TRACK occupied (1ATKR drop contact). 3ATl track light is illuminated for either route, but 3AT2 track light which is also required for either route has the extra indication for the operation of 101 points. When the points are moving the NWKKR will be de-energised which puts a flashing illumination on 3AT2 lamp until the points are detected normal, when 101 NWKKR will energise and put a steady white light in 3AT2 route indication. 22.6 ROUTE and TRACK INDICATIONS CONTINUED  3AT4, 3AT3 route diagram lights operates only when route 3B is set. i.e. The white route light illuminates when 3B route is set, 3 B UR energised and 3A track is clear 3ATKR energised. The red track light illuminates when 3A track is occupied by a train via 3ATKR drop contact. The group of track lights having been selected by the position the points have operated to i.e. normal via front contacts of the NWKKR (Normal Detector Diagram Relay). 3AT5, 6 and 7 route and track lights will illuminate when 3A route is set. The direction of the route now being set to Down Relief line (points reverse) as indicated by the RWKKR (Reverse Detector Relay) being energised. The remaining route and track lights will operate in a similar fashion to 1BT1 indications as already described.    

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Deepu Dharmarajan -
Posted 125 days Ago

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Deepu Dharmarajan -
Posted 125 days Ago

SOLID STATE INTERLOCKING

  CONTENTS 1. Principles of Redundancy 2. General Description 3. Interlockings, Panel Processors and Panel Multiplex 4. Data Transmission 5. Long-line Link 6. Location Circuitry 7. Technicians Terminal 8. SSI Design & Testing 1. PRINCIPLES OF REDUNDANCY 1.1 General Solid State Interlocking (SSI) has been developed as an electronic replacement for present day signalling technology. The aim of the development is to provide a·safe and reliable system employing the latest micro-computer techniques and which will become the standard for the future. Solid State Interlocking is not just an interlocking system. The term SSI refers to a complete signalling system i.e. from the signalman's controls right down to the connecting cables to trackside equipment. It is therefore, not just  the electronic equivalent of a relay based interlocking as we know it. The use of SSI eliminates signalling relays (apart from track circuit and certain interface relays), and virtually all lineside multicore cables, which are replaced by twisted pair data links over which the signalling information is transmitted. Buildings to house the equipment are much smaller as a result. There is no need for remote interlockings. 1.2 Basic System Design Due to the highly predictable failure modes of relays as used in conventional  signalling circuitry the designers of signalling systems could produce circuits which  would remain safe under all probable fault  conditions. The failure modes of  electronic devices however are unpredictable, therefore, to ensure the safe operation of an electronic system a fresh approach to the problem is required. 1.2.1 Principles of Hardware Redundancy As previously stated the SSI system employs microprocessors to carry out the necessary functions. The basic principles of hardware redundancy involve the duplication of the microprocessors associated with a particular part of the system. Each processor working independently, which, under normal circumstances should provide the same results (outputs). In addition some means of comparing the outputs is required to ensure that they are in fact in agreement. In the event of a failure occuring in one or other of the microprocessors, the outputs would not coincide. The comparator would detect the disagreement, but (not knowing which of them was providing the correct output) would cause that part of the system to shut down. To prevent the highly improbable situation where the  second processor later fails  in the same way and so recreates agreement, an internal "security" fuse is blown, thereby disconnecting that part of the system permanently until replaced. This practice is adopted for that part of the system which connects directly to the external equipment (Trackside Functional Modules - to be dealt with later), where the effect of any fault would only cause localised interruption. Principles of Redundant Systems Practical Triplicated System - Majority Voting 1.2.2 Principles of Majority Voting If a duplicated system was adopted for the Central Interlocking electronics,. any disagreement detected by the comparator would shut down the entire interlocking leading  to a total interruption to the control of traffic. The method adopted in this case is to triplicate the interlocking microprocessors, again comparing the outputs. Should a failure occur in one of the interlockings its output would not coincide with the other two, which by their own agreement would out-vote the failed interlocking, causing it to disconnect itself from the system. Providing the two remaining interlockings continue in agreement, the system will still function, during which time relevant action can be taken to restore it to its normal operational state. Should however, one of the remaining interlockings develop a fault prior to the restoration of the triplicated system then the interlocking would shut down. Provided each interlocking is sufficiently reliable individually, the failure of a second interlocking before the initial fault has been rectified is very unlikely. This arrangement therefore not only ensures the safe operation of the interlocking but also greatly improves its availability. 1.2.3 Practical Approach to Majority Voting The arrangement for the Majority Voting system suggests the use of an intrinsically  safe voting circuit which implies the use of safety relays. This is clearly not an ideal  solution if we are trying to remove costly relays from the system. The system used  in practice is arranged so that all three interlockings compare their own outputs with the other two. In the event of a disagreement, the outputs can be "jammed", or disconnected and the module which does not agree with the other two can blow an internal "security"  fuse thereby disconnecting itself permanently from the system. Should the faulty module be unable to blow its own fuse the other two can jointly blow the fuse of the faulty module. The modules ability to blow these fuses is tested at regular intervals. Basic SSI System Structure 2. GENERAL DESCRIPTION 2.1 Introduction The basic structure of an SSI controlled installation will consist of:- An operating panel, which is outwardly identical to that of a conventional modern installation and which will contain panel multiplexing equipment to facilitate communications with the central interlocking, or A VDU based control interface such as the Integrated Electronic Control Centre (IECC). One or more microprocessor controlled Central Interlockings, the number being dependant on the size and complexity of the area to be controlled. A Technicians Terminal providing fault diagnostic, event logging and certain control facilities. A duplicated internal data link to provide communication between interlockings (where more than one is provided). A duplicated external data link between each interlocking and the  equipment  it controls at the trackside. A number of trackside modules which have access to the data links and include equipment which interfaces directly with the lineside signalling equipment, i.e. signals and points. 2.2 The Central Interlocking Each Central Interlocking comprises a number of modules housed in a standard  19" equipment rack. The different types of modules are briefly described below. 2.2.1 Multiprocessor Module (MPM) The controlling element of each Central Interlocking employs three modules of this type configured to carry out the interlocking  function, and are responsible for the safe execution of the interlocking process and issue of correct instructions (telegrams) to the lineside equipment. They also control the management of the redundancy system (majority  voting), of which they each form a part. The interlocking modules are triplicated for availability and the system will continue to operate as a duplicated system on failure of the first module. A multiprocessor module is also used as the diagnostic processor. In this case it is configured to monitor the flow of data on the data link and communicate with the technicians terminal. As it does not perform any vital safety functions and availability is not critical (i.e. it is acceptable simply to exchange the module if it should fail)  it  is not duplicated. Panel Processor, Multiprocessor and Memory Modules The following neon monitoring lamps are provided on each module which indicate when lit: Power module energised Fused supply redundancy management fuse intact System module on line 2.2.2 Panel Processor (P.P.M) The purpose of the panel processors, of which there are two in each system for availability, is to relieve the interlocking modules of the non vital task of servicing the signalmans panel. They communciate with the panel multiplexing equipment housed in the signalmans console and also peripheral equipment such as the train describer. Two neon lamps monitoring "power" and "system" are provided on each module. 2.2.3 Memory Module (MM) These plug into the front of MPM's and PPM's and carry the read only memory (EPROM) for the main processor. The EPROMS hold the fixed programs and the geographic data and thus configure the module to both function and site. The label colouring gives a quick guide to the type of memory module. Module Type Background Lettering Interlocking MPM Black Silver Diagnostic MPM Red Silver Panel Processor Module (PPM) Green Silver Simulator MPM Yellow Black Design Workstation MPM Silver Black Deswign Workstation PPM Silver Green RETB MPM Blue Silver RETB PPM Gold Black 2.2.4 Technicians Terminal The Technicians Terminal is provided as an essential aid to fault diagnosis in the SSI system. It incorporates a monochrome VDU, keyboard and printer and is connected to the central interlocking. The keyboard may be used to request specific status information or to apply restrictive controls to the interlocking. Information requested by the technician, fault messages, and restrictive controls appear on the VDU. The printer provides a hard copy. 2.2.5 Data Link Module (D.L.M.) These modules provide signal conditioning and matching between the data links (both internal and trackside) and the system electronic modules. As both data links are duplicated a DLM is required for each. They are found therefore at the Central Interlocking and also in the trackside apparatus cases. The pair of DLM's can link the two data links to six trackside modules. A neon lamp indicates the 110V power supply to the module. 2.3 The Panel Multiplex System When an SSI is used in conjunction with a signalman's panel it is necessary to provide an interface between the panel processors in the interlocking and the lamps and buttons on the panel. The interface equipment is referred to as the panel multiplexer but is not part of the standard SSI system. Consequently no one standard design exists and the equipment installed at any particular location will depend largely on who installed it and when. Toe two systems currently being used for the panel multiplexer are the Westinghouse S2 and the GEC RM. In simple terms the panel multiplex equipment forms one end of a TDM link  between the panel and the interlocking cubicle. The outputs from the  equipment  drive the panel indications directly and the inputs are the switch and push button contacts. A panel multiplex system is not required when the SSI is controlled from Integrated Electronic Control Centre (IECC) In this case, the panel processor communicates directly with the display system and other IECC sub-systems via a duplicated communications network. 2.4 The Data Link The data link is the means of communicating outputs from the interlocking to the external signalling equipment and the indications from that equipment back to the interlocking. It replaces the multicore cables used in a relay interlocking. The trackside data link consists of dedicated screened twisted pair cables (duplicated for availability) over which information between the interlocking and the  trackside equipment is transmitted in half duplex. As the link carries safety information and is the only connection between an  interlocking and the trackside  equipment that it controls, its security is important.  The  information in the form of input telegrams (to the interlocking) and output  telegrams  (from  the  interlocking), is protected by two levels of coding (Hamming and Manchester II coding)  and the use of high signal levels. A separate Internal Data Link will be required where more than one interlocking is provided and information has to be passed between interlocking cubicles, eg. route requests, aspect sequence or approach locking release. As this link is also used for vital information the same level of protection as the trackside data link is provided. 2.5 Trackside Equipment The modules at the trackside are located in conventional apparatus cases and are connected to the data link via Data link Modules identical to those at its Central Interlocking, and line termination units which provide surge protection. Each DLM has six outputs and can, connect up to 6 trackside modules. These modules known as Trackside Functional Modules (TFM) are divided into two types: Point Modules and Signal Modules. They convert  the data information received in output telegrams to power level outputs required by conventional lineside signalling equipment. The state of external signalling functions (e.g. detection, track circuits, filament  proving) is detected by these modules and returned to the Central Interlocking in the form of input telegrams. For this purpose the modules generate special signals which replace the usual 50v d.c. feeds. Having passed through the relevant circuitry  these signals are returned to the module which converts them into the data required for the input telegrams. Two types of module are provided which can deal with all normal types of trackside equipment. 2.5.1 Points Module This module has been designed to drive directly clamp-lock type point machines although other types of machine may be controlled via interface relays. Up to 4 point ends allocated to a maximum of 2 point control numbers can be driven by each module, which also has provision for their detection plus inputs from other signalling fanctions. The points module contains 5 indication lamps which when lit indicate: Power module energised System module operational i.e. security fuse intact Rx Data own data being received Points X                   }                                   } module outputs operational Points Y                   }   X and Y is the nomenclature used to refer to the two sets of points which can be operated by each point  module. The point numbers are allocated to the X and/or Y module outputs at the design stage and will be found in the module schedule in the location diagrams. 2.5.2 Signal Module The signal module is designed to directly feed colour light signals and is also sufficiently flexible to cope with all signalling functions other than points. One signal module can cater for one or two signals depending on the complexity. It  has the facility  for lamp  proving and inputs from other signalling functions. This module has 4 indications similar to those mentioned above but only one "output" lamp is required to monitor the operational state of all module outputs. Data Link and Trackside Functional Modules 3. INTERLOCKINGS, PANEL PROCESSORS AND THE PANEL MULTIPLEX 3.1 Interlockings 3.1.1 Capacity of a Central Interlocking Unlike a relay interlocking, each SSI Central Interlocking (CI) has a maximum size in terms of signals, points, routes etc. These restrictions are due to the available memory size, addressing constraints and the processing power available in the multiprocessor modules. Several interlockings can be linked to overcome these restrictions. The capacity of a single central interlocking is defined by the interlocking memory all.ocation and the permissible Trackside Functional Module addresses. The limits are:- Signals 128 maximum; all types Points 64 maximum point numbers (single and/or double end) Track Circuits 256 maximum, including sections of a multi-section track circuite (e.g. a 2 section track circuit counts as 3 track circuites) Routes 256 maximum; a route is allocated for each slot or release. No routes are allocated for auto-signals. The maximum permissible number of routes could be a limitation in a complex station area. Trackside Modules 63 maximum. This is the most likely limiting factor. When designing a new interlocking it is normal to allow at least 10% spare capacity for future modifications Data complexity may also be a limiting factor, but this is unlikely, and calculation is a complex operation. It is outside the scope of this course. 3.1.2 Connection of Interlockings A signalling installation of any significant size will have more than one interlocking. The internal data link is capable of connecting up to 30 interlockings. This number is limited by available addresses but is large enough for all practical purposes. The boundaries between interlockings should be chosen on similar principles to those for relay interlockings, that is, to minimise the quantity and complexity of signalling data required to be communicated between interlockings. The ideal interface is at automatic signals. An SSI may control more than one area e.g.  one  interlocking controlling a complex station area and another controlling the simpler areas each side of the station. It should be noted that each interlocking should be totally within one signalman's control area (unless an IECC is used). 3.1.3 Interlocking Nomenclature Each interlocking will be given a name of up to 8 characters, typically an abbreviation of the signal box name and/or name of the interlocking area, e.g. LIVST1, LlVST2,  LIVST3 or LlVST3, LIVSTE, BETHGRN etc. The Interlocking will also be given an identity number (1-30) which is  unique  within  the signal box  or  control  centre. The identity number is included in the interlocking  data and is also wired into the interlocking MPM plug coupler. It is used to:- ensure interlocking MPMs are plugged into the correct cubicle. identify messages on the Internal Data Link. provide additional protection against cross talk on the Data links to the Trackside Functional Modules. (Where Trackside Data Links of adjacent  control centres are in close proximity the interlockings concerned must have  different identity numbers.) identify the interlocking to the Technicians Terminal. The interlocking data is also given a version number (0 - 255), which is included in the interlocking MPM data. A reduced form of the version number is wired into the  interlocking MPM connector, and  ensures that the correct version of data is contained by an interlocking MPM when plugged into the interlocking cubicle. The version number should start at zero when the Interlocking is first  commissioned and be increased by one at the commissioning of each subsequent alteration.  A  "sub-version" or "modification" number is also included in the data to distinguish  between intermediate issues produced during testing. The version and modification number system is also used to identify the different issues of other types of data used in the system (e.g.Panel Processor, Diagnostic etc), but it is not incorporated into the plug coupler wiring. 3.1.4 Interlocking Operation The interlocking MPM contains several processors each with their own program. All except the main processor deal with communication on the data links, coding and  decoding messages and checking for corruption. The main processor runs the functional program to · operate on the data. The main processor memory is divided into a number of areas. Program & Fixed Data which makes the MPM act as an interlocking. The same program is inserted in every interlocking module. Signalling Data - Fixed Geographical Data to configure the interlocking to a particular site. This includes tables of all valid signalling functions in the interlocking and the necessary interlocking logic (i.e. a translation of the control tables compiled in a form which the interlocking program can understand). State of the Railway - Stores the current state of every signalling function and is used in conjunction with the fixed data to determine whether a particular function can be operated e.g. signal cleared, points moved etc. Program variables -Working area for the main running program. On a cyclic basis, the interlocking performs the following activities:- Examines the incoming bits representing track circuits, lamp proving or point detection and updates the State of the Railway Memory. Examines the State of the Railway Memory for the various controls (say for a signal) and modifies the output bits if appropriate. Examines the Subroutes (route locking) to see if they may be freed to release a section of route locking.   While a delay in executing (c) would not lead to an unsafe situation, it  is obviously .  desirable to respond quickly to (a) or (b). The limitation to 63 trackside modules  (rather than 127 or 255) is a compromise between the length of time taken to  process the information and the response time acceptable in a safety system. State Of The Railway Memory Details BYTE BIT FUNCTION APPROXIMATE RELAY EQUIVALENT SIGNAL MEMORY 1 7 Train Operated Route Release - Approach Lock Free & No Train Approaching ALSR/TPR/TZR   6 Not red retaining     5 Route indicator lamp proved UECR (BR practice)   4 Signal stick SR   3 Aspect disconnected %   2 Temporary approach control %   1,0 Train past signal (approach lock release) ALSR (part) 2 7 Lamp alight ECR   6 Automatic (A)SR   5 Approach locking free ALSR   4 Signal aspect control UCR   3 Button pulled (FM)R down   2-0 Aspect code HR,HDR,DR 3 7-0 Approach lock timer (seconds) AJR POINTS MEMORY 1 7 Point Key (Lever) Normal (N)R   6 Points called normal NLR   5 Points detected normal NWKR   4 Points Key (Lever) Reverse (R)R   3 Points called Reverse RLR   2 Points detected Reverse RWKR   1 Points disable normal %   0 Points disable reverse % State Of The Railway Memory Details (continued) BYTE BIT FUNCTION APPROXIMATE RELAY EQUIVALENT ROUTE MEMORY   1 Route Set RUR (NLR down)   0 Route prohibit/disconnect %     TRACK CIRCUIT MEMORY   1 7 Track Circuite Clear TPR   6 Technician's control (set to occupied) %   5 Track Circuit Occupied TPR down   4 Not used     3-0 Track Circuit Clear Counter TPR delay 2 7-0 Track Circuite Timer TJR/TJPR FLAG MEMORY 1 bit only Sub route free USR Other functions (e.g. ground frame)   TIMER MEMORY 1 7-0 Other timers not included elsewhere POJR etc. % Restrictive control operated from technicians terminal 3.2 Panel Processor The. function of the panel processors in an SSI Interlocking is to interface with the Train Describer and with the Panel Multiplex system which drives the indicators on  the signalman's panel and detects operation of push buttons and switches. The panel processors are not part of the safety system and duplication is provided to achieve high availability. As with the Interlocking Processors themselves, the program in the Panel Processors is identical for all applications, and the logic required to control the panel indications and interpret push button and switch operations is stored in the processor's memory as tables of geographical data which are interpreted by the program. 3.2.1 Memory Areas a) State of the Railway The Panel Processor gets its information about the current state of the railway by  copying across areas of the Interlocking Memory. Each location in these parts of the Panel Processor is updated once in every interlocking major cycle of approximately  0.8s. To reduce the amount of data to be transferred, only parts  of  the  Interlocking  Memory are copied, so the Panel Processor contains a sub-set of the information in the Interlocking. b) Input Image The input image contains a copy of the information received in the last valid message from the panel multiplex, describing the state of the switch contacts in the panel. The Steady State Input Image stores the current state of every input, and an additional Active Input Image indicates that the signalman has operated a switch or button which may require action. The Input Image contains space for 256 contacts. c) Output lmage The Output Image contains the information which is sent to the Panel Multiplex to control the indications on the Panel. These indications are either flashable or non-flashable. Non-flashable indicators are grouped at the start of the Output Image and are allocated one bit each; if the bit is set the indicator is illuminated. Flashable indications are allocated two bits each and are grouped at the end of the Output Image ; the two bits are interpreted as a code to mean "extingushed", "illuminated-flashing", or "illuminated-steady". The total Output Image contains 192 bytes, giving space for 1536 non-flashable or 768 flashable outputs, or appropriate combinations of the two. Panel Multiplex - General Arrangement 3.3 The Panel Multiplex A Panel Multiplex System is required to convert the serial data stream transmitted from the Panel Processor into the drives to individual lamps or LEDS on a conventional signalman's panel, and to sample the state of all the panel switch contacts on a regular basis and make-up a serial stream for transmission back to the Panel Processor. · In each case the message corresponds to the contents of the corresponding memory area in the Panel Processor, with each byte converted into serial form and transmitted in address order. The messages also contain control characters which define the start and end of the message and a status byte which is used to monitor the correct operation of the panel multiplex. A further control character is used to identify the change from information for non-flashable to flashable indications. 3.3.1 Message Format The message format for in   puts and outputs is similar. Information is transmitted seqentially in one long message. Once the message is completed the cycle repeats. There is no provision for "Immediate Access". Information is grouped together in "bytes" of 8 bits each plus start, stop and parity  bits. The complete message contains a string of data bytes together with various control characters.   STX Status DATA DATA   DATA DCI DATA DATA   DATA ETX BCC         Non-flashing outputs   Flashing outputs     Next Cycle STX  -  Start of Transmission DCI   -  Data Control Character - end of non-flashing outputs ETX  -  End of  Transmission BCC  -  Block check  -  a further parity check  on the message The first byte of every message contains status information and checks the operational state of the Panel Multiplexer. It originates from the Panel Processor, appearing as the first byte in the output message. On receipt by the output card concerned it is fed to the first input card where it is modified before appearing as the status byte in the input message back to the Panel Processors to provide the checking functions. The status byte also contains information to drive the signalmans alarms "Critical", "Non-Critical" and "Normal Working Failed". The Panel Multiplex also drives the "Indications Failed" alarm and returns the "Alarm Acknowledge" button pressed to the Panel Processors. 3.3.2 The Westinghouse S2 Panel Multiplex System Each panel processor in the Central Interlocking cubicle is connected  via a current loop data link to one of the two scanner modules in  the  Panel  Multiplex  output  housing.  These  are both connected to all DOP cards via their respective  highways. The scanners accept the output data in serial form and transfer it to each  DOP in turn.         - As both panel processors are producing the same data, only one scanner is programmed to be "on line", with the provision to change over to the other under certain fault conditions. The two scanners in the input housing collect the data from the DIP cards before transmitting it serially to the two panel processors. Each DIP or DOP card caters for 32 Inputs or Outputs and requires 4 consecutive bytes of data (8 for flashable outputs) as shown below. The first DIP or DOP card is limited to 24 inputs/outputs to cater for the status bits. STX BYTE 0 STATUS BYTE 1 DATA BYTE 2 DATA BYTE 3 DATA BYTE 0 DATA BYTE 1 DATA BYTE 2 DATA BYTE 3 DATA     DIP/DOP CARD 0 DIP/DOP CARD 1   4. DATA TRANSMISSION 4.1 Introduction The Central Interlocking communicates with the Trackside Functional Modules via the Data Link cables. Commands from the interlocking are sent as output telegrams and replies from the trackside modules are termed input telegrams. The transmission method used is half duplex, controlled from the Central  Interlocking. Each trackside module is addressed in sequence from the central interlocking via the output telegrams. The interlocking waits for each module to  reply before sending out the next output telegram, however if no reply is received within a certain delay period the interlocking will output the next telegram and not wait for a reply. This means that failure to obtain a reply will not stop the system but  the trackside module in question must wait until the next time it is addressed via an output telegram before it can transmit its data. 4.2 Message Format The format for both input and output telegrams is identical. SYNC CLOCK RECOVERY DIR 1 BIT INTLKG IDENTITY 5 BITS MODULE ADDRESS 6 BITS DATA 8 BITS STATUS 5 BITS PARITY 5 BITS The first part of any message consists of Synchronisation and Clock recovery bit  patterns used to condition the receiving processors to be ready to accept it, and for the processor to improve its estimation of the message timing. This is followed by a direction bit abbreviated DIR in the format diagram which is set at "0" for an output telegram and "1" for a reply. There are then  two address sequences. The first being the interlocking identity  which is a 5 bit pattern and whose purpose is to ensure that each trackside module  only accepts data from its own interlocking. The second address sequence contains the unique address of the trackside module being serviced and consists of a 6 bit sequence which gives a maximum capacity of 64  addresses. Address 00 is assigned to the Diagnostic MPM which receives its information from the data link. The other 63 are allocated to the trackside modules. Following the address are 8 bits of data, 5 status bits and 5 parity bits. 4.3 Output Telegrams In output or command telegrams the status bits are not used and are therefore all set to "0". Also the data pattern varies between signal and point modules  i.e.  although 8 bits are allocated and can be used by signal modules, point modules can only control two sets of points therefore only 4 bits are required  (i.e. "X"  N, "X"  R, "Y"  N "Y"  R) for this purpose, the remaining 4 bits being held at "0". 4.4 Input Telegrams These messages carry indication and proving data back to the interlocking. The status bits, are used in input telegrams to provide certain monitoring information.  Reply message data and status information given is illustrated later. 4.4.1 Signal Module - Reply Message Bits 7 and 6 are used to provide lamp proving of signals and route indications and  bits 5-0 are available for other signalling inputs i.e. filament failure, track circuit indications etc. 4.4.2 Point Module - Reply Message Input telegrams from point modules always reserve bits 7-4 for the detection of  the possible two sets of points as shown in the diagram. The remaining 4 bits are available for other signalling inputs. 4.4.3 Status Bits Status bits are used in reply telegrams for both signal and point modules. Only 5 bits are transmitted but when printed on the technicians terminal appear as 8 bits of which bits 2-0 are not used and are usually set to "1". Bits 7 and 6 indicate the state of  the data links and should both be "1" indicating  that they are good. Bit 5 indicates the state of the module output interface i.e. the ability to drive the apparatus, and should be "1". If the output of a signal module fails this bit will change to "0" and the module will go into its RED RETAINING  state which  maintains the signal at danger. If it goes to "0" for a point module then it indicates that one or both of the point outputs have failed and are inoperative. Bit 4 indicates the state of the module input interface which is the input sensing, i.e. detection circuits. This bit again is normally at "1" and will change to "0" if the two microprocessors in the module fail to agree on the state of an input. This condition is likely to be caused by a module fault. Bit 3 is not used in a signal module and is set permanently at  "1".  In  a  point  module controlling clamp locks which require two outputs i.e. valve and motor, a failure within a module could energise the motor drive to a machine which was not requested by the interlocking. The detection of this situation would cause bit 3 to change to "0". Typical Reply Telegram - Data & Status Bits - Signal Module Typical Reply Telegram - Data & Status Bits - Points Module 4.5 Trackside Data Link & Data Link Modules Each leg of the basic trackside data link has a DLM in the central interlocking cubicle feeding a DLM in each location. To extend the data link, two DLMs  can  be connected in a "back to back" configuration to operate as a repeater on the trackside data link. Each DLM has two out puts to the data link ("Data Link L" and "Data Link R") which can be used to split the data link to feed separate branches according to the physical layout of the area. Trackside data links may take many forms. The following restrictions apply. For each data link section the distance between the two furthest  extremities  is limited to 8Km. At these two extremities a 100 ohm terminating resistor must be provided. Where no repeaters are connected this distance may be increased to 10Km. Each data link can be extended by using additional data link sections, linked by pairs of DLMs in back-to-back repeater mode, but the number of repeaters between the Central Interlocking and any extremity must not exceed four. Thus the maximum distance from the interlocking to the furthest extremity is five sections at 8Km, i.e. 40Km. Spurs may be provided but each spur should be limited in length to 1Km and the total length of the data link section and its spurs must not exceed 10Km. Spurs start at a simple T junction in the data link and if a spur's length exceeds that laid down in 1) or 3) then either a repeater should be provided in the spur, or a repeater provided at the junction. Any DLM, whether connected to TFMs, LDT or Central Interlocking can be placed in any position in a section. Thus a data link section does not have to be end fed by a Central interlocking Protection of DLMs against lightning strikes is provided at the cable input to locations. Various different types of circuits and devices are in use to provide the most effective form of protection in specific situations. In order to provide more helpful messages associated with faulty data links the diagnostic processor is programmed with details of the various branches  in  the data links, including the relative positions of all DLMs and TFMs. This information can most  easily  be visualised in the form of an analysis map. Data Link Analysis Map Typical Data Link Configurations 4.6 Data Link Cable The data link cable is 2 core solid conductor (2c .1/1.22mm) with red and blue insulation. The metal moisture barrier is not connected to earth since it is too light weight to provide immunisation in a.c. traction areas, but it does balance the cable cores relative to earth. The connections throughout the data link must be maintained in the correct phase as the data signal is polarity sensitive. Two versions of the cable are available, one has a thin sheath and is intended for use in cable troughing, the other has a thicker sheath and may be mole ploughed. Alternatively telecomms cable to BR Spec. 887 may be used. 4.7 Internal Data Link The internal data link is required when interlocking cubicles need to transfer interlocking information. The operation of this link differs from the external data link in a number of important ways. Up to 30 interlocking cubicles can be connected to one internal data link, which is arranged as a star network. The centre of the network is a pair of busbars which also have two 100 ohm terminating resistors connected in parallel across them. Each interlocking cubicle connected takes it in turn to put information onto the link. The message format is shown below for one such message. SYNC CLOCK RECOVERY INTLKG IDENTITY 5 BITS 15X8 bit BYTES OF DATA Addresses 64-78 120 BITS TOTAL PARITY 8 BITS Synchronisation and clock recovery are required as in the external data link in order to condition the receiving processors. This is followed by the interlocking identity of the interlocking sending the message (the same identity as used in the external data link). Then follows 15 blocks (bytes) of data each containing 8 bits, for convenience these 15 bytes are referred to as addresses 64 - 78. All other interlockings receive the 15 bytes of data but will only extract those bytes which they are programmed to take. So for example the message from interlocking "1" may consist of bytes 64 and 65 going to interlocking "2", bytes 66 and 67 going to interlocking "3" and bytes 68 to 70 going to interlocking "4". Each byte of data can be treated either as an 8 bit code (giving 256 combinations) used normally for route requests between interlockings, or as 8 individual bits to represent individual functions. The message is completed by 8 bits of parity which is the Hamming code and the whole message is Manchester II coded to give the same level of safety protection as is given to the external data link. The interlockings take it in turn to transmit their messages onto the internal data link, the order being set by the identity numbers of the interlockings. Toe data link has  been designed so that should one interlocking stop or for any reason fail to transmit its message the other interlockings can carry on and will not wait indefmitely for the missing message. 5. LONG LINE LINK & LONG DISTANCE TERMINAL 5.1 Long-Line Link The Long Line Link is used in place of all, or part of, a Trackside Data Link to extend the range beyond the usual 40km limit. It uses standard telecomms PCM systems to transmit the messages. A Long Distance Terminal (LDT) acts as an interface between the SSI equipment and CCITT G703 Contradirectional Interface. To provide the extra security needed in diversely routed telecomms systems, the  LDT adds a Control Centre Identity Number to each message as it enters the link, and checks and removes it as the message leaves the link. This Control Centre  Identity Number (between 1 and 2047) must be unique within a railway administration or more importantly within the whole communications network used for long line links. On BR the unique number is allocated by the headquarters office for each control centre or signal box. The Long Line Link  is duplicated, as with Trackside Data Links, and is connected  direct to the Interlocking via an LDT.  These two LDTs are mounted in the  interlocking cubicle in place of the DLMs for the Trackside Data Iink. A mixture of Trackside Data Links and Long Line Links both connected directly to the interlocking is not allowed. An LDT is then used whenever a connection to TFMs or, via a further DLM, to a Trackside Data Iink is required. 5.2 Range of Long Line Link The maximum length allowed for a Long Line Link is determined by the propagation delay through the telecommunications system from the interlocking LDT to the trackside LDT and will typically be in the range 560-780km when the trackside LDT is directly connected to TFMs only. Where the trackside LDT is connected to a  trackside datalink, the allowable Long Line Link delay must be reduced to take account of the time taken for messages to pass from the trackside LDT to the most remote TFM. It is often desirable to provide diverse routing for the A and B datalink paths through the telecommunications network. The only additional restriction imposed is a  maximum difference in arrival times of messages at any TFM. If there is no diversity in the trackside datalinks, this difference in path length through the  telecommunications system is 460-630km for typical equipment. Where the routing  of  the baseband datalinks differ, this will also have an effect on the difference in arrival time of messages at each TFM over the  two paths. 5.3 The Long Distance Terminal The LDT is mounted in the same size box as a DLM. It has six TFM connections  which can be connected according to the same rules as a DLT. Each LDT   is a  duplicated processor as it is modifying safety information. The 75 way plug coupler has the control centre identity wired in separately for each processor - as with the module address for the TFM. In addition to the 11 inputs to each processor for the control centre identity, a further input indicates whether the LDT is at the interlocking or remote from it. The power consumption of an LDT is 20VA. Long Line Link and Long Distance Ternminal 6. LOCATION CIRCUITRY 6.1 Introduction The various location circuits can be split into three definite areas: Power Supplies. Trackside Module Output Circuits. Trackside Module Input Circuits. 6.2 Power Supplies Each trackside module must be connected to a separate, isolated 110v a.c. supply to eliminate the effect of earth loops in certain failure modes. Each point module also requires a 140v a.c. supply which will be internally rectified to produce a 122v d.c. availability for clamp lock valve and motor drives. Where 650 volt power distribution is provided, a range of 650v input transformers is available:- 650/110v,   500VA for a single signal module 650/110/110v,  500/500VA to power two signal modules 650/140/110v,  4CL/100VA for a single points module (4 clamp locks) The location Data Llnk Modules may be connected to any 110v Trackside Module supply. Where more than one Trackside module is fitted, the Data Link Modules should be connected to separate supplies to improve availability. DLMs may alternatively be fed from a battery backed 12V dc supply. This is typically used for a back to back repeater location, especially if fed from a "non-guaranteed" supply. Other 110v 50Hz signalling equipment may be connected to a module power supply transformer subject to loading constraints, otherwise a separate transformer may be required. Power ratings (maximum) of SSI equipment are:- Data Link Module 110 V  50 Hz  7 VA   :  12VDC   7VA Single Module 110  V  50  Hz  35  VA  internal, plus external load Points Module 110  V  50 Hz  35 VA internal 140  V  50 Hz to external load --depends on points connected 6.3 Trackside Module Output Circuits 6.3.1 Signal Modules   All signals including automatic and semi-automatic signals are controlled by direct connection to signal modules. In addition other types of signalling functions can be operated e.g. BR AWS where a transformer rectifier or relay interface will be required. Each module can provide up to 8 controlled outputs (numbered 7-0)  at  110V  50  Hz  to operate various signal and route indicator arrangements. The most restrictive aspect of  any signal controlled by a particular module is connected to one of two  outputs (7  or  3) which have the facility to provide what is called a "red retaining" feed, which in the event of a module failure will energise to illuminate that lamp. Note that, as there are only two red retaining feeds per module, SRA double light signals will require a complete module. Signals with flashing (or pulsating) aspects can be catered for. They require extra  outputs in order to control the flashing.  When the signal is required to flash outputs  5 and 6 turn on and off to create the flashing while outputs 0 and 1 remain on to provide a low current level (via the resistors) to hold up the signal EKRs and  increase lamp life. Note, however, that in the output telegram bits 5 and 6 will be "1" for a steady or flashing aspect and bits 0 and 1 will be "0"  for a steady  aspect and  "1" for flashing. Bits 0 and 5 correspond to the top yellow while bits 1 and 6 correspond to the bottom yellow. Signal lamps which are permanently lit e.g. shunt signal pivot lamps and  L.O.S. signals are fed directly from the module fuse, termed the fixed source. All outputs from a module must have a return path to one of five current path connections (numbered 0-4). Current sensing (lamp proving) is provided on current paths 1-4, but current path 0 does not have current sensing and so is used for all output circuits not requiring lamp proving. The values of current proving on paths 1-4 are standard (as shown below), but may be reduced by adding an external resistor and modifying th e module strapping. Current Path      1 2 3 4 35W (1xSL35) 120W (i.e. 2x60W bulbs) 70W (PLJI) 35W (1xSL35) 6.3.2 Point Modules All motorised points will be controlled and detected via  the  point  modules. These  are designed to drive directly clamp lock mechanisms but, due to having only one point motor output per point end, will operate other types via interface relays. Each module can provide up to 8 d.c. outputs i.e. 4 motor drives and 4 valve drives  (2 normal and 2 reverse). To drive combined electrical machines the valve outputs  are used to operate the point contactor relays (N/RWR) over whose contacts the  point motor feeds are connected. Note the 1000 ohms 6 watt dropper resistors required to reduce the dc valve output to operate 50v relays. 6.4 Trackside Module Input Circuits Both signal and point modules are able to send information about 8 functions back to the interlocking by way of the input telegram. Each input will respond only to the  pseudo random binary coded signal generated within that module and output via he BXI/NXI and BXE/NXE supply connections of the module. These two input supplies BXI/NXI and BXE/NXE are identically coded but are electrically isolated from each other. BXI/NXI should be used for input circuits  internal to the location and BXE/NXE for input circuits external to the location. This  segregation of supplies allows vital internal inputs to be single cut. Each input will respond to either supply. As each input has BX and NX terminals then each can be either single or double  cut. Where single cutting is used, the BX circuit is taken via the relay or other contact and the NX terminal is linked to the input supply NX via a terminal strip to allow a  meter  to be used for testing. An input will detect an open circuit when the loop resistance is greater than 3.5 Kohms and will detect a closed circuit when the loop resistance is less than 500 ohms. Module inputs may be used to monitor contacts in another location, saving on the number of modules required. 6.4.1 Signal Modules Of the 8 inputs to a signal module bits 5-0 may be used to monitor general signalling  circuits e.g. TRs, first filament proving. Inputs 7 and 6 are used for lamp proving (Input 7 = current path 1, input 6 = 1 of current paths 2, 3 or 4). 6.4.2 Point Modules Of the 8 inputs to a point module only bits 3-0 may be used for general signalling inputs. Bits 7, 6 are used to monitor the detection of the "Y" points and bits 5, 4 are  used to monitor the detection of the "X" points. It was originally found that point modules monitoring detection were able to detect momentary breaks in detection caused by vibration of trains passing over the points. These would be unnoticed with a normal relay circuit. In order to avoid problems  from this effect the detection inputs have been redesigned with the equivalent of a  "slow to drop relay" feature thus preventing slight vibrations from causing loss  of  detection,  momentary replacement of signals to danger and unnecessary fault messages. The usual detection arrangement is for the special input signals BXE,NXE to be passed through the detection springs in the machine directly and then fed back into the relevant detection inputs on the module. The down proving of the contactor relays will be achieved by one of the general purpose inputs on the point module. Typical Signal Module Wiring BR 4 Aspect Signal with Junction Indicator, Position Light Subsidiary and AWS Typical Signal Module Wiring for Flashing Yellow Aspects Typical Points Module Wiring Two Double Ended Clamp Locks Point Module Outputs for Point Machine Operation Typical Trackside Module Input Circuits Typical Point Module Inputs (Clamp Lock Detection) Typical Point Detection Circuits for Electric Point Machine 7. THE TECHNICIANS TERMINAL 7.1 Introduction The provision of a diagnostic aid for fault finding has been considered an essential part of the SSI system. Its purpose is to interpret the messages transmitted between the various parts of the system and thus largely replaces the process of tracing voltages in circuits with a voltmeter. Additional facilities include the ability to apply restrictive controls to the interlocking. A magnetic tape record of changes to signalling inputs, outputs and panel requests is provided. The technician's terminal contains a specially configured multiprocessor module called the "Terminal Processor" and this is used to control the other parts of the technician's terminal which consists of a printer, a VDU, a keyboard, a data recorder and a modem link. A printer is provided to give a permanent record of all fault messages, it can also be used by the technician to provide information for fault finding.  A VDU is provided  in addition to the printer, the printer normally only prints out the fault messages and the VDU is used by the technician. The modem is included so that a technician's terminal, remote from the  interlocking, can be used in much the same way as the local terminal. This could be useful if  second line technical support staff are located some distance from the interlocking. The tape cassette data recorder provides a record of all changes in the system including signalling input and output messages, panel requests, faults, and control alterations from the keyboard. This could provide useful historical information in the event of an incident. Each tape drive is used alternately, previous data being overwritten. If it is required to retain the data, the appropriate tape cartridge must be exchanged. One technician's terminal has the capacity to serve up to six interlockings, but a separate diagnostic processor is required for each. 7.2 General Information Each line of output printed starts with a four digit sequence number which is automatically incremented. In addition the date and time are printed with certain  messages, this can   be in one of two forms. A. (date) (time) e.g. 05.03.85 12.23.36 GMT B. (time)            e.g. 12.23.36 7.3 Fault Messages For most of the time the terminal will not be required for information or commands  and instead the printer will be available to print out failure messages as they are detected by the diagnostic processor. Failure messages in general consist of two lines. The first line consists of the following: Sequence Number Time Message Type including Interlocking Identity The interlocking identity is the eight character abbreviation of the name of the . interlocking from which the message originated as used in the geographic data for that interlocking e.g. LSPA. In the case of messages originating from the technician's processor itself, the name TECHNICIANS TERMINAL is used. There are four classes of fault message, each of which has a special group of symbols to make class identification easier and quicker. They are as follows: Class of Fault Fault Symbol FAULT !!!! INTERMITTENT FAULT %%%% FAULT CLEARED **** ALARM @@@@ A fault is declared intermittent if it has occurred, cleared and then occurred again as shown in the example below. No further messages or alarms will occur once a fault has been declared intermittent until the fault entry is REMOVED from the fault list . The second line consists of the following: Sequence Number Failure Description The following are a small selection of the messages that could be produced. a) 5515     13:34:08    !!!!   FAULT ON LSPA      5516                             SIGNAL 41 RED LAMP A total lamp failure has occurred in 41 signal red aspect at 13:34. b) 5819    17:10:44  **** FAULT CLEARED ON LSPA     5820                          NO REPLY. TRACKSIDE FUNC. MODULE 10 BOTH LINKS A previous message would have stated that the interlocking was not receiving data from TFM 10 on either data link. This fault has now cleared. C) 5552    13:45:53   %%%% INTERMITTENT FAULT ON TECHNICIAN'S TERMINAL      5553                                    DATA PANEL I/P 0 On at least two occasions the technician's terminal has received corrupted data from the PPM link on I/P port 0. d) 5771 17:09:10 @@@@ ALARM ON LSPA      5772                  DIAGNOSTIC PROCESSOR OUTPUT BUFFER OVERFLOW The diagnostic processor has been unable to cope with all the fault messages being generated. e) 5508 13:32:08 !!!! FAULT ON LSPA      5509                     MONITORING LOC106.4ELK EARTH LEAK WARNING An earth leakage current has been detected  at location  106.4. This message  is an example of how specialised messages can be added to the standard messages and generated when a specific change of state occurs. 7.4 Information Requests Before requesting information from the terminal it is necessary to electronically unlock the keyboard by typing in a four digit combination code, preceded by . The code will not be printed on the terminal. If an incorrect code is entered, the terminal will print. INCORRECT CODE (time) KEYBOARD LOCKED If the correct code is entered, the terminal will reply KEYBOARD UNLOCKED and will then print the current terminal configuration followed by the display mode prompt which is an arrowhead symbol ">". The terminal must be configured to accept information from specific interlockings connected to its six ports, this configuration is printed when the keyboard is unlocked as a reminder to the user. An example printout is shown below. 0484 KEYBOARD UNLOCKED 0485  0486 IDENT NAME PORT 0487 0 0488  1 0489   2 0490   3 0491   4 0492    5 0493   0494   > To LOCK the keyboard, type Lock and the terminal will reply (time) KEYBOARD LOCKED If the terminal is left unused for 30 minutes unlocked, it will lock the keyboard automatically and print the keyboard locked message. The complete list of requests, commands and controls and their operation is not included. However, a summary of the main facilities is given to give an appreciation of the use of the technician's terminal. 7.4.1 Fault Summary To obtain a listing of current faults, type FAULT terminal will then print a numbered list of faults If a fault occurs and is subsequently cleared, its status in the list will change from  "fault" to "fault cleared", but will remain in the list. If the fault occurs again before the "fault cleared" has been removed from the list, its status changes to "intermittent fault". 7.4.2 System Activity To display system activity on the printer, type DISPLAY (name) (device)............(device)  (name) is the interlocking code name and (device) is the device type to be logged,  as follows: TRACK for track circuit indication changes POINTS for points indication changes SIGNALS for signal indication changes One or more device types may be specified, separated by commas. The terminal  will then start to log activity with the relevant time. 7.4.3 Telegram Contents To display the contents of specified telegrams, type TELS (name) (address 1)...........(address 4)  Name is the name of the interlocking, and address 1 etc. are the addresses of telegrams to be examined. Up to 4 addresses may be specified. The terminal will immediately reply with the current state of the specified telegrams, and will printout each telegram contents again whenever it changes. Each telegram description occupies one line and takes the following form. TELS  LSPA  22.23 0507  09.21.53  AD OUT DATA   IN  DATA   OUT  STAT  IN  STAT 0508                         76543210   76543210   76543210    76543210 0509  09.21.58  22   10001000    10001000   00000000    11111111 0510  09.22.00  23    10000000    10001000   00000000    11111111 0511   09.23.23  22    10000001 0512   09.23.23   22   10001000 0513   09.24.23   22    10000100 0514   09.25.23    22   10000001 0515   09.25.23     22   10001000 0516   09.25.50     23   00100100 0517   09.25.51     23                         11001010 0518   09.26.03     23     10000000 0519   09.26.04      23                             10001000 0520  > OUT means from  the interlocking to the module. IN  means to the  interlocking from the module. DATA means interlocking information, i.e. controls or indications. STAT means the check that the module is operating correctly. Eight bit binary numbers are printed in the order bit  7, bit 6 .......,  bit 1,  bit 0 When the data and status are first printed, all four sets of information are displayed on one line. When a change occurs, only the particular part containing  the changed information is displayed. The printout continues until terminated by typing 7.4.4 Control List To obtain a list of all controls currently set on a specified interlocking (e.g. route disconnections), type LIST (name)  terminal will then request the interlocking to send a list of all controls currently set. 7.5 Interactive Commands As well as displaying data and information necessary for general maintenance and fault finding it is possible to send commands to the interlocking in order to change various parameters. It is necessary to leave display mode, which can be thought of as the lowest mode of operation, and enter "command" mode. To enter command mode, type COMMAND    The terminal will reply COMMAND MODE prompt will change to "*" to indicate that the terminal expects interactive control commands. To return to display mode type 7.5.1 Clearing Fault Records Most types of  fault  registered in the fault table will automatically be changed  from  "fault" to "fault cleared" status when the fault has been rectified. However some faults, particularly intermittent faults, require this change of status to be done manually. To clear a fault record, type CLEAR n n is the number of the fault to be deleted. The  terminal will then print out the fault  message concerned and ask for confirmation. When confirmed the terminal will print FAULT CLEARED. 7.5.2 Removing Cleared Faults To remove all "Fault Cleared" status faults from the fault table, type REMOVE The terminal will then reply ALL CLEARED FAULTS REMOVED The table will then be compressed, and a new "FAULT" command will be needed to establish the new numbers of the faults remaining in the list. 7.6 Interlocking Controls Before any alterations can be made to the interlocking it is necessary to enter the highest mode of operation, "control" mode. To do this type CONTROL  The terminal will reply CONTROL MODE. ENTER NAME AND PURPOSE The user must then type in his name and the reason for altering the controls. This will be recorded as part of the logged data on the tape cartridge. The entry may occupy more than one line. Therefore, to terminate this entry type twice. The terminal will interactively ask for the interlocking name and the control required. There is a choice of controls which may be applied, these are ASPECT DISCONNECTION TEMPORARY APPROACH CONTROL TRACK CIRCUIT OCCUPATION ROUTE PROHIBIT POINTS DISABLE START (see 7.7) STOP (see 7.7) Enter the control required (only first four characters necessary). After the "*" prompt enter ON or OFF to apply or remove the restrictions, followed by the device reference number for the device to be controlled, obtained from the interlocking reference manual. ON and OFF commands will be coded by the terminal processor, and sent via the panel processor to the interlocking. Typing only will cause the terminal  to ask  for another control. If an ON or OFF command was issued, the interlocking will reply to the terminal, which will print out the identification of the device controlled as it appears on the control panel, and not as entered. If an incorrect command was entered, an error message will be printed. If the command was valid, the terminal will ask ENfER EXECUTION CODE*, the word "EXEC" must now be entered which will cause the terminal to reply COMMAND EXECUTED.If an incorrect command code or no code is entered it will print CONTROL NOT ACCEPTED. This process may be repeated as necessary. The following is an example of how to disable points 231 so as to make the field sidings out of use. Normal print shows the text generated by the terminal and bold text is the user input. 0538    COMMAND 0539    COMMAND MODE 0540   *CONTROL 0541    17.09.86   09.31.24   BST CONTROL MODE, ENTER NAME AND PURPOSE 0542    *M.SMITH. TAKE FIELD SIDINGS OUT OF USE 0543      0544     0545     ENTER INTERLOCKING NAME *LSPA  0546     ENTER CONTROL REQUIRED *POINTS  0547     POINTS DISABLE *ON  11 0548      POINTS DISABLE 231 ON 0549     ENTER EXECUTION CODE * EXEC  0550     CONTROL EXECUTED 0551     POINTS DISABLE *  0552     ENTER CONTROL REQUIRED *    0553     ENTER INTERLOCKING NAME *    0554     *  0555     > LIST  0556     NO SUCH INTERLOCKING 0557     > LIST LSPA    0558     POINTS DISABLE 231 0559     END OF LIST 0560  > 7.7 Power Failures In the event of a complete power failure to the interlocking one of two sequences will occur depending on the length of time the power is lost. The interlocking MPMs compare memories and decide on the type of start to adopt. 7.7.1 Cold Start If the power is off for more than approx. 6 hours the interlocking will have lost all the information in the State of the Railway Memory including any restrictive controls. Before normal operation can continue it is necessary to start the interlocking from the technician's terminal. This is done in control mode. A 4 minute time-out period and the START command must have occurred before normal operation can resume, however the START command may be given at any time after the power has been restored either during or after the timing out period. Any controls applied before the power failure will have been lost and MUST be re-entered before giving the START command. As 6 hours may elapse before a cold start is necessary, it should never be required under normal circumstances. 7.7.2 Warm Start If the power is off for less than approx. 6 hours then data will not be lost and no action will be required by the technician, however the signalman will have to reoperate any routes previously set. 7.7.3 Four Minute Tune-out Occasionally after a warm start, a discrepancy in route set memories may be found by the Interlocking MPMs during memory comparison. This can occur if a route was being set or released at the instance of power failure. In this situation, a modified warm start will occur where all routes are released but points are immovable, signals held on, and signalman's controls ineffective for a four minute time-out period. All train movements should have come to a stand in this period. This timing out is indicated to the signalman and on the technicians terminal. The timing out period also applies to every cold start. 7.7.4 Stopping an Interlocking The STOP command can be used to stop an interlocking to enable a large number of controls to be set or cleared. In the stopped state, an interlocking will still report the positions of all trains, but all signals will be held at red, and all points will be locked in their curent position, and the signalman's controls will be ineffective. 7.8 Data Link Interogator A small portable unit is available which can be connected to the data link (normally at the line termination unit) which can be used to display the individual messages sent between the interlocking and the TFMs. The information displayed will be exactly the same as the information given on the technician's terminal using the TELS command. 7.9 Go/no go Tester When it is anticipated that a point or signal module may have to be changed it is important that any replacement module taken out to the location is known to be working.  A  GO/NO GO test unit may be available to test point and signal modules quickly and simply before leaving. Detailed instructions on how to operate the unit may vary but it will consist basically of plugging the module into the tester with the appropriate connector plug and then starting  the automatic test routine. Simple indications will then indicate when the test is complete and whether the module is good. Using the GO/NO GO tester will deconfigure the module of its interlocking identity to allow it to be moved from one interlocking to another. 8. SSI DESIGN & TESTING SSI requires a fundamental departure in design principles from relay interlockings. Instead of designing physical circuits, much of the information must be coded into stored computer data. The SSI design workstation has been developed to enable designers to prepare and test geographic data for SSI signalling projects without a detailed knowledge of the computer languages used. The design engineer will never need to amend the SSI programs; in fact the workstation does not give him the facility to do so. 8.1 The Design & Test Process The stages involved in the design and testing of the geographic data for an SSI signalling project are summarised on page 55. The processes on the left half of the figure are basically manual procedures which have direct equivalents in the design and testing of conventional signalling schemes. Some of these processes make use of the Design Workstation as a means of storing information and of carrying out tests in the design office rather than on-site. The processes on the right half of the figure are mainly automated procedures carried out within the Design Workstation. 8.2 The Design Process Signalling plans and control tables must be prepared in the same manner as for conventional installations. The adoption of SSI has resulted in some changes to the format of control tables as it is important that the information from which  the interlocking data is compared is complete. Many control tables have in the past made certain assumptions regarding standard controls and these have not been shown. It is important that the data preparation engineer has all required controls documented before input starts. The first major task, once plans and control tables are available, is the allocation of all items of lineside equipment to trackside modules. Each function must be provided with the required number of inputs and outputs. In general, point operation outputs must be provided by points modules, all other outputs will be provided by signal modules. If the overall number of trackside modules exceeds the capacity of a single interlocking, the overall control area must be divided between a number of SSI Central Interlockings. The boundaries should be determined so that the data passing between adjacent interlockings is minimised. A section of automatic signalling is ideal although this will not always be possible. The number of trackside modules is the most likely limit on the area of one interlocking, although other constraints such as the number of signals, routes, points or track circuits (or even the total ·volume of data - not yet known - could be a limitation. The module allocation should also include the suitable positioning of data link modules as repeaters. Any one interlocking can only operate with the standard data link or the long distance terminals, not a mixture of both. This is due to the different communications software used. The module allocations will be stored on a database within the Design Workstation,  which is capable of generating printed listings in a variety of formats. The next task is Data Preparation. This is the specification of the geography of the railway and all necessary signalling controls in a form which the workstation compiler can understand. It is still in a user readable form (source code). From this data, the SSI workstation will compile various data files for use by the·  interlocking modules, the panel processor modules, the diagnostics and the simulator for testing. 8.2.2 Data Preparation The SSI system must know the identity of all functions which it controls or may receive inputs from. A series of identity files lists all functions. If a function does not appear in the identity file, the interlocking software will not recognise it. The identity files for interlocking XXN would be:- XXN.TCS Track circuits XXN.SIG Signals XXN.PTS Points XXN.ROU Routes XXN.FLG Flags (any other two-state inputs, outputs or data required by the interlocking - e.g. Train ready to start indicators and ground frame release, also includes sub-routes and sub-overlaps XXN.ELT Elapsed timers (other than signal or track circuit timers which are already assumed to exist for each route and track circuite) XXN.QST Route requests XXN.BUT Panel switches and buttons XXN.IND Panel indications SSI Design and Data Preparation Other files will determine how the interlocking operates. The interlocking requires the following additional files:- XXN.IPT All input functions from the trackside modules (external data link) and other interlockings (internal data link) XXN.OPT All output functions, internal and external XXN.FOP Flag operations. This includes route releasing of sub-routes XXN-PRR Panel requests. This requires all the conditions for setting of a route or a set of points and will contain the equivalent of the direct locking and the route locking in the signals controls  XXN.PFM Points free to move - all point locking controls - equivalent to the WZR in a realy interlocking although somewhat simpler since all locking on points is applied by sub-routes and sub-overlaps XXN.MAP Geographical map of track layout used for detecting approaching trains in the approach lock release function The panel processor modules require the following files:- XXN.PSD Signal indication data XXN.PPD Points indication data XXN.PTD Track and route indication data XXN.OTD Other indications data XXN.PBK Panel button and key data The diagnostics MPM will also require file XXN.DIA which is a map of the data link to allow the diagnostic processor to deduce faults from the data flowing (or not flowing) on the data links. Some of the data will also be used by the simulator. At this stage, all data is held by the workstation. When testing is satisfactorily completed, the data can be loaded on to EPROMs for installation into the modules on site. Files can be listed in a variety of formats to enable checking to be carried out. 8.2.3 Testing A major difference between SSI and conventional interlockings is that a large proportion of the testing can be done on the design workstation. Most of the functional testing of the interlocking is done in the office. The simulator is used in place of the data link and trackside modules. The tester has the facility to operate a simulation of the signalman's control panel and change the state of·all inputs to the interlocking. The simulator consists of a simplified SSI cubicle, containing only one interlocking and panel processor, the simulator MPM connected to its VDU and an interface processor connected to a mouse or trackerball input, communications to the main workstation computer and a tape cartridge unit. This can be used to read the data held on tapes retrieved from working interlockings for investigation. Testing on site can therefore be confined to the communication between the interlocking and the trackside module inputs and outputs. The logic of the interlocking does not need to be re-tested. It is also possible to prepare and test interlocking data for several stages of a multi-stage job in advance. The EPROMs are exchanged at the time of the alteration: 8.2.4 The Checking Process Just as wiring diagrams must be independently checked against the signalling plan, control tables and other source documents specifying the signalling requirements and controls, so must the SSI data. Some of the checking processes can be automated. Others still require a systematic manual check. The final check must always be on the data which is used by  the SSI, not on the source code input during data preparation. This can be checked for equivalence by a process of decompilation. The object code is converted back to the source code and compared with the original. This checks the. compilation process and can be fully automated. Checking that the data corresponds to the control tables and to signalling principles and standards is not yet an automated process. The engineer responsible for checking must inspect all the data to ensure correlation with the written controls. Although not automated, the task can be made easier by the production of listings of various parts of the data files arranged in a specified order. This will enable the checker to find all references to a particular function. Different versions of data can be compared to identify all differences. This assists the checker in ensuring that intended modifications have been carried out. As the control tables are essentially written documents, it may prove possible in the future for control tables to be prepared in a suitable format for direct compilation into SSI data. This would further simplify the checking process. The final manual check would be on the control tables themselves. The remainder of the data checking could be done by decompilation. If the control tables were prepared as a database,  it might also be possible to identify automatically whether converses of each control had been entered. 8.3. Analysis of Tapes The SSI design workstation is equipped with a tape cartridge reader which can be used to examine the contents of a tape. This is a useful aid for examining failures and incidents where allegations of irregular operation of equipment or movement of traffic is alleged. By monitoring all the input and output telegrams, the tape holds a complete record of the time of every change of state of the equipment. Typical Design Workstation Configuration 9. The Future SSI has already had a major impact on the control of signalling.  It  is  however  unrealistic to assume it is the final stage of signalling  development.  Technology  will  continue  to improve and one day SSI  in its present  form  will  no doubt  be obsolete. For the present, it is unlikely that any major changes will take place in the interlocking software. As so much effort is required in the development and validation of safety  software, significant changes have to be justifiable in financial terms. At the trackside, however, major changes may have to be accommodated. SSI has  already been employed successfully in the control of ATC driven trains. This  has, however required an additional interface between the trackside module and the ATC equipment. With greater interest in automatic train protection, a system which could interface ATP transponders and coded track circuits directly with SSI trackside modules would be a great advantage. Track circuits are already on the market which can drive a trackside module input without the need for a track relay. Train detection has traditionally been done by track circuits. With the increasing  interest in axle counters, a trackside module which could receive the input from the rail mounted equipment is under development. The counting logic would be carried out within the central interlocking. As well as reducing equipment complexity, and  hopefully  cost,  this  would extend still further the range of the axle counter.  Suitable protection will have to be provided against false operation due to timing of telegrams. As yet, no vital data link exists between SSI installations at different sites. The internal  data link is designed for communication between interlockings in the same  building.  With the more widespread application of SSI, the need for such a link increases. At present, the only means available for conveying data such as aspect sequences across boundaries between SSI installations is a back to back arrangement of trackside modules.      

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Deepu Dharmarajan -
Posted 126 days Ago

REMOTE CONTROL SYSTEMS

  CONTENTS 1. Introduction 2. Direct Wire Systems 3. The Reed FDM System 4. Principles of Time Division Multiplexing  5. The Westinghouse S2 TDM System. 1. INTRODUCTION 1.1 The need for Remote Control Most modem signalling systems using relay technology for safety circuits have interlockings placed at strategic junctions, stations and level crossings. In order to avoid the need to staff each interlocking individually, remote control systems have been used to allow centralised control of a large area. Although some early systems used relays, remote control was one of the first  areas  of signalling technology to employ electronics. This is because the electronic portion  of  the system did not have any responsibility for safety. In the context of railway signalling, the term remote control has therefore come to mean the control and indication of an interlocking or specific signalling circuit from  a  signal box through a non-vital system. If the system should fail in any way, the  interlocking controlled ensures the safety of train operation. Some remote control systems can, however, convey vital signalling information. In  this case all interlocking circuits are located at the same site as the signalman's  control panel and a vital remote control link replaces the circuits from the  interlocking to equipment. The system has been designed such that failures will not  cause false operation of points or signals. 1.2 Methods of Remote Control 1.2.1 Direct Wire As its name suggests, each function employs a physically separate wire or pair of wires. Individual circuits, often with a common return, connect the Signal Box to the Remote Relay Room. Paired telecomms cable or special micro core cable with small non-vital relays are used. Such systems are usually "point to point" systems to avoid terminating the cable in many places. 1.2.2 Frequency Division Multiplex Electrical signals may be transmitted over the same conductors at different  frequencies. Filter circuits may be employed to separate the required signal from  all  other unwanted signals. Therefore, more than one function may operate over one line pair. Each function has a set frequency (normally in the audio range). Each frequency can be injected  onto the line without affecting any other frequency. Functions may be added  to or removed from the line at any point. FDM Systems arr usually non-vital systems, but some FDM systems are suitable for vital signalling circuits. 1.2.3 Time Division Multiplex Instead of using different frequencies, time division multiplex (TDM) divides a fixed duration cycle into a number of time slots. The state of each circuit in turn  is  transmitted over a single line pair. Each function has its own time slot. A TDM  system is only capable of transmitting information between fixed points. Fail safe  operation is  provided by the relay interlocking concerned, so the TDM system may be non-vital. 1.3 Applications of Remote Control Systems 1.3.1 Relative Costs For a direct wire circuit,  a cable core must be provided for each function, plus  some form of return conductor. Additionally a relay is required for each circuit. For an FDM System, the cable requirement  is limited  to a line pair, so  the cost  of  cable is only related to distance, not number of functions. The system costs are most significant  in  the provision of transmitters and receivers and, therefore, the number of functions to be transmitted dictates the cost of the whole system. Line Amplifiers do lead to extended systems having a greater cost per km than a short system. T.D.M. systems need only a line pair and, at long intervals, line amplifiers.  Thus  route costs are low. Transmitter and Receiver equipment is, however, expensive to  provide initially. Additional functions cost little to add once the basic equipment is available. 1.3.2 Typical Uses T.D.M. Systems are usually employed to  convey  large  amounts of information  between fixed points, normally a Signalbox and the remote interlockings it controls. If the remote interlocking is close to the signalbox, a direct wire system may be used. TDM Systems are now economic over very short distances. FDM Systems are not cost-effective for conveying large amounts of information  between two points. They are generally installed in the following situations:- Where the number of channels required is fairly small, or Where the sources or destinations of the information are distributed along the track, or Where the circuits concerned are signalling safety circuits, in which case  a  Vital Reed FDM system must be used. Typical application of Remote Control Systems is shown on the following page. Typical Application of Remote Control Systems 1.4 Response time of Remote Control Systems The response time of a Direct Wire system to a change in any one function  is the time taken for the relevant relay to operate. With an FDM System, the response time of the filter will dictate the operation time'. This should be less than 1 second. The response time of a TDM System to the change of any one function input varies greatly according to the type of system used. Synchronous systems, transmitting data in strict rotation, may respond very quickly to a change if that bit of data was about to be sent. However, if that information had just been transmitted then a delay of a whole data scan would ensue. Thus, the response time may be from virtually zero to perhaps 5 seconds according to the type and size of system. TDM Systems that have the ability to interrupt the synchronous flow of information to send urgent data will generally ensure that the changed data will be received within 50mS of occurring. 1.5 Remote Control Failures 1.5.1 Direct Wire Direct Wire Systems are, technically, the simplest remote control systems. Consequently, they have little which can go wrong. Total system failure can only be caused by power failure,  (in which case other  more important functions will have failed too), or by damage to the cable. Individual relay failures or deterioration of the cable with age may affect individual functions. 1.5.2 F.D.M. As the components of an FDM system are distributed along the system, the effects of  a single failure may be limited. Few faults would cause a total failure. Such faults include a line failure at or near the relay room end of a system or a power supply  failure at the relay room. Line failures would generally lead to a partial system failure. Those parts of the  system beyond the point of failure would be inoperative whilst those before would continue normal operation. The failure of a line amplifier or its power supply would lead to similar partial system failures. Failure of an individual transmitter or receiver (or its power supply if it is the sole function driven from that power supply) will only, in general, affect that function. 1.5.3 T.D.M. TDM systems are totally dependant on the satisfactory operation of the line, multiplexing equipment and modulating equipment. A failure in any of those parts of  the system is liable to cause total loss of functions. Failure of the circuits relating to  individual inputs and outputs will result in the loss of a  limited number of functions  (generally no more than those processed through one input/output card). 2. DIRECT WIRE SYSTEMS The simplest way of allowing a signalman to exercise control over an interlocking  that  is remote from the signal box is by extending the panel to interlocking circuits  using individual relay circuits. Conventional safety relays and  signalling  cables  are  expensive and  unnecessary for non-vital circuits. Direct wire systems normally employ lightweight cable and  non-vital relays. The circuits will typically use standard telecomms type paired cable. The smaller conductor size reduces the cost relative to using standard signalling cable. The relays should have a high coil impedance to minimise voltage drop effects along  the line. However, a high coil impedance increases the sensitivity of the circuit to induced voltages from parallel circuits. Relays of up to 6000 ohm have been use . 2.1 Return Conductors All direct wire systems need a return conductor. The nature of the return conductor will depend on the individual installation: Individual return for each circuit. Single return for small group of say 4, relays possibly making use of diversity..(i.e. NWKR and RWKR never up together). Common return for all circuits. "Balanced" common return for circuits in both directions. Typical circuits for a balanced microcore system are shown below. Microcore Remote Control Circuits as Used on B.R. 2.2 Microcore Systems In the early days of remote control, British Rail used a specially manufactured type of cable designed so that the return of each circuit could be commoned with all other returns. This, therefore, requires the return conducfor to be of larger size than the circuit cores.  However, to minimise the size of the return conductor, return currents for each direction are "balanced" against each other within one core. Atypical micro core cable is shown  in the following diagram. The core of  the cable acts as the common return conductor and is made up of 56 0.3mm copper strands, sheathed in polythene. The circuit conductors, each a PVC insulted 0.4mm  conductor, are layered around it. 360 cores require nine layers. Water and rodent barriers are incorporated into the outer sheaths. Section Through "Microcore" Cable 2.3 Immunity to A. C. Traction A line circuit running parallel to AC. electrified tracks will be subject to induced voltages. The voltage induced in the circuit will increase as the circuit length  increases. Consequently, the CCITT recommends that the circuit length be restricted to a length so that under full traction load the induced longitudinal voltage does not exceed 110 volts RMS and under traction  fault conditions  it does not exceed  430 volts RMS. In practice,  the length of circuit that meets this requirement is 2km for a 25kv traction supply. Any circuit that is required to extend over a longer distance must comprise two or more cut section circuits. In practice the cost of cut-sections rules out direct wire systems longer than 2km in electrified areas in favour of TDM Systems . In general, the comparative cost of  specialised cables and processor controlled TDM systems is such that microcore   and similar systems are more expensive than TDM 3. THE REED FDM SYSTEM Although several types of FDM systems have been produced, the most widely used and still currently available system is the GEC reed FDM system. This will therefore be used as the example for a typical FDM system. 3.1 Basic Principles A transmitter is used  to generate  a signal  at a particular  frequency,  whilst  a receiver  acts as a detector. The transmitter contains a bandpass filter connected  in  the feedback path of an  oscillator. The oscillator produces a sinusoidal signal at the filter frequency.  This  signal is connected to the line circuit only when the control contact is closed. The receiver uses a bandpass filter to filter out all the unwanted signals present on  the line to leave only the desired frequency.  The output from the filter is amplified,  rectified and fed to the relay coil. The relay will only operate when the appropriate  frequency is present on the lines. Three systems are in widespread use,  RR2000, RR3000 and RR4000.  A frequency range  - of 350 to 900Hz is used. RR2000 can be used as a vital system but is not fully traction immune. It operates over 51 vital channels. A further 12 non-vital channels and two universal spare channels are also available. RR3000 is a simpler, non-vital system employing a single tuned reed filter instead  of  the double tuned filter of  the vital RR2000  and  RR4000 systems. The same number of channels is available. The RR4000 system is a vital traction immune system. It employs only 16 channels. It  may be used to provide traction immunity for detection and other similar circuits  in areas with both a.c. and d.c. traction. Signal voltages in the range 0.3 - 0.6 volts are typical. 3.2 Reed Filters Frequency discrimination is provided by a tuned reed filter - a mechanical reed  assembly  which only vibrates within a very narrow signal bandwidth. 3.2.1 The Double Tuned Reed filter The double tuned reed filter contains two reed assemblies joined together by a connecting plate. Each assembly contains a steel rod (or reed) clamped in a brass  mounting block which also supports a coil and a small permanent magnet.  The  reed is 38mm long and 3mm in diameter. It is shaped at one end (the  neck) and  may be tuned to the desired natural frequency of vibration by removing metal from  the neck.  Both reeds in one filter are tuned to the same frequency of vibration. To prevent external electro magnetic pick up in the output coil of a receiver filter, it is shrouded by a mu-metal  screen. Mechanical interference is kept to a minimum by mounting the complete unit in resilient mounts. The reed filters used for transmitters and for receivers are not interchangeable, due to slight differences in the tuning of the two reeds, and in the electrical components included within the units. If an alternating signal is applied to the input coil, it will magnetise the reed with  alternate N and S poles at the frequency of the signal. The reed will be attracted and  repelled  by  the poles of the permanent magnet, and will attempt to vibrate. If the frequency of the signal applied to the coil is the natural frequency of the reed,  these vibrations will be quite large. If the two frequencies are not the same, there will be very little vibration.  Assuming  that  the two frequencies are the same, the  vibrations will be transmitted through the mounting and the second reed will begin  to vibrate.  The  movement of the second reed within the field of the permanent magnet will create a changing magnetic field at the frequency of vibration. This changing magnetic field will induce an alternating voltage in the ouput coil. There will only be an appreciable output voltage from the second coil when the input frequency is the frequency to which the reeds have been tuned. The Double Tuned Reed Filter will not respond to any frequency other than that to which it was originally tuned. If either of  the reeds changed its natural frequency,  there would  be no output from the filter and  the  unit would  fail "right  side".  The filter is therefore suitable for use in vital signalling circuits. The double tuned reed filter has a very small bandwidth  (0.65  -  0.9Hz).  This  makes  the filter very selective, and allows a channel separation of approximately 4Hz. 3.2.2 The Single Tuned Reed Filter The single tuned  reed  filter contains one tuned reed and one dummy reed. The  tuned reed is mounted in the same assembly as one half of the double tuned filter.  The dummy reed forms the fixed core of the dummy coil. The reed coil and  the  dummy coil are identical, each having two windings and acting as a transformer. The input voltage is divided equally between the two primary windings, and  provided  the input is not at the resonant frequency of the reed, the reed will not  vibrate.  The outputs  from the secondary windings are equal in amplitude but are connected in opposite phase so that the voltages cancel out. When the input is at  the  resonant  frequency,  the reed will vibrate, and will alter the output from the  reed coil.  The outputs from the two coils will then be unbalanced and a large voltage will appear at the output. Since the resonant frequency of the filter depends upon  only one reed, it is not suitable for use in a vital system. Damage to the reed could change its natural  frequency and allow signals of a different frequency to be received. 3.3 Type RR Systems 3.3.1 The RR2000 System The RR2000 System has 51 frequencies available for vital functions (f1- 51) and a further 12 available for non-vital functions (f81-92). Two frequencies (f71 and 72) are available as universal spares (see later). Some of the 51 vital frequencies are within the 50Hz even harmonic bands and are only considered suitable for vital circuits in non-electrified areas. A complete transmitter requires a transmitter amplifier and a double-tuned transmitter filter. All amplifiers are interchangeable, the filters are unique to each channel. A complete receiver requires a receiver amplifier and a double tuned receiver filter. The output from the receiver amplifier is fed to a Reed Follower Relay. 3.3.2 The RR3000 System The RR3000 system is a development of the RR2000 system as used for non-vital circuits. By using circuits and components not suitable for vital systems the cost of a non-vital installation is reduced. Sixty three non-vital channels (fl-51 and f81-92) are available, suitable for use anywhere. The channel frequencies are the same as the RR2000 system, including the two universal spare channels (f71 and 72). The transmitter is a single unit mounted in a BR930 series relay case which contains an amplifier and a single-tuned reed filter. A complete receiver requires a receiver amplifier and a receiver filter.  A  reed follower relay is not necessary as the receiver amplifier contains a miniature non-vital follower relay. 3.3.3 The RR4000 System The RR4000 system is a development of the RR2000 system as used for vital circuits. It uses the same equipment, but with a different group of frequencies. Sixteen vital channels (f401-416) are available, suitable for use in any electrified area including mixed a.c. and d.c. traction. The maximum size of one system is 16 channels. The output from the receiver feeds a vital reed follower relay. Reed FDM Transmitter and Receiver Block Diagrams Transmitter Receiver Reed Filters Double Tuned Reed Filter Single Tuned Reed Filter Single Tuned Reed Filter Circuit 3.3.4 Frequencies Used The range of frequencies available is determined by the mechanical characteristics of the Reed filter. All the frequencies lie between 300Hz and 900Hz with a separation of approximately 4Hz. The actual frequencies are chosen to reduce the effects of intermodulation between channels and interference from 50Hz traction supplies or overhead power lines. Intermodulation reduces the number of channel  slots available. Whenever two  frequencies are applied to the line, they interact to produce further frequencies. As the number of frequencies present increases, so does the number of additional frequencies produced. These additional frequencies cannot be used for other channels. For vital systems, especially where electric traction is used, frequencies near the harmonics of the  50Hz power supplies are considered unsuitable. The frequency  of  the 50Hz  mains is usually regulated to within the range  49.5Hz  -  50.5Hz. To  allow a margin for safety, reed system frequencies are excluded from the range  49Hz  -  51Hz and its harmonics.  If an excessive amount of 50Hz interference occurs on a Reed system,  it could lead to saturation of the various transformers  used in the system, which  has the effect of increasing the number and strength of  the intermodulation products. Consequently,  fewer frequencies are available for vital Reed systems used in electrified areas. Whilst such an occurence is possible, it is somewhat unlikely, and is not considered necessary to take such precautions for non-vital Reed systems. 3.4 Reed FDM Equipment 3.4.1 The Transmitter : RR2000 and RR4000 Systems Transmitters are of type RR1000, RR1001 or RR1002. The connections to the RR1000 and RR1001 transmitter amplifiers are identical. The RR1002 has a 350mV output (A1-D2) in addition to the normal 650mV output (A1- D1). A double-tuned filter is connected in the feedback path of the amplifier to form an oscillator, which will oscillate only at the frequency of the filter. Since the amplifier is designed so that the output will never rise under failure conditions, the transmitter is suitable for vital circuits. The output of the transmitter is connected via a transformer to isolate the d.c. voltages in the amplifier from the line circuit. The oscillator normally runs continously, and the output is connnected to the line  by a contact between terminals A4 and D4. In this configuration, the  follower relay at  the receiver should respond within 1 second. An alternative method of operation is to put the controlling contact in the supply to terminal A2/D3 (link A4-D4). In this configuration, the oscilllator will begin to  operate once the contact is closed, and the operation of the follower relay is then delayed  by  3-4  seconds. Since the contact also controls the power to  the amplifier, the output is removed as soon as tne contact is opened - as with the instant operation. This delayed operation could be used (for example) for track circuit repeat relays.  This configuration is rarely used in practice. It could offer some power savings when used for circuits which are normally de-energised. 3.4.2 The Reciever : RR2000 and RR4000 Systems The circuits of all the receiver amplifiers are very similar. The line signal is applied  to the input coil of the Reed filter, and if the correct  frequency is present in the signal,  the filter gives an output. This signal is amplified and rectified (half-wave) then fed to the Reed Follower relay. The output to the Reed Follower relay is  nominally 12  volts  d.c.  The amplifier circuit is of "fail-safe" design, so that the gain cannot increase even if components fail. The amplifier is not frequency selective,  so  that  any signal introduced will be amplified, rectified and fed to the relay. The RR2002 is a more sensitive receiver than the RR2001 or the newer RR2003,  but  it cannot be immunised. It  is mainly used on Duplex systems where the signal  available at the receiver is lower than normal. It is also extensively used on Type  RT Reed track circuits. 3.4.3 The Reed Follower Relay The Reed Follower Relay (ZS2411) is a miniature signalling relay with contacts suitable for use in vital signalling circuits, and a coil designed to operate from the output of a receiver amplifier. It has 6 Front and 3 Back contacts. 3.4.4 The Transmitter : RR3000 System A single tuned reed filter is connected in the feed back path of an amplifier to form  an oscillator which oscillates at the resonant frequency of the filter. The  output  is connected via a transformer to keep the amplifier d.c. bias voltages isolated from the line circuit. The control contact between terminals D4 and D7 in series with the output transformer gives an instant output. There is no provision for delayed output operation. 3.4.5 The Receiver : RR3000 System The line signal is applied to the input coil of the reed filter, and if the correct  frequency signal is present, the filter will give an output. This signal is then  amplified and rectified and fed to the relay. The design of the amplifier is not to "fail safe" standards. The internal reed follower relay has three change over contacts and one back contact wired to the terminals of the unit. Terminal D2 is connected to the relay coil  to act as a test point. With the 12v supply present, if D2 is linked to D1 (or A1 on the RR3001),  the relay may be energised without a reed signal during testing. The relay energisation may be monitored from terminal D2. 3.4.6 Two-part Transmitters and Receivers In two-part transmitters and receivers, the amplifier is clipped to the top of the reed  filter and secured by a screw. The filter is fitted with coding pins to ensure that the correct type and frequency of filter is used in any one position.  All the electrical  connections are made via the amplifier which does not have any coding. The combined unit fits a standard BR plugboard although it projects about 1" below the bottom of the plugboard and requires  a special retaining clip. Transmitter Circuits Receiver Circuits 3.4.7 Transmitter Repeater Units When a number of systems all start from the same location, it is likely that the same Reed frequencies are used more than once. Transmitter Repeater Units (TRU's)  may be used to reduce the number of transmitters required. The TRU is driven by  one  transmitter, and provides three or four separate isolated switched outputs. The master transmitter is set to transmit continuously and may feed up to seven TRU's. 3.4.8 Universal Spare Channels Two universal spare channels (f71 and 72) are available for use in non- vital RR2000 and RR3000 systems. They reduce the number of spare filters required by allowing a temporary change in frequency for a circuit whilst a faulty filter is repaired or replaced. The filters have red (f71) and white (f72) labels for rapid identification. Universal spares may not be used in vital systems. 3.4.9 Power Supplies Transmitters, receivers, and transmitter repeater units all require a 12 volt d.c. smoothed and stabilised power supply. A full range of power supplies is available to suit most situations. Each FDM system at one location  must  have  a separate  PSU  -  One  PSU  must  NEVER feed two systems. This is to ensure that signals do not leak from one system to another via the power supply. D.C. Power supply connections must be as short as possible for similar reasons. 3.5 Design of Reed FDM Systems 3.5.1 The line Circuit Any two conductors are suitable for a Reed system line circuit, although a twisted pair is preferable as the effects of crosstalk are minimised.  When used for vital  systems,  the choice of line circuit is more restricted: a twisted pair is recommended, but a signalling multicore or overhead pole route may be used if certain conditions are observed. These conditions are: Alternate layers of conductors must have opposite directions of rotation (ie  not Unilay); A pair may not contain cores from different layers of a cable; Transposition of conductors may be necessary with multicore cable  or  on  a  pole route. 3.5.2 Transmitters and Receivers One transmitter and one receiver are required for each channel in the system. Transmitters are connected in series with/the line since their output impedance is low when turned on. Receivers have a high input impedance, and are connected across the lines. When a transmitter is turned off its output impedance rises. To prevent this from reducing  the signal level of other channels, a resistor of about 30 ohms is connected across the output terminals of each transmitter. This also allows a transmitter to be removed without affecting the operation of the rest of the system. Since the receivers are connected across the lines, they may  also  be  removed  without affecting the other channels. The control circuit to the transmitter should  be run in a twisted pair. There is no  restriction on its length within one relay room or location, however,  it is usually  convenient  to have  the controlling relay located adjacent to the transmitter. The circuit from the receiver to the reed follower relay should also be run in a twisted pair, and should not be more than 20m long. Contacts of signalling relays should  not  be included in this circuit since a receiver can be damaged if it is energised with an open circuit output. (Exceptionally, cross proving contacts may be included if a reed circuit is used for detection). 3.5.3 Line Amplifiers On lengthy systems, the resistance of the line acts to reduce the level of the signals on the line. To counteract this effect, a line  amplifier may be installed to boost the signal level. For a circuit using 1/0.85mm signalling cable, or any cable pair with a similar resistance, the distance between line amplifiers will be about 4km. Transmitters and receivers between line amplifiers will  reduce  the  signal levels in the system, and additional line amplifiers may need to be inserted to counteract these losses. The requirements for line amplifiers and/or line isolating transformers (used for traction immunisation - see 3.5.7.) for any  Reed FDM system can be calculated  given a knowledge of the equipment characteristics. Such calculations  would  be  necessary if a non-standard type of cable were employed, or in the case of duplex system. However, for many standard systems, a set of design rules avoids  the  needs for calculation. The following "rules" concern the location of line amplifiers and the use of  line amplifiers in place of line  isolating transformers. There must be fewer than 25 transmitters in a section leading up to a line amplifier. There must be no more than 17 Receivers in a section leading on from a  line amplifier. There must be no more than 4 transmitters in a section leading up to a line isolating transformer. There must be no more than 4 receivers in a section leading on from a line isolating transformer. There is normally no restriction on the numbers of transmitters and/or  receivers at a signal box provided the connection to the line is via a line amplifier. A "section" is from the output of the previous line amplifier, or up to the input of the next line amplifier as appropriate. It includes any intermediate line isolating transformers. If the number of transmitters or receivers exceeds these limits, then additional  line  amplifiers may be needed. Examples of two typical systems are shown on the following page. 3.5.4  Branch Systems Many arrangements of branched systems are possible, a few examples are shown. The indications from the branch signals could be connected by extending the loop from the main part of the system, provided the length of the loop is short. An alternative is to feed the signal from the transmitters to a line amplifier. Since the output impedance of the amplifier is low, it may be connected in series with the line (as with a transmitter), to inject the signal into the main part of the system. Diverging systems may have the receivers wired across an extension of the lines, or a line amplifier may be installed in parallel with the lines, and its output used to feed the branch system. 3.5.5 Duplex Operation Most Reed FDM systems convey information in one direction only over one pair of wires (Simplex operation). However, it is possible to construct a Reed system where signals are transmitted simultaneously in both directions over one pair of wires  (Duplex  operation). They need to be very carefully designed, and arc more difficult to set up than ordinary simplex systems. Intermediate line amplifiers are not possible as they only pass signals in one  direction. Duplex systems are generally only practical for short distances and carrying a small number of functions. In general it will be preferable to use separate systems for controls and indications. 3.5.7 Immunisation In a.c. traction areas, or where there are overhead power lines running parallel with  the railway, it is necessary to sectionalise the line every 2km to satisfy the CCITT safety requirements. The line amplifier provides isolation every 4km as it is fitted  with transformers in its input and output. Additional isolation may be achieved by inserting a Line Isolating Transformer  midway between the line amplifiers. However, line isolating transformers may not  be used at adjacent isolating points. Both the Line Amplifier and the Line Isolating Transformer are designed to reduce  the level of 50Hz signals present on the line. Receivers on vital systems must also be protected against the effects of induced  50Hz signals. A separate immunisation unit which acts as a filter  for  mains  frequencies  is  used  in conjunction with each receiver. 3.5.7  Lightning Protection Lightning protection is often provided on the lines of Reed systems to reduce the effect of lightning surges on the equipment. The level of protection depends on the  incidence of storms and the construction of the line. Full protection requires the  provision of surge diverters and surge protection units. Surge diverters operate by providing a low resistance path to earth for current surges. Unfortunately their use increases the risk of earth faults on the system, and the potential for wrong side failures due to increased crosstalk between systems. Consequently, surge diverters may not be used for vital systems in multicore cables. 4. PRINCIPLES OF TIME DIVISION MULTIPLEXING 4.1 Introduction As the name implies a TDM system works by connecting each circuit in tum to the line, ie. time is divided between the various circuits. TDM systems are used to transmit large numbers of functions between two fixed points, eg. Power Signal Box (OFFICE) and remote Relay Room (FIELD).  They  are  purely transmission systems which replace cable conductors, repeat relays, etc between the two points. Fail safety is not required, as this feature is provided by the usual relay interlocking circuitry. 4.2 Uniselector Analogy The principle of the TDM system can be represented diagrammatically by two uniselectors (rotary switches), one at each end of the system, which rotate in synchronism. The inputs to the fixed contacts of the office uniselector are via control contacts,  ie. push button, control relay contacts etc, the outputs from the field uniselector being fed to the respective repeat relay coils. Because the uniselectors are synchronised in their rotation each output will  be  connected to its respective input during one step of the cycle. 4.3 Concept of Stored Instruction It should be apparent that each output relay  is only connected to its input for a relatively short period compared with the time for a complete cycle of the system.  To maintain continuity between the control relay contact and the output relay coil, each output must be stored in some way and applied to its output relay until the following scan, which would then confirm whether or not its input had changed state. This ensures that the output relay repeats its input completely, apart from a short time delay (less than one complete cycle) whenever the control relay changes state. The method of storage may be by the use of relays incorporating a stick feature  or  by electronic means employing digital storage circuits, ie. Bistable Circuits. TDM Principles 4.4 The Basic T.D.M. System The basic system comprises:- Digital Transmitter which scans the information to be conveyed from the various signalling inputs and arranges it into a suitable form for transmission; ie. representation of the inputs in pulse train (serial) form where a 1 bit indicates an input contact closed and a 0 bit an input contact open. Frequency Shift Carrier Transmitter which, using frequency shift keying techniques, causes each logic level to modulate a high frequency sine wave carrier signal to different frequencies representing those logic levels. Unmodulated pulse trains are not usually suitable for direct transmission over long distances due to degrading of the signal along the line. Carrier Receiver, at the remote location, which demodulates the incoming signal back into pulse train form Digital Receiver which processes the information received and directs it to the relevant signalling output 4.5 Synchronous and Asynchronous Systems Information may be transmitted in several formats. Synchronous transmission is the continuous transmission of data in order (as demonstrated by the uniselector). In practice a synchronising signal is sent to ensure that counters at each end of the system are in step at the beginning of each scan of information. The transmission will be in strict order, regardless of urgency or importance of data. Asynchronous transmission is the transmission of data as and when it changes ("immediate access"). There may be periods of time, therefore, during which no transmission is made. Generally, the data is grouped into "words" associated with "addresses". When one bit of data changes, the system will transmit the address of which that data is part and follow it with all the data associated with the address including the changed data. Systems adopted for railway use are based on both synchronous and asynchronous transmission techniques. Some systems are purely synchronous: none are purely asynchronous - even if no data changes there will be a transmission after a  certain maximum time has expired to ensure that the receiver can check that the transmitter is still operative. Many systems therefore adopt a combination of synchronous and asynchronous transmission. Although most combined systems use addressing in some form or other, they will transmit synchronously (including sending the addresses) unless urgent information (a data change) occurs. When a data change occurs the system completes transmission of its current word and then immediately switches to the data requiring immediate attention. 4.6 Transmission 4.6.1 Simplex and Duplex Transmission For a remote control system to function there must be a transmission line between the office and field. The terms simplex and duplex relate to whether information can be passed along this transmission line in one direction only or in both directions. Simplex - Information passed in one direction   Duplex - Information passed in both directions simultaneously   There are two further variations:- Half duplex systems operate from office to field and from field to office over  one pair of wires but at different times. Thus, at any one time information is being transmitted in one direction only. Two way simplex is two independent Simplex systems operating in opposite directions over separate pairs of wires. 4.6.2 Modems For information to be transmitted along a transmission line the basic information is modulated with a carrier frequency at the Transmitter and Demodulated at the receiver. This Modulation and Demodulation may be done internally within the equipment or externally in a separate unit. If it is done SEPARATELY, the equipment is referred to as a modem (MOdulator & DEModulator). The term modem is often used even if the unit only performs one of the two functions (Modulation or Demodulation). 4.7 Multistation Working 4.7.1 Control System Multistation working is when one office serves more than one field station. The field stations are in parallel with the transmission line, each field station demodulating  all information but ignoring all data not addressed to it. 4.7.2 Indication System Several field station transmitters send information to one office receiver. As only  one transmitter may send information at any one time, the transmission timings  must be controlled. This is generally done by the outgoing control system, a transmission from the office prompting a return transmission from the field station addressed. 4.8 Principles of Parity Protection 4.8.1 The Need for Parity Protection Electrical interference may alter the state of  one or  more  bits of  the data  transmitted. Since all information bits in a system are independent of each other, the receiver has no way of knowing whether any individual bit is the same as when transmitted. Parity requires the information arriving at the receiving end to be the same as that  which was sent from the transmitting end. To ensure that the received information is on par (ie. equivalent) to that sent, additional information must be given. This information is in the form of an additional bit or bits (ie. parity bit/s ) transmitted with the data. The receiver is provided with the means to  generate its own parity bit/s from the (apparently) genuine information received. These local parity bits are then  compared with the equivalent parity bits actually received. Any discrepancy means that errors have occurred. The received information must  be regarded as suspect and discarded. 4.8.2 Odd Single Bit Parity Single bit parity has one parity checking bit per block (or word) containing information bits. In systems using odd single bit parity, the parity  bit  is generated  as a 1 or a 0 to make  the total number of 1's in the block (or word) an odd number. The parity bit ensures that there will be at least one transition (ie. change of level) in each block or word whatever the information bit pattern may be. 4.8.3 Even Single Bit Parity The parity bit is generated as a 1 or a 0 to make the  total  number  of  1's  in  the  complete block or word an even number. The situation when all information bits are 0's must be avoided as the parity bit will  not then force a transition. 4.8.4 Odd Interleaved Parity Two parity bits are generated per word, the first to give odd parity to the bits in the odd numbered position in the word and the second to give odd parity to the bits in the even numbered positions in the word. e.g.                             Individual Data Bits                                    P1 P2 Complete Word   1 0 0 1 0 1 1 1 0 0 0 1 1 0 1 1 1 1 1 0 1 0 0 1 Odd Bits               1      0    0    1    0   0    1   1   1   1    1    0 Even Bits              0     1    1    1    0    1    0    1   1    0    0     1 4.9 TDM Standby Arrangements TDM Systems are the most common method  of  controlling remote interlockings. The failure of such systems can cause complete loss of communication between the signal box and all functions at the interlocking with potentially the greatest disruption to traffic. It is usual to provide standby lines, in a separate cable and cable route where available. Changeover may be automatic, or  manual.  Additional facilities may be  provided to minimise disruption to traffic. 4.9.1 Local Emergency Panels The object of providing a local operating panel at each interlocking was to allow  local operating staff to control the interlocking under remote control failure  conditions,  often under the telephoned supervision of the signalman. This arrangement has met with varying degrees of success (dependent on the availability of suitably trained staff at the time of the failure) and may not be considered suitable for all situations. Even if a local emergency control panel is not provided, it may still  be desirable to provide an indication panel for the use of maintenance staff. A local panel has full control and adequate indication facilities.  A switch will allow  local staff to observe the indications at any time as required but a key operated switch must be operated to take control. Access to the key must be restricted to authorised staff. Operation of the key switch will disconnect the interlocking from  the TDM system  and link the control circuits to the local panel. In some countries, local panels are provided for normal operation of interlockings; the main control centre handles all through traffic but the local operators take control for shunting movements. 4.9.2 Override Systems The purpose of providing override controls is to allow the signalman to have limited  control of an interlocking, generally to permit the most frequently used movements. The level of control provided will vary according to the needs of the interlocking  concerned.  At the simplest level, when the signalman turns the override switch to  the  "AUTO"  position, straight through routes will be set and then work automatically. There are situations where such simple controls would be too inflexible to continue  operation of a train service. In such cases, selective override would be provided.  The signalman may choose which selection of conflicting routes he requires to set.  For example, at a double junction he may be able to select routes to/from main or to/from branch. Routes from shunt signals are not usually available in override. When a remote control system fails, it is likely that routes already set will remain set until the passage of trains restores the signals to danger. With a simple override system, the "through routes"  will continue  to work automatically. In an emergency, the signalman may tum the override switch to the "Signals On" position to stop all trains. Override controls will be carried either in a Direct Wire system or in an FDM System. The initiation of override disconnects the interlocking from the failed TDM System  and establishes the controls as allowed through the override system. When the remote control system has failed the signalman's indications will not be updated. The design of the system must allow for this. Leaving the indications  as  they were immediately before the failure may be useful in the short term but after a few minutes this will be totally misleading. The most popular practice is to blank out all indications from the affected area. It is possible to flash selected indication  lamps  (e.g. the red trak  lights)  at the extremities of the area concerned. 4.9.3 Duplicated Systems When the cost of setting up an override system  with  sufficient  flexibility is of the  same order as the cost of the main system, then a duplicated TDM system provides a better alternative. In general, both the control system and the indication system are duplicated and  the signalman may individually switch between Control Systems 1 and 2 between Indication Systems 1 and 2. The routing of the systems shall be such that systems 1 and 2 are in separate  cables in separate cable routes wherever possible. At the transmitting end data is made available to each system independently, using  a relay to provide the isolation  necessary.  Data is transmitted to the far end  through both systems (if working) and the selection of which data to use is made at  the  receiving end.  Back contacts of the system selection relays are used so that any failure of the selection circuits connects both systems (which will normally agree) rather then leaving no control at all. 4.10 Interfacing TDM Systems TDM system outputs may take many forms. With older systems, a d.c. supply to a relay repeating the input function was the only output possible. Modem systems  may perform  the non-vital interlocking functions within the TDM system. 4.10.1 Output Buffering The outputs from a control system feed relays in the interlocking. Those relays fed by a TDM system often have a separate supply with additional smoothing. This helps to keep interference from the normal relay room supplies away from the TDM system. Outputs from an indication system will be fed to buffer relays. The contacts of these relays will be combined to produce the appropriate panel indications: Track and Route  lights routed according to point setting, steady and flashing feeds combined as required. 4.10.2 Panel Interface Relay Units The wiring for panel indications, requires a large number of similar circuits. For instance, signal indications are the same for each signal, route and track circuit indications through point work are very similar for each point end. Some systems employ Panel Interface Relay Units (PIRU) to combine the interlocking information sent via the TDM to drive the indications on the signalling control panel. Most of the circuits are fairly standard - plain line track circuits, points (single and double ended) and signals (aspect and push button indications). The circuits can therefore be incorporated into pre-wired units. 4.10.3 Panel Processing The above interfacing can be done electronically instead of using interface relays. Panel Processing TDM Systems perform the same function as interface relays within the TDM system itself. The incoming information is processed to provide the panel indication outputs. Such systems are usually microprocessor driven. The processing may therefore be done by the microprocessor that controls the TDM receiver, or by a separate microprocessor provided for the purpose. The incoming data can also be processed to provide a serial data link to the train describer. Since the panel indications for each interlocking area  are produced by the TDM system for that interlocking, it is necessary to provide links between the TDM systems to ensure that all the flashing indications are synchronised. Panel processing systems remove the need for panel interface relays on the indications link. The outputs drive the indications directly - at a.c. for lamps or d.c. for LEDs. The control link is not affected, and still feeds repeat relays at the interlocking from the buttons and switches on the panel. Part of the design of a panel processing TDM system will be the preparation of the data to convert the signalling data from the remote interlocking into each individual panel indication (single lamp or group of lamps). 4.10.4 Button Processing If the processing element is extended to the control link, the "TDM" system can replace the relays in the interlocking that perform the non-vital locking functions. A Button Processor system performs all the functions of the push button circuits and checks route availability. Once a route has been requested, it will check  that  all  the  points are "correct or free" and that no opposing routes are set. It will then call  the points to the required position and finally set a route from the signal which will  follow the lie of the points. In order to check route and point availability, the button processor will require additional information from the interlocking above that needed to provide the panel processing for the indications.        · Therefore, instead of the large quantity of relays in a route setting interlocking which are provided purely for the route selection logic, a single output can be provided to set or cancel each route and to move points normal or reverse. As a result of these developments, the more usual position for the TDM equipment at  the control centre is now behind the panel instead of in a separate equipment room. 5. THE WESTINGHOUSE S2 TDM SYSTEM As an example of a modern TDM system, an overview of the Westinghouse S2 system is included to complete this section. 5.1 Introduction The S2 system consists of a relatively small number of different modules, which may be interconnected in a multitude of different configurations. This allows each  system to be tailored to local requirements, but at the same time keeping the  number of different types of spares required to a minimum. Although this section is intended primarily to cover conventional remote control applications, the applications for which an S2 system may be used include:- point to point remote control systems multi-drop remote control systems train describer input interfaces SSI panel multiplexing Substation or traction control systems The S2 may also be used in association with an STD Bus computer system to  provide additional applications, such as : panel and button processing train describers 5.2 Basic Building Blocks The primary item of equipment in an S2 system is the Input/Output  (I/O) assembly, which is a printed-circuit rack containing the following types of cards : Digital Input (DIP) Analogue Input (AIP) Digital Output (DOP) Selex (switchgear/contactor control) Energy Totaliser Link Scanner Carrier A monitor card may also be included to aid fault-finding. On small systems a power supply unit (PSU) may be mounted within the I/O assembly, on larger systems it is rack-mounted below the I/O assembly to give room for more DIP/DOP cards. Similarly, on some later systems a separate modem may be used  instead of a carrier card, again leaving space for more DIP/DOP cards. An alarm monitor panel, separate to the I/O assembly, is used to provide fault and alarm indications for the technician. This also controls the indications on the signalman's panel. 5.3 Dual Channel Systems Whereas any fault on a DIP or DOP card will usually only affect the inputs or outputs on that card, any fault on the scanner, carrier or data link circuit will affect the  complete system. A second data highway within the S2 system provides the facility to duplicate these common modules, so that if a fault occurs on any part of one  data link  the  system will continue to function over the duplicate link. This is termed a "dual channel" system. 5.4 Typical Configurations Each DIP or DOP card handles 32 bits. Up to 16 input and output cards may be provided in any combination within each  sub-rack, the S2 system being inherently duplex. This number is reduced to 12 cards in certain cases, for example where a power supply is mounted in the sub-rack. A "dual housing" system is used where up to 32 cards are required, with a maximum of 16 each input and output. A pair of link cards is used to connect two standard sub-racks to  form a single system. Only one Scanner card (or 2 in a dual channel  system) is used, in the first sub-rack. Alternatively, a "multi rop" type system may be used. In this case, the office end can be increased by adding separate "slave" sub-racks, with their. own Scanner cards. The slave sub-racks can only be used for outputs. The field sub-racks need not all  be in different relay rooms, two or more may be sited in the same relay room if a large number of inputs/outputs are needed. 5.5 Panel Processors With a simple remote control system, the inputs  to a  DIP  card  are used to directly  control the outputs from the corresponding DOP card at the other end of the link: On an indication system, for example, track circuits, point detection, route set  information is fed in at the field (relay-room) end, to operate  corresponding  indication relays at the office (panel) end. The circuits to illuminate the various  panel indications are then driven by the appropriate combination of relay contacts.  Because this is non- vital circuitry, it can be performed instead by a "Panel  Processor"  computer. Similarly, a "Button Processor"  can be used to replace the non-vital relay circuits that decide which points to call and which routes to set depending on the buttons the signalman presses. An "STD Bus Processor" computer can be incorporated within the S2 system, as shown, to perform panel processing and button processing features.  The STD Bus  Processor  consists of a number of cards mounted in another card rack separate to the I/O housing. 5.6 Train Describer Interfacing Where the S2 system incorporates  an STD bus panel and button processor,  then  it  is able to use its route set and track circuit occupied data to supply the stepping information for the train describer. The necessary stepping data is fed from a separate data link from the STD bus processor. An alternative arrangement is where the necessary track circuit,  route set, etc. contacts  from the relay room are used as inputs to an S2 system which feeds the data link to the  train describer. In this case, the S2 system is  being  used  as  an  input  buffer for the T.D. computer. 5.7 SSI Panel Multiplexer A similar arrangement is used for the SSI panel multiplexer. In this case, the S2 system is being used by the SSI panel processors as an input buffer for the panel buttons & switches, and as an output buffer for the panel indications. 5.8 Main Parameters System Capacity   Up to 512 inputs/outputs per housing, in groups of 32. (384 when PSU is fitted within housing). Response Time All DIP cards in an I/O housing are seiviced at least once every 300 msecs. A.S.D. serviced within 30 msecs. Inputs Designed to be fed from relay contacts. Contact wetting current 2mA. Contact wetting voltage 50V d.c. or 24V d.c. 1Kohm read as a closed contact. Outputs To switch a relay or lamp load of up to a maximum of 350mA at 50V d.c. or 24V d.c./a.c. Power Supply   12 volts ±5% Operating Temp. 0 0 to 70 0 C Ambient. Parity  One parity bit (even parity). Carrier System Frequency shift key (FSK) Transmission  Freq.  MARK : 1.7KHz +400Hz SPACE : 1.7KHz -400Hz Transmission  Speed 1200 baud Transmission  voltage level +10dbm = 2.45V  -  0dbm   =   775mV -35dbm    = 13.8mV   -------------------------------------------------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------------------------------------------------  

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