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Deepu Dharmarajan -
Posted 22 days Ago

SIGNALLING A LAYOUT | PART 3

Signalling

CONTINUED FROM - SIGNALLING BOOK | CHAPTER 3 | PART 2 SIGNALLING BOOK | CHAPTER 3 | PART 3 CONTENTS 1. Introduction - In Part 1 2. Headway - In Part 1 3. Positioning of Running Signals - In Part 2 4. Types of Signal - In Part 2 5. Points and Crossings - In Part 3 6. Track Circuits - In Part 3 7. Identification of Signals, Points & Track Circuits - In Part 3 8. Examples - In Part 3   5. POINTS AND CROSSINGS Although, in general, the siting of points and crossings on an existing railway will be dictated by permanent way design considerations, it is left to the Signal Engineer to determine the operation of the points. Furthermore, the Signal Engineer may require additional trapping protection to be provided on occasions and such cases must be referred back to the Permanent Way Engineer or other responsible engineer. In the case of combined track remodelling and resignalling projects, it is sometimes possible to provide simpler or improved signalling controls by minor alterations to the track layout. Close co-operation between the Signal Engineer and the Permanent Way Engineer is essential if the optimum results are to be achieved. 5.1. Position and Numbering of Points Any set of points will be defined as lying in its Normal position for one route and its Reverse position for the other route. The Normal position of the points will be shown on the signalling plan as follows:- A similar convention applies to switched diamond crossings, if used. Points should be numbered in such a way that any point ends required to work simultaneously carry the same number. To localise failures, it is not advisable to number more than two ends to work together. In addition, Solid State Interlocking (SSI) equipment is normally only configured to operate single and double ended points, although in certain circumstances three ends can be accommodated. For control purposes, each end has to be identified separately (A or B) but this may not need to be shown on the signalling plan. A convention must be determined for identifying A and B ends (e.g. A end nearest control centre or A end at lowest reference distance etc.) and strictly observed. On TfNSW network  a down train will meet the A end first. 5.2 Ground Frames Ground frames control infrequently used points, usually outside interlocking areas. Although referred to as ground frames, they may equally well be locally operated control panels. In its most common form the ground frame consists of just 2 levers, the point lever and a release lever (which will also work the F.P.L. if the points are normally facing). Movements over the points during shunting are usually controlled by handsignal, although extra levers may be provided to control or slot signals which the train must pass during shunting. Note the use of separate releases where the ground frame controls more than one function. Instead of providing an electric lock on the release lever, a separate key is electrically released when the signalman operates the release button. This key is then used to release the ground frame release lever. It remains captive until the ground frame is normalised and can then be returned to the instrument to give back the release. 5.3 Trapping Protection It may be necessary to request trap points (normally known as catch points on TfNSW) to be provided at certain locations: At the exit from sidings, where they lead on to running lines, catch or trap points must be provided to prevent an unattended vehicle running away or a shunting movement overrunning and fouling the running line. Where a full overlap cannot be obtained and movements are required to closely approach a converging junction, catch or trap points leading away from the running line can be used as an overrun in place of the normal overlap. On railways where a distinction is made between passenger and non-passenger lines, trap points may be used where the non-passenger line joins the passenger line. Where trap/catch points occur in track circuited lines many railways employ a track circuit interrupter to ensure a derailed vehicle which is still fouling the track, although not standing on the rails, remains detected. The track circuit interrupter is normally insulated from the rail on which it is mounted and bonded in series with the opposite rail. 6. TRACK CIRCUITS Track circuits shall be provided in a manner which permits maximum flexibility with minimum expense and complexity. 6.1 Overlaps Running signals should, in general, be provided with separate berth and overlap track circuits, the berth track circuit terminating immediately beyond each signal. This will ensure the signal is replaced to danger at the earliest opportunity after the train passes. Where more than one overlap is required, a joint must be provided at the end of each overlap. Calculation of overlaps has already been covered in the earlier sections dealing with the positioning of signals and trainstops. However, old TfNSW  practice on overlaps is summarised below. 6.1.1. Where Trainstops Are Not Fitted The overlap is a margin to allow for braking errors. There is no positive means of stopping the train if a driver completely misses or misreads a signal. As such it is an approximate distance based on experience, rather than one which has been calculated on any scientific principle. The standard SRA overlap is 500 metres. This may be smaller or greater than the actual braking distance. Where speeds are low, this is sometimes reduced. Recommended overlap lengths are:- 6.1.2 Sydney Metropolitan Area (Open Sections) If  trainstops are fitted,(recently ATP rollout has taken place which will remove the significance of  mechanical trainstop) the overlap must be based on emergency braking distance for the prevailing speeds and gradients. The following example shows how this may be calculated. To simplify the calculation when dealing with gradients it is often easier to express the braking rate as a percentage of the acceleration due to gravity (g = 9.8m/s 2 ). Braking distance = v 2 /2a (where a = braking rate, v = train speed) = 100v 2 /2g(%B + %G) %B = Braking rate as a percentage of g %G = Gradient as a percentage (down gradients negative) If the line speed is 25 m/s, the braking rate is 10% and the gradient is 1% down, the emergency braking distance and hence the overlap will be:- 100 x 25 2 / 2 x 9.8 x (10 - 1) = 62500 / 176.4 This would give a minimum overlap of 354 metres. This would probably have to be increased by a suitable margin to allow for less than 100% braking performance (e.g. some brakes isolated, wet or greasy rails, delay time for brake application). Where available, braking tables or curves should be used. If the full overlap is foul of junctions or station platforms, a reduced overlap should be considered. The train speed would have to be suitably reduced by a low speed or conditional caution aspect at the previous signal. 6.2 For Points and Crossings The positioning of track circuit joints to prove clearance will depend on the dimensions of the rolling stock in use. One must first determine the difference between the maximum vehicle width and the width of the widest vehicle in service. The position must then be found where the rails leading away from the crossing are at least this distance apart (normally adding a small safety margin). At this point, the extreme ends of vehicles on the adjacent tracks will not be foul of each other. Measuring away from this position, the joint must be located at a distance greater than the maximum end overhang of any vehicle. This is obtained by measuring from the centre of the outer axle to the extreme end of the vehicle. Track circuits should allow maximum flexibility of use of the layout. In particular, where the track layout permits parallel moves, the signalling must not prevent them. Joints should be positioned to achieve the earliest release of points after the passage of a train consistent with safety, economy and practicality of installation. Example 1 Joint A allows simultaneous moves over both ends of crossover normal. Joint B allows points to be moved as soon as train leaves points. Joints C, at clearance point, allow movements across crossover with Tracks X and Y occupied. It is common on plans to place joints C opposite the tips of the points. Example 2 Joints A allows parallel moves. Joints B allow points to be freed as soon as junction cleared. Joints C are set back at clearance point. These may also be the overlap joints for signals approaching the junction. Joint D will be dependent on factors other than the requirements for operation of the junction, eg. the position of the protecting signal. 7. NUMBERING OF SIGNALS, POINTS AND TRACK CIRCUITS To enable all signalling controls to be specified, each signalling function must be uniquely identified. It aids design, testing and fault location if this is done in a logical and orderly manner. In particular, confusion is avoided if different types of functions are numbered in different number or letter series. The main functions which need to be numbered are:- Main Signals Shunt Signals Points Track Circuits Ground Frame & other releases Separate number series should be provided for each type of function (points, signals etc.). Main and shunt signals may be numbered in the same or separate series. Lines for each direction of traffic are normally designated UP and DOWN. Signals reading in the Down direction normally carry odd numbers with the lowest number at the Up end of the control area. Signals reading in the Up direction normally carry even numbers, again with the lowest number at the Up end. Points will be numbered with the lowest number at the Up end of the control area. Where possible suitable gaps should be left in the numbering sequences in anticipation of future alteration. Distinct branches should be numbered in separate series. Historically, several different conventions have been used for identification of track circuits. Each has advantages and disadvantages. One common method is to use a simple numbering sequence. The disadvantage of numbers is that, on a large installation, very large numbers or duplicate number sequences need to be used (with greater risk of errors in design and testing). Another alternative which has been used is to number track circuits based on the distance along the line. This results in track circuits in one locality having long and very similar numbers. Again confusion and errors may result. TfNSW  uses a system based on the signal numbers. The first track past signal 5 would be 5A, the next 5B and so on. The suffix E is not normally used. The BR standard is now to use letters. Each track circuit indicated to the signalman should be identified using two capital letters, arranged alphabetically in a logical sequence. Letters I and O are not used. Where a number of track circuit sections have a common indication they should have the same identity plus an individual suffix number, eg. AA1, AA2 etc. This arrangement is simple but does not give any indication of the relative locations of tracks and signals. 8. EXAMPLES A few examples are now given of some of the more commonly found track layouts and suggested arrangement of signals. They do not cover all situations. In practice, different requirements will conflict. The signal engineer must resolve these conflicts in the most effective and economic manner 8.1 Junctions The logical arrangement at a junction is for the protecting signal to be as close to the junction as possible. For diverging movements this ensures that trains are not checked too far from the junction, while for converging movements it reduces the chances of trains being checked due to conflicting moves on the junction. The signal next in rear of the junction cannot be cleared unless the section is clear up to the junction signal, and the overlap beyond. It is preferable that the overlap is not fouled by conflicting moves, so ideally the signals protecting the junction should be placed overlap distance in rear of the junction. If large overlap distances make this impractical, a reduced overlap clear of the junction should be considered. In this case the signal in rear should have its full overlap clear of the junction. 8.2 Station Platform with Loop It is usually desirable for headway reasons to site a signal at the end of the platform. This provides a platform starting signal and also protection for any level crossing at this point. In situations where there is no platform starting signal, there is a risk that a station stop will divert the driver's attention sufficiently for him to forget the aspect displayed by the previous signal. After restarting his train, he could approach the next signal at an unsafe speed. In the above example, signal A is located at full S.B.D. from signals B & C. For main line running this is satisfactory, but for a move into the loop the time taken for the train to slow to 25 km/h over the crossover may adversely affect the headways. A better arrangement is shown below : Signal A is moved closer to the turnout. If this results in inadequate braking distance from signal A to signals B & C, signal D must be a 4 Aspect signal. Signal A would only need to be 4 aspect if the signal ahead of C was less than braking distance. 8.3 Terminal Stations The station throat track capacity must be at least double that of the approaching line. This is because some arriving and departing movements will completely block all other routes. The signal reading into the platforms should be as close as possible to the plaforms. If this signal does not have an overlap clear of points, the signal in rear should do so to allow trains to approach unrestricted. Signal spacing on the approach to the station should be as close as possible consistent with standing room and headway requirements. The first signal leaving the station should be as close as possible (whilst retaining necessary train standage clear of the pointwork), to allow the best possible aspect on the platform starting signals. The standage requirement may have to be reduced to maintain adequate line capacity on the departing line. The platform entry signal 3 exhibits stop and caution aspects only for running moves. Buffer stops are equivalent to a signal permanently at stop. Subsidiary shunt signals are provided to enable trains or locomotives to enter occupied platforms. If wrong line shunting is required, a shunt limit board must be provided at a position which permits adequate standing.  

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Jyoti TV -
Posted 25 days Ago

Fixed Block Vs Moving Block

Signalling

  Significant developments are made to railway signalling from Fixed block era to Moving Block, Communication based Train Control System . The below comparison table shows some of the major differences between conventional fixed block systems and moving blocks and the advantages. No. Fixed Block (Absolute Block ) Moving Block 1 Trains are defined per fixed block and only one train in a block at a time. That is protected train routes in a fixed block Trains are considered as moving blocks and distance between trains is maintained at safe distance.   2 In a three aspect fixed block conventional signalling minimum distance between following train with proceed authority  towards preceding train  is twice the maximum braking distance for the worst-case rollingstock operating in the line plus safety margin provided by overlap beyond a stop signal In a moving block system minimum distance between the following train with proceed authority  towards the preceding train  is just the braking distance needed for the following train plus a safety margin required by the CBTC system 3 Position of limit of authority is restricted to see a Signal (By driver) visible continuously for 3 seconds Position of limit of authority don’t have such restriction. 4 Even if fixed block signalling system is protected with ATP system, the train has to pass over a transponder to receive a new limit of authority , until train sees a transponder it travels with restricted speed set by the previous transponder Limited authority is continuously updated as there is continuous two way communication between onboard and trackside ATC equipment.   5 High level of operational variability and driver to driver run time variation  can cause delays , affect performance ATO can enable  continuous , consistent automated driving profile and thereby eliminate driver run time variance 6 Large quantity of track side equipment to be maintained, including signals  Trackside signals are used for train recovery during complete ATC non availability thereby eliminate the requirement for Signals 7 If additionally protected with ATP(Automatic Train Protection) , will ensure trains don’t SPAD (Signal Passed at Danger) by automatic enforcement of Movement Authority limit and Automatic enforcement of speed limit Note : If Manual Trainstops or AWS are implemented it's still degraded compared to ATP Maintain two-way radio communication with each train on the network, monitoring train position with onboard equipment and thereby ensuring safe train separation by sending limit of Movement Authority (MA) to each train on the network. It also enforces this limit with overspeed protection 8 Train detection equipments such as Track Circuits , axle counters are mandatory to ensure the fixed block is free before sending a train Train detection is based on onboard equipment,and secondary train detection systems such as Axle counters or track circuits are ‘not necessary ‘ unless degraded modes of operation needed 9 More number of Wayside equipment such as Signals are required Uses  onboard VDU (Video Display Unit ) Note:Signals might be used for secondary signalling or degraded mode of operation or train recovery during complete failure of ATC(Automatic Train Control)  system 10 Pedestrian crossing and level crossings are allowed as the headway (Headway is the distance between vehicles in a transit system measured in time or space. The minimum headway is the shortest such distance or time achievable by a system without a reduction in the speed of vehicles) are relatively high Pedestrian Crossing and Level crossing are ‘possible’  to integrate with CBTC , however the whole purpose of headway reduction will be impacted and are not commonly implemented. In nutshell  both are contradictory requirements (Arguably ) Note: No provider has successfully implemented a level crossing with a CBTC system for heavy traffic road users 11 Less capacity , safety,reliability, serviceability, and resilience High  capacity,safety ,reliability,serviceability, and resilience 12 Schedule optimisation is limited possibility Schedule optimisation possible after a disruption  with faster recovery 13 Real time Passenger information cannot be accurate Precise Passenger Information Possible and can predict the exact time of arrival 14 No coasting ability to conserve  Coasting or other alternate strategy to conserve energy.

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Deepu Dharmarajan -
Posted 58 days Ago

SIGNALLING A LAYOUT | PART 2

Signalling

CONTINUED FROM - SIGNALLING BOOK | CHAPTER 3 | PART 1 SIGNALLING BOOK | CHAPTER 3 | PART 2 CONTENTS 1. Introduction - In Part 1 2. Headway - In Part 1 3. Positioning of Running Signals - In Part 2 4. Types of Signal - In Part 2 5. Points and Crossings - In Part 3 6. Track Circuits - In Part 3 7. Identification of Signals, Points & Track Circuits - In Part 3 8. Examples - In Part 3 3. POSITIONING OF RUNNING SIGNALS If we are starting with a blank track layout, we need a logical method of setting out the signals in order to produce a signalling plan. As running signals must fulfil the needs of both headway and braking distance, it is usual to position running signals first. Shunting and subsidiary signals are dealt with after the running signals have been placed. 3.1. Headway Constraints First plot the positions of the running signals on the principal running lines. Then proceed to lower priority lines in order of importance. It is often difficult to decide where to start. If a station exists on the layout it is usual to start by plotting platform starting signals, and then continue by plotting the signals in rear and in advance to be within the tolerance of minimum separation (for braking distance) and maximum separation (for headway) for the type of signalling to be employed. It is also desirable to position signals close to facing points at junctions so that the driver does not have a long distance to travel to the turnout. This will minimise delay to traffic and reduce the possibility of signals being misread. Service braking distance must be provided from the first cautionary aspect to the signal at danger in every case. The maximum distance from the first caution to the red is set by the headway requirement. Ensure that any large excess over service braking distance is within acceptable limits. 3.2. Other Constraints In addition to headways, other constraints must be borne in mind. These include junctions, further stations, tunnels, viaducts and level crossings. There may be many places where it is required to stop a train for operating reasons. The engineer will have very little choice in the position of these signals. Conversely there are also many places where it is highly undesirable to stop a train and signals must be positioned to avoid these. Other factors to consider are the visibility of the signal to the driver, the practicality of installing a signal at a particular site and ease of access for maintenance. Signal A has been placed at a distance greater than service braking distance from B because it would have otherwise stood on the points 201. If a line is generally signalled with 2 or 3 aspect signals and it seems necessary to have two signals spaced closer together than service braking distance, remember that the next signal in rear must be capable of displaying a medium aspect to give an earlier warning of the need to stop. If a suitable signal does not already exist, an additional signal will have to be introduced. A signal should be positioned so that a train stopped at that signal does not: Stand in a tunnel (wholly or partially). This would not apply to underground passenger railways where special provision has been made in the design of the trains and/or tunnels to ensure the safe evacuation of passengers in an emergency. Stand on a viaduct, unless special provision has been made for safe evacuation of passengers and/or access by emergency services. Foul a junction. Stand partially at a platform (unless the passenger doors can be kept closed by the train crew). There are occasions when, due to local circumstances, these requirements cannot be wholly met but every effort should be made to comply. Additional considerations will apply on electrified lines to ensure that trains are not brought to a stand in neutral sections or gaps in the conductor rail. If possible, heavy freight trains should not be stopped on steep falling or rising gradients, especially in combination with sharp curves. 3.3. Examples of Standage Constraints Ensure maximum length train can stand in platform. Ensure that maximum length train can stand clear of junction fouling point to allow other movements to pass behind it. Signals on adjacent running lines should as far as possible be placed opposite each other. This minimises the chance of drivers reading the wrong signal. It also simplifies the design and installation of power supply and location equipment. 4. TYPES OF SIGNAL Running signals may be divided into three general groups according to the form of control exercised by the signalman. 4.1. Automatic Signals Automatic signals are designed to operate only according to the presence of trains on the track circuits ahead. The signalman does not have to set the route for each train. Usually he will not have any facility to set routes but may in certain circumstances be provided with a switch or button to replace the signal to danger in emergency. A signal may be shown as automatic if all the following conditions can be met:- No points in the route to the next signal. No points in the overlap beyond the next signal (Exceptionally, simple facing points may be allowed). No directly opposing routes within the route or the overlap. No ground frames, controlled level crossings or other equipment with which the signal must be interlocked. The normal aspect of an automatic signal (i.e. the aspect shown when there are no trains present) will generally be a proceed aspect. As the signalman is not directly concerned with the operation of automatic signals, some other facility may be required to stop trains in an emergency. If it is decided that this facility is required, options available are:- Individual replacement switches or buttons on the signalman's panel (for all automatic signals or selected signals only) Grouped replacement switches or buttons. Each one can replace a group of consecutive signals on the same line to danger) A replacement switch mounted on or near the signal, usually requiring a special key to operate. Earlier British practice was to provide replacement facilities on automatic signals in any of the following circumstances:- Controlling the entrance to a section in which a level crossing equipped for automatic operation is situated. Controlling the entrance to a section in which a tunnel or viaduct is situated. Controlling the entrance to a section in which an electrical traction break is situated. If not otherwise required, on at least every fifth signal in any section of automatic signals and at any other signal where required for operating purposes. Since the accident at Clapham Junction in 1988, this policy has now changed to one of providing some form of emergency replacement for all automatic signals. On all new installations, this is by means of an individual button on the panel. Automatic signals must be recognisable as such to the driver. In the event of a signal failure and loss of communication with the signal box at the same time, the driver can then pass the signal at danger and proceed at extreme caution to the next signal (prepared to stop short of any obstruction). Some railways identify their automatic signals by a different style or colour of identification plate. SRA (TfNSW) practice is to offset the lower signal lights (or marker light) 204mm to the right of the upper signal lights. If clearance constraints make this impossible, and the lights must be in line, a separate plate with a white letter A on a black background is provided. 4.2. Semi-Automatic Signals In many areas signal boxes or local ground frames are provided which provide access to sidings or are not continuously manned. Signals must be provided which permit through traffic to operate when the frame or signal box is unmanned. These signals have to operate automatically for much of the time but must also be capable of control by the local operator. Semi-automatic signals are provided in this case. When the signal box is switched out or the local frame is locked normal, the signal functions as an automatic signal. Once again, the driver must be aware of the correct action to take in the event of failure. A distinct identification plate is used on some railways. The driver must then confirm that the ground frame or local signal box is not in use before treating it as an automatic signal. SRA (TfNSW) practice is to provide an internally illuminated "A" indication below the semi-automatic signal (which otherwise has the same appearance as a controlled signal). The "A" is illuminated only when the signal is working automatically. It may also be necessary to divert any signal post telephone circuit to another supervising signal box when the local control is not in use. 4.3. Controlled Signals Any signal other than those described above will be a controlled signal. It must be controlled from a signal-box (other than by Emergency Replacement). It will usually require a lever, switch, button, key or plunger to be operated for each movement. Controls may be provided to allow a controlled signal to operate automatically (i.e. without re-setting the route for each movement). It must be decided whether this should be apparent to the driver. BR practice is not to provide any distinct identification on the signal. The driver will always treat it as a controlled signal, even when working automatically. This is because it is unsafe to adopt any form of "stop and proceed" working where there are points ahead of the signal which may be moved. A signal will normally be "Controlled" if there are points and/or conflicting routes in the route or overlap. 4.4. Signal Identification Plates All stop signals and/or all signals provided with a signal post telephone should be provided with an identification plate. As stated earlier this may be of a different style according to the type of signal (controlled, automatic or semi-automatic). When talking to the signalman, the driver should be able to identify where he is, even if this information is also shown on the signalman's telephone equipment. Other signals (e.g. distants and repeaters) may also be identified for maintenance requirements. Some controlled signals in particular positions may need to be specially identified. For example, the "accepting" signal on approaching an interlocking from a section of automatic signalling is specially plated to remind the driver that he is no longer under the control of automatic signals. 4.5. Signal Aspects Having decided on the necessary position of each running signal on our plan, we must now ensure that we depict each signal to show the correct combination of signal aspects. This will be governed by two main factors:- the type and distance of the next signals ahead; whether it is necessary to give warning to the driver to stop. whether the signal or the next signal ahead is a junction signal. Any signal that has more than one running route is a junction signal and, as such, must provide the driver with the appropriate turnout aspect and/or route indication when required. For all junction signals on the signalling plan, an adjacent box should be included showing the signal number, description of each route, its exit signal, and the route indication (if any) displayed. 4.5.1. Aspects for Through Running (Single light) In single light signalling areas a stop signal must at minimum have a head with a red and a green light, with a marker light below. If the next signal ahead is a stop signal at greater than braking distance, a caution aspect must be provided. If the signal ahead is at less than braking distance and the following signal section is also shorter than braking distance, the signal must display also a medium (pulsating yellow) aspect. The signalling plan will show a letter "P" against the signal to indicate that it displays a pulsating yellow aspect. If there is braking distance between the next two signals, the medium aspect is not required. Single light signal heads capable of showing only two lights should be shown on the signalling plan with the actual colours required (R for red, Y for yellow and G for green). Distant signals will usually display caution and clear only. If there is inadequate braking between the next two adjacent stop signals ahead, a medium aspect (pulsating yellow) will also be required. 4.5.2. Aspects for Through Running (Double light) All double light signals have two signal heads, one below the other. The top head is the stop signal and the lower head is the distant for the signal(s) ahead. If the signal is not a junction signal, the upper head will be red & green only. The form of the lower head will depend on whether three or four aspects are required. The, rules are exactly the same as for double light but the aspects are different. The lower (distant) signal head will display red and green only for 3 aspect signalling, red,yellow and green for 4 aspect. The provision of low speed aspects is dealt with elsewhere in these notes. 4.5.3. Junction Signalling (Single Light) The indication of a route diverging from the main line will be by either a turnout signal (maximum of one route to left and/or right) or a multi—lamp route indicator in conjunction with the main aspect (more than one route to left or right). When the turnout signal is used, the main signal remains at red. All turnout signals must be capable of displaying a caution (three steady yellow lights) and may display a medium turnout aspect (three pulsating yellow lights) when the signal ahead is showing a proceed aspect. When a route indicator is used, the main signal will display a steady or pulsating yellow (according to the next aspect ahead) and the appropriate route indication will be displayed. Clear signals are not given through turnouts. 4.5.4. Junction Signalling (Double Light) The indication of a turnout on a double light signal is by a yellow in the upper signal head. All junction signals therefore require an upper signal head with red, yellow and green lights. The lower signal will still indicate the state of the signal ahead, red if the first signal ahead past the junction is at stop, yellow if the next signal displays a proceed aspect. If a junction signal is set for the turnout (either caution or medium) the previous signal will display a medium aspect, never a clear. Route indicators may be used where two or more turnout routes exist. 4.5.5 Low Speed Signals Section 2.5 has dealt with the main situations in which low-speed signals are used. Firstly, check whether a conditionally cleared caution could adequately fulfil the operating requirements (the overlap should be at least 100m for a conditional caution). Low speed signals are not necessary for normal through running. They should, however be considered in cases where reduced overlaps can aid the regulation of traffic and/or headway for stopping trains and a conditional caution is not appropriate. It is also recommended to provide low speed signals through any area where a track circuit would otherwise control three or more running signals. This is to localise the effect of failures by restricting the number of handsignalmen required in the event of track circuit failures. 4.6 Shunting and Subsidiary Signals Having catered for all running moves, we must now provide for shunting and other non-running movements. Before starting to place signals on the plan, make sure you know exactly what movements are required. Any movements which are not signalled will have to be authorised by handsignals. Handsignalled movements on lines where the majority of trains are properly signalled are disruptive to normal traffic and allow the possibility of human error. Conversely, signals provided for movements which are never used are an additional and unnecessary initial cost to the project. They also represent a continuing maintenance cost and a potential source of additional failures. Although the terms are often used interchangeably, there is a distinction between shunting and subsidiary signals. Subsidiary signals are part of a main running signal. Shunting signals are independent. Subsidiary signals therefore only need a proceed aspect - the main signal provides the stop aspect. Shunting signals must display both stop and proceed aspects. Subsidiary signals can broadly be divided into the following functions:- To shunt from a running line (in the normal direction of traffic) into a siding. To move forward from a running signal into an occupied section. A main route to the same destination may already exist. The provision of both main and shunt routes could assist operations in critical areas during track circuit failures. On a multiple track line, to shunt on to another line in the opposite direction to normal traffic. To move forward to a shunt signal facing the normal direction of traffic. On absolute block lines, to permit a train to pass the starting signal at danger for shunting purposes only. The shunting movement must return behind the starting signal Unless the movement is on to a section of line which is not fully signalled there will need to be an exit signal to limit the extent of the movement. Independent shunting signals can broadly be divided into the following functions:- To shunt between running lines from a position where no main signal is provided. To enter, leave or shunt between sidings. To shunt in the opposite direction to normal traffic. To limit the extent of any shunting movement (including "shunting limit" boards). The diagram below shows examples of some common applications of shunting and subsidiary signals. 4.6.1. Calling-on and Subsidiary Shunting Signals This will be provided where a movement must be authorised to pass a main signal at danger to enter a section which is or may be occupied. An example would be the coupling of two portions of a train in a station platform. Signal 4 on the diagram has a subsidiary provided for this purpose. The usual aspect displayed is a miniature yellow. Some older double light signals display an internally illuminated "CO". 4.6.2. Dead End Signal This will be provided where a movement must be authorised to pass a main signal at danger to enter a dead end siding via a facing turnout from the main line. It displays a miniature yellow light and is offset to one side of the signal post (according to the direction of the movement). Signal 5 is an example of this. 4.6.3. Shunt Ahead Signal Used to shunt ahead of the starting signal and mounted below the main signal. Used on single light signalling only and displays a pulsating miniature yellow light. Signal 7 is provided with a shunt ahead signal to enable long trains to draw forward past the signal before shunting back over the crossover. This type of signal will normally be found in single light signalling areas only. 4.6.4. Dwarf and Position Light Shunt Signals Shunting signals normally have two aspects - stop and proceed. The stop aspect is two red lights and the proceed aspect is a single yellow light. This instructs the driver to proceed at caution. It does not guarantee that the line ahead is clear. SRA (TfNSW) uses both dwarf and position light shunting signals. The difference between the two types of signal is the orientation of the lights. The choice of signal type will depend mainly on lineside clearances. On a position light signal, the two red lights are side by side, the yellow light is above. A dwarf signal has the three lights vertically arranged; the red lights are at the top and bottom with the yellow light between. Route indications are provided where required, particularly where wrong line movements are signalled. 4.6.5. Shunting Limit Boards Effectively a shunting signal fixed at danger, a shunting limit signal faces in the opposite direction to normal traffic and is used to limit the extent of a wrong line shunting movement. An example is shown on the down line. This would enable trains to shunt out of No. 1 siding on to the down line before proceeding forward. Without the board there would be no signal to prevent the wrong line movement continuing indefinitely on the down line. 4.6.6. Facing (or Preset) Shunt Signals Occasionally, shunting movements in the normal direction may be required to start from a position where a running signal is not provided. Such a shunt signal must therefore be passed by normal running movements. To avoid the driver seeing a yellow light after he has just passed a main signal showing clear (and possibly braking unnecessarily) "facing" shunt signals are provided with an additional green light to show clear when the previous main route is set past the shunt signal and the signal is showing clear. Signal 55 is a facing shunt signal. 4.6.7 Point Indicators Point indicators should be provided on any points (whether facing, trailing or catch points) where the driver is responsible for observing the position of the points before proceeding over them. The points will usually be hand worked, as shown in siding 1 on the example. Where regular shunting takes place without the need for the signalman to set the route for every move, point indicators will be displayed. These will be selected by a separate button on the signalman's panel. This is preferred to providing two shunt signals with opposing locking removed as it avoids the possibility of two trains approaching each other both under proceed aspects. 4.7 Trainstops SRA (TfNSW) provides trainstops on most of the Sydney metropolitan area. Double light signalling is normally provided. All electric multiple unit trains are provided with tripcock equipment which will apply the brakes if a train passes a raised trainstop. The trainstops are provided at each main stop signal and in certain other locations (e.g. exits from depots and sidings) to prevent a rear end collision with another train. If the signal is at danger, the trainstop will be raised. A train irregularly passing a signal at danger will be tripped and brought to a stand within the length of the overlap. Where trainstops are to be used, the engineer must ensure that the length of each overlap is adequate for emergency braking at the highest speed at which a train is likely to pass the signal. Obviously the trainstop cannot ensure total safety if all trains are not fitted but it can make a major contribution to safety in areas where trains regularly run at close headways. An important part of the preparation of the signalling plan is therefore to decide where trainstops are to be positioned. This is closely associated with the calculation of overlaps. It may often be more important to accurately position the overlap for track circuit clearance purposes, then work back to the position of the signal and the trainstop. A low speed signal tells the driver that there is little or no overlap beyond the exit signal. Running speeds will be low (normally less than 35km/h). The low speed overlap will be based on the passing speed of the low speed signal. However, the driver could fail to brake, or even accelerate after he has passed the low speed signal. This would leave an inadequate low speed overlap. Intermediate trainstops are therefore often provided between a low speed signal and the next signal, to be lowered only after sufficient time has elapsed for the train to have reached the trainstop at or below the correct speed. The following general rules therefore apply to the positioning of trainstops:- A trainstop is required at all stop signals. It must always be on the same side of the line. SRA (TfNSW) provides trainstops on the left hand side, London Underground and British Rail use the right hand side of the track. Additional trainstops may be required on the approach to stop signals with a reduced overlap where a speed reduction has already been enforced at a previous signal. As an example, a low speed signal reading into a station platform could have a low speed aspect to allow early entry of following trains. The overlap associated with this may be 100 metres or less, even reducing almost to zero. To ensure that a train does not accelerate to a speed which would render the overlap inadequate, an additional trainstop is provided on the approach to the exit signal after the low speed signal. The lowering of this trainstop is timed to trip a train which is running above the permitted speed.  The positioning of trainstops therefore has to take account of the braking and acceleration characteristics of the train and the length of the overlap. The calculation can become very complex so a simple example is used here to illustrate the possibilities. In the following diagram, the two stop signals are 200 metres apart. For headway and/or junction clearance purposes, it has been decided that only a 50 metre overlap is available beyond the second signal. We will assume that the train passes the first signal, displaying a low speed aspect at 27 km/h or less (otherwise it would have been tripped). This example will assume a typical service braking rate of 0.9 m/s 2 , an emergency braking rate of 1.4 m/s 2 and an acceleration rate of 0.55m/s 2 . These are typical of those which have been used for SRA (TfNSW) signalling for electric multiple units although the actual performance of the trains which will use a line must always be confirmed, and gradients taken into consideration. The train should under normal circumstances brake to a stand at signal 2 along or below curve A. The trainstops should ensure that the train will come to a stand within the overlap, should the driver fail to take the correct action to control his train. There are various possibilities which may arise. The signal engineer must decide whether to allow fully for all of these or whether circumstances will permit some relaxation. After passing signal 1 at the permitted speed (27 km/h in this example) the driver could totally fail to brake. Even worse, he could accelerate after passing signal 1. We could assume either no acceleration, acceleration due to gradient only or acceleration under full power. Whichever is chosen, the overlap should be greater than the emergency braking distance from signal 2. If this is not the case, an intermediate trainstop (labelled ITS) must be provided which should be timed to lower just before the train reaches it on a normal service braking curve (point X on the diagram). Curve D shows the effect of this trainstop on a train accelerating under full power. With the intermediate trainstop having been passed at the correct speed (lowered before the arrival of the train), the train could then accelerate at full power towards signal 2. In this case the trainstop at the signal will ensure the train stops within the overlap. Curve B shows the likely speed profile of the train in this situation. Even with these safeguards it is possible that a train could stand just past signal 1 on the timing track circuit for the intermediate trainstop. The trainstop would lower after the prescribed time interval and the train could then accelerate under full power towards signal 2 without the protection of the intermediate trainstop. It will be seen from curve C that the train will overshoot the overlap, passing the overlap joint at up to 9 m/s. To overcome this, the length of the timing track circuit for the intermediate trainstop must be limited such that an accelerating train could pass signal 2 at a speed no higher than that possible on curve B. Alternatively, an additional intermediate trainstop could be provided to check the train speed at an earlier point. SRA (TfNSW) practice in open (i.e. above ground) areas is to allow some margin for possible acceleration but not the deliberate full acceleration of curve C. In tunnel sections where the driver's perception of speed and distance may be affected, the positioning of trainstops and their associated timing track circuits should cater for all possibilities. It should be noted that due to the introduction of newer trains with better acceleration characteristics, the protection provided by certain older sections of signalling is now reduced. It will still protect against most normal occurences other than the deliberately malicious driver intent on overriding the protection of the signalling equipment. Typical distances for open areas are as follows:- For following trains and overlaps less than 50 metres, the intermediate trainstop is positioned 100 metres from the end of the overlap with a timing track circuit between 80 and 220 metres in length. For overlaps clear of fouling movements, the overlap should be at least 100 metres and the intermediate trainstop 200 metres from the fouling point. In addition, any previous signal whose full overlap extends beyond the fouling point should be conditionally cleared to caution. This arrangement is not recommended where signal spacing exceeds 500 metres. TO BE CONTINUED - SIGNALLING BOOK | CHAPTER 3 | PART 3...........

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Deepu Dharmarajan -
Posted 71 days Ago

BASIC SIGNALLING PRINCIPLES | PART 2

Signalling

CONTINUED FROM - SIGNALLING BOOK | CHAPTER 2 | PART 1 SIGNALLING BOOK | CHAPTER 2 | PART 2 CONTENTS 1. Introduction - In Part 1 2. Signal Aspects - In Part 1 3. Signalling Principles - In Part 2 4. Drawing Standards - In Part 2 5. Interlocking Principles - In Part 2 6. Train Detection & Track Circuit Block - In Part 2 7. Colour Light Signals - In Part 2 8. Control Panels & Other Methods of Operation - In Part 2 9. Colour Light Signalling Controls - In Part 2   3. SIGNALLING PRINCIPLES   Any railway administration must have a set of rules which determine the basic principles of design and operation of the signalling system. In some cases they may be carefully documented in detail, in others they may have developed through many years of custom and practice. At the very minimum, the operating rules must define the meaning of each signal aspect. British Rail has a set of Standard Signalling Principles. They will not be referred to directly in this course but many of the BR principles are similar to SRA (TfNSW) practices. 4. DRAWING STANDARDS Most readers will be involved in the design, specification, installation, testing or maintenance of signalling equipment. They will inevitably have to convey  large amounts of technical information to others. This is usually done by means of drawings. It is important to appreciate the impact of drawings on engineering activities. They are used to:- Specify a signalling system Agree the specification with the users (operating department etc.) Agree the specification with suppliers/contractors Estimate costs Order materials Construct and install equipment Test an installation for correct operation Maintain the equipment Locate and rectify faults The information included in the drawing will vary considerably according to which of  the above purposes it will serve. A drawing will generally need  to be read  by someone  other  than  the person  who  produced it. In the same way that persons talking to each other need to speak the same language, engineers need to use common conventions and symbols in their drawings to convey the necessary information. If a drawing is not understood, it is of no practical use. SRA (TfNSW) have developed a large range of standard schematic and circuit symbols to depict signalling equipment and electrical circuits. A copy of these symbols is provided with these notes. Also provided are the main schematic symbols likely to be used on British signalling plans. These are incorporated in a British Standard -  BS  376.  As this has not been revised for a number of years, certain additional symbols not included in BS376  are now in regular use. In most cases, each railway administration will have its own company standards for the production of technical drawings. It is nevertheless important that the signal engineer should be able to ensure that each drawing is responsible for issuing, conveys the necessary information. This may include the use of symbols and terminology peculiar to the signal engineering profession or even to a particular company. 5. INTERLOCKING PRINCIPLES To understand some of the basic principles of interlocking, it is best to start by referring to a simple mechanical signalbox. Most Readers will not be engaged in the installation of mechanical equipment, but many mechanical signalboxes still exists and it provides a simple example which demonstrates the general principles. Each lever in the frame has a normal and a reverse position. For signals, the normal position is always associated with the danger or stop aspect.  Moving the lever to the reverse position operates the signal to the proceed aspect. With points, normal and reverse have similar status, each being associated with one of the two possible positions of the points. However, the normal position is generally used to set points for main routes. This terminology has been carried forward to electrical signalling although levers are no longer used. lt is therefore essential to remember the association between the terms normal and reverse and the state of the equipment. In the mechanical signalbox depicted below, the levers are mechanically interlocked. A signal lever cannot be moved from normal to reverse  unless all point levers are in the correct position. Once the signal lever is reversed, the point levers for that  route  and  any which provide additional protection, cannot  be moved from  their current position (normal or reverse). Signal levers reading over the same  portion of route in opposite directions cannot be reversed at the same time. Starting signals 3 & 7 when operated will not lock any other lever. They will however be electrically controlled by the block equipment to the adjacent signal boxes. Home signal 2 requires points 5 normal. Conversely, 5 points reverse will lock  signal 2 in the normal position. Signal 2 need  not directly lock signal 4 as the signals  require 5 points in opposite positions. To reverse 4 signal lever requires 5 points reverse AND 6 signal normal. To reverse distant signal lever 1 requires signals 2 AND 3 reverse. In colour light signalling practice there is no equivalent to this type of interlocking as distant signals will usually work automatically, controlled by the aspects of the stop signals ahead. It should be evident from the above examples that all basic interlocking is reciprocal (ie. if 4 reverse locks 6 normal then 6 reverse must lock 4 normal, if 5 is required reverse to release 4 then 4 in the reverse position will lock 5 in the reverse position). The reciprocal nature of locking is inherent in the construction of any mechanical system but in electrical systems the engineer must ensure that it is provided. It is a useful  check to ensure that for each basic interlocking control the converse is also specified. It is possible to produce a complete set of interlocking controls (the  locking  table). However, as modern signalling systems do not employ lever frames, the format shown is no longer used. As its main purpose is to specify the construction of the mechanical interlocking, the converse of the releases is not shown, neither is the locking applicable for moving the lever from reverse to normal. Although adequate for this purpose, it is totally inadequate for an electrical system. RELEASED BY (Req Lever Reverse)   LEVER NUMBER LOCKS (Req Lever Normal) 2.3 1     2 5   3   5 4 6   5 2.8 5 6 4   7     8 5 7.8 9    release the lever in the left hand column, the other levers must be in the position shown.   REQUIRES LEVERS LEVER NUMBER N -> R R ->N 1 2R.3R   2 5N 1N 3   1N 4 5R.6N   5 2N.8N 4N.6N 6 4N.5R   7   9N 8 5N 9N 9 7R.8R   6. TRAIN DETECTION & TRACK CIRCUIT BLOCK The development of a safe, reliable means of detecting trains, the track-circuit, allowed a major advance in safety and ease of operation. The earliest application of track circuits was to prevent a signalman forgetting a  train standing at his home signal, and giving permission for another train to enter the section. To do this, the berth track circuit bolds the block instrument at "train on line". The use of track circuits was then extended to cover sections of line which were out of sight of the signalman, and also to lock facing points while trains were passing over them. It was soon realised that a track-circuit could be used to ensure that the whole of the section was clear. There would then be no need for signalmen to supervise the entry and exit of trains, to ensure the section was clear. "Track-Circuit Block" was thus created and block instruments could be dispensed with. With track-circuit block, the rear signalman does not have to ask permission to send a train forward, be can do so whenever the track circuits are clear up to the end of the overlap. 7. COLOUR LIGHT SIGNALS The development of track-circuit block made it possible for signals on plain line to work automatically - a signal could  show clear when the section track circuit was clear, and stop if otherwise. Normally, no action would be necessary by the signalman, other  than  to observe that the trains were running normally. This, in turn, made it economic to have short block sections, allowing increased line capacity, as a signalbox was no longer needed for each block section. The use of automatic colour light signals soon became widespread. The signal aspects were  and still are as described in section 2. Usually the appearance of  the  signal  is  slightly modified to identify it  to the  driver  as an  automatic.  This may be by  means of  a sign or as in SRA (TfNSW) practice, by offsetting the  upper  signal  head to the left for double light  signals  and by offsetting the marker light towards the track for single light signals. The manner in which colour light signals are used will differ according to the required capacity of the line. 7.1.  2 Aspect Signalling This is a direct colour light replacement for the mechanical distant and stop signals. The block section is the length of track between two successive stop signals.  Each stop signal will have an associated distant signal at least braking distance from it. Block sections will generally be long, typically several times normal braking distance. 7.2.  3 Aspect Signalling To increase the frequency of trains on a line, the block sections must become shorter. When the length of the block section is not  significantly greater than normal braking distance, 3 Aspect signalling economises on the number of signal posts required by combining the two signals at the same position along the track. Each stop signal also displays the distant aspect for the next stop signal. Each signal can display stop, caution or clear. The length of the block section must always be greater than or equal to braking distance. 7.3.   4 Aspect Signalling On high speed lines or those with a high traffic density, it is often necessary to have block sections shorter than braking distance. It is then necessary to give  the  driver  an  earlier  caution indication, as he has insufficient distance to stop between seeing the caution and arriving at the stop signal. In such cases, the signal in rear of the caution shows a medium aspect as a Preliminary Caution. This is a "4 aspect" signalling system as each signal can display four distinct indications to the driver. Although, in theory, capacity could be increased further by the introduction of additional aspects, few railways have found it necessary to do so,  unless  associated  with  the introduction of automatic train control. It is  likely  that  too many  different  aspects  would lead to confusion. If the total length of two adjacent block sections is less than braking distance due to signal positioning requirements, it would appear that a further aspect is necessary. SRA (TfNSW) practice however is to repeat the medium caution in this situation. British practice is to ensure that signals are suitably spaced to avoid this situation. Note that the additional "low speed" aspect used on many SRA (TfNSW) signals is not for increasing headways at normal speed. Although  it often forms  part of  the normal sequence of aspects to bring a train to a stand, its overlap generally coincides with  the caution aspect and does not affect the overall line capacity. Its purpose is to allow trains to close up to each other after their speed  has been safely  reduced. It is particularly useful in the vicinity of stations to minimise the effects of station stops on line capacity, although its inclusion in the normal aspect sequence can be restrictive if a full overlap beyond  the signal at stop is available. This will be covered in more detail in later sections. The existence of low-speed aspects does not need to be taken into account  in determining the capacity of a line for through running at normal line  speeds, unless  the  low speed overlap lies beyond the caution overlap for the signal in the rear. 8. CONTROL PANELS & OTHER METHODS OF OPERATION The introduction of colour-light signals, and power-operated points, in tum allowed the bulky and cumbersome lever-frame to be replaced by modem signalboxes with panels. The standard British type of panel has for many years been the "Entrance-Exit" (N-X) type, with push-buttons for setting routes. Each button has 3 positions: middle, pushed and pulled. The button is sprung to return to the middle position after it is either pushed or pulled. To set a route and clear a signal, the entrance  button  corresponding  to that signal  must  first be pushed and released. This  button  will flash,  to indicate  it is the selected  entrance.  Toe next button pressed is taken to be  the exit or  destination.  Provided  the  route  between  the two buttons is both valid and available, then the route will  set,  the  entrance  button  will change to a steady white light, and in addition white route lights will illuminate to the destination. With the route set, any points will move to the required position automatically.  Provided the route is clear, the signal will then clear. To restore the signal to red, and release the route, the entrance button is pulled. If required, the points can be controlled manually from the panel. Each set  of  points  is provided with a three position switch for this purpose.  With  the  switch  in  the  central position, the points will move automatically as  routes are set.  Alternatively,  it  may  be turned either left to move the points normal, or right to move them reverse. The position of all trains in the panel box area is indicated by red track circuit lights on the panel, normally appearing in the same aperture as the route lights. Indications are also provided for each signal, and each set of points. Unlike a lever frame, where the signalman can only pull a lever if it is safe to operate that signal or set of points, with a push-button panel the signalman is always able to operate the buttons or switches - but the trackside equipment will only respond provided it is safe to do so at that time. The "interlocking" is used to ensure this safety. Conventionally, the interlocking has been done with relay circuits, a typical panel signalbox requiring many thousands of relays. Relay technology, although very reliable in operation, is now being replaced on many railways by electronic or processor based systems. British Rail, in conjunction with Westinghouse and GEC, have developed "Solid State Interlocking" (S.S.I.), which is now being used in a large number of installations, achieving significant savings in space and cost. SSI also has the advantage that alterations to the signalling controls do not require extensive alterations to physical wiring. Most of the controls are stored as data which can be prepared off-site beforehand. Improvements in technology have not only revolutionised the interlocking equipment. Attention has also been given to the interface with the signalman. Although S.S.I. may be operated from a conventional control panel, it is becoming more usual to use video display units (VDU's). These can either be used as a direct replacement for the control panel or as part of a much larger integrated system for providing all train running information to signalmen, passengers and other operating staff.   As an example, the BR IECC (Integrated Electronic Control Centre) includes a train describer system, automatic route setting to a stored timetable, train reporting, passenger information systems, communication with adjacent signal boxes and extensive monitoring facilities. If all trains are running normally, the signalman can sit back and watch the trains go by while the Automatic Route Setting does most of the work. SECTION OF A TYPICAL CONTROL PANEL (BR Style) 9. COLOUR LIGHT SIGNALLING CONTROLS   This section describes the normal controls which would be found on a modem colour light signalled layout operated from a control panel. 9.1. Types of Route A ROUTE is the section of track between one signal and the next.  All  routes  have  an entrance and an exit. A signal may have more  than one route if  there  are  facing  points ahead of it. Although the exit is usually another signal, it may be a buffer stop (terminal platform or siding) or an unsignalled portion of the railway (depots,  yards or  sidings).  A route is uniquely defined by the number of the entrance  signal,  a suffix  defining  the direction of the route (in order from left to right as seen by the driver - normally a letter although some railways use numbers) and,  where  necessary,  a letter denoting  the class of the route. The type of the route is determined by the purpose of the train movement. In  British terminology these are known as classes of route. Each class of route will  have different controls applied. SRA (TfNSW) does  not  use  the term class; however,  there are  three general types of route (four in British practice). A signal may have more than one type of route to the same exit. 9.1.1 Main Routes A main route is from one main running signal to the next. The signal proves all track circuits clear and points correctly set and locked up to the next signal, which is proved alight. In addition, a further distance beyond the exit signal is also proved clear with points set. This is known as an "OVERLAP". The purpose of the overlap and the determination of its length will depend on the type of railway, the setvice operated and the provision of any protective devices to prevent a train running past a signal at danger. In the Sydney metropolitan area, trainstops are provided which are set to operate a tripcock on the train's braking system if a signal  is passed at danger or in some cases approached at too high a speed. In this case the length of  the overlap should be sufficient for a train which bas been tripped to stop within the overlap. Overlaps distances may therefore vary for each signal according to line speed and gradients. Under present day operating conditions,  the worst case overlap  would  be of  the order  of  830 metres for a line speed of 115 km/h on a  1 in 50 (2%) down gradient. Overlaps may often be longer than the signal sections. Elsewhere, trainstops are not provided. Unless and until some form of automatic train protection is provided, there is no certain means of ensuring that a driver will not inadvertently pass a signal at danger. The driver bas the final responsibility for obeying the signals. So, whatever the length of overlap, there is no guarantee that it will be adequate for all situations. It can therefore be considered as a margin for error if the driver misjudges his braking or the train braking system does not perform adequately. A nominal 500 metres is the present standard. This has been shown by experience to be adequate for most situations. In special circumstances, the overlap distance may be reduced. The end of the overlap is indicated on signalling plans, and often on the signalman's panel. Routes giving a low speed aspect may also be classified as main routes although the overlap will be much shorter (often 100 metres or less). Some caution or low speed aspects may be conditionally cleared (i.e. approach controlled) to permit a shorter overlap to be used at the next signal. In British practice such routes would be defined as "warning" routes. SRA (TfNSW) does not make such a distinction. 9.1.2. Calling-on Routes Some railways prefer a separate type of route for passenger trains running into occupied sections (e.g. bringing a second train into a partially occupied platform. This is known as a calling-on route and will require a distinct aspect, the main aspect remaining at stop or danger. Although calling-on signals exist on SRA (TfNSW), there is now no distinction between calling-on and shunting routes. Calling-on moves will be made under the authority of a subsidiary shunt signal (see 9.1.3.). 9.1.3. Shunt Routes A shunt route is used for low speed (usually  non-passenger)  movements,  e.g. into or out of sidings or for shunting between running lines. Any move into a line which is not proved clear, e.g. a siding, and any move from or up to another shunt signal or "limit of shunt" is classed as a shunt move. Shunt routes may be from dwarf or position light shunt signals or from a main signal, using a subsidiary signal on the same post. Route indications are provided where required. For a shunt route, the signal proves all points correctly set and locked. Proving of track circuits will depend on the policy of the railway concerned and local operating requirements. If it is regularly required to shunt into an occupied line, track controls should not be provided. Some sidings, of course, may not even be track circuited. Where a shunt move is made using the subsidiary aspect of a main signal, the train should first come to a stand. This can be partially achieved by using only a short range signal. However, some railways require the subsidiary signal to be approach controlled by timed track circuit occupation. For a shunt move from a ground-shunt signal there is no requirement for approach control, although it is sometimes provided. The train should either be approaching at low speed anyway or it will have set back behind the signal and must first stop before reversing direction. Where propelling moves (i.e. with the driver at the rear of the train) are regularly made past a shunt signal, some railways employ "I.AST WHEEL" replacement of the signal aspect so that the signal does not go back to danger until the driver has passed the signal. In such cases the signal continues to show a proceed aspect,·even, when the train occupies the first tracks beyond the signal, and is only replaced when its berth track clears. 9.2. Approach Locking  When a route is set, the interlocking will lock all the points in the correct position, and lock out any conflicting and opposing routes. The signalman must not be allowed to restore the route, and release this locking, with a train approaching the signal. This is called "APPROACH LOCKING". Once a signal has cleared, its route cannot be released until either:- the train is proved to have passed the signal a suitable time delay has elapsed, allowing an approaching train to see the replaced signal (or any cautionary aspects leading up to it) and be brought safely to a stand without any risk of passing the signal at danger. there is proved to be no train approaching ("Comprehensive Approach Locking") Proving that the train has  passed  the signal  is done by monitoring  the sequential  operation of the track circuits immediately beyond the signal. 9.3 Point Controls Although the signalman has a switch for manual control of each set of points, they are normally controlled automatically by the setting  of routes. The points are  then  locked  by the route set over them. The points are also locked by the track circuits over them, so that they cannot be moved under a train. Where a set of points has more than one end, then they are locked by the tracks over all ends. If a track circuit adjacent to the points is positioned so that a train standing on one of the diverging tracks could be foul of a movement over the other track  (a "foul" track circuit) it must be proved clear before the points are allowed to move to the position which would allow the fouled movement. 9.4. Route Locking Once a train has passed a signal, its route can be restored but any points, conflicting routes, etc. ahead of the train must remain locked. This is done by the "route locking", which is indicated by the line of white lights on the signalman's panel. The release of  route locking must first be preceded by the release of approach locking (i.e. it is safe to start releasing the route. If the route is cancelled after the train enters the route, the white lights extinguish behind, releasing the points for other moves. The white  lights always remain alight in front of the train, holding the points ahead locked. If there is no train in the route at the time of release and the approach locking has proved that there is no train approaching or it is safely at a stand, the whole of the route  will release immediately.

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Esat Kepenekli -
Posted 81 days Ago

A Solution to the Impacts of Climate Change on Rail Infrastructure

Rail Tracks

The ability to detect the presence of a train on a particular stretch of track is a key enabler for automatic signalling, and hence modern train control. There are two types of technology generally used for train detection, a track circuit or an axle counter. Track Circuits also have a side function (usually without any commitments) to detect complete rail breaks to an extent with the employed impedance bonds, but they are not able to catch many of the broken rail cases, and the recent trend is to use axle counters instead of track circuits. There are many benefits of using axle counters in comparison to track circuits, like lower life-cycle costs, higher reliability, and better management of long sections. It should be noted that the widespread use of axle counters may provide great benefits for interlocking, however, the axle counters do not provide any information at all for whether the rail physical condition is in a safe state for train traffic or not. This means that when we start using axle counters, verification of rail condition with an additional monitoring system becomes vital to know whether there are any defects in the rails. If this aspect is neglected somehow, it seems quite likely that this can lead to disastrous consequences both for ASSET & PASSENGER SAFETY. The World’s Best Railway Infrastructure Owners are aware of the RISKS and they are searching for an Innovative & Accurate SOLUTION to the possible “Broken Rail” issues. Broken Rail Detection (BRD) systems are being offered to close the safety gaps related to the rail integrity monitoring aspects. And, early detection of rail flaws is being more vital each day, due to increased speeds in rail transportation, either for passenger or freight trains. If track circuits are used at a railway line, it is surely needed to deploy a supportive BRD system to close the safety gaps, however, if axle-counters are used, a reliable BRD system definitely becomes a “MUST-HAVE” for safe rail transport operation. The rail-mounted RailAcoustic® solution validates the health of the rail, identifies any breaks as soon as it occurs, and accordingly notifies the rail status immediately for the train dispatcher. RailAcoustic® thus increases throughput as tracks can be verified for operation instead of being blocked for days due to derailment accidents that can also have severe consequences. RailAcoustic® is designed for easy installation and track maintenance through the clamp mechanisms attached to the rail bottom without opening any holes or drilling on the rails. Its receivers identify even the partial rail cracks before a conventional track circuit could detect an electrical disconnect in the rail. Any complete break or a major partial break in the rail can be identified with a very accurate location within 100 m precision for safe train operation and ease of track maintenance. Rail-mounted RailAcoustic® components report to the back-office system to verify any detection. Messages are then passed to the signaling system or train control to take immediate action on the approaching or next trains passing the located breaks. This way, RailAcoustic® offers a near real-time detection and verification of breaks in rails – for safer and more profitable operation. The RailAcoustic® technology is demonstrated at High-Speed-Rail (HSR). The system is successfully in operation on a 90 km double-track stretch of the TCDD Konya High-Speed line, since 2018. Now, the installation and commissioning of the system continue for an 11 tunnel slab-track part (37 km) of the Sivas High-Speed line, to be integrated into the Siemens-provided CTC system. It is a proven, supportive, safety “enhancement” tool that does not need a SIL Certification in the short term, since it is not a component of mainline signalling but rather a very critical safety improvement for monitoring the RAIL and TRACK CONDITION. It solves a very critical issue in the railway industry with its methodology patented in the US, EU, China, Japan, India & Turkey, and has a great technical potential in the global rail industry subject to potential collaboration opportunities in different territories with diverse market needs. It has train monitoring abilities, which railway operators can benefit a lot. It is a result of 10 years-long research and development efforts that had been put in operation after extensive acceptance tests during the trial and commissioning phases of the client. The technology is unique and does not have any reasonable solution alternatives around the world offering a complete and stand-alone solution for high-speed railway lines, modernized conventional lines, and metro lines especially with continuously welded rails and limited ballast rock contact at the rail bottoms. Actually, as per the new approach with increased speed expectations in rail transport; it is obvious that a train should not be released to a line before being sure that especially the close segments of the tracks are safe for traffic. Only, then after "verifying the health status of rails and tracks", the interlocking and signalling come up to the fore, for a safe train presence monitoring and plotting of a route!  RailAcoustic® detects defects such as complete rail breaks and partial rail cracks, as well as other abnormalities like ballast washouts, floods, and landslides  The system 7/24 continuously senses: Partial Cracks on the Rails Complete Rail Breaks Significant Internal Defects Train Flat-Wheels Train Movement (with precise Speed info) Rail & Environmental Temperature Floods Landslides Washouts Buckled Rails Derailed Cars (only for low-speed freight rolling stock) The inventor and manufacturer of the system is Enekom, a technology company that is ready to be in collaboration with any parties, to enhance the safety of railways for protecting the assets and people. Please contact for further information: Esat Kepenekli – Contract and Commercial Manager Cell: +90 - 537 609 6498 (WhatsApp) Email: esatkepenekli (at) enekom.com.tr

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Sotto -
Posted 90 days Ago

Custom HVAC Control Panel for Sleeping Car Compartments

Rollingstock

Around 100 control panels with integrated compartment control technology including all validations - in just 9 months from the drawing board to delivery with a strong partner. We offer # project management, # standards management, # hardware design, # software design, # mechanical design, # product design, # procurement, # assembly and testing  all from a single source! Together with our QM-validated supplier base, we realize your project. Feel free to talk to me!

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Contact . -
Posted 96 days Ago

PantoSystem Implemented for Siemens eHighway Project

Automatic Train Supervision

    The customer The German government has introduced several initiatives to promote overhead contact lines for trucks, also known as eHighway. This solution makes road freight transport more energy-efficient and environmentally friendly [1] . The latter point is especially important and urgent, as the German government´s climate protection plan calls for reductions in CO 2 emissions by 40% from the transport sector by 2030 [2] . Since 2018 the Ministry of Environment in Germany is funding field trials of the eHighway system on real highway [3] . The challenge is to ensure that operations of this solution can be scaled up, which the users will be much more numerous as well as diverse. To prepare for this, the experience and solutions from PantoInspect were called upon. Germany’s transport ministry has announced the scaling-up phase of eHighway in Germany. Analysis from among other Germany’s National Platform for New Mobility (NPM) show that electrifying 4.000 km of motorways by 2030 is a cost-effective way to reach the climate targets. Analysis also shows the potential benefits of expanding the concept to neighboring countries such as Denmark and Sweden [4] . Ultimately, as contact line technology is in global use and climate change is a global problem, the objective is to spread the eHighway concept to the rest of the world. Since the eHighway project has come very far in the technical development stage, the team is now part of Siemens Rail Infrastructure, the division responsible for electrification of rail, and now also road. The eHighway project started in 2010 with the aim of developing two main components, namely the catenary system for use on motorways and pantographs for electrified trucks. In 2017, Siemens Mobility was commissioned up to €15 million ($16 million) by the German state of Hesse to build a 10 km overhead contact line for electrified road freight transport on a motorway. The eHighway project, which was part of one of the first three test tracks on a German motorway, running between the interchange Mörfelden (close to the Frankfurt airport) and the interchange Weiterstadt (close to Darmstadt).   The challenges/problems An important task to the eHighway team was to find a pantograph monitoring solution that was suitable for electrified trucks that could be connected to the overhead contact line. It was important for the team to have a system that could inspect the pantograph of the trucks to ensure the availability of the catenary system on the highway. Therefore, the eHighway team was looking for an inspection system that could help them detect defect pantographs to prevent potential damage of the catenary system. They also needed an inspection system that could help them detect if the pantograph is in an operating state and check that wear on the carbon strips was within an acceptable range. In addition, making sure that the pantograph had no other mechanical deformations that could potentially damage the catenary system. One of the main challenges was to find a pantograph monitoring system for electrified trucks, which could be installed above an overhead line in the highway environment. Electrified trucks do not have metal wheels, and therefore two pantographs are needed to establish two electric poles from which they can draw the power from. For this reason, pantographs on electrified trucks normally have four carbon strips and two overhead contact lines, unlike a train pantograph, which usually has two carbon strips and a single overhead contact line. Since the pantographs on the trucks contain more parts, the monitoring system required more sensors and technology than the usual system used for railways to ensure that the truck can leave the electrified lane and connect to it again.   The solution To ensure a high availability of an eHighway, it is important that no defective or worn-out pantographs will contact the overhead contact line. Since the operator of an eHighway System has no direct influence on the technical condition of the participating vehicles, it is very important to monitor the technical conditions of the connected vehicles. Siemens Mobility evaluated the Pantoinspect sensor system at the eHighway test facility in Groß-Dölln because the combination of camera and laser scanner provides the necessary basic requirements, for checking eHighway pantographs. With the results of the laser scanner, the geometric dimensions of the pantograph can be verified and compared with the limit values ​​stored in the Backend Monitoring System. Critical wear and tear as well as geometrical deviations can be detected and transmitted to the operation and control center. If necessary, an operator can use the high-resolution camera images to verify a detected deviation and inform the user that his pantograph is damaged, and the use of the overhead line is no longer permitted. The evaluation showed, that for a later series production some potential for optimization will be necessary, however the main task can be fulfilled with the PantoInspect portfolio.   Werner Pfliegl, Product Management of Siemens Mobility GmbH, Germany said: “PantoInspect was chosen by the eHighway team because the company has the advanced technical expertise and many years of proven track record in supplying some of the major infrastructure owners and rail operators in the global railway industry. The PantoSystem was very beneficial for the eHighway project since the team considered it as an all-in-one system that combines both a camera system and a laser system”.   The eHighway team also believed that the software was very good at providing statistical data to give the operator a detailed overview of the condition of the pantograph. PantoInspect carried out a lot of research and development to build up a model which was able to recognize every part of the pantograph on electrified truck correctly. The triggering system was also challenging in the beginning since the data on the speed of the vehicle needed to be found through the laser scanner itself to trigger the camera system correctly. However, PantoInspect managed to make extensive modifications to both the hardware and software to meet the requirements of the eHighway project.  The laser scanning device of the PantoSystem helped the team to build 3D models of the pantographs, which detected the working condition of the pantograph. The camera system was also used as a backup system to help the operator verify potential pantograph defects. They also believe that the system can help the owners of electrified trucks to get data on worn-out pantographs and ensure less maintenance of the catenary system as well as reduce the risk of damaged overhead contact lines. Siemens Mobility sees many advantages in using the PantoSystem for future applications in both electrified trucks and railways to help prevent an installed technical base from any type of damage. The team also see many future potentials in using the PantoSystem on 1000s of km of electrified tracks on motorways to evaluate the condition of the catenary system and for maintenance purpose. The system could potentially also help the BAG (Bundesamt für Güterverkehr) to identify electrified truck with defect pantographs, during their regular inspections, and thereby maximize safety on the highways. The PantoSystem can help Siemens offer a complete solution which includes both the identification of trucks as well as detection of defect pantographs, and thereby add great value to the company. This fits very well with PantoInspect´s vision of creating environmentally friendly solutions for both electrified railways and trucks.     About PantoInspect PantoInspect was the first company world-wide to develop an automated pantograph inspection system, in partnership with Banedanmark, the Danish railway infrastructure owner, around 2008. Today, PantoInspect is one of the world’s most recognized and respected brands and a market-leading manufacturer and supplier of automated and real-time Wayside Pantograph Monitoring systems to the global Railway industry. We have supplied several pantograph monitoring systems to some of the world’s leading infrastructure owners and rolling stock operators such as Deutsche Bahn, RATP, Infrabel, Sydney Trains, Network Rail, and TRA.     PantoInspect  Titangade 9C Copenhagen 2200, Denmark www.pantoinspect.com Email: contact@pantoinspect.com Tel: +45 3318 912       [1] https://www.bmvi.de/SharedDocs/EN/Dossier/Electric-Mobility-Sector/electric-mobility-sector.html [2] https://www.oeko.de/fileadmin/oekodoc/Climate-friendly-road-freight-transport.pdf [3] https://ec.europa.eu/jrc/sites/jrcsh/files/20201028_eu-hgv-workshop_sue_public.pdf [4] https://www.linkedin.com/posts/steen-n%C3%B8rby-nielsen-5736886_tysklands-transportministers-klimaplan-for-activity-6732401194108620800-6Ybn 

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Contact . -
Posted 96 days Ago

Innovative PantoSystem Prevents Service Disruptions to Paris RER Network of RATP

Automatic Train Supervision

      The customer RATP is a state-owned public transport operator and the biggest transport company in Paris with 60,000 people responsible for engineering, exploitation, and maintenance. The company provides multiple transport modes such as metros, buses, trams, and regional express rail (RER) network. RATP has a total of 28 lines of metro, trams, and RER in the Parisian metropolis.   The challenges/problems Within a two-week interval, incidents related to the spring box of two separate pantographs running on opposite train tracks, were identified. In one of the incidents, the abnormal wear of the carbon strip kept deteriorating, and when the carbon strip finally had a pitch angle between -3,8° and -3,4°, the PantoSystem generated a level 1 alarm in one of RATP´s RER networks, indicating a warning of high importance. After examining the 3D images of the pantograph, the PantoInspect team urgently sent an e-mail to warn RATP about the carbon strip, which had clearly been bended. Immediately after, the exploitation team of RATP took the train off the track and when the problem was investigated by the maintenance team, they confirmed that the horn of the pantograph was hit by an unknown object, causing the spring box to twist on one side.   The solution As the PantoSystem has not yet been validated by formal tests, the RATP does not yet have a dedicated team to handle the train alarms and take appropriate action, and that is why, they were very pleased to receive a direct warning from PantoInspect, that a train required attention. The company was also very satisfied that the PantoSystem enabled them to detect the consequences of the twisted or broken spring box, by accurately measuring the geometry of the pantograph. The automatic system is important due to the fact that RATP has about 90 km of tracks on each direction, a total of 180 km track on both directions, and since this type of problem does not happen frequently, manually identifying this type of defect throughout the RATP fleet would have been very time-consuming and costly for RATP as it is not visible from the ground. Additionally, to manually investigate if more trains were affected would again require a major effort.                Figure 3: Broken spring box             About PantoInspect PantoInspect was the first company world-wide to develop an automated pantograph inspection system, in partnership with Banedanmark, the Danish railway infrastructure owner, around 2008. Today, PantoInspect is one of the world’s most recognized and respected brands, and a market-leading manufacturer and supplier of automated and real-time Wayside Pantograph Monitoring systems to the global Railway industry. We have supplied several pantograph monitoring systems to some of the world’s leading infrastructure owners and rolling stock operators such as Deutsche Bahn, RATP, Infrabel, Sydney Trains, Network Rail and TRA.   PantoInspect Titangade 9C Copenhagen 2200, Denmark www.pantoinspect.com Email: contact@pantoinspect.com Tel: +45 3318 9120

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Somnath Pal -
Posted 109 days Ago

QUANTIFIED RAMS BASED RAILWAY ASSET MANAGEMENT

Rail Asset

  Railway Asset Management provides Sustainable Infrastructures through evidence-based decision making to achieve the optimum performance with Economic benefit while ensuring Safety and Integrity. It covers defining Asset Management Policy, Strategy and Framework. Key factors to consider are the physical deterioration, obsolescence, operation and maintenance of the system. Corrective Actions are based on management Data Reviews. Asset Managers must perform Risk Analysis and Predictive Analysis for Maintenance planning. In addition, a Qualitative Vulnerability Analysis and Managerial Oversight Risk Analysis should be performed to evaluate System Safety Robustness.  After defining the System Reliability, Reliability Allocation to sub-systems are fixed and various Design and Manufacture criterions are followed with trade-off between Performance and Service life-cycle Cost. Failure probabilities are calculated after Mitigation of critical Failure Modes. Cost models on maintenance optimization can be based on Markov model with Inspection and Replacement policy. Incentive on improved Reliability and Supply of specific Reliability Data for the Equipment must be implied in Supply Contract, considering other performance aspects.  Acceptance Testing should comply with Reliability Targets and specify Accelerated Stress Test Duration, including Burn-in periods, if any. Maximum Likelihood Estimation for Failure is calculated before Asset acceptance. While increasing Reliability, Preventive Maintenance reduces Availability and might introduce new failures. So, Predictive Maintenance using Diagnostics and Prognostics is a better Option. Comparisons between Repair and Renewal are chosen to maximize Availability. MTTR must comply with 95% Confidence that Repairs are performed within defined duration. Optimum Inspection Interval must be calculated from Failure Rates, Inspection duration and Repair time. Adequacy of Spare Parts and Location of Stores, whether Centralized or Distributed, are to be specified after calculations to provide maximum Availability.  Reliability Growth testing must be done to verify stipulated MTTF. To avoid any lapse during On-site Maintenance Activities due to Human Errors, specific Checklists, Maintenance Tools and, Drawings must be available. Proper updated Training is mandatory for the Concerned men-at-site. Cloud-based Intelligent Safety Asset Management can implement Expert Systems, Video Conferencing with Experts during emergency and Video Surveillance of Construction Sites. Finally, Asset Management Audits check whether the specified strategies are being followed.

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Deepu Dharmarajan -
Posted 208 days Ago

TRAIN DESCRIBERS

Signalling

    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 208 days Ago

RECENT DEVELOPMENTS IN SIGNALLING

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 209 days Ago

PRINCIPLES OF TESTING

Signalling

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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