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

Note: While these notes are based on the authors' understanding of current railway signalling practice in the United Kingdom/Australia and elsewhere, they must not be taken to modify or replace any existing rules, instructions or procedures of any railway administration. Where any apparent conflict exists, reference should be made to the appropriate documents produced by the administration of your organization or the operator of your railway.

1.             INTRODUCTION 

These notes deal with the principles of testing a new or altered block 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. Verification & Validation requirement of modern signalling system (Eg:Communication Based Train Control ) are more stringent and shall be referred to  CENELEC -EN50128 - Railway applications - Communication, signalling and processing systems - Software for railway control and protection systems & CENELEC -EN50129-Railway applications - Communication, signalling and processing systems - Safety related electronic systems for signalling.

This article cover the site specific testing V&V Process for modern signalling will be published in another article.

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.

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 this article.

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.

1.4.        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 comm1ss1oning. 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:-

a) What will be tested?

b) How many staff, and with what specific skills, will be required to undertake all testing?

c) How long will the testing take, both before and during commissioning?

d) When will the equipment be available for testing and when is it required to be in service?

e) In what order should the tests be carried out?

f) What additional resources (equipment, transport, staff ) 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.

a) 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.

b) 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 

1.1.      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:-

a)Location cases are correctly labelled .

b) All equipment is installed as specified on the drawings, to the correct layout and actually present.

c) All equipment which is pin coded or otherwise uniquely configured to its mounting (e.g. signalling relays) is of the correct configuration.

d) Cables and wires are of the correct size and type, correctly terminated and properly secured where appropriate.

e) Equipment is 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.

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:-

a) Continuity, earth, and insulation tests on all cables.

b)Adjust and/or set all Where seals are provided, these should be in place before testing is complete.

c) 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.

Toe 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. Toe 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 de-energises 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(If present)  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(if incandescent signal used )  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. For LED signal lamp proving relay shall be tested (ECR) .Some modern interlocking products have direct signal driving card  ,capable of detecting current for lamp proving functionality .This shall be tested for  the functionality when LED signal fail.

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 many 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.For ETCS Level 1 ,Transponder position shall be checked against transponder layout plan /signalling scheme plan. functionality shall be tested to ensure signal aspects are replicated and signals transmitted to train antenna to capture.

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 de-energises. 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.  Axle Counters

The full length of the axle counter section must be examined to ensure that its limits agree with the bonding plan.

A wire count should be carried out at all disconnection and termination points.

Axle counter power On test shall be performed and section occupancy and clearance shall be checked by running Trains .

Axle counter data upload check list shall be completed with file name ,version CRC   and shall be maintained with relevant signatories signing the form.

Counter RESET functionality shall be carried out to check the counts “forgotten’ are reset  via train sweeping and counter reset to be tested .

 5.6.   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 bums 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.

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 situation 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.

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 signaling.

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:-

a) Relays - "up" or "down", "normal" or "reverse".

b) Points - "left hand switch closed" or "right hand switch closed"

c) 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 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.

d) 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:-

a) 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.

b) 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.

c) 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.

NOTE : Read Chapter CH23B | "Verification ,Validation and Trial Run "  detailing a CBTC  system approach testing model