EN 50155:2007

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Railway applications - Electronic equipment used on rolling stockŽelezniške naprave – Elektronska oprema na voznih sredstvihApplications ferroviaires - Equipements électroniques utilisés sur le matériel roulantBahnanwendungen - Elektronische Einrichtungen auf SchienenfahrzeugenTa slovenski standard je istoveten z:EN 50155:2007SIST EN 50155:2007en,fr,de45.060.10Tractive stock29.280Electric traction equipmentICS:SIST EN 50155:2002/A1:2003SIST EN 50155:20021DGRPHãþDSLOVENSKI
STANDARDSIST EN 50155:200701-oktober-2007

EUROPEAN STANDARD EN 50155 NORME EUROPÉENNE
EUROPÄISCHE NORM July 2007
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2007 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 50155:2007 E
English version
Railway applications -
Electronic equipment used on rolling stock
Applications ferroviaires -
Equipements électroniques utilisés
sur le matériel roulant
Bahnanwendungen -
Elektronische Einrichtungen
auf Schienenfahrzeugen
This European Standard was approved by CENELEC on 2007-03-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
ICS 45.060.10 Supersedes EN 50155:2001 + A1:2002

This European Standard was prepared by the Technical Committee CENELEC TC 9X, Electrical and electronic applications for railways.
The text of the draft was submitted to the Unique Acceptance Procedure and was approved by CENELEC as EN 50155 on 2007-03-01.
This European Standard supersedes EN 50155:2001 + A1:2002.
This EN 50155:2007 has been aligned with the new EN 50121 series and addresses some Portuguese comments.
The following dates were fixed:
– latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement
(dop)
2008-03-01 – latest date by which the national standards conflicting with the EN have to be withdrawn
(dow)
2010-03-01
This European Standard has been prepared under a mandate given to CENELEC by the European Commission and the European Free Trade Association and covers essential requirements of EC Directives 96/48/EC and 2001/16/EC. See Annex ZZ. ____________

- 3 - EN 50155:2007 Contents 1 Scope.5 2 Normative references.5 3 Definitions.7
4 Environmental service conditions of operation.8
4.1
Normal service conditions.8 4.2
Special service conditions.10
5 Electrical service conditions.10
5.1
Power supply.10 5.2
Supply.12 5.3
Installation.12 5.4
Surges electrostatic discharge and transient burst susceptibility tests.12 5.5
Electromagnetic compatibility.12
6 Reliability, maintainability and expected useful life.12
6.1
Equipment reliability.12 6.2
Useful life.13 6.3
Maintainability.13 6.4
Maintenance levels.13 6.5
Built-in diagnostics.14 6.6
Automatic test equipment.14 6.7
Alternative methods for fault diagnosis.14 6.8
Purpose built test equipment and special tools.14
7 Design.15
7.1 General.15 7.2
Detailed practices - Hardware.15 7.3
Detailed practices - Software.17 7.4
Equipment features.19
8 Components.20
8.1
Procurement.20 8.2
Application.21
9 Construction.21
9.1
Equipment construction.21 9.2
Component mounting.21 9.3
Electrical connections.22 9.4
Internal flexible wiring (electrical and optical).23 9.5
Flexible printed and strip wiring.23 9.6
Printed board-flexible and rigid.24 9.7
Protective coatings for printed board assemblies.24 9.8
Identification.25 9.9
Mounting.25 9.10
Cooling and ventilation.25 9.11
Materials and finishes.26

10.1
General.26 10.2
Functional safety.26 10.3
Personnel safety.26
11 Documentation.26
11.1 Supply and storage of documentation.26 11.2
Hardware and software documentation.26 11.3
Documentation requirements.28
12 Testing.29
12.1
Categories of tests.29 12.2 List of tests.30
Annex A (informative) List of subclauses in which agreement between the parties (e.g. user and manufacturer) is mentioned.40 Bibliography.41 Annex ZZ (informative) Coverage of Essential Requirements of EC Directives.42
Figure 1 - System interfacing with the typical EMC areas A, B and C .16 Figure 2 - Supply overvoltage .34 Figure 3 - Alternative test for supply overvoltage.35
Table 1 - Ambient temperature.9 Table 2 - List of tests.30

- 5 - EN 50155:2007 1 Scope
This standard applies to all electronic equipment for control, regulation, protection, supply, etc., installed on rail vehicles and associated with: - either the accumulator battery of the vehicle; - or a low voltage power supply source with or without a direct connection to the contact system (transformer, potentiometer device, auxiliary supply); with the exception of electronic power circuits, which conform to EN 50207.
This standard covers the conditions of operation, design, construction, and testing of electronic equipment, as well as basic hardware and software requirements considered necessary for competent, reliable equipment.
Additional requirements in other standards or individual specifications may complement this standard, if they are justified.
Specific requirements related to practices necessary to assure defined levels of functional safety are to be determined in accordance with 4.6.3.1 and 4.6.3.2 of EN 50126 and its informative Annex A. Software safety integrity level of 1 or higher shall only be considered when it is shown that a residual safety risk remains and that it has to be carried by the software driven programmable electronic system. In such a case (i.e. software safety integrity level 1 or higher), EN 50128 is applicable.
For the purpose of this standard, electronic equipment is defined as equipment mainly composed of semiconductor devices and recognized associated components. These components will mainly be mounted on printed boards.
NOTE Sensors (current, voltage, speed, etc.) and firing unit printed board assemblies for power electronic devices are covered by this standard. Complete firing units are covered by EN 50207.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 50121-3-2 2000 Railway Applications - Electromagnetic compatibility Part 3-2: Rolling stock – Apparatus EN 50125-1 1999 Railway Applications – Environmental conditions
for equipment– Part 1: Equipment on board rolling stock EN 50126 Series Railway applications - The specification and demonstration of Reliability, Availability, Maintainability and Safety (RAMS) EN 50128 2001 Railway applications - Communication, signalling and processing systems -Software for railway control and protection systems EN 50163 1995 Railway Applications - Supply voltages of traction systems EN 50207 2000 Railway applications - Electronic power converters for rolling stock
(IEC 61287-1:1995, related) EN 60068
Series Environmental testing (IEC 60068 series) EN 60068-2-1 1993
Environmental testing – Part 2: Tests – Test A: Cold (IEC 60068-2-1:1990) EN 60068-2-2 1993 Environmental testing – Part 2: Tests – Test B: Dry heat (IEC 60068-2-2:1974 + IEC 60068-2-2A:1976) EN 60068-2-30 2005 Environmental testing – Part 2: Tests – Test Db and guidance: Damp heat, cyclic (12 + 12 hour cycle) (IEC 60068-2-30:2005)

Series Railway applications –
Electrotechnical equipment for rolling stock
(IEC 60077 series, modified) EN 60249-2-15
1994 Base materials for printed circuits – Part 2: Specifications -- Specification No. 15: Flexible copper-clad polyimid film, of defined flammability (publication withdrawn) EN 60297
Series Mechanical structures for electronic equipment - Dimensions of mechanical structures of the 482,6 mm (19 in) series (IEC 60297 series) EN 60352 Series Solderless connections (IEC 60352 series) EN 60352-1 1997 Solderless connections – Part 1: Wrapped connections - General requirements, test methods and practical guidance (IEC 60352-1:1997) EN 60352-2 2006 Solderless connections – Part 2: Crimped connections - General requirements, test methods and practical guidance (IEC 60352-2:2006) EN 60529 1991 Degrees of protection provided by enclosures (IP Codes)
(IEC 60529:1989) EN 61000-4-4 2004 Electromagnetic compatibility (EMC) – Part 4-4: Testing and measurement techniques - Electrical fast transient/burst immunity test
(IEC 61000-4-4:2004) EN 61082 Series Preparation of documents used in electrotechnology (IEC 61082 series) EN 61249
Series Materials for printed boards and other interconnecting structures (IEC 61249 series) EN 61249-2-7 2002 Materials for printed boards and other interconnecting structures –
Part 2-7: Reinforced base materials, clad and unclad - Epoxide woven E-glass laminated sheet of defined flammability (vertical burning test), copper-clad
(IEC 61249-2-7:2002) EN 61249-2-10 2003 Materials for printed boards and other interconnecting structures –
Part 2-10: Reinforced base materials, clad and unclad - Cyanate ester, brominated epoxide, modified or unmodified, woven E-glass reinforced laminated sheets of defined flammability (vertical burning test), copper-clad
(IEC 61249-2-10:2003) EN 61373 1999 Railway applications - Rolling stock equipment - Shock and vibration tests (IEC 61373:1999) EN 62326 Series Printed boards EN 123000 1991 Generic specification - Printed boards EN 123200 1992 Sectional specification - Single and double sided printed boards with plated-through holes EN 123300 1992 Sectional specification - Multi-layer printed boards EN 123400 1992 Sectional specification - Flexible printed boards without through connections EN 123500 1992 Sectional specification - Flexible printed boards with through connections EN ISO 9000-3 1997 Quality management and quality assurance standards Part 3: Guidelines for the application of ISO 9001 to the development, supply and maintenance of software (ISO 9000-3:1991) EN ISO 9001
Quality management systems - Requirements (ISO 9001) EN ISO 9002
Quality systems - Model for quality assurance in production, installation and servicing (ISO 9002) IEC 60605 Series Equipment reliability testing IEC 60617 Database
Graphical symbols for diagrams

- 7 - EN 50155:2007 3 Definitions
For the purposes of this standard, the following definitions apply:
3.1 printed board base material cut to size containing all holes and bearing at least one conductive pattern. Printed boards are typically subdivided according to: - their structure (e.g. single and double-sided, multilayers) - the nature of the base material (e.g. rigid, flexible)
3.2 printed board assembly printed board with electrical and mechanical components and/or other printed boards attached to it with all manufacturing processes, soldering, coating, etc., completed
3.3 plug-in unit unit which plugs into a subrack and is supported by guides. These units can be of various types, ranging from a printed board with components mounted in a frame or box type unit, designed with a plug-in connection
3.4 subrack structural unit for housing printed board assemblies and/or plug-in units
3.5 rack free-standing or fixed structure for supporting electrical or electronic equipment (e.g. subracks)
3.6 cubicle any enclosure for housing electrical and/or electronic equipment
3.7 line replaceable unit unit designed to be exchanged as a result of on-vehicle fault diagnosis, e.g. a subrack, or plug-in unit
3.8 performance check short form performance test which is carried out during and after environmental tests, sufficient to prove that the equipment is within its operational limits, and that it has survived an environmental test
3.9 control system voltage supply voltage supply used to power the vehicle control equipment The supply may be derived from a vehicle battery. The battery may be charged from battery chargers, auxiliary inverters and motor-alternator or motor-generator sets with associated electronic regulations Where the control system voltage supply is derived from a battery, the nominal and rated control system voltages are defined in 5.1. Where no battery is fitted, the nominal control system voltage is the normal controlled level of that voltage
3.10 vehicle wiring all wiring which can be connected to the control system voltage supply, wherever located, and all other wiring external to the electronic equipment under consideration

3.12 surge non-periodic and relatively short positive or negative (or both) variable (voltage or current) between two steady states It may be produced by the normal operation of equipment within the vehicle, caused generally by the discharge of energy when inductive circuits are switched It may be present either on the control system voltage supply, or on wiring connected directly to switched inductive circuits, or coupled electrostatically or electromagnetically from such wiring into other wiring The effective value of the source impedance of a transient will depend upon the manner of its generation and coupling
3.13 burst repetitive pulses occurring during a fixed time interval They may occur during normal operation of the vehicle, typically resulting from unstable arc conditions
3.14 failure termination of the ability of an item to perform a required function A temporary malfunction will not be considered a failure provided that: a) The equipment recovers normal operation automatically following malfunction b) The malfunction is not apparent to the vehicle operating staff; for example, fault indicators do not light up.
NOTE Attention is drawn to the possibility of a consequential failure of a second item of equipment resulting from a temporary malfunction of another item of equipment connected to it.
3.15 damage any change in visual appearance or alteration of mechanical integrity
3.16 useful life under given conditions, the time interval beginning at a given instant of time and ending when the failure rate becomes unacceptable, or when the item is considered not repairable as a result of a fault or for other relevant factors
NOTE For a repairable item the individual useful life may be ended by a failure which is not considered as repairable for any reason.
4 Environmental service conditions of operation
4.1 Normal service conditions
4.1.1 Altitude
The altitude at which the equipment is normally to function does not exceed the values called for in EN 50125-1, Subclause 4.2. When it exceeds this figure, compliance with the requirements shall be defined by agreement between manufacturer and user.
4.1.2 Ambient temperature
Electronic equipment shall be designed and manufactured to meet the full performance specification requirement for the selected temperature categories as stated in Table 1.

- 9 - EN 50155:2007 The design shall take into account temperature rises within cubicles to ensure that the components do not exceed their specified temperature ratings. In addition, the equipment shall meet the special short-term start up thermal conditions as stated in column 3. In this interval the full performance ratings may be relaxed, but the maximum air temperature surrounding the printed board assembly according to column 4 shall not be exceeded.
Table 1 - Ambient temperature Column 1 Column 2 Column 3 Column 4 Class Ambient temperature outside vehicle (EN 50125-1,
Table 2, Column 1) °C Internal cubicle temperature
°C Internal cubicle overtemperature during 10 min
°C Air temperature surrounding the printed board assembly
°C T1 -25
+40 -25
+55 +15
-25
+70 T2 -40
+35 -40
+55
+15 -40
+70 T3 -25
+45 -25
+70 +15 -25
+85 TX -40
+50 -40
+70 +15 -40
+85
NOTE The differences between EN 50155 Table 1 (column 2) and EN 50125-1 Table 2 (column 3) are mainly due to the following reasons:
EN 50125-1 refers to a general application, where cubicles are provided without any particular thermal design.
In electronic equipment, a thermal design is usually needed, to guarantee a convenient minimum and maximum ambient temperature for the electronic components. The components reliability is very sensitive to the ambient temperature. The values given for the maximum temperatures inside the cubicle has been restricted to a choice of two to allow manufacturers to have only two classes of cards.
For peripheral units (measuring transducers, etc.), or if the equipment is in a decentralized configuration, then if the above ambient temperature ranges are exceeded, the actual temperatures occurring at the location of the equipment concerned shall be used in the design.
Rapid external ambient temperature variations resulting from running through tunnels shall be taken into account. For this purpose the rate of change of external temperature shall be assumed to be 3 °C/sec, with a maximum variation of 40 °C .
4.1.3 Shock and vibration
The equipment shall be able to withstand, without deterioration or malfunction, vibrations and shocks that occur in service. In order to provide some reasonable degree of confidence that it will survive the specified useful life under service conditions, it shall be capable of meeting the vibration, shock and bump test as described in 12.2.11. For these purposes the equipment is specified as having the electronic units installed complete, and supported in their designed fixings, with anti-vibration mounts where fitted. For the typical values of shocks and vibrations in real service, reference is made to EN 61373.
4.1.4 Relative humidity
The equipment shall be designed for the following humidity stresses (limit values) over the relevant range of the external ambient temperature as defined in 4.1.2: - yearly average ≤ 75 % relative humidity,
- 30 consecutive days in the year: 95 % relative humidity.

4.2 Special service conditions
Special arrangements shall be agreed between the appropriate parties involved when service conditions can be proved to be different from those mentioned in 2.1 (e.g. electronic equipment mounted on the bogie or integrated within a power converter etc.). Checks for the effectiveness of such arrangements can, if required, form the subject of optional type tests which can be carried out on the vehicle itself in accordance with methods to be agreed between the user and the manufacturer.
4.2.1 Atmospheric pollutants
The equipment may be expected to be exposed throughout its life to various pollutants (e.g. oil mist, salt spray, conductive dust, sulphur dioxide.). The types of pollutants and their concentration should be defined in the tender documents.
5 Electrical service conditions
5.1 Power supply
5.1.1 Supply from accumulator battery
The nominal voltage of equipment (Un) so supplied shall be selected from amongst the following values:
24 V, 48 V, 72 V, 96 V, 110 V
NOTE 1 These nominal voltage values are given only as standardising values for the design of equipment. They should not be considered as the off load battery voltages since these are determined by the types of battery, the number of cells and the operating conditions.
NOTE 2 Different voltage variations may be used, following EN 60077. In this case compliance with the requirements should be defined by agreement between manufacturer and user.
5.1.1.1
Variations of voltage supply
Electronic equipment supplied by accumulator batteries without a voltage stabilizing device shall operate satisfactorily for all the values of the supply voltage within the range defined below (measured at the input terminals of the equipment). The supplier of the electronic equipment shall specify its power consumption in order to enable calculations for the battery cabling.
Minimum voltage: 0,7 Un
Nominal voltage: Un
Rated voltage:
1,15 Un
Maximum voltage:
1,25 Un Voltage fluctuations (e.g. during start-up of auxiliary equipment or voltage oscillations of battery chargers) lying between 0,6 Un and 1,4 Un and not exceeding 0,1 s shall not cause deviation of function. Voltage fluctuations lying between 1,25 Un and 1,4 Un and not exceeding 1 s shall not cause damage: equipment may not be fully functioning during these fluctuations. In the case of thermal engines, see also 5.1.1.3.

- 11 - EN 50155:2007 5.1.1.2
Interruptions of voltage supply
Interruptions of up to 10 ms may occur on input voltage as defined below: - Class S1: no interruptions - Class S2: 10 ms interruptions
This shall not cause any equipment failure.
The time values specified are for nominal voltage and the choice of classes shall be defined by the system designer.
5.1.1.3
Variations of voltage supplies for rolling stock powered by thermal engines
At start-up of thermal engines the voltage supply system shall be designed to guarantee the supply to the essential electronic equipment during the whole starting sequence.
5.1.1.4
D.C. ripple factor
All batteries on charge have a pulsating voltage, the d.c. ripple factor of which, unless otherwise stated, shall not be greater than 15 % calculated from the equation:
Umax - Umin
d.c. ripple factor =  x 100
Umax + Umin
where Umax and Umin are the maximum and minimum values, respectively, of the pulsating voltage.
The minimum and maximum voltages as defined in 5.1.1.1 however shall not be exceeded.
5.1.2 Supply by a static converter or a rotating set
In the case of equipment supplied with power from a stabilized source, (e.g. a static converter or a rotating motor-generator set provided with a regulator), electronic equipment shall operate satisfactorily for values of the supply voltage lying between 0,9 and 1,1 Un, where Un is the nominal voltage and can be either d.c. or a.c. In addition, for operating equipment, voltage fluctuations lying between 0,7 Un and 1,25 Un not exceeding 1 s and also between 0,6 Un and 1,4 Un not exceeding 0,1 s are allowed.
5.1.3 Supply change over
In the case of equipment supplied with power alternatively from an accumulator battery and a stabilized source (d.c.), the equipment shall operate satisfactorily under the conditions stated in 5.1.1, 5.1.1.1, 5.1.1.4 and 5.1.2. - Class C1: at 0,6 Un during 100 ms (without interruptions). - Class C2 during a supply break of 30 ms.

In the case of electronic equipment with a supply derived directly from the overhead line or third rail (e.g. control electronics of a self starting static converter), the equipment shall operate satisfactorily for values of contact line voltage as described in EN 50163.
5.2 Supply overvoltages
All connections to electronic equipment capable of being connected to the control system voltage supply shall withstand:
a) the supply overvoltages as specified in 5.1.1.1 and/or 5.1.2 (as appropriate); b) the application of supply overvoltages as specified in 12.2.6. Overvoltages shall be assumed to be generated with respect to the control system voltage supply return potential and to be present only as an increase to the level of the control system voltage, which shall be assumed to be present before and after the application of the overvoltage. Overvoltage of opposite polarity to the control system voltage supply need not be considered. Overvoltage exceeding 1,25 Un longer than 0,1 s shall be assumed to occur only in the case of a failure in the control system voltage supply.
5.3 Installation
The supply to the electronic equipment should be provided by a separate conductor connected as directly as possible to the source. This conductor should be used only for the supply to electronic circuits. The installation of the electronic equipment shall be arranged so as to reduce, as far as possible, the effects of external electrical disturbances. Suppression should be provided at the source of electrical interference. If one pole of the battery of the vehicle is connected to the vehicle body, this shall be specified. Where several manufacturers supply electronic equipment having common direct connections, a single reference point of equi-potential shall be established by mutual agreement.
5.4 Surges, electrostatic discharge and transient burst susceptibility tests
All electronic equipment shall withstand surges, electrostatic discharge and transient burst susceptibility tests as specified in EN 50121-3-2. The tests are specified in 12.2.7
5.5 Electromagnetic compatibility
The equipment shall be protected so as not to be adversely affected by conducted or radiated interference as required in EN 50121-3-2 and shall not emit radio frequency interference (RFI) in excess of the level defined in EN 50121-3-2. The tests are specified in 12.2.8.
6 Reliability, maintainability and expected useful life
6.1 Equipment reliability
6.1.1 Predicted reliability
The user may require the manufacturer to predict his reliability figure or meet the user's reliability target. The method of calculation shall be agreed at the time of tendering between the manufacturer and the user, and shall be in accordance with a recognized standard.

- 13 - EN 50155:2007 6.1.2 Proof of reliability
Where the user has specified a required reliability level, the following actions are necessary. The equipment performance shall be carefully monitored. The equipment manufacturer and the user shall agree to record all actions carried out on the equipment. To demonstrate the reliability level of the equipment a defect report will be presented at the end of a mutually agreed period (km or service hours) identifying the components replaced (circuit reference number, type, manufacturer, number of manufacturing lot, kilometres and/or operating hours etc.), the definition and cause of faults (design weakness, software, component problems etc.). In order to show whether the equipment meets its stated reliability requirements, the equipment should be subjected to a reliability evaluation. IEC 60605 may be used as a guide. The detailed reliability evaluation procedure shall be stated in the contract.
6.2 Useful life
The useful life of the electronic equipment, unless otherwise agreed at the time of tendering between the equipment manufacturer and the user, shall be taken as 20 years. When the manufacturer intends to use components with a known life less than the useful life of the electronic equipment, their use and procedures for their regular replacement shall be agreed between the involved parties.
6.3 Maintainability
Unless otherwise agreed, equipment shall be designed such that regular periodic maintenance shall not be necessary. Special maintenance requirements, if any, shall be defined by the user at the time of tendering. Printed board assemblies, and/or subracks shall be capable of being individually tested. In addition, the equipment manufacturer shall advise what maintenance procedures are necessary or prohibited.
NOTE Maintenance processes such as ultrasonic cleaning, connecting of diagnostic test equipment, electrical insulation testing, and transportation packaging arrangements, can reduce the equipment reliability level, through additional stressing of the assembly and components.
6.4 Maintenance levels
6.4.1 On-vehicle diagnosis and repair
The user and manufacturer shall agree on the nature of units (e.g. subracks or plug-in units) to be exchanged as a result of on-vehicle fault diagnosis. These units, defined as line replaceable units, shall be designed to be easily exchanged. The user and manufacturer shall also agree on the use of any specialised tools required in this maintenance procedure. Equipment shall be designed such that a failed line replaceable unit can be identified by the use of either suitable portable test equipment or built-in diagnostics, both with associated test instructions. Maintenance or diagnostic procedures at this level shall not require the removal or replacement of any component of the Line Replaceable Unit.

Equipment shall be designed such that test equipment with associated test instructions shall enable the full diagnosis and validation of performance of each type of train-borne equipment in repair centres by qualified personnel. Equipment shall be constructed such that access necessary for diagnosis and repair can be achieved without damage or undue disturbance to the components or wiring. In addition, printed board assemblies shall have test facilities (e.g test plugs, test pads etc.) to aid the diagnosis and repair process.
6.5 Built-in diagnostics
Indicators to assist diagnostic maintenance shall be used where appropriate, in order to display status of input data, output data, main control functions, power supplies, etc. Self test routines shall be capable of providing clear indication of the operational status of the equipment. Any built-in diagnostic facilities capable of exercising rather than monitoring the equipment shall be suitably interlocked to prevent interruption of the normal operation of the equipment other than under test conditions. The use of extra components for built-in diagnostics shall not considerably influence the reliability of the equipment, and shall be taken into account in reliability calculations.
6.6 Automatic test equipment
The user may require to use a specific type of automatic test equipment for fault location either on or off the vehicle. If this is required, details of such test equipment and its interfacing with train-borne equipment, e.g. bed of nails or guided probe (for off-vehicle repair), or equipment connector (for on vehicle diagnosis), shall be provided by the user at the time of tendering. It is permitted to remove plug-in units which do not contribute to the function of the equipment, to facilitate the connection of Automatic Test Equipment.
6.7 Alternative methods for fault diagnosis
Where train-borne electronic equipment has been developed or tested using proprietary test equipment the manufacturer may offer this as an alternative for fault diagnosis within repair centres, provided that use of such equipment is practical to the installation and all support details are made available to the user.
6.8 Purpose built test equipment and special tools
The prior approval of the user shall be obtained regarding the use of items requiring tools other than readily available industrial tools. Where purpose built test equipment and/or special tools are required to carry out the user's formal maintenance procedures, this equipment, or alternatively the manufacturing and procurement details for it, shall be offered for sale to the user. Test equipment does not necessarily have to comply with this standard.

- 15 - EN 50155:2007 7 Design
7.1 General
7.1.1 Quality management
All design shall proceed according to EN ISO 9001. The design process shall be visible and auditable. If the user requires details of this process for tender evaluation, he shall define this in the tender documents. Particular attention is drawn to the need implicit in the use of EN ISO 9001, for all system, hardware, and software design to proceed according to clearly laid down functional and interface specifications.
7.1.2 Life-cycle
All design shall proceed according to a defined life cycle model, which shall be laid down in the quality plan.
7.2 Detailed practices - Hardware
7.2.1 Interfacing
All interfaces shall be so implemented as to allow the equipment to meet its requirements in respect of:
- electromagnetic compatibility;
- potential differences;
- personnel safety and to control propagation of damage arising from external faults. The user may require galvanic isolation to meet the above. In this case the requirement and particular areas for its application shall be declared at the tender stage. An example of system interfacing with various EMC areas is given in Figure 1.
7.2.2 Fault protection
Outgoing cables shall be rated to at least the current limit value of the protective device for that circuit. Equipment shall be protected against external faults (e.g. short circuit or open circuit conditions as appropriate). Regulated power supply units for electronic equipment shall incorporate current limiting to minimise the use of fuse elements. If the user wishes to forbid the use of fuses internal to the equipment, this shall be declared at the time of tendering.

Figure 1 - System interfacing with the typical EMC-areas A, B and C

- 17 - EN 50155:2007 Where protective devices of the tripping type are incorporated in the output circuits, the available current under short circuit conditions shall be sufficient to operate them. In addition, devices with manual resetting shall be easily accessible. Any protective devices used shall be so arranged that the risk of fire within the equipment is minimised.
7.2.3 Referencing power supplies
The output of galvanically isolated power supply units should not be allowed to float. When the outputs are not referenced to a voltage source (e.g. battery or voltage supply) then one of the supply rails should be connected to the vehicle frame or a defined earth point. This reference and the means of connection should be defined and mutually agreed.
7.2.4 Interchangeability
All individual printed board assemblies forming part of a system shall be functionally complete and fully interchangeable with any other unit of the same functional type without the need for any recalibration of the hardware after the board has been inserted in the system.
7.2.5 Reduction of supply voltage
The equipment shall not suffer damage, when the supply is, or falls, below the lowest limit of its specified source voltage, irrespective of the rate at which the voltage changes. In addition, the equipment shall not generate any spurious output which could lead to consequential failure of any other equipment under these conditions.
7.2.6 Polarity reversal
To prevent any damage to the equipment, electrical or mechanical means shall be provided to ensure protection against polarity reversal of the incoming power supply.
7.2.7 Inrush currents
The design of the equipment shall take account of inrush currents which may occur at the time of switch-on, so that protective devices do not trip and no damage occurs.
7.2.8 Spare capacity
If the user requires spare capacity (e.g. spare inputs, spare outputs, CPU loading, etc.) for system expansion or changes during the equipment life-cycle, he shall specify this at the tender stage. Compliance with these requirements shall be included in the design process.
7.3 Detailed practices - Software
7.3.1 General
EN 29000-3 shall be used for the application of EN ISO 9001 for software. Requirements and recommendations of EN 29000-3 shall have mandatory effect. Configuration management procedures shall run in parallel with life-cycle activities covering all the software and tools used for its development and its maintenance. Life-cycle issues and documentation of the software development shall be covered. The development of the software shall be structured into defined phases and activities. All information pertinent to the design of the software shall be recorded.

a) Software requirements phase
In this phase all the requirements of the software shall be captured and documented in a software requirements specification, including interfaces to the system environment and to the other softwares.
b) Software design phase
In this phase, the architecture of the software shall be defined, the modules specified and the code written, ensuring that all elements meet the requirements as defined in the software requirements specification. In addition 5.3.2 should be taken into account.
c) Software testing phase
This phase covers the testing of the software at each of its design levels to ensure its correctness and consistency with respect to its specification. Test results shall be recorded.
d) Software/hardware integration phase
In this phase the hardware and software shall be integrated and tested to ensure compliance with the requirements of the system (e.g. as defined in the software requirements specification).
Test results shall be recorded.
e) Software maintenance phase
It is important that the dependability of the software is not compromised when making corrections, enhancements or adaptations. The measures taken shall be defined and documented.
7.3.2 Software design measures
The following measures shall be used, unless the rationale for any alternative has been documented and agreed with the user.
NOTE Explanations on these and other useful measures may be found in EN 50128 (Annex B).
7.3.2.1 Modular approach
The software shall be broken down into small comprehensible parts in order to manage its complexity. That includes taking measures
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