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To install electronic equipment on a train it must comply with certain criteria for environmental, shock, vibration, power supply, EMC, power surge, ESD and transient factors that could occur when in use.
For obvious reasons, systems must be reliable and able to withstand more abuse than a standard embedded computer, especially if employed for telematics, engine control or other critical roles within the vehicle.
The standard assumes that systems on rolling stock will need to operate 24/7 for 30 years or approx 250,000 hours, without failure. This means that train control systems must be designed to withstand the toughest environmental conditions. It’s also important that systems do not interfere with each other when installed in close proximity; space is often tight in control panels so equipment can be mounted close together.
We have tried to summarise the basics of the complex EN50155 regulations below:
- Temperature Systems must be able to operate over a wide temperature range of -40°C to +85°C, although only some of the parts need to cover this ambient temperature range for 10 minutes during start up. The power supply, specifically, must work efficiently (85% or higher). This is to reduce the dissipated power that would otherwise be lost as heat. The supply must be efficient over a wide range of voltage and load conditions and must have thermal management, usually a heat sink arrangement.
- Shock and Vibration As expected, shock and vibration requirements are strict with systems entering a harsh environment like rolling stock. The spec calls up a separate standard (BS EN 61373:2010 Railway applications. Rolling stock equipment. Shock and vibration tests). Shock and vibration requirements are split into three categories - body mounted, bogie mounted and axle mounted; the latter being extremely severe.
- Power Supply The power supply is a critical component for electronic equipment used in trains. A wide range of voltages are used on rolling stock and the standard includes 24, 48, 72, 96 and 110VDC. Normally a 4:1 input voltage range is practical for system designs - 10-40V, 18-72V and 40-160V are common converters used. The standard also includes a requirement for the power supply to deal with interruptions by still delivering an output during a 10ms power outage.
- Electromagnetic Compatibility The EN50155 standard calls on the EN50121-3-2 standard (Railway applications. Electromagnetic compatibility. Rolling stock.) which is 20 pages long and calls on a number of other standards. Needless to say, the requirements for passing the desired standards are strict to ensure the equipment does not produce noise levels that could interfere with other equipment located in the same vicinity.
- Performance and Reliability This is always of the highest importance within a certification like EN50155 and the standard calls for a very particular quality process to be in place by the manufacturer. Clearly, quality components and manufacturing standards are included as part of the design for any system with such high MTBF requirements.
What Are The Type Approval Tests for EN50155 Certification ?
At the end of the EN50155 document there is a checklist of all the type approval tests and how to carry them out on a particular piece of electronic equipment alongside the pass/fail criteria.
These are as follows:
- Visual inspection
- Performance test
- Low temperature operation test (minimum operating temperature for 2 hours)
- Dry heat test (maximum operating temperature for 6 hours)
- Confirmation of operation over the full input voltage range
- Surge, ESD and transient tests
- Electrical insulation test
- Vibration, shock and bump test
- EMC Test
There are also a set of optional tests depending on the final application:
- Damp heat cyclic test
- Water-tightness
- Production stress screening
- Low temperature storage (-40°C for 16 hours)
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