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TANSPORTATIONComputer systems for railwayapplicationsBy Barbara Schmitz, MEN Mikro ElektronikMore and more electronicsystems are being built intotrains, the underground,streetcars and buses. If youtalk about the overall railwayengineering market, youdon’t only mean vehicles – inwhich areas and applicationscan one find these computersand which functions do theytake over? And why are theyso different to the office PCor the one at home?Figure 1. Redundant railsignalling system in 2oo3architecture Common studies like that of the SCI Verkehrroughly divide the railway market into vehicles,system technology and infrastructure. Whilethe overall market has a volume of 143 billioneuros (according to UNIFE 2012 for 2011),about 60% of the business amounts to vehicles,just over 30% to infrastructure and less than10% to system technology. The term infrastructureincludes the track system and electrificationwhere no computers are needed.System technology comprises traffic managementand train protection as well as informationtechnology, including passenger information,passenger safety and fare management.In all areas computers are of vital importance.What’s obvious in passenger information,which is customer-oriented to meet the usualconvenience and standard of living, has to beclarified for traffic management and train protection.Ever increasing speeds with more andmore dense traffic on the track and finally theharmonization of rail networks across countries(ERTMS, CRTMS, PTC) as well as the increasein safety and economic efficiency would beimpossible to achieve without powerful computerson the wayside and in the railwaycontrol center or in the central control room.This makes system technology the smallestbut fastest growing segment of the railwaymarket – not just in Asia, with a market shareof over 30%, but also in Western Europe (insecond place with almost 30%) and NorthAmerica/NAFTA (third place with nearly 20%).While UNIFE assumes that the entire worldwidemarket will annually grow by 2.0% to2.5% until 2015/16, it expects an annual growthof 6% for traffic management and train protection,and of 4% for information technology.Let’s go back to the vehicles, which take up almosttwo thirds of the global market volume.The average annual growth rates depend onthe vehicle type and country (and new acquisitionor maintenance) and are between 0 and4%. The biggest driving force behind this liesin equipping the vehicles with computers fortrain protection and control. Of course, thecomputers on board the vehicles fulfil manyother tasks, too. These include the control ofvital functions (e.g. drive, brake, power supply,tilting technology), safety management (doors,light, etc), and convenience functions (heating,air conditioning, etc) inside the vehicle.If you compare a computer inside a rail vehicleor in train protection with computers in otherembedded applications, you will see two strikingdifferences. On one hand, electronics for arailway-compliant control have to meet moresevere requirements with respect to robustness,reliability and availability, and demand correspondingprecautions and thorough knowledgein design, production, qualification and productcare. The EN 50155 standard defines rules regardingdifferent environmental impacts. Theoperating temperature is divided into twoclasses. Tx prescribes that the computer canbe operated between -40°C and +70°C, for example,and for 10 minutes even up to +85°C.The electronics in the system must be coatedby a special varnish for protection against humidityor condensation. It may also be necessaryto protect the housing against splashingwater. The standard also prescribes shock andvibration tests over a specific frequency range.In addition to common EMC inspections, thebehaviour in case of overvoltage is tested. Failure-freeoperation of electronics must be guaranteedeven with supply voltages between 70%and 125% of the nominal voltage. The basicmaterial for printed circuit boards is definedwith regard to flammability. Solder connectionsor other connections with insulation displacementare subject to the respective standards,and so on.Depending on the application, only parts ofthe EN 50155 standard need be observed, orelse all of its provisions. The European DINEN 50155 standard (German VDE 0115, internationalIEC 571-x) „Railway applications -Electronic equipment used on rolling stock“is issued by the European organization forelectro-technical standardization, CENELEC,and was first published in 1995. It is very de-May 2013 8