The fast growth of communications and the demand for improved economics, efficiency and safety for railway traffic necessitates new technologies for their communication networks (Picture 1). Since 1997 32 European Railway Authorities have already committed themselves to the introduction of the digital communication network GSM-R. For this new mobile transmission system enclosures are required which will fulfil specific future demands of the railway and the prevailing environmental conditions.

Analogue and digital communications technology

Since 1982 Funkwerk AG in Kölleda, supplier of system solutions for the communications technology, develop and manufacture analogue railway technology, used by European railway systems The introduction of the digital transmission system GSM-R is leading to a generation change of the end equipment.

For this Funkwerk have developed and configured the modular GSM-R equipment range for the transmission of speech and data. They supply complete systems consisting of a user platform, speech equipment, electronic box and complete cabling and are ready for installation by the end user. The use of GSM-R for the ETCS (European Train Control System) and FFB (Funk-Fahr-Betrieb = transmission for train operation) enables the data transmission of the trains' steering and safety information as well as new transmission applications, such as the future extension of GPRS for the use of innovative data services.

Until the end of 2004 approx. 9,000 locomotives of the German Railways are scheduled to be equipped with these new end units to GSM-R standard (Picture 2). Supply contracts have already been signed with other European railway operators and concrete negotiations are underway to equip the railways with digital communication technology. In order to guarantee smooth running of the railways in the build up phase (including border-crossing traffic) the parallel operation of several networks is necessary. Apart from the new GSM-R units, dual mode train transmitters are used that operate in the analogue as well as in the digital network.

Packaging for GSM-R systems

During their selection of suitable packaging solutions for the GSM-R systems Funkwerk AG had to observe certain criteria. Because of the differing installation conditions for 9,000 locomotives the variety of the different enclosures needed for the GSM-R systems is almost insurmountable. And, of course, apart from demands for cooling, EMC and the need to be shock and vibration proof they had to fulfil all the railway specific guidelines and standards.

A most functional and flexible packaging solution was demanded. The supplier had to be flexible in order to react to the new requirements of the end user as quickly as possible and in a most unbureaucratic manner. The management at Funkwerk AG decided upon co-operation with Schroff and so far have not regretted this decision.

19" with and without enclosure

The system architecture of the final units contain universal and standardised interfaces and plug-in units, which are configured as 19" boards. The 19" plug-in technology guarantees easy and fast changeover of plug-in units and the possibility to use the plug-in units in all equipment variations or types.

Depending on environmental temperature and functionality the type of units was reduced to seven types at Funkwerk. Amongst these are systems which are integrated in different enclosures and solutions in subracks which themselves are installed in existing racks inside the locomotives. The GSM-R systems inside the enclosures as a rule are installed in the driver's cab of the locomotive. The use of Schroff's highly flexible conceptline cases and europacPRO subracks contributed largely to this type reduction.

Modular and flexible

With the modular europacPRO subrack different heights, widths and depths can be configured competitively and without great assembly effort from standard assembly parts . Expensive customised units as a rule are superfluous. The basic model consists of two side panels and four horizontal rails.

With the extensive range of accessories the user has the possibility to retrofit his subracks step by step, depending on demand. Especially in respect of EMC this is a great advantage, as it is often not determined at the beginning of the development of a product which degree of EMC shielding will be required for the application. For instance contact springs, which can be inserted between the individual assembly parts such as cover plates and side panels, or conductive textile shielding in the front panels of plug-in units, guarantee safe HF shielding. Guide rails as part of the standard range allow flexible arrangement of all board positions and also have some advantageous features such as the insulated board guidance, coding facility of 19" plug-in units, ESD clip for board guidance and board protection. The europacPRO is based on Al sheets and Al extrusions. As Schroff anodizes all front facing surfaces and chromates all rear surfaces, the user obtains not only scratch proof but also optically appealing surfaces. Thanks to the hard anodised coating they can be used without further surface treatment.

Mobile use and little space

The main demand on the enclosure solutions is optimum cooling and a compact assembly, which required little space. The temperature range of - 25 to + 55 °C therefore required a corresponding heat exchanger to be integrated on one side of the case. EMC shielding and good shock and vibration properties were tested by an independent laboratory.The mobile use in different rail vehicles puts high demands on the case and the installed electronic components. The reliable function of the systems has to be guaranteed.

The dimensions of the cases used were determined through the limited space available at the installation site and are based on the conceptline case range. The complete unit is delivered pre-assembled by Schroff (Picture 3). At Funkwerk the backplane, plug-in units and special railway specific power supplies are installed and connected.