Rail
Tailored HEITEC housing solution for a railway control unit
Karl Brand, Harrion AB, HEITEC AG representative in Scandinavia talks about how they built a custom housing solution for the signal controllers for a central computer unit in a railway application
Karl Brand T
here are strict regulations on applications in transportation technology. Ultimately, human lives
depend on a properly functioning railway control system, for example. As a safety- relevant element, it must function reliably and without interruption. This not only applies to its continuous functionality, but also to factors like resilience and maintenance-friendliness as well as its interaction with other parts in a regulated environment. For example, if maintenance or a repair is necessary, it must be possible to perform it quickly and easily. All the constituent parts employed – including the housing technology that accommodates the control electronics – play an important role in realising this objective. It was precisely for this application area that Bombardier – the world’s leading supplier of traction and control equipment for rail vehicles – needed a custom system platform for housing the signal controllers for a central computer unit in a railway application. The electronics business area of the Erlangen-based company HEITEC, designed and produced this platform using its expertise in electronics mounting systems. The system is installed either in containers near the rails or in a station’s signal room. The device is a typical wayside train monitoring system (WTMS). The function of the equipment electronics is to “scan” the signals and lamps on the line and analyse their significance. Based on this data, the electronics system sends a message (in this application, graphically
22 June 2017
called a “telegram”) to a specific balise in the rail bed. The telegram contains information about the state of the lamp signals and the distance to the next balise as well as information that can influence the train’s braking distance: for example, the line gradient. The balise in the track functions, in effect, is an information point that saves this data and transmits it to the computer of the approaching train like a transponder. The computer is monitored by the train driver. The essential requirements for the system and its housing depend on the environment. For example, interruption- free data communication and a very high level of protection against harsh ambient conditions such as moisture, dust, high temperatures, and vibration. Some of these factors were vital, because the system is deployed in the Australian desert where large variations in ambient conditions occur, and in some cases extreme temperature fluctuations need to be taken into account.
Because the application area is in a demanding environment, with massive external influences on the mechanical state, the housing system needed to meet certain normative requirements. Standard DIN EN 50125, for example, specifies the ambient conditions for equipment used in railway applications in Europe, and Section 3 of the standard explicitly outlines the ambient conditions for signal and
telecommunications equipment. The application area of this standard extends to the development and operation of stationary and mobile signalling and telecommunications equipment, including instruments used for testing, measurement, and display. The standard defines conditions for equipment in various environments, parameters for calculating reliability, availability, maintainability, and security (RAMS), and service life, factoring in the ambient conditions (source: VDE). A system like the one described here has already been in service for about 25 years; it must remain reliably operational throughout a temperature of from -40° to +70°C. In addition to these framework conditions, specific implementation criteria were also essential for realising the project. One requirement was rapid handling. It only took a few weeks from the preparation of the first drawing through development of the prototype to the test phase, thanks to the service synergies at
Components in Electronics
HEITEC’s centre of competence. The company also focused on a very good price/performance ratio, which was achieved thanks to the optimised design and availability of standard components. A low-cost but robust aluminium housing provided the outer cover, while the interior fixtures of the housing HEITEC used HeiPac Vario module rack elements. The HeiPac Vario series is the most versatile 19” module rack family in the portfolio, allowing the most complex potential applications to be implemented using many size variants and accessories. The aluminium module racks are obtainable in various 19” heights, such as 3HU or 6HU, are designed for card formats up to 220 mm in depth, and are adaptable to the architecture required in each case. Special requirements for the front panel, cable ducts, power supply, and other components are easy to manage, thanks to the framework’s modularity. The product line is also tested for vibration and shock in accordance with IEC 600-68-2-6 test Fc and IEC 600-68-2- 27 test EA; although vibration damping is not a prerequisite because the application is not on board a train. The directive for electromagnetic compatibility 89/336/EEC/EN55011:1998/A1:1999 Group 1, Class A (since April 2016 Directive 2014/30/EU), was derived from a previous system. The housing provides maximum space combined with cable routing matched with absolute precision to the customer’s application. Thanks to the optimised design, additional machining operations like drilling apertures for the cable glands in the cover plate can be performed at low cost. The cover connections are sealed to prevent dust penetration and corrosion. Strong PG screw connections were used for the fixed cable glands. The complex cabling is routed
from a central point in the housing, with the cables connected securely and clearly by means of advanced screwless and compact Wago terminal blocks.
Another important point was corrosion
protection. The aluminium housing was painted and provided with protection Class IP-54 against dust and spray to prevent corrosion. All circuit boards have protective lacquering. Great attention was also paid to ensuring that there is no exposed copper in the housing: in other words, the finish on the circuit boards prevents oxidation and increases reliability. With respect to the design of the front, the only condition Bombardier specified was a robust, transparent, industrial-grade front panel. For the choice of material, HEITEC opted for Makrolon, a form of highly durable thermoplastic polycarbonate notable for its great strength and resistance to water, oil, oxidation, and mechanical forces, as well as its good insulating properties.
Summary
Designers and manufacturers of housing systems for critical electronics applications in railway engineering need to gear up to the extremely high requirements of this market and comply with numerous standards. A precertified system family like Heipac Vario Mobil is recommended for this requirement.
HEITEC was able to provide a technically
efficient, low-cost, and – most importantly – a fast solution to meet Bombardier’s specific requirements for the format and number of cards needed as well as the stability and standardisation of the WTMS mechanism. The modular concept provides maximum options, robustness, and reliability at a minimum expenditure with a simple adaptation.
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