International Railway Journal - October 2008 - (Page 39) Signalling Alister - a new direction in interlocking technology As the first generation of electronic interlocking becomes more difficult and costly to operate and maintain, Funkwerk Information Technologies has developed a new interlocking based on standard components that is claimed to be cheaper, more efficient, and flexible. Detlef Bahr, sales manager for signalling technology, outlines the philosophy of Alister. M OST signalling is performed by mechanical, electromechanical and relay interlockings which are reliable but costly to operate. In many cases these installations have already reached the end of their service lives, and in order to be able to offer a modern and attractive rail service, need comprehensive modernisation. However, proprietary specialised developments of electronic interlockings are not the answer here because the obsolescence of critical components becomes an increasingly crucial costdriving issue. Due to the rapid development cycles in the electronics industry, core elements of the first generation of electronic interlockings are no longer available. The lifetime of the electronic hardware proved to be much shorter than that of traditional interlockings, and as a consequence these proprietary solutions need continuous re-design, resulting in high life-cycle costs. To provide a more competitive solution, Funkwerk Information Technologies pursued a new approach based on standard industry components. The idea is to share the hardware basis with many more industrial applications. Standard programmable logic controllers (PLC) have been in use in large numbers and for long periods in industrial automation, including fail-safe applications, for many years. They have proved to be extremely safe, reliable and economical. This is why Funkwerk IT decided to use these standard components in all signalling applications. A fail-safe PLC provides the technological platform for the new electronic interlocking system called Alister. The first installation of this kind of SIL 4 interlocking system based on industrial standards is under development for the German Rail (DB) line between Kiel and Flensburg in An Alister interlocking work station. northern Germany. It is a single-track line with passing loops at stations and carries two to six trains an hour. Many such regional lines in Germany are controlled by rather old equipment which requires each station to be staffed: conventional electronic interlockings are too complex and expensive to be installed on such lines. The Alister interlocking has been developed for lines like these and is now being adapted for use in Germany. Man-machine interface The basic Alister concept consists of a man-machine interface with fail-safe indication including automatic route setting and train describer. It also has a vital interlocking kernel using fail-safe PLC (SIL 4). A local interlocking is installed in every station. The interlocking commands are transmitted to the trackside installations by safe Ethernet communications based on the standard Ethernet protocol. Trackside elements such as signals, axle counters, point machines and level crossings are triggered by standard input/output modules, in some cases using special adapter modules for customer-specific interfaces. An important feature of Alister is its decentralised structure with input/output modules located in the immediate vicinity of the trackside elements. In order to improve the operational efficiency, local interlockings can be operated and monitored from a regional control centre. During the development of Alister, Funkwerk IT decided in favour of a scalable design which meets the specific requirements of regional networks. Instead of a complex specialised solution, Alister offers a modern standard solution at a much lower cost. The electronic interlocking can be easily upgraded, re-organised and linked to any existing system. In addition, it is compact and easy to operate. Thanks to the modular concept of Alister, PLC upgrading, further development and replacement of components is easy. The biggest advantage is that any alterations to the hardware or software affect only single modules rather than the entire system. IRJ October 2008 39
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