Abstract
During 40 years safety relays have been the predominant technology in practical use for railway signalling systems with fail-safe demands. During the last two - three years computers have been introduced for vital functions. To fulfil fail-safe requirements different methods have been used to overcome the non-asymmetric fail-function of electronic components and systems. This paper will cover some different methods and evaluate them. As a result an approach to achieve a fail-safe computer system will be suggested. In a computer system for vital functions the information is processed twice by two independently designed and executed program versions in the same computer resulting in a safe and economic solution. The first LME computerbased interlocking plant is now being delivered and the experience of the development work is covered. Modern Automatic Train Control (ATC-) system is now equipped with microcomputers. Experience from development and field tests of an intermittent ATC-system is summarized. The two projects make it evident that general, standard computers can be used for fail-safe systems, if careful adaption of fail-safe design philosophy is maintained.
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