The REPOINT fault-tolerant switch

‘Repoint Light’ is the development name for a novel POE (Points Operating Equipment) concept currently under development by Loughborough University, assisted by a range of industrial partners/stakeholders. The concept involves lifting the switch rails out of a positive register before traversing them, providing for ‘passive locking’ at each actuation location and enabling, for the first time, functional redundancy of point machines. The design also features line-replaceable, ‘hot swappable’ maintenance elements. Functional redundancy and hot-swaps are not new to the signalling infrastructure, a successful and widely adopted example being SSI. Repoint is the first application of these principles to POE. The project goal is to achieve TRL7 (demonstration in a railway environment) for a points actuation, locking and detection solution capable of attaining RAMS performance far in excess of any solution currently on the market. The technical development of the prototype is well underway and the signalling-related elements of this development are described in this paper. It is a non-trivial task to combine functionally redundant motor controllers and detection voting with the safety-critical command and detection circuits of the interlocking. Inspiration has been sought both from the architecture of SSI and approaches to safety critical sensing from the aerospace industry, in order to engineer a solution which satisfies all requirements. This paper justifies the use of functional redundancy and describes the proposed architecture for combining multi-channel actuation and detection elements into a single-channel interlocking.