Interlocking Hardware
SSI utilises a 2-out-of-3 redundancy architecture, whereby all safety-critical functions are performed in three separate processing lanes and the results voted upon. An SSI interlocking cubicle comprises three Interlocking Processors or Main Processor Modules (MPMs), two Panel Processors and a Diagnostics Processor (DMPM). An SSI system can operate on two MPMs in the event of the failure of one. It does not need the DMPM to function as an interlocking, as this drives the technician's terminal only.
Read more about this topic: Solid State Interlocking
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