Solid State Interlocking

Solid State Interlocking (SSI) is the brand name of the first generation processor-based interlocking developed in the 1980s by British Rail's Research Division, GEC-General Signal and Westinghouse Signals Ltd in the UK. It was a forerunner to the modern computer-based interlocking (CBI) systems in widespread use today.

Solid State Interlocking (SSI) is the brand name of the first generation processor-based interlocking developed in the 1980s by British Rail's Research Division, GEC-General Signal and Westinghouse Signals Ltd in the UK. It was a forerunner to the modern computer-based interlocking (CBI) systems in widespread use today. ==Technology== ==History== Throughout much of the 20th century, early signal boxes that were typically manually-operated and limited to line-of-sign operations were being progressively replaced by larger power signal boxes, which made extensive use of electromechanically-operated relays that required sizable equipment rooms and frequent servicing. During the 1970s, these relays, which were relatively labour-intensive to produce as well as being expensive to maintain, were anticipated to rise in both cost and difficulty to procure as the wider electronics industry was in the process of transitioning to solid-state electronics. By the late 1970s, it was becoming apparent that a software processor-based system could have the potential to succeed relay based interlockings. Accordingly, a team at British Rail Research Division begun in-depth work into the prospective replacement of BR's existing electromechanical relay-based interlocks by electronic SSI. The benefits of such a scheme included achieving greater levels of both reliability and speed while also reducing space and wiring requirements. During 1980, three reports produced by a SSI working group were published; these detailed the planned pilot scheme, the safety impact, and the new technology's effects. It was determined that introducing SSI offered savings in three key areas – interlocking equipment, line circuits, and panel circuits; furthermore, that the correct safety techniques would provide an adequate safety level in principle, which had been developed from experiences gained with other microprocessor systems that were then being introduced to the market. It was decided to base SSI around a second-sourced microprocessor that was a widely used industrial standard at that time, and was amply supported with software development aids. A key target for the development of SSI was to achieve a cost saving of 15 percent in comparison to traditional relay interlocks. Another key objective was to avoid any changes to the view of the signalling system to both operators and drivers alike. Development of SSI was delivered under a tripartite agreement between British Rail, GEC General Signal, and Westinghouse Signals. The BR team were responsible for much of the work behind the design and development of both the hardware and software, including the scheme design language, data transmission system, trackside interfaces, safety validation, and overall project management; GEC and Westinghouse's principal task was to produce the fully-engineering production equipment. The majority of the interlocking software was written by a single individual. Achieving appropriate production standardisation and approval for general use proved to be a time-consuming process. During the 1990s, various upgrades and improvements to SSI were mooted. However, these ambitions were heavily disrupted by the privatisation of British Rail and the dismantling of BR's research division. The short-lived privately-owned infrastructure company Railtrack was alleged to have been unsupportive of further SSI deployments, opting to favour computer-based interlocking (CBI) systems for its major signal renewals instead. During the 21st century, several third party companies have developed and offered their own enhancements to SSI; these have included new graphical user interfaces, diagnostic tools, safety verification technologies and expanded compatibility with fibreoptic links. ==References== ===Citations=== ===Bibliography===

Text derived from https://en.wikipedia.org/w/index.php?oldid=1378629345 under CC BY-SA 4.0; modifications have been made.