WESTLOCK Interlocking is a

Computer-based Interlocking Computer-based interlocking is railway signal interlocking implemented with computers, rather than using older technologies such as relays or mechanics. General CBIs are mostly implemented in two parts; a section that implements the safety and ...

(CBI) product now sold and maintained by Siemens Mobility Limited, following their purchase of

Westinghouse Rail Systems Westinghouse Rail Systems Ltd (formerly ''Westinghouse Signals Ltd'') was a British supplier of railway signalling and control equipment to the rail industry worldwide. Its head office was in Chippenham, Wiltshire, where it manufactured a varie ...

. Westlock builds on many of the features that made SSI popular in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

. This includes re-use of SSI's

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming ...

and its track-side hardware. In addition to backwards compatibility with SSI, Westlock provides additional capacity. This is currently estimated to be around four times that of an SSI, giving it the capability to control over 300 Signalling Equivalent Units (SEUs). Leamington Spa was the test site for Westlock, and was its first operational site. It was also SSI's test site more than 20 years earlier.

Hardware

A Westlock system is divided into a number of components, called the Central Interlocking Processor (CIP), Trackside Interface (TIF) and Technicians Workstation (TW). The hardware used by the TIF and CIP is similar, based around a 2-out-of-3 architecture, whereby all

safety-critical A safety-critical system (SCS) or life-critical system is a system whose failure or malfunction may result in one (or more) of the following outcomes: * death or serious injury to people * loss or severe damage to equipment/property * environme ...

functions are performed in three separate processing lanes and the results voted upon. This provides some fault tolerance whereby a single module can fail and the system can continue operating in 2-out-of-2 mode.

Central Interlocking Processor (CIP)

A CIP consists of 3 main processor modules which perform the safety-critical interlocking functionality. In addition it possesses two communications modules which provide redundant

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...

connectivity (duplicated for availability) and two digital input modules (duplicated for availability) which can service up to 32 local inputs.

Trackside Interface (TIF)

A TIF also contains 3 main processor modules and two Ethernet communications modules, but additionally has two SSI communications modules, which are used to interface to an SSI compatible data links. The TIF itself does not perform any interlocking functionality, it operates only as a protocol converter.

Technicians Workstation (TW)

The TW is provided to diagnose faults in the track-side equipment and also within the Westlock equipment. It provides a graphic interface which includes a map of the area of Railway under control and operates on an industrial PC platform.

References

* * {{railwaysignalling Railway signalling control Interlocking systems