WESTLOCK Interlocking is a Solid State Interlocking

Solid State Interlocking

Solid State Interlocking 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.- Interlocking hardware :...

 (SSI) product by Westinghouse Rail Systems

Westinghouse Rail Systems

Westinghouse Rail Systems Ltd is a British supplier of railway signalling and control equipment to the rail industry worldwide. Its head office is in Chippenham, Wiltshire, where it manufactures a variety of mechanical and electrical/electronic railway signalling equipment...

.

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

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

. This includes re-use of SSI's programming language

Programming language

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

 and its external 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

Leamington Spa

Royal Leamington Spa, commonly known as Leamington Spa or Leamington or Leam to locals, is a spa town in central Warwickshire, England. Formerly known as Leamington Priors, its expansion began following the popularisation of the medicinal qualities of its water by Dr Kerr in 1784, and by Dr Lambe...

 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

Life-critical system

A life-critical system or safety-critical system is a system whose failure ormalfunction may result in:* death or serious injury to people, or* loss or severe damage to equipment or* environmental harm....

 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

Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

 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.