PROCESSOR BASED INTERLOCKING (Alstom)
Shortly after the invention of microprocessors in the early 1970's, GRS Research Engineers began investigating methods and techniques to harness this new technology for the vital fail-safe control of interlocking equipment. In 1975, they began developing a series of hardware and software techniques that permitted a single microprocessor to operate in a vital fail-safe system. This series of techniques was trademarked as GRS Safety Assurance Logic (SAL™). The first commercial product released using SAL techniques on a microprocessor merged with a vital relay was the MICROCHRON ® Timer in 1981. This vital timer was a direct replacement for a family of vital motor timers and was switch settable in one second increments from one second to one hour. This product has been enormously successful with more than 10,000 units shipped since its introduction.
GRS Research Engineers continued to build upon the concepts of SAL. In 1978, they brainstormed an approach to expanding these techniques into a general purpose application programmable interlocking control product. Utilizing mathematical principles from communication security and from cryptographic technologies, the engineers extended the SAL techniques to an enhanced set of techniques referred to as Numerically Integrated Safety Assurance Logic (NISAL ™). These techniques became the backbone of a major new product line known as the Vital Processor Interlocking (VPI ®) Control System. After extensive prototype testing at several North American and European test sites, the first in-revenue service installation of this product occurred in January, 1986 at the Clinton Interlocking plant in Chicago, Illinois on a Chicago & Northwestern Railway's freight and commuter rail line into the Northwestern Terminal.
In 1913, a brand new Grand Central Terminal in New York City opened for service utilizing the latest in state-of-the-art electric interlocking equipment from GRS. This largest of North American passenger terminals utilized this equipment until 1993 when the latest state-of-the-art processor based central control systems teamed with a geographically distributed system of 17 VPI Interlocking Control systems were placed in service as part of a major terminal refurbishment project. This terminal consists of 211 switches, 189 signals, and 295 track circuits and sees in excess of 700 electrified commuter trains per day, primarily during four hours of rush hour service.
VPI Systems have evolved in ability and sophistication. VPI systems may be configured and application programmed from a simple vital fail-safe interlocking control to a highly sophisticated, fully automatic driver-less
transit application with VPI in control of both the interlocking and the block-line functions. A single VPI system can be configured to control a simple remote holding signal or a single turn-out control point or up to a large interlocking of some 25-30 switch machines and related signals. Larger interlocking plants can be configured with a distributed arrangement of VPI systems.
As the company reaches the century mark, ALSTOM Signaling, Inc. (formerly General Railway Signal Company) has manufactured and deployed more than 1000 VPI systems for 54 different customers in 15 countries. These systems have accumulated more than 55,000,000 operating hours without a single reported safety incident.