|2011 - July - Allan - The Application of Distributed Architectures on Vital Interlocking Systems|
Dwayne Allan B Eng (Hons), PGradCert (Railway Signalling), AMIRSE, MIEAust, CPEng
Distributed control systems have their heritage in manufacturing, process or other forms of dynamic systems in which the control of sub-systems is distributed throughout the system but controlled by one or more programmable logic controllers (PLC's) in a central location. This philosophy is often applied in process environments with equivalent SIL requirements to railway signalling systems.
This paper will outline the use of distributed architectures in a railway signalling context, in particular the system flexibility and resultant changes in system design and requisite cost implications for railway authorities when used as vital interlocking systems. Sample system layouts using traditional and distributed architectures will be reviewed as well as the benefits and limitations of the each system application.
The advancements in PLC technology its application in safety-critical systems will be reviewed. The open data communications functionality and the streamlined programming techniques used as part of industrial automation applications will be outlined. How these advancements and techniques are used in a railway signalling interlocking application will also be discussed. In particular, the use of function blocks and function calls to create a library of signalling principles will be addressed.
An overview of the significant benefits of applying industrial automation philosophies to railway signaling projects will be provided. The impact of these benefits on the Total cost of Ownership of distributed architecture systems using industrial automation technology will also be discussed.