The Use of Programmable Logic Controllers in Railway Signaling Systems

Abstract

The railway computer signaling systems should be realized using devices fulfilling specific requirements: high level of reliability, verification to enter safety conditions (errors detecting and the proper reaction), modularity, possibility to link to the network, possibility to connect many railway external devices (train sensors, signaling lights, track occupancy control circuits), possibility to link the external railway infrastructure to different control devices, possibility of work in the severe exploitation conditions (temperature, dampness, vibration). Such requirements can be ensured by the use of Programmable Logic Controllers (PLC). Computer devices based on PLC controllers are small sized, and have great possibilities of controlling, testing, diagnostic, and self-diagnostic. This paper presents computerized railway signaling systems used in Poland, which operate based on modern PLC controllers. The railway signaling systems’ software consider different requirements and fit to local topographic conditions, according to the imposed high level of safety.