PLC
Programmable Logic Controller
An industrial digital controller used to automate, monitor and control railway equipment and processes using programmed logic and field input/output signals.
Detailed explanation
A Programmable Logic Controller (PLC) is a robust industrial computer designed to monitor inputs, execute programmed control logic and operate outputs connected to equipment and machinery.
PLCs receive information from field devices such as sensors, switches, relays, detectors and measuring instruments. The programmed logic processes these inputs and generates commands to equipment such as motors, pumps, fans, valves, contactors and other controlled devices.
In railway infrastructure, PLCs are widely used within station and tunnel mechanical and electrical systems, ventilation systems, pumping and drainage systems, traction power facilities, depots and other automated infrastructure.
PLCs may operate equipment locally while communicating status, alarms and measurements to higher-level systems such as Supervisory Control and Data Acquisition (SCADA) or Building Management Systems (BMS). They may also receive supervisory commands from these systems.
Depending on the application, PLC architectures can include redundant processors, distributed input/output modules, communication networks and fail-safe features to achieve the required availability and reliability.
Where PLCs perform safety-related functions, appropriate safety PLC architectures and safety integrity requirements must be applied rather than relying on a standard industrial PLC.
Railway applications
mainline, high_speed, metro, light_rail, freight, depot
Standards and references
IEC 61131 series; IEC 61508 where applicable to functional safety; IEC 62443 series for industrial automation and control system cybersecurity