Distributed control system

A distributed control system (DCS) is a control system used to control industrial processes in which control functions are distributed among multiple autonomous controllers like Programmable Logic Controller (PLC) connected by a communication network. These controllers are typically located near the process equipment or within plant control areas, while operator interfaces, supervisory control, alarm management, and process monitoring are commonly provided through centralised operator stations. This architecture contrasts with centralised control systems, in which control functions are performed primarily by a central controller or computer system. By distributing control functions across multiple controllers, a DCS can improve system availability, scalability, and fault isolation, while reducing the amount of dedicated point-to-point wiring required for large industrial processes.

DCS first emerged in large, high value, safety critical process industries, and were attractive because the DCS manufacturer would supply both the local control level and central supervisory equipment as an integrated package, thus reducing design integration risk. Today the functionality of supervisory control and data acquisition (SCADA) and DCS systems are very similar, but DCS tends to be used on large continuous process plants where high reliability and security is important, and the control room is not necessarily geographically remote. Many machine control systems exhibit similar properties as plant and process control systems do.

Structure

The key attribute of a DCS is its reliability due to the distribution of the control processing around nodes in the system. This mitigates a single processor failure. If a processor fails, it will only affect one section of the plant process, as opposed to a failure of a central computer which would affect the whole process.