Distributed control system is a specially designed control system for controlling complex, large and geographically distributed applications in industrial processes. Here, controllers are distributed throughout the plant area.

These distributed controllers are connected to field devices and operation PCs through high-speed communication network, as shown in the figure.

The discrete field devices (such as sensors and actuators) are directly connected to the input and output controller modules through the communication bus. These field devices or intelligent instruments can communicate with PLC or other controllers, and interact with real-world parameters such as temperature and pressure.

The controller is geographically distributed in each part of the control area and connected to the operation and engineering stations for data monitoring, data recording, alarm and control purposes through another high-speed communication bus.