An automatic control system in which multiple computers control multiple control loops in the production process, while allowing centralised access to data, centralised management and centralised control. Distributed control systems use microprocessors to control each loop separately, while small and medium-sized industrial control computers or high-performance microprocessors are used to implement the upper level of control. Information is exchanged between the circuits and between the upper and lower levels via high-speed data channels. Distributed control systems have functions such as data acquisition, direct digital control, human-machine interaction as well as monitoring and management. Distributed control systems are developed on the basis of computerised supervisory control systems, direct digital control systems and computerised multi-level control systems and are a more complete control and management system for production processes. In a distributed control system, microprocessors are installed near the measuring devices and control actuators by area, spreading the control functions as far as possible and concentrating the management functions relatively . This decentralised control method improves the reliability of the control and does not cause the whole system to lose control due to computer failure. In the event of a failure at the management level, the process control level (control loop) still has independent control capability and the failure of individual control loops does not affect the overall situation. Compared to computerised multi-stage control systems, distributed control systems are more flexible in structure, more rational in layout and less costly. 

The DCS is flexible and can be composed of dedicated management computer stations, operator stations, engineer stations, recording stations, field control stations and data acquisition stations, or general purpose servers, industrial control computers and programmable controllers.

The process control level at the bottom is generally achieved by decentralised on-site control stations, data acquisition stations and other local data acquisition and control, and is transmitted to the production monitoring level computer through the data communication network. The production monitoring level provides centralised operation and management of the data from the process control level, such as various optimisation calculations, statistical reports, fault diagnosis and display of alarms. With the development of computer technology, the DCS can be networked with higher performance computer equipment as required to achieve more advanced centralised management functions, such as planning and scheduling, storage management, energy management, etc.

Since the introduction of Honeywells first distributed control system, TDCS-2000, in 1975, distributed control systems have been widely used in various fields of industrial control, and have gradually become the mainstream system for automatic control in the process industry with its high reliability, convenient configuration software, rich control algorithms and open networking capabilities.

To date, hundreds of manufacturers around the world have developed more than 1,500 types of distributed control systems of various types. DCS is favoured by industrial users for its advanced, reliable, flexible and easy control as well as reasonable price, and is widely used in metallurgy, power, chemical, petroleum and paper industries.