What Is a Distributed Control System?

Distributed control system (Distributed Control System, DCS), also known as distributed control system, is a computer control system for centralized management and distributed control of the production process. ^[1]

Distributed control system (Distributed Control System, DCS), also known as distributed control system, is a computer control system for centralized management and decentralized control of the production process. With the continuous improvement of modern large-scale industrial production automation level and the increasingly complex process control requirements An integrated control system came into being, which integrated computer technology,

The development of distributed control systems is divided into four stages:

In the first stage (1975-1980), representative products mainly include TDC2000 from Honeywell, Network90 from ABB Baily, Spectrum from Foxboro, and Centum from Yokogawa, Japan. It is mainly composed of process control unit (PCU), data acquisition device (DAU), CRT operation station, monitoring computer and data highway (HW).

The second stage (1980-1985), the main representative products are Honeywell's TDC3000, Japan's Yokogawa's Centum A, B, D and so on. It is mainly composed of local network LAN (IEEE 802.4 and ISO 8802/4 communication standards), multi-function controller (MC), enhanced operating station EOS, universal operating station US, internet connector GW, system management module SMM, and host computer HC composition.

The third stage (1985-1990), DCS

The distributed control system is generally divided into three layers: the process control layer, the production monitoring layer, and the centralized management layer. The process control layer at the bottom is generally implemented by decentralized field control stations, data collection stations, etc. on the spot, and transmitted to the production monitoring layer computer through the data communication network. The production monitoring layer performs centralized operation management on the data from the process control layer, such as various optimization calculations, statistical reports, fault diagnosis, and display alarms. With the development of computer technology, DCS can implement higher-level centralized management functions such as scheduling,

Distributed control system is developed on the basis of computer supervisory control system, direct digital control system and computer multi-level control system. It is a relatively complete control and management system in the production process. Has the following characteristics:

(1) High Reliability Because DCS distributes the system control functions on each computer and the system structure adopts fault-tolerant design, the failure of one computer will not cause the loss of other functions of the system. In addition, because each computer in the system has a relatively simple task, a dedicated computer with a specific structure and software can be used for the functions that need to be implemented, so that the reliability of each computer in the system is also improved.

(2) Open DCS adopts open, standardized, modular, and serialized design. Each computer in the system uses local area network to communicate and realize information transmission. When you need to change or expand the system functions, you can easily add the new computer to the system communication network or remove it from the network, which will hardly affect the work of other computers in the system.

(3) Flexibility Software and hardware configuration according to different process application objects through configuration software, that is, to determine the measurement and control signals and the connection relationship between each other, select the applicable control law from the control algorithm library, and call the basic graphic composition from the graphics library Various monitoring and alarm screens are required, so as to easily constitute the required control system.

(4) Easy to maintain. A single small or micro-dedicated computer with simple and convenient maintenance features. When a certain part or a certain computer fails, it can be replaced online without affecting the operation of the entire system to quickly eliminate the fault. .

(5) Coordination Each workstation transmits various data through the communication network, the entire system information is shared, and the work is coordinated to complete the overall function and optimization of the control system.

(6) Complete control functions. Rich control algorithms, integrating continuous control, sequence control and batch processing control, can achieve advanced control such as cascade, feedforward, decoupling, adaptive and predictive control, and can easily add required Special control algorithm. ^[3]