System Name
The term “distributed control system” was derived by translating the product names of foreign companies. Due to the numerous manufacturers and varying system designs, each system has its own unique features in terms of functions and characteristics. Therefore, the naming of the products also varies. In China, there are different names used during translation, the most common ones being distributed control system (distributed control system, DCS), total distributed control system (total distributed control system, TDCS), and distributed computer control system (distributed computer control system, DCCS). [6]
The differences in names merely reflect the differences in naming intentions and translation, while the essence of the system remains the same and the underlying meaning is consistent. The Chinese power industry commonly refers to it as a distributed control system. [6]
System Interpretation
DCS typically adopts a hierarchical structure, with each level consisting of several subsystems. Each subsystem achieves specific limited goals, forming a pyramid structure. Reliability is the lifeblood of DCS development, and to ensure high reliability of DCS, there are three main measures: first, widely applying highly reliable hardware equipment and production processes; second, widely adopting redundancy technology; third, extensively implementing fault-tolerant technology, self-diagnosis, and automatic processing techniques in software design. Currently, the MTBF of most distributed control systems can reach tens of thousands or even hundreds of thousands of hours.
A distributed control system is a system with multiple physical and logical resources (multiple computers or processing units, multiple data sources, multiple instruction sources and programs) distributed, using a certain network or communication network for resource interconnection, with high local resource autonomy ability, mutual cooperation ability among resources, and overall coordination and control ability of resources. It can achieve dynamic management and allocation of distributed resources, parallel operation of distributed programs, and computer network control systems with decentralized functions. The meaning of the distributed control system mainly focuses on “dispersion”, and the meaning of “dispersion” includes several aspects. [6]
Dispersed Configuration
The geographical locations of each controlled device are dispersed, and the corresponding system control equipment is also configured in a dispersed manner. Multiple microprocessor-based distributed control units respectively undertake different control tasks. [6]
Function Dispersion
The functions of the distributed control system are not concentrated in the central control unit. Instead, they are distributed among various dispersed control units; moreover, the data acquisition, process control, operation display, monitoring operation, self-tuning, etc. of the control system are also decentralized and relatively independent. [6]
Display Dispersion
The display function of the distributed control system can not only be concentratedly presented on the central operation station, but also be dispersed to local operation stations. The central operation station has the ability to display all information of any dispersed process point in the entire system, and can be displayed on different display terminals; the local operation station can not only display on-site information through the on-site control unit at any time, but also the third and fourth generation distributed control systems can call information from other local operation stations or the central operation station at any local operation station for decentralized display. [6]
Database Dispersion
Modern distributed control systems mostly adopt distributed database systems, with local databases set up in the field control units and control stations, and shared by the entire system. [6]
Communication Dispersion
The distributed control system adopts local network communication technology. Each process unit in the network has equal communication control rights and can achieve decentralized communication. [6]
Power Supply Dispersion
The distributed control system provides independent power supply devices for different control units, enabling the distribution of system power supply and improving the reliability of the system. [6]
Load Dispersion In the distributed control system, the overall tasks are reasonably distributed to each control unit. One control unit only assumes the control tasks of several local control loops or subsystems. The workload of the entire system is distributed, and the load of each control unit is basically uniform. [6]
Distributed Hazards
“The implementation of ‘distributing'” means that the hazards of the entire system are distributed.