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The basic idea of distributed control is centralized management and decentralized control. That is, the process of automatic control in process industry is separated from the management process of the operation management personnel; The automatic control process of process industry is completed by each control station relatively independently, while the management of the automatic control process by the operator is completed by the operation station in the central control room. On the one hand, the central operation station and each field control station operate independently, which limits the faults in the local scope, greatly improving the overall safety and reliability of the automatic control system; On the other hand, real-time data communication and information exchange are carried out with each other, which realizes the operation personnel to manage and adjust the whole automatic control process in the operation station of central control room.

The main task of the field control station is to realize the automatic control of the production process. Therefore, it must be able to automatically collect the production information of various process parameters (such as temperature, pressure, flow, viscosity, component, level height, etc.) of all process media, as well as the operation status of the equipment (such as valve opening, pump start and stop, equipment vibration, mechanical displacement), Then, a lot of numerical calculation is carried out according to the control program programmed in advance. Finally, the standard analog signal (or on/off) is output to drive various valve, motor and other actuators, adjust various process parameters, and realize the automatic control of production process; In addition, it also communicates with the operation station in real time, transmits all kinds of production information collected to the operation station for the operator to use, and receives the instructions issued by the operator through the operation station to adjust the automatic control scheme in real time and optimize the production process. Therefore, it also needs to have standardized communication interface. At present, all kinds of PLC have such functions, and its capacity is flexible, easy to expand, the configuration of control scheme is simple and easy to learn, and the better the performance price ratio is, so it is the ideal choice for small and medium DCS operating stations.