P0917MF FOXBORO
describe
Examining the hierarchical structure of DCS, the DCS level and control management level are the two most basic components that make up DCS. The process control level specifically implements decentralized control functions such as signal input, transformation, operation, and output. In different DCS, the control devices at the process control level are different, such as process control units, on-site control stations, process interface units, etc., but their structural forms are roughly the same and can be collectively referred to as on-site control units (FCUs).
DCS is a “decentralized control system”, while PLC (programmable logic controller) is just a control “device”, the difference between “system” and “device”. The system can achieve the functions and coordination of any device, while the PLC device only implements the functions that this unit has.
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In terms of network, DCS network is the central nervous system of the entire system, which is a safe and reliable dual redundant high-speed communication network, and the system has better scalability and openness. However, PLC, as it mostly works as an individual, adopts a single network structure when communicating with other PLCs or upper computers, and the network protocol often does not comply with international standards. In terms of network security, PLC does not have good protection measures, so we adopt dual redundancy of power supply, CPU, and network
CS considers the overall plan, and the operator station has the function of an engineer station. After the installation of the operation plan program, there is a close joint relationship between stations. Any station, any function, and any controlled device are interlocked and controlled in a coordinated manner; The system composed solely of PLC interconnections has a loose connection between stations (PLC and PLC), which cannot achieve coordinated control functions.
