P0904HA FOXBORO

P0904HA FOXBORO

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.

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.

Hardware Architecture

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 security: To ensure the safety and reliability of the equipment controlled by DCS, DCS adopts dual redundant control units. When important control units fail, relevant redundant units will switch to working units in real-time without disturbance, ensuring the safety and reliability of the entire system. The system connected by PLC has basically no concept of redundancy, let alone redundant control strategies. Especially when one of its PLC units malfunctions, the entire system has to be stopped before replacement and maintenance can be carried out and reprogramming is required. So the DCS system has a higher level of safety and reliability than PLC.