PLC和DCS控制系统有何区别
01
The origin is different.
PLC is born for discrete sequential control. We first developed a generation of programmable controllers using relay control devices. With the development of integrated circuit technology and computer technology, there are now five generations of PLC products.
DCS was born for continuous process control. It is based on microcomputer processing, characterized by decentralized risk control and centralized business management, integrating new computer technology, communication technology, CRT technology, and control technology, namely 4C technology, a new control system. The concept of DCS system is “decentralized control” and “centralized management”, which is an automated control system.
02
Different application fields.
In terms of process control, PLC is applied in fields such as aerospace, steel, tobacco, pharmaceuticals, food, metallurgy, mining, water treatment, transportation, etc.
DCS is mainly used for process control and is applied in automation fields such as power generation, petrochemicals, steel, petrochemicals, and metallurgy. Among them, the main control units of aerospace, thermal power, nuclear power, large-scale petrochemicals, steel, etc. currently need to use DCS for control.
03
The environment is different.
PLC is generally used in environments with few points and large switch quantities.
DCS is applied to large-scale continuous control environments with multiple points.
04
Database and programming language are different.
PLC has two databases, upper and lower, mainly used for sequential control, using logical variables for judgment and output. The lower computer adopts ladder diagram programming, and the upper computer uses SCADA as the control interface for the upper computer data acquisition and monitoring system.
A unified database for DCS upper and lower levels, with lower level functional blocks as programming tools. The upper level has its own independent visual control system control interface.
05
The control methods are different.
In terms of processing IO signals, PLC manufacturers are accustomed to converting all signals into digital quantities for processing.
In terms of processing IO signals, DCS manufacturers are accustomed to converting all signals into analog quantities.
06
The redundancy methods are different.
The hardware dual machine hot standby redundancy mode of PLC is dual rack, dual power supply, dual processor, and dual network card redundancy mode, which is equivalent to two sets of hardware equipment redundancy.
DCS is a dual machine hot standby redundant architecture composed of two integrated DPUs.
07
Different advantages.
The cost advantage of PLC small-scale systems makes them more advantageous in small and medium-sized discrete control work.
DCS is more like a packaged system, and using corresponding modules can facilitate system configuration and expansion horizontally. DCS provides better convenience and protection, and cannot be used in SIS/ESD systems.