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Use the most simple based on difference between DCS and PLC and application -

by:Coolmay     2020-07-01

the topic of DCS and PLC in the industry has been discussed for at least 40 years, to understand what everybody in the debate, instrument man have to find out the difference between DCS and PLC, objective understanding these fundamental differences, according to the requirements of product and rational choice and application of DCS and PLC controller.

1, DCS is focused on the overall control system, PLC and focus on the local logic control is this why? Who is this provide? Why so divided? This is because the DCS from analog meter, give priority to with analog. DCS lay particular stress on the process control can realize the PID, feedforward, cascade, multistage and selective control of complex control, emphasis on the accuracy of continuous process control; PLC was developed electrical relays, give priority to with digital quantity, PLC controller for general industrial control field, strong commonality. General PLC only PID function, its as DCS control precision is high.

2, DCS and PLC of the differences in communication of DCS adopt the internationally used TCP/IP protocol, which is what we call the Internet interface, has good versatility and expansibility; And the PLC communication is multifarious, 如PPI,网络设备,网络通讯协议,现场总线,USB等) , often want to randomly after PLC setup the increase and decrease of operator station are more difficult. On the network security, Internet domain concentrated a large number of technical personnel in the work in the network security, PLC communication security has no good protection. DCS with overall consideration, operator station also have engineers station function, running between station and station plan program is a joint partnership after bottoms, each station, each kind of function, each kind of charged are interlock control devices, control and coordination; And composed of PLC connected system, the loose connection between PLC and PLC, couldn't do the coordination control function.

4, DCS and PLC on the points of difference between DCS points to many, generally above 500; PLC points less, usually at around $100, more than 500 basic did not use by all can be connected with the PLC control system, PLC system cost will be high. In DCS updated control scheme, the engineer in the engineer station will be compiled control scheme bottoms command, bottoms program is accomplished by the system automatically, do not affect the original control system running. Change control of PLC program, you first need to clear what is a PLC, the program compiled by the compiler to the corresponding PLC controller, debugging time cost is high, is not conducive to maintenance in the future.

5, the differences between the software DCS system has powerful software package that can be targeted according to the requirements development process parameters configuration and control algorithm software, with functions of formula, DCS convenient than PLC application software. Industrial site selection of the DCS and PLC? Recommend that mainly depends on the selection of investment and use in what place. Such as boiler burner logic control and protection with PLC suitable than DCS, and some, such as the steam turbine regulating system has many analog probe, DCS is more appropriate, don't blindly worship of DCS and ignoring the PLC!


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