086348-001 ABB 控制器模块

In terms of the scale of the application object.

PLC is generally used in small automatic control places, such as the control of equipment or a small amount of analog control and interlocking, and large applications are generally DCS. Of course, this concept is not very accurate, but very intuitive, we used to put more than 600 points of the system called DCS, less than this scale called PLC. Our heat pump and QCS, horizontal product matching control system is generally called PLC.

Said so much PLC and DCS difference, but we should realize that PLC and DCS development to today, in fact are close to each other, strictly speaking, now PLC and DCS has not been able to cut, many times between the concept has been fuzzy. Now, let's talk about the similarities.

In terms of function.

PLC has the analog quantity Control function, some PLC system analog quantity processing capacity is even quite powerful, such as Siemens S7 400, AB Control Logix and Schneider Quantum system. DCS also has quite strong logic processing capacity. For example, we have realized all possible process interlocking and equipment linkage start and stop on AC800F.

In terms of system structure.

PLC and DCS basic structure is the same. PLC development to today, has been fully transplanted to the computer system control, the traditional programmer has been eliminated. Small application of PLC generally use touch screen, large-scale application of PLC comprehensive use of computer system. Like DCS, the controller and IO station use the field bus (generally based on RS485 or RS232 asynchronous serial port communication protocol bus), if there is no expansion requirements between the controller and the computer, that is to say, only the use of a computer, will also use the bus communication. But if there is more than one computer use, the system structure will be the same as DCS, the upper computer platform using Ethernet structure. This is one of the reasons why the concept of PLC and DCS is fuzzy after large scale.