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Configuration maintenance functions include logical configuration, download and modification, operation debugging, remote diagnosis, etc.
In early stage, PLC was mainly ladder diagram, DCS was mainly module function diagram. After years of development, the International Electrotechnical Commission has stipulated five programming languages through iec1131-3 standard. At present, the mainstream DCS and PLC all show that they meet this standard and support several or all of them. Considering the development efficiency and program readability, the function diagram and sequence function diagram of modules are becoming the main programming methods. Trapezoidal logic and structured text have become the development tools of custom modules. Large PLC is more and more like DCS in configuration mode, and the gap is narrowing gradually, while small PLC is still based on ladder diagram.
After years of development, DCs has accumulated a large number of advanced algorithm modules. For example, the device level module of network6000+ has completed the basic control and fault alarm function of equipment oriented in a module. It has been transmitted by this module in network communication, which greatly improves the efficiency of software development. A device pole module is equivalent to 0.5K ladder logic. PLC needs to complete the same function, it is much more cumbersome.
PLC is generally a large floor frame, closed i/o module, closed structure is advantageous and improve the reliability of i/o module, anti RF, antistatic, anti-damage. The i/o points of PLC module are 8, 16 and 32.
DCS is mostly 19 inch standard case plus plug-in i/o module, i/o module is exposed structure. Each module has 8 and 16 i/o points, and rarely uses 32-point modules
This structure of DCS is mainly used in large control objects, and 19 inch standard case is easy to be densely arranged, and less i/o points are due to the requirement of dispersion. The large base frame of PLC, the closed module structure is more flexible in management and configuration, and the reliability of single equipment is higher. Therefore, many DCs also absorb the advantages of PLC in structure, and adopt similar packaging structure as PLC, such as i/a adopts metal shell and network-6000+ adopts conductive plastic shell.
In the early days, DCS, as a system, was a special device provided by DCs manufacturer. PLC manufacturers generally do not provide human-computer interaction devices, and they often use general monitoring software to complete them (such as iFIX, InTouch, Kingview). The integrated human-computer interaction device of DCs has the characteristics of professional function and good stability, but its price is also very high. With the rapid development of PC technology, some general monitoring software has developed rapidly, and the function and performance gradually exceed the special equipment provided by DCs manufacturers. Therefore, many DCS manufacturers have gradually abandoned the special human-computer interaction device, and also used the general monitoring software as PLC. DCS manufacturers use general monitoring software not simply assemble, but on the basis of general monitoring software, through cooperative development, the accumulated network communication technology and system self diagnosis technology have been retained and inherited in the form of special software package.
