According to the different functions of PLC, PLC can be divided into three categories: low-grade, middle-grade and high-grade.

1, a low-grade PLC, has basic functions such as logic operation, timing, counting, shifting, self-diagnosis and monitoring. , some also have a small number of analog input/output, arithmetic operation, data transmission and comparison, communication and other functions. Low-grade PLC is mainly used in single-machine control system with logic control, sequence control or a small amount of analog control.

2. In addition to the functions of low-grade PLC, mid-grade PLC also has powerful functions such as analog input/output, arithmetic operation, data transmission and comparison, number system conversion, remote I/O, subroutine, communication networking and so on, and some of them also have functions such as interrupt control and PID control. Mid-range PIQ is suitable for more complex control systems.

3. High-grade PLC, in addition to the functions of mid-range computer, has added special functions such as signed arithmetic operation, matrix operation, bit logic operation, square root operation, tabulation, table transmission and so on. High-grade PLC has powerful communication networking function, which is generally used for large-scale process control or forming a distributed network control system to realize factory control automation.

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Matters needing attention in using plc:

The circuit between power supplies with incorrect grounding points may generate destructive current, thus damaging the equipment.

The grounding requirements of PLC system are strict. It is better to have an independent dedicated grounding system, and at the same time, we should pay attention to the reliable grounding of other equipment related to PLC. When multiple circuit grounding points are connected together, unexpected current will be generated, which will lead to logic errors or damage the circuit.

The reason of different grounding potentials is usually that the grounding points are too far apart in the physical area. When distant devices are connected by communication cables or sensors, the current between the cable and the ground will flow through the whole circuit. Even in a short distance, the load current of large equipment can change between it and the ground potential, and it can also directly generate unpredictable current through electromagnetic action.

Baidu encyclopedia -PLC