In the early phase of PLC development, it was mainly used for the logical control of the switching value. With the further development of PLC technology, its application areas are expanding. It can beused and collected and saved not only for switching control, but also for analog and digital control. Data, networking, communication, etc. Today, the PLC has become one of the core components of industrial control. The main advantages are perfect functions, high stability, strong interference suppression capability,good scalability, simple hardware maintenance and simple programming. The downside is that the price is higher and the volume is larger.