plc基础知识（Basic knowledge of PLC）.doc

plc基础知识（Basic knowledge of PLC） One, a brief introduction Over the years, programmable controller (PLC) has been developed from its generation to the present, which has realized the leap of logic to storage logic. Its function is from weak to strong, The progress of logic control to digital control is realized. The application field is small to large, which realizes the simple control of the single device to the competent motion control, the process control and the distribution control The crossing of a variety of tasks. Todays PLC has greatly improved its capabilities in handling analog, digital, human-computer interfaces and networks, becoming the dominant control device in industrial control. It is playing an increasingly important role in all walks of life. Second, the application domain of PLC At present, PLC has been widely used in various industries, such as steel, petroleum, chemical industry, electric power, building materials, machinery manufacturing, automobile, light spinning, transportation, environmental protection and cultural entertainment. The use cases are mainly divided into the following categories: 1. Control of switching volume logic The traditional relay circuit is replaced by logic control and sequence control, which can be used for the control of single equipment and multi-machine group control and automatic assembly line. Such as injection molding machine, printing press, Stapling machine, assembling machine tool, grinding machine, packing production line, plating pipeline, etc. 2. Industrial process control In the process of industrial production, there are some continuous changes such as temperature, pressure, flow rate, liquid level and speed (i.e., analog quantity). The PLC adopts the corresponding A/D and D/A conversion modules and various types The control algorithm is used to deal with the simulation and complete the closed loop control. PID adjustment is a kind of adjustment method used in general closed loop control system. Process