Since PLC came into being, it has realized leap-type development from wiring logic to storage logic. Its function from weak arrive strong, carried out logic control to digital control. Applications become more and more widely, It made a leap from simple control for single equipment to various tasks such as motion control, process control, distributed control, etc. Nowadays PLC has greatly improved its capabilities in analog processing, digital operation, human-computer interface and networks, becoming an essential control equipment in industry control fields, developing a more and more big function in all walks of life.
......