The PLC system can query the operation data in real time and monitor the on-site operation status of the crane. It can start and stop the motor and set the operating frequency through the human-machine interface in the control room, so as to improve the speed control system of the traditional crane and improve its safety and controllability. . There are many types of PLC, which can be divided into small PIC control, medium PLC control and small PLC control according to the control scale, and the control scale is divided according to the number of DO points configured. At the same time, the corresponding PC function is determined to a certain extent by the number of LO points. Accordingly, large-scale port machinery usually adopts large-scale PLC, while small-scale PLC is mainly suitable for ordinary cranes.