With the extensive application of PLC in industrial production, its reliability and stability problems become more prominent, and people's requirements for the whole system become higher and higher. On the one hand, people want the control system composed of PLC to have as few faults as possible; On the other hand, I hope that once the system breaks down, Jane can break the fault part as soon as possible and repair it as soon as possible, so that the system can work again. In order to find out the fault part of the system as soon as possible, the faults can be roughly classified as follows: