An Example of PLC Fault Analysis

An example of covered fault of Siemens S5-115U PLC was analyzed and discussed in detail. The symptom 1, CPU of PLC started up slowly and data could not be transferred by network after running. The symptom 2, two output points in an I/O module of PLC were set immediately after starting up, and failed to be controlled logically. It was found that the PLC starting up slowly was caused by fault I/O module, which influenced the bus communication as well, while PLC was running, and led to wrong address. PLC could back to normal once the fault module was replaced. Some experiences about S5-115U PLC were obtained:the function of fault diagnosing was unperfect. An fault I/O module would influence the starting up of PLC, and might misfuction the starting up of CP1430, and it was not necessarily the I/O module where the symptoms emerged had problems. The communication configuration program of CP1430 could be stored in FLASH-RAM, or in RAM of CP1430, among others. Those experiences were good for maintenance.