PLC Communication Fault Diagnosis
At about 11 pm, the driller was pulling out of the hole. Suddenly, the winch stopped, all the indicators on the control box in the driller's room went out, and the driller reported that the system could not be used. Rushed to the driller's room in time to check. It was found that the et200 communication module of the driller's room control box reported a red light fault, but the power supply of the power module was normal. According to the fault phenomenon, it was judged that it should be the communication fault of the PLC system. Immediately go to the control room to check the cup status. The CPU fault indicator lights up to display the communication fault.
1. Because there is no computer software and program, the location of the fault point cannot be viewed directly, so it can only be checked one by one.
According to experience, the communication cable from PLC control panel to driller's room is easily damaged when it is often moved, and the connectors at both ends are often plugged and loose. Therefore, the 2-terminal plug was checked first, and the communication cable was measured with a multimeter. As a result, the cable connector and cable were not damaged or loose. After plugging in, the test communication fault still exists.
2. In this case, you can only check one by one from one end of the communication to the other end.
Since the frequency converter is one end of communication, first check the first section of cable from the frequency converter to the touch screen in the control room and the communication plug. The cable connection and disconnection are normal and the connector resistance is normal. Then check the communication cable and connector from the touch screen to the CPU in the second section. The cable is connected and disconnected normally and the connector resistance is normal. Then check the communication cable and connector from CPU to the external plug of SCR room, and the cable is connected and disconnected normally. Check the cable and connector from the station communication module et200 in the driller's room to the touch screen in the driller's room. The cable is connected and disconnected normally. It is found that the connector of et200 is grounded and the resistance value is normal. Therefore, it is considered that the grounding affects the communication, so the other cable connected to the repeater is temporarily removed for communication test, and the fault still exists.
3. At this time, it can only be judged that there may be a problem with the hardware module.
Therefore, inertia thinking judgment may be that the communication module et200 may be damaged, so replace a new et200 module immediately, and the test fault still exists. Randomly judge that there may be a problem with the CPU. Replace a CPU for testing, and the problem still exists.
4. Considering that the communication cable may be disturbed, a temporary cable from CPU to remote et200 communication module is simply used, but the problem still exists.
5. Finally, considering the grounding problem of et200 module, although the resistance value is normal, it may damage small internal electrical components, so the communication connector of et200 is removed for re inspection, and it is found that there are abnormalities. This situation rarely occurs at ordinary times, so it is felt that there may be a problem during inspection, and a new PROFIBUS communication connector is replaced. And power on the test, and the communication returns to normal. Remove the zero hour cable and use the original communication cable. The communication is normal.
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