Siemens PLC 300 analog input fault
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I have 2 Siemens PLC AI modules on site; all the signals are 4-20mA, and they are all fully utilized. Suddenly, all signals showed the lowest value (25% negative of the range), with only the last point of the first module showing 25% positive (which is obviously also incorrect). I removed the signal wires for each channel one by one; it was only after removing the last wire from the first module that everything returned to normal except for the first channel of that module. The other channel continued to malfunction, even though it had been working fine before. I checked the signal wires and found no issues such as grounding problems, open circuits, or short circuits. The module also did not report any errors, and the other digital input/output modules were functioning normally as well. The signal uses power + to instrument +, and the instrument negative terminal to module 2 (7, 12,.). . . ), Module 5 to power negative
Confirm that the feedback signal at the site is normal, with no power interference. Then try restarting it after a power outage; if that doesn’t work, contact the manufacturer
I reversed the order of the two modules; the channels that were working properly remained so, and those that weren’t still didn’t work, confirming that there was nothing wrong with the modules. Use a signal generator to send signals; air cannot be pumped in from the safety side ； The module can be connected, and the channel is fine. To fix it, I simply replaced all the wiring on the board, and then everything worked normally. Upon investigation, a rat nest was found-------