Detection of faults in PCS7 input modules
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Dear friends: I have a question； Our DCS system is the Siemens PCS7 system, and it has been functioning normally up to now. A week ago, the workshop stopped production for extensive modifications to the process pipelines, and some on-site instruments were removed ； After on-site cleaning, a lot of pipe welding work was carried out. Three days ago, we suddenly noticed that on the DCS monitoring screen, many liquid level and temperature display points appeared black, indicating abnormal readings ； From the monitoring screen, I copied down the parameter points that showed abnormal values; 8 of these points were from the same 8-channel AI input module. I went to the site to check the gauges on site; the displays of the 8 level transmitters and temperature transmitters on this module were not lit (under normal conditions, these displays show liquid crystal numbers) ； Obviously, no power supply is reaching it. These 8 points are on the same 8-channel AI input module ； The number on the module is 453A6. I went to take pictures of this AI input module; I saw that the module with the number 453A6 has indicator lights that are identical to those of the adjacent AI module. Experts, please advise on how we should resolve this fault issue What could be the reasons for the damage to this module? Could it be related to electric welding of pipes on site? ? Seeking advice ； Seeking advice
1. Conduct a more thorough AI-based card inspection: The cards with numbers A435A7, A8, A9, and A6 on the right are of the same model; all of them are 6ES7134-6GF00-0AA1. You can try swapping them to see if there is any issue with the cards, and also check the card bases. 2. Check the power supply: Do you measure 24VDC on the transmitter side at the site? If not, can you check whether the power supply is working properly? Check whether the 24VDC power supply for the pressure transmitters, temperature sensors, and other devices connected to card A6 is functioning properly. Generally, the 24VDC power comes from a 24VDC power supply circuit with fuses in the control cabinet; verify whether the fuses have blown.
Hello, please give me some advice. Our input card with the number A6 has its wiring as shown in the attached diagram. Going directly from the circuit board to the terminal block, I measured each circuit above the fuse, and there was no DC23V voltage. This base with the number A6 is a white base, followed by the gray bases A7, A8, A9, A11, A12, and A13. For the circuit boards on the gray base at the back, all circuits are functioning properly, and there is a DC22V voltage present. The external 20V power supply with label A6 should be fine. Only on this power-supplying A6 base board, none of the 8 circuits it has have voltage. We replaced the base and the circuit board, but neither of those solutions worked. Please give some advice
Clearing the clouds reveals the blue sky. Our own instrument supervisor replaced the circuit board and also replaced the base ； After spending over 10 hours on it, the problem still wasn’t solved. Later, we called a friend who specializes in automation for help ； After having an in-depth conversation, I explained the situation to him in detail. He analyzed: Both the circuit board and the base have been replaced, and besides, the base generally doesn’t get damaged. He asked us to completely remove the 8 instrument wires under this module, and then connect them one by one from the bottom up, so that we could identify the faulty cable. Following this plan, we removed the 8-channel instrument wires and connected a single channel separately; the instrument on that channel displayed properly on the DCS.
The problem is obvious: it’s an issue with the instrument cable. We estimate that large-scale cutting and welding were taking place in the workshop, and it was likely the falling slag that burned the cables inside the cable tray. An investigation is needed. .
Well, based on your description, the first thing to check, as is normal, should be the electrical issues. If the indicator light at the site does not shine, check whether there is voltage on the side of the site; if not, go to the control room and disconnect the corresponding wiring terminals to measure the output voltage. If voltage is present, it indicates a problem with the cable; if no voltage is present, continue to investigate further by replacing the card components and fuses. It’s not possible to replace the card module right away; it seems like you guys must have been panicked because you hadn’t encountered this situation before
Yes, it took over 10 hours, and when the problem still hadn’t been solved, I panicked.
The case has been solved. The instrument cable of one circuit is grounded. The kind installation crew member fixed an instrument cable to the galvanized pipe. The tape covering the wire end happened to be damaged, resulting in grounding.