Sudden significant change in the vibration monitoring probe of the compressor unit
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Our plant’s main fan unit vibration monitoring system uses the Bentley 7200 system; last week, the two probes in this system that measured the same location experienced sudden large fluctuations, which triggered an alarm. After analysis, it was determined that this alarm and the associated phenomenon were false alarms; both probes returned to normal operation after about ten seconds each, but this occurrence happened twice on the same day. The probe at this location was removed and reinstalled during the maintenance work in February 2008; it has been functioning normally ever since the maintenance was completed. There have been no other changes in the Bentley system, and all other probes are also working properly. I would like to ask my colleagues who have experienced this phenomenon to share their insights; thank you very much!
It is likely caused by the looseness of the probe itself; tightening and adjusting it again after parking in the future should prevent this issue from occurring.
It could be due to a loose probe, or it might be caused by loose wires leading from the probe. Such large fluctuations are mostly caused by loose sensors or terminal connections, resulting in poor contact. However, if both probes experience large fluctuations simultaneously, the possibility of a problem with the probes themselves is very low; and if the alarm is a false alarm, it is likely due to electromagnetic interference. Were there any phone calls made or motors started and stopped in the vicinity at the time of the incident? One can first check and rule out the possibility of loose connections in the probe leads before proceeding with further detailed analysis.
I would like to ask the original poster: on what basis do you say that it was a false alarm when calling the police? How can I tell the difference between real and fake alarms? “During the maintenance in 2008, it was disassembled and reassembled – how was the maintenance carried out? Is it definitely better after disassembly and reassembly than without it? In addition to the points mentioned on the 3rd floor, it is also necessary to check whether the temperature at this measurement location has risen.
The vibrations of the two measurement points on the same axis rise and fall simultaneously. Can you see the waveform when the vibration increases? It is possible to determine the cause based on the waveform – whether it is actual vibration or interference, and if it is interference, what type of interference it is. Logically, since both change simultaneously, the possibility of an issue with the axis is greater, while the possibility of a problem with the sensor is much smaller. As for the issue with the shaft, the only thing that comes to mind right now is whether there might be a temporary shaft current; I haven’t thought about other possibilities such as situations where it is present at times and not present at other times. This post was last edited by mirook on 2009-3-31 08:54]
I think the reason might be an issue with the shielding of the probe circuit, which is causing interference; check the grounding. It’s unlikely that the probe is loose, but it’s possible to check whether there is any looseness in the pigtail wires of the probe and the wiring of the circuit.
Perhaps it was too hasty, and the issues weren’t explained clearly, causing everyone trouble – sorry about that. The vibration at that point appeared twice in the Intouch alarms, with each oscillation lasting around ten seconds; the temperature at that point didn’t change, and all other process parameters were normal. The probability of both probes failing at the same time is very low. It was a day off at that time, with no construction work in progress. We considered the possibility of electromagnetic interference, and we also thought that impurities in the lubricant might cause sudden changes in the value of electric eddy currents on the surface of the probes. During the maintenance in 2008, after removing the probes, we conducted vibration tests on each one using vibration calibration instruments, and recorded the test data as well as the manually drawn variation curves; all defective probes were replaced. We are all experienced workers with over a decade of work experience; we still have a sense of responsibility at work. Our professional skills aren’t outstanding, but they’re passable. Thank you all for your valuable suggestions; it’s a great learning opportunity. Thank you very much.
Well, I found the insightful comments from everyone above very helpful; it was educational. Thank you. Personally, I think it might be due to a loose probe, or interference caused by the possibility of grounding in the extension cable.
We have tested that if someone nearby uses a walkie-talkie or phone, the signal experiences significant fluctuations.
Our factory uses the 3500 system, and similar issues have occurred there as well; it was later found that welding activities taking place on site were causing interference from direct current. I’m not sure if the same thing happens in your area
Pay attention! Pay attention! Pay attention! Experienced users who have used the Bentley system are encouraged to share their insights.
It happens often; I don’t know the reason. Once I thought it was due to a loose connection, but I’m not sure about the other cases.
May I ask the original poster, has your problem been resolved? In the past two days, our unit has encountered similar problems to those you’re facing. Our unit is equipped with a 3500 system, and there are 4 vibration points that show fluctuations simultaneously; process parameters such as temperature and pressure remain unchanged. However, vibrations have occurred twice throughout the night, and we are still unable to identify the cause. Could you tell us how you resolved such problems?
Two suggestions: First, the terminal connections are loose; second, the shielding of the extension cable is inadequate – replace the cable!
Thank you, it’s exactly what I need right now :)