Emergency help
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This post was last edited by wmhfxx on 2010-6-17 at 19:01. The pressure reading PI005 at the inlet pipe of the main fan was inaccurate; an inspection revealed that the issue lay with the signal cable between the DCS cabinet and the field equipment – this cable went directly into the CS3000 card without passing through an isolation barrier. To resolve this problem, a signal cable from a nearby unused instrument, ZI001 (which provides feedback on the valve position of the main fan), was used to replace the faulty cable. During this replacement, the signal ZI006 IOP was affected (though this was not detected). At 18:20:48, the value of this signal suddenly increased from the normal level of -0.027 to 1.000 MM, yet the system did not shut down – the alarm signal was not part of the interlock mechanism, whose threshold value was 0.7 MM. The trend chart showed a vertical increase in the IOP signal; after 15 minutes, at 18:35:59, another vertical increase occurred, with the value reaching 1.125 MM, which triggered the automatic shutdown of the main fan as a safety measure. Almost at the same time, PI005 was being processed (the terminal wires in the cabinet were first connected; a multimeter was used on site to verify 24VDC and to determine the positive and negative poles before making the connections on site). The meter showed NR at 18:21:45 (indicating that both the positive and negative poles had been connected to the meter), it showed IOP at 16:22:04, and then NR again at 16:22:14. I would like to ask everyone what might be the possible causes of this incident?
It feels a bit strange! There is an impact on the two terminals; check carefully as the interlock has been interrupted.
To prevent further losses, the main fan was started quickly; the management did not order an investigation for fear it would disrupt normal production, so nothing was known about the matter.
Could an increase in current be the reason for the sudden jump in displacement from a normal PV of -0.027 to PV=1.000 MM? If loose connections at the terminals caused by issues during wiring result in a rise or fall in PV voltage? Experiments were conducted on-site: the PV value dropped after all three wires connected to the displacement were removed.
We encountered a similar situation: a large pump stopped operating due to vibration-related interlocks. Electrical and mechanical inspections revealed no issues, but an inspection of the instruments showed that the wiring terminals at the site were loose. After tightening them, the pump started working again without any such problems.
It is necessary to explain whether the use of walkie-talkies at that time could cause electromagnetic interference and lead to an increase in current
It seems that the wires were moved during operation, and the connection terminals are loose as well. We had an incident here: once, while checking the wires, we opened a cover plate and then closed it again; nothing else was touched, but that caused the machine to stop working. Upon investigation, it was found that the SOE was caused by a power outage in the DO, which led to the valve closing and thus the shutdown of the equipment. Later, when I checked the wiring of this valve, it was indeed loose. When working on this line, we need to check the several points that are close to the connection points. If interlocking is involved, we must first obtain an interlocking work order to disable it, and we should also inform the process engineers about this. I’m just worried that I might touch other wires during the operation. . .
This post was last edited by Hardmen on 2010-6-16 at 12:34. The factors related to the walkie-talkies also need to be checked; our float level gauge has an impact of nearly 30%
Reply to 1# wmhfxx: From the symptoms, it seems that an external interference is causing the issue; I think it’s a problem with the walkie-talkie, as it was used too close to the wiring terminals of ZI006.
Are there any other explanations? I would appreciate it if the experts here could help analyze it.