Damn fluctuations
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This post was last edited by hanlaowu318 on 2022-1-29 at 17:17. It involves a horizontal liquefied gas pressure vessel in the device; the composition of the medium is 97.4% isobutane, 1.01% n-butane, 0.76% isopentane, and 0.53% propane. The operating temperature is 40°C, and the operating pressure is 0.55 MPa. A double-flange differential pressure level gauge is used for measuring the liquid level. The current phenomenon is that the liquid level starts to fluctuate around 8 a.m. every day; as shown in the DCS trend chart below, stabilizing the situation was achieved by switching the liquid level control valve to manual control. A solution is sought. On the curve in Figure 2, blue represents the liquid level, while red indicates the opening degree of the control valve. It fluctuates around 8 o’clock every day and returns to normal around 17:00.
Are there any photos of the installation of a double-flange differential pressure level gauge?
There is air inside the capillary of the differential pressure transmitter, right?
1. First, does the on-site (actual) level gauge fluctuate during remote transmission of fluctuations?； 2. If there are regular fluctuations on time for three days or more in a row, and the overall trend is normal, valves and the process are more likely to be the cause ； 3. Upon checking the valve positioner/feedback rod area/PID, this divergent trend appears to be more of an output issue. Would it be convenient to display the valve position and liquid level on the same screen?
First, it is necessary to determine whether the level fluctuations represent the actual values; if not, the level gauge should be examined, while if they do represent the actual values, then the valves and the process conditions should be investigated. In my opinion, it’s highly likely that your liquid level represents the actual value; given these regular fluctuations on a daily basis, consider whether there are other factors at play, or any other processes taking place.
The periodic and fixed fluctuations take into account the intervention of operator shift changes. The newly installed device takes circuit checks into account to determine if there are any miswired connections or signal interference.
It must be a problem with the valve positioner; when it reaches a certain position, the valve undergoes significant reverse changes uncontrollably. It needs to be inspected, repaired, or replaced.
I’ve encountered this situation: the noise level increases significantly around 7:30 in the morning, while it drops noticeably around 10:00 at night. The analysis suggests that people start working at around 7:30 in the morning, which leads to increased electricity consumption and a rise in ground current, thereby raising the ground voltage； Work ends around 10:00 p.m., electricity consumption decreases, the ground current drops, and the ground level falls. The conclusion was to focus on checking the ground resistance of the grounding system for any loose connections; one such loose connection was found, and after it was fixed, normal operation was restored.
Issues with valve positioners. Check the valve opening, commands, and liquid level on the same trend.
It’s not just for three consecutive days; fluctuations start around 8 o’clock every day, and normal conditions are restored around 17:00