Automatic start of standby pump
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In our fluid collection tank pumps, when the level exceeds 80%, the backup pump starts automatically. However, in some abnormal situations, the backup pump may start automatically even when the liquid level is below 80%. We have checked this several times and suspect that it might be due to interference issues; but tests for interference and checks of the grounding system showed no problems. The control system we use is INTOUCH. Could anyone please help analyze this situation?
There is a dead zone here. . . Take a good look; we’ve encountered similar situations before as well. I hope this can help you
The reasons need to be analyzed: 1. Are the startup conditions met for the standby pump to start automatically? (The actual liquid level is less than 80%, but the displayed level may show 80%, which will also trigger it.) ； 2. Check electrically for any defects that could cause malfunction ；
Is there a problem with the transmitter, causing large fluctuations in the liquid level signal? Fluctuations that exceed 80% for short periods trigger the startup of the backup pump. This path is the input section. It is also possible to check the output section, the DCS output relays, and the electrical components to see if there are any poor contacts or faulty operations.
INTOUCH is the upper-level software; is your logic written inside it? By looking at the historical trends to see if there have been instances when the liquid level exceeded 80 for a short period, a few-second delay can be added to the logic to reduce false triggers
There is a problem with the control system; it is recommended that the instrument maintenance personnel perform recalibration. There may be discrepancies – the actual value at the site might be as indicated, but it isn’t shown in the indoor readings, or there could be other reasons
Hello, OP. For this situation, you can try performing signal filtering. The specific simple method is as follows: delay the signal output by 500ms before execution. (There are more rigorous filtering methods than mine; you can think further about it – my approach is just for reference.)
Is the method you mentioned workable? I hope to discuss this with you. . .
Hello! I have worked on projects before and encountered similar situations. You can contact me by phone; I will write the program based on the details of your process.
This post was last edited by hxm20041010 on 2012-2-10 at 13:32. I agree with this statement; I have encountered such a situation, and the reason is that the liquid level signal fluctuates greatly, reaching over 80% for a moment, which causes the backup pump to start automatically. I think it is because the sampling period of the higher-level software INTOUCH is longer than that of the controllers (DCS, PLC, ESD), which is why we cannot see on the historical trends or records any instances when the value exceeded 80% for a moment
When interlock control is in use, the level transmitter’s signal is definitely processed through a DCS, PLC, or some type of secondary instrument before being used； In the case of a safety system, an action (switch) must be taken at the site to control the actuator (pump); for ordinary interlocks, it is sufficient to use a transmitter to convert the signal (soft switch). The approach proposed by the colleagues on floors 5 and 7 is acceptable – introducing a delay in the output can help deal with issues such as fluctuations in liquid level or interference