PID tuning
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Dear everyone, our company has a steam heater. As shown in the diagram, a top control valve is used to regulate the level of the condensate. The level control is often unstable; in the trend chart, black represents the level of the steam condensate, while red indicates the position of the control valve. I would like to ask if the gain setting of this valve might be inappropriate, and whether it needs to be adjusted Thank you
Just based on these two images of yours, no adjustment is needed; whether the level fluctuates or not, it is the level that determines the low-level setting, right?
It’s all due to the liquid level; the TC3120 is not in automatic mode and its output is at 100%. Why, when the liquid level fluctuated little, did the valve position oscillate almost all the way from 50% to 16%?
Based on your diagram, it is suspected that the operator changed the set value for the liquid level. In the middle part of the curve, even when there was no significant change in the liquid level, the outlet valve continued to close gradually, until it finally reached 0. Theoretically, the set value should be higher than the current liquid level, and the valve would then close in response in an attempt to raise the liquid level. And it is clearly visible from your graph that for some curves, as the liquid level drops, the valve actually opens further. Also, the time value on the horizontal axis of your trend chart is too large; normal valve response changes are not that slow.
LC3120-SP is the curve of the set value; it can be seen that the set value was indeed changed from 72% to around 68%, but it still seems there’s a problem since the valve position remains at a lower level
Looking at the second half of the first graph, the liquid level shows a steady and normal trend, indicating that the PID parameters are fine. The fluctuations in the first half require further investigation to determine the exact cause; it’s necessary to check whether the valves are stuck. The process setpoint in the middle section is very high; the valve remains closed, and there are upward trends indicating that the valve positioning is not optimal ；
Oh, if the TC3120 isn’t set to automatic mode, shouldn’t it be 0%?
Actually, I wonder if the controlled parameters for this process are appropriate? You have a steam heater – why do you need to control the level of condensate water? Shouldn’t it be the temperature of the medium being heated that matters? Where are your valves? Could you take a complete picture? Is the valve tag number LC or TC? This of yours is a bit like a deaerator, but it seems to be based on indirect heat exchange. You’d better understand the process well; if it’s done incorrectly, your control system won’t work properly.
LC controls the condensate level in the heat exchanger, while TC controls the temperature of the fluid to be heated; the outputs of these two controllers are controlled using a low-value selection mechanism
The first half was indeed quite stable; with no changes in other process conditions or set values, the liquid level suddenly fluctuated, and the valve position kept decreasing – it’s really confusing
It seems that this valve has two controls: one for the liquid level, and another one that is likely for pressure (temperature can’t change that quickly). It appears that the pressure has suddenly dropped. It would be best to disable pressure regulation and keep only level control.