How to determine the accurate action time of a self-regulating valve that moves too fast or too slowly?
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I don’t know much about automation, and I would like to ask you some questions. Sometimes the self-adjusting valve obviously cannot be adjusted. The questions are as follows.: 1. The action is too fast, which means the valve position changes too fast, resulting in a large difference in the peak value of the fluctuation curve. 2. The adjustment is too slow, the valve position changes slowly, and the adjusted value fluctuates more and more, and finally directly exceeds the alarm value. 3. Valves with complex control loops, such as when adjusting steam, need to be sensitive, but the valve position action needs to be smaller, but when cascaded with temperature, the response needs to be slow, and the valve position action should also be smaller, because the temperature always takes time to measure. 4. How to measure the adjustment time and valve position movement that should be set for a self-adjusting valve? Due to the above problems, many of our self-adjusting valves are all manually adjusted like furnishings. . . It makes no sense at all. I hope you can give me some useful knowledge.
There are usually two parameters in the adjustment of self-regulating valves, one is the K value and the other is the T value. The K value is equivalent to an amplification factor and the size of the response value. The T value is the response time and how fast the valve responds when a deviation occurs. Some valves are more complex and have multiple coefficients to adjust. If the problem you mentioned exists, it is because there is a problem with the parameters or conditions when selecting the valve, the valve characteristic curve is wrong or the flow parameter is too different. Also, do not change the original parameters casually.* * It would be difficult to handle.
I don’t know whether you chose an electric or pneumatic regulating valve. Usually the regulating valve has a K value or CV value, which is the flow capacity index of the regulating valve. It is usually better to ensure that the regulating valve works within the opening range of 30%---80%. In addition, the action time parameter T of the control valve must be adapted to the action frequency you need. After these two aspects are met, the problem of tuning the adjustment parameters arises, that is, the PID parameter tuning must be reasonable. From what you said above, I think 80% of the time it is caused by unreasonable PID parameter tuning.
It can only be adjusted on the system, look at the curve, try a few more times
Thank you all, I have thought about it and am going to test it on the actual system, cooperate with the instrument computer personnel to make actual adjustments, and then see the effect. thank you all
1. Valve selection problem. The action time parameter T of the regulating valve must be adapted to the action frequency you need. 2. The problem of PID parameter setting in DCS. Hardware (on-site) and software must be combined to control it well! It’s too complicated!
Adjust the PID parameters of the instrument
Under normal circumstances, your working conditions must first be relatively stable. Under peak and valley process conditions, no matter how good the valve is, no matter how good the PID parameter value setting is, your adjustment cannot achieve satisfactory results. If the process change process has a small deviation from the design, and the valve action is too slow or too fast, there is a problem with the PID setting. After some actual adjustment, it should be ok. For temperature system: P (%) 20--60, I (min) 3--10, D (min) 0.5--3 for flow system: P (%) 40--100, I (minutes) 0.1--1 for pressure systems: P (%) 30--70, I (min) 0.4--3 for liquid level system: P (%) 20--80, I (points) 1--5 I hope the above parameter settings will be helpful to you!