The automatic adjustment of the SAMSON control valve has excessive fluctuations
Thread Content
This post was last edited by liu530014416 on 2022-6-16 at 15:27. 1. Dear teachers, it’s a new unit with new control valves; the material is a liquid at room temperature. This problem has existed since the unit was put into operation – the automatic control results in excessive fluctuations, while the flow rate is stable when controlled manually. Adjusting the PID parameters in the control room doesn’t help (it’s really not related to the PID). We just replaced it with a new Samson locator yesterday, but the problem persists. What could be the cause? 2. Another Samson steam cartridge control valve: at 35% opening, the flow rate is 5000; at 36% opening, the flow rate remains unchanged, while at 37% opening it rises to 5500. The normal flow rate is around 5300. This is also why automatic adjustment isn’t possible – has this regulator not been replaced yet? What is the reason for this? The pressure before this control valve is 10 bar, and the pressure after it is 4 bar. If a new control valve is installed, should a cage-type one or a single-seat one be chosen? 3. Are there any parameters of the locator that need to be changed?
There is a cam piece in the locator; check whether reverse installation is required, and see what the instructions say. For reference.
The first PID was not tuned properly, and the CV value selected for the second control valve was too high.
This has caused oscillations; it’s possible that the PID parameters aren’t adjusted properly. Try reducing the integral and proportional terms to see if there’s an improvement. Additionally, large fluctuations in the detection signal can also cause fluctuations in the output.
Check the CV value and reduce the integral and derivative settings a bit; if the flow requirement is not high, a orifice plate can be installed at the outlet of the control valve to regulate the flow
The last edit to this post was made by dellkey on 2022-6-16 at 11:10. To quickly find the optimal control parameters for PID tuning, you can use the following mnemonic: To determine the best parameters, check them in ascending order； First proportion, then integration, and finally add the differential ； The curve oscillates very frequently; the scale dial needs to be enlarged ； The curve floats around the large bay; turn the scale dial inwards ； The curve deviates slowly from its original state, and the integration time decreases ； The curve has a long fluctuation period, so the integration time needs to be increased further ； The curve oscillates at a high frequency; first reduce the derivative ； Large drift results in slow fluctuations. The differential time should be increased ； The ideal curve has two waves, with the first one being higher and the second lower, in a 4:1 ratio ； Examine carefully, make adjustments as needed, and conduct thorough analysis – the quality of the adjustments will not be poor.
This system has a relatively large relative time lag; first, weaken the integral action (by increasing the integration time), then reduce the proportional action to prevent oscillations, and finally gradually restore some of the integral action. Due to the relatively large relative time lag, there are certain limitations on the integration time; otherwise, oscillations are likely to occur.
The pure lag time is nearly two minutes; the best approach is to identify the cause of this pure lag, or to use a control method that incorporates lag compensation. If a control method with lag compensation is not used, the integration time must be greater than 3 minutes.
Judging from the diagram, there seems to be something wrong with the PID parameters according to my understanding; reduce the proportional value and increase the integral value, and try it step by step
With this trend of yours, it’s becoming erratic – it’s not a PID issue……