The regulation system has large fluctuations
Thread Content
Three identical sets of equipment, each with its own inlet flow control. The control valves of units A and B remained stable with no fluctuations after the DCS was switched from manual to automatic mode. When the regulator of unit C is switched from manual to automatic mode, the flow rate experiences significant fluctuations and jumps. Upon verification, the P, I, D tuning parameters of devices A, B, and C are exactly the same. After switching the control room to manual mode, no fluctuations were observed in the on-site control valve either. What is the reason?
Is the valve opening fixed when operated manually, and is there any fluctuation in flow rate?
According to the poster, it remains stable after switching to manual mode; therefore, there should not be any major issues with the opening degree of the valve itself. Check the control logic: whether there is any drift or fluctuation in the flow signal, if there are any interferences; also check whether other parameters upstream and downstream remain stable when the control valve is set to manual mode, and what happens once it is set to automatic mode
There are various reasons for this: issues related to the conditional system itself, abnormal fluctuations in the system, and also improper tuning of the PID parameters. There is no fixed value for PID parameters; different systems require adjustment and optimization, so it is necessary to investigate each situation individually.
There are many reasons, you can’t figure them out, and I can’t understand them either. PID: three cows with three heads each; all three nozzles can bite. Just tweak and adjust it randomly – spend a few days fiddling with it, and maybe one day you’ll manage to get it set up properly. . . . Wish you success in your endeavors. Wish you get a bonus to support two mistresses.
The poster mentioned that the operation is stable when using manual control but experiences large fluctuations when switching to automatic mode; if it’s a pneumatic valve, the poster might want to check whether there is any air leakage or backflow in the cylinder
When the valve was tested individually after the system was shut down, it was found to operate in a sluggish and uneven manner; at 60%, its position fluctuated greatly (it would sometimes settle at 30% and sometimes at 60%), taking over 30 seconds to stabilize at 60%.
Let’s analyze the reasons together. The valve is a 60-degree V-ball control valve, and a knocking sound can be heard when the valve is closed, resulting from the impact between the valve seat and the valve disc. I believe the possibility of a failure in the actuator is very low.
Swap the C regulator with the A or B regulator and you’ll know where the problem lies
The focus is on thoroughly inspecting the internal components of the valve body, checking whether the valve core and valve stem are loose, whether the valve seat is loose, the sealing material of the valve stem, and the surface of the valve core’s V-ball, among other things.
You need to first roughly determine whether the sticking and poor performance are caused by the positioner or by the valve itself. Manual operation throughout the process; it’s best to compare the feel with other valves of the same model. I think it’s mostly a problem with the valve itself; if possible, it’s recommended to disassemble it for inspection.