Is it a problem with the valve positioner?
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Yesterday, I encountered a problem while working with a gauge; it was a flow control valve used as a secondary circuit for level control. When the flow control valve is operated manually, the flow rate remains very stable; however, when it is set to automatic mode or in cascade mode, the flow rate fluctuates greatly. The team leader said it’s due to the valve positioner; is that true? Won’t the valve positioner have any impact when it is operated manually?
Although modern automatic control systems all have a disturbance-free switching function, it is still better to use manual control until the set value is close to the measured value, thereby reducing automatic disturbances and ensuring a smoother operation. The automatic fluctuation is extremely large, indicating that the PID parameter values have not been set properly; it is necessary to reset them to appropriate values.
Well, but I want to know first, without considering PID settings, whether this situation is related to the valve positioner
It’s not certain that it’s a problem with the locator. But based on what you’ve described, a problem with the locator is the most likely possibility. It is also necessary to consider factors such as whether the circuit is functioning properly, whether the PID parameters are correct, and whether there is air leakage in the valve cylinder. The cause must be identified by ruling out possibilities one by one.
What the team leader and the experienced worker mentioned at that time was the issue with the locator; if it’s a problem with the locator, then it makes sense to use a cascade control system. I just want to ask whether, in the case of a locator problem, manual operation would not be affected?
Manual operation works normally; it’s just that automatic mode cannot be used. It’s not a problem with the valve positioner, but rather the PID parameters for the auxiliary control system haven’t been set properly
Personally, I think this issue is related to both the positioner and the PID. The stability when operating manually indicates that the valve can remain at a constant opening degree, which results in stable flow rates with no significant variations. Large fluctuations in flow rate after switching to automatic mode indicate that the valve is constantly adjusting itself as it fails to find an appropriate opening degree; this is related to the dead zone and gain factor of the valve positioner, as well as the settings of the PID controller. Comprehensive management is still better.
The P, I, D settings of the valve should be adjusted； The appropriate output curve converges and remains stable.
Personally, I don’t think it has much to do with the locator; if there’s a problem with the locator, the valve will definitely experience fluctuations even when operated manually. The reason is that the PID parameters aren’t properly adjusted
It doesn’t seem to have much to do with the positioner; the fact that it can be stabilized manually indicates that the positioner is working properly
Switch to manual control at the central control panel and verify the valve position on-site; the problem is likely not related to the valve actuator, but rather to unstable liquid level. It is recommended to switch to manual mode