CM50 Boundless Control - Rapid relay switching
Recently I have posted a query regarding CM50 controllers.
Now, as I tune each one them, one CM50 is giving me some headache.
I am implementing a boundless control for a loop. Other loops I have tuned are doing fine exept this one. The relays for open and close command are rapidly switching.
I have configured sets of PID parameters even copying known working ones from other loops just to know what is wrong. Only when I increase values in the travel time, the rapid switching decreases but the controller action is to OPEN only the valve even if it is very far from the setpoint and needs to close already.
Also, the deadband is very puzzling to me because when I input none (0), the controller does not respond at all.
Can somebody here give me some useful tips or advise on how to implement this boundless control?
Thank you very much. Hoping for your responses.
Voted best answer
it is difficult to give you exact pointers without knowing 100% of the PID values and settings you currently have. However, I can advise you on a few points. The biggest mistake people make witht his type of control is not knowing the valve travel time. This is the time it akes the valve to travel from fully open to fully closed. Your integral time (I) MUST be longer than this travel time or you will see rapidly switching relays. Your valve travel is fixed so once you have the correct value you will not need to change it.
Regarding the deadband, this is a parameter that works around the setpoint, what is the setpoint you have? This will make a massive difference on the behaviour you see.
Thank you very much for your answer. PID parameters are below:
P = 100; I = 10S D = 0; Travel Time = 41S
Starting parameters only, when I adjust P&I, nothing happens but now that you have mentioned that Integral must be greater than travel, I will try it.
My understanding for deadband is that it will maintain the PV around the setpoint, based on the deadband configured.
By the way, thanks for answering also my other query. Controller has "UNKNOWN ERROR" during its Power On Self Test (POST).