Contrologix PID output locks up

[diat150]

Hello,


I have a flow control PID that keeps locking up. It seems to control fine but after a while the output no longer moves. For instance right now the cv is stuck at 84.85. right now I dont have the tuning parameters very aggressive because we are experimenting with running the valve in auto as opposed to manual, which is the way they have been running for years. I didnt write this program, just here helping out.


The process error is constantly changing, right now it is around .2% setpoint is currently 4 but if I drop to 3 then the cv starts moving again. Just wondering what could possibly be causing this. Maybe there is a setting that doesnt allow a change when the error is low?

 

[Robb B]

There might be a deadband value entered. Is this PID or PIDE instruction? Can you post a screenshot of the configuration?

 

[diat150]

There is a zero crossing deadband of .5


I didnt see any other deadband setting.


It is a pide

 

[Robb B]

What does the 0.5 represent? Percentage? Engineering units? Raw value?

Can you do a trend on it? Capture the setpoint, process variable, error and control output. If everything is scaled into engineering or percentages, it's easier to understand.

 

[diat150]

it appears that the .5 deadband is what was causing the output to stop. Thanks for your help.