When in automatic mode, if the PV arrive to the Upper instrument range, the PID output goes to overflow and remain in overflow. The PID in his way does not control the out.
The PID has these parameters:
I have set the function to only P and the PID has reset the overflow and started again to adjust the PID OUT in accordance to PV/SP and gain.
Why thi error occur and how is possible to auto reset the overflow ?
Please find some detail on the attached picture.
- You say the "master" PID output is saturating. But your picture shows a flow controller, which would typically be the slave in a master/slave relationship.
- Is this a pre built master/slave function block or is it something you built ?
- Rather than experiment with a live plant, Can you duplicate the behaviour in a soft controller and simulate the feedbacks ?
The next issue is, "does it matter anyway " (because the slave loop should deal with this) ....
- When the output of the master goes saturated, what does the setpoint of the slave loop do ? Does the slave continue to function properly ?
- More importantly, when the masters PV falls below setpoint how does the output react ? Does it come back into range quickly or does it remain wound up for a long period of time ?
- If it is actually the output of the slave loop that is saturating, then again, does it matter ? The actuator cant go above maximum. How quickly does the output come back into range and what happens when it does ?
One of the possible reasons couuld be that you didn't limit the output.
Have a look in the following InteractionPar of the PID block:
- LimitOutput - should be TRUE (the default Init value is false)
- OutMaxLimit = 100.0 for example
- OutMinLimit = 0.0 for example (in my case I didn't want the output to go below 20)