Quantum PID2 loop oscillation

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Thread Starter

Scott Palmer

Has anyone seen a major oscillation from their PIDs in the modicon quantum? I'm controlling a caustic pump to raise our pH; The output of he controller actually starts tracking down before the PV ever begins to move towards the SP. I've changed my reset, and my gain to try to slow it down, but the change is very little at best. Any ideas?
 
I doubt it's your Modicon, it sounds like a classic tuning issue.

Check out the suggested pH tuning parameters in the on-line article "Getting Loopy with Control Loops" at
http://www.controlglobal.com/articles/2005/432.html?SESSID=db5984bc7d4fb6d1746c64b5a85e3af0

Be aware that the PB setting (proportional band)is the inverse of what you mentioned, gain.

The pH tuning parameters suggest a loop highly sensitive to gain, meaning a low to very low gain setting (or high to very high PB setting), but unlike a flow loop, the integral or reset action is extended, multiple minutes per repeat.

Be sure you know what units your reset/integral action is, minutes/repeat or repeats/minute.

Bud
 
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Scott Palmer

Thanks for the heads up on the PB, surely that isn't helping things. The reset is "reps/minimum" Dare I ask what that is representing? Thanks again.
 
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