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<== Date ==> <== Thread ==>

Subject: Re: EPID bumpless restart
From: "Pearson, Matthew R." <pearsonmr@ornl.gov>
To: "Crisp, Daniel" <CrispD@nscl.msu.edu>
Cc: "tech-talk@aps.anl.gov list" <tech-talk@aps.anl.gov>
Date: Wed, 29 Nov 2017 21:38:05 +0000
Hi,

> 2)      How to best implement a deadband? (It appears there was a thread about the ODEL field being present, but not used in the epid support code? Am I wrong? Is this still the case?)
> Especially for some magnets that require a less frequent touch, I’d like the epid to only act on the supply when the error reaches a larger percent difference. Specifically, I’d like it to only react to errors in field greater than, say, .01% of the target field. We had tried to simply decrease the KP value enough that resulting P values are less than what can be acted on by the supply (supply doesn’t recognize a difference in set points differing by the 3rd significant figure), but this isn’t ideal.

I had the same issue. We use the ePID record to control a needle valve on our cryostat systems (to control the flow of Helium). In the end I implemented a database wrapper around the ePID that has a deadband and a timer. If the error is within the setpoint deadband, and has been for X seconds, then I disable the control using FBON. The timer part is important, otherwise the control will be disabled as soon as the error reaches the edge of the deadband.

Cheers,
Matt



References:
EPID bumpless restart Crisp, Daniel

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