RE: ePID deadband on output

[Mark Rivers <rivers@cars.uchicago.edu>]

Sorry for the delay in replying, this seems good to me as well.

Mark


-----Original Message-----
From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Benjamin Franksen
Sent: Monday, August 25, 2014 5:14 AM
To: tech-talk@aps.anl.gov; 'Core-Talk'
Subject: Re: ePID deadband on output

[cross-posting to core-talk]

On Thursday 14 August 2014 18:13:15 Pearson, Matthew R. wrote:
> I'm using the ePID record to control a needle valve filling a cryostat
> with helium. The needle valve is controlled by a stepper motor. The
> ePID is giving good results, but I found the need for a deadband on
> the PID output. This is to avoid continually driving the motor to and
> fro by just a few steps. I implemented it via set of database
> records, and included a timer to tell me how long the helium pressure
> has been within a deadband, and then I disable the PID output (by
> setting FBON).
>
> However, I'm wondering if's a common enough use-case to be implemented
> in the ePID record. It would mean adding some additional fields,
> something like:
>
> DBS - the deadband size
> DBTS - settling time in the deadband (to avoid sitting on the edge of
> the deadband) DBT - time in seconds since we entered the deadband
> window
> DBIN - binary flag to indicate we are in the deadband
>
> If ABS(CVAL-VAL)<=DBS, and DBT>=DBTS seconds, then disable FBON.
>
> If ABS(CVAL-VAL)>DBS then reset DBTS and enable FBON.
>
> And to maintain current behavior, keep DBS=0 (the default).
>
> The database version is working fine, but it's quite a few records and
> I suspect it would be much simpler in the soft device support.

Sounds like a pretty good idea to me.

Cheers
Ben
--
"Make it so they have to reboot after every typo." ― Scott Adams


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