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

Subject: RE: ePID deadband on output
From: "Dalesio, Leo" <[email protected]>
To: Mark Rivers <[email protected]>, "'Benjamin Franksen'" <[email protected]>, "[email protected]" <[email protected]>, "'Core-Talk'" <[email protected]>
Date: Mon, 25 Aug 2014 15:14:16 +0000
Time can be captured in the integral term of the ePID. If that term continues to push the change up, it will exceed the position.
Is that the argument for putting it in the ePID? We don't integrate the error if it is inside the deadband? Is this the only term that does not care inside a given deadband? 
This looks like a good discussion for either the code-a-thon or a side meeting at the EPICS meeting.
________________________________________
From: Mark Rivers [[email protected]]
Sent: Monday, August 25, 2014 11:03 AM
To: Dalesio, Leo; 'Benjamin Franksen'; [email protected]; 'Core-Talk'
Subject: RE: ePID deadband on output

That's an interesting point.

The motor record already has a deadband.  Matt, did you try just using the deadband on the motor record?

I don't think it has the concept of the time inside the deadband though.

Mark


-----Original Message-----
From: Dalesio, Leo [mailto:[email protected]]
Sent: Monday, August 25, 2014 9:51 AM
To: Mark Rivers; 'Benjamin Franksen'; [email protected]; 'Core-Talk'
Subject: RE: ePID deadband on output

Does the deadband belong on the ePID or the motor record?
It seems like more of an output issue - not an algorithm issue.
Bob
________________________________________
From: [email protected] [[email protected]] on behalf of Mark Rivers [[email protected]]
Sent: Monday, August 25, 2014 10:39 AM
To: 'Benjamin Franksen'; [email protected]; 'Core-Talk'
Subject: RE: ePID deadband on output

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

Mark


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Benjamin Franksen
Sent: Monday, August 25, 2014 5:14 AM
To: [email protected]; '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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Replies:
Re: ePID deadband on output Pearson, Matthew R.
References:
ePID deadband on output Pearson, Matthew R.
Re: ePID deadband on output Benjamin Franksen
RE: ePID deadband on output Mark Rivers
RE: ePID deadband on output Dalesio, Leo
RE: ePID deadband on output Mark Rivers

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