RE: EPID bumpless restart

["Crisp, Daniel" <CrispD@nscl.msu.edu>]

Hello Mark,

 

Ah, great! For what it’s worth, that looks good to me. I’ll try this tomorrow and let you know how it works. I’ll also double check how the bumpless restart is/isn’t acting so I can answer Matthew.

 

Thank you for the quick responses!

-Dan

 

 

From: Mark Rivers [mailto:rivers@cars.uchicago.edu]
Sent: Wednesday, November 29, 2017 6:57 PM
To: Crisp, Daniel <CrispD@nscl.msu.edu>; tech-talk@aps.anl.gov
Subject: RE: EPID bumpless restart

 

Hi Daniel,

 

I think this patch to devEpidSoft.c should implement ODEL.  Let me know if this works and I will commit it.

 

diff --git a/stdApp/src/devEpidSoft.c b/stdApp/src/devEpidSoft.c

index 62c753f..118fb0c 100755

--- a/stdApp/src/devEpidSoft.c

+++ b/stdApp/src/devEpidSoft.c

@@ -41,6 +41,8 @@

  *  dT(n)   Time difference between n-1 and n

  */

 

+#include    <math.h>

+

#include    <alarm.h>

#include    <dbDefs.h>

#include    <dbAccess.h>

@@ -207,7 +209,9 @@ static long do_pid(epidRecord *pepid)

     pepid->dt   = dt;

     pepid->err  = e;

     pepid->cval  = cval;

-    pepid->oval  = oval;

+    if ((pepid->odel != 0) && (fabs(pepid->oval - oval) > pepid->odel)) {

+        pepid->oval  = oval;

+    }

     pepid->p  = p;

     pepid->i  = i;

     pepid->d  = d;

 

Mark

 

 

From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Crisp, Daniel
Sent: Wednesday, November 29, 2017 2:48 PM
To: tech-talk@aps.anl.gov
Subject: EPID bumpless restart

 

Hello,

 

I'm currently using the EPID record to stabilize a dipole fields. It is reading a magnetic field from a hallprobe controller, and driving a power supply current to match the hallprobe reading to a target value specified by the user.

 

1)      How can I make the EPID record perform a ‘bumpless restart’?

Currently, if the power supply set point is significantly changed while the EPID feedback is off, the epid record will drive around the supply wildly once turned back on. I have some channels set up which pause a user’s request to turn on feedback until the ‘<epid_channel>.I’ field can be automatically set with the live value in the supply. And when I monitor the ‘<epid_channel>.I’ value, I see that it in fact does get set, but it then gets overwritten and ignored. What’s the best way of dealing with this?

 

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 3^rd significant figure), but this isn’t ideal.

 

Thank you!

-Dan