Experimental Physics and
Industrial Control System

Tim Mooney <[email protected]> · Fri, 18 Aug 2006 09:39:57 -0500

LYNCH, Damien wrote:

I am interested in the response to the following question as well (as I have
just started using EPID this week myself).
Another question with regard to replacing pid by epid: Apart from teh above
scaling issue, have I understood it correct that if the following scenario:

a pid record controlling an ao record, the latter in OMSL=closed_loop,
output OIF=incremental mode, DOL referencing pid's DM
would be replaced by
epid record having OUTL point to ao record's VAL, ao record in OIF=full and
OMSL=supervisory mode?

Yes.  This allows the epid record to control any record, to have its output
value transformed by a calc expression, etc.
I see the EPID record producing a value that should be added to the ao
record's VAL field, implying the ao record should have OIF=Incremntal. But
with the EPID record putting OVAL into what's pointed to by OUTL (ie the ao
record) I'd expect to have OMSL=supervisory in the ao record.

Hang in there and see what happens as the controlled value responds to the

new output value. With KP!=0 and KI==KD==0, you should see ERR=VAL-CVAL, and
OVAL=KP*ERR. If not, do a "dbpr" on the record and send that. There might be

some control field we're not thinking about with an unexpected value.
The way I read the doco I thought EPID would calculate a value that would be
put into the ao record (not added to what's already there).

That's the way it's supposed to work.
--
Tim Mooney ([email protected]) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System