Re: Stupid question of the day

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Graeme,

I suspect your problem is not in the database but rather configuring the EPID record a run-time.  There is really no database configuration required, just load an EPID record and configure it with the OPI.  Here is a screenshot of an EPID record I have set up for temperature control.  

The Readback is 13ETC_1:Ti0, which is the first temperature channel on a Measurement Computing ETC thermocouple module.  

The output PV is 13MNIR:E1608:Ao1, which is the first analog output on a Measurement Computing E1608 multifunction module.  That analog output drives a power supply that heats the sample.  Note that the link has the PP attribute, which means that the analog output record will process when it is written to.  That is important.

In this case the Readback link is NPP, so it will not process, the PID record just gets the most recent value.  The EPID record is set to scan at 0.1 second period.  I could have also set the Readback link to CP, which would cause the EPID record to process each time the Readback changed.  In that case I could set the EPID SCAN field to Passive.

If I were to turn the feedback On here it would begin to work.  It's not physically connected now so I can't show that.

Let me know if you have questions or problems.  I can come by your beamline.

Mark

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Graeme Winter via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, January 30, 2026 1:03 PM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Stupid question of the day

 

Hello all, happy Friday

I am trying and failing to get a simple EPID running - from the documentation 

EPID Record epics-modules.github.io

It should be as simple as running an IOC with this compiled in (e.g. stdApp from std-R3-6-4)  with a “sensible” database and configuration then all should be good, but I don’t appear to be able to get the right combination of spells - certainly due to my general ignorance of this area

Simplistically I would expect to pass input, output PVs, some demand PV value, a cycle time and KP, KI, KD and it should “just work” when the PID loop is enabled but this has thus far proven to be beyond my reach

Does anyone have simple example st.cmd and db file which I can use for this? My attempts at hacking the ones included in std bundle have been unsuccessful

Many thanks in advance as always, and best wishes Graeme