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

Subject: Re: Variable scan rate
From: Maren Purves <m.purves@jach.hawaii.edu>
To: Steven Hartman <hartman@fel.duke.edu>
Cc: Emmanuel Mayssat <emmanuel_mayssat@lynceantech.com>, EPICS tech-talk <tech-talk@aps.anl.gov>
Date: Thu, 5 Jan 2006 07:50:45 -1000 (HST)
On Thu, 5 Jan 2006, Steven Hartman wrote:

On Thu, 5 Jan 2006, Emmanuel Mayssat wrote:

The record starts in passive mode When I change the temperature
settings, the record should have a high scan rate. When the readback
stabilizes, the scan rate should decrease and after some amout of time
go back to passive.

The SCAN field can be modified at runtime. You can have some routine do a put into this field, or perhaps do it within the database using a calc and an mbbo or a calcout. I have a couple of records where the SCAN rate can be set by the operator using an MEDM "menu" button. But for something like the temperature readback, I would just leave it at the fast rate all of the time.


just concerning the fast scan rate: we monitor cryogenic temperatures
with scan rates of 10 seconds. As any failure we consider likely requires
human intervention, any scan rate faster than human response time
would be overkill (also, consider physically possible temeprature
changes versus resolution of the measuring device) - in our case
'response' will at minimum require walking down a flight of stairs
at 14,000 ft elevation, and possibly driving a few to 30 miles.
10 seconds is adequate for us, you may want 1 second or even 0.5.

'Passive' doesn't sound like a good idea though.

Maren
References:
Building JCA1 John Faucett
Variable scan rate Emmanuel Mayssat
Re: Variable scan rate Steven Hartman

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