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<== Date ==> | <== Thread ==> |
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Subject: | Re: Variable scan rate |
From: | Maren Purves <[email protected]> |
To: | Steven Hartman <[email protected]> |
Cc: | Emmanuel Mayssat <[email protected]>, EPICS tech-talk <[email protected]> |
Date: | Thu, 5 Jan 2006 07:50:45 -1000 (HST) |
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.