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

Subject: Alarm for noisy readback channel
From: Paul Nord <Paul.Nord@valpo.edu>
To: EPICS Tech Talk <tech-talk@aps.anl.gov>
Date: Wed, 22 Feb 2012 16:29:22 -0600
I've got a network device that's misbehaving.  It "sometimes" reports an absolutely ridiculous value.  I'd like to set an alarm on this PV but I don't want the alarm sounding once or twice an hour when there's not really anything wrong.  (Never cry wolf.)

In the typical failure mode it reports a "crazy" value once and then goes back to the normal value.  (The device actually returns the voltage value for a channel when you ask for a current.  And it formats a reply and happily returns "Current: 3600 A", which would be impressive for a supply running at 3600 V.  It works out to 13 MegaWatts.  The real current is just ~100 uA.)

What's the best way to deal with this?
	A CALC pv that takes this value as an input but returns zero if the reading was outside of some range?
	A CALC pv that counts the number of readings which are outside of the proper range?  (e.g. A>1.0?(VAL+1):0 )

Are there other good mechanisms?

Paul


record(ai, "$(SYSTEM):measurement_current_$(SLOT)$(ID)")
{
 field(DTYP, "Snmp")
 field(SCAN, ".5 second")
 field(PREC, "6")
 field(EGU,  "")
 field(INP,  "@$(HOST) pwd WIENER-CRATE-MIB::outputMeasurementCurrent.$(SLOT)$(ID) Float: 100")
 field(ADEL, "1")
}



Replies:
RE: Alarm for noisy readback channel Pierrick M Hanlet
Re: Alarm for noisy readback channel J. Lewis Muir
RE: Alarm for noisy readback channel Allison, Stephanie

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