RE: Alarm for noisy readback channel

[Pierrick M Hanlet <hanlet@fnal.gov>]

Hi Paul,
Not in the record, but if you are using ALH as an alarm handler, there is the ALARMCOUNTFILTER which
allows you not alarm on spurious values.  A description can be found in:

http://www.slac.stanford.edu/grp/ssrl/spear/epics/extensions/alh/ALHUserGuide.html

I hope that this helps,
Pierrick

________________________________________
From: tech-talk-bounces@aps.anl.gov [tech-talk-bounces@aps.anl.gov] on behalf of Paul Nord [Paul.Nord@valpo.edu]
Sent: Wednesday, February 22, 2012 4:29 PM
To: EPICS Tech Talk
Subject: Alarm for noisy readback channel

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")
}