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

Subject: Re: AlarmHandler - filtering vs. HYST
From: "Ernest L. Williams Jr." <ernesto@ornl.gov>
To: Brian McAllister <mcallister@mit.edu>
Cc: Terry Carlino <carlino@jlab.org>, tech-talk@aps.anl.gov
Date: Fri, 14 Apr 2006 17:22:47 -0400
On Fri, 2006-04-14 at 15:03 -0400, Brian McAllister wrote:
> [ This is a bit late, just catching up. ]
> 
> >>> On 4/7/2006 at 12:31:30 EDT, Terry Carlino wrote:
> 
>   > Probably the best way to compensate for this problem. thanks.
> 
>   > Steve Lewis wrote:
> 
>   >> Try this (one of the best features of ALH): use
>   >> 
>   >> $ALARMCOUNTFILTER count seconds
> 
> This will help you, but (IMO) the best solution for any alarm hovering
> around a transition value is almost always to set HYST appropriately in the
> record. I realize you would have to convince others to modify the databases
> for this.
> 
> The ALH filters ignore alarms regardless of the size of the change that
> induced them, whereas HYST allows you to ignore only changes that are "not
> significant".
> 
> HYST also has the advantage of controlling alarms at the source, so if you
> use alarm status for other purposes, such as colors or visibility on
> displays, these will also be "filtered" and users won't get used to
> ignoring them if they flash.
> 
> You should look at the "NOACK Transient" mask in ALH.  With this set, when
> the PV goes out of alarm ALH will stop beeping at you.
> 
> [ minor rant follows ]
> 
> I believe that *all* analog ADC inputs with alarms should have HYST>0 (as
> well as MDEL/ADEL>0, for efficiency).  The minimum value for HYST should be
> just over 1 bit, so you won't generate alarms if the ADC is sitting on a
> bit transition.
> 
> I also believe that alarm limits, especially MINOR alarms, should be
> influenced by operational reality as well as engineering design.  If the
> normal value of an analog input is close enough to an alarm limit to
> generate alarms when no action is actually required, that limit should
> probably be changed.
> 
> Based on personal experience I can state that any significant number of
> "nuisance" alarms will lead to users becoming less reactive to real alarms.
> 
> We were having enough issues with operators silencing ALH "forever" (so
> they wouldn't be annoyed by "false" alarms) that I modified ALH to put a
> black border around the button on the screen so you could tell it was
> silenced without opening the alarm window.
Seems like a nice addition. What version of ALH did you add this
feature?  Finally, could you submit a patch to the APS (Janet Anderson)
for review and possible inclusion into the main ALH distribution.





> 
> ----
> Brian McAllister                                   Senior Software Engineer
> mcallister@mit.edu                      Bates Research & Engineering Center
> (617) 253-9537                                                Middleton, MA


References:
Re: AlarmHandler - filtering vs. HYST Brian McAllister

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