Experimental Physics and
Industrial Control System

Jameson Graef Rollins <[email protected]> · Fri, 18 Jul 2014 17:09:30 -0700

Hi, folks.  I've been wondering about this question for a while, and
have therefore assumed it's impossible, but I thought I would ask here
in case there's something I don't know about...

Is it possible to set an EPICS AI or AO record to alarm on being NOT
EQUAL to a set value?  In other words, I don't want to set a range, I
want on alarm if and only if .VAL != X.

As far as I can tell such a thing is not possible, which has always
seemed odd to me.  If it's only possible to set a range for alarms
(HIGH/LOW, HIHI/LOLO, etc.) then it's actually impossible to cover the
case where you want a record to take on only a specific value.

I guess the problem is that the alarms activate on equality (VAL == LOW,
VAL == HIGH).  If instead the alarm conditions were:

  VAL == LOW
  VAL >= HIGH

then we could cover the equality case by setting LOW = HIGH = X, in
which case we would have an alarm if VAL != X.

Is it truly impossible to achieve this currently?

jamie.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System