Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 24 Sep 2015 12:12:29 -0500

Hi Patrick,

On 09/24/2015 11:24 AM, Patrick Thomas wrote:
> Is it possible to set the alarm severity of a channel from the values
> (not alarm severities) of other channels?
> 
> For example, in TwinCAT the validity of a given channel is determined by
> the values of multiple other channels. Would it be possible to set the
> alarm severity of that channel to invalid in EPICS based on the values
> of those other channels?

It is possible for a custom or subroutine record-type to manipulate its
alarm status and severity almost any way that it wants to, the behavior
just has to be implemented in C code. Whether any existing record types
can do what you want is a different question though; I can only answer
that for the types included with Base.

Assuming you understand the alarm rules for the standard scalar record
types based on their VAL field, there's really only one other way to
trigger alarms: Record types that support simulation usually have the
ability to set an alarm when they go into simulation mode (see SIMM,
SIML), with the severity controlled by the SIMS field. Of course that
does modify the processing of the record, so it might not be useful to you.

The use of MS/MSS/MSI flags on input links is the other way to
manipulate alarm severities; you might be able to insert ai records in
the path to your other channels and use their HIHI/HIGH/LOW/LOLO fields
to do what you need, but beyond this you're probably limited to coding
your own behaviour in either sub/aSub or custom record types.

HTH,

- Andrew

-- 
Light thinks it travels faster than anything but it is wrong.
No matter how fast light travels, it finds the darkness has
always got there first, and is waiting for it.
    -- Terry Pratchett, Reaper Man

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System