Experimental Physics and
Industrial Control System

Dear Colleagues,

 

Recently, when I was working with Phoebus Alarm system to develop the alarms, I found the alarm filter does not work as expected, here is the example:

 

1. Let’s say ‘alm_pv’ is a non-latched alarm PV, and ‘alm_pv_filter’ is the filter PV which is used to enable/disable ‘alm_pv’;
2. The filter is “alm_pv_filter==1”, ‘alm_pv_fitler’ is initialized with 1, ‘alm_pv’ is set to 1 (1 is MAJOR, and 0.5 is MINOR, 0 is OK)
3. From the Phoebus Alarm table, I see ‘alm_pv’ is major, and listed in the alarm table;
4. Now I set ‘alm_pv_filter’ as 0 to disable alarm ‘alm_pv’, I see ‘alm_pv’ is removed from the alarm table;
5. Now I set ‘alm_pv_filter’ as 1 to enable alarm ‘alm_pv’ again, and expected that the ‘alm_pv’ would be showing up in the alarm table again, but it was not! It does not show up, until, see next line;
6. Then I changed ‘alm_pv’ to 0 to make it OK, and changed it to MAJOR again by setting with 1, it appeared in the alarm table again.

 

So it seems that alarm is only triggered when the status is changed.

Is that true that what 5. described is exactly how the Phoebus alarm system works?

 

Thanks,

Tong