Multiple terms with hold off periods defined

Each term monitors and tracks its hold off period independently. If multiple terms go into alarm at different times, multiple hold off periods will be in effect with different start and end times.

Pipeline Monitor (PLM) term alarm messages, and the associated event messages, generally indicate all the terms that are in alarm. For example, if ST1 is in an alarm state, and a new alarm for ST2 is announced, the new alarm will indicate that ST1 and ST2 are in alarm. However, when hold off periods are defined, terms that have held alarms will not appear in the alarm message. For example, say ST1 goes into alarm, and a hold off period starts causing a subsequent ST1 alarm to be held. Shortly after, ST2 goes into alarm. The alarm message raised when ST2 goes into alarm will only indicate that ST2 is in alarm.

Event messages always reflect all terms that are either in alarm or returning to normal regardless of whether an alarm or return-to-normal alarm is held. Hence, in the previous example, even though the alarm message only shows ST2 as in alarm, the event message at the same time will show that both ST1 and ST2 are in alarm.

Example – Multiple terms with hold off periods

In this example, terms ST1 and ST2 both have hold off periods and go into alarm at different times.