Understand alarm re-annunciation hold off period

Use the alarm re-annunciation hold off period column to define a period within which the system will hold off on re-announcing alarms for a particular term. This helps reduce the number of alarms presented to the Controller if the underlying alarm condition is the same.

When you define a hold off period, the system will either announce or hold both defined alarms and return-to-normal alarms. Alarms and return-to-normal alarms are considered announced if they appear in the Alarm Summary window. Conversely, alarms and return-to-normal alarms are considered held if they do not appear in the Alarm Summary window. In all alarm cases, the Pipeline Monitor (PLM) and the specific term will still indicate as being in alarm on the relevant PLM record fields and term information fields. Consequently, the PLM records appear in an alarm state on the PLM Summary window.

After the term goes into alarm and the alarm is announced, a hold off period for this term is triggered. The system generates an event indicating that a hold off period for the term has started, and the start time of the hold off period is recorded.

During a hold off period, the following behavior is expected:

• The first return to normal alarm is announced.

• Subsequent alarms and return to normal alarms are held.

• Events always generate regardless of the hold off state.

When a hold off period expires, the system generates an event indicating that the hold off period is over. There are a few possible scenarios:

• If the term is now in a normal state, then nothing further happens.

• If the term is now in an alarm state because it has been in that state for the entire hold off period (without returning to normal), then nothing further happens.

• If the term is now in an alarm state because it returned to normal after the first alarm and a subsequent alarm had been held during the hold off period, the alarm will be re-announced, and a new hold off period will start.

  Important: In the case of a mode switch or a failover, the hold off period will continue to be monitored based on when it was originally triggered prior to the service interruption.

Example – A term goes in and out of alarm multiple times during a hold off period:

The following diagram shows the timeline of the first short term alarm (ST1) that has a configured hold off period. The diagram illustrates the state of the term (in alarm or normal) and Alarm Summary window activity.