Understand Pipeline Monitor (PLM) deviation alarms

The Pipeline Monitor (PLM) application provides four independently adjustable limits to be applied against the balance for each of the nine balance periods:

• An over (positive) volume deviation from balance.

• An over (positive) deviation % of flow value.

• A short (negative) volume deviation from balance.

• A short (negative) deviation % of flow value.

For any period, either volume deviation or deviation percentage will be checked depending on configuration for the period, but not both. An alarm is generated if the deviation is outside a limit.

A PLM system can be in violation of more than one alarm limit at any time. If the PLM system is not suspended, and at least one alarm limit is in violation, the PLM system is marked as being in the alarm state. An entry exists in the Alarm Summary for any PLM system that is in the alarm state. The entry identifies any alarm limits that have been violated.

If a limit that was not previously in alarm is violated for a PLM system that is already in the Alarm state (due to another limit having been violated), a new alarm is generated and the previous alarm is removed. The alarm message indicates the following:

• All alarm limits that have been violated.

• Each period for which an alarm limit is violated, including the current deviation for the period.

The severity and message for each of the three possible states for a PLM region are definable by entries in the default PLM message set following the standard convention for RealTime message sets.

You also have the option to use an extended message set to assign different severities to the nine terms. Each of the nine states in the extended message set corresponds to a PLM period (three for short term, three for long term, and three for extended term). When a term is in an alarm state, the message corresponding to that term is located and its severity is used. If more than one term is in alarm, the system will use the highest severity among all the terms in alarm. To use the extended message set, configure your PLM record to use the PLM_TEMPLATE message set and customize the severities for the nine additional states. For an example customization, see message set PLM_RUPTURE.

Two independent systems are available to reduce false alarms: Alarm Suppression and Dynamic Alarm Limits. They do not work concurrently. If Dynamic Alarm Limits are enabled, the RealTime Alarm Suppression functionality will not work. For more information, see Understand Pipeline Monitor (PLM) Alarm Suppression and Understand Pipeline Monitor (PLM) Dynamic Alarm Limits.