Understand Pipeline Monitor (PLM) Dynamic Alarm Limits

Note: The Pipeline Monitor (PLM) application supports scenarios where both Alarm Suppression and PLM Voting are configured. However, Alarm Suppression and Dynamic Alarming are mutually exclusive—if Dynamic Alarming triggers are specified, Alarm Suppression will be automatically disabled.

For Alarm Suppression purposes, the following PLM States can be used: NORMAL, ALARM, SUSPEND, NO-CALC, METER-ERROR, STALE-RECORD, RECORD-RESET, PIPELINE-RESET, ALARM-RESET, UNIT-P-MISMATCH, ST-1, ST-2, ST-3, LT-1, LT-2, LT-3, XT-1, XT-2, and XT-3.

The Dynamic Alarm Limits utility reduces nuisance alarms by temporarily expanding the alarm limits for the calculated balance (deviation) whenever there is an event represented by a state or value change in a AVEVA Enterprise SCADA point assigned to the plm region. AVEVA Enterprise SCADA points that have these events are referred to as "triggers." The event is of a type that will cause a change in calculated linepack that does not represent the real current linepack. For example, if a pump is turned on, a pressure wave down the pipeline will occur. This will lead to a jump in telemetered pressure and an apparent linepack change that is not really occurring. By capturing the state change to the status or multistate point representing that pump, the balance alarm limits can then be adjusted to allow for the apparent imbalance that results.

The plm record will be in one of the following states according to trigger activation:

• Steady State – No trigger is in effect. No adjustments are in effect on the alarm limits. This state exists whenever the timestamp for all trigger points (field plm.DATrigger[].decaystimer) is 0.

• Transient State – One or more triggers are in effect for any balance period. Alarm limits will be adjusted. The state exists whenever the timestamp for a trigger point is positive (it is set to current time whenever a trigger event occurs). This is shown in the state transition diagram below.

  

When in a Transient State, the adjusted alarm limits will generally go from a period where they remain constant (the Hold period) to a period where they are declining to the configured Steady State limits (the Decay period). This progression is not absolute as there are a number of factors which can cause a declining limit to re-enter a Hold period.

The diagram below shows the logic followed each time that a plm record is processed.