Telemetry failures

A meter, tank, or linepack input is flagged as stale when a telemetry failure is detected. This can occur due to a communication outage affecting the connection to the remote, an outage affecting the remote itself, or a reading that is deemed invalid because it is outside the acceptable range as configured in the high limit check and low limit check values for the PLM volume device. For a tank, input is also flagged as stale if the tank or its underlying devices are in instrument failure condition.

Pipeline Monitoring (PLM) will address the telemetry failure in the following ways:

• A value of zero will be assigned to the volume change for every minute while the telemetry failure is in effect.

• The associated PLM record for the meter, tank, or linepack will be flagged as stale.

• The PLM record will stop calculating and an alarm activates alerting the Controller to the situation.

  Note: Linepacks that have Batch Tracking as the source application will always be set as fresh. Linepacks coming from a third-party application where the linepack is saved to an analog record have the potential to be set as stale.

By default, when the telemetry failure to the meter, tank, or linepack ends, the system will backfill the array elements that were assigned zero during the telemetry failure using the following procedure:

• The system will wait for two consecutive processing cycles before starting the backfill procedure. During these cycles, the system will continue to assign a value of zero to the minutely volume change.

• On the third processing cycle, the system will determine the total volume change since the telemetry failure was detected.

• The system will calculate an average volume change by dividing the total volume change over the number of one minute intervals since the telemetry failure has been detected until the current minute (inclusively).

• The system will assign the calculated average volume change to every minute that was set to zero due to the telemetry failure.

• Periodic volume balances are calculated with these retroactively assigned volume changes.

The Administrator has the option to disable this backfill behavior by selecting the Do Not Backfill Term Data option on the PLM configuration record. If this option is selected, the minutely values that were set to zero due to the telemetry failure will remain unchanged after recovery from the failure.