Understand the Pipeline Monitor (PLM) signature plot

Note: Although this section refers to signature plots of long-term and short-term windows, only the 1-minute short-term window has been implemented as part of the Pipeline Monitor (PLM) application. This signature plot is based on the 60 most recent minutely readings of metered flow into and out of a region, along with the 60 corresponding minutely linefill calculations within that region.

References in this section to signature plots of long-term windows are for information only. The PLM application currently supports all of the data collection and calculations for six separate windows (three short-term windows and three long-term windows). However, the signature plot is only available for the 1-minute window.

The signature plot shows volume balance or volume imbalance in terms of flow differences and linepack changes. A signature plot is available for each time window in a section bounded by flow meters. Signature plots are used:

• During pipeline operation to help Controllers determine the possible causes of leak alarms or false alarms triggered by volume imbalances.

• During a commissioning period for adjusting relevant parameters such as filtering coefficients, or bulk modulus.

Controllers can view the signature plot on the PLM Detail window in easy eXtended Operator Station (ezXOS). For more information, refer to the AVEVA Pipeline Operations for Liquids Controller documentation.

Volume balance is calculated in a pipeline section bounded by flow meters using the following equation:

where:

Vout - Vin = is the volume difference between outlet and inlet points during a given time period.

∆LP = is the change in linepack in the pipeline section bounded by the flow measurements during that same period.

This expression can be plotted as a diagonal line with a slope of -1 in an X-Y coordinate called a signature plot. The figure below shows the relationship between volume difference and linepack change in a signature plot.