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AVEVA Pipeline Operations for Liquids

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Pipeline Monitor (PLM) period balances

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  • Last UpdatedApr 24, 2025
  • 3 minute read

Using a history of volume change totals and balances calculated per minute, balances can be calculated over user-defined intervals. There are 9 intervals that can be defined:

  • Three short-term intervals: Interval available is from one to 60 minutes.

  • Three long-term intervals: Interval available is from one to 24 hours.

  • Three extended-term intervals: Interval available is from one to 60 days.

For each interval, limits to the deviation can be defined and alarms issued if they are violated. For more information, refer to Understand Pipeline Monitor (PLM) deviation alarms for details.

In order to summarize the volume changes and balances for the periods, a history of the instantaneous volume data is maintained. The most recent 60 minutes of the instantaneous data is kept. At the top of each hour the volume changes and balances from the past 60 minutes is totaled and saved. The past 24 hours of the hourly volume data is kept. At the top of each day, the volume changes and balances from the past 24 hours is totaled and saved and these day totals are saved for 60 days.

Calculating the balances for each interval is done in the same way:

  1. Calculate the filtered volume changes from each element of the history that belongs to the interval. These are displayed on the Pipeline Monitor (PLM) Control window in easy eXtended Operator Station (ezXOS). This includes:

    • Meter In

    • Meter Out

    • Linepack (linefill)

    • Tank

    • Delta Flow

  2. Sum the filtered balance from each element of the history that belongs to the interval.

    This is displayed on the PLM Control window under the Deviation column in easy eXtended Operator Station (ezXOS).

  3. Compute the percentage balance, which is shown under the %Dev column on the PLM Control window.

The following table describes the Volume Balance Calculation for each Period Type.

Interval Type

Volume Balance Calculation

Frequency of Calculation

Short term

Σ balance from each minute over preceding configured interval.

Once per minute.

Long term

Σ balance from each hour over preceding configured interval, to the top of the last hour.

Once per hour, at the top of the hour that has been configured in the plm record as the Top of Day (TOD) hour. For information about the different options that PLM supplies for the configuration of the TOD hour, refer to Configure the Main tab on the Pipeline Monitor (PLM) record and Understand Top of Day (TOD) configuration respectively.

Extended term

Σ balance from each day over preceding configured interval, to the top of the last day.

Once per day, at the top of the hour that has been configured in the plm record as TOD hour. For information about the different options that PLM supplies for the configuration of the top of day hour, refer to Configure the Main tab on the Pipeline Monitor (PLM) record and Understand Top of Day (TOD) configuration, respectively.

Example

Consider the balances at 10:10 AM, on January 30, with TOD Hour set at midnight:

  • 20 minute short-term period: Balance is sum of one minute balances from 9:50 to 10:10.

  • 6 hour long-term period: Balance is the sum of one hour balances from 4:00 to 10:00.

  • 4 day extended-term period: Balance is the sum of one day balances from 0:00 January 26, to 23:59:59 January 29.