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Set Mass Calculation for Elements

Elements that participate in the mass balance need to have a mass calculated for each flow, transfer and inventory Element in the model. Examples of ways to get the mass Attribute value are as follows:

  • Directly from a PI Point
  • Calculated from a Volume
  • From a Level Gauge
  • Determined in Self-Calculated Inventories

Mass - Directly from a PI Point​

When a mass is stored in a PI Server as a tag value, you can use the PI Point Data Reference to retrieve its value. It is important to know what the data is that is being stored in PI. In order to import the correct value into the analysis case, you need to know whether the value is a continuous mass rate or a mass measurement and also what the unit of measure is for the value.

See the PI Point Data Reference topic found under Data Reference for more information about configuration options.

Mass – Calculated from a Volume​

To calculate a mass from a volume and density, use the Unit of Measure Data Reference to calculate the Mass. The volume and density Attributes have sources for their values, and you can use the Unit of Measure Data Reference (see [Unit of Measure Data Reference](/DocumentDepot/DocSFHub/docs_2026/docs-sf-system/DATA-REFERENCE/UOM/unit-of-meas-data-ref-intro) found under Data Reference) to make this calculation.

It is important to determine that the volume used in this calculation is a Net Volume and not a Gross (Observed) volume. You can use the Gross to Net Volume calculation of the Sigmafine Data Reference to aid in this intermediate calculation.\See Sigmafine Data Reference found under Data Reference for more details.

Mass – Calculated from a Level Gauge​

To calculate the mass from a level or gauge value measurement, use the Strapping Table or Polynomial Equation calculations in the Tank Volume from Gauge Data Reference. \See Tank Volume from Gauge Data Reference under Data Reference for more details.

Mass - Determined in Self-Calculated Inventories​

If an inventory mass is not measured and you want it to be calculated during the mass balance, follow these steps.

  1. Set the Attribute SelfCalculatingFlag to True in the element. Note that in Sigmafine 4.4 and later, you cannot change this Attribute name from the default name of SelfCalculatingFlag.

  2. In the initial Case for an analysis series, adjust the value of the Reconciled Quantity in the Case results to the opening quantity for the inventory. The analysis rule uses the reconciled value Attribute in each prior Case for initialization. Therefore, the mass must be set manually in the first case. To set the value of the mass, create an adjustment in the attribute.

    \Adjustments are described in Creating an Adjusted Value found under Server & Client.

This is the logic used to calculate quantity in self-calculated inventories.

When the Analysis Rule is set to use the previous Case for inventory opening quantity, the reconciled quantity is defined by this equation:

Reconciled Quantity = Reconciled Quantity Previous Case + Quantity from Flows In - Quantity from Flows Out

If values exist for both a measured quantity and a reconciled quantity, then the value for the measured quantity is used.