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Gas Meters with Moledular Weight Comparison Between Cases

This analysis rule indicates the in-service gas mass/volume measurement elements with a change of molecular weight value between Cases that is greater than the configured delta limit (difference). The limit is in percent of value and in engineering units. A limit of zero means that the limit has not been configured. The limit must be greater than zero for the limit to be used.

Any in-service gas meter with a molecular weight value change greater than the configured limit is reported to the Case log, which you can view in the Log tab of the Case Properties window. The output contains a list of meters in violation, and a description of the violation.

The following table lists a sample log output for this analysis.

Sample Log

TimeSeverityElementAttributeMessage
9/1/2005 10:05...REPORTING METER WITH ZERO MW AND NONZERO MEASUREMENT
9/1/2005 10:05WarningMeterBMolecularWeightCurrent Case: 90, Previous Case:45, Diff: 45, %Diff: 50

Analysis Method​

  1. Collect a list of all gas meter elements in the current Case that satisfy the following criteria:
  • Status Attribute value is IS (In Service)
  1. Collect all of the in service gas meter elements from the previous case.
  2. Calculate the difference and percentage change between the current Case and previous Case values. If the absolute value of the difference or percentage change breaks the configured thresholds report the offending element.
  3. Write to the log section of the case. Report the test name and the Measurement Basis. Report the list of offending meters, ordered by name and cause of violation.

Configuration Using the Wizard​

The configuration of the Gas Meter's molecular weight comparison between cases is a selection of the General Gross Error Analysis Rule. You open the window for configuring the test (shown in the following figure) from the General Gross Error Analysis Rule Wizard.

  1. Open the Gross Error Configuration window as described in Configuring - General Gross Error Analysis Rule.

  2. On the Liquid/Gas Meters tab, select Gas meter molecular weight comparison between cases.

    A Gas meter molecular weight comparison between cases - Attributes window opens.Figure 399: Gas meter molecular weight comparison between cases - Attributes window

  3. Select the Attributes according to the following table:

    Attributes

    SelectionsDescription
    Molecular WeightMeter Molecular weight. The default is 'MolecularWeight'.
    DifferenceEnter a value in the engineering unit of the Measured attribute.
    Percent DifferenceEnter a value in percent.
    StatusMeter in/out of service status. This defaults to 'ObjectStatus'.

  4. Enter the Difference and Percentage Difference thresholds.

  5. Click OK to finish the configuration.

    The text "CONFIGURED" displays next to the 'Gas meter molecular weight comparison between cases' selection.

  6. To run this test, see Running the General Gross Error Analysis.