K143 – Calorific Value and Relative Density – ISO 6976


Form: K143 – Calorific Value and Relative Density – ISO 6976

Form Reference: C111

Calculation Details


This test can be used to validate the standard density, relative density, molecular weight, calorific value and/or Wobbe index of a gas composition being calculated by a flow computer.

Test Equipment

No test equipment is needed for this test to be carried out.


In this example the 1995 version of the ISO 6976 standard is used.

The options here are selected so that a simple gas composition is entered with a C6+ split.

Molecular Weights are rounded. This uses the molar mass vales found in Table 1 rather than calculating them using full precision from the atomic masses given in the footnote of Table 1.

Ideal Calorific Values set to be calculated from the values in Table 3 rather than Tables 4 & 5 for mass and volumetric values respectively.


When setting up the form it is good practice to set the components to “User Entry With Default” as this means values that are zero or not represented in the composition do not need to be explicitly entered as zero every time a test is run. If using a fixed composition it would make sense to enter that while setting up the test so to avoid repeating the task and risk typing errors. For the C6+ split the ratios have been fixed.


This form has several outputs.

Outputs that are not needed to be displayed can be removed in the test form by clicking Manage on the Outputs section of the Configuration ribbon.

The error mode will be percentage of calculated value.

The source type here is set as user entry, however, if the FM²P.net system is set up to do so, OPC Server can be selected to automatically read the value being used by the flow computer.

The units are set as kg/Sm³ as default for standard density, MJ/Sm³ for volumetric calorific value and compressibilities should be shown as decimal numbers.

The typical tolerances for this test is 0.001 %.