However, in some circumstances, an alternative approach using ordinary least squares may be acceptable and calculation of uncertainty in processed mole fractions in this situation is described in Annex C.Ĭalculate the uncertainty of the raw mole fraction for components determined directly by using the appropriate equation selected from Table 1.Ĭalculate the uncertainty of the raw mole fraction for any additional components determined indirectly by using the appropriate equation selected from Table 2. ISO 6974-1 recommends the use of the generalized least squares (GLS) approach for calculation of the processed mole fraction.

Annex A provides a method for use when the methane-by-difference approach (see ISO 6974-1:2012, Annex C) is employed. Subclause 5.3 describes methods for estimating the uncertainties of processed mole fractions calculated from raw mole fractions using the conventional normalization method.

Uncertainties associated with the component mole fractions shall be calculated in accordance with ISOIIEC Guide 98-3.įor Type 1 analyses in accordance with ISO 6974-1, the uncertainty calculation includes random and systematic uncertainties from three main sources: uncertainty of the certified reference mixtures, uncertainty of analysis and uncertainty of the data fitting procedure.įor Type 2 analyses in accordance with ISO 6974-1, the uncertainty calculation includes both random elements and systematic errors introduced by the assumption of a linear response through the origin, the systematic errors being calculated from the results of the initial performance evaluation. ISO 6974-2:2012 pdf download-Natural gas一Determination of composition and associated uncertainty by gas chromatography一 Part 2: Uncertainty calculations.

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