ISO 6974-2:2012 pdf download.Natural gas -Determination of composition and associated uncertainty by gas chromatography — Part 2: Uncertainty calculations.
5.2 Principles
Uncertainties associated with the component mole fractions shall be calculated in accordance with ISO/IEC Guide 98-3.
For Type 1 analyses in accordance with ISO 6974-1, the uncertainty calculation includes random and systerratic uncertainties from three main sources: uncertainty of the certified reference mixtures, uncertainty of analysis and uncertainty of the data fitting procedure.
For 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.
Subolause 5.3 describes methods for estimating the uncertainties of processed mole fractions calculated from raw mole fractions using the conventional normalization method. Annex A provides a method for use when the methane-by-difference approach (see ISO 6974-1:2012, Annex C) is employed.
ISO 6974-1 recommends the use of the generalized least squares (GIS) approach for calculation of the processed mole traction. 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.
5.3 Step 9— Calculation of uncertainty of mole fractions
5.3.1 Determining the equations to be used
5.3.1.1 General considerations
The equations to be used in this step for calculating the uncertainty of mole fractions are given in 5.3.2 and 5.3.3. The equations to be used should be determined by following the three-stage process described in 5.3.1.2 to 5.3.1.4.
Uncertainties associated with the component mole fractions shall be calculated in accordance with ISO/IEC Guide 98-3.
For Type 1 analyses in accordance with ISO 6974-1, the uncertainty calculation includes random and systerratic uncertainties from three main sources: uncertainty of the certified reference mixtures, uncertainty of analysis and uncertainty of the data fitting procedure.
For 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.
Subolause 5.3 describes methods for estimating the uncertainties of processed mole fractions calculated from raw mole fractions using the conventional normalization method. Annex A provides a method for use when the methane-by-difference approach (see ISO 6974-1:2012, Annex C) is employed.
ISO 6974-1 recommends the use of the generalized least squares (GIS) approach for calculation of the processed mole traction. 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.
5.3 Step 9— Calculation of uncertainty of mole fractions
5.3.1 Determining the equations to be used
5.3.1.1 General considerations
The equations to be used in this step for calculating the uncertainty of mole fractions are given in 5.3.2 and 5.3.3. The equations to be used should be determined by following the three-stage process described in 5.3.1.2 to 5.3.1.4.
