ISO 06143 pdf download – Gas analysis -Comparison methods fordetermining and checking the compositionof calibration gas mixtures.
The recommended number of calibration points is greater than the number of indeterminate parameters of the analysis function because it is also necessary to validate the function chosen, It calibration experiments were only based on the minimum number ot calibration points, it would be necessary to validate the analysis function using additional reference gas mixtures. It Is better, instead. to Incorporate these additional reference points’ into the set of calibration points so as to reduce the calibration uncertainty of the estimated parameters.
For the majority of comparison methods, an appropriate zero gas’ will provide a valid calibration point.
) Step E: Select reference gas mixtures %t,i. M,,2 M,, such that their analyte contents .q. x ;,, span an appropriate calibration range, I.e. approximately equally spaced, with one value below the lower limit and one value above the upper limit of the analytical range.
The analyte contents shall be determined independentty to the greatest possible extent. Dilution series may only be used under the conditions specified in 5.4.2.
If Interferences between mixture components cannot be safely excluded, it may be necessary to use reference gases of similar composition to those of the calibration gases considered, for the critical components. In any case, it is recommended to use reference gas mixtures with the same complementary gas.
Calibration designs using equally spaced values for analyte contents are not the optimum choice for cases of strongly non-linear response. They are, however, well suited for linear and moderately non-linear responses. as considered in this International Standard [see C). step C).
Step F: Estabesh the standard uncertainties i4r1). i4v2) i4r,j ot the analyle contents x1. x. t,.
For reference gas mixtures prepared or analysed by recently standardized methods, the standard uncertainty for the content of each speofied component should be contained in the certificate of mixture composition.
For reference gas mixtures with other specifications of uncertainty. e.g. In terms of tolerance limits, these data have to be converted into standard uncertainties. If and t are the lower and upper tolerance limit of the anatyte content, and if all the vakies within this interval are equally likely as potentially true values, the data recommended for use as the analyte content and its standard uncertainty are the mean and the standard deviation of a rectangular distribution between the tolerance limits as follows:
NOTE 2 The invidual weighted cHerences call be used as a cagnostic tad for identifying potential outhers among the caithiation data,
In addition to the procedures described above, every calculated response curve has to be inspected vualty. This visual inspection is necessary to reveal nonsense correlahons which can occur without being detected by local examination 04 the curve fit to the calibration points, Such nonsense correlations are liable to occur in the case of polynomial response functions, which can exhibit non-monotonic behaviour with excellent local fit. Another case of nonsense correlations can occur it, by mistake, one of the calibration data uncertainties is very small. Then this calibration point Is given erroneously a very high weight. Consequently, the response curve is forced through this point with little impcwtance given to the other calibration points.
5.2.3 Examining compliance with uncertainly requirements
For the spec1iled analytical range, an upper bound is determined for the uncertainty of the prospective results based on the analysis function. This upper bound is compared with the acceptable uncertainly.
NOTE The calciifated tmceilainty takes 45 highest values at the bflits of the calibration range.
ISO 06143 pdf download – Gas analysis -Comparison methods fordetermining and checking the compositionof calibration gas mixtures
