BS ISO 12963:2017 pdf download – Gas analysis Comparison methods for the determination of the composition of gas mixtures based on one- and two-point calibration
6 Principle
6.1 General requirements The composition of a gas mixture is determined by separate measurement of the amount fraction of every specified componen t. “Separate” implies that the response obtained for the component of interest is treated independently of any other response obtained for any other componen t. It does not impede obtaining several responses for several components in the same instrument run. Therefore , the procedure for determining the amount fraction of only one specified component is described. Possible interferences of other components on the measurement ofthe component ofinterest shall be avoided or corrected for separately. This subject is not further addressed in this document. The procedure for determining the amount fraction X of a specified component X in a sample of a gas mixture , or in a series of such samples , is performed in a sequence of steps as summarized below.
a) Specify the analytical range of interest , R , i. e. the range of the amount fraction x to be determined , and the acceptable or required (if applicable) uncertainty level
b) Specify the analytical method and the measuring system to be used:
1) calibration range (to encompass the analytical range);
2) composition , including uncertainty , of the calibration gas mixtures;
3) parameters of the analytica l method;
4) measuring conditions;
5) number and sequence of calibration measurements
c) Select,from the list given in 6.2, an approach for calibration and determining the amount fractions of components in unknown samples in the regular, i.e. daily mode when one- and two-point basedanalysis functions are used.
d) For the relevant ranges of responses and component amount fractions, determine the uncertainty level of the prospective results based on the analysis function. If the result is acceptable,performance evaluation was successful.
For the calculation of the measurement uncertainty of results obtained in the regular calibrationmode, an estimate u(4) for the contribution of possible nonlinearity of the system is needed. Thisestimate is calculated in a performance evaluation of the system according to Clause 8and Annex C.The evaluation is best done after the specifications according to a) to c) are set. The estimate isused in all subsequent regular calibrations until there is reason to assume significant changes inthe instrument performance. The main reasons for such changes are given in 9.1.
e)Perform calibration and measurement according to the steps given in Clause 7.6.2Calibration methods
The following calibration methods for determining the amount fraction of a specified component in anunknown gas sample may apply:
a) single-point exact-match calibration (SPEM) and direct transfer of value and uncertainty of the matching calibration gas mixture;
b) single-point through origin calibration (SP0) and transfer of the value assuming a straight-linecalibration function through the origin;
c) two-point calibration using a single-point and a blank (TPB) calculation of the value from a straight-line analysis function;
d) two-point calibration: bracketing using two calibration gas mixtures (TPC).NOTE Multipoint calibration (MPC) uses at least three calibration points.
7Main procedure
Stability of the system within the period of time equal to a normal calibration interval shall bedemonstrated during method validation.The use of unstable systems is strongly discouraged in general,in particular for designs SPO and TPB in 6.2.For use of designs SPEM and TPC with not sufficientlystable systems,see Annex A.
7.2Sequence of operations (overview)
Figure 1 illustrates the basic steps of carrying out measurements according to the calibration methodsdescribed in this document. Aims, steps and frequency of the performance evaluation are describedin Clause 8.
7.3 Calibration and measurement designs7.3.1 General
All designs as specified in 6.2 consist of four basic steps, namely
– step A: calibration of the instrument;
– step B: measurement of the sample;
– step C: calculation of the unknown amount fraction of the component in the sample;
-step D: calculation of the uncertainty of the amount fraction of the component.
ln practice, steps A and B apply in order to adjust the calibration gas mixture to the unknown sample,in particular for SPEM and SP0.For SPEM, the calibration gas mixture shall resemble the unknown (see7.3.2); for SPO0, the measured response of the sample shall be in the predefined range in the vicinity ofthe response of the calibration gas mixture.BS ISO 12963 pdf download.