ISO 13752 pdf download.Air quality — Assessment of uncertainty of a measurement method under field conditions using a second method as reference
1 Scope
This International Standard specifies a method for assessing the measurement uncertainty of a calibrated measurement method (test method) applied under field conditions using a second method as a reference (reference method). The reference method may not necessarily be a legally prescribed measurement method. The measurement uncertainty is derived from measurements made in parallel on real samples by comparing the measured values of the test method with those of the reference method. The result is only valid within the range of the measurements obtained. The test is designed especially for method validation.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 6879:1 995, Air quality — Performance characteristics and related concepts for air quality measuring methods . ISO 91 69:1 994, Air quality — Determination of performance characteristics of measurement methods
NOTES 1 The first assumption can be considered as fluctuations of the background or intercept value b 0 without fluctuations of the slope b 1 and the second as fluctuations of the slope without fluctuations of the background or intercept value. 2 The value of the coefficients of the regression function (estimation of bias) is not seriously affected by deviations from the assumption on the standard deviation. However, the estimated random part of measurement uncertainty heavily depends on the assumption. The general variance function used in this International Standard accounts not only for the variability of intercept and slope but also for statistical noise, the standard deviation of which is proportional to the square root of the value itself (approximately proportional to the square root of x)
5 Requirements
5.1 General The method described in this International Standard requires that: — a linear relationship exists between the variables compared; if the relationship is different but mathematically known the procedure may be adapted. — the measurement errors of the test method are normally distributed. — the measurement uncertainty of the reference method is insignificant compared to that of the test method; if not, it is falsely attributed to the test method and this will result in overestimating its measurement uncertainty. — the impact of differences in composition between the air sampled by the two methods is negligible compared to the expected uncertainty of the test method; if not, this error component is falsely attributed to the test method and will result in overestimating measurement uncertainty. The uncertainty of the coefficients calculated by this International Standard will be reduced by increasing the number of measurement pairs. Therefore, it is recommended that at least 30 measurement pairs be obtained if the general variance model described in this International Standard is applied.5.2 Test method (y-method) Specify all steps of the measurement method which will be subject to the assessment and execute the measurements as specified. 5.3 Reference method (x-method) In view of the provisions and environmental conditions, e.g. interfering substances, temperature etc., to be expected at the test site, investigate whether the assumption is justified that the x-method yields insignificant uncertainty compared to the y-method. This investigation may be based on the properties of the measurement principle, literature data or results of laboratory tests or field tests. Describe the x-method in detail and execute the measurements accordingly.