Measurement Uncertainty - Requirements Set In Iso/iec 17025 And Iso 15189 Accreditation

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Uncertainty of measurement is defined as a “parameter, associated with the result of a measurement that characterizes the dispersion of the values that could reasonably be attributed to the measurand” (the measurand is the particular quantity subject to measurement) (International Vocabulary of Metrology, 2008).

There is growing recognition of the importance of Measurement Uncertainty (MU) to assuring the reliability of measurement. This is reflected in the standards ISO/IEC 17025 and ISO 15189, which contain specific requirements concerning these issues. The reactions to these developments range from interpretation at a minimal level, to extensive calculation of the uncertainty associated with each contributing factor. Uncertainty of measurement is best estimated within the individual laboratory/measurement environment. All factors which will have a significant influence on the test or measurement result must be included in the estimation process.

Measurement Uncertainty Categories

Following are the measurement uncertainty categories for the tests identified on the laboratory’s proposed scope ...
... of accreditation:
1. Qualitative or semi-quantitative tests for which measurement uncertainty budgets will not be required.
2. Published or standard test methods that specify limits to the values of the major sources of uncertainty of measurement and specify the form of presentation of calculated results. In such cases, the laboratory is considered to have satisfied this clause by following the test method and reporting instructions in their entirety.

• Chemical, environmental or biological test methods based on
published regulatory or consensus methods (e.g. AOAC, ASTM, APHA/AWWA, EPA) for which the measurement uncertainty is not defined in the method. For these types of tests, uncertainty estimates are required and can be determined using appropriate, published guidance documents such as the ISO/IEC “Guide to the Expression of Uncertainty in Measurement Guide documents, for example. Also, there may be test methods that have no significant sources of uncertainty other than random error and when this is the case, determining the random error satisfy the requirement for uncertainty estimation.

1. Test methods that need identification of the major components of uncertainty and a reasonable estimate of measurement uncertainty.
2. Test methods that need identification of all components of uncertainty and detailed measurement uncertainty budgets calculated in accordance with published methods that are consistent with those described in the ISO “Guide to the Expression of Uncertainty in Measurement”.

For ISO/IEC 17025 accredited laboratories, it is a common practice of Reporting measurement uncertainty in test and calibration certificates. With such requirements, an online course on Measurement Uncertainty Training is provided by Punyam Academy. By enrolling it users/participants will learn about Uncertainty Measurement overview, steps of calculation and examples for Mechanical, Dimensional, Electro-technical and Thermal Calibration.