Recently, the China National Accreditation Center for Conformity Assessment has organized a series of special investigations, combined with the hot issues of concern in the industry, and launched a series of accreditation review cases for CNAS-CL01 "Accreditation Criteria for Testing and Calibration Laboratories".
7 Process Requirements
7.6. Evaluation of measurement uncertainty.
Overview: Identification of the ** of measurement uncertainty and the assessment of measurement uncertainty should take into account all significant contributions (76.1）
Requirements for calibration laboratories (7.)6.2）
Requirements for testing laboratories (7.)6.3）
The problems with this clause mainly focus on the flaws in the measurement uncertainty analysis and evaluation process.
cnasPublished documents related to the assessment of measurement uncertainty
Mandatory Required Documents:
CNAS-CL01-G003 "Requirements for Measurement Uncertainty".
This document is based on the CNAS-CL01 Guidelines for the Accreditation of Competence in Testing and Calibration Laboratories and the ILAC-P14 ILAC Policy on Measurement Uncertainty in the Field of Calibration, in conjunction with the relevant content of the ILAC-G17 Guidelines for the Measurement Uncertainty in the Testing Field.
The document is intended for testing laboratories and calibration laboratories, as well as for testing and calibration activities of conformity assessment bodies such as medical laboratories, inspection agencies, biobanks, reference material producers (RMPs) and proficiency testing providers (PTPs).
The contents of the document include:
General Requirements. Requirements for calibration laboratories.
Requirements for testing laboratories.
Guidance documents (not mandatory):
CNAS-GL006 Guidelines for the Evaluation of Uncertainty in Chemical Analysis
CNAS-GL007 "Guidelines for the Evaluation of Measurement Uncertainty in the Electrical Appliance Field".
CNAS-GL010 "Guidelines and Examples for Uncertainty Evaluation of Measurement in Physical and Chemical Testing of Materials".
CNAS-GL016 "Guidelines and Examples for Evaluating the Uncertainty of Physical and Chemical Testing and Measurement in the Petroleum and Petrochemical Field".
CNAS-GL022 "Guidelines for Assessing the Uncertainty of Detection and Measurement Based on Quality Control Data Environment".
CNAS-GL023 "Guidelines for Measurement Uncertainty Assessment of Typical Parameters in the Field of Automobile and Motorcycle Testing".
CNAS-GL026 "Guidelines and Examples for Measurement Uncertainty Assessment in the Radio Field".
CNAS-GL043 Guidelines for Evaluating the Measurement Uncertainty of ELISA Tests in Veterinary Testing Laboratories
CNAS-TRL-001 "Medical Laboratory—Evaluation and Expression of Measurement Uncertainty".
CNAS-TRL-002 "Examples for Evaluation of Uncertainty in Textile Testing and Measurement".
CNAS-TRL-003 Evaluation and Examples of Calibration and Measurement Capabilities (CMC).
CNAS-TRL-007 "Application of Measurement Traceability of Typical Inspection and Testing Equipment in the Construction Field in the Evaluation of Uncertainty of Test Results".
Measurement uncertainty rating
7.6.1 Laboratories should identify the contribution of measurement uncertainty. When assessing measurement uncertainty, all significant contributions, including those from sampling, should be taken into account using appropriate analytical methods.
Interpretation:
This clause requires laboratories to identify all possible uncertainties**, including sampling, when conducting measurement uncertainty assessments. Even if the potential for uncertainty is small, there must be evidence to prove whether the uncertainty can be ignored.
Uncertainty includes, but is not limited to, the reference standard and reference material used, the method and equipment used, the environmental conditions, the performance and condition of the calibration article being tested, and the operator.
The contribution of sampling to uncertainty should be considered when the accreditation criteria first proposed uncertainty assessment, although the impact of sampling on uncertainty is still in the exploration stage, but laboratories still need to consider it as much as possible.
The laboratory performing the test should assess the measurement uncertainty. When it is difficult to critically assess the measurement uncertainty due to the detection method, the laboratory should base the evaluation on the basis of an understanding of the theoretical principles or practical experience using the method.
Note 1: In some cases, accepted test methods prescribe limits for measurement uncertainty and specify how the results of calculations are presented, which laboratories meet as long as they comply with the test methods and reporting requirements.76.3 requirements.
Note 2: For a particular method, if the measurement uncertainty of the results has been determined and verified, the laboratory does not need to rate the measurement uncertainty for each outcome as long as the laboratory demonstrates that the identified key influencing factors are controlled.
Note 3: For more information, see ISO IEC Guide 98-3, ISO 21748 and ISO 5725 series of standards.
Interpretation:
This clause is a requirement for testing laboratories to evaluate measurement uncertainty, and in the new version of the accreditation criteria, the requirements for evaluating measurement uncertainty are basically the same for testing laboratories and calibration laboratories.
7.6.Notes 1 and 2 of the 3rd article describe two specific situations.
In the CNAS-CL01-G003 "Requirements for Measurement Uncertainty", the requirements that were originally only applicable to calibration laboratories are put into the general requirements, such as 45 and 4Clause 6, which now applies equally to testing laboratories. Moreover, the requirements for CL01 are specified in detail in this document, and the laboratory should also comply with these requirements when operating the management system.
The requirements for testing laboratories in Chapter 6 of CNAS-CL01-G003 are as follows for examples, and please refer to the document for others.
For testing laboratories, 6Article 1 clearly stipulates that "the testing laboratory shall analyze the contribution of the measurement uncertainty to the test results and shall evaluate the measurement uncertainty of each measurement result expressed numerically." ”
If the test result is not numerically expressed or based on a numerical value (e.g., pass, fail, negative, positive, or visual and tactile definitive tests), it is advisable for the laboratory to use other methods to assess measurement uncertainty, such as the probability of false positives or false negatives. (cnas-CL01-G003:2021 p. 6.)Article 2).
When a testing laboratory adopts a new testing method, the measurement uncertainty should be re-evaluated according to the new method. (cnas-CL01-G003:2021 p. 6.)Article 5).
For the confirmation of non-standard methods, the evaluation of measurement uncertainty should be included, and this requirement can be found in CNAS-CL01-G003:2021 No. 66.
For the measurement uncertainty, different types of laboratories are quite different, if you need the software testing laboratory "Measurement Uncertainty Evaluation Procedure" as a reference, you can send me a private message.
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