The concept, requirements, and approach of value traceability
1. The concept of quantity transfer and quantity traceability
The quantity transfer is the whole process of transferring the measurement unit value reproduced by the national benchmark to the next level of measurement standard through verification/calibration (or other transmission methods), and then passing it to the work measuring instrument step by step to ensure that the measured object The value is accurate and consistent.
Accuracy refers to the degree to which the measurement result is consistent with the measured true value. That is, within a certain measurement uncertainty, error limit or allowable error range.
Consistency means that on the basis of a unified unit of measurement, no matter when, where, what method is used, what measuring instrument is used, and by whom, as long as the relevant requirements are met, the measurement results should be consistent within a given range.
The premise of accurate and consistent measurement means that the measured value must have characteristics that can be linked to national measurement benchmarks and international measurement benchmarks, that is, the measured value is traceable.
What is quantity traceability? The definition given in JJF1001-1998 "General Metrology Terms and Definitions" in 8.10 is "through an uninterrupted chain of comparison with a specified degree of uncertainty, so that the value of the measurement result or measurement standard can be related to the specified reference standard, usually with national measurement standards or international measurement standards." It can be seen from this that quantity traceability is the reverse process of quantity transfer. Value transfer is the top-down transfer of the value reproduced from the national measurement reference to the measurement standards at all levels step by step until the work measurement instrument; and value traceability is the bottom-up traceability of the measurement value to the national measurement reference, but this traceability is a conscious act, and it does not have to be traced through the first level.
2. Requirements for value traceability
On December 31, 2005, the General Administration of Quality Supervision, Inspection and Quarantine issued the "Administrative Measures for the Accreditation of Qualifications of Laboratories and Inspection Agencies", in which Article 30 stipulates: "Laboratories and inspection agencies shall conduct verification and calibration in accordance with relevant national technical specifications or standards before using measurement and testing equipment that affects the accuracy of testing and calibration". Article 31 stipulates: "Laboratories and inspection agencies shall ensure that their relevant measurement and calibration results can be traced back to national basic standards to ensure the accuracy of the results". 5.6.1 of ISO/IEC 17025:2005 "Standards for the Accreditation of Competence of Testing and Calibration Laboratories" states: "All equipment used for testing and/or calibration that has a significant impact on the accuracy or validity of testing, calibration and sampling results (e.g. equipment used to measure environmental conditions) shall be calibrated before being put into use." 9.1 of the "Evaluation Guidelines for Accreditation/Review Accreditation of Metrology" states: "Measurement and inspection equipment that has an impact on the accuracy and validity of the inspection must be calibrated and/or verified (verified) before being put into use."
3. Ways and means of value traceability
(1) Guarantee of value traceability
Our country promulgated the "Measurement Law" as early as 1985, and also formulated its supporting regulatory documents, and formulated a relatively complete verification system table, verification procedures and measurement technical specifications, etc., which provided legal guarantee and technical basis for value traceability.
A set of metrology administrative institutions and metrology technical institutions have been established in accordance with the law. These institutions are performing their respective functions and providing metrology technical services and management services for all sectors of society, ensuring the unification of the national measurement unit system and the accuracy and reliability of the measurement value. At present, a complete measurement basic system and measurement standard system have been formed. A complete range of measurement benchmarks and standards have been established in the China Academy of Metrology and the China Institute of Testing Technology, and they have participated in international comparisons many times to achieve international mutual recognition.
(2) The way to trace the value
In the CNAL/AR10:2002 "Value Traceability Policy" states: "CNAS recognizes the validity of our country's legal measurement system and the traceability provided by CNAS-accredited calibration laboratories", and further elaborates six ways to achieve value traceability directly or indirectly. In summary, there are four points: first, it is directly sent to a qualified verification/calibration institution for inspection and calibration to achieve value traceability; second, the laboratory establishes the highest standard (reference standard), and conducts internal inspection and calibration to achieve value traceability; third, through the use of certified standard materials (CRM) to achieve value traceability; fourth, when traceability to national standards (standards) is not possible or applicable, it should be traced back to recognized physical standards (standards, reference substances), or through comparison tests, participation in competence verification and other means to provide proof.
