ALTERNATIVE EVALUATION THE RESULTS OF KEY COMPARISONS OF NATIONAL STANDARDS

Abstract

In the framework of the Agreement of International Committee on Weights and Measures on Mutual Recognition of national standards, calibration and measurement certificates issued by national metrology institutes (NMIs), key comparisons serve as the basis for establishing calibration and measurement capabilities of NMI with implemented quality management system. On this basis, the competence of a specific NMI to perform calibration of working standards and measuring instruments for the customer laboratories is determined. In order to attract as many NMIs as possible to participate in key comparisons of standards, Regional Metrology Organizations are widely involved in conducting such comparisons. The practical application of traditional evaluation the results of key standards comparisons and displaying them in the special database of key comparisons (KCDB) of International Bureau on Weights and Measures (BIPM) may be difficult for some NMIs and for national laboratories accredited by national accreditation bodies that wish to use NMI calibration services. This is due to the fact that the KCDB BIPM only displays the degree of equivalence of a NMI standard with corresponding expanded uncertainty without any other characteristics for evaluating calibration or measurement capabilities. The paper presents a proposed alternative evaluation of results of key comparisons of standards, which simplifies the analysis of calibration services by NMIs. It envisages the use as a criterion of consistency of the results obtained from the comparisons of the En index to analyze the degree of equivalence of the NMI standard and the corresponding extended uncertainty. The practical application of the evaluation for results of key comparisons of standards of electric power is considered. This contributes to a more streamlined calibration of work standards for specific established purposes for both NMIs and accredited laboratories.