Possibilities of Linking Results of EURAMET and COOMET Key Comparisons for Power

The outcomes of the CIPM MRA are the internationally recognized Calibration and Measurement Capabilities (CMCs) of the participants of comparisons. Main results of the participating laboratories of National Metrology Institutes (NMIs) and Designated Institutes (DIs), measuring the same power in a framework EURAMET.EM-K5.1 and COOMET.EM-K5 key comparisons (KCs), are presented. 12 NMIs/DIs took part in EURAMET.EM-K5.1 KC. 13 NMIs/DIs participated in COOMET.EM-K5 KC. UME (Turkey), UMTS (Ukraine) and SMU (Slovakia) were joint participants in EURAMET.EM-K5.1 and COOMET.EM-K5 KCs. For Global Metrological Traceability, it is advisable to use a methodology for linking the results of Constative Committees (CCs) KC to Regional Metrology Organizations (RMOs) KC. The linking procedure of RMOs К C with respect to reference value of CC KC is described. Linked results of EURAMET.EM-K5.1 and COOMET.EM-K5 KCs for power are presented. Special conclusions on the results of UME, UMTS and SMU who participated in both KCs are presented.


Introduction
The Mutual Recognition Arrangement (MRA) of the International Committee for Weights and Measures (CIPM) [1] plays an important role for Global Metrological Traceability (GMT) [2]. Key comparisons (KCs) of the national measurement standards in different fields of measurements are the special comparisons of National Metrology Institutes (NMIs) and Designated Institutes (DIs) in the frame of Constative Committee (CC) of CIPM and Regional Metrology Organizations (RMOs). KCs of RMOs are equivalent to CC KCs.
For all KCs (CCs and RMOs) the reference value (RV) of KC and degree of equivalence (DoE) of the national measurement standards with corresponding uncertainty are established [3]. DoE is obtained as the deviation of its measurement result from the KC RV, together with the uncertainty associated with this deviation according to the CIPM MRA. DoE derived from an RMO KC has the same status as that derived from a CC KC. The CIPM MRA describes in general how the data of KC will be evaluated, but many different ways of evaluating KC data have been suggested [4][5][6].
RMOs have procedures for carry out the comparisons, in particular the Euro-Asian Cooperation of National Metrological Institutions (CООМЕТ) and the European Association of National Metrology Institutes (EURAMET). Results of KCs CC and KCs RMOs are published in special Key Comparison Database (KCDB) of the International Bureau of Weights and Measures (BIPM) [7]. Only CООМЕТ has guidelines on KC data evaluation [8].
The outcomes of the CIPM MRA are the internationally recognized Calibration and Measurement Capabilities (CMCs) of the participating in comparisons. The internationally recognized NMIs and DIs CMCs are those that are published in the KCDB of BIPM [9,10].
Establishment of GMT is carried out in accordance with procedures through international comparisons of the national measurement standards of NMIs or DIs. For GMT, it is advisable to use a methodology for linking the results of CC KC to RMO KC and RMO KC to other analogical RMO KC [11,12]. Refer methodologies can be used for practical assessment of results of specific RMOs KCs as an extension of the technical basis of confirmation of CMCs of NMIs or DIs.   Table 1. Table 1 RVs and uncertainties for EURAMET .EM-K5 . 1 and COOMET .EM-K5 KCs Power factor The degrees of equivalence of i-th NMI or DIs and its expanded uncertainties with respect to the KC RV are estimated as [8]: Result for all NMI/DIs participants of both KCs satisfies the condition of performance and characterizes good data consistency.

Evaluation of results of EURAMET and COOMET key comparisons
The DoE of i-th NMI/DI with respect to linking to CCEM-K5 is estimated as where D i is result from EURAMET.EM-K5.1 or COOMET.EM-K5 for a NMI participant in respectively KC only; d i is best estimate of result from i-th NMI/DI to linking to CCEM-K5.
Measurements from the linking NMIs/DIs provide estimates for the correction Δ. The correction Δ is then calculated as the weighted mean of the linking NMIs/DIs estimates, that is: is calculated as: O. Velychko [14,15], Table 2, 3 respectively and on Fig. 1-5. UME (Turkey), UMTS (Ukraine) and SMU (Slovakia) were joint participants in EURAMET.EM-K5.1 and COOMET.EM-K5 KCs. The sign "*" (only for COOMET.EM-K5 KC) indicates those NMIs/DIs that participated in both comparisons and have two different results.
DoE difference (the smaller the number module, the better) and DoE uncertainty difference (the sign "-" means less uncertainty) of NMIs/DIs in COOMET. EM-K5 and EURAMET.EM-K5.1 KCs are presented in Table 4.

Conclusion
KCs play an important role in internationally recognizing the measurement results of NMI/DI and achieving traceability of GMT. Obtained results for all NMIs/DIs of both KCs have good data consistency. Those KCs will be able to provide support CMCs entries for NMIs/DIs for power in Appendix C of the CIPM MRA.