Regional Metrology Organization Research Articles

COOMET key comparison COOMET.PR-K1.a.2018 for spectral irradiance 250 nm to 2500 nmm, final report

Main textThis report describes the Key Comparison COOMET.R-K1.a.2018 for spectral irradiance in the wavelength range of 250 nm to 2500 nm, conducted by the Regional Metrology Organization "Euro-Asian Cooperation of National Metrological Institutions" (COOMET). The comparison was, in fact, a combination of three bilateral comparisons with the same link/pilot laboratory - the All-Russian Research Institute for Optical and Physical Measurements (VNIIOFI), the Russian Federation. The non-link laboratories were the Belarusian State Institute of Metrology (BelGIM), Belarus, the National Scientific Centre "Institute of Metrology" (NSC IM), Ukraine, and the National Metrology Institute of Türkiye (TÜBİTAK UME), Türkiye.The aim of the comparison was to link the BelGIM, NSC IM and TÜBİTAK UME measurement results to the CIPM key comparison CCPR-K1.a.2017, conducted by the Consultative Committee for Photometry and Radiometry (CCPR).Tungsten quartz halogen lamps of the FEL type (1000 W) were used as artefacts. Each participant used its own set of lamps. The sequence of measurements was participant - pilot - participant. The pilot measurements of the described here COOMET comparison were performed in a short time (within three months) after completing the measurements of CCPR-K1.a.2017, where VNIIOFI also was a pilot, which provided a high quality link.NSC IM performed measurements in the full spectral range, from 250 nm to 2500 nm, while BelGIM and TÜBİTAK UME managed to cover the range from 250 nm to 1100 nm only.The analysis of the comparison was performed following the approach described in the Appendix A of the Guidelines for CCPR and RMO Bilateral Key Comparisons (CCPR-G5). Differences from KCRV of BelGIM and TÜBİTAK UME, for the most of the measured wavelengths, do not exceed 2% and are within the expanded uncertainties. For NSC IM the differences from KCRV are within or comparable with the uncertainties in the IR range, from 900 nm to 2500 nm, but become larger with decreasing wavelength in the visible and UV reaching 9% at 250 nm.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Estimating the long-term drift of travelling measurement standards for comparisons

In metrology, it is essential to analyse the instrumental drift of measuring instruments and measurement standards. Each reference instrument is periodically calibrated according to a frequency determined by the laboratory. Calibration establishes the metrological state of the instrument on a certain date of calibration. However, it is necessary to know the state of the measuring instrument during or after the calibration.
 Reliable accounting for drift plays an important role in maintaining measurement accuracy. Otherwise, it can lead to significant measurement errors. Accounting for time drift is mandatory when conducting international comparisons of national measurement standards. The drift uncertainty can be evaluated from its history of successive calibrations. In the absence of such a history, the magnitude order of the calibration uncertainty can be estimated.
 The analysis of the long-term drift of travelling measurement standards is limited to examples of key and supplementary comparisons of measurement standards of electrical capacitance. Quite a lot of such comparisons were conducted both by the Consultative Committee for Electricity and Magnetism (CCEM) and by most of the Regional Metrology Organizations (RMOs). There are international standards and guides that describe various statistical methods of analysing the measurement results.
 For capacitance measurement standards, time drift is predictable and nearly linear. For comparisons of measurement standards, a linear model is more than often applied, as a travelling measurement standard with excellent stability characteristics is used. The consistent results have been obtained. The linear model was applied to estimate the drift of travelling measurement standards during the key and supplementary comparisons (COOMET.EM-K4, COOMET.EM-S4, and COOMET.EM-S13) of measurement standards of electrical capacitance. The estimation of the long-term drift of measurement standards of electrical capacitance as travelling measurement standards for comparisons using a polynomial regression are presented.

Analysis of a regional metrology organization key comparison: model-based unilateral degrees of equivalence

A statistical testing method is developed to analyze a Regional Metrology Organization (RMO) key comparison (KC) with linking to the corresponding KC conducted by the International Committee of Weights and Measures (CIPM). We establish a statistical model to which a generalized least-squares method is applied to determine a linking invariant, ensuring that the CIPM KC reference value is unchanged by the analysis. The proposed method generally gives different unilateral and bilateral degrees of equivalence (DOEs) from those assessed by other methods. The approach accounts for uncertainty information provided by all participating laboratories and correlation information provided by the linking laboratories. Since decisions are made on the basis of calculated DOEs, we emphasize that it is valuable to have adequate knowledge of the properties of methods used for analyzing the results from an RMO KC.

Main results of supplementary comparisons of high voltage and current measuring systems

High voltages of alternative current (AC) are important because they are needed for numerous applications in physics and engineering. High AC voltages are also used to test insulating materials for their dielectric properties. Calibrations of instruments for high-voltage measurements should provide metrological traceability to national standards. This applies to the requirements for both voltage measuring instruments and current measuring instruments. The transformer for high-voltage measurements is used to reduce the values of currents and voltages during measurements in high-voltage electrical networks.
 Voltage transformers (VTs) are used to accurately measure high AC voltages. Current transformers (CTs) are used to convert line currents in power systems to levels that are acceptable for other measuring instruments, which are necessary to trip protective devices. There are measuring installations that are well known for accurate measurements of the CT coefficient for large primary currents, and systems for determining the behaviour of the industrial current and VT under distorted waveforms, etc. The calibration of a high voltage measuring system must be traceable to national or international measurement standards. Mutual comparisons of calibration results of CT and VT standards are carried out with the participation of several national laboratories.
 The results of high voltage transformer measuring systems (GULFMET.EM-S6) and high current transformer measuring systems (GULFMET.EM-S7) supplementary comparisons are described. The comparisons were carried out between national laboratories from three Regional Metrology Organizations. In general, the participants of both comparisons have demonstrated a good agreement of the results in the ratio error and phase displacement for high voltage and current. The comparison results may be used to improve the participants’ existing calibration and measurement capabilities entries in the Key Comparison Database (KCDB) of the International Bureau of Weights and Measures (BIPM).

Involvement and use of European Metrology Programme for Innovation and Research EMPIR in the Czech Metrology Institute – a positive example of the use of European cooperation

The Czech Metrology Institute (CMI) has been the national metrology institute of the Czech Republic since 1993. The significant development of the CMI's fundamental metrology departments and the gradual growth of the CMI's scientific and research capacities are linked to its successful participation in the European Metrology Research Programme (EMRP) and the European Metrology Programme for Innovation and Research (EMPIR). In total, 28 countries have participated in the EMPIR Programme, with Switzerland, Norway, Serbia, Bosnia and Herzegovina, Turkey and the UK in addition to the EU Member States. The necessary organisational and administrative background for the realisation of the EMPIR Programme was provided by EURAMET e.V., a European Regional Metrology Organisation operated as a non-profit association under German law. The most important benefit of the Programme for the CMI and the Czech Republic is the successful implementation of the research results of individual EMPIR projects. Within the framework of this implementation of the EMPIR results in the CMI, 6 new state measurement standards of the Czech Republic have already been established and another 4 are in the stage of preparation for announcement. Furthermore, 23 new or significantly modified measurement methods have been developed based on the results within the CMI and are now provided as a service by the CMI. Finally, participation in the EMPIR projects has been used to train 42 new CMI scientists in various fields of measurement. If to add to this the use of the results of the former EMRP Programme, it can be concluded that the development of metrology at the CMI over the last 10 years has been strongly conditioned by successful participation in European Metrology Programmes and the ability of the CMI to subsequently apply the results of individual projects to its laboratory practice.

Calibration of GNSS stations for UTC

Global navigation satellite system (GNSS) time transfer has been used for four decades in the generation of universal time coordinated (UTC), starting with GPS in the 1980s. Calibration of GNSS receivers is then essential to ensure that time links used in UTC are accurate and remain stable with time. In this paper we study the different calibration schemes based on relative calibration of GNSS receivers that have been operated to fulfill these goals. We specially focus on the current calibration scheme in operation since 2014 and based on a collaboration between the BIPM and the Regional Metrology Organizations. We show that the achieved accuracy and long-term stability of calibration results, thus of UTC time links, are well in line with the stated uncertainties. We study an extended set of absolute calibration results and show that they complete and validate the BIPM scheme, and that relative calibration is still the essential tool to ensure accurate time links for UTC.

RESEARCH OF LONG-TERM DRIFT OF THE NATIONAL INDUCTANCE STANDARD

Inductance measurements is important for all branches of technology related to the application of electricity: energy and electronics, radio and television, transport and communication, and scientific research. Electromechanical devices and electronic components can be characterized using impedance measurements to identify the parameters of their equivalent electrical model. New inductance measurement methods are being developed in specific fields of activity. Manufacturers of standards and measuring instruments of inductance develop special handbooks outlining various methods of inductance measurement. The State Primary Standard of Ukraine for inductance and loss angle tangent reproduces and transmits a unit of inductance in the range from 1∙10-6 H to 10 H at a frequency of 1 kHz. It is keeping in the SE “Ukrmetrteststandard” and participated in several comparisons of national standards within the framework of the activities of regional metrological organizations. The calibration and measurement capabilities of inductance measurement of national laboratories of different countries were studied to analyze and compare the capabilities of the national standard with the standards of other countries. Long-term instability studies of inductance measures of 1 mH, 10 mH and 100 mH, which are part of the national standard unit of inductance, have been conducted. The research period covered from 2009 to 2022. It was established that the drift lines of the specified inductance measures can be described using linear approximations. The rationale for choosing inductance measures of 10 mH and 100 mH for their use as transmission standards in the calibration of standards, which were organized and conducted by SE “Ukrmetrteststandard” as their pilot laboratory, is given.

AFRIMETS.AUV.A-S2 final report, calibration of a multi-function acoustic calibrator

Main textResults of Regional Metrology Organisation supplementary comparison AFRIMETS.AUV.A-S2 concerning the calibration of a Brüel & Kjær 4226 multi-frequency sound calibrator are reported here. Sound pressure level results at frequencies from 31.5 Hz to 16 kHz and nominal sound level settings of 94 dB and 114 dB, were evaluated for consistency, the calculated comparison reference values and Degrees of Equivalence are reported here. The comparison's purpose was to prove technical capabilities supporting the submissions of calibration measurement capabilities in the BIPM key comparison database. The light shines quite far, the new calibration measurement capabilities that may result from this work underpin some important fundamental acoustic calibration services, e.g., sound calibrators, sound level meters and personal sound exposure meters. These instruments are intrinsic to the effective monitoring and implementation worldwide of human hearing conservation and hearing loss assessment programs, all of which impacts quality of life. According to the World Health Organization, nearly 1.5 billion people experience some decline in their hearing capacity during their lives [1].To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Digital Representation of Measurement Uncertainty: A Case Study Linking an RMO Key Comparison with a CIPM Key Comparison

This paper considers a future scenario in which digital reporting of measurement results is ubiquitous and digital calibration certificates (DCCs) contain information about the components of uncertainty in a measurement result. The task of linking international measurement comparisons is used as a case study to look at the benefits of digitalization. Comparison linking provides a context in which correlations are important, so the benefit of passing a digital record of contributions to uncertainty along a traceability chain can be examined. The International Committee for Weights and Measures (CIPM) uses a program of international “key comparisons” to establish the extent to which measurements of a particular quantity may be considered equivalent when made in different economies. To obtain good international coverage, the results of the comparisons may be linked together: a number of regional metrology organization (RMO) key comparisons can be linked back to an initial CIPM key comparison. Specific information about systematic effects in participants’ results must be available during linking to allow correct treatment of the correlations. However, the conventional calibration certificate formats used today do not provide this: participants must submit additional data, and the report of an initial comparison must anticipate the requirements for future linking. Special handling of additional data can be laborious and prone to error. An uncertain-number digital reporting format was considered in this case study, which caters to all the information required and would simplify the comparison analysis, reporting, and linking; the format would also enable a more informative presentation of comparison results. The uncertain-number format would be useful more generally, in measurement scenarios where correlations arise, so its incorporation into DCCs should be considered. A full dataset supported by open-source software is available.

The measurements results adjustment by the Least Square Method

The method for processing of the measurement results obtained from Comite International des Poids et Measures (CIPM) Key, Regional Metrology Organizations (RMO) or supplementary comparisons, from the proficiency testing by interlaboratory comparisons and the calibrations is proposed. It is named by authors as adjustment by least square method (LSM). Additive and multiplicative parameters for each measuring standard of every particular laboratory will be the results of this adjustment. As well as the parameters for each artifact.
 The parameters of the measurements standards are their additive and multiplicative degrees of equivalence from the comparison and the estimations of the systematic errors (biases) from calibrations. The parameters of the artifacts are the key comparisons reference value from the comparison and the assigned quantity values from the calibrations.
 The adjustment is considered as a way to solving a problem of processing the great amount of homogeneous measurements with many measuring standards at a different comparison levels (CIPM, RMO or supplementary), including connected problems.
 Four different cases of the adjustments are considered. The first one is a free case of adjustment. It was named so because of the fact that none of participants has any advantage except their uncertainties of measurements.
 The second one is a fixed case of adjustment. Measuring results of RMO and supplementary comparisons are rigidly linked to additive and multiplicative parameters of measuring standards of particular laboratories participated in CIPM key comparisons.
 The third one is a case of adjustment with dependent equations. This one is not so rigidly linked of the new comparisons results to previous or to some other comparisons as for fixed case. It means that the new results of comparisons are influenced by the known additive and multiplicative parameters and vice versa.
 The fourth one is a free case of adjustment with additional summary equations. In that case certain checking equations are added to the system of equations. So, the sum of parameters multiplied by their weights of all measurement standards for particular laboratories participated in comparisons should be equal to zero.

30 years to COOMET: results and prospects for cooperation

The history of Euro-Asian Cooperation of National Metrological Institutions (COOMET) has already spanned three decades (12 June 1991 is considered the date of its establishment – the day when the COOMET Memorandum of Understanding was signed). COOMET is an officially recognized regional metrology organization, as well as a regional legal metrology organization. Cooperation in COOMET and its outcomes allow member countries to successfully tackle metrological issues, faced by the national economy under market globalization, as well as to ingrate in the international metrological system. A brief overview of the history of creation and results of activity of COOMET is provided. The effectiveness of cooperation is evaluated, the promising areas of COOMET's activities are outlined.

Force AFRIMETS supplementary comparison AFRIMETS.M.F-S2

Main textThe Regional Metrology Organization AFRIMETS Technical Committee in Mass and related Quantities (TCM) Working Group Force (WGF) met in July 2018 in Enugu Nigeria during the 12th General Assembly (GA) and made a decision to carry out an AFRIMETS supplementary comparison for the unit of force. This comparison, named the AFRIMETS.M. F-S2 supplementary comparison, in the force range of 250 kN and 500 kN. This comparison was planned to demonstrate the degree of equivalence between the national standards of force and to provide evidence for the Calibration and Measurement Capability (CMCs) claimed by the participating National Metrology Institutes (NMIs) in the AFRIMETS region, and particularly the who did not participate in the global CCM.F-K2 KC. The AFRIMETS TCM approved that KEBS of Kenya to serve as the pilot laboratory. and PTB of Germany to would be link laboratories. Although not part of the AFRIMETS region, PTB from EURAMET was invited to participate and provided the reference values while NMISA provided the transfer standards used during the comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The features of the CIPM MRA implementation by the Azerbaijan Republic

Participation in the Mutual Recognition Arrangement (MRA) of the International Committee on Weights and Measures (CIPM) offers great opportunities for recognition in other countries of the results of calibration and measurements performed by National Metrology Institutes. The Azerbaijan Republic signed the Memorandum of Understanding of Euro-Asian Cooperation of National Metrological Institutions (COOMET) in 2007 and the Metre Convention in 2015. The Azerbaijan Institute of Metrology (AzMI) also signed the CIPM MRA in 2015.Within the framework of the CIPM MRA, AzMI has been participating in nine international comparisons of the national measurement standards from 2012 to 2019 in four measurement areas (EM, M, RI, T). Key and supplementary comparisons of the measurement standards in different areas of measurements are carried out by Regional Metrology Organizations (RMOs), in particular COOMET. The results of five COOMET comparisons are published in the Key Comparison Database (KCDB) of the International Bureau on Weights and Measures (BIPM) already for EM, M, and T.AzMI has total 25 published entries of calibration and measurement capabilities (CMCs) in KCDB of BIPM: 24 entries for temperature (T) and one entry for viscosity (M.V). The Institute has the ability to prepare for the publication of CMCs for EM and M. The Institute also can prepare for the publication of CMCs for RI, EM (using future results of comparison for electric resistance standards), and M (using future results of comparison for density of liquids and comparison for liquid volume).

Supplementary comparison EURAMET.EM-S42, comparison of lightning impulse (LI) reference measuring systems

Main textIn 2016 the Consultative Committee for Electricity and Magnetism (CCEM) commissioned a supplementary comparison EURAMET.EM-S42 of Lightning Impulse (LI) measurement systems. This comparison was piloted by RISE (Sweden, formerly SP), and it was supported by VTT MIKES (Finland) and FFII LCOE (Spain). Eleven National Metrology Institutes (NMI) and two Designated Institutes (DI) from four Regional Metrology Organizations, EURAMET, COOMET, APMP and SIM, took part in the comparison.A commercial travelling measuring system (TRMS) for Lightning Impulse (LI) measurement was adopted for the comparison. The TRMS consisted of a 700 kV resistive voltage divider and a transient recorder with computer. The TRMS was calibrated by the pilot lab in November 2016 before start of the comparison, and the first circulation was between five EURAMET NMI/DIs. After an intermediate calibration by the pilot lab in July 2017, the TRMS was circulated between seven NMI/DIs in the other regional organisations. On the return of the TRMS in March 2019 a final calibration was made by the pilot lab.The measured parameters are defined in IEC60060-1. Test voltage value (U t), front time (T 1), time to half value (T 2) and relative overshoot (β') were measured for full impulses; and extreme value (U e) and time to chopping (T c) for front chopped waveform. The test voltage value ranged from -700 kV to 700 kV with two full and one chopped impulse waveform. A set of preferred voltage levels and waveforms was defined. The obtained expanded uncertainties (k = 2) of the comparison reference values (CRV) were: <0.3% for U t, <1.3% for T 1, <1.0% for T 2, <0.4% for β', <0.6% for U e and <1.4% for T c.The transfer reference measuring system of the previous LI comparison (EU-SMT4-CT98-2270), arranged between 1999 and 2002, is linked to this comparison. The link is established by comparing VTT MIKES system used 20 years ago with that used in this comparison.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report on GULFMET supplementary comparison of AC energy (GULFMET.EM-S5.1)

Main textA bilateral supplementary comparison for standards of electrical energy has taken place within the framework of GULFMET. The comparison, piloted by State Enterprise 'Ukrmetrteststandard' - UMTS (Ukraine), has involved two laboratories (UMTS and QCC EMI, United Arab Emirates) from regional metrological organizations GULFMET and COOMET. The results presented in this report provides confidence in maintaining traceability for active energy and reactive energy for 1.0, 0.5 Lag, 0.5 Lead power factors at frequencies of 50 Hz and 53 Hz.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Evaluation of the results of regional metrology organisation comparisons and national inter-laboratory comparisons for electrical quantities

The global metrological traceability fully depends on the implementation of international mutual recognition agreements in field of metrology. The linked results of international comparisons of national standards for alternating current/direct current (AC/DC) voltage transfer difference measurements and electrical power measurements, and national inter-laboratory comparison AC/DC voltage transfer difference and electrical power measurements at industrial frequency was presented. The main goal of this inter-laboratory comparison was the assessment of calibration laboratories capabilities that perform calibration in AC/DC voltage transfer difference and electrical power measurements. The consistency of the data obtained using the En numbers and Chi² test was estimated.

АЛЬТЕРНАТИВНЕ ОЦІНЮВАННЯ РЕЗУЛЬТАТІВ КЛЮЧОВИХ ЗВІРЕНЬ НАЦІОНАЛЬНИХ ЕТАЛОНІВ

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.

SIM.M.T-S2 supplementary bilateral comparison calibration of a reference torque wrench final report

A Regional Metrology Organization (RMO) key comparison on the calibration of a reference torque wrench was carried out between the Centro Nacional de Metrologia (CENAM, Mexico) and the Instituto Nacional de Metrologia (INM, Colombia), between September 2017 and October 2017. The results of this comparison are reported here, along with descriptions of torque standards used by CENAM and INM, and the uncertainty budget for these standards. This report also describes the protocol for the comparison and presents the data acquired. The results are analyse, determining the degree of equivalence between the torque measurements from CENAM and INM.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final report on AFRIMETS supplementary comparison AFRIMETS. T-S2): platinum resistance thermometer and digital thermometer calibrations over the range -50 °C to 450 °C

A Regional Metrology Organization (RMO) supplementary comparison of platinum resistance thermometer and digital thermometer (AFRIMETS.T-S2) was carried out among AFRIMETS member NMIs namely the National Metrology Institute of South Africa (NMISA), Laboratoire Public d'Essais et d'Etudes - Laboratoire National de Métrologie (LPEE-LNM), Ghana Standards Authority (GSA), and Agence Burkinabé de Normalisation, de la Métrologie et de la Qualité (ABNORM) between Dec 2015 and Sept 2018. The temperature range of the inter comparison is -50 °C to 450 °C. The results of this comparison are reported in this document, along with descriptions of the Artefacts and devices used during measurement. This report also presents the uncertainty budget. The results are analysed and En values are reported.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

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 КC 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.