First international comparison of three different tabletop Kibble balances from 1 mg to 10 g

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Abstract

An international comparison of three tabletop Kibble balances for the calibration of small mass standards is reported. Two independently manufactured sets of OIML E$_1$ accuracy class weights with nominal values of \SI1}\milli\gram}, \SI50}\milli\gram}, \SI200}\milli\gram}, \SI1}\gram}, \SI6.62607015}\gram}, and \SI10}\gram} were circulated among the participating institutes. The balances, operated at Technische Universität Ilmenau (Germany), Physikalisch-Technische Bundesanstalt (Germany), and the National Institute of Standards and Technology (USA), realize the unit of mass from the fixed numerical value of the Planck constant and apply the Kibble balance principle to milligram- and gram-level mass calibrations. The mass sets were also calibrated independently by accredited laboratories of the manufacturers using the conventional substitution method in accordance with OIMLR111. Measurements with the three Kibble balances were performed fully blind, without knowledge of the manufacturers' calibration results or those of the other participants. Data exchange was implemented using Digital Calibration Certificates, and automated evaluation enabled consistent, reproducible, and immediate comparison of results upon unblinding at the Kibble Balance Technical Meeting (November 2025, BIPM). A generally good agreement between the reference values established by the Kibble balances and the conventional calibration results was observed over the range from \SI1}\milli\gram} to \SI10}\gram}. The comparison demonstrates the potential of tabletop Kibble balances to provide calibrations of small and non-standard mass values with uncertainties at the E$_1$ and E$_2$ levels, and highlights the metrological benefits of digitally supported comparison procedures.

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Mass metrology

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