In 2006, to make a contribution to the redefinition of the kilogram, NIM proposed a joule balance method, inspired by that of the Kibble balance but somewhat different from the watt balance method. In 2013, a model apparatus NIM-1 was built to verify the principle of the joule balance. NIM then began building a new improved joule balance, NIM-2, operating under vacuum, with the aim of determining the Planck constant with uncertainty at the 10-8 level. In May 2017, the NIM-2 result was submitted to Metrologia and accepted by the CODATA Task Group on Fundamental Constants (TGFC) as input data.
By 2018, the Type A uncertainty of NIM-2 has been decreased to 5×10-8(k=1), which lays a solid foundation for China to independently establish the equipment for the realization and value dissemination of kg. NIM-2 will participate in the key comparison organized by the BIPM from 2019 to 2020.
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