The Improvement of Joule Balance NIM-1 and the Design of New Joule Balance NIM-2

TL;DR

This paper discusses improvements to the Joule balance NIM-1 for measuring the Planck constant and introduces the design of a new, more compact Joule balance NIM-2 to enhance measurement accuracy and reliability.

Contribution

The paper reports significant uncertainty reductions in NIM-1 and presents the design of the innovative NIM-2 Joule balance for future precision measurements.

Findings

Uncertainty reduced from 7.7×10^{-5} to 7.2×10^{-6}

Planck constant measured as 6.6261041(470)×10^{-34}Js

Design of a new compact Joule balance NIM-2

Abstract

The development of the joule balance method to measure the Planck constant, in support of the redefinition of the kilogram, has been going on at the National Institute of Metrology of China (NIM) since 2007. The first prototype has been built to check the feasibility of the principle. In 2011, the relative uncertainty of the Planck constant measurement at NIM is $7.7\times10^{-5}$. Self-heating of the coils, swing of the coil, are the main uncertainty contributions. Since 2012, some improvements have been made to reduce these uncertainties. The relative uncertainty of the joule balance is reduced to $7.2\times10^{-6}$ at present. The Planck constant measured with the joule balance is $h=6.6261041(470)\times10^{-34}$Js. The relative difference between the determined h and the CODATA2010 recommendation value is $5\times10^{-6}$. Further improvements are still being carried out on the NIM-1 apparatus. At the same time, the design and construction of a brand new and compact joule balance NIM-2 are also in progress and presented here.