The Recent Research on the NIM-2 Joule Balance

The National Institute of Metrology (NIM) proposed the joule balance in 2006. With more than ten years efforts, NIM has built two generations’ joule balance apparatus. In 2019 and 2021, the NIM-2 joule balance participated in the key comparisons of kilogram realizations with a combined relative standard uncertainty of 4.5×10
^-8
and 4.0×10
^-8
separately. At present, the main uncertainty contributions are from the alignment, external field, statistical, etc. To improve the NIM-2 joule balance, approaches including the integrated mechanism of force-measurement and guidance, a high resolution programmable current source, the synchronous measurement of the flux linkage and the displacement and the vacuum mass transfer apparatus, etc. are in progress and presented here.