The Recent Progress of the NIM-2 Joule Balance

In 2017, we have published a measurement result obtained with the NIM-2 joule balance and the relative standard uncertainty is 2.4×10^-7. Since then, a series of approaches have been carried out to decrease the main uncertainty contributions. A new permanent magnet has been constructed to get higher magnetic field. A magnetic shielding and compensation coils were used to decrease the effect from the environment. The alignment was improved by a parasitic displacements measurement system and the using of a new suspension system. By Sept. of 2019, the type-A uncertainty of NIM-2 has been reduced to 3×10^-8. In Oct. 2019, the NIM-2 joule balance participated in the key comparison (CCM.M-K8 2019).