In 2017, we published the first measurement result with NIM-2 joule balance and the relative standard uncertainty is 2.4E-7. Since then, a series of improvement approaches have been carried out to upgrade the NIM-2 joule balance towards the E-8 level relative uncertainty. The main approaches include a permanent magnet as well as a two-layers magnet shielding to decrease the main uncertainty contribution from the external magnetic field, a parasitic displacement measurement system and a new suspension for improving alignments and a new mass translation stage constructed with all nonmagnetic materials, etc. By September of 2019, when the NIM-2 joule balance is used to calibrate a 1 kg mass, the type A relative standard uncertainty has been reduced to 3E-8(k=1) and the combined relative standard uncertainty is less than 1E-7(k=1). In Oct. and Nov. of 2019, a 1 kg Pt/Ir mass and a 1 kg stainless steel mass were measured with the NIM-2 joule balance, the relative standard uncertainties are 5.2E-8 and 6.5E-8 respectively. The relative difference between the measured values and the calibration values obtained from the mass group are 4E-9 and 3E-8 respectively.

中文翻译：

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2017年以来NIM-2焦耳平衡的升级

2017年，我们发布了第一个NIM-2焦耳天平测量结果，相对标准不确定度为2.4E-7。此后，进行了一系列改进方法，将 NIM-2 焦耳平衡升级到 E-8 级相对不确定性。主要方法包括永磁体和两层磁体屏蔽以减少来自外部磁场的主要不确定性贡献、寄生位移测量系统和用于改善对准的新悬架以及由所有非磁性结构构成的新质量平移台到 2019 年 9 月，使用 NIM-2 焦耳天平校准 1 kg 质量时，A 类相对标准不确定度已降至 3E-8(k=1)，组合相对标准不确定度为小于 1E-7(k=1)。在十月和十一月。2019年，用NIM-2焦耳天平测量了1 kg Pt/Ir质量和1 kg不锈钢质量，相对标准不确定度分别为5.2E-8和6.5E-8。测量值与从质量组获得的校准值之间的相对差异分别为 4E-9 和 3E-8。