In 2017, the second generation of the Joule balance achieved a measurement uncertainty of $2.4 \times 10^{-7}$ . The main source of the uncertainty is identified as the effect of the external field, resulting in $1.7 \times 10^{-7}$ in the uncertainty budget. Hence, two solutions are proposed in the Joule balance to eliminate the effect of the external field, i.e., the magnetic shielding and compensation coils. This paper first gives an overview of the constructions of the shield and the compensation coils. Then, the flux linkage difference of the external field is measured under different conditions. Last, the effect of the two solutions is verified through the experiments. Based on the measurement results, it can be found that the uncertainty resulting from the effect of the external field in the Joule balance will be reduced to $1.4 \times 10^{-8}$ when the two solutions are applied.

中文翻译：

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焦耳平衡中外场效应的消除

2017年，第二代焦耳天平实现了测量不确定度 $2.4 \times 10^{-7}$ . 不确定性的主要来源被确定为外部场的影响，导致 $1.7 \times 10^{-7}$ 在不确定性预算中。因此，焦耳平衡中提出了两种解决方案来消除外场的影响，即磁屏蔽和补偿线圈。本文首先概述了屏蔽和补偿线圈的结构。然后，在不同条件下测量外场的磁链差。最后通过实验验证了两种方案的效果。根据测量结果可以发现，焦耳天平中外场效应产生的不确定度将降低为 $1.4 \times 10^{-8}$ 当应用这两种解决方案时。