提高低温电流比较仪测量准确度的几方面措施

通过对低温电流比较仪系统及运行过程的研究，发现了氦气气压波动、冻结磁通引起的附加噪声以及线圈匝数增多时分布电容引起的电流跳跃是限制系统不确定度停留在10^-9量级而不能进一步提高的原因。提出了一种新型的气压滤波器滤除了附加噪声。还改进了电路动态特性，改善了前馈补偿环节，把匝数比提高了5倍。运行过程中的电流跳跃现象也被消除。采用这些措施后，信噪比提高了5倍，新建的低温电流比较仪的测量准确度提高到了10^-10量级。

Measures for Improving the Accuracy of Cryogenic Current Comparator

With the analysis of Cryogenic Current Comparator (CCC) system and its operation process, it is found that the limitation to the improvement of uncertainty of CCC is the disturbance and additional noise from the pressure fluctuation of helium gas and frozen flux, as well as the working current jumping caused by the parasitical capacitance and inductance in the CCC windings. A new type of pressure filter was designed to eliminate the additional noise. The dynamic characteristic and feed-forward circuit are also improved, so that the turn number ratio can be increased 5 times and current jumping eliminated. With these measures, the S/N ratio is better than that before by 5 times or more. Experiment results show that the uncertainty of CCC newly established is up to several parts in 10~(-10).