新型计算电容基准电补偿理论及关键技术研究

To establish one new vertical calculable cross capacitor standard with movable and fixed guard electrodes is one of the hottest issues in current international metrological research. It can combine the quantized hall resistance standard together for measuring the fine structure constant more accurately. In the meantime it is not noly the unique standard appratus at the level of a few parts in one hundred million but also the traceability source of ac impedance system including capacitors, inductors and ac resistors. This application project is focused on the key technology problems of novel national calculable cross capacitor. The theoretical analysis about the generation mechanism of the end effect error, which is the maximum uncertainty source, will be carried on. The simulation of the two-dimensional electrical field distribution inside this capacitor by adpoting our unique electrical auxiliary electrode instead of international common modified cone-end spike for compensating the end effect error should be also undertaken with electromagnetic finite element analysis software. On basis of the simulation results, the optimum design of electrical auxiliary electrode can be manufactured. One set of model device with the same size as the actual NIM's calculable cross capacitor is designed and assembled in order to investigate the influence of close approach nonlinearity, eccentricity error and so on when using the auxiliary electrode. In addition the unique measurement function of the electrical compensation method requires the further research to find one method for the improvement of its measurement sensitivity. This function can not only offer one effective way for the assembly and adjustment of the novel calculable cross capacitor but also monitor the slight change of the diagonal spacing between four main stainless bars after the normal operation for a few years, which can not be realized by using the mechanical compensation modified cone-end spike.

建立新一代立式可动屏蔽型计算电容基准是目前国际计量学界的研究热点，其与直流量子化霍尔电阻基准相结合可更准确地测量精细结构常数，还是传统电工领域唯一能达到亿分之几水平的基准装置，同时也是交流阻抗包括电容、电感和交流电阻的溯源源头。本项目定位于研究我国新型计算电容的关键技术问题，主要是理论分析立式计算电容系统中最大的不确定度来源端部效应误差产生的机理，采用电磁场有限元软件仿真用来补偿端部效应且不同于国外通用机械改良型钉子头法的本项目所独有的电补偿法的计算电容内部二维电场分布，并以此为基础研制出最优结构的电补偿电极。同时独立设计研制一套与实际计算电容尺寸一致的模型装置，以用来研究采用最优结构 电补偿电极后的诸如接近效应误差、偏心误差等对最终计算电容测量不确定度的影响。此外研究提高电补偿电极独有的监测计算电容四根主电极对角极间距微小变化的测量灵敏度方法，以确保整体装置的安装调节和日常维护。

建立新一代立式可动屏蔽型计算电容基准是目前国际计量学界的研究热点，其与直流量子化霍尔电阻基准相结合可更准确地测量精细结构常数，还是传统电工领域唯一能达到亿分之几水平的基准装置，同时也是交流阻抗包括电容、电感和交流电阻的溯源源头。本项目定位于研究我国新型计算电容的关键技术问题，主要是理论分析立式计算电容系统中最大的不确定度来源端部效应误差产生的机理，采用电磁场有限元软件仿真用来补偿端部效应且不同于国外通用机械改良型钉子头法的本项目所独有的电补偿法的计算电容内部二维电场分布，并以此为基础研制出最优结构的电补偿电极。同时独立设计研制一套与实际计算电容尺寸一致的模型装置，以用来研究采用最优结构 电补偿电极后的诸如接近效应误差、偏心误差等对最终计算电容测量不确定度的影响。此外研究提高电补偿电极独有的监测计算电容四根主电极对角极间距微小变化的测量灵敏度方法。本项目所完成的研究成果是：1）通过实心黄铜实心结构、黄铜中空结构和殷钢中空结构所总结出来的相关规律以及三维电磁场仿真数据，本项目最终完成了最优结构中空殷钢电补偿电极的研制，并完成了一套与立式计算电容本体尺寸一致的模型装置。大量的模型试验证明，该电极的补偿端部效应效果要比改良型钉子头好一个量级，同时具备非常好的鲁棒性、更小的接近效应误差以及低一个数量级的偏心效应误差，而且也证明了其对主电极表面连续短小缺陷及同一锥度倾斜同样也具有很好的补偿效果。2）本项目还设计完成了对其虚拟电气终端面长度的测量，证明仅需增加其整体长度不到1mm并且不需改动任何计算电容本体其他机械结构就能直接实现对目前改良型钉子头的替换。3）本项目还验证了其具备足够的测量灵敏度，能够实现监控可动屏蔽电极的在本体安装及短期运行时的偏心状态，同时还要能监控计算电容本体长期运行后可能存在的四电极准确位置微变引起的极间距变化，进而对计算电容是否处于正常工作状态以及其本体系统运行故障的快速判断和维修保养提供了有效的监测手段。本项目获正式授权的国家发明专利2项，发表SCI/EI共计9篇英文论文（5篇SCI和EI双收录，其他3篇EI收录），4篇国内核心期刊论文，完成了课题立项时的研究目标。