A new type of active simulated inductance standard is proposed to achieve high-stability inductors that are endurable for transportation. The scheme is suitable for simulating inductors from the microhenry range up to the henry range with similar electrical characteristics. Two 10 mH simulated standards have been fabricated with a target long-term stability of 1 mu H/H. These standards were initially investigated using NIM's primary inductance standard.

基于一种交流电桥自动辅助平衡方法,中国计量科学研究院(NIM)研制了新一代二端对电容电桥装置.电桥采用固定比率的感应耦合比率臂电桥,通过复用比率,用单一电桥即实现了计算电容过渡和电容10:1传递;采用一种改进的靴带法实现电桥感应比率臂比率的精确校验.该装置用于电容单位的量值复现和标准电容器的高准度量值传递.利用新一代二端对电容电桥装置,可从计算电容装置复现1 pF电容值,并实现电容1 ～ 100pF的十进制量值传递,电容量值传递相对标准不确定度可达5×10-9(1 592Hz).采用该电桥参加了10 pF和100pF电容国际关键比对(CCEM.K4-2017),中国比对成绩优异,数据均非常接近关键比对参考值(KCRV),其中100 pF的结果最接近KCRV,与KCRV取得了很好的一致性,从而获得国际互认.

针对立式计算电容最大不确定度来源的端部效应误差,中国计量科学研究院经过多年改进,研制出的最优中空电补偿电极在计算电容模型装置上,没有采用加装钉子头进行补偿的电补偿方案,并完成了诸如端部效应误差的补偿效果、偏心效应误差等电气性能验证试验,成功应用在新一代立式计算电容装置上.实验结果表明,采用电补偿方案的新一代立式计算电容装置复现1 pF电容单位的相对标准不确定度为1.0×10-8.

The experiments were carried out aimed to compare the capacitance measured in terms of the new calculable capacitor standard to the capacitance measured in terms of the von Klitzing constant ( RK) using the quantized Hall resistance (QHR). The experiment systems such as the calculable capacitor, the quantized Hall resistance standard, and the impedance measurement chain are briefly presented. The recent two key comparison results on capacitance and resistance standards are also introduced.

The latest optimal hollow active auxiliary electrode (OHAAE) has been developed and adopted in the NIM's new vertical calculable cross-capacitor (VCCC) since 2018. The further research including the additional function of the latest OHAAE for the dissemination experiment, the robustness of the best compensation voltage ratio kbest in the actual VCCC and the improvement of the laser interferometry system is investigated. After the re-evaluation for the frequency coefficient, the standard uncertainty of reproducing 1 pF capacitance unit from the NIM's new VCCC with the latest OHAAE applying the kbest is estimated as 10.0×10 -9 .

To compensate the end effect error in a vertical calculable cross capacitor with a fixed and a movable guard electrode, two different methods, a nosepiece and a modified active auxiliary electrode, are usually adopted at National Measurement Institutes across the world. However, the latter electrical approach can be more difficult when assembling the mirrors in the resonant cavity of the Fabry-Perot laser interferometer. This paper describes a novel hollow active auxiliary electrode that can satisfy the optical requirements. The model test experimental results show that it has the same or better compensation effectiveness for the end effect error in comparison with the modified active auxiliary electrode.

This paper describes the progress on a new measurement of von Klitzing constant \pmb(Rk) through an experiment linking the new calculable capacitor and the quantized Hall resistance by means of a quadrature transfer at NIM. The recent improvements of the new calculable capacitor, the optical interferometry, the impedance measurement chain are presented.

The optimal hollow active auxiliary electrode is developed and its further investigations including the determination of the best compensating voltage ratio, robustness, eccentricity and so on are reported. Furthermore, its additional functions, such as measuring the eccentricity of movable guard electrode and monitoring the possible position changes of four main bars after long-term operation, are proposed and verified.

A digital impedance bridge with auto-balancing source ratio is described in this summary paper. Unlike impedances can be compared in audio frequency range with arbitrary magnitude and phase ratio produced by two digital generators. An automatic source balance method is introduced to the bridge with no need for fine adjustment of the complex source ratio and faster balancing of the bridge. The synchronous sampling method is adopted to measure the complex ratio at different frequency in normal conditions. Preliminary tests on L-R comparison were carried out.

A new type of calculable capacitor was initially built at the National Institute of Metrology, China, in cooperation with the National Measurement Institute, Australia. The capacitor realized the SI unit of capacitance at 1 pF, with an uncertainty of 20 parts in $10^{9}$ . A simplified operational approach was used that avoids the complex substitution measuring process with small-value capacitors. The details of novel aspects of the installation and adjustment processes are presented, together with the experimental results and an initial uncertainty estimation.

To recover alumina and silica from alumina rich fly ash, a predesilication process has been developed to extract glassy amorphous silica from the fly ash. The predesilication apparent reaction kinetics in 15 wt-% NaOH solution were studied. The results showed that the predesilication process followed a shrinking unreacted core model of decreasing particle size. The apparent reaction rate of the predesilication process was predominantly controlled by internal diffusion, then by chemical reaction and last by fluid film diffusion. The apparent reaction activation energy for the process was found to be 14.2 kJ mol(-1) and the pre-exponential factor was 0.024. Using the leaching process, about 57.56% of glassy amorphous silica was removed from alumina rich fly ash, the silica content being reduced from 40.20 to 26.96% in the resulting dried desilicated fly ash. This study provides a theoretical foundation for the separation of alumina and silica and the design of a predesilication reactor.

A digital sampling system which can fast compare inductors with ac standard resistors in the frequency range between 20 Hz and 20 kHz is described. It can also precisely measure inductance at heavy current or high voltage. Inductors from 10mH to 10H in the low audio frequency range can be measured with the least relative uncertainty of 50 to 100 parts in 106.