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After continuous investigation on the electrical compensation method for the end effect error in the new vertical calculable cross-capacitor (VCCC), the latest optimal hollow active auxiliary electrode (OHAAE) has been developed and successfully substituted for the current geometrical nosepiece at one end of the movable guard electrode at the National Institute of Metrology, China (NIM). The critical electrical characteristics of the latest OHAAE are investigated by the model tests and eventually implemented with the least mechanical modifications to the new VCCC at NIM. The standard uncertainty of the reproduction of 1 pF capacitance unit from the new VCCC by adopting the latest OHAAE is decreased to $10.5 \times 10^{-9}$ in comparison with that of $20.0 \times 10^{-9}$ by the geometrical nosepiece.

Different from the noise thermometer in a substitution configuration, a superposition configuration allows a reference signal to be injected into the sense resistor so that the thermal voltage noise and the reference signal can be simultaneously transferred to the measurement electronics through the same transmission line. The construction of a quantum-voltage-calibrated superposition noise thermometer is presented in this paper and preliminary experiments are conducted to demonstrate its feasibility for temperature measurements. A polynomial fitting is used to fit the transfer function of the connection network between the QVNS and the sense resistor.

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 ( $R_{\mathrm{K}}$ ) 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.

Measuring Variable-frequency big current has a great technical difficulty, you first need transfer Variable-frequency big current to small current is easy to measure, and then transfer variable frequency small current to a voltage. In this paper we uses a zero flux current transformer transfer high current into a small current, after then use a shunt transfer alternating current to a variable frequency voltage, realizing high accuracy variable-frequency big current calibration, measurement uncertainty up to 1×10-4,which can meet the needs of the current calibration,it has been used in many project, and achieved good results.

After the continual investigation on the electrical compensation method for the end effect, the optimal hollow active auxiliary electrode (OHAAE) has been successfully developed and substituted for the current nosepiece in the new vertical calculable capacitor (CC) at NIM. Applying the best compensation voltage of ${U_{\text{best}}}$ obtained from the model tests, the initial measurement result by the OHAAE in the new vertical CC for reproducing the 1 pF capacitance of the same commercial capacitor agrees with that by the nosepiece in the level of ${6.0\times 10^{-9}}$ .

This paper describes the progress on a new measurement of von Klitzing constant $\pmb{(R_{\text{k}})}$ 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.

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.

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.

In this paper an improved bootstrap method used for the calibration of inductive voltage dividers(IVDs) is described which uses a special constructed reference transformer to decrease the system errors due to the screen current. The reference transformer is wound with a triaxial cable which was divided into two equal lengths by a break in the both of the outers. A initial measurement result shows that the error introduced by the changes of the reference voltage ratio is less than 1nV/V at 1592Hz by using this reference transformer.

A two terminal-pair coaxial AC bridge is constructed at NIM for high precision capacitance transfer, in which, an auto auxiliary source balance method is proposed and achieved. The error introduced by auto source balance circuit is at negligible level. The bridge can transfer capacitance from 1 pF to 100 pF with an uncertainty of 1 × 10−8 (k = 1) at low audio frequency.

Traditionally, the most precise way to get the mutual inductance value is by a Campbell calculable mutual inductor. Here, an approach of measuring the mutual inductance at low frequency with compensation method is described. A multi-channel direct digital frequency synthesis source is developed to provide stable and precise phase. The mutual inductance is traced to the value of the frequency and resistance directly. The measurement uncertainty is 0.43 ppm at present and could be improved further.