Jianting Zhao

Recent Development on the Joule Balance at NIM

The precise measurement of Planck constant h to establish a kind of quantum mass standard is an important but very difficult work. The Joule Balance method, for the same purpose but different from Watt Balance method, has been going on at the National Institute of Metrology for three years. All the measurements were carried out in the atmosphere of an air-conditioned room. The uncertainty is several parts in 104 (k=1) and expected to be improved when superconducting coils and other approaches are used further. The principle and progress are described here.

A Compensation Method With a Standard Square Wave for Precise DC Measurement of Mutual Inductance for Joule Balance

The precise dc-based measurement of the mutual inductance is one of the key issues in the Joule Balance method used to determine Plancks constant h. Here, a new compensation method with a standard square wave is provided. The dc value of the mutual inductance is obtained by measuring the integral area of the induced voltage. To increase the accuracy of this integral method, we just accurately measure the residual area observed between the induced voltage of the mutual inductor and a synchronously generated standard square wave. Experimental results indicate that this approach is consistent with the previous frequency extrapolation method within 1 ppm. The measurement uncertainty is estimated to be about 0.22 μH/H for the 340-mH mutual inductor at room temperature. A better result of 0.1 ppm could be obtained when the superconducting coil is used.

A compensation method to measure the mutual inductance at low frequency

Traditionally, the most precise way to get the mutual inductance value is by a calculable mutual inductor. Here a new approach of measuring the mutual inductance at low frequency with compensation method is described. The mutual inductance is traced to the value of the frequency and resistance directly. The measurement uncertainty is 0.1ppm and could be improved further.

The progress of joule balance in NIM

The precise measurement of Planck Constant h to establish a kind of quantum mass standard is an important but very difficult work. The Joule Balance method, for the same purpose but different from Watt Balance method, is going on in NIM for three years. The principle and progress are described.

A Compensation Method to Measure the Mutual Inductance at Low 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.

An improved bootstrap method for the calibration of inductive voltage dividers

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.

The static state analysis of the balance suspension system for its displacement measuring

In order to precisely measure the displacement of the coil suspension system of the Joule Balance in the static state, we give a detailed analysis about its influence factors in this paper. We designed a dual-frequency laser interferometer system to measure the movement of the coil suspension in vertical direction. And a supporting device was designed to support the coil for the aim to make it more stable. The result showed that the coil suspension system is affected by ground vibration, temperature drift, stress release, pendulum swing. The drift of the coil suspension is about 120nm among 3 minutes without supporting device, the data is greatly reduced after we support it.

Preliminary results on GaAs-algaas heterostructure quantum Hall resistance standard by the NIM

Till now, quantized Hall devices distributed by the BIPM are used in NIMs quantized Hall resistance standard. In this paper, we report the preliminary results of quantized Hall devices with GaAs-AlGaAs heterostructures fabricated by ourselves. The device is with AuGeNi contacts for reliability consideration, but the contacts are with relatively large resistances for layer contents and annealing condition was not optimized for 2DEG and low temperature. The large contact resistance caused additional noises and we observed anomalous values for i = 2 quantized Hall step. Next step, The AuGeNi contacts will be optimized.

The equivalent circuit of the ac resistor and the equi-potential shielding with 1/2 voltage

The ordinary equivalent circuit of the AC resistor is not exact enough when the parasitic parameters of the resistor are considered. At the same time, the traditional shielding with potential equal to the lower voltage terminal of the resistor will contribute additional parasitic capacitance to the resistor and will deteriorate the calculated result of AC/DC difference. Using an equi-potential shielding with 1/2 voltage of the resistor is helpful to decrease the AC/DC resistance difference.

GaAs/AlGaAs quantum hall resistance devices with AuGeNi and in contacts

We present in CPEM 2012 the latest quantum Hall (QH) experimental results of GaAs-AlGaAs Hall devices fabricated by NIM. AuGeNi and In are utilized as the contacts material. Precision measurement indicates quantized Hall devices with low contact resistance and good breakdown current are obtained.