Lu Yunfeng

The joule balance in NIM of China

The advantage of the joule balance over the classic watt balance is that the dynamic measurement in the watt balance is replaced by a static measurement, which makes the whole measurement procedure easier. The main problems in the joule balance are the precise measurement of mutual inductance and coil heating. These problems and recent progress in the development of the joule balance are described and discussed in this paper. The whole system is at the stage of being adjusted and improved. The principle of the joule balance has been demonstrated by a measurement of the Planck constant, h = 6.626 104(59) × 10−34 J s with an 8.9 ppm measurement uncertainty.

Development of 10kΩ quantum Hall array resistor

We reported the fabrication and characterization of the 10kΩ standard resistor which consists of 12 single quantum Hall bars on the AlGaAs/GaAs 2D electron gas wafer. The designed deviation of this resistor with the 10kΩ value is - 3.42×10⁸ Ohm/Ohm. The preliminary DCC (digital current comparator) measurement shows that the value of the 10kΩ standard resistor deviates from the designed one of (-34.6 ±7.97) ×10^-8Ω/Ω. Accurate measurements are in progress.

Application of capacitive displacement sensor on Joule Balance

This paper gives a high precision capacitive displacement sensor design which is applied in the Joule Balance proposed by NIM, China. The plate of sensor is made by non-magnetic material, and is for the Joule Balance special use. The distance of the capacitive displacement sensor reaches to 1mm. And the resolution is less than 0.019µm full scale, in part range of the full scale, this data will be far less.

A method to correct inductive voltage dividers error caused by capacitances between winding and screen

Distributed shunt impedances and leakage impedances in the windings of inductive voltage dividers (IVDs) cause the major components of ac voltage ratio errors, and these two kinds of errors had been well investigated from both theory and experiments. The winding -to-screen capacitances of IVDs can also introduce small but significant ratio error. A theoretical analysis result for this kind of error has been obtained, and a method to correct this kind of error has been presented.