AC shunt calibration using a current‐bridge method and its validation

Abstract

An AC shunt calibration system using a current-bridge method is developed, and its measurement uncertainties are estimated. A comparison of the calibration results obtained using the current-bridge method with the results using DC resistance and AC-DC difference methods was performed to verify the system. These comparison results show that the current-bridge-based system performs well with small measurement uncertainties for both the AC resistance and phase angle of the AC shunts up to 1 kHz.

Effect of Current Heating on Accurate Measurements of AC Shunt Resistors at DC to 3 kHz

“…[3,4] The principle of current-bridge method is to compare input current with a current derived from the output of the shunt resistor. The current derived from the shunt resistor is produced with a buffer amplifier (BUF) and a calibrated 1 kΩ ac standard resistor.…”

“…[3,4] However, the measurement system that uses current bridge method had the limitation of the measurement frequency range because of the leak current due to the stray capacitance. However, the expansion of the measurement frequency and current ranges are needed.…”

“…For these situations, an ac shunt calibration system has been developed and measurement results for both the ac resistance and phase angle were verified up to 1 kHz. [3,4] However, expansion of the measurement frequency and current ranges are needed for the evaluation of harmonic characteristics and high-frequency applications. [5] This paper describes the modified current-bridge method and its measurement uncertainties of the frequency range up to 3 kHz and the current dependencies of shunt resistors for both ac resistance and phase angle.…”

Error Analysis of Improved Current‐Bridge Method for Accurate Low‐Impedance Measurement

“…If the in‐phase and quadrature components of standard ac resistor, current transformer, and current comparator are evaluated using respective standards in advance, the in‐phase and quadrature components of shunt resistor can be obtained. In the current‐bridge circuit developed based on such principle, each circuit is designed focusing on measurement of utility frequencies, and its mathematical model applies multiple approximations . However, in order to perform accurate measurement for lower impedance at higher frequency, not only an available frequency and load characteristics of signal processing circuit need to be improved, but also the influence of leak current due to parasitic capacitance which can be neglected at utility frequency needs to be considered.…”

“…Thus, we developed current‐bridge circuit which can measure an ac resistance and phase angle of shunt resistor simultaneously at an high accuracy . However, the nominal value of the shunt resistor capable of measurement with the developed current‐bridge circuit was around 100 mΩ and the frequency was limited under 1 kHz . Thus, in order to realize accurate measurement of low‐impedance device, we worked to improve the current‐bridge circuit.…”