Direct Measurement of AC Current by Measuring the Voltage Drop on the Coaxial Current Shunt

An accurate direct measurement of ac current that avoids complex and time-consuming ac–dc current transfer measurements by directly measuring the ac voltage drop of coaxial current shunts is described. Evaluation of custom-developed coaxial current shunts for long-term drift, self-heating effects, and loading using a commercial ac voltmeter is presented. By correcting only the shunts' long-term drift, direct ac current measurement uncertainties below 55 $\mu\hbox{A/A}$ are attained in the frequency range of 20 Hz–30 kHz and for currents ranging from 100 mA up to 10 A.