A Coaxial Time Constant Standard for the Determination of Phase Angle Errors of Current Shunts

This paper describes a new method to determine the phase angle errors of ac shunts by measuring the inductance and distributed capacitance. A 1-Ω shunt of coaxial design has been developed as the time constant standard. A coaxial inductor with identical structure as the time constant standard has been developed. A four-terminal mutual inductor has also been built for the measurement of the inductance of the time constant standard. The method is based on the use of a binary inductive current divider to compare the inductor with the mutual inductor. The standard uncertainty of the inductance measurement of the time constant standard is within 28 pH at frequencies up to 200 kHz. The expanded uncertainty of the phase angle errors is from 0.4 μrad at 1 kHz to 80.0 μrad at 200 kHz at 1 A.