We have developed an AC standard shunt of smaller phase angle, temperature coefficient and aging effect than those of conventional shunts. So, we describe the performance and the structure of the shunt. Generally, shunts are used in AC current measurements. However, these shunts include inductance and distributed capacitance, thus, the resistance is affected by the measurement frequency. For that reason, we have developed a highly stable AC standard shunt which can be used in the frequency range of DC to 1 kHz. The rated values of the shunt are 0.1O, 10 A. At first, we developed a four-terminal-type metal foil resistor (10 ohm, 0.3 W) which is designed to make small secular change of characteristics, small temperature coefficient and small inductance. Then, we connected one hundred of resistors in parallel on a circumference. The calibrated phase angle and the calibrated resistance value (0.1 ohm) of the extended uncertainty (2s equivalent) at 1 kHz, 10 A of the AC standard shunt were 1 mrad and 2 ppm, respectively. The secular change in the resistance of the AC standard shunt was 2.5 ppm per year, and the temperature coefficient of the resistance was 0.2 ppm/?. The secular change in the phase angle was negligible. In AC power measurements, the phase angle error of the current affects the accuracy of measurements. We have been able to perform accurate AC power measurements using the developed AC standard shunt. |