Digital Sampling Setup for Measurement of Complex Voltage Ratio

This paper describes a universal digital sampling setup for measurement of a complex voltage ratio. The setup was primarily designed for calibration of a phase angle error of current shunts, but it can be used for calibration of wide range of impedance standards in full complex plane. The setup allows calibration of impedances down to submegaohm range with compare currents up to 10 A and frequencies up to 100 kHz. The setup was also successfully used for comparison of inductive voltage dividers with ratio uncertainty approximately 1 mu V/V. Achieved expanded uncertainties are a few microvolts per volt for near unity voltage ratio and up to 35 mu V/V for voltage ratio 1: 10 at 100 kHz. The phase uncertainty is below 1 mu rad at 1 kHz and below 50 mu rad at 100 kHz for ratio 1: 10 (confidence level 95 %). Due to the used signal processing techniques, the setup can be used to measure complex voltage ratio even with just a few millivolt voltages at the inputs.