Impedance comparison at power frequency by asynchronous sampling

We present a measurement setup for the comparison of four-terminal impedances at power frequency, based on synchronous sampling of the voltage drops on the impedances placed in series. Complex impedance ratio is determined with a sine-fitting technique. The impedances can have different moduli and phase angles; the setup is optimized for impedances having moduli ranging below 100 Ω. Although an evaluation of measurement uncertainty is still in progress, it is expected to be better than 1 × 10^-4.