Ratio Comparisons of Impedance Standards

The application of a readily assembled comparator circuit, previously used in the comparison calibration of inductive and resistive voltage dividers, has been extended to cover the comparison of impedance standards. As an example requiring the most stringent performance from the circuit, the comparison of four-terminal inductance standards and their absolute determination in terms of the unit of capacitance have been studied. A data-reduction procedure has been devised to utilize a partial set of pair-wise comparison measurements to establish the absolute scale of inductance from 10 henrys to 500 μH. A realistic assessment of system errors has been incorporated in the data reduction, which establishes the absolute accuracy at approximately 0.003 percent over the whole range. Determination of the quality factor Q of the inductors to better than 0.2 percent has also resulted from these measurements, principally at 1 kHz.