Automatic bridge for comparison of inductance standards

A high-precision multi-range unbalanced transformer bridge KWL5 designed for calibration of standard inductors of the same nominal value is described. The basic theory of the bridge is presented. Design, application and characterisation of the instrument which enables the direct measurement of differences of both impedance components (real and imaginary) is presented. The instrument was designed to compare inductors of values from 100 μH to 10 H in the frequency range from 100 Hz to 10 kHz with the smallest uncertainty possible. Repeatability of the results obtained by the use of the KWL5 bridge is better than 10 ppm. Coherence equal to or better than 5 ppm for frequency range up to 10 kHz was obtained.