A system for calibration of inductance standards based on a simple unbalanced transformer bridge

An unbalanced transformer bridge designed for inductance standard calibration is described. Basic theory of the bridge is discussed in which two components of the unbalanced voltage are measured and used to determine a ratio of compared inductance standards. Significant sources of errors are analyzed and numerical limits given. The uncertainty of comparison, in the frequency range 100 Hz-2 kHz, is assessed to be smaller than 30 ppm for 10 mH-1 H standards and smaller than 100 ppm for 1 mH-10 mH standards. The bridge is convenient for automatic operation.