Bridges for calibrating four-terminal-pair standards of self-inductance at frequencies up to 10 kHz

Two bridges for calibrating four-terminal-pair (4TP) standards of self-inductance in the frequency range from 500 Hz to 10 kHz are described. The first is a multifrequency double-balance bridge for linking inductance to capacitance and the second one is a modified Maxwell–Wien bridge, in which inductive voltage dividers in conjunction with fixed resistance and capacitance standards are used as balance controls. Precision voltage followers serving as unity-gain isolators assure that negligible currents are drawn from high potential terminals of 4TP bridge elements. When a procedure based on the interchange of the followers is applied, the effect of their gain errors is minimized and, for example, the value of a 100 mH inductor can then be measured with an uncertainty (k = 2) less than 2 µH at 1 kHz