Electronic ac Mutual Inductance Bridge for Measuring Small Susceptibilities at Low Temperatures

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Abstract
An electronic ac mutual inductance bridge is described, in which a vacuum tube and a fixed mutual inductance are combined to form an accurately variable mutual inductance. The variation is obtained by means of decade resistors. The primary and secondary self‐impedances are constant, independent of the mutual inductance setting, and can be made substantially lower than is possible with comparable conventional variable mutual inductances. The bridge is designed to be suitable for use in balancing multiturn mutual inductances to permit susceptibilities of samples of 1 cm3 volume to be measured at low temperatures with a precision of ±2×10−7 emu/cm3. Details are given of the bridge circuit and of a typical multiturn mutual inductance; an outline of some typical susceptibility measurement results is appended.