A simple variant of the conventional methods of displacement measurement based on differential inductance variation is described. The theory of the transducer and an operational amplifier method of finding the difference between two oppositely varying inductances are presented. The major limitations of the method on linearity, sensitivity, and stability are discussed. A brief comparison with the wellhyphen;known bridge methods is given. The prototype instrument has a dc output whose amplitude is proportional to the displacement and whose polarity indicates the direction of displacement. It has a sensitivity of 50 mV/mgr;m, resolution of about 0.08 mgr;m, and a maximum nonlinearity error of about 2percnt; for a displacement range of plusmn;100 mgr;m. An application of the transducer system in the measurement of the reaction torque of a rotating machine delivering or receiving power is also given.
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