Abstract: An apparatus and method for measuring the inductance of a wire-loop without direct reference to any particular time-constant or frequency. Low-frequency noise induced into the wire-loop is canceled within the detector circuit and crosstalk between a plurality of adjacent wire-loops is nullified using passive transformers. New wire-loop configurations utilize the permeability-modulated carrier referencing to provide repeatable inductive signatures with less intrusive, and non-intrusive installations.

Abstract: An oscillator circuit for use with a wire-loop inductive sensor and method for use. The oscillator circuit includes two balanced capacitors coupled to the wire-loop sensor, and an excitation circuit connectable with the capacitors at a selected polarity. Wherein, when the excitation circuit is connected to the capacitors, one of the capacitors is charged while the other capacitor is discharged, and both of the capacitors are discharged when the excitation circuit is disconnected to produce a pair of decaying oscillations having a caduceus-shaped output. The oscillator circuit highly attenuates common-mode noise detected by the wire-loop and differential noise from both ambient and crosstalk sources is filtered by active isolation.