Instrumentation circuitry for an inductive wear debris sensor

The design of instrumentation circuitry for an inductive sensor to detect small metal particles is presented. The sensor, designed for counting and characterizing wear debris particles in lubrication oil, detects changes in the inductance of a small coil as metal particles pass through it. A change in inductance produces a differential voltage at the output of a Maxwell-Wien bridge, which is then amplified and rectified to produce a DC voltage pulse detectable using standard data acquisition components. For iron particles approximately 75μm and 150μm in diameter, the circuit produces output voltage pulses of 381mV and 693mV, respectively.