Improving sensitivity of an inductive pulse sensor for detection of metallic wear debris in lubricants using parallel LC resonance method

Detection of small metallic wear debris is critical to identify abnormal wear conditions for prognosis of pending machinery failure. In this paper we applied an inductance-capacitance (LC) resonance method to an inductive pulse debris sensor to increase the sensitivity. By adding an external capacitor to the sensing coil of the sensor, a parallel LC resonance circuit is formed that has a unique resonant frequency. At an excitation frequency close to the resonant frequency, impedance change (and thus change in voltage output) of the LC circuit caused by the passage of a debris particle is amplified due to sharp change in impedance at the resonant peak; thus signal-to-noise ratio and sensitivity are significantly improved. Using an optimized measurement circuit, iron particles ranging from 32 to 96 mu m and copper particles ranging from 75 to 172 mu m were tested. Results showed that the parallel LC resonance method is capable of detecting a 20 mu m iron particle and a 55 mu m copper particle while detection limits for the non-resonance method are 45 and 125 mu m, respectively. In contrast to the non-resonant method, the sensitivity of the resonance method has been significantly improved.