Interference reducing by low-voltage excitation for a debris sensor with triple-coil structure

Abstract

Dielectric impurities, such as air bubbles and water droplets, which flow along lubrication systems can severely interfere with the performance of inductive debris sensors due to coil parasitic capacitances. This study proposes a novel triple-coil debris sensor with low voltage excitation to reduce the influence of variations in coil parasitic parameters and to improve the resistance to interference of dielectric impurities without sacrificing sensitivity to metallic particles. The sensor utilizes a 3-turn excitation coil made of Litz wire and two identical 60-turn sensing coils made of enameled wire. A sensor prototype with a compact and efficient signal processing system is constructed and several experiments are conducted to test its performance. Results show that the sensor can successfully detect 300 µm (diameter or D) high-carbon steel particles, 558 µm (D) copper particles, and 491 µm (D) aluminum particles in an oil pipe with an outer diameter of 50 mm. Comparative experiments indicate that for the sensor with conventional excitation method, the amplitude of the interference induced by an 8.5 mm (D) water droplet is equivalent to that of the interference induced by a 524 µm (D) ferrous particle, and a 10 mm (D) air bubble may be mistaken as a 557 µm (D) ferrous particle. No interference occurs under the same conditions for the sensor with low voltage excitation.