Improvement of Sensitivity and Detectability of the Three-Coil Wear Debris Detection Sensor Using LC Resonance Method and Modified Lock-in Amplifier

Abstract

That how to improve the sensitivity and the detection ability of the Large-caliber sensor is critical to satisfy the requirement of heavy vehicle wear condition monitoring. In this paper, we introduced the LC resonance principle to the design of sensor with large flow channel (7mm). The resonant exciting coil increases the impedance change of the exciting circuit caused by wear particles which magnify the current difference between the two exciting coils and improve the sensitivity of the sensor. The resonant induction coil greatly suppresses the interference signals and magnifies the weak induced electromotive force which is beneficial to enhance the detection ability. In order to boost the detectability for different materials particles, a phase controlled variable-frequency exciting system (PCVFES) was adopted to automatically switch the exciting frequency between 284kHz for ferromagnetic particles and 420KHz for non-ferromagnetic particles. For the weak signal detection, based on the essential characteristic of the signal, we apply a simpler method that modified lock-in amplifier (MLIA) rather than the conventional algorithms (Wavelet transform, EMD). Results show that using these methods the sensitivity and the detection ability of the sensor are significantly improved and the 75μm iron particles and 220μm copper particles were successfully detected which realizes the initial abnormal wear monitoring for the large flow project.Key words: wear debris detection; resonance method; sensitivity; phase controlled variable-frequency exciting system (PCVFES); modified lock-in amplifier (MLIA) IntroductionThe wear is the most common fault modality in mechanical equipment and also is one of the major obstacles affecting the normal operation of machinery and equipment. With the development of modern industry, the demands about continuity of production and the reliability of mechanical equipment continue to increase, therefore, that the ability to precisely monitor the wear condition of mechanical equipment and to prevent serious malfunction caused by excessive wear gradually show its significance. The wear debris detection sensor is thus an effective tool for wear condition monitoring [1] and starts to show its great vitality because of the high detection efficiency, veracity and the ability to timely reflect the wear state changing process of equipment.At the present, some research institutions have manufactured various kinds of wear debris detection sensor based on different physical principles mainly including optics (light scattering and diffraction), ultrasonic, electrics (capacitance, resistance and inductance) and image [2] . By comparing these sensors' properties, it is shown that the optical wear particle detection sensor is easily affected by the bubbles in the oil and gives false negative results. And the ultrasonic wear particle detection sensor is easily disturbed by background noise and has lower

Wear debris measurement in lubricating oil based on inductive method: A review

“…The impedance change of the LC circuit caused by the passage of debris particles changes sharply at the resonance peak, which causes the voltage signal output to be amplified. 59 Jia et al 60 introduced LC resonance principle in the design of large flow channel (7 mm) sensor. The change in impedance of the excitation circuit caused by wear particles is much greater than that of the excitation coil, and the current difference between the two excitation coils also increased, amplifying the weak inductive electromotive force, and improving the detection capability of the sensor.…”