Abstract: In order to improve the sensitivity of the on-line wear particle monitoring sensor,an electromagnetic wear particle sensor with a built-in nanocrystalline magnetic ring was proposed.By establishing a numerical model of the sensor's internal magnetic field distribution and output induced electromotive force,the influence of size properties of the induction coil ring and the excitation coil rings on the sensitivity of wear particle monitoring sensor was systematically analyzed.The simulation and experimental results show that the nanocrystalline magnetic ring has a significant influence on the sensor sensitivity.Moreover,adding magnetic rings to both the excitation coil and the induction coil can dramatically increase the amplitude of electromotive force induced by wear particles to 4~7 times.Therefore,the monitoring ability of the designed sensor can improve effectively,especially for the small wear particles of 50 μm to 100 μm.The study is of great significance for the early fault diagnosis and fault warning of large mechanical equipment.