Research on the coupling relationship between metal particles in lubricating oil and inductive coils based on self-excitation single coil

Characterizing the operational wear status of mechanical equipment based on online monitoring of metal particles in lubricating oil plays a significant role in the effect of equipment fault diagnosis technology. According to the theoretical analysis of the electromagnetic induction principle and Biot–Savart’s law, combined with the finite element simulation analysis, systematic study and analysis were conducted on the distribution of magnetic field inside a single inductance coil, the coupling relationship between metal particles in lubricating oil, and the inductance coil. This paper analyzed the effects of four important design parameters that were the excitation frequency, the inside diameter of the coil, the turns number of the coil, and the length of the coil. On magnetic field uniformity and monitoring sensitivity, experiments demonstrated that: the correlation between the uniformity of the magnetic field on the testing surface of the sensor inductance coil and the coil radius and length is the highest, followed by the correlation with the number of coil turns. The correlation with the excitation frequency can be ignored in a negligible manner. In addition, experimental results indicated that if the ratio between the inside diameter of the inductance coil and the length of the coil (R/L) was less than 0.41, the magnetic field uniformity would reach over 91%. Meanwhile, results showed that the sensitivity of the sensor to ferromagnetic and non-ferromagnetic particles increased with the decrease in the coil inner diameter and inductance and increased with the increase in the excitation frequency. There is a specific length that can make the sensor coil monitoring, which is the most sensitive.