Sensing Model of Metal Particles in Nonuniform Time-Harmonic Magnetic Field for High-Sensitivity Debris Sensor

Inductive debris sensors play an important role in monitoring the oil condition of rotating and reciprocating machinery. The sensor is based on a time-harmonic magnetic field and has the advantage of strong detection ability for nonferromagnetic particles. The sensing mechanism of metal particles is the foundation for optimizing sensor performance and extracting debris information. The sensing model of metal particles in a nonuniform time-harmonic magnetic field is presented in this article. First, the magnetization model of metal particles in a time-harmonic field is introduced. Then, a magnetic field model of the coil in multiple mediums is established, and the magnetic field expressions of three typical sensing units are obtained. Next, a sensing model for metal particles at any position is obtained by combining the magnetization model and the magnetic field model. By comparing the signal features under different paths, the influence of a nonuniform magnetic field is proved. Experiments are conducted on the detection characteristics of built-in magnetic core sensing unit and external magnetic core sensing unit, and the design principle of sensing unit with soft magnetic medium is proposed. This study provides support for the design of high-sensitivity, robust inductive debris sensors.