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Electromagnetic Sensor for Detecting Wear Debris in Lubricating Oil

The detection technology on wear debris in lubricating oil is critical to ensure the safe operation of the engines in the aerospace industry. In this article, a triple-coil reverse double-excitation solenoid sensor is discussed. Inside the sensor, electromagnetic field generated by two excitation coils is sensitive to the occurrence of wear debris, and its changes can be captured by the induction coil. Thus, the impedance and inductive voltage of the induction coil can be used to detect the wear debris. Assuming the debris is spherical, an electromagnetic model is established. Via time-harmonic electromagnetic field analysis method, the expressions of the induction coil’s impedance increment and inductive voltage are derived. The relationships between the impedance increment and the parameters of the debris and the coils are investigated. The theoretical results are validated by Maxwell from Ansys, Canonsburg, PA, USA, simulations and experiments. In order to get an accurate voltage output signal, a passband filter amplifier is designed to connect to the output of the induction coil and empirical mode decomposition is presented to process the digital voltage signal. The derivation method on the coil impedance increment and inductive voltage and the signal processing method can be extended to design sensors measuring more complicated wear debris.