A Bridge-Type Inductance Sensor With a Two-Stage Filter Circuit for High-Precision Detection of Metal Debris in the Oil

A bridge-type inductance sensor with a two-stage filter circuit for high-precision detection of metal debris in the oil is proposed. The sensor mainly consists of a bridge-structure sensing unit and a two-stage filter circuit. The sensing unit consists of two double-wire solenoid coils (as the detection unit and the reference unit, respectively) and a Wheatstone bridge -structure. This structure enhances the response of the detection unit to the magnetic field disturbance generated by the wear debris and can improve the detection accuracy of the sensor. Furthermore, a circuit with rectification, amplitude modulation, and amplification functions is introduced to eliminate the noise interference from the environment and the system, and to accurately extract the weak abrasive signals that are submerged in the noise. Meanwhile, by adjusting the passband gain of the two-stage filter circuit, the measurement range of the sensor voltage value is improved. Experimental results show that adding a two-stage filter circuit can improve the resolution of the sensor, and can effectively detect $45~\mu \text{m}$ iron particles. The sensor provides technical support for the modularity and portability of the testing instrument, which is essential for fault diagnosis and prevention of the hydraulic systems.