Design of capacitance lubricating oil grains detecting system based on ring electrode

In abnormal operation,friction pair will produce large metal wear debris about tens of micron in size.When the impedance method is used to detect grains,very high sensitivity is necessary. So,a ring electrode capacitive sensor with a differential structure is designed. By replacing the complex signal processing circuit,capacitance-to-digital converter AD7746 is used to convert capacitance sensor output into digital signal directly,simplifying the electronics,and minimizing the interference of distributed and parasitic capacitance. Experiment result shows that the system has high sensitivity with resolution of 0.125 fF.