Study on a Novel Eccentricity Sensor Based on Alternately Detecting Cylindrical Capacitances

The paper presents the scheme of a convenient and cheap eccentricity sensor which directly submits the digital results through communication ports. The novel sensor consists of four capacitors, formed between the inner and a segment of the outside cylindrical conductor. Alternately measuring every pair of nearby capacitors provides the possibility to electrically disconnect the inner conductor so as to avoid contact problems of rotor. The relation between the position of the inner conductor and the capacitance is discussed and a convenient way is adopted to replace the analytical solution with a fitting function so that the series parameters are optimized from FEM (finite-element-method) result and calibration experiments. The offset in two orientations leads to corresponding changes on the four capacitors. The algorithm is presented to acquire the offset from synthesis of the segment capacitances. The circuit is designed to alternately combine the nearby capacitances and disassemble into every one with microprocessor. The assembled capacitance is precisely measured with the special IC CDC (capacitance-digital-convert). The planar offset is eventually drawn out and displayed and submitted. The eccentricity sensor shows many particular advantages such as contactless surface, electrical disconnection from the rotor, etc