A Full 360° Measurement Range Liquid Capacitive Inclinometer with a Triple-Eccentric-Ring Sensing Element and Differential Detection Scheme

Abstract

This paper proposes a low-cost and full 360° measurement range inclinometer based on fluidic motion. The inclinometer is fabricated using printed circuit board manufacturing techniques. The principle is via measuring two channels of capacitance changes between three plates, which are partially filled with nonconductive liquid to obtain two amplitude modulation quadrature signals as the resolver. In this inclinometer, the electrode subdivision is changed from the traditional radial direction to a circumferential direction by a triple-eccentric-ring sensing element to achieve full-range measurement capability from 0° to 360°. In addition, the application of a differential detection scheme leads to the dc capacitance C0 being eliminated in the measurement, resulting a high voltage-to-capacitance ratio in a low voltage source requirement. Both analytical calculation and finite-element analysis verified the feasibility of the principle. Furthermore, nonlinear error simulation is conducted and the main effected reason is figured out. Finally, a prototype is fabricated and assembled. Experimental results show that sensor can measure the tilt angle in a range of 360°, with an accuracy of 0.1° and a resolution better than 0.01°.