Design of Capacitive Sensor for Phase Concentration Measurement in Two-phase Flow

Concave capacitive sensors are widely applied for phase concentration measurement in two-phase flow. Fringing electric fields exist between any two concave capacitance electrodes of finite length and the additional capacitance these fields add is not easily accounted for. It is important to account for fringe effect in many capacitive sensing applications in order to ensure accurate measurement results. In this paper, a capacitive sensor with axis and radial grounded guard electrodes is proposed. The performance of the sensor with and without guard electrodes in term of fringe effect and output linearity is investigated. For the determination of the optimal structure of the capacitive sensor, numerical simulation and response surface method are adopted. Numerical simulation and static phantom experiments show the effectiveness of the proposed capacitive sensor which allowed a significant reduction of the fringe effect and good linearity and good sensing field homogeneity.