ABSTRACT
In order to measure and control the linear motion of different objects or machineries, a contactless capacitive sensor is proposed in this preliminary study. In this paper, a proof of concept of this sensor’s design and performance is reported. In a traditional capacitive-type displacement sensor, the effect of two parallel plates’ effective overlap area or the distance between them is considered as a variable sensing parameter, where the dielectric medium between them is considered as constant. Moreover, in order to obtain the signal based on this parameter, any single plate should be moved along with the object motion. Thus, electrical connectivity with this movable plate may lead to a mechanical error. To overcome this difficulty, the proposed design presents a concept where the dielectric medium between the two plates is moved along with the object and the plates remain fixed. Thus, its movable sensing part is completely separated from the electrical interface. Therefore, it is immune to the mechanical error. Here, the linear displacement is sensed by the effect of the push–pull mechanism. This state-of-the-art design is composed of two parallel conductive plates and a single dielectric plate, thus forming two capacitors. Moreover, the differential output of these two capacitors shows good linearity and sensitivity in terms of capacitance. Furthermore, a simple signal processing circuit is used for converting this capacitance into analog voltage. By using a laboratory prototype, a sensitivity of 18 mv/mm and a nonlinearity of ±2.6% have been achieved for the linear displacement in the range of ±30 mm.
