Research On Mechanism Of Capacitive Sensor And Realization Of Its Measuring System

Because of its extraordinary performance and low cost, capacitive displacement sensor has always been playing an important role in measuring field since its birth. Actually, it has been almost 30 years ever since such sensor was introduced into domestic measuring field. However, after 30-year's development, the performance of relative localized products still cannot equals to that of foreign ones. Furthermore, the realization of such products inherits formerly existing ones, to which extent it also contains innovation.Considering above, this thesis first studies the measuring principle of phase-discrimination capacitive sensor, then constitutes the mathematical model of the sensor under several reasonable approximations. Through basic research, the measuring foundation of capacitive sensor is re-evaluated, indicating that why the type of this sensor studied is phase sensitive. Secondly, through error analysis of modulated sensor output, the theoretical error is described. From an engineering perspective, a feasible method of theoretical error arresting is presented. After calculation, an optimum ratio between the length of emitting electrode on the sliding plate and that of reflecting electrode on the fixed plate is acquired. Based on the ratio, a new optimization of structural design, which exactly meets the demand of the ratio, is presented along with a more compact and feasible design. Simulations verify the error arresting effect of presented designs. Finally, the thesis presents the planning of the sensor's ASIC, according to special demands of involved structural designs. Two key modules of the ASIC, DPLL and PD-Counter, which is the key technology of phase-discrimination capacitive sensor measuring, are proposed, forming the IP core of ASIC.