Research On The Capacitive Displacement Sensor

With a low output impedance, small power, good dynamic characteristics, little release of heat, small electrostatic force, high sensitivity, non-contact measurement, strong adaption to high temperature, radiation, vibration and other adverse conditions, capacitive sensor has been widely used in displacement, vibration, angle, acceleration, pressure, differential pressure, liquid level, moisture content and others. Because of parasitic capacitance, production technology, output of measure circuit and capacitance are non-linear, capacitive sensor measurement range has been greatly restricted. Then it is necessary to design a circuit for capacitive sensor with good linear. It is also very important to find the methods to increase the measure range of capacitive sensors, as well as research to capacitive sensor characteristic curve fitting.This paper's main task is to study capacitive displacement sensor and design a new type displacement sensor which can be widely used, with professor Tang Deyao's patented named a capacitive measure circuit and its application.This paper mainly include the following content:1). To study capacitance measure circuit base on imaginary part method. Analyzing the cause of the non-direct proportion output of capacitance measure circuit and finding out the ways to overcome the output of non-direct proportion by simulation and experiments. Circuit modeling for capacitive displacement sensor probe, then simulating and analyzing parasitic capacitance effect to the measure results of the circuit. It presents parasitic capacitance compensation technique which can be offset impact of parasitic capacitance. Dynamic characteristics of the circuit is also analyzed.2). According to the characteristics of capacitive displacement sensor circuit, compare sine wave with triangular wave by stimulated. Then conclude that triangle wave is more suitable for AC excitation power supply than sine wave. Two precision rectifier circuit are simulated, and analyze their Anti-jamming performance. Triangular wave generating circuit, precision rectifier circuit, filter circuit and zeroing circuit are designed.3). To improve Lagrange data fitting of numerical calculation method, presents dynamic segmentation Lagrange curve fitting method.