Study And Design Of A Capacitance Type Linear Displacement Sensor

Capacitive sensor with small dissipation power, low output impedance, small electrostatic force, good dynamic performance,high sensitivity, strong adaptability, and can realize the advantages of non-contact measurement, is widely used in displacement, vibration, Angle, acceleration, pressure, differential pressure, liquid level measurement. But due to the parasitic capacitance, production technology, output signal of capacitance detection circuit and capacitance size present nonlinear, etc, the effect of the capacitive sensor is limited resolution and measurement range.In this paper, the current widely used capacitance measurement circuit are summarized and analyzed. On this basis, the design of the measurement circuit is given priority to with capacitive digital conversion chip, using differential measurement method, developed a large range of differential variable area capacitance displacement sensor measurement.This thesis mainly completed the following content:1) By reading the literature, complete capacitive displacement sensor overall scheme design. Sensors to achieve design requirements, the mechanical structure of the sensor design, and size of each part is given and the design principle of the structure.2) Complete the design of control circuit of capacitance type linear displacement sensor. Based on the capacitance to digital conversion chips of the sensor signal, signal acquisition, filtering, capacitance digital conversion work. This sensor by ATmega8AVR chip as the core chip, with capacitive sensor as the sensitive element, to digital conversion chip capacitor AD7150capacitance acquisition and digital conversion, digital current conversion chip AD4204-20ma industrial output current.3) Complete control circuit design and debug program. Master control chip ATmega8L and capacitors to digital conversion chip AD7150implementation through the IIC bus communication,4-20ma current chip AD420through three bus communication agreement. Initialization program work process is:the main control chip ATmega8L capacitance AD7150digital conversion chip, and reads the digital signals, after processing is completed, send data to AD420chip, AD420converts digital quantity to4-20ma industrial electric current for long-distance data transmission.4) The capacitance type linear displacement sensor testing experiment. On the stability of the sensor, linearity, sensitivity and resolution for data analysis.Theory and experimental data indicate that this sensor has long measurement range, the circuit has simple structure, good stability and zero drift small advantage.