The Research Of Capacitance Sensor Based On Displacement Measurement

There are many tools for measuring displacement on the market. Capacitive sensor is one of these measuring tools, which has these advantages of the simple structure, the low output impedance, good dynamic performance, high sensitivity, non-contact measuring and so on. However, capacitive displacement sensor is deficient. Firstly, due to the small output signal of the capacitance sensor, it makes great trouble for data collection. Secondly, the relation between input and output exhibits non-linearity in the capacitive sensor. Therefore, the emphasis and difficulty lie in how to extract capacitive signal and how to carry out effective non-linearity correction, which influences the performance of the capacitance sensor.Based on the characteristic of output signal from the differential area-changing capacitive sensor, the paper studies capacitance detection circuit and non-linear calibration technology. Considering the parasitic capacitance and distributed capacitance of the capacitance sensor, we use precision capacitance detection circuit and improve accuracy of the capacitive detection. In order to solve the problem of nonlinearity, we take advantage of curve-fitting method to achieve nonlinear self-correction system. We complete calibration test by displacement measurement. According to the experiment data, the functional relationship between the displacement and the voltage is deduced. With the analysis of the maximum relative error, we complete the study purpose of nonlinear self-correction of capacitance sensor. The non-linear error is reduced from5.6%to1.0%～1.2%. The paper combines the capacitive sensor and single chip microcomputer. We store the functional relationship into SCV and design an intelligent measuring system which has conditioning circuit of capacitance sensor, direct current regulation circuit, temperature gathered circuit, alarming circuit, key-press circuit, reset circuit, LCD display circuit and serial communication with PC circuit. System software is developed by the Keil C51.In a word, the paper has achieved the research of the differential area-changing capacitive sensor based on displacement measurement and has completed successfully expected research work. The designed system can be used in the measurements such as the deformation of the object, and the range of the measure scale is from-2.5mm to2.5mm, and the resolution is0.1um.