Integrated Precise Capacitance Micro Displacement Measurement System Based On Embedded

Capacitive displacement sensor has the advantages of simple structure,high resolution,strong anti-interference ability,good dynamic characteristics,and so on.It is an important measurement method of non-contact micro-displacement measurement,and has been more and more widely used in precision machining,high-precision positioning,high-precision measurement and other fields.With the rapid development of science and technology and industry,the pursuit of capacitive micro-displacement measurement performance index is getting higher and higher,forcing continuous improvement of the sensor deficiencies.The resolution and measurement range of the capacitive sensor are greatly limited by parasitic capacitance,the sensor probe structure,and the nonlinearity of the output signal of the capacitive detection circuit with the size of the capacitance.Therefore,it is of practical significance to design a capacitive micro-displacement measurement system with large range and high precision.This paper develops a large-range micro-displacement measurement system based on embedded platform.Firstly,the capacitance gradient theoretical model is analyzed for the sensor probes of variable dielectric type,variable pole distance type and variable area type.According to the output characteristic curve of displacement and capacitance gradient,the variable area type sensor is finally selected.A cylindrical capacitive sensor is designed,and its theoretical output characteristics are linearly related,which can meet the design requirements of large range of micro-displacement measurement system.Then,this paper uses the fully driven cable technology,from the sensor probe to the signal path of capacitance processing and conversion circuit,effectively solve the nonlinear error caused by parasitic capacitance to the measurement system.Due to the complex structure of the traditional capacitor detection circuit,and easy to produce distributed capacitance and mechanical error,and in order to conform to the development trend of intelligent and modular measurement system,this paper chooses the highly integrated capacitance digital converter AD7747 as the core of the signal processing and conversion circuit,which greatly simplifies the circuit structure.Finally,the capacitance micro-displacement measurement system based on embedded also integrates LCD display module and temperature and humidity sensor module,which is highly expandable and more portable.According to the structure of the sensor and the shape of the displacement device,a special calibration platform is designed with SOLIDWORKS,and various performance indicators of the measurement system are analyzed.The actual measurement curve was obtained after the least square polynomial fitting of the original data by MATLAB software.On this basis,the resolution experiment,repeatability experiment and linearity experiment of the measuring system are carried out.The final results show that the resolution,repeatability and linearity of the integrated precision capacitance micro-displacement measurement system developed in this paper are 1.674μm,0.83%,0.003 p F and better than1.2% in the measurement range of 6mm.