High Speed Frequency Measurment And Non-Linearity Correction Of Frequency Modulated Capacitive Displacement Sensor

With the advantages of simple structure, high accuracy, fast response and no contact measurement, capacitance sensor has been widely used in the domains of precision machining, ultra-precision orientation, ultra-precision measurement and so on. However, due to the small output signal of the capacitance sensor and the non-linearity of the Input-Output curve, how to gain the capacitive signal and how to carry out effective non-linearity correction, has become the key which influences the performance of the capacitance sensor.Based on the processing of output data from the frequency modulation type capacitance sensor, this paper gives the in-depth study on the technology of measuring frequency and the technology of non-linearity correction. The main research is given as follows:Firstly, in this paper the method of measuring frequency is concluded and summarized. The circuit of measuring frequency based on FPGA is designed. The method on the synchronous multi-cycle frequency measurement is improved, and the VHDL program of the multi-cycle frequency measurement is given;Secondly, the application of Artificial Neural Networks (ANN) technology on non-linearity correction and curve fitting is studied. The emulator of non-linearity correction, which is based on Fourier Progression Artificial Neural Networks (FANN), is realized, at the same time the naturalization of the non-linearity correction program to Digital Signal Processor (DSP) is achieved;Third, the hardware circuit based on TMS320VC5402 of non-linearity correction and data processing is designed, including FLASH memory, serial data transfer and LCD display module;Finally, the experiment is carried out to testing the performance of the frequency measurement module and the non-linearity correction module. The result of the experiment affords the principle and reference to improve the capability of the capacitance sensor system.