Signal Conversion And Non-Linear Correction Of Capacitive Displacement Sensor

With the advantages of simple structure, high accuracy, fast response and non-contact measurement, capacitance sensor is widely used in ultra-precision measurement, nanotechnology, precision engineering and so on. There are two technical difficulties in designing capacitance sensor. One is frequency to voltage transformation and the other is non-linear correction.Research is done on these two problems. The main research is given as follows:1. The signal transformer module is designed by super heterodyne operating mode. The frequency is transformed into voltage successfully. The generating circuit of local oscillation signal used in the mixing is designed with the technology of Directly Digital Synthesis (DDS). The amplitude and frequency of the local oscillation signal is more stable and accurate than the signal generated by other methods.2. Based on Field Programmable Gate Array (FPGA), the circuit of non-linear correction module is designed to achieve basic functions. Compared with other methods, curve fitting is selected to correct the non-linear of sensors. Floating-point numbers in the operating process use IEEE754 standard. The program is written by Very High speed integrated circuit hardware Description Language (VHDL).3. Appropriate analog to digital conversion chip and digital to analog conversion chip should be selected according to the measuring accuracy and response speed of this design. Then sampling circuit is designed to get data and digital to analog conversion circuit is designed to drive the next chip.Program and circuit are designed for the signal transformation module and the non-linear correction module. At last, experiment is done to prove the correctness and efficiency of the design.