The Design And Development Of Fiber Grating Demodulation System Based On FPGA

The cost and volume of the fiber Bragg grating (FBG) demodulation system is one important factor which affects application of FBG sensor in actual engineering. Therefore, finding a low-cost and small-volume FBG demodulation system is the key problem of the practical application for FBG sensor.This thesis has introduced the coupled mode theory, analyzed the temperature and strain sensing principle, and studied the principle and solutions of the cross-sensitivity of FBG. The application of wave division multiplexing, time division multiplexing and space division multiplexing in fiber grating demodulation technology have been analyzed and compared. Then, the thesis introduced the principle of four kinds existing wavelength demodulation methods of FBG. Through analyzing and comparing the performance of the matched grating filter method, the unbalanced Mach-Zehnder interferometer method, the tunable narrow-band light source method and the tunable Fabry-Perot filter method, finally chose the tunable Fabry-Perot filter method as the demodulation system method. This thesis designs the FBG demodulation system scheme, each function component of the demodulation system has been analyzed and confirmed, and the fiber Bragg grating sensing system was set up and debugged. The principle of reference grating for calibrating wavelength has been analyzed, and a reference grating and an F-P etalon are used to calibrate the wavelength. In this thesis, the hardware circuit of the demodulation system which used the FPGA chip EP1C12Q240C8 as the controller has been designed, included the core circuit of FPGA, the sawtooth wave generating circuit, the data acquisition circuit and the data upload circuit. The control procedure of D/A converter has been completed using VHDL in Quartus II software, then realized sawtooth wave voltage output from 0 to 20 V. The Nios system of data acquisition circuit and the network interface circuit has been designed through the SOPC Builder. The control program of ADS1601 and RTL8019AS is developed by Nios II software, then the collection and transmissiom of the data has been realized.