| The wavelength demodulation system of Fiber Bragg Grating?FBG?sensor is the core of FBG sensing system.At present,the tunable F-P?Fabry-Perot?filter method is the most frequently used demodulation method of FBG.This method has the advantages of fast demodulation speed,wide demodulation range and high demodulation accuracy.However,Pb(Zr1-xTix)O3?PZT?,the cavity length adjusting element in F-P filter,has nonlinear characteristics,such as temperature drift,hysteresis and creep.These characteristics make the output wavelength of F-P filter change with time nonlinearly,which brings about the problem of large wavelength demodulation error and low sensing precision.In order to solve the above problems,we study the hysteresis and creep characteristics of PZT in F-P filters,and propose a F-P filter-based wavelength demodulation method based on thermal etalon and hysteresis and creep compensation control of the PZT.The driving voltage of PZT is controlled to change nonlinearly with time so that the wavelength of the broadband light source output through the F-P filter can be changed at equal intervals with time.The peak wavelength of the etalon transmission spectrum is thus obtained,changing linearly with time.It acts as a"tick"for the wavelength scale and provides an accurate wavelength reference for demodulating the wavelength of the sensing grating.By designing the driving voltage control scheme of PZT hysteresis and creep compensation,the FBG sensing experiment system is built and the control and signal processing software is written.A FBG sensing system based on the above F-P filter demodulation method is implemented,and 8 different temperature values are measured by the sensing system.The experimental results of the FBG temperature measurement show that,compared with the method without hysteresis and creep compensation control,the proposed method improves the temperature measurement accuracy about 20 times and the temperature measurement error is less than 0.5?. |
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