Research On The Fluid Pressure Sensing Technology Based On The Fiber Bragg Grating

Pressure is one of the most fundamental parameters. Pressure measurement in high accuracy, safe, and reliable manner is of great significance in the industry productions, especially in the potentially flammable and explosive situation. Accordingly, it is urgent to research and develop a high-accuracy pressure sensing system that can be applied in the flammable and explosive environment.In recent years, more and more researchers and engineers show great interests in the applications of the fiber Bragg grating (FBG) sensing and measuring technologies, which have already been applied successfully in the pressure-sensing field. A novel fluid pressure sensing system based on both the FBG and the Bourdon tube is presented and demonstrated in this thesis. Firstly, the basically optical sensing characteristics of the FBG are introduced in detail, and its temperature and strain characteristics are measured experimentally. Secondly, the characteristic of the displacement v.s. the applied pressure of a C-shape Bourdon tube (CBT) is studied, and a non-contact measurement of this characteristic is realized using CCD imaging and computer-image-processing technologies. Thirdly, CBT's characteristic of the strain v.s. the applied pressure is studied, on the basis of this, a new scheme of the straight Bourdon tube (SBT) is presented, a SBT is designed and fabricated, and then the strain-pressure characteristics of both the CBT and SBT are measured experimentally using a strain measuring technique, a comparison between the CBT's and SBT's straincharacteristics is also made. Finally, theoretical models of a FBG fluid pressure sensing system scheme based on the Bourdon tube are developed, and a FBG-based fluid pressure sensing system using the transverse strain-pressure characteristic of the SBT is designed and set up. The experimental results have shown that the shift of the central reflecting wavelength of the FBG is 0.78nm when the applied pressure varies in the range of 0-80KPa, and the pressure measurement sensitivities are as high as 9.660 + 10-3pm/Pa and 9.665 + 10-3pm/Pa when the pressure is increased and decreased respectively, corresponding to pressure sensitive coefficients of 6.219 +10-3MPa-1 and 6.222 +10 -3MPa-1, which are approximately 3141 times greater than that of a bare FBG(1.98 +10-6MPa-1). In addition, the center-reflecting wavelength shift of the FBG varies in good linearity with the applied pressure.