| This paper focuses on research on the fiber grating sensing technology, enhanced sensitivity technology, and its applications on the temperature and pressure measurement, including the basic theory of fiber grating, the sensing mechanism of fiber grating, the increasing of temperature and the experimental researches on the resisting high temperature and pressure FBG (Fiber Bragg Grating) sensor in the lab.Firstly, the recent developments in the technologies of sensing fiber gratings, the FBG sensing technology development in the world, and the characteristic of FBG sensor are reviewed. The theory of the FBG's coupling model was studied. The temperature, strain and pressure sensing principles of fiber grating were analyzed.Secondly, various methods of improving sensitivity of FBG were analyzed according to the low sensitivity of bare FBG. To improve the pressure sensitivity of FBG, one kind of method was proposed based on the Bourdon and cantilever beam of uniform strength. In the pressure range from 0 to 10 MPa, 56 times of the pressure sensitivity coefficients of this kinds of FBG sensors was realized. The influencing factor to sensitivity was analyzed and the result was verified by experiment. Another kind of FBG based on the FBG was developed on the plate stuff. Its temperature sensitivity coefficients in the temperature range from 0℃to105℃are 3.2 times of that of bare FBG.Finally, under the circumstances of high temperature and high pressure in the oil/gas down-hole, high temperature and high pressure experiments to bare FBG were carried out, and the nonlinear phenomena of FBG are studied. To the temperature and strain cross sensitivity question of fiber grating, a feasible solution was presented based on elastic cylinder twin fiber gratings, that pressure and temperature can be measured at the same time. The sensor is fit for the circumstances of high temperature and high pressure in the oil/gas down-hole, and the result of experiment indicates its efficiency and practicality. |
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