Simultaneous Measurement Of Liquid Level And Temperature Based On Fiber Bragg Grating

With the properties of anti-electromagnetic interference, electronic insulation, anti-corrosion, high sensitivity and small size, fiber sensor can be applied to the hostile environment of high temperature, strong causticity and strong magnetic field, and has become a focus in sensing fields. As an indispensable part of fiber sensor, fiber Bragg grating (FBG) sensor has become impeccable gradually. Compared with other fiber sensors, sensors based on FBG, which are modulated with wavelength, are more insusceptible to interference of external environment. What's more, they are more precise and more stable, and are apt to distributed measurement and demodulation. Seeing that fiber Bragg grating has numerous advantages, this thesis is going to apply FBG to simultaneous measurement of the liquid level and temperature in the inflammable environments.This thesis is related to knowledge of several subjects such as materials science, informatics, optics, and mechanism. Main jobs covered are as following:1. First of all, this thesis analyzes the present methods based on fiber to measure liquid level and the simultaneous measurement of liquid level and temperature, and proposes the superiorities of simultaneous measurement of liquid level and temperature based on FBG2. Then it states the working principles of FBG, and analyzes the sensing properties of FBG in strain, temperature and pressure. At the same time, it attaches importance to the problem of strain and temperature cross-sensitivity based on FBG, and proposes the method of measuring liquid level and temperature respectively.3. On the basis of the concluding of the existing research findings, it puts forward a liquid level sensor structure of high sensitivity, which adopts the cantilever beam of equal strength, the diaphragm and the L-shaped lever. By establishing the mathematical model of sensor, the author analyzes the influence of every structure parameter of sensor towards the whole property of the sensor, and selects the proper parameter, so as to be applied to simultaneous measurement of liquid level and temperature and finish the whole design structure.4. This thesis also analyzes demodulation techniques of the present FBG, puts forward the double-edge filter method based on LPG in FBG demodulation system, and gives the structure chart of the whole system.5. Finally, the thesis further analyzes the shortcomings of the sensor structure, and proposes the improving direction.The contribution of this thesis is to provide some bases towards discriminating measurement of FBG and the research of liquid level sensor, and to lay the solid foundation of the practical application of FBG in the inflammable environment such as the oil depot and chemical industry.