双布拉格光纤光栅液位及液体密度传感器的研究

发布时间：2018-01-24 06:49

本文关键词： 光纤布拉格光栅液位液体密度功率解调连续测量　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：液位测量及液体密度测量对现代工业生产和日常生活都具有重要意义。光纤布拉格光栅(FBG)液位及液体密度传感器因具有体积小,响应速度快,灵敏度高等优点而得到广泛研究。目前,基于FBG的液位及液体密度传感器的响应信号主要是FBG的布拉格波长。本文首次提出的利用双布拉格光纤光栅结构的液位及液体密度传感器区别于传统FBG传感器成功实现了功率解调机制。首先,本文对双布拉格光纤光栅结构传感器的传感机制进行了理论分析,我们利用一对相同的光纤布拉格光栅及耦合器组成了基本的传感结构,当广谱光源的光进入耦合器经其中一根FBG反射后,再通过耦合器进入另一根FBG,最终在后者的透射谱中形成两个峰,我们将其称之为左峰和右峰。当外界物理量使其中一根FBG的布拉格波长发生漂移时,两个峰的功率也随之改变,通过测量两峰的功率差就可以实现对外界物理量的测量,这就是基于双布拉格光纤光栅结构的传感器的基本原理。与此同时我们还发现双布拉格光纤光栅传感器的精度受FBG初始反射率影响。反射率越大,传感器的精度越高。接着,本文先利用两根反射率相同,布拉格波长均在1532 nm左右的光纤布拉格光栅FBG1和FBG2搭建成了液位传感装置,液位影响施加在FBG1上的轴向力进而影响它的布拉格波长。FBG1的反射峰射入FBG2,在FBG2的透射谱中原布拉格波长两侧出现两个峰。这样,这两个峰的功率差就受到了液位的调制。本文在理论上模拟了在液位测量过程中双峰的产生及变化过程。实验中实现了对不同密度液体液位的连续测量,研究了温度变化对测量过程的影响,并发现可以通过改变传感探头的底面积来满足不同的测量需求这一有趣的现象。实验数据线性良好,精度可达0.92 d Bm/mm。最后,本文又利用两根反射率相同,布拉格波长均在1540 nm左右的光纤布拉格光栅串联搭建成了液体密度传感装置。液体密度同时影响施加在两个FBG上的轴向力,其中一个FBG的透射谱射入到另一个FBG中,在后者的透射谱中会观察到一个新的峰,我们称之为“X”峰。这样“X”峰的功率就受到了液体密度的调制。文中在理论上模拟了“X”峰的产生并且分析了“X”峰功率随液体密度变化的过程。实验中我们利用”X”峰功率的线性变化区间实现了对液体密度的测量,研究了轴向力引起的非均匀应变和温度变化对测量过程的影响,并发现可以通过改变传感探头体积来满足不同的测量要求。实验结果与理论分析一致。测量精度可达42.87 d Bm/(g/cm3)。
[Abstract]:Liquid level measurement and liquid density measurement are of great significance to modern industrial production and daily life. Fiber Bragg grating (FBG) liquid level and liquid density sensors have small size and fast response speed. The advantages of high sensitivity have been extensively studied. The response signal of liquid level and liquid density sensor based on FBG is mainly the Bragg wavelength of FBG. In this paper, the liquid level and liquid density sensor based on double fiber Bragg grating structure is different from the traditional FBG sensor for the first time. BG sensor successfully realizes the power demodulation mechanism. Firstly. In this paper, the sensing mechanism of double fiber Bragg grating sensor is analyzed theoretically. We use the same pair of fiber Bragg grating and coupler to form a basic sensing structure. When the light of the broad spectrum light source is reflected by one of the FBG couplers, the two peaks are formed in the transmission spectrum of the latter. We call it the left peak and the right peak. When the external physical quantity makes the Bragg wavelength of one of the FBG drift, the power of the two peaks also changes. The measurement of external physical quantity can be realized by measuring the power difference between the two peaks. This is the basic principle of the sensor based on the double fiber Bragg grating structure. At the same time, we also find that the precision of the double fiber Bragg grating sensor is affected by the initial reflectivity of FBG. The higher the precision of the sensor. Then, the liquid level sensing device is constructed by using two fiber Bragg grating (FBG) FBG1 and FBG2, which have the same reflectivity and the Bragg wavelength is about 1532nm. The effect of the liquid level on the axial force applied on the FBG1 further affects its Bragg wavelength. The reflection peak of FBG1 is emitted into FBG2, and there are two peaks on both sides of the original Bragg wavelength in the transmission spectrum of FBG2. The power difference of the two peaks is modulated by the liquid level. In this paper, the generation and variation of the double peaks in the measurement of liquid level are simulated theoretically. The continuous measurement of liquid level with different density is realized in the experiment. The influence of the temperature change on the measurement process is studied, and it is found that the different measurement requirements can be satisfied by changing the bottom area of the sensor probe. The experimental data have good linearity. The precision can reach 0.92 d Bm / mmm. finally, the two reflectance are the same. Fiber Bragg gratings (FBG) with Bragg wavelength of about 1540 nm are connected in series to form a liquid density sensing device. The liquid density simultaneously affects the axial force applied on two FBG. The transmission spectrum of one FBG is injected into another FBG, and a new peak is observed in the transmission spectrum of the latter. We call it "X" peak. In this way, the power of "X" peak is modulated by the density of liquid. In this paper, the generation of "X" peak is simulated theoretically and the "X" peak is analyzed. In the experiment, we use the linear range of "X" peak power to measure the liquid density. The influence of non-uniform strain and temperature change caused by axial force on the measurement process is studied. It is found that different measurement requirements can be satisfied by changing the volume of the sensor probe. The experimental results are in agreement with the theoretical analysis. The measurement accuracy can reach 42.87 d Bm / g / cm 3.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN253;TP212

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