本文關(guān)鍵詞： 光纖布拉格光柵 液位 液體密度 功率解調(diào) 連續(xù)測量　出處：《吉林大學》2017年碩士論文　論文類型：學位論文

【摘要】：液位測量及液體密度測量對現(xiàn)代工業(yè)生產(chǎn)和日常生活都具有重要意義。光纖布拉格光柵(FBG)液位及液體密度傳感器因具有體積小,響應(yīng)速度快,靈敏度高等優(yōu)點而得到廣泛研究。目前,基于FBG的液位及液體密度傳感器的響應(yīng)信號主要是FBG的布拉格波長。本文首次提出的利用雙布拉格光纖光柵結(jié)構(gòu)的液位及液體密度傳感器區(qū)別于傳統(tǒng)FBG傳感器成功實現(xiàn)了功率解調(diào)機制。首先,本文對雙布拉格光纖光柵結(jié)構(gòu)傳感器的傳感機制進行了理論分析,我們利用一對相同的光纖布拉格光柵及耦合器組成了基本的傳感結(jié)構(gòu),當廣譜光源的光進入耦合器經(jīng)其中一根FBG反射后,再通過耦合器進入另一根FBG,最終在后者的透射譜中形成兩個峰,我們將其稱之為左峰和右峰。當外界物理量使其中一根FBG的布拉格波長發(fā)生漂移時,兩個峰的功率也隨之改變,通過測量兩峰的功率差就可以實現(xiàn)對外界物理量的測量,這就是基于雙布拉格光纖光柵結(jié)構(gòu)的傳感器的基本原理。與此同時我們還發(fā)現(xiàn)雙布拉格光纖光柵傳感器的精度受FBG初始反射率影響。反射率越大,傳感器的精度越高。接著,本文先利用兩根反射率相同,布拉格波長均在1532 nm左右的光纖布拉格光柵FBG1和FBG2搭建成了液位傳感裝置,液位影響施加在FBG1上的軸向力進而影響它的布拉格波長。FBG1的反射峰射入FBG2,在FBG2的透射譜中原布拉格波長兩側(cè)出現(xiàn)兩個峰。這樣,這兩個峰的功率差就受到了液位的調(diào)制。本文在理論上模擬了在液位測量過程中雙峰的產(chǎn)生及變化過程。實驗中實現(xiàn)了對不同密度液體液位的連續(xù)測量,研究了溫度變化對測量過程的影響,并發(fā)現(xiàn)可以通過改變傳感探頭的底面積來滿足不同的測量需求這一有趣的現(xiàn)象。實驗數(shù)據(jù)線性良好,精度可達0.92 d Bm/mm。最后,本文又利用兩根反射率相同,布拉格波長均在1540 nm左右的光纖布拉格光柵串聯(lián)搭建成了液體密度傳感裝置。液體密度同時影響施加在兩個FBG上的軸向力,其中一個FBG的透射譜射入到另一個FBG中,在后者的透射譜中會觀察到一個新的峰,我們稱之為“X”峰。這樣“X”峰的功率就受到了液體密度的調(diào)制。文中在理論上模擬了“X”峰的產(chǎn)生并且分析了“X”峰功率隨液體密度變化的過程。實驗中我們利用”X”峰功率的線性變化區(qū)間實現(xiàn)了對液體密度的測量,研究了軸向力引起的非均勻應(yīng)變和溫度變化對測量過程的影響,并發(fā)現(xiàn)可以通過改變傳感探頭體積來滿足不同的測量要求。實驗結(jié)果與理論分析一致。測量精度可達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.
【學位授予單位】：吉林大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN253;TP212

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