氣體偵測技術在各領域上的應用十分廣泛，從儲氣場域安全監測、手術有害氣體監控到半導體製程都可見到。該技術主要奠基在分子吸收光譜及可調二極體雷射上，而應用環境可區分為高溫（引擎燃燒室等）及一般室溫情況。本論文旨在開發二氧化碳氣體偵測技術相關的兩類演算法，分別為直接吸收光譜技術（direct absorption spectroscopy, DAS）及波長調變光譜技術（wavelength modulation spectroscopy, WMS），並實際建置DAS架構的系統，進行二氧化碳氣體濃度量測。
演算法的部分分成DAS和WMS兩類。在DAS的模擬中，使用到的是探討物質光吸收最重要的定理——比爾-朗伯定律（Beer–Lambert law），搭配含有氣體分子吸收譜各項參數的HITRAN資料庫，模擬出二氧化碳的吸收譜線，再以譜線下的面積來推算出預設氣體濃度。由於實際量測會遇到干擾的問題，所以我們也在模擬訊號中加入1/f雜訊並觀察其對系統的影響。至於WMS的模擬，我們在DAS線性變化的雷射光頻率上疊加一高頻正弦載波，在接收端解調變的部分則是使用數值方式及模擬鎖相放大器原理兩方法，最後在計算氣體濃度時，則採用了Peng Zhimin與Ding Yanjun等人的作法——與DAS相同之譜線下面積計算方式得出預設氣體濃度。在模擬結果上，DAS法在受與訊號平均功率比值70的雜訊影響時，濃度誤差約30%；另外在模擬所使用到的幾種方法上，以模擬鎖相放大器解調變的WMS法為最佳。
在實驗的部分，我們實際設計了DAS的系統，初步先以電磁閥給氣系統進行二氧化碳純濃度的量測，之後將再設計改用質量流量控制器(mass flow controller, MFC)給氣的系統，以進行不同濃度上的量測。在數據處理上，使用Lorentzian擬合減少雜訊以及累積10筆濃度量測值做平均的方式，以提高系統穩定性，最後再搭配校準線校正，在量測100%、60%及30%的二氧化碳氣體濃度下，誤差約在20%以內。

The purpose of this study is to develop two types of algorithms: (1) direct absorption spectroscopy (DAS) and (2) wavelength modulation spectroscopy (WMS), for carbon dioxide detection, and to realize a DAS-based system.
For DAS, we use the Beer–Lambert law and HITRAN database to simulate the absorption spectra of carbon dioxide at different concentrations. The pre-set concentration can be estimated through calculation of the area under spectrum. To be more realistic, we also add 1/f noise to the simulated measurements to see how this noise influences the estimated results. For WMS, we superpose a high-frequency sinusoidal modulation to the laser injection current in DAS. At the receiving end, two different methods are used to demodulate the signal. Finally, we use the method proposed by Peng Zhimin to calculate gas concentration. The simulation results indicate that when SNR is 70, the estimated error in concentration can be as high as 30% in the DAS system. On the other hand, this error is reduced to 5% in the WMS system.
In the experiment with the implemented DAS system, both solenoid valves and mass flow controllers (MFCs) are used to supply gas. For data processing, we apply the Lorentzian fitting to measured absorbance data and calculating gas concentration with area under fitting curve. In order to improve accuracy and overcome system error, taking an average of ten concentration results and performing a concentration calibration are applied. By this method, the concentration error can be within 20% when measuring the gas having a carbon dioxide concentration of 100%, 60%, and 30%.

摘要……………………………………………………………………………………………i
Abstract………………………………………………………………………………………ⅱ
致謝…………………………………………………………………………………………ⅲ
目錄…………………………………………………………………………………………ⅳ
表目錄………………………………………………………………………………………ⅵ
圖目錄………………………………………………………………………………………ⅶ
第一章 緒論…………………………………………………………………………………1
1.1 研究背景…………………………………………………………………………1
1.2 論文架構………………………………………………………………………3
第二章 理論…………………………………………………………………………………4
2.1 比爾-朗伯定律…………………………………………………………………4
2.2 譜線致寬效應與線型函數………………………………………………………6
2.2.1 自然、碰撞致寬與羅倫茲線型……………………………………………6
2.2.2 都卜勒致寬與高斯線型…………………………………………………8
2.2.3 Voigt線型函數…………………………………………………………10
2.3 吸收光譜技術……………………………………………………………………12
2.3.1 直接吸收光譜技術………………………………………………………12
2.3.2 波長調變光譜技術………………………………………………………15
第三章 模擬與實驗規劃…………………………………………………………………20
3.1 模擬規劃………………………………………………………………………20
3.1.1 HITRAN光譜資料庫……………………………………………………20
3.1.2 直接吸收光譜技術………………………………………………………21
3.1.2.1 模擬過程…………………………………………………………21
3.1.2.2 雜訊影響模擬……………………………………………………26
3.1.3 波長調變光譜技術………………………………………………………28
3.1.3.1 模擬過程…………………………………………………………28
3.1.3.2 雜訊影響模擬……………………………………………………33
3.2 實驗規劃………………………………………………………………………35
第四章 模擬與實驗結果…………………………………………………………………40
4.1 模擬結果………………………………………………………………………40
4.1.1 直接吸收光譜技術……………………………………………………40
4.1.2 波長調變光譜技術……………………………………………………42
4.2 實驗結果………………………………………………………………………49
4.2.1 系統儀器特性量測……………………………………………………50
4.2.2 數據前處理……………………………………………………………52
4.2.3 量測結果與校正………………………………………………………55
4.2.4 系統改進趨勢…………………………………………………………59
4.2.5 系統雜訊分布…………………………………………………………60
第五章 結論………………………………………………………………………………61

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