本文選題：氣體傳感　切入點：石英增強(qiáng)光聲光譜技術(shù)　出處：《山東大學(xué)》2017年碩士論文

【摘要】：水蒸氣濃度檢測技術(shù)是當(dāng)今氣體傳感領(lǐng)域中的一項重要課題。在天然氣運(yùn)輸、電力傳輸、食品安全、工業(yè)冶煉以及精密器械維護(hù)等方面,水蒸氣的濃度要求非常苛刻,需要嚴(yán)格控制,所以迫切需要對水蒸氣濃度檢測技術(shù)進(jìn)行深入地研究。石英增強(qiáng)光聲光譜(quartz-enhanced photoacoustic spectroscopy)技術(shù)簡稱QEPAS技術(shù),是近年來痕跡氣體檢測研究中一種新的方法,與傳統(tǒng)光聲池方法以及其他傳統(tǒng)檢測方法相比,在體積、成本、靈敏度和抗干擾方面都有著一定的優(yōu)勢,尤其是它不受激光器、準(zhǔn)直器等內(nèi)部含有的微量水蒸氣的影響,克服了吸收光譜法固有的水底問題。本文通過對基于QEPAS的水蒸氣濃度檢測系統(tǒng)的研究,闡述了相關(guān)原理,實現(xiàn)了系統(tǒng)的功能,優(yōu)化了光路與信號檢測電路,采用的鎖頻法解決了檢測過程中出現(xiàn)的問題和矛盾,最終達(dá)到了低濃度水蒸氣的準(zhǔn)確標(biāo)定。QEPAS技術(shù)原理涉及到紅外光譜氣體的吸收理論以及由于吸收產(chǎn)生的多次諧波理論。本文通過氣體分子紅外吸收、氣體分子的吸收定律、線性函數(shù)、波長調(diào)制,逐步闡述和推導(dǎo)了 QEPAS技術(shù)的原理,然后又對石英音叉的壓電特性等機(jī)理進(jìn)行了詳細(xì)描述。根據(jù)QEPAS原理與相關(guān)的電路知識,本文詳細(xì)介紹了系統(tǒng)各部分的功能、組成和設(shè)計思路,組建起了 QEPAS水蒸氣濃度檢測系統(tǒng),對程序、系統(tǒng)參數(shù)設(shè)定完畢后,在大氣中檢測出水蒸氣的濃度,初步實現(xiàn)了系統(tǒng)的功能。為了提升系統(tǒng)的檢測精度,對影響系統(tǒng)信噪比的激光器調(diào)制幅度、鎖相放大電路參數(shù)進(jìn)行了優(yōu)化,使信噪比提升了 1倍。對共振管和音叉的特性做了細(xì)致的研究,確定了最優(yōu)的共振管結(jié)構(gòu)和尺寸,發(fā)現(xiàn)了音叉在共振管結(jié)構(gòu)中中心頻率變化很小而帶寬變化明顯。確定了 QEPAS水蒸氣濃度檢測的新方法——鎖頻法。針對激光驅(qū)動信號掃描法與鎖頻法進(jìn)行理論分析與實驗驗證,證明了鎖頻法在光聲光譜系統(tǒng)中的巨大優(yōu)勢,并將鎖頻法應(yīng)用到了系統(tǒng)中,二次諧波信號的信噪比得到了質(zhì)的飛躍,空氣中的信噪比達(dá)到了 500。標(biāo)定了 QEPAS水蒸氣濃度檢測系統(tǒng)的檢測極限為200ppm,精度在某些濃度下可以達(dá)到6ppm,最后探究了系統(tǒng)的穩(wěn)定性以及石英音叉特性的長期穩(wěn)定性。
[Abstract]:Water vapor concentration detection technology is an important subject in the field of gas sensing. In the fields of natural gas transportation, electric power transmission, food safety, industrial smelting and maintenance of precision instruments, the concentration requirements of water vapor are very stringent. It needs strict control, so it is urgent to study the detection technology of water vapor concentration. Quartz enhanced photoacoustic spectroscopy (QEPAS) technique is a new method in trace gas detection in recent years. Compared with the traditional photoacoustic cell method and other traditional detection methods, it has some advantages in volume, cost, sensitivity and anti-interference, especially it is not affected by the trace water vapor contained in the laser, collimator, etc. In this paper, the principle of water vapor concentration detection system based on QEPAS is discussed, the function of the system is realized, and the optical circuit and signal detection circuit are optimized. The frequency locking method is used to solve the problems and contradictions in the detection process. Finally, the accurate calibration of low concentration water vapor is achieved. The principle of QEPAS technology involves the absorption theory of infrared spectrum gas and the theory of multiple harmonics due to absorption. In this paper, the absorption law of gas molecule is obtained by infrared absorption of gas molecule, the absorption law of gas molecule, and the absorption law of gas molecule. Linear function, wavelength modulation, the principle of QEPAS technology is expounded and deduced step by step, and then the piezoelectric characteristics of quartz tuning fork are described in detail. According to the principle of QEPAS and related circuit knowledge, In this paper, the function, composition and design idea of each part of the system are introduced in detail, and the QEPAS water vapor concentration detection system is constructed. After the program and system parameters are set up, the water vapor concentration is detected in the atmosphere. In order to improve the detection accuracy of the system, the modulation amplitude of the laser and the parameters of the phase-locked amplifier circuit which affect the SNR of the system are optimized. The signal-to-noise ratio is doubled. The characteristics of the resonant tube and the tuning fork are studied carefully, and the optimal structure and size of the resonant tube are determined. It is found that the center frequency of tuning fork changes very little and the bandwidth changes obviously in the resonant tube structure. A new method of detecting QEPAS water vapor concentration, frequency locking method, is established. The theoretical analysis and experimental verification of laser driven signal scanning method and frequency locking method are carried out. It is proved that the frequency locking method has great advantages in the photoacoustic spectrum system, and the frequency locking method has been applied to the system, and the signal-to-noise ratio of the second harmonic signal has achieved a qualitative leap. The signal-to-noise ratio in air reaches 500ppm. The detection limit of QEPAS water vapor concentration detection system is 200 ppm, and the precision can reach 6 ppm at some concentrations. Finally, the stability of the system and the long-term stability of quartz tuning fork are discussed.
【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TP274

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本文編號：1666509