AN ALL-FIBER GAS SENSING SYSTEM USING HOLLOW-CORE PHOTONIC BANDGAP FIBER AS GAS CELL

An all-fiber compact gas sensing system using a hollow-core photonic bandgap fiber (HC-PBF) as a gas cell is proposed in this paper. Compared with the present reported microstructured optical-fiber gas cells, the HC-PBF gas cell proposed here has relatively lower transmission loss and much simpler construction. The total transmission loss through the HC-PBF gas cell is demonstrated experimentally to be as low as 1.5 dB and the time taken for gas to get into the 90-cm-cell, under the free diffusion condition, is approximately 11 min. Combining the HC-PBF gas cell with a tunable fiber laser, an all-fiber gas sensing system is developed. The properties of the proposed system are demonstrated experimentally by detection of carbon monoxide (CO) and acetylene (C₂H₂). Approximately linear relationships between the system responses and the concentrations of the detected gases are experimentally demonstrated. The minimal detectable concentration of CO of 300 ppm and C₂H₂ of 5 ppm are also achieved respectively by the experiments.     

光谱吸收型光纤多气体传感系统

基于气体的近红外吸收机理，研究了一种可以检测多种气体的全光纤传感方法，采用光纤光栅波分复用技术．通过光纤光栅和压电陶瓷（PZT）对宽带光源LED进行波长调制，获得与相应气体吸收峰相对应的窄带反射出射光，检测二次谐波，实现对多种气体的较高灵敏度测量。利用二次谐波与光纤光栅透射光强的比值来消除光路干扰。建立了谐波检测的数学模型，进行了光纤C2H2和CO气体测量系统的实验研究。     

SIMULTANEOUS MEASUREMENT OF STRAIN AND TEMPERATURE WITH POLARIZATION MAINTAINING FIBER BRAGG GRATING LOOP MIRROR

□ A novel simultaneous method of strain and temperature measurement based on a polarization maintaining fiber Bragg grating loop mirror is proposed and demonstrated. The sensing head was composed of a fiber loop mirror and a section of fiber Bragg grating made of a polarization maintaining fiber. The Bragg wavelengths of the fiber grating in the polarization maintaining fiber were along slow and fast axis showing different sensitivities to strain and temperature with the interferometric peak wavelength of the fiber loop mirror. By monitoring the shifts of the Bragg wavelength and interferometric peak of the fiber loop mirror, with its temperature sensitivity of 0.1167 nm/°C and strain sensitivity of 0.0093 nm/μ?, a temperature measurement resolution about 0.009°C and a strain measurement resolution of 1.08 μ? was achieved theoretically and experimentally.     

基于谐波检测的光谱吸收型光纤瓦斯传感器

针对目前煤矿普遍采用的热催化瓦斯探测传感器的检测灵敏度低、环境干扰大的缺陷,设计了基于谐波检测的光谱吸收型光纤瓦斯传感器。该传感器采用锁相放大器为核心的微弱信号处理电路,通过对一次谐波和二次谐波的实验数据进行数据拟合,实现了对瓦斯气体浓度的实时精确检测。实验结果表明:该传感器能够有效地提取瓦斯浓度变化信息,测量误差小,灵敏度高。     

基于波长调制技术的甲烷气体浓度检测的研究

与谐波检测相结合的波长调制技术是目前检测有害气体的主要方法。主要是用实验的方法找到了甲烷气体在1 650 nm附近的一根吸收线,然后采用正弦信号对激光器的驱动进行了调制,实现了甲烷气体浓度的谐波检测。用锁相放大器RS830来提取二次谐波,然后根据锁相放大器的原理,用LabVIEW软件实现了锁相放大器的设计,来提取一次谐波信号,节约了成本。由气体吸收室中的GRIN透镜引起的标准具效应是影响检测灵敏度的主要原因,最后对该噪声和其他可能的影响进行了分析。     

Characterization of displacement sensing based on fiber optic microbend losses

This article theoretically and experimentally characterizes single-mode fiber bending losses and associated sensing. As the bending radius decreased, the losses increased significantly, and shock phenomena were observed in the loss curve. Theoretical analysis shows that these processes were caused by coupling between fundamental models spreading in the optical fiber and whispering gallery mode spreading in the cladding and coating layers. Based on the principles of single-mode fiber bending losses, a loss modulator was designed to bend the single-mode fiber and produce losses due to external displacement. A displacement-loss model was constructed and the results were consistent with the theoretical analysis. The displacement resolving power of the loss modulator was 1 µm. The displacement measurement was from 0–350 µm, resulting in losses from 0–25 dB.     

基于啁啾光纤光栅的电压传感性能研究

电压的实时测量是电力系统稳定、安全的关键。提出了一种基于啁啾光纤光栅的电压传感器,利用压电陶瓷的逆压电效应带动黏贴在其上面的传感啁啾光栅发生形变,使传感啁啾光栅的波长发生漂移,通过检测传感啁啾光栅和参考啁啾光栅反射光包络的强度变化,获取被测电压的幅值和频率信息。理论分析了电压与光功率变化的关系,搭建了带温度补偿的双啁啾光栅传感系统,实验研究了传感器的静态和实时动态特性。实验结果表明,该传感器的相关系数R2为0.999 8,电压灵敏度达到0.048mW/V,既能直接检测直流电压,也能较好地检测交流电压及其频谱信息,为在复杂环境评估电能质量提供了参考。     

基于光电技术的GIS设备微水在线检测方法的研究

GIS设备中微水含量超标威胁设备的安全及稳定运行。本文基于光电技术,研究了光谱吸收型光纤传感器检测GIS设备中的微水含量。采用半导体激光器光源,通过光源调制实现谐波检测,消除光源的不稳定和变化所引起的误差。光电测量方法不仅能精确测量微水含量,而且能实现在线检测,安全可靠。     

基于电压调幅的超声波流量计研究

针对非稳态流场中流体测量时存在的问题,在超声波流量计过零点检测判定渡越时间的基础上,采用电压调幅的方法产生超声波换能器激励信号,然后通过检测接收信号的幅值变化特征点定位波形。针对流场中流速不稳定可能导致的波形不稳定情况,采用中值滤波的方法减小误差。为避免ADC芯片位数和AD转换速率限制导致渡越时间测量误差问题,在数字波形特征点判定基础上,采用过零点检测从模拟波形上获得渡越数据。实验结果表明,该方法具有一定的可行性,可以达到对超声波脉冲序列准确处理、定位的目的,测量误差可以控制在在1.5%以内,可以达到二级精度仪表的要求水平。     

High-limit detection and accurate analysis of acetylene in transformer oil gases with a tunable laser-based photoacoustic spectrometer

Acetylene in transformer oil is an important feature gas, which can reflect early discharge faults. A tunable fiber laser photoacoustic (PA) spectrometer based on second harmonic modulation, with its fast response and good noise immunity, can be well applied to detect trace gases. In this work, the second harmonic PA measurement of the acetylene gas at the 1530.3709 nm transition line is demonstrated. An accurate analysis of acetylene in transformer oil gases is ensured by using an overcomplete-independent-component-analysis(ICA)-basis BSS model and a five-point-sampling method to improve the detection limit from 1.12 to 0.71 ppb. The experiment for detecting and analyzing acetylene in transformer oil gases shows that the discharge acetylene productivity can reach 303.72 ppb/s with a dynamic response time of less than 10 s, relative error of about 1.40%, and relevance coefficient up to 0.99946. At room temperature and atmospheric pressure, this can meet the demands of acetylene detection and analysis in early or ultra-early predictions of transformer discharge faults.     

Accurate measurement of NMR amplitudes using a computer-controlled wide line cw nuclear double resonance spectrometer

A computer-controlled cw nuclear magnetic double-resonance spectrometer, designed for studying the spin-lattice relaxation of quadrupolar nuclei in single crystals, is described. Resonances are detected by a Robinson spectrometer using a technique involving sinusoidal field modulation in conjunction with first and second harmonic phase-sensitive detection. The output of the first harmonic detector provides an error signal, which is used to 'lock' the spectrometer to the center of the resonance. The output of the second harmonic detector is used as the measure of NMR amplitude. Comprehensive tests have shown that the amplitudes of weak NMR signals can be compared with an accuracy of better than +/-0.1%. Numerous precautions to obtain such accuracy are discussed.     

Simultaneous measurement on gas concentration and particle mass concentration by tunable diode laser

The method of simultaneous measurement on gas concentration and particle mass concentration by tunable diode laser absorption spectroscopy is developed. The method is validated using a 1.58 μm diode laser with wavelength modulation spectroscopy. The experimental environment of particulated gas flow is imitated by adding uniform-sized quart sands into CO₂ gas. Calibrated second harmonic signals are proved to be independent of particle effects but only depend on gas concentration, and particle mass concentration can be calculated from the attenuation of laser power. This technique would be helpful to improve the quality and applicability of tunable diode laser absorption spectroscopy in emission monitoring.     

用激光外差技术高精度测量目标速度

搭建了外差探测实验平台,分别选用漫反射目标及类简谐运动模型作匀转速运动及变速运动的测量目标,应用激光外差探测技术实现了对匀转速运动及变速运动物体的速度测量.在匀转速测量过程中,同时采用外差探测法和振幅调制法测量了漫反射目标正负两个方向转动的速度,共得到133组不同的转速结果.通过调整实验系统,亦实现了对类简谐运动目标的...     

基于TDLAS的烟气中CO浓度混合取样式在线监测

燃煤锅炉烟气中不完全燃烧产物CO是燃烧效率监测的重要依据,其存在浓度高、波动剧烈、分布不均匀等特点,采用TDLAS技术中波长调制光谱结合稀释法对烟气中CO浓度进行了混合取样式在线监测。首先基于谐波理论推导出4次谐波与1次谐波免标法测量公式,其次对CO激光器频率调制和光强调制的相位差及电流调谐系数进行了标定,并采用标准气体结合直接吸收法对赫里奥特池光程进行了测量,然后在此基础上对浓度与谐波比值曲线进行了数值计算和实验验证。最后将该装置应用于燃煤电厂,将省煤器出口烟道分为6个区域,各区域安装一个稀释取样探头,在稀释取样过程由于降低了烟气露点无需做除水处理,6路经过稀释后的烟气混合后进入赫里奥特池后实现免标定高精度测量。该监测装置实现了连续稳定运行,运行中使用Testo350便携式分析仪与现场测量数据进行了对比,二者测量结果一致,误差小于1×10~(-6)。     

Characterization of infrared gas sensors employing hollow-core photonic crystal fibers

Infrared gas sensors employing hollow-core photonic crystal fibers are reported. A hollow-core photonic crystal fiber in the gas cell of the sensor was inserted between a single mode fiber and a multi-mode fiber in the light path. The gaps between the facets of hollow-core photonic crystal fiber and single mode fiber were optimized to increase the coupling efficiency. The gas chambers were modified to reduce the time for filling. Broadband and laser sources were employed to determine acetylene at concentrations between 0% and 0.6%. The resolution was 0.084 ppm and the stability was 0.556%. These sensors have promising applications for trace gas measurements.     

弹光和电光级联的组合相位调制型椭偏测量术

利用弹光调制器的偏振调制优势,提出了将弹光调制器和电光调制器级联的组合相位调制型椭偏测量术。该技术采用单光路实现信号探测,通过切换电光调制器的两个工作状态,并结合数字锁相信号处理技术来完成样品反射光的p分量和s分量的幅值比Ψ和相位差Δ的全范围高精度测量。对提出的新型椭偏测量原理进行了分析,搭建了相应的实验系统。完成了弹光调制器的调制电压峰峰值和相位调制幅值关系的定标,定标结果优于99.05%,然后还采用系统初始偏移值的方法对实验系统进行了校准。最后,运用该系统对石英玻璃反射样品进行了实验分析,得到的Ψ和Δ的测量精度分别优于0.08°和0.81°。实验结果显示系统校准有效地消除了电光调制器和弹光调制器的剩余双折射引入的测量误差;数据采集和处理时间均在ms量级。提出的测量技术具有宽光谱测量、工作稳定、重复度高、测量速率快、成本相对较低和系统便于工业自动化集成的潜在优势。     

差分式中红外一氧化碳检测仪的研制

根据CO分子在中红外波段的吸收特性,利用红外热辐射光源(IR55)和双通道热释电探测器(LM244),研制了一种差分式CO检测仪。通过双通道锁相放大器对探测器输出的两路信号进行处理,有效地抑制了系统噪声,提高了仪器的检测精度。介绍了系统的检测原理,给出了光学系统和双通道锁相放大器的实现方案,该锁相放大器能提取的最小标准信号幅度为1 m V,移相误差小于0.2%。利用配备的体积分数为0~1×10~(-3)的CO样品,开展了气体检测实验。实验结果表明:系统的检测下限为1×10~(-5),相对测量误差小于15%。当气体体积分数为0×10~(-6)时,测得浓度的波动范围为-5.2×10~(-6)~6.2×10~(-6)。考虑静态配气时气体在气室中扩散的时间,仪器的响应时间约为58~62 s。同基于量子级联激光器和分布反馈激光器的CO检测仪相比,所研制的仪器具有结构简单、性价比高等优势,在煤矿、环保等场合的CO检测方面具有较好的应用前景。     

痕量N2O气体检测系统的设计与实现

建立了基于光谱吸收技术的检测系统,用于快速、准确地测量N2O气体浓度。首先,从理论上证明了二次谐波、一次谐波与N2O气体浓度之间的关系;然后,设计了痕量N2O气体浓度检测系统,利用光源调制、锁相放大等技术,实现了强杂波背景下气体浓度弱信号的解析;最后,实验测试了系统的检测性能、抗干扰能力及检测结果的可重复性。测试结果表明,系统能够在0～1%有效检测N2O气体浓度,检测下限为5.0×10-5,相对检测误差为0.11%,检测结果线性方程为Y=192.699 09 X-0.006 24,线性度为0.998 07。多次检测实验表明,系统相对标准偏差为0.137%,CO2、O2、水蒸气等常见气体对检测结果无影响。改变激光器的中心波长,该方法亦可用于CO2,CH4等其它温室气体的检测。     

超声锁相热像技术检测接触界面类型缺陷

为了提高超声锁相热像技术(ULT)的检测效率并获得最佳检测结果,对超声波调制、热图序列处理和检测参数选择进行了研究。阐述了超声锁相热像技术的检测原理并进行了理论分析,建立了ULT的检测系统。采用方波调制的超声波激励试件,用红外热像仪记录试件表面热图,并用瞬态处理方法对热图进行锁相处理得到相位图和幅值图实现对缺陷的检测。用该方法检测了钢板表面及近表面的微裂纹(微米级)和铝合金板内不同深度缺陷等接触界面类型缺陷。结果表明,检测A3钢板材料表面(近表面)裂纹时,调制频率可选择0.5Hz,接触压力约0.25kN,激励头与微裂纹的距离对检测结果几乎无影响,激励位置可根据试件结构而确定;由于降低调制频率可提高缺陷的检测深度,检测铝合金材料时,调制频率≤0.3Hz能够探测到4mm深度的缺陷;另外,该方法能够准确检测蜂窝夹层结构的脱粘缺陷。研究表明,研制的检测系统数秒内即可完成对接触界面类型缺陷的准确检测。     

基于FPGA在线气体检测系统设计

以FPGA为平台设计一套TDLAS在线气体检测系统。在线气体检测需要高精度以及快速的数据分析和处理速度。相比于传统单片机,FPGA在工作速度以及功耗等方面具有较大优势,可以保证数据分析和处理的实时性;基于TDLAS（可调谐二极管吸收光谱学）的二次谐波检测技术可以减小噪声等因素带来的影响,保证检测结果的精度。本文详细介绍了系统的检测原理以及TDL驱动电路的设计方法,并由FPGA产生所需调制信号。该系统适用于现场高精度高速度的气体监测。