痕量N_(2)O气体检测中数字锁相放大器的设计  

Design of digital lock-in amplifier in trace N_(2)O gas detection

作　　者：杨云鹏 刘新楠 贾俊杰 郜峰 夏华 李奇峰[1] 马翔云 Yang Yunpeng;Liu Xinnan;Jia Junjie;Gao Feng;Xia Hua;Li Qifeng;Ma Xiangyun(School of Precision Instrument and Opto-Electronics Engineering,Tianjin University,Tianjin 300072,China)

机构地区：[1]天津大学精密仪器与光电子工程学院,天津300072

出　　处：《电子测量与仪器学报》2024年第7期116-122,共7页Journal of Electronic Measurement and Instrumentation

基　　金：天津市公共卫生科技重大专项(21ZXGWSY00050)项目资助。

摘　　要：针对笑气(N_(2)O)等气态物质的滥用,基于量子级联激光器与波长调制技术相结合的检测方法,可以对吸食人员呼出笑气浓度进行检测,实现吸食人员的现场快速鉴定。针对检测过程中激光器光强抖动带来的测量误差,提出一种适用于痕量N_(2)O气体检测中数字锁相放大器的设计。该锁相放大器中集成了激光器光强调制模块,当碲镉汞探测器接收到吸收后的光强信号后,同时在FPGA中进行一次和二次谐波的解调,并对二次谐波进行归一化处理,避免光强抖动对测量的影响。使用该锁相放大器对检测系统的性能进行评估,通过质量流量控制器配置不同浓度N_(2)O气体,当激光器调制频率为5kHz,测得归一化二次谐波峰值平均值与N_(2)O气体浓度值之间的线性拟合度为0.992 1。使用Allan方差对检测系统的检出限进行评估,当系统的积分时间为0.1 s时,N_(2)O气体的检出限为17.7×10^(-9);积分时间为6.3 s时,N_(2)O气体的检出限达到最低为8.9×10^(-9)。该锁相放大器具有集成度高、检测速度快、信噪比高等优点,适用于痕量N_(2)O气体的现场快速检测。Aiming at the abuse of gaseous substances such as nitrous oxide(N_(2)O),the detection method based on the combination of quantum cascade laser and wavelength modulation technology can detect the concentration of nitrous oxide exhumed by users,and realize the rapid on-site identification of users.Aiming at the measurement error caused by laser light intensity jitter,a digital phase-locked amplifier for trace N_(2)O gas detection is proposed.The laser light stress modulator is integrated in the phase-locked amplifier.When the mercury cadmium telluride detector receives the absorbed light intensity signal,the first and second harmonics are demodulated in FPGA at the same time,and the second harmonics are normalized to avoid the influence of light intensity jitter on the measurement.The performance of the detection system is evaluated by using the phase-locked amplifier.The mass flow controller is used to set different concentrations of N_(2)O gas.When the laser modulation frequency is 5 kHz,the linear fitting degree between the normalized second harmonic peak value and the N_(2)O gas concentration is 0.9921.The detection system detection limit is evaluated using Allan variance.When the system integration time is 0.1 s,the detection limit of N_(2)O gas is 17.7×10^(-9);when the integration time is 6.3 s,the detection limit of N_(2)O gas reached its lowest value of 8.9×10^(-9).The phase-locked amplifier has the advantages of high integration,fast detection speed and high signal-to-noise ratio,and is suitable for the field rapid detection of trace N_(2)O gas.

关 键 词：笑气 量子级联激光器 波长调制技术 FPGA 

分 类 号：TP23[自动化与计算机技术—检测技术与自动化装置] TM935.37[自动化与计算机技术—控制科学与工程]