数字正交锁相放大器的研制及其在甲烷检测中的应用  

Development of a Digital Orthogonal Lock-in Amplifier and Its Application in Methane Detection

作　　者：刘慧芳[1] 李彬[1] 何启欣 党敬民[1] 于红艳[2] 郑传涛[1] 王一丁[1] 潘教青[2] 

机构地区：[1]吉林大学电子科学与工程学院,集成光电子学国家重点联合实验室吉林大学实验区,长春130012 [2]中国科学院半导体所材料科学重点实验室,北京100083

出　　处：《光子学报》2016年第4期18-23,共6页Acta Photonica Sinica

基　　金：国家科技支撑计划项目(Nos.2013BAK06B04,2014BAD08B03-4);国家自然科学基金项目(No.61307124);吉林省科技发展计划项目(Nos.20120707,20140307014SF);长春市科技发展计划项目(Nos.11GH01,14KG022)资助

摘　　要：利用可调谐二极管激光吸收光谱技术检测气体浓度时,为了从红外传感信号中提取一次及二次谐波信号来表征气体浓度,研发了一种基于数字信号处理器的数字正交锁相放大器.介绍正交锁相放大原理,设计谐波提取算法,给出数字正交锁相放大器的软硬件实现方案.利用配备的浓度为1%~5%的甲烷样品以及研制的锁相放大器,开展气体实验.实验结果显示,当甲烷浓度为5%时,在二次谐波对应的频率点处,测得的系统信噪比为34dB,表明设计的锁相放大器具有较好的性能;测得的二次与一次谐波信号峰峰值的比值与气体浓度成线性关系;考虑动态配气以及气体沿管道传输的时间,检测系统的响应时间约为96~98s;气体浓度为20 000ppm时,测试浓度波动范围为-92ppm^+118ppm;根据Allan方差预测的系统检测下限为29.52ppm.与模拟锁相放大器以及商用锁相放大器相比,本文研制的数字正交锁相放大器硬件结构简单、体积小、成本低、易于集成,在红外气体检测领域具有很好的应用前景.By using Digital Signal Processor（DSP）,a digital lock-in amplifier was experimentally demonstrated for extracting 1fand 2fsignals in gas detection based on Tunable Diode Laser Absorption Spectroscopy（TDLAS）.The orthogonal lock-in amplifying theory was introduced,the algorithm for extracting harmonic signals was designed,and both hardware structure and DSP software were proposed.By using the prepared CH4 samples within the concentration range of 1%-5% and the developed lock-in amplifier,detailed experiments were carried out to derive the device′s performances.As shown by experimental results,the system′s signal-to-noise ratio at the frequency of 2fsignal is 34 dB under the CH4 concentration of 5%,which indicates good functions of the lock-in amplifier.The amplitude ratio between 2fand 1fsignals is linear to gas concentration.Considering gas preparation and diffusion time,the response time of the detection system is about 96- 98 s.The concentration variation is-92ppm-＋118ppm for the measured CH4 sample with a concentration of 20000 ppm.The limit of detection obtained from the Allan variance is 29.52 ppm.Compared with analog and commercial lock-in amplifiers,the self-developed device shows great applications in infrared gas detection because of its simple structure,small size,low cost and easy integration.

关 键 词：光电子学 红外光谱学 气体检测仪 红外吸收 数字锁相放大器 谐波分析 数字信号处理器 

分 类 号：TN21[电子电信—物理电子学]