A dual-gas sensor system is developed for CO and CO_2 detection using a single broadband light source, pyroelectric detectors and time-division multiplexing(TDM) technique. A stepper motor based rotating system and a single-reflection spherical optical mirror are designed and adopted for realizing and enhancing dual-gas detection. Detailed measurements under static detection mode(without rotation) and dynamic mode(with rotation) are performed to study the performance of the sensor system for the two gas samples. The detection period is 7.9 s in one round of detection by scanning the two detectors. Based on an Allan deviation analysis, the 1σ detection limits under static operation are 3.0 parts per million(ppm) in volume and 2.6 ppm for CO and CO_2, respectively, and those under dynamic operation are 9.4 ppm and 10.8 ppm for CO and CO_2, respectively. The reported sensor has potential applications in various fields requiring CO and CO_2 detection such as in the coal mine.
A portable dual-channel digital/analogue hybrid lock-in amplifier（LIA） is developed,and its amplitude detection error is less than 10% when the signal-to-noise ratio（SNR） is larger than-12 d B.Then,a differential mid-infrared methane（CH4） detection device is experimentally demonstrated based on a wideband incandescence wire-source and a multi-pass spherical reflector.The experiments are carried out to obtain the sensing performance of the device.With the absorption length of only ~4.8 cm,the limit of detection（Lo D） is about 71.43 mg/m3,and the detection range is from 0 mg/m3 to 5.00×104 mg/m3.As the concentration gets larger than 714.30 mg/m3,the relative detection error falls into the range of-5%—＋5%.Two seven-hour-measurements are done on the CH4 samples with concentrations of 1.43×103 mg/m3 and 4.29×103 mg/m3,respectively,and the results show that the maximum relative error is less than 5%.Because of the cost effective incandescence wire-source,the small-size and inexpensive dual-channel LIA,and the small-size absorption pool and reflector,the developed device shows potential applications of CH4 detection in coal mine production and environmental protection.
Based on direct absorption spectroscopy(DAS), a portable methane(CH_4) detection device was implemented. The device mainly includes a dual-channel non-dispersive infrared sensor(integrated with an infrared light source, light path and pyroelectric detector), a driving circuit of the sensor, an ARM11 embedded Win CE system, and a Lab VIEW-based data-processing platform. Experiments were carried out with prepared CH_4 samples to investigate the sensing performance. The relative detection error is less than 9.14% within the measuring range of 0—7×10^(-2). For a CH_4 sample with concentration of 0(i.e., pure nitrogen), the measured concentration fluctuation range is-1.2×10^(-5)—+2×10^(-5). An Allan deviation analysis on the gas sample with concentration of 0 indicates that the 1σ limit of detection(LoD) of the device is 4.8×10^(-6) with an average time of 1 s. Experiments were performed on three CH_4 samples with different concentrations to test the response time, which is validated to be less than 20 s. Due to the small size of the ARM11 embedded system and the powerful data processing capability of the Lab VIEW platform, the proposed portable and miniaturized CH_4 sensor shows a good application prospect in mining operations and some other industrial fields.
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。
