为了满足城市管网日常维护中对甲烷(CH4)泄漏检测的需求, 研制了一种基于可调谐半导体激光吸收光谱(TDLAS)技术的吸入便携式CH4探测仪,其重量仅为1.4 kg, 体积为22 cm×10 cm×10 cm。仪器内部采用中心波长为1654 nm的分布反馈式激光器作为光源, 集成了物理基长8.5 cm、有效光程2.25 m的光学多通池。系统基于STM32F405单片机控制激光器产生稳定的调制 激光,配合信号采集处理单元实现对吸收信号的采集,并利用数字锁相放大器提取信号中的二次谐波分量,反演 得到待测气体浓度。对探测仪进行标定和稳定性实验,结果表明二次谐波信号幅值与气体浓度有良好的线性关系, 系统测量精 度为±3.05%, 仪器的最小可探测极限为0.88 ppm, 其精度与便携性满足实际检测需求。

In order to meet the requirement for detecting the methane (CH4) leakage in the daily maintenance of the network of gas pipelines in cities, an inhaled portable CH4 detector based on tunable diode laser absorption spectroscopy (TDLAS) technique has been developed, whose weight is only 1.4 kg and volume is 22 cm×10 cm×10 cm. A distributed feedback laser with a central wavelength of 1654 nm is used as the light source in the instrument and an optical multi-pass cell with a physical basic length of 8.5 cm and an effective optical path of 2.25 m is integrated. The system based on STM32F405 generates a stable modulation laser by controlling laser, and acquires the absorption signal by the signal acquisition and process unit, then a digital lock-in amplifier is used to extract the second harmonic component in the signal to get the concentration of gas. Calibration and stability tests of the detector are carried out. Results show that there is a good linear relationship between the amplitudes of second harmonic signal and gas concentrations. The measurement accuracy of system is ±3.05% and the minimum detectable limit is 0.88 ppm. The precision and portability of the instrument meet the requirements of actual measurement.