基于TDLAS-WMS的痕量甲烷气体检测仪

甲烷是一种无色、无味、易燃、易爆的气体，不仅造成煤矿作业的重大安全隐患，而且又是温室效应的重要气体之一，对于甲烷气体的监测具有极其重要的意义。采用混合可调谐二极管激光吸收光谱(TDLAS)与波长调制光谱(WMS)的检测技术，利用甲烷的2v3(第二泛频带)带R(3)支带吸收谱线，设计并研制出痕量甲烷气体检测仪。通过调谐系数-0.591 cm-1·K-1，采用改变DFB激光器工作温度的方式来获得甲烷在1.654 μm处的最佳吸收谱线。待DFB激光器激射中心谱线选择后，通过调节其注入电流幅值来获得合适的发光强度。同时，结合频率调制技术将待测信号频率移至高频区，减小1/f噪声。在光学结构方面，采用有效光程为76 m的herriott气室，确保对痕量甲烷气体进行检测。利用该痕量甲烷气体检测仪，在被测气体浓度为50～5 000 μmol·mol-1的范围内，对二次谐波信号进行了提取，并利用最小均方误差准则分别对气体浓度、信噪比的关系、谐波峰值信号与气体浓度的关系进行了线性拟合，最低检测限达到了1.4 μmol·mol-1。实验表明，谐波波形对称性良好，未观察到强度调制现象，消除强度调制等因素对谐波检测的影响。

The Trace Methane Sensor Based on TDLAS-WMS

Methane is a colorless, odorless, flammable and explosive gas, which not only is the cause to induce significant security risk in coal mining operation, but also one of the important greenhouse gases, so the monitoring of methane is extremely critical. A trace methane gas sensor is designed and developed using the combination of tunable diode laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS) detection technology, which is based on the methane R(3) absorption branch in 2v3 second harmonic band. Through tuning parameters -0.591 cm-1·K-1, using the method that change the working temperature of distributed feedback (DFB) laser to obtain the best absorption wavelength of methane at 1.654 μm. When the mid-wavelength of DFB laser is selected, the appropriate emitting intension can be obtained via adjusting the amplitude of inject current of DFB laser. Meanwhile, combining the frequency modulation technology to move the bandwidth of detection signal from low frequency to high frequency to reduce the 1/f noise. With aspect to the optical structure, utilizing herriott cell with 76 m effective optical path to guarantee the detection of trace methane is successful. Utilizing the proposed trace methane sensor to extract the second harmonic signal of detected methane in the range of 50 to 5 000 μmol·mol-1, and adopting minimum mean square error criterion to fit the relationship between methane concentration and signal noise ratio, harmonic peak signal and methane concentration, respectively. In addition, the minimum detection limit is 1.4 μmol·mol-1. The experiment results show the symmetry of harmonic waveform is good, no intensity modulation, and the factor of intensity-modulated impacts on harmonic detection is eliminated.