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介绍了可调谐半导体激光吸收光谱技术(TDLAS)原理和实验系统,并对系统噪声进行了分析;以体积比浓度为90×10-6和30×10-6的NH3为例,利用TDLAS系统采集了该浓度气体的二次谐波原始光谱。为改善光谱信号,分别用五种数字滤波方法对原始光谱进行了滤波处理比较,做了NH3的浓度梯度实验并对浓度为20×10-6 NH3进行了长时间监测实验。实验结果表明,算术平均-小波变换滤波相比其他方法更有效地对原始光谱信号进行了改善,提高了系统信噪比和信号平滑度,使系统浓度检测限由原来的10×10-6降低到1.25×10-6,信噪比提高了约14倍,为逃逸氨极低浓度检测提供了一种较为有效的数据预处理方法。
The principle and experimental system of tunable semiconductor laser absorption spectroscopy (TDLAS) are introduced, and the system noise is analyzed. Taking NH3 with volume concentration of 90 × 10-6 and 30 × 10-6 as an example, the TDLAS system is used to collect The second harmonic of the gas concentration of the original spectrum. In order to improve the spectral signal, five kinds of digital filtering methods were respectively used to filter the original spectra. The NH3 concentration gradient experiment was done and the long-time monitoring experiment was carried out with the concentration of 20 × 10-6 NH3. The experimental results show that compared with other methods, the arithmetic average-wavelet transform filter improves the original spectral signal more effectively, improves the signal-to-noise ratio and signal smoothness, and decreases the detection limit of the system from 10 × 10-6 To 1.25 × 10-6, the signal to noise ratio increased by about 14 times, providing a more effective data preprocessing method for the detection of very low ammonia concentration.