可调谐激光痕量气体检测中的数字滤波技术的优选

为改善可调谐二极管激光吸收光谱(TDLAS)系统的检测性能,以浓度为50×10-6和17×10-6的H2S气体检测为例,根据TDLAS系统的噪声特征,选择了4种数字滤波技术并利用Visual C++软件分别编写了程序对二次谐波原始信号进行压噪和有效信号的提取。结果表明,采用非线性最小二乘法与数字平均滤波技术相结合,使系统理论检测极限由原来的30×10-6提高到了5×10-6量级;对于反演后气体的浓度信号则采用Kalman滤波进行再去噪,使信噪比提高了近8倍。比较结果表明,经过上述滤波处理,TDLAS系统的信噪比和检测极限性能有明显改善。本文的上述方法实际应用到我们的TDLAS在线工业排放气体的测量系统中,取得了良好的效果。

Selection of digital filtering techniques in trace gas concentration detection with a tunable diode laser absorption spectroscopy

In order to improve the signal-to-noise ratio(SNR) and the detection limit of the tunable diode laser absorption spectroscopy(TDLAS), the system′s second-harmonic signal and noise are analyzed.Then four kinds of digital filtering techniques are used for comparison, and four corresponding software programs written by Visual C++ language are used for noise compression and signal extraction from the original noised second-harmonic signal.Finally, the α-β-γ filter and Kalman filter are used for denoising and data smoothing.The results show that the detecting limit is improved from 30 ppm to 5 ppm by introducing least square-method and the SNR is enhanced to 8 times by using the Kalman filter.This method is applied to the TDLAS on-line industrial gas monitoring system,and a good result can be obtained.