激光气体分析仪中数字滤波器的设计

由于基于可调谐二极管激光吸收光谱（TDLAS）技术的激光气体分析仪的二次谐波信号中存在较大的系统噪声，本文利用有限长单位冲激响应（FIR），提出了激光气体分析仪的二次谐波在线滤波方法。在分析FIR数字滤波器原理的基础上，利用MATLAB窗函数设计了适合本激光气体分析仪的数字滤波器。然后，将仿真的FIR数字滤波算法移植到激光气体分析仪嵌入式系统中。最后，比较了滤波前后二次谐波信号波形，说明了在激光气体分析仪嵌入式系统中采用基于FIR数字滤波器滤波算法的可行性。实验结果表明：FIR数字滤波器对一组二次谐波信号进行滤波的运算时间为230ms，滤波后的二次谐波信号波形获得了较好的去噪效果，能够满足激光气体分析仪对含有噪声的二次谐波信号进行平滑去噪的要求，且滤波算法结构简单、运算时间短、可移植性强。

Design of digital filter in laser gas analyzer

Due to the presence of system noises in second harmonic signals of a laser gas analyzer based on Tunable Diode Laser Absorption Spectroscopy（ TDLAS）, this paper designs an Finite Impulse Response（FIR） based filtering scheme to realize the online filtering of second harmonic of the laser gas analyzer. First, based on the theory of FIR digital tilting, a FIR digital filter is designed with window functions based on a MATLAB （ Matrix laboratory） software platform. Then, the corresponding algorithm is transplanted to the embedded sys- tem of laser gas analyzer. Finally, on the basis of waveform analysis of the second harmonic signals before and after filterings, it proves the feasibility of the proposed filter algorithm that the FIR digital filter is embedded system to realize the online filtering of second harmonic in the laser gas analyzer. Experimental results indicate that algorithm computation time for one set of second harmonic signal is 230 ms. The FIR filter can effectively filter out the interference signals of second harmonic by comparing the waveforms of the second harmonic sig-nals before and after filterings. The FIR digital filter can basically meet the requirements of laser gas analyzer for denoising, smoothing the second harmonic signals with noises, lowering computational complexity as well as enhancing the performance of transplanting.