基于TDLAS的红外湿度检测中的小波去噪实验研究

为了有效抑制可调谐二极管激光吸收光谱法(TDLAS)进行红外湿度检测中的噪声,采用多阈值小波去噪方法对测量通道和参考通道间的差分信号做降噪处理,然后基于数字锁相放大技术从去噪后的差分信号中提取二次谐波信号,最终根据谐波信号的幅值大小确定湿度数值。给出了多阈值小波去噪算法的流程,并做了实验验证。分析显示,本文方法可有效抑制噪声的影响,在极低湿度条件下仍可较好地提取出二次谐波信号。利用制作的湿度检测系统,结合配备的密闭湿度环境,开展了检测实验。结果表明,采用小波去噪后,检测下限可由0.2%降至0.08%,极低湿度条件下(0.2%)的测量误差可由48%降至7.9%,其它浓度下的测量误差小于5%。同时,由于噪声被很好抑制,检测系统的测量标准差小了1个量级,从而改善了系统稳定性。本文的小波去噪方法也可用于具有类似机理的红外气体检测系统中以改善性能指标。

Experimental research on wavelet denoising in infrared humidity detection based on TDLAS technique

In order to suppress the influence of noise introduced in infrared hum idity detection based on tunable diode laser absorption spectrum (TDLAS) technique,multi-threshold wavelet denoi sing is firstly introduced on the differential signal between detection channel and reference channel,then the se cond-order harmonic component is extracted from the differential signal through the digital phase lock-in amplifier,and finally the humidity value is determined according to the amplitude of the second-order harmonic com ponent.The filtering procedure of multi-threshold wavelet denoising is proposed,and related experimental verif ication is carried out on the algorithm.The analysis results indicate that this technique can effectively sup press noises,and the second-order harmonic component can still be well extracted under extremely low humidity.By using the developed detection system and the prepared hermetic environment,the humidity measurement is perform ed thoroughly.Experimental results show that,by using multi-threshold wavelet denoising,the detection lim it can be dropped from 0.2% to 0.08%,the detection error under the humidity of 0.2% can be decreased from 48% to 7.9%,and that under other humidity is less than 5%.Because the noise is well suppressed through wavelet d enoising,the standard deviation of the system is minimized by one order of magnitude,and the detection stability is therefore improved.The wavelet denoising technique can also be adopted in other infrared detection systems with similar p rinciple for enhancing performance.