Study On Signal Denoising Method In Gas Concentration Measurement By Laser

The TDLAS technique is a gas measurement method with high resolution,high measurement speed,non-contact measurement and many other excellent characteristics,and it is one of the research hotspots in the field of measurement.Different from the traditional measurement method,the information of the gas can be obtained by measuring the attenuation degree of a certain spectrum of the laser passing through the gas with the TDLAS technique.Owing to the natural advantages,it has been widely used in our daily life.Since the absorption peak quality in the second harmonic of the signal measured by TDLAS directly affects the accuracy of the gas information,this paper mainly studies the method of improving the second harmonic quality by the noise reduction method.The main work of this paper is as follows:(1)By introducing the gas sensor,the differences between the TDLAS and other measurement methods have been outstood.For further introducing the TDLAS method,the development history,the noise reduction technology,the basic spectral absorption theory of TDLAS technology and the possible source of noise in the measurement have been deeply investigated.(2)Several conventional denoising methods,Wiener filter,Butterworth filter,median filter,moving average filter,wavelet filter have been introduced,and two signal decomposition methods,the EMD and VMD method,have been detailed analyzed and some numerical simulations are developed to verify that the VMD method is superior to the EMD method in decomposing the multi-band aliasing signals.(3)Inspired by the excellent numerical properties of the VMD method and the wavelet semi-soft threshold method,a new signal denoising strategy combining the improved VMD method and the wavelet semi-soft threshold method is proposed,which effectively filters and suppresses the noises in the second harmonic of the TDLAS simulation system.The proposed method weakens the adverse effect of the noise on the final absorption peak and improves the accuracy of the final results.The numerical simulation results show that the proposed method can obtain signals with higher signal to noises ratio and less distortion in the noise reduction method considered in this paper.