Research On Several Factors Affecting The Accuracy Of Laser Gas Analyzer

The gas analyzer based on Hollow Waveguide(HWG)and Tunable Laser Absorption Spectroscopy(TLAS)has many advantages,such as good selectivity,high sensitivity,good explosion resistance and rapid response.Therefore,it has attracted the attention of scholars ranging from domestic to overseas.Measuring accuracy of this analyzer is affected by many factors.Three important factors of them were investigated in this paper,namely,adsorption-desorption characteristics of HWG,nonlinear response characteristic of signal channel and high resolution spectroscopy.The main works are summarized as follow:First,investigation of adsorption-desorption characteristics of Hollow Waveguides.The TLAS experimental system was designed to study the capillary adsorption characteristic of HWG.By changing the experimental conditions,the effects of purge speed,initial concentration of gas and temperature on adsorption-desorption characteristics of HWG were investigated.The experimental data were processed.And the experimental results were analyzed and discussed.Second,measurement and correction of the nonlinearity response of signal channel.Based on TLAS technique,an experimental system was built to obtain the calibration curve of the detector.By changing the detector of experimental system,calibration curves of a photovoltaic detector and a photoconductive detector were measured and analyzed respectively.Third,measurement and evaluation for high precision and high resolution reference spectral data.Firstly,a DFB-ICL laser(central wavelength 3337 nm)was linearized,and then it was used in the measurement system of high precision and high resolution spectroscopy.The performance of the spectral measurement system was analyzed and evaluated in terms of wavenumber,resolution,noise and optical stripe.The high precision and high resolution absorption spectra of dimethyl sulfide(DMS)at v1 and v8 were obtained.According to the international uncertainty analysis model-GUM model,the uncertainties of wavenumber and absorbance of the DMS spectroscopy were evaluated.The absorption cross section of the experimental spectral data was calculated and its uncertainty was evaluated.Multi-spectral peak fitting with Voigt function was performed for the recorded spectral data and the PNNL data.The differences of full width at half maximum(FWHM)and integral absorbance between recorded spectral data and the PNNL data were quantitatively analyzed.And the reasons for the great differences were analyzed.In this paper,the influence of purge speed,initial concentration of gas and temperature on adsorption-desorption characteristics of HWG were investigated and some qualitative conclusions were obtained.These conclusions have great referential significance for measuring accuracy of gas analyzer.The calibration curves of a photovoltaic detector and a photoconductive detector were obtained and they could be used to correct the non-linear response of the two detectors.The medium-infrared high precision and high resolution spectral data of DMS were obtained.It provided a more accurate basis for atmospheric retrievals of DMS in the mid-infrared spectral region.The results of this paper have great supporting significance for improving the measuring accuracy of gas analyzer based on HWG and TLAS technology.