Research On Data Acquisition And Processing Method Of High Performance FTIR Spectrometer

According to the requirement from high performance FTIR instrument to high precision sampling and processing method.In this paper the influence of sampling errors on interferogram is studied.The improved method of data sampling and processing based on "Brault" method is designed and implemented.The synchronous sampling method is studied on this basis,And finally the improved method of data sampling and processing based on "Brault" method are tested and analyzed.Several typical sampling errors in the FTIR spectrometer are analyzed,and based on these types of errors,the mathematical model of interferogram with no and sampling errors are established and simulated when the incident light source is monochromatic and ploychromatic light.The relative error of the spectral intensity at different sampling errors is calculated.Based on the system of laser triggered sampling and processing,the influence of the number of interferometric data points on the recovery spectrum during the phase correction of interferogram is studied.The changes of the SNR of the Mertz phase correction method with 65536 and 1024 data points are compared and analyzed.The results show that the SNR of the spectrum in the 2100?2200cm-1 and 2500?2600cm-1 band is 1.9 and 3.4 times that of the latter,respectively.using 65536 data points for phase correction.Since the laser triggered sampling method can not improve the sampling error caused by the uneven motion of the moving mirror of the interferometer through the later phase correction.Therefore,the development of high performance FTIR spectrometer needs to improve the data sampling and processing methods.A method of interferogram reconstruction with good environment adaptability and high sampling frequency is studied.Therefore,the improved method of data sampling and processing based on "Brault" method is studied and implemented.It can reduce the stability and collimation of optical path,simplify the processing of optical path adjustment and increase the range of measurement.The synchronous sampling method is studied,which synchronize the sampling and interpolation of the laser and infrared signals,ensures the consistency of time and simplifies the extraction of the zero-crossing information of the laser interference signal,and reduces the complexity of the data processing.The data processing time and SNR of the improved method of data sampling and processing based on "Brault" method and the laser trigered sampling method are compared.The experimental results show that the improved method of data sampling and processing based on "Brault" method,and the SNR is higher than that of the latter,1.4 times as much as that of the latter.Taking the CO2,CO and CH4 gases in the air as an example,the detection limits and detection accuracy of the two methods are compared.The experimental results show that the detection limit of CO2,CO and CH4 in the background air are 5.8,1.8 amd 4 times higher than those of the laser triggered sampling method,and the detection accuracy are 5.9,2.4 and 4 times higher than those of the latter,respectively.In order to verify the influence of the data sampling and processing method based on equal time interval on the performance of the instrument,the experimental observation was carried out.The results show that data sampling and processing based on equal time interval can be used for continuous monitoring.