Application Research Of Greenhouse Gas Sensor Based On TDLAS Technology

Gas concentration detection has extremely important applications in all aspects of industrial production and air pollution prevention.TDLAS,whose Chinese full name is tunable diode laser absorption spectroscopy.This technique uses different gases to correspond to different optical absorption peak lines to measure the concentration of gas to be measured.The technique can obtain the value of the absorbance function by direct scanning subtraction method or wavelength modulation method,etc.,and then obtain the corresponding gas absorption signal according to the law of Beer-Lambert.And then this signal will be amplified and filtered by the circuit.The ratio of the incident light intensity can be obtained as the absorbance function value,and then calibrated to determine the calculation mode of the sensor,and finally the gas concentration value of the component to be measured can be obtained.This photoelectric detection method has the advantage of high detection sensitivity.This method can quickly and accurately detect trace gases.In addition,the high selectivity of light absorption can eliminate background interference between different gases.Finally,the technology also has response in fast time,no sampling pre-processing,core components and measurement environment isolated from each other for maintenance.In recent years,the global effect of the greenhouse effect has become more serious.The greenhouse effect is directly generated by greenhouse gases.In addition to carbon dioxide and methane,water vapor is also one of the greenhouse gases.Because it is too widely distributed,it is not included in various international conventions.In addition,many provinces in China have issued policies on the regulation of smoke and gas,including Hebei,Shandong and others.The whitening of the flue gas is to remove the influence of water vapor in the flue gas on the environment.Therefore,the detection for methane,carbon dioxide and water vapor is urgently needed.The paper mainly studies laser sensors for greenhouse gases such as methane,carbon dioxide and water vapor.From the background of the subject,to the technical principle,to the core technology and algorithm,theoretical simulation by LabVIEW,laser principle and light wavelength selection of different gases.The part of the chamber,part of the circuit,algorithm and structural of the optical sensor were designed and then corresponding calibration experiments were completed.In the traditional calibration experiment,the correlation coefficient R2=0.9979.In actual use,the average PPMV in the measured space is 6355.6.The range is 30 and the overall standard deviation is 7.88.In addition to the traditional calibration method,the paper finished the preliminary calibration experiment of methane gas using long optical path chamber.It is preliminarily believed that the switching point between direct subtraction method and harmonic method is PPMV=20000,and the correlation coefficient can reach R2=0.9999.It is necessary to introduce a quadratic term at the direct method.At the same time,it is designed and realized to calibrate the water vapor using the high temperature and high humidity environment box and the high temperature-constant temperature saturated water field calibration.The paper collects all stable data of the humidity points,using three calibrations.The correlation coefficient R2=0.9977.In the calibration of high temperature waters,the humidity detection trend of temperature rising,temperature decreasing and retesting tend to be consistent.The work of the paper proves the convenience of TDLAS technology and the practicality of the sensor.