Research And Design Of High Precision Infrared Absorption Multi-gas Sensor

In2013severe fog and haze weather greatly influenced people’s daily life,environmental problems have become increasingly prominent. Hazardous gasdetection is getting more and more researchers’ attention. In this paper, I have adetailed study about infrared gas detection technology, gas absorption cellreflection principle and ZEMAX software. Through the molecular structure ofmethane, ammonia, carbon monoxide and HITRAN database data, I determinethe three types of gas near infrared wavelength range of wavelength, intensity ofabsorption lines. By studying the pressure broadening, Doppler broadening andVoigt broadening of these three mechanisms, analyze the relationship among thepressure, temperature and gas absorption coefficient. According to the lambertbeer’s law, I calculate the different gases’ optical path length. Put forward theideas of design high precision of gas absorption pool, and much gas absorptionpool light reflection principle is studied in detail in the internal and the position oflight spot on the surface is calculated. And by adjusting the angle of mirror andthe source light’s angle, improve the gas cell’s structure, improve the utilizationrate of the reflection mirror, eventually making the design of the gas cell, the baselength is280mm, the measuring accuracy of carbon monoxide is at least200ppm, ammonia’s measuring accuracy is at least20ppm, methane’s measuringaccuracy is at least2ppm. Also study the principle of Herriot cell and light on thereflective surface of light distribution in detail, comparing two kinds of gas cell, Iconcluded the advantages and disadvantages.In this paper according to the theory data of calculation, combine withoptical software ZEM-AX, both the gas absorption cell are simulated, eventually making the light that in the gas absorption cell which is280mm long, reflect32times, so that the longest optical path can reach8.96m, the volume of0.00256m3.The Herriot Cell which its base length is205mm, the light reflected in this gascell at most50times, the optical path length is10.25m, volume is only0.00188m3.By using software simulation, I verify the feasibility of high precision of gasabsorption cell.In conclusion, I have carried the detailed research on the optical part of theinfrared absorption spectrum theory of gas cell, two different kinds of calculationmethod about cells’ parameters are given, also I detail the optical softwareZEMAX. To improve the accuracy of gas absorption cell this behavior has greatfurther significance.