| In recent years,with the rapid development of petroleum,chemical industry and electric power,the leakage accidents of poisonous and harmful gases are increasing day by day.These lead to air pollution and explosions,seriously harming the ecological environment and human safety.Traditional gas sensors,such as electrochemical gas sensor and catalytic combustion gas sensor,can only detect gases at a fixed point,but can’t image the leaking gas.Passive gas leak infrared imaging detection has the characteristics of long detection distance,wide monitoring range,and no need for radiation sources.It can efficiently and intuitively observe the location and status of gas leaks.However,refrigeration infrared detectors are widely used in infrared imaging detection system of gas leakage.This kind of detector is expensive and has a limited detection range,because it can only image in medium-wave or long-wave infrared.Therefore,it is of great significance to study wide-band uncooled infrared imaging technology for gas leakage detection.Firstly,based on the principle of gas molecular vibration and infrared absorption,the radiation transmission model of passive gas infrared imaging was studied.The analysis methods of infrared focal plane detector response and infrared imaging system noise equivalent temperature difference were sorted out.The equivalent blackbody temperature difference model for gas was established,and the matching relationship between the detection system response band and gas infrared radiation and absorption bands was clarified.The infrared radiation absorption characteristics of methane gas were analyzed,and the influence of gas temperature,concentration,and background temperature on the total radiation amount of gas was investigated.Secondly,based on the theory of complex color difference and mechanical positive group compensation,a transmission-type wide-band non-cooled infrared zoom optical system was designed.The system has a focal length of 25 mm to 75 mm.The working wavelength is 3μm to 12μm.Suitable for 640×512 resolution,pixel size 17μm uncooled wide band infrared detector The total length of the system remains unchanged at 160 mm during the zoom process.The design results show that the modulation transfer function of the system is close to the diffraction limit at 30lp/mm,and the imaging quality is good and meets the design requirements.Thirdly,based on the vector wave aberration theory,the characteristics of image aberrations such as spherical aberration and coma in off-axis systems with eccentricity and tilt were analyzed,and the solution method for initial values of eccentricity and tilt in off-axis systems was studied.A 3-mirror zoom off-axis optical system with a focal length of100 mm to 300 mm and a field of view angle of 2.66° to 1.34° was designed,also suitable for a non-cooled wide-band infrared detector with a resolution of 640×512 pixels.The design results show that the modulation transfer function of the system is close to the diffraction limit at 30lp/mm,and the imaging quality is good and meets the design requirements.Finally,an experimental platform was set up outdoors to simulate a methane gas leak scenario,and the effects of single-band and wide-band infrared imaging systems on methane gas leaks were compared and analyzed.The imaging effect of gas leaks was tested under different detection distances,weather conditions,and optical system focal lengths.The experimental results show that when the response band of the detector includes the band where the gas infrared absorption peak is located,the leaked gas can be effectively detected,and the closer the detection distance,the higher the sensitivity and the better the detection effect.The detection effect is better in winter than in summer due to the temperature difference between the leaked gas and the environment. |
