Studies On Key Technology Of Infrared Thermal Imaging Detection And Identification System For Methane Gas

The leakage phenomenon of natural gas during the process of mining,transportation,storage and utilization appears frequently,not only leading to energy losses,but also causing fires and explosions,which seriously threaten the safety of people's lives and property.Methane is the main component of natural gas,and its effective detection and recognition is of great significance to the timely discovery of natural gas leakage accidents.Presently,the gas detectorscommonly used are easily poisoned,easily disturbed by other gases,and with large volume,which seriously restrict application and popularization in industrial field.However,the gas passive infrared imaging detection technology has advantages of long distance detection,gas types detectable,no need for infrared radiant source,relatively simple structure and direct imaging and so on,which arose great attentions.Therefore,studies on gas passive infrared imaging detection and recognition system with wide waveband and high sensitivity has great theoretical and practical significance.Based on the passive imaging technology researches of un-cooled infrared focal plane detector,methods from two aspects consisting of dual-infrared optical imaging and optical thin film technology have been studied to explore high detection sensitivity,which can break throughthe key technology of methane gas detection with the recognition system for infrared thermal imaging technology and make the detection and recognition of methane gas effectively come true.Based on the theory of gas passive infrared thermal imaging detection,a gas infrared detection method covering both medium and long infrared wavebands has been proposed.By combining the dual-infrared waveband infrared imaging optical system,narrow-band filtering system,signal processing and output system effectively,taking the method of modular design,and according to the technical indexes of the system,technical research key technologies of each part have been studied and infrared thermal imaging of methane gas detection and recognition system have been designed and realized,which can realize high sensitivity passive detection recognition for methane gas quickly and accurately.According to the technical requirements of the system for infrared optical imaging subsystem,theory of chromatic aberration and thermal aberration correction for dual-infrared waveband thermal imaging system has been studied and the dual-infrared waveband optical system of middle and long infrared wavebands has been completed.Choosing the un-cooled detector and by matching lens materials and lens mechanical materials,the passive optical athermal system has been designed,which consists of 4 lenses with 3 aspherical surfaces and the optical transfer function(MTF)of the whole field of view is basically unchanged of more than 0.3 at various temperatures.Manufacturing errors andalignment errors of the system are analyzed,and the imaging quality of the system is stable with the very small error values in the setting tolerance range.Dual-infrared waveband antireflection coatings have been developed on the surfaces of the lenses and the average transmittance of each optical lens is higher than 95%,which meets the transmission requirements of the system.Aiming at the technical requirements of infrared thermal imaging methane gas detection and recognition for infrared narrow-band filtering system,based on the infrared absorption spectrum characteristics of methane gas,the parameters of narrow-band filters have been optimized and it can be made by physical vapor deposition technology.On the basic theory of optical films and the characteristics of optical materials,combining with film design software,the double-sided membrane design has been realized by using the separation technologyprinciple.It overcomes problems of thickness a single mask layer and excessive stress.The reverse analysis method can be utilized to reverse the experimental test results,and the causes of the errorshave been analyzed by study of the distribution of the sensitivity of the films.Using different monitoring methods,and combining with film design software,the design,processing and testing of two narrow band filter films of 3.31?m and 7.669?m have been completed.After completing the design and processing of dual-infraredwavebands optical imaging system,narrow-band filtering system,signal processing and output system,the infrared thermal imaging methane gas detection and identification prototype has been integrated.To ensure the safety of the experiment,the gas flow control module has been used to control the gas release accurately.After tests of different gases,the detection and recognition with this equipment can be realized only for methane gas.The digital image processing technology has been applied to improve the image quality and based on these,the detection experiments of methane gas at different concentrations and different detection distances have been completed,and the imaging quality and response time have been analyzed.The results show that the methane detection and recognition system of infrared thermal imaging can meet the requirements of the target.The research methods and results in this paper have important guiding significance for the implementation of methane gas.