Research On Intelligent Sensors Of Aircraft Fuel System Based On Laser Absorption Spectroscopy

With the increase of air capacity requirement,the safety of aircraft becomes more and more important.All kinds of aircraft accidents caused by fuel tank explosion directly affect the performance and reliability of aircraft.As a result,Onboard Inert Gas Generation System（Onboard Inert Gas Generation System）has been developed over the past few decades to reduce oxygen concentrations by filling tanks with nitrogen.The oxygen concentration sensor plays a central role in the control of the OBIGGS,a suitable oxygen concentration sensor is very important to the OBIGGS.Most of the traditional oxygen detection methods are electrochemical detection methods,which need direct contact with the gas to be measured.The Measurement Method Needs High Temperature Pretreatment,low safety,short life,low efficiency,and it is difficult to measure on-line,the oxygen concentration sensor based on Tunable Diode LSER Absorption Spectroscopy（TDLAS）can realize non-contact measurement with high safety,high precision,short measurement period,on-line measurement and easy to use.At present,the technology of super-small TDLAS oxygen concentration sensor,which is suitable for the inerting system of aircraft fuel tank,is mature abroad,such as Oxigraf Company in America.In this paper,oxygen concentration is measured based on absorption spectroscopy.The main contents are as follows:The working principle of TDLAS has been studied deeply,including Lambert’s law,the choice of the broadening and absorption lines,and the selection of the characteristic lines near 760 nm of oxygen molecule,the system structure of the sensor is studied and the system is designed.Then,a simulation platform is built by making full use of the simulink module of MATLAB software,which includes the modules of laser,gas chamber and data processing,the research of simulation will provide the theoretical basis and foundation for the next hardware selection.On the basis of the design of TDLAS oxygen concentration sensor system,the hardware design of the laser transmitting unit is completed,including the selection and comparison of the laser,the Distributed Feedback（Dfb）butterfly laser is selected,based on the temperature-sensitive characteristic of semiconductor,the method and principle of TEC Temperature Control and the design of temperature control circuit are studied.Then the hardware design of the gas chamber and the weak signal detection and processing unit is completed.The type of the common gas absorption pool is compared and Herriott type gas chamber is selected,and a hardware design for the lossless connection of the photodiode.In order to amplify the weak signal and denoise it by difference,the preamplifier and difference amplifier are designed,on the basis of which,in order to obtain the signal output with higher precision,the mathematical mechanism of the lock-in amplifier is studied and the hardware design is completed.Finally,the circuit board and the data acquisition card are designed based on the selected components,and the upper computer measurement system is programmed based on LABVIEW software.Through the above work,it makes a contribution to the localization of oxygen concentration sensor based on TDLAS,and realizes the design and verification of the device for measuring gas concentration based on absorption spectrum technology,it will lay a solid foundation for the development of the next generation prototype.