Research And Experiment On Optical Fiber Fuel Level Measurement Based On Reflection And Side Coupling On Fiber-Optic End Face

Fuel level measurement is the key technologies in aircraft fuel systems.At present,the capacitive level sensor is widely used at home and abroad.But such method is easily interfered by external factors like temperature and electromagnetic.In order to solve this problem,researchers have been exploring and developing new liquid level sensors and in which,the optical fiber is widely valued due to its simple structure,electrical insulation,stable physical characteristics,anti-electromagnetic interference ability and other excellent properties.Combined with the demand of aircraft fuel system,the thesis propose a new method for measuring the fuel level based on reflection and side coupling on fiber-optic end face.And based on the method above,two sensors are developed,an oil level alarm and an oil level sensor.The main content of the thesis are as follows:The basic principle of optical fiber liquid level measurement method is introduced.With multimode step index fiber as the object,transmission path and output characteristic of light in flat end-face optical fiber are analyzed,and the reason for the change of optical power in optical fiber with the refractive index of the external medium is explained.After that,the optical transmission characteristics of the slanting end face fiber are studied,and the optimum angle of oblique section and incident light angle are deduced.Finally,on the basis of the slanting end-face fiber,the theory of side coupling between two optical fibers is theoretically analyzed,and the feasibility of the liquid level measurement method is verified by simulation.Based on the theoretical analysis,an oil level monitoring system for point liquid level measurement is proposed,including oil level alarm,signal processing circuit and data display platform.And the relevant performance of the system was tested by experiment.The results showed that the system had the precision of 1mm,good hysteresis,repeatability and temperature adaptability,and no obvious drift.In order to measure continuous liquid level,some improvements are made on the basis of oil level alarm,and then,an optical fiber oil level sensor for is proposed.The relevant performance of the sensor was tested by experiment and the results showed that the sensor had high sensitivity,a resolution of 1mm,good hysteresis and repeatability.