Study On Hot-typed Gas Flow Rate Meter Based On Inter-mode Interference Principle

The measurement of the velocity is of great significance in many fields such as environmental protection,energy and medicine.Compared with the traditional electric sensor and the mechanical velocity sensor,the fiber optic sensor has the characteristics of small volume and anti-electromagnetic interference,which can be used in harsh environment,and can realize long-distance signal transmission.The fiber optic sensor will become one of the key technologies in micro velocity measurement field in future.Most of the existing optical fiber optic velocity sensor is based on the fiber grating structure,and has the disadvantage of low sensitivity and the phenomenon of fiber grating chirp.Therefore,an all-optical hot-wire anemometer based on the structure of inter mode interference is proposed in this thesis.The main contents in this thesis are listed as follows:Firstly,different type of gas velocity meter are introduced,as well as their theory.The research status of the traditional velocity sensor and the fiber velocity sensor is reviewed,especially the development of optical fiber thermal velocity sensor.The traditional velocity sensor and the fiber optic velocity sensor research status at home and abroad are recalled,especially the development of optical fiber thermal velocity sensor for recent years.The advantages and disadvantages of several fiber optic thermal flow velocity sensor are analyzed,which leads the related research in this thesis.Secondly,the basic principle and flow rate sensing characteristics of fiber optic mode interference sensor are studied.The inter-mode interference and four-layer medium model of the fiber is simulated by MATLAB.The simulation results show that the temperature sensitivity of the inter-mode interference velocity sensor is 5 times of that of the fiber grating velocity sensor with the same length of the proposed sensor.Thirdly,two kinds of reflection-based inter-mode interference sensors with multi-mode coupling and core-offset coupling are proposed.Rsoft simulation and theoretical analysis are used to select the sensor parameters.The fabrication of the above two kinds of structures is accomplished,and the experimental platform of 0m/s-8m/s is built.Fourthly,the temperature,power heating and the wind speed sensing characteristics of multi-mode coupling sensor and the core-offset coupling sensor are analyzed.The results show that the sensor resolution of the range of 0m/s?1m/s is 0.01 lm/s and the sensitivity is 1716pm/(m/s).The advantages and disadvantages of the two kinds of sensors are compared and analyzed,and the corresponding optimization scheme is put forward to improve the performance of the sensor.The micro-velocity sensing characteristics of the fiber optic inter-mode interference structure is studied in theory and experiment.Because the sensor is based on light heating,the electromagnetic interference can be avoided.Meanwhile,the sensor with characteristics of safe explosion-proof,small volume,long distance transmission and sensitivity,which can be applied to detect the leakage of gas.