Phase Demodulation Method And Stability And Repeatability Of Fiber Optic Oxygen Sensor Based On Fluorescence Quenching

The detection of oxygen concentration has vital significance in many aspects, such as medicine, environmental protection, petrochemical industry, industrial production, food preservation, production control and so on. Meanwhile the fiber optic oxygen sensor based on fluorescence quenching has become a new hot research and made great progress because of its high accuracy, high sensitivity, simple structure, working under the bad environment, short response time and realizing to monitor the oxygen concentration in real-time and continuous.The fiber optic oxygen sensor based on fluorescence quenching is using the equation of Stern-Volmer to demodulate the information of oxygen concentration. Both the fluorescence intensity and fluorescence lifetime can be used for demodulating the oxygen concentration. Due to the instability of fluorescence intensity we choose measuring the lifetime of fluorescence to measure the oxygen concentration. As the method of phase shift being a kind of common demodulation method, the detection of phase difference is particularly important.Based on the above background, we have carried on the theoretical analysis and experimental research on the fiber optic oxygen sensor based on fluorescence quenching. The thesis mainly has the following contents and innovation points:1. The significance and the main method of detecting oxygen concentration are introduced. The present research situation and domestic and international development of fiber optic oxygen sensors are introduced respectively, including fiber optic sensor, gas sensor and fiber optic oxygen sensors.2. Detection principle including the generation and quenching of fluorescence based on the fiber optic oxygen sensor are introduced. The principle of phase shift method to measure the lifetime of fluorescence is mainly introduced. What’s more the correctness of the theory is verified by formula deduction.3. The choice of main components (oxygen sensing film, light source, filter, photoelectric detector) of the fiber optic oxygen sensor based on fluorescence quenching principle is introduced. The basic structure of the sensor is analyzed. The basic principle of the designed circuit is studyed deeply. The designed circuit mainly include the driving circuit of light source control circuit and photoelectric detection circuit.4. Two new methods of the phase detection in the measurement of oxygen concentration are introduced subtraction circuit and vector phase lock amplifying circuit. The basic circuit and it’s principle of design are mainly introduced. The phase detection of this two methods is verified through the electrical signal. Finally the subtraction circuit is applied to the measurement of oxygen content. A standard signal source producing mini angle is introduced and applied to the subtraction circuit to verify the phase detection of mini angle.5. The main factors influencing the stability and repeatability of fiber optic oxygen sensor system are analyzed. It mainly contains four aspects:environmental temperature, the stability of the anaerobic phase, circuit and light path. Method of using the reference light path to improve the stability and repeatability of the phase difference detection is mainly introduced.