Study On Theory And Experiment Of Optical Fiber Fluorescence Temperature Sensor

Temperature measuring is one of the important subject in the fields of measurement science and engineering technology. Innumerable industrial process, biomedical monitoring systems and environmental regulatory systems depend on accurate, reliable temperature information in order to function effectively. In particular, the requirement to measure temperature in inaccessible or difficult circumstances, such as those in RF radiation, or other noisy electromagnetic environments, has been the imperatives in the development of optical sensors for this purpose. The optical fiber fluorescence temperature sensing system is a preceding problem in this research area. This paper set the goal for finding out new fluorescence temperature sensing material to meet different demands, raising the reliability and sensitivity of the temperature measuring system. The system adopts the LED as excitation light source in order to gain more advantages than that of the traditional method such as configuration, control mode and lifetime. With the optical fiber link, it forms optical fiber fluorescence temperature sensor. The mode of measurement is either touch or not touch to the object measured. The main research work is as follows:(1) The temperature sensing theory of fluorescence material is discussed based on electron transition process. The temperature sensing characteristics of solid state laser crystal, rare earth compound and rare earth doped optical fiber are introduced. By experiments the spectrum of some rare earth compounds excited by visible light region are given. LED is determined as the excitation light source by comparing several light source characteristics.(2) The high fluorescence collection efficiency probe is designed by studying the optical configuration and combination of the system for weak fluorescence signal and the loss of optical fiber, lens and filters.(3) Both on time domain and frequency domain, the detection for lifetime of weak fluorescence signal is studied. On the frequency domain, the mathematic model of two methods involved the relation between the excitation light and temperature, fluorescence and temperature. Under the condition of excitation light and fluorescence mixing, the selection principle of modulation frequency of light source and sample frequency of system is given. On the time domain a new method based on Hilbert Transformation is mentioned for phase sensing detection (PSD) of fluorescence lifetime. The mathematic model of this method is set up, eliminating the low pass filter, restricting the leak of the excitation light some extent. The fluorescence signal is sine wave owing to the sine diving for excitation light, and its duration is the same with that of the excitation light, but phase is lag. A new method based on across correlation and chaotic system is given for detecting the weak fluorescence signal improving the signal noise ratio of the system. The detection means for multi fluorescence convolution is studied. Each fluorescence lifetime is decomposed by Prony's algebraic method without iteration process.(4) A temperature measuring system based on LED light source is designed, and the transfer model and noisy model of every section is given. For raising the resolution of detecting circuit, a dual phase locked loop (PLL) is designed. Its operation principle is analysed. The overall system is control by microcontroller.(5) The experiments are done for optical fiber fluorescence temperature sensing system including the absorption spectrum and emission spectrum of several fluorescence materials, spectrum of LED, testing of dual PLL and the relation between the fluorescence lifetime and temperature.