Study On FBG Temperature Sensing Technology

Fiber Bragg grating (FBG) sensor, which uses the property that the Bragg wavelength is sensitive to temperature and strain, is a new kind of fiber optic sensor. In addition to having the same functions as the traditional electric sensors, the FBG sensor also has some special characteristics such as distributed sensing, immune to electromagnetic interference, high precision and long-term stability. So it has widely applicable perspective in many fields such as the structure monitoring of large compound material and concrete, the performance monitoring of the intelligent materials, electrical power industry, medicine industry, chemical engineering etc. Study on FBG temperature sensing not only meets the need of temperature measurement, but also provides the basis of temperature compensation in strain measurement.According to the existed researches, FBG has stable sensing properties, and thus is an ideal kind of temperature sensing material. But only after the FBG is encapsulated with proper method, it can become a sensor that is applicable in engineering. In this thesis, study is focused on FBG temperature sensing technology, and the main tasks are as follow:After study on the FBG sensing technology, the design requirements of FBG temperature sensor is put forward, according the practical needs in engineering. On the basis of research on the current status of FBG temperature sensor encapsulation, and the characteristics of existed encapsulation structures, a new encapsulating method using thin steel tube is put forward. Then we study the effects of this encapsulating method on the FBG temperature properties by experiments. We also perform some theoretical analyses on the experimental results. We have drawn the following conclusions:1) The encapsulated FBG temperature sensor will have good repeatability if tensile force is put on the FBG during the process of encapsulation.2) The encapsulated FBG temperature sensor has higher temperature sensitivity than that of the bared FBG.3) The encapsulated FBG temperature sensor has good linearity.So, we can say that the FBG temperature sensor encapsulated in this new structure has good temperature properties, and thus has applicable values.In this thesis, we also introduced the basic principles of fiber grating wavelength demodulation system. Some common used demodulation methods are discussed, with emphasis on the tunable fiber Fabry-Perot (F-P) filter demodulation method. As last, a completed FBG temperature sensing is constructed.