Study On Liquid Characteristics Testing Based On Optical Fiber Echo

As an emerging sensing technology, fiber sensing has been widely used in many fields such as aerospace engineering, oil domain, electricity field, nuclear industry, medical treatment, military and scientific research. Compared with the traditional sensors, fiber sensors have the unique advantages of anti-electromagnetic interference, electrical insulation and corrosion resistance. They can work normally in extreme environment of high voltage, high noise, high temperature and strong erosion. According to the characteristics of fiber sensors, optical fiber can be made into many kinds of special sensors in order to process the various testing. Liquid characteristics testing is one of the most important applications of fiber sensing.Concentration is one of the main parameters of liquid solutions. The technology testing and controlling of concentration are wild used in many fields of production and life. They are the important technique means of improving and ensuring product quality. There have been many studies on optical testing methods of concentration at home and abroad.On the basis of further studies on fiber sensing theory, a new method based on fiber echo signal is proposed to test the refractive index and concentration. An experimental system has been set, and a number of experiments have verified the feasibility of methods proposed. The major study of this dissertation covers the following aspects:1. It involves the in-depth study on the mechanism of light propagation in fiber and the interaction of light and medium at the interface. The situations are very different from each other. The characteristics of medium can be found out by analyzing the echo signal. It can lay a theoretical foundation for liquid characteristics testing.2. On the basis of further study on the interaction between light and medium, a method of liquid characteristics testing is proposed. The coupling loss, micro-bend loss, intrinsic loss and polarization fading have been discussed.3. A set of experimental system has been put up in order to meet the need of liquid characteristics testing and apply the necessary requirement. The optical circuit, fiber probe and the acquisition device are the three main parts of experimental system.4. A number of experiments have been held to test the performance of experimental system. The experiments of pure water, gas90#, gas93#,gas97# and diesel-10# have verified the refractive index testing method. The experiments of sucrose solution, NaCl solution and ethanol solution have verified the concentration testing method. The feasible basis for liquid characteristics testing based on fiber echo signal are proved.