Fiber Bragg Grating Sensing Technology And High-temperature Survey Application On Aluminum Electrobath

Aluminum is an important basic raw material for our country's economy development. In recent years, with the growing demands for aluminum and the enhancement of national environment protection policies, aluminum-electrolysis technics has developed rapidly in our country by using the big pre-baked electrobath. But the distinct defect is the pre-baked electrobath's short life-span, especially the dilapidations of electrobathes make the aluminum electrolysis companies suffer loss in business. Therefor it's necessary to measure the electrobath's temperatures at the lateral steel-plate, the bottom steel-plate and the cathode steel-stick. Combining with other parameters, we can judge where and how the electrobath is dilapidated. At the same time, these temperature measurement values are useful for the electrolyte temperature management, the energy balance management and the materials balance management. At present, these temperatures are measured by workers using handy infrared thermometers. Howerer, on the one hand, the labor intensity is high, the high-temperature and strong magnetic field in the aluminum electrolysis plant endange the workers' health; On the other hand, the infrared thermometer often doesn't work at strong magnetic field, and the real-time temperatures cannot be measured constantly, so the hidden troubles cannot be found in time.The fiber grating sensing technology provides a better method to measure these temperatures. Because it is small, passive and immune to electromagnetic interference. It can be easily multiplexed. It can also be monitored remotely and constantly in real-time. Recently, domestic and overseas researchers and engineers have pay more attention to the study of fiber Bragg grating(FBG) on high-temperature survey, and in China some valuable research results had also been achieved in this area.Firstly, the forming mechanism, fabrication and apodization of FBG were introduced; The reflection spectra of Gaussian-apodized grating and raised-cosine-apodized grating were simulated by using transfer matrix method and Runge-Kutta method respectively; The basic parameters of FBG sensors and the factors affecting FBG reflection and transmission spectra were analyzed; The mathematic model of FBG temperature sensing was deduced.Secondly, The demodulation technologies based on current representative distributed FBG sensing multiplexing networks were introduced; The narrowband scan laser demodulation principle, process and characteristics were discussed based on wavelength division multiplexing and space division multiplexing sensing network, and the narrowband scan laser demodulation took the sm125 module as an example, the sm125 module was produced by the American MOI company; A secondary development of the data retrieval and processing software based on the sm125 module and TCP/IP had been done, a friendly user interface was formed at last, and the software could monitor and save the interrelated data; Digital signal processing technique to improve wavelength detection precision, and peak-wavelength detection algorithm were detailed.Based on theoretical discussions and demodulation above, experiment systems were set up, CPC coating FBG and polyimide coating FBG were selected as experiment objects. The relationship of reflection wavelength and temperature of these two gratings were researched. For CPC coating FBG, let the temperature vary from 40 centigrade to 200 centigrade, and for polyimide coating FBG, let the temperature vary from 50 centigrade to 300 centigrade. The wavelength stabilities of these two gratings were also researched, and the experimental data were analyzed.Next, after we visited the aluminum electrolysis plants of the Yankuang Ke-Au Aluminum Ltd., one FBG temperature-survey project were designed, including encapsulation of high-temperature FBG sensors, design of sensor-clamps, design of transmission main, design of optic-route and software programme. Together 208 temperature-points can be measured real time and constantly. That's to say, the cathode steel-stick temperatures of two electrobathes can be surveyed real time and constantly.Finally, the main tasks and conclusions in this thesis were summarized and the study contents of next step were pointed out.