Research On Distributed Fiber Optic Temperature Measurement System And Its Application To High-temperature Monitoring Of Alumina Electrolysis Bath

The traditional temperature measurement system has weak resistance to electromagnetic interference,poor corrosion resistance,small temperature measurement range,and it cannot monitor temperature in real time.With a single sensing fiber,the distributed fiber optic temperature sensor(DTS)system can realize the real-time remote measurement of continuously distributed temperature field along the fiber.Since the DTS system based on Raman spontaneous scattering principle in the UK in 1980 s,DTS system has been widely used in smart grid,transportation,coal mine safety and other fields due to its own unique advantages.According to different application requirements,improving the performance indicators of the DTS system is the key to realizing the real-time,safe,continuous,automatic monitoring.Under the environment of high temperature,strong magnetic field,and high current in alumina electrolysis bath.It is necessary to study the DTS system with high accuracy of temperature measurement,high temporal resolution and high spatial resolution.In this thesis,the spatial resolution of cm level is achieved by using the selfdesigned pulsed light source and Avalanche Photo Diode(APD)module.Analyzed the temperature data by DTS system for alumina electrolysis bath,verified the feasibility and reliability of the DTS system for high-temperature monitoring of alumina electrolysis bath,and its temperature error is within the allowable range of the aluminum industry,the specific research is as follows:(1)Analyzed the current situation of aluminum industry,the temperature monitoring method of alumina electrolysis bath,the status of domestic and international research on the spatial resolution of the DTS system.And described the principles of optical time domain reflection(OTDR)techniques and Raman scattering.Secondly,the method of temperature demodulation was determined,and the temperature monitoring was carried out on the coal mining area and belt transport system.(2)The OPA858 is used as the op-amp chip and the DC634 A module as the APD bias power supply,the DTS system was built.The performance parameters of the system and their influencing factors are described in detail,and relevant gradient experiments are conducted.A combination of cumulative average denoising and wavelet soft threshold denoising is used to improve the signal-to-noise ratio of the system,temperature fluctuation has been improved from ±4℃ to ±1℃.(3)A pulsed light source is designed in this thesis and the parameter configuration software is designed using C#.Firstly,a pulse width of 5ns was achieved by designing a narrow pulse drive circuit for the DFB laser.Through experiments to verify the relationship between wavelength and temperature for 0.1nm/℃,designed MAX1978 temperature control module.Secondly,the optimal parameters of Erbium-doped Fiber Amplifier(EDFA)were determined by Opti System simulation.Finally,the DTS system with the pulsed light source and APD achieves centimeter level spatial resolution.(4)Used the DTS system to monitor the temperature of alumina electrolysis bath,the selection of temperature measurement fiber optic cable and the laying of fiber optic cable in the field are introduced.By analyzing the temperature data of the DTS system,the process of aluminum electrolysis is briefly described in three parts: the initial stage,the roaster stage,and the aluminum electrolysis stage.The DTS system has proven that it can monitor the temperature of alumina electrolysis bath.Temperature monitoring of cathode square steel verifies that the DTS system can distinguish temperatures at different locations.To further verify the reliability of the DTS system,compare using IR remote thermometers,the maximum absolute error of the DTS system is 17.8°C,and the relative error is less than 6.31%,the measurement error is within the requirement of aluminum industry.