Sensores de nível de interface água-óleo em fibra óptica baseados em grades de Bragg
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Data
2020-05-27
Autores
Ludke, Fabio Giesen
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Universidade Federal do Espírito Santo
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This Master Thesis presents the study of fiber Bragg grating (FBG) sensors applied in the measurement of water and oil interface level. Using industrial rubber diaphragms, which has a fiber Bragg grating installed inside, it is possible to measure the level of interface water-oil. The measurement is performed by monitoring the pressure change on each diaphragm caused by the variation in the interface level. The FBG sensors are non-conductive, resistant to electromagnetic interference (EMI) and they are intrinsically safe to be installed in explosive environments. Techniques of FBG inscription known as phase mask and plane-by-plane have been used to manufacture the fiber sensors. Using a spectrometer, the coupled light propagating through the fiber sensor can be interrogated. The analyzes are performed searching for the central wavelength for each FBG used. The stress on the FBG causes a shift in the central wavelength proportional to the level of the interface between the different fluids, for example water and oil. Thus, as water and oil have different densities and depending on the amount of material that is inside the tank, the diaphragms with FBG undergoing higher or lower deformation and causing a proportional wavelength shift variation of the FBG peak. The main materials used in the production of the FBG sensors are silica optical fiber, thermoplastic polyurethane and nitrile rubber. Nitrile rubber corrosion resistant, including use in the oil industry. A methodology was developed for production of FBG sensors with diaphragms printed on the 3D printer and using the nitrile rubber vulcanization. The sensor developed through the vulcanization of nitrile diaphragms with FBG inside was produced using a press system with temperature control. The influence caused by the variation in the diaphragm thickness is observed in the tests with diaphragms produced on 3D printer. This variation doesn’t change the linearity of the system, but change its sensitivity. The measured sensitivities were 7.5 pm/kPa and 5.2 pm/kPa for the diaphragm of 1.2 mm and 2 mm, respectively. The operating range of this interface level sensor varies from 0 to 78 cm. The resolution of the system is approximately 0.01 cm. For interface levels ranging from 0 cm to 78 cm, the standard deviation varied from 0.13 to 0.28, respectively. The average differences calculated for interface levels varying between 0 cm and 78 cm, resulted in standard deviation ranging from 1.09 to 0.43, respectively. It was possible to identify the oil and water interface level in the tests with nitrile diaphragms. As a result, an equation was obtained, where it is possible to determine the interface level through the diaphragm deformation, showing this system has potentiallity to evolve to a product in the near future
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