Desenvolvimento de um sistema de monitoramento do nível de águas de rios

Abstract

This work proposes a system for monitoring the water level of rivers based on fiber Bragg gratings and the hydrostatic force´s principle. The system consists of a cylindrical buoy, protected by a column, which produces a longitudinal tension in a FBG embedded in a silicone rubber, as result of the buoyancy force exerted by the water. The calibration of the sensor showed that it is possible to tune the maximum water level that the system can measure by increasing the grating depth in the silicone rubber. The increase of the depth also increases the non-linearity in the sensor response, but the results obtained show that it is possible to use linear approximations in different regions of the sensor response. The results of the tests in the water column showed that mechanical vibrations can be distinguished from the increase in water level because they are short duration events. The tests also showed that the system can measure levels up to a limit of approximately 12 meters high from the water level. The crosssensitivity problem can be overcome by the use of a second grating encapsulated in a needle to distinguish the temperature effect from increasing water level. The responses of the gratings can be used to decrease the effect of the temperature on the sensor response used to measure the water level and to identify that there is a temperature variation. In addition, the needle encapsulated grating showed an applied force sensitivity very small, practically nil when compared with the sensitivity of the grating inserted in the silicone. This feature allied to the thermal response of the gratings allows the distinction of temperature effects from the increase of the level of the rivers. The results of this work show the potential of the use of fiber Bragg gratings sensors in the development of river level monitoring systems in flood risk areas.