Sensor de nível tipo deslocador com autocompensação da densidade do líquido

Abstract

Level measurement plays a crucial role in a wide range of scientific and industrial applications, such as agriculture, hydrology, soil science, oil, pharmaceutical and food industries, among others. Due to the need of measuring level in different environments and for different liquids, granulated solids or powder, several sensors have been proposed to this end, for example, capacitive, infrared, hydrostatic, ultrasonic, radar, laser, optical, displacer, among others, each having its pros and cons. In particular, displacer-type level sensors are highly linear, precise and exact for a given working condition, in addition to having low cost and being easily installed. However, these sensors estimate liquid level indirectly by measuring the buoyancy forces on a displacer connected to a strain gauge, which makes it highly sensitive to variations in liquid density. As a consequence, it is also sensitive to variations in the liquid temperature, since the density is sensitive to temperature. This makes displacer level sensors unfeasible in industrial applications that do not keep such quantities in a range tight enough to ensure low measurement errors (e.g., oil, food and pharmaceutical industries). As a way to allow for the use of displacer-type level sensors in industrial applications, it is proposed in this work and it was also built a new displacer-type liquid level sensor self-compensating for liquid density. The proposed method uses the ratio between the buoyancy forces measured by two displacers and two load cells to make it density independent and, as a consequence, temperature invariant. Such characteristic is observed in the simulations results. The prototype experimental results show that the system has high linearity, it is able to mitigate the sensitivity to the density of the measurand, and it has potential to make precise measurements.