Displacer-type liquid level sensor with liquid density auto-compensation

In the classic displacer-type liquid level measuring method, liquid level is calculated via the buoyancy force exerted by the liquid on a displacer. This technology has high linearity, precision, accuracy, ease of installation and low cost. Nonetheless, displacer level sensors have significant sensitivity to variations in liquid density, which hinder its use in industrial applications that such quantity is not held constant. In this paper a novel displacer-type liquid level sensor is presented and analyzed. The innovation of the new sensor consists of adding another displacer and thus calculating the new measured value by the quotient of the buoyancy forces of both displacers. Therefore, the new measurement is ideally insensitive to the variations in liquid density. A prototype was built and prototype results presented high linearity, being able to mitigate the sensitivity to the liquid density, increasing accuracy in the measurements

Modeling of FiO2 delivered by self-inflating ventilation device: Modelagem de FiO2 entregue por bolsa auto inflável

During the COVID-19 pandemic, professionals in the medical field have been using bag resuscitators, also called bag valve masks, to provide respiratory support for patients for long periods. A relevant issue arising because of such use is the little information regarding the FiO2 delivered by these devices, leading to toxic effects of O2 and its waste. This paper presents a model that relates volume, respiratory frequency, and flow in an O2 line with the FiO2 delivered by bag resuscitators. The model was obtained based on a formal procedure and data from a 1500 ml Hsiner bag resuscitator collected in the literature, both presented in this paper. Then, we compared through Bland-Altman analysis the FiO2 values estimated by our model with the ones from data considering different bag resuscitators to evaluate the amplitude of the errors it can generate. The average error for Hsiner and Laerdal bag resuscitators was less than 0.035 (or 3.5%) and less than 0.063 (or 6.3%) for Ambu devices. The maximum error found for Ambu bag resuscitators was high. The obtained model presented satisfactory errors, compatible with the uncertainty levels associated with FiO2 measuring instruments and blenders, meaning the model can be used to estimate the delivered FiO2 accurately. Additionally, the procedure presented in this paper can be used to obtain specific models for bag resuscitators of other companies, equipping professionals with tools that can accurately estimate FiO2

Stability of keyed systems based on main control objective.

Atualmente, verifica-se um interesse crescente de grupos de pesquisa pelos sistemas híbridos, em particular no que diz respeito aos sistemas chaveados. Diante da necessidade de se desenvolver ferramentas que possam auxiliar os trabalhos nessa área, principalmente na análise de estabilidade, nesta tese de doutorado é proposto um novo campo de análise de estabilidade de sistemas chaveados baseado na determinação de um objetivo principal do sistema. Baseado nesta proposta, existe a possibilidade de que os subsistemas tenham pontos de equilíbrio diferentes, ou até que alguns deles sejam instáveis. De acordo com esta abordagem, apenas o subsistema principal precisa ser globalmente assintoticamente estável. No entanto, ao ser realizado o chaveamento, a estabilidade de Lyapunov muitas vezes não se aplica, visto que, para os sistemas chaveados, a norma das variáveis de estado do sistema pode crescer temporariamente. Assim, uma alternativa à estabilidade de Lyapunov é a estabilidade prática, voltada às aplicações, que está baseada em uma abordagem mais quantitativa. Neste contexto, são abordados os sistemas quasi-estáveis, nos quais as condições da estabilidade de Lyapunov são atendidas após um tempo τ. Para tanto, nesta tese são propostas uma definição de quasi-estável e duas proposições com condições suficientes do tipo Lyapunov para este tipo de estabilidade. Adicionalmente, são apresentadas neste trabalho três proposições, que devem auxiliar na análise de estabilidade de um número significativo de sistemas que apresentem essa característica de objetivo de controle principal, ainda que no caso de controle chaveado não-linear. As contribuições deste trabalho são ilustradas mediante a apresentação de simulações e resultados experimentais. Tais resultados abrangem a área de controle de processos químicos e navegação de robôs móveis.Nowadays, a growing interest of research groups for hybrid systems can be seen, especially for the switched systems. Due to the need to develop tools that can assist the work in this area, mainly in sense of the stability analysis, in this PhD thesis is proposed a new field of stability analysis of switched systems based on the choice of a main objective for the system. As a result of this proposal, there is the possibility that subsystems may have different points of equilibrium, or even some of them can be unstable. According to this approach, only the main subsystem needs to be globally asymptotically stable. However, when the switching is performed, the Lyapunov stability is often inappropriate, since the norm of state variables may temporarily grow for the switched systems. Thus, an alternative to Lyapunov stability is the practical stability, focused to applications, which is based on a quantitative approach. In this context, this work addresses the quasi-stable systems, which are systems that met the Lyapunov condition after a time τ. In this way, this PhD thesis proposes a definition of quasi-stable and two propositions with sufficient conditions for this kind of stability.Additionally, in this work, three propositions are presented, which should help in the stability analysis of a significant number of systems with the main control objective characteristic, including the case of nonlinear switched control. The contributions of this work are illustrated by the presentation of simulations and experimental results. These results cover the control of chemical processes and mobile robot navigation areas