This paper aims the planning, construction and modeling of a low-cost multivariable level plant for didactic purposes. The developed model has two pumps that feed four tanks coupled to each other. Between the tanks and the pumps, there are inlet and outlet valves that can change the system dynamics according to its opening configuration. To automate the pumps and read the instrumentation used, the Arduino microcontroller was chosen because it is a model of great use in the academic environment and of easy parameterization. For sensing, the HC-SR04 ultrasonic sensor was chosen, which already has native compatibility with the microcontroller. In order to validate the constructed plant, it was necessary to identify its model, using the empirical step response method for this purpose. In this way, this work has both qualitative and quantitative characteristics, since the planning and construction of the didactic plant involved an exploratory research of the problem, and then the modeling and simulation method was applied to obtain the mathematical model of the plant. Finally, an experimental research was conducted, comparing the data obtained in the real plant with the model data for validation. Having completed all research stages, the work result is a didactic plant with good linearity, able to provide implementation of level control strategies of coupled tanks and to assist in teaching and learning subjects that involve concepts of dynamic systems, besides multivariable systems identification and control.
Neste artigo, o Método do Relé será utilizado para identificar regiões diferentes de um sistema não linear, aproximá-las às de um sistema linear de primeira ordem com atraso de transporte e sintonizar controladores do tipo PI para estas regiões. Será aplicado o controle utilizando escalonamento de ganhos, e sua resposta temporal será comparada à de um controlador PI de ganhos fixos sintonizado na região central do sistema. Seu desempenho também será avaliado quanto a rejeição a distúrbios. O sistema utilizado é uma planta didática de controle de nível, composta por dois tanques, uma bomba e uma válvula proporcional pneumática. Os resultados indicam que o PI de ganhos fixos apresenta menor tempo de acomodação nas regiões mais altas do tanque, enquanto o de ganhos variáveis se mostrou mais rápido em regiões mais baixas. Considerando o ambiente industrial, o Método do Relé mostrou ser uma boa técnica de autotuning, pois é pouco invasivo e permite sintonizar controladores de maneira simples, atendendo às especificações mesmo em sistemas não lineares.
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