Desenvolvimentos mecânicos e computacionais de suporte às medidas com sensores termoelásticos

Abstract

The hydrostatic pressure inside the cell or simply cell turgor is an important component of texture in vegetables and is directly related to firmness. The decrease in cell turgor of plant organs is also an indicator of loss of tissue water. This effect can be perceived visually by wilting accompanied by a dry appearance with the loss of brightness and color of products, which influences consumer perceptions about its quality. Within this context has been crafted technique for measuring turgor with Thermoelastic Probe® (TP) based on the principle of measuring isovolumetric. After an extensive literature review found that the published studies on TP, presented further on control theory and modeling of physical phenomena involved in the measurement of turgor. However not bring practical results, containing automated measurements of cell turgor in plants. This study aimed to fill this gap. In this direction was made improving of the method to manufacturing the sensor and a new mechanical design for TP. The attainment of the sensors is given through the steps of stretching the capillary, making the tip, sanding, filling and sealing fluid sensor. The method for obtaining the proposed sensor showed minimal utilization rate of 27.0% representing an improvement of 540% over the figures provided by the available literature. Since the new mechanical design of TP significantly improved the alignment and relative positioning of the sensor, sample and image capture system. The process of exchange of sensor and positioning of the sample for measurement of turgor was also facilitated, resulting in an average time of 5 minutes to perform these tasks. This marked a breakthrough since the previous version, users reported that this task could take up to 60 minutes. Both activities related to the new mechanical design of the ST and the improvement of the methodology for obtaining sensor thermoelastic were preparatory to the development of automatic control of turgor measurement. The automation of the measurement process was performed after the implementation of a software to detect the position of the meniscus oil / cytoplasm based on the determination of the difference in contrast between the phases formed by the fluid sensor (oil ) and intracellular fluid. For automatic control of the position of the meniscus, was implemented a Proportional Integral type controller. The proposed values for the parameters of controller allowed the control of the selected position of the meniscus and automatic - x - determination of turgor pressure in cells of onion (Allium cepa L.). In an unprecedented manner, this paper makes the first successful experiment in automatic determination of cell turgor in plant organs with Termoelastic Probe.