Design and uncertainty analysis of a weighing system for continuous measurement of crop evapotranspiration
2011
Oliveira, Aureo Silva de | Vellame, Lucas Melo | Junior, Jorge Luiz Copquer dos Santos | Vellame, Júlio Melo
Electronic systems for collecting crop evapotranspiration data use load cells as the sensing element. The present work aimed at developing and evaluating a load cell-based weighing system for use with small to medium size continuous weighing lysimeters. It was used a single 300-kg capacity load cell whose signal was conditioned through a differential amplifier to an analogical signal varying from 1 to 5 V. The signal was then converted to digital number through an A/D converter working in the 0 to 10 V range. The A/D circuit allowed reading up to four analogical signals by means of a computer program developed for that purpose. To assess the performance of the weighing system the uncertainty parameters repeatability, hysteresis, linearity and overall accuracy were considered. The overall accuracy, which combines the effects of the other errors, was lower than 1 mm suggesting the suitability of the system for daily ET measurement with low-volume continuous weighing lysimeters. The final cost of the weighing system was less than a thousand dollars and all the components, from load cells to personal computer, can be found in local retail stores
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