| Resumo: |
Liquid levels are measured in a variety of agricultural applications, and are often measured manually, which can be time-consuming and labor-intensive. Rapid advances in electronic technologies have made a variety of inexpensive sensing, monitoring, and control capabilities available. A monitoring system was developed and evaluated for automatic measurement of liquid levels, and demonstrated by monitoring water levels in evaporation pans used in evaporation studies and irrigation scheduling. The system is composed of an ultrasonic sensor, a microcontroller-based data logger, and a temperature sensor. The ultrasonic sensor measures the distance from the sensor to the liquid surface. Air temperature is measured by the temperature sensor, and is used to compensate for changes in the speed of sound due to air-temperature variations to improve accuracy of ultrasonic distance measurements. The datalogger is programmed to take measurements and to store data on a memory card which can be downloaded for processing and analysis. All components of the system were assembled in a PVC housing. The system was tested in the field, and resulted in water levels measured by the system corresponding very closely to those measured manually (R2 > 0.98). This system is inexpensive, with total cost of US$85, and easy to build, install, and maintain. In addition to monitoring liquid levels, the system could be adapted to a variety of other measurements. Keywords: Ultrasonic sensor, liquid level, microcontroller, open-source hardware, datalogger, USA
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