Submitted to: Agricultural Engineering International: CIGR Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2013
Publication Date: 12/30/2013
Citation: Fisher, D.K., Sui, R. 2013. An inexpensive open-source ultrasonic sensing system for monitoring fluid levels. Agricultural Engineering International: CIGR Journal. 15(4):328-334.
Interpretive Summary: Liquid levels are measured in a variety of agricultural applications. Evaporation pans, for example, are used in evaporation studies and for irrigation scheduling, with changes in water level related to environmental demand and water use of crops. Water levels are often measured manually, however, which can be time-consuming and labor-intensive, often resulting in infrequent measurements being taken. Agricultural engineers in the USDA ARS's Crop Production Systems Research Unit at Stoneville, MS developed an inexpensive monitoring system consisting of open-source hardware and software components to automatically and continuously measure and store water-level information. Field testing of the system showed that water levels measured with the automated system corresponded very closely to those measured manually. This inexpensive ($85) system was easy to build, install, and maintain, and provides information much more frequently and reliably than could be obtained manually. The results of this effort show that open-source hardware can be used to develop inexpensive monitoring devices, not only for monitoring evaporation pans, but which could also be implemented or adapted to a variety of other measurements.
Technical Abstract: Fluid 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 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 distance from the sensor to the fluid 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 so that the accuracy of ultrasonic distance measurements can be assured. The datalogger is programmed to take measurements and store the 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 approximately $85, and easy to build, install, and maintain. In addition to monitoring fluid levels, the system could be adapted to a variety of other measurements.