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Pivotrac Application Georgia Approximately 200 groundwater-supplied irrigation systems were selected for monitoring. Iniation and stop times for irrigation pumping had to be recorded for our deliverables to USGS. Jerry Abts of Pivotrac, Inc., Denver, Colorado, was awarded a contract to install and maintain monitoring units on irrigation systems chosen and calibrated by our UGA Ag Water Pumping team. Pivotrac adapted their trademark Pivotrac unit and made other modifications to supply data to us in an automatically updated database of observations.
In it's earlier deployment, particularly in the Midwest and Texas, Pivotrac units used broad-spectrum radios to communicate from center pivots to base stations and pivot operators. Each unit recorded specific events - pivot power up or down, pivot wheels engaged or disengaged, and water pressure rising above or falling below preset limits that indicated normal operation. At any change in event, pivot operators were notified by pagers, and they could determine if the events were expected, or were a sign of power or other systems failure. Operators could also view a secure website to examine status of all of their systems and get reports of seasonal activity.
In our Dougherty Plain, Georgia, deployment, Pivotrac determined that the level topography and pine trees in close proximity to fields would interfere excessively with broadband communications. The manufacturer of the units, Automata, Inc., Nevada City, Ca, modified these for communication by analog cell signal using the carrier signal used to locate cell phones. Because of cell communication provider and FCC rules, the units were modified to limit communications to 17 or fewer calls per day. This would prevent a malfunctioning unit from taking excessive bandwidth. Each brief carrier signal was time-tagged by the cell communication company, and it was then forwarded by internet to computers in Colorado, California, and Tifton, Georgia. Both text file and Access database entries were made for each event. Multiple locations as well as multiple data forms provided backup, and allowed Automata and Pivotrac to monitor performance and make corrections.
Typical installations on pivots
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Typical installations on pivots
Installations For selected systems, the irrigation system, most often a center pivot, was run under full operating conditions, and flow rates were measured closely using a strap-on sonic device. Calibrated flow was used in subsequent calculations of withdrawal rates during pressurized operation.
Pivotrac remote transmitting units (RTUs) were attached onto the pivot panel door or sometimes on an added metal plate mounted on the tower. Magnets held the unit in place. Power, 120 VAC, for the unit was supplied from the panel's supply to a power regulating AD converter that maintained a 12 VDC lead-acid battery. Both data logger and radio were powered from that. Connections to one leg of the pivot's drive power were made to detect when systems had been engaged. A air/water flexible tubing was connected from a port on the irrigation system main pipe to a pressure gauge/switch in the RTU. That switch triggered pressure on/off events. An external antenna was added to the RTU's and the unit programmed to communicate with the nearest tower.
As operated in 2001-2003, RTU's initiated an internal clock for each functioning, accumulating minutes that the power or pressure was engaged. After 5 minutes (initially) had elapsed following a change of state for power, movement, or pressure, a status report was transmitted providing the status of all the switches, as well as the timer accumulator value, and a value indicating the delay time. The delay prevented frequent attempts to communicate as pressure reached and fluctuated around the trigger pressure before finally reaching its full operating pressure. Subsequent changes in state were delayed for progressively longer periods, up to 4 hours to minimize communications. With delay time known, it was possible to always determine the time of change in state that triggered an event. While all of the data were transmitted, we primarily used time of pressurized flow start and stop. If the RTU was powered continuously, it would also report a once-per day "heartbeat" providing the switch status and accumulated pumping time.
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