Author
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Smith, Lowrey |
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Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/1/2001 Publication Date: 7/1/2001 Citation: Smith, L.A. 2001. Autocal automatic flow controllers for aerial application. Applied Engineering in Agriculture. 17(4):449-455. Interpretive Summary: Automatic flow controllers use Global Positioning (GPS) data to compute the airplane's ground speed and then use the swath width (provided by the pilot before takeoff) to compute the correct flow rate to be delivered to the spray boom. This required flowrate is then compared to the actual flow rate from a flowrate sensor to evaluate the application error. If flow adjustment is required, the controller automatically adjusts a valve to achieve the required flow to the boom. These calculations and adjustments are performed multiple times per second to maintain the correct application rate as the plane's ground speed varies. Performance tests on the controller demonstrated that the AutoCal automatic flow controller was capable of maintaining accurate control of flowrate while performing aerial application jobs. During application runs, the flowrate was corrected more than two times per second in order to track changing flow requirements due to changing ground speed. Average measured error varied from 0.64% to 1.60% as application rate varied from 9.4 L/ha to 88.9 L/ha while spraying 12.9 ha using 10 spray passes. Speed variation while making individual spray runs during this test ranged from 4.8 km/h to 33 km/h. Volume error for each flowrate-adjustment interval was computed for each spray run. The controller required less than 0.5 s to reduce the cumulative error for the run to less than 37% of its initial value. Technical Abstract: The AutoCal I and AutoCal II automatic flow controllers, marketed by Auto Control, Inc. of Houma, LA, were evaluated using test protocols that included a range of application rates and "real world" applications on large areas. Both units were effective in maintaining accurate control of flowrate while performing aerial applications jobs. The primary difference between the two controllers was that the AutoCal I controlled flow directly by adjusting the boom valve and the AutoCal II controlled the flowrate indirectly by adjusting a bypass valve located between the pump outlet and inlet. The AutoCal I had a maximum error of 1.55% while applying 37.4 L/ha (4 gal/acre) under controlled conditions. Experimental error in neither system was significantly affected by application rate. Theoretical error, expressed as the area between the required flowrate and actual flowrate curves, tended to increase with the number of spray runs used to spray a field. Theoretical error was 0.79% for five spray passes and increased to 3.2% for 20 spray passes. Experimental errors for the AutoCal II flow controller varied from 0.64% to 1.60% while making applications using rates that ranged from 9.4 L/ha to 88.9 L/ha (1 gal/acre - 9.5 gal/acre). Controller response was compared using the decay of cumulative remaining error for each spray run. The resulting time constants indicated that the controllers reduced remaining error to less than 37% of its initial value in less than 0.5 s. |
