Impact of response characteristics of an agricultural sprayer control system on nozzle flow stabilization under simulated field scenarios

• Published in: Computers and electronics in agriculture 2015-03, Vol.112, p.139-148
• Main Authors: Sharda, A., Fulton, J.P., McDonald, T.P.
• Format: Article
• Language: English
• Subjects: Computer simulation; Control systems; Controllers; Distribution; Ground speed; Liquid application; Precision agriculture; Pressure; Simulation; Sprayers; Sprays; Stabilization; Valves; Variable rate application
• ISSN: 0168-1699; 1872-7107
• DOI: 10.1016/j.compag.2014.11.001

•Practice of programming one VCN would not provide optimum nozzle flow response.•Greater application errors for scenarios involving sprayer acceleration and deceleration.•Operator behavior impacted response and application errors during speed changes.•Brake point digit exhibited greater impact in reducing stabilization time.•Future controllers need robust control algorithms to auto-selection of VCN. Rate controllers with automatic section control (ASC) capabilities represent sprayer technology used to not only regulate application flow rate to compensate for variations ground speed and target rate but also change in spray width. Ideally, ASC should maintain precise control to ensure uniform application, but the precision of that control is limited by the speed at which the controller can respond to variations in those conditions. The response characteristic of the controller is normally a selectable feature using a value programmed by the user, often called a valve control number (VCN). The choice of a VCN for a given spray system is a compromise between selecting a high rate of response to rapidly varying conditions and potential oscillations in output flow rate that might be induced. Both types of errors result in off-rate application. The objective of this study was to investigate the magnitude of off-rate errors caused by a range of VCN choices for simulated field conditions. Nine valve calibration numbers (VCNs) were selected for five simulated but common field operating scenarios. Simulations were conducted using a LabVIEW program to send predetermined navigation (GPS NMEA strings) and control commands to specify ground speed and boom-section actuation status to the rate controller. Variations in flow rate during simulations were measured using nozzle pressure transducers mounted across the spray boom. Results indicated manufacturer-recommended selections for the VCN (743) were not optimal and using alternate values reduced flow stabilization times in response to simulated changes in ground speed by up to one third (VCN 313). Brake point reduced nozzle flow stabilization time to a higher degree than the valve speed. The largest errors were observed when the sprayer was undergoing simulated acceleration or deceleration plus experiencing a change in nozzle actuation, emphasizing the relationship between operator driving choices and overall application errors. These results suggested using a single VCN in all operating conditions would not be appropriat