Spray Coverage and Droplet Size Uniformity of Pulse Width Modulation (PWM) Systems at Different Duty Cycles and Frequencies

Highlights Developed a methodology to quantify the spray coverage and droplet size uniformity of the PWM system. Evaluated the PWM systems to quantify the spray coverage and droplet size uniformity at different combinations of frequency and cycle. Abstract. Correct operability and accurate spray coverage are essential to minimize off-target application and mitigate potential environmental and human health concerns in chemical applications. PWM control system can provide a uniform application pressure during operation to maintain the target application rate and droplet size. However, little knowledge exists on the impact of PWM system frequency on spray coverage uniformity. Therefore, this study was conducted to (1) develop a methodology to quantify spray coverage from a self-propelled agricultural sprayer utilizing PWM systems during field operation and (2) quantify the spray coverage, droplet size, and their uniformities when using sprayers with PWM systems operating at different frequencies. John Deere ExactApply TM system (PWM1) and Case IH AIM Command FLEX II TM system (PWM2) were operated at the frequencies of 15, 30, and 10 Hz and 15, 20, and 30 Hz, respectively, and at 35%, 50%, and 75% duty cycles. Both sprayers have the same nozzle spacing of 0.51 m and boom height of 0.61 m above the target, thereby providing similar operating speeds for all selected duty cycles. The pressure and application rate for both systems were set at 276 kPa and 10 Lha -1 , respectively. After spraying, the water-sensitive cards (WSCs) were collected and then scanned at 600 dpi. The scanned WSCs were processed using a custom MATLAB program to assess the spray coverage and droplet size uniformity. The results showed that spray coverage uniformity from each PWM system varied with different frequencies and duty cycle combinations. The coverage uniformity results indicated that producers might consider implementing a 30 Hz frequency for the PWM1 system in order to achieve greater spray coverage area (20.0%) and higher spray coverage and droplet size uniformity (95.0%). For the PWM2 system, the producer might consider a 20 Hz frequency for greater spray coverage area (17.0%). There was no significant difference between spray coverage uniformity, droplet size and droplet size uniformity when operating the PWM2 system at 20 and 30 Hz. Overall, the results exhibited that greater spray coverage and droplet size uniformity could be achieved when PWM spray systems were operated at frequencies greater than 20 Hz. Keywords: Droplet size uniformity, Pulse width modulation system (PWM), Spray coverage uniformity.