ASABE Technical Library - Abstract

Abstract. Chemical application is an integral part of crop care replacing mechanical operations. Applications usually occur multiple times to address crop stress from weed competition, fungus, nutrient deficiency, and neighboring crop. Today, advanced sprayers automatically control individual sections and nozzles to accommodate increased machine size and travel speeds. Yet, automatic control raise concerns for flow based systems regarding coverage accuracy and uniformity during speed changes. New commercial systems apply product at constant pressure using varied duty cycles of Pulse Width Modulated (PWM) solenoids to maintain a constant application rate. However, concerns exist in terms of dynamic spray coverage. This study combined a full-system audit and high speed imagery to study the dynamic effect of solenoid On/Off latency on spray fan pattern and product distribution. Study objectives were to investigate the On/Off time latency in PWM nozzles, determine if active nozzles affect spray fan pattern latency, and develop flow characteristics to simulate dynamic spray coverage.

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A PWM system along with rate controller was installed on a 21.5 ft boom-section sprayer with 13 nozzles. A Raven Viper 4 system regulates sprayer system pressure and flow while the Capstan Pinpoint™ controller controls the system pressure and active nozzle configuration while adjusting the duty cycle. Results indicate the pressure latency remained constant regardless of active nozzles. On/off-time latency was found to be 20 ms to reach system pressure after energizing and de-energizing a nozzle solenoid. However, after de-energizing a nozzle solenoid, the nozzle continued spraying at system pressure for 10 ms. Static spray fan pattern deposit prove the system applies the correct rate per pulse; however, on/off-time latency create varying coverage as quantified in the dynamic simulation. As found with high-speed images, deposit time was consistently found to be 65 ms from when the nozzle solenoid is energized with an average droplet speed of 467 in/s. Fast travel speed result in a higher duty cycle and longer on-time with increased coverage efficiency. To conclude, PWM spray systems apply an accurate amount of flow per pulse regardless of active nozzles with uniform coverage occurring from higher duty cycles.