Nozzle pressure uniformity and expected droplet size of a pulse width modulation (PWM) spray technology

Abstract

Pulse width modulation (PWM) is currently implemented in agricultural sprayers to deliver the expected flowrate by managing the duty cycle and maintaining the target pressure and provide the desired droplet size. However, there are still issues about the application errors caused by the pressure variations when using this system as it may result in pesticide resistance and product loss. Field tests were conducted in a 30.0 ha (ha) and 54.0 ha fields to assess the pressure uniformity and the expected droplet size of the PWM technology. These parameters were also translated to an equivalent value if a flow-based system will be used during operation.Results showed that pressure mostly remained within the acceptable range in both fields. Pressure CV were within 10.0%, indicating the system's ability to provide acceptable pressure at varying conditions. However, nozzle pressure still varies, especially at the outer boom section where frequent duty cycle variation occurs. Pressure also deviates during acceleration and deceleration, indicating the system's latency to respond rapidly on changing conditions. In a flow-based system, the pressure varies due to varying speed as dictated by field terrain, curvilinear paths, and headland maneuvers. The droplet size also deviates from the expected droplet spectra based on the nozzle manufacturer’s specification when using a PWM system. However, the PWM system can still provide the target droplet size if a nozzle selected provides the desired droplet spectra in a wide range of pressure. In a flow-based system, the droplet size was expected to vary because of the fluctuation in application pressure due to speed changes during operation.