Laboratory Tests on Longitudinal Distribution by Using Pulse Width Modulation

Pulse width modulation is asystem to adjust the flow rate of field sprayers by pulsing an electronically-actuated solenoid valve with afrequency of 10 to 20Hz. In comparison to apressure controlled flow rate pulse width modulated nozzles create aconstant droplet size spectrum as well as auniform spray pattern. However, from the theoretical point of view it is expected that pulsing impacts the longitudinal uniformity of the spray pattern. The objective of this study was to evaluate the longitudinal uniformity with apulsing frequency of 10Hz at different travel speeds and duty cycles under controlled conditions in atest application laboratory.Analysis of spray patterns was carried out by using water sensitive paper and optical recording. The evaluation showed that pulse width modulation caused an irregular spray distribution with an undulated concentrated spray depending on travel speed and cycle duty. Pulsed nozzles showed high variation coefficient values as compared to unpulsed nozzles and this supported the visual experience. However, no impact was found in field trials using apostemergence contact herbicide and the application showed auniform impact on weeds. Moreover, under controlled conditions high frequencies of 20Hz indicated an even spray distribution with variation coeffient values of less than 10%. The investigations suggest that pulse width modulation is auseful system for an even spray distribution, flow rate regulation and aconsistent droplet size spectrum.