Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Highlights

PWM valves were tested for accurate modulation of hollow-cone nozzle flowrates up to 40 Hz PWM frequency.

Abstract. Pulse width modulation (PWM) solenoid valves are a critical component of precision sprayers equipped with crop detection sensors to achieve accurate variable-rate applications of pesticide in real time. However, the slow speed of PWM valves can impede the efficiency of high-speed detection sensors. Based on previous investigations of 12 commercially available PWM valves operated up to 50 Hz frequencies, two of the valves with the highest modulation capability were selected for continuous investigations on their flow rate modulation accuracy and pressure stability for hollow-cone nozzles. Tests were conducted with two different-sized hollow-cone nozzles controlled by each PWM valve. Variables included 4 modulation frequencies ranging from 10 to 40 Hz, 6 duty cycles (DUCs) from 10% to 100%, and 3 operating pressures (1034, 1380, and 2068 kPa). Flow rates were measured by instantaneously weighing the mass of water discharged from nozzles while pressure profiles were measured with two pressure transducers located upstream and downstream the PWM valve. In general, both PWM valves were able to modulate flow rates of the two hollow-cone nozzles up to 40 Hz modulation frequencies with limited DUC ranges even though one valve performed slightly better than the other. When the nozzles were manipulated functionally with assigned DUCs and frequencies, the flow rate modulation errors of PWM valves ranged between 0% and 35%, while the average root mean square errors (RMSEs) ranged between 6.9% and 14.7% for combinations of all pressures, frequencies, and DUCs tested. Thus, there would be potential benefits to integrating these two high-frequency PWM valves into precision orchard sprayers operated at high pressures to further improve the variable-rate application accuracy.