Nozzle flowrate modulation capability of PWM valves operated at high frequencies and pressures

Authors: CAMPOS, JAVIER - The Ohio State University; Zhu, Heping; Jeon, Hongyoung; ROMAN, CARLA - The Ohio State University; SALCEDO, RAMON - The Ohio State University; OZKAN, ERDAL - The Ohio State University; GIL, EMILIO - The Ohio State University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2024
Publication Date: 2/1/2025
Citation: Campos, J., Zhu, H., Jeon, H., Roman, C., Salcedo, R., Ozkan, E., Gil, E. 2025. Nozzle flowrate modulation capability of PWM valves operated at high frequencies and pressures. Journal of the ASABE. 67(6): 1521-1532. https://doi.org/10.13031/ja.16128.
DOI: https://doi.org/10.13031/ja.16128

Interpretive Summary: Laser-guided intelligent spray technology has been developed and rapidly adopted by specialty crop growers to significantly reduce pesticide waste, increase production profitability, and safeguard the environment. However, the technology still needs improvements to increase its precision capability. This is because mechanical actions of existing key components cannot catch up with the laser sensor detection speed. In this research, two high-speed solenoid valves were investigated for their accuracy to modulate flow rates of nozzles commonly used in intelligent orchard sprayers. Test results demonstrated that these valves could improve the spray application accuracy and efficiency possibly by up to 4 times if they could be successfully integrated into the variable-rate orchard sprayers. Thus, this research has provided promising information for future design of mechanical components that can be used in precision sprayers to further minimize pesticide use.

Technical Abstract: Pulse width modulation (PWM) solenoid valves are a critical component of precision sprayers equipped with crop detection sensors to achieve variable-rate applications of pesticides in real-time. However, the slow speed of PWM valves may impede the potential of the high-speed sensors to further improve the application accuracy. Based on previous investigations of 12 commercially available PWM valves operated up to 50 Hz frequencies, two PWM 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 with 10-Hz intervals, 6 duty cycles (DUCs) (10, 30, 50, 70, 90, and 100%), and 3 operating pressures (1034, 1380, and 2068 kPa). Flow rates were measured by instantaneously weighing the mass of water discharged from nozzles, and pressure profiles were measured with two pressure transducers located upstream and downstream the PWM valve. Flow rates of nozzles modulated with both valves increased linearly as DUC increased. 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 all pressures, frequencies, and DUCs tested. In general, both PWM valves had comparable accuracy to modulate flow rates of the two hollow-cone nozzles operated at 1034, 1380, and 2068 kPa pressures. Thus, there would be potential benefits to integrate these two high-frequency PWM valves into precision orchard sprayers operated at high pressures to further improve the variable-rate application accuracy and efficiency.