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Title: Spray outputs from a variable-rate sprayer manipulated with PWM solenoid valves

item SILVA, J - Federal University - Brazil
item Zhu, Heping
item CUNHA, J.P.A.R. - Federal University - Brazil

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2018
Publication Date: 6/10/2018
Citation: Silva, J.E., Zhu, H., Cunha, J. 2018. Spray outputs from a variable-rate sprayer manipulated with PWM solenoid valves. Applied Engineering in Agriculture. 34(3):527-534.

Interpretive Summary: Successful use of precision pesticide sprayers is of great importance to ensure a bountiful and high quality of plant products in crop production. Development of variable-rate sprayers capable of delivering variable amounts of pesticide to match crop structures has gained great attentions recently. To achieve variable spray rates, nozzles used on sprayers are manipulated by pulse-width-modulated solenoid valves. However, flow rates of these nozzles vary with operating pressures when the sprayers are discharging variable outputs. In this research, variations in the total flow rate of multiple solenoid valve controlled nozzles were quantitatively determined, and two-variable linear regression equations for the total flow rate with number of active nozzles were established to predict spray outputs under varied and constant pressure conditions. Consequently, this information will be used to develop a feedback control system for future intelligent sprayers to further improve their chemical delivery accuracy.

Technical Abstract: Pressure fluctuations during variable-rate spray applications can affect nozzle flow rate fluctuations, resulting in spray outputs that do not coincide with the prescribed canopy structure volume. Variations in total flow rate discharged from 40 nozzles, each coupled with a pulse-width-modulated (PWM) solenoid valve, were determined for a variable-rate sprayer. Variables for the total flow rate measurements were number of active nozzles ranging from 1 to 40 and PWM duty cycle ranging from 10% to 100%. Experiments were conducted under varied and constant operating pressure conditions. Under the varied pressure condition, the operating pressure in the spray line was not adjusted when either the number of active nozzles or PWM duty cycle was changed. Under constant pressure condition, the operating pressure was maintained at 242 kPa. The total flow rate increased as duty cycle and/or number of active nozzles increased under both pressure conditions. However, the operating pressure in the spray line dropped considerably as either the number of active nozzles or duty cycle increased under the varied pressure condition, resulting in significant lower total flow rates compared to the constant pressure condition. The differences in total flow rates between the two pressure conditions increased as duty cycle and number of active nozzles increased. To improve future intelligent sprayer accuracy, two-variable regression equations were established to predict and control total flow rates with different duty cycles and numbers of active nozzles operated simultaneously.