Development of Digital Flow Control System for Multi-Channel Variable-Rate Sprayers

Abstract. Precision modulation of nozzle flow rates is a critical step for variable-rate spray applications in orchards and ornamental nurseries. An automatic flow rate control system activated with microprocessors and pulse width modulation (PWM) controlled solenoid valves was developed to control flow rates of multi-channel nozzles independently for variable-rate sprayers. The system consists of a data acquisition module, a data processing module, and a flow rate control module. An embedded computer along with a touch screen was used to process control algorithms and allowed communication between the sprayer operator and the control system. The flow rate control module was designed with multi-channel driver circuits for activating the solenoid valves and driver protection circuits for avoiding surge voltages due to frequent on/off actions of the solenoid valves. Laboratory tests were conducted to verify the accuracy of the control system with three nozzles (0.530 to 1.703 L min^-1) at four different operating pressures (138 to 345 kPa) and ten duty cycles (10% to 100%). The microcontroller-controlled circuit precisely produced PWM signals with desired pulse widths to match the duty cycles, and linear spray outputs were achieved accurately with the duty cycles of the PWM-controlled solenoid valves. With the protection circuit for the solenoid valve drivers, the longevity of the solenoid valves increased from 350 to 2,426 h. The system offers flexibility in choosing the number of connection channels needed for the number of nozzles individually or in a group on sprayers. Accordingly, together with canopy structures and travel speeds from laser scanning or other sensors, this compact control system is capable of performing variable flow rate functions for multiple nozzles separately.