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Development of digital flow control system for multi-channel variable-rate sprayers
- H. Liu, H. Zhu, Y. Shen, Y. Chen, H. E. Ozkan
- Transactions of the ASABE 2014 v.57 no.1 pp. 273-281
- algorithms, automation, canopy, foliar spraying, laboratory techniques, microprocessors, nozzles, process control, sprayers, valves (equipment), variable rate application
- 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 consisted 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 communications between sprayer operators and the control system. The flow rate control module was designed with multi-channel driver circuits for activating solenoid valves and driver protection circuits for avoiding surge voltages due to frequent on/off actions of solenoid valves. Laboratory tests were conducted to verify the control system accuracy with three nozzles (0.530 to 1.703 L min-1) at four different operating pressures (138 to 345 kPa) and 10 duty cycles (10 to 100%). The microcontroller (MCU)-controlled circuit precisely produced PWM signals with desired pulse widths to match the duty cycles, and linear spray outputs were achieved accurately with duty cycles of PWM-controlled solenoid valves. With the protection circuit for solenoid valve drivers, the longevity of solenoid valves increased from 350 to 2,426 hours. The system had flexibility to choose 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 compacted control system was capable of performing variable flow-rate functions for multiple nozzles separately.