Abstract
To realize site-specific and variable-rate application of agricultural pesticides, accurately metering and controlling the chemical injection rate is necessary. This study presents a prototype of a direct nozzle injection system (DNIS) by which chemical concentration transport lag was greatly reduced. In this system, a rapid-reacting solenoid valve (RRV) was utilized for injecting chemicals, driven by a pulse-width modulation (PWM) signal at 100 Hz, so with varying pulse width the chemical injection rate could be adjusted. Meanwhile, a closed-loop control strategy, proportional-integral-derivative (PID) method, was applied for metering and stabilizing the chemical injection rate. In order to measure chemical flow rates and input them into the controller as a feedback in real-time, a thermodynamic flowmeter that was independent of chemical viscosity was used. Laboratory tests were conducted to assess the performance of DNIS and PID control strategy. Due to the nonlinear input–output characteristics of the RRV, a two-phase PID control process obtained better effects as compared with single PID control strategy. Test results also indicated that the set-point chemical flow rate could be achieved within less than 4 s, and the output stability was improved compared to the case without control strategy.
Highlights
Previous studies have pointed out that there are advantages to realizing site-specific and variable-rate application of pesticides [1,2,3]
Chemical application rates can only be varied by changing the liquid delivery pressure, but the pressure changes unexpectedly affect the droplet size spectra and spray distribution pattern of the nozzles [4]
The delivery pressure of carrier stream is maintained at the same level, as are the pressure at the nozzles, the droplet size spectrum and the spray distribution pattern [5]
Summary
Previous studies have pointed out that there are advantages to realizing site-specific and variable-rate application of pesticides [1,2,3]. Over-application of chemicals increases the cost of crop production, and increases the risk of environmental contamination and the exposure hazards to operators. Insufficient application of chemical may cause a decrease of crop yield, or make the weeds chemical-resistant. Chemical application rates can only be varied by changing the liquid delivery pressure, but the pressure changes unexpectedly affect the droplet size spectra and spray distribution pattern of the nozzles [4]. The delivery pressure of carrier stream is maintained at the same level, as are the pressure at the nozzles, the droplet size spectrum and the spray distribution pattern [5]
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