Control Methods of Direct Nozzle Injection System

Abstract:

To realize sitespecific and variablerate application of agricultural pesticides, accurately metering and controlling the chemical injection rate is necessary. This study presented a prototype of direct nozzle injection system (DNIS) based on which method of controlling chemical injection rate was studied. In this DNIS, a rapidreacting solenoid valve (RRV) was utilized for injecting chemicals, and it was driven by pulsewidth modulation (PWM) signal at 100Hz, adjusting the chemical injection rate with varying pulse width. A closedloop control strategy based on proportional-integral-derivative (PID) method was applied to meter and stabilize the chemical injection rate. Laboratorial experiments were conducted to assess the performance of RRV, including effect of PWM signal with startup time on pesticide injection, the power consumption of RRV, the input-output characteristics of RRV, and the time elapsed of shutting down pesticide flux completely. The performance of DNIS and PID controller on stabilizing pesticide injecting rate was also evaluated, not only output of flowmeter but also electric conductivity measuring method were employed to indicate the stabilization of pesticide. Test results showed that RRV was capable of precisely metering chemical injection rate. With PID controller, the setpoint chemical flow rate could be achieved within less than 4s, and the stability of chemical flow rate was also improved against without control strategy.