Closed-Loop Control of Chemical Injection Rate for a Direct Nozzle Injection System

Sensors (Basel). 2016 Jan 20;16(1):127. doi: 10.3390/s16010127.

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.

Keywords: closed-loop control; direct nozzle injection; pulse width modulation; thermodynamic flowmeter; variable-rate application.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agriculture / instrumentation*
  • Agriculture / methods*
  • Agrochemicals*
  • Engineering / instrumentation*
  • Equipment Design
  • Pesticides*
  • Thermodynamics
  • Viscosity

Substances

  • Agrochemicals
  • Pesticides