title: Closed-Loop Control of Chemical Injection Rate for a 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 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.
authors.affiliation: School of Information Science and Technology, Beijing Forestry University, Beijing 100083, China. caixiang617@gmail.com.
authors.forename: Xiang
authors.initials: X
authors.lastname: Cai
authors.affiliation: Department of Agricultural Engineering, University of Bonn, 53115 Bonn, Germany. martin_walgenbach@t-online.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Walgenbach
authors.affiliation: Department of Agricultural Engineering, University of Bonn, 53115 Bonn, Germany. malte@uni-bonn.de.
authors.forename: Malte
authors.initials: M
authors.lastname: Doerpmond
authors.affiliation: Department of Agricultural Engineering, University of Bonn, 53115 Bonn, Germany. lammers@uni-bonn.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Schulze Lammers
authors.affiliation: College of Information &amp; Electrical Engineering, China Agricultural University, Beijing 100083, China. pal@cau.edu.cn.
authors.forename: Yurui
authors.initials: Y
authors.lastname: Sun
mesh_terms: D000383:Agriculture / Q000295:instrumentation* / Q000379:methods*; D016573:Agrochemicals; D004738:Engineering / Q000295:instrumentation*; D004867:Equipment Design; D010575:Pesticides; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D016573:Agrochemicals; D010575:Pesticides
keywords: closed-loop control; direct nozzle injection; pulse width modulation; thermodynamic flowmeter; variable-rate application