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Sensors 2016, 16(1), 127; doi:10.3390/s16010127

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

1
School of Information Science and Technology, Beijing Forestry University, Beijing 100083, China
2
Department of Agricultural Engineering, University of Bonn, 53115 Bonn, Germany
3
College of Information & Electrical Engineering, China Agricultural University, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Academic Editor: Vittorio M. N. Passaro
Received: 19 October 2015 / Revised: 2 January 2016 / Accepted: 14 January 2016 / Published: 20 January 2016
(This article belongs to the Section Physical Sensors)
View Full-Text   |   Download PDF [2671 KB, uploaded 20 January 2016]   |  

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. View Full-Text
Keywords: variable-rate application; closed-loop control; pulse width modulation; direct nozzle injection; thermodynamic flowmeter variable-rate application; closed-loop control; pulse width modulation; direct nozzle injection; thermodynamic flowmeter
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Cai, X.; Walgenbach, M.; Doerpmond, M.; Schulze Lammers, P.; Sun, Y. Closed-Loop Control of Chemical Injection Rate for a Direct Nozzle Injection System. Sensors 2016, 16, 127.

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