Nozzle Flow Rate, Pressure Drop, and Response Time of Pulse Width Modulation (PWM) Nozzle Control Systems

Highlights Nozzle pressure drop varies between PWM systems at different application rates and application pressures. Change in flow rate with respect to the expected flow differs between PWM systems at different rates and pressures. There was a latency before the system reached the target application pressure. PWM systems operate at less time than the specified duty cycle which may cause application errors. Abstract. Three PWM nozzle control systems, Capstan PinPoint II, John Deere ExactApply, and Raven Hawkeye, referred to as S1, S2, and S3, were used in this study. Data on nozzle pressure, boom pressure, flow rate, and response time were recorded under different duty cycles (25%, 50%, 75%, and 100%) and operating frequencies (10 Hz, 15 Hz, and 30 Hz) for different application rates (112.2 L ha-1 and (187.1 L ha-1) and application pressures (275.8 kPa and 448.2 kPa) at 1kHz using a LabVIEW program and a cRIO data acquisition system. Results indicated that the PWM systems perform differently when operating at various application rates, pressures, duty cycles, and system frequencies. Each PWM system provided a different pressure drop at the nozzle during operation. The increase in application rate and target pressure increased pressure drop. The percent change in flow rate with respect to the expected flow was also significantly different between the PWM systems, which could be due to the differences in pressure provided at the nozzle during operation. The PWM systems also showed latency before reaching the target application pressure during operation and operated at less time than the specified duty cycle at stable target pressure while also continued to spray even after the solenoid valves were closed. The application pressure during peak and fall time and time of stable application pressure within a cycle should be given careful consideration when selecting a PWM system, as they can contribute to product application errors. Operators should also consider the pressure drop both with the selected PWM system and target application rates to set-up the system to apply at the desired pressure. The manufacturers mostly recommend operating the PWM system at 10 Hz system frequency. But for the purpose of this study, the system frequency of each PWM system was varied to 10 Hz and 15 Hz for S1, 15 Hz and 30 Hz for S2, and 10 Hz, 15Hz, and 30 Hz for S3. Producers should expect a difference in pressure drop, stabilized pressure application time, and flow rate if they opted to operate at a higher frequency. The results of this study were only applicable to the type of nozzle bodies and nozzle tips used. The data will differ based on the dual orifice valve coefficient equation. The larger the second orifice, the more the pressure drop. This will affect the final orifice pressure, as well as the flow rate. This study did not address the impact of flow resistance caused by the differences in the design of nozzle bodies and nozzle types.