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

Abstract

HighlightsNozzle 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 for 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 systems S1, S2, and S3, respectively, were used in this study. Data on nozzle pressure, boom pressure, flow rate, and response time were recorded with different duty cycles (25%, 50%, 75%, and 100%) and operating frequencies (10, 15, and 30 Hz) for two application rates (112.2 and 187.1 L ha-1) and two application pressures (275.8 and 448.2 kPa) at 1 kHz using a LabVIEW program and a cRIO data acquisition system. Results indicated that the PWM systems perform differently when operating at different application rates, pressures, duty cycles, and frequencies. Each PWM system provided a different pressure drop at the nozzle during operation. The increase in application rate and pressure increased the 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 for less time than the specified duty cycle at stable target pressure while also continuing to spray even after the solenoid valves had closed. The application pressure during peak and fall times and the time of stable application pressure within a cycle should be given careful consideration when selecting a PWM system, as they can contribute to application errors. Producers should also consider the pressure drop with the selected PWM system and target application rate to set up the system to apply at the desired pressure. Manufacturers mostly recommend operating PWM systems at 10 Hz. For the purpose of this study, the operating frequency of the PWM systems was set to 10 and 15 Hz for S1, to 15 and 30 Hz for S2, and to 10, 15, and 30 Hz for S3. Producers should expect differences in pressure drop, stabilized pressure application time, and flow rate if they choose to operate at a higher frequency. The results of this study are only applicable to the types 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 greater 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 differences in the design of nozzle bodies and nozzle types. Keywords: Nozzle flow rate, Pressure drop, Pulse width modulation control modules, Response time.

Vibration Analysis of Pulse-Width-Modulated Nozzles in Vineyard Blast Sprayers

“…The modification of the duty cycle was related to the hydraulic shock derived from closing the valves suddenly at high frequency, which often resulted in the undesired effect of rising the system pressure. These results confirm those found by other authors finding differences between the rated duty cycles and the actual duty cycles applied [21][22][23]. The principal reason to introduce PWM solenoid valves in individual nozzles is the accurate variation of flow in real time without altering the system pressure, as a result of fast valve movements derived from high frequency actuation and the advantages of operating PWM valves from computers.…”

“…In a different study, ref. [22] addressed three different PWM nozzle control systems and found significant differences among the three systems in pressure drops, stabilized pressure application time, and flow rate, confirming that PWM systems can deliver incorrect flow rates caused by variations in the control time cycle determined by peak time, stabilized application pressure time, and fall time. Similarly, ref.…”

Key Technologies for an Orchard Variable-Rate Sprayer: Current Status and Future Prospects

“…Moreover, it had a quick response time and high accuracy. However, droplet sizes were inconsistent at low duty cycles under low operating pressures [8,61,[69][70][71][72]. Butts et al [69] recommended that the PWM sprayer should only be equipped with non-venturi nozzles and operate at a pressure of not less than 276 kPa and a duty cycle of not less than 40% to ensure proper spray performance.…”

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“…However, they recommended using water-sensitive cards to further evaluate the actual droplet size distribution. The same research team [20] studied three different PWM nozzle control systems and recorded nozzle pressure, boom pressure, flow rate and response time for different duty cycles. Significant differences were found between the three systems in pressure drop, stabilized pressure application time and flow rate.…”