Spray Coverage and Droplet Size Uniformity of Pulse Width Modulation (PWM) Systems at Different Duty Cycles and Frequencies

The pulse width modulation (PWM) spray system is the most advanced technology to obtain variable rate spray application without varying the operative sprayer parameters (e.g. spray pressure, nozzle size). According to the precision agriculture principles, PWM is the prime technology that allows to spray the required amount where needed without varying the droplet size spectra which benefits both the uniformity of spray quality and the spray drift reduction. However, some concerns related to the effect of on–off solenoid valves and the alternating on/off action of adjacent nozzles on final uneven spray coverage (SC) have arisen. Further evaluations of PWM systems used for spraying 3D crops under field conditions are welcomed. A tower-shaped airblast sprayer equipped with a PWM was tested in a vineyard. Twelve configurations, combining duty cycles (DC: 30, 50, 70, 100%) and forward speeds (FS: 4, 6, 8 km h−1), were tested. Two methodologies, namely field-standardized and real field conditions, were adopted to evaluate the effect of DC and FS on (1) SC variability (CV%) along both the sprayer travel direction and the vertical spray profile using long water sensitive papers (WSP), and (2) SC uniformity (IU, index value) within the canopy at different depths and heights, respectively. Furthermore, the SC (%) and deposit density (Nst, no stains cm−2), determined using short WSP, were used to evaluate the spray application performances taking into account the spray volumes applied. Under field-controlled conditions, the pulsing of the PWM system affects both the SC variability measured along the sprayer travel direction and along the vertical spray profile. In contrast, under real field conditions, the PWM system does not affect the uniformity of SC measured within the canopy. The relationship between SC and Nst allowed identification of the ranges of 200–250 and 300–370 l ha−1 as the most suitable spray volumes to be applied for insecticide and fungicide plant protection products, respectively.

With recent advances in spray technology and rising interest in site-specific applications, it is imperative to assess the performance of the latest application technologies to ensure effective pesticide applications. Thus, a study was conducted to compare and evaluate the performance of two different flow control systems [rate controller (RC) and pulse width modulation (PWM)] on an agricultural sprayer while simulating different site-specific application scenarios. A custom data acquisition and logging system was developed to record the real-time nozzle flow and pressure across the sprayer boom. The first experiment measured the response time to achieve different target application rates in single-rate site-specific (On/Off) states at varying simulated ground speeds. The second experiment examined the response time for rate transitions in variable-rate application scenarios among different selected target rates at varying simulated ground speeds. Across all the application scenarios, the PWM system consistently outperformed the RC system in terms of response time and rate stabilization. Specifically, the PWM system exhibited significantly lower mean rate stabilization times compared to the RC system during single-rate application states. Similarly, in the variable-rate application states—where the rate transitions were evaluated—the PWM system consistently displayed shorter mean rate transition and stabilization times compared to the RC system. Overall, the findings from this study suggest PWM systems tend to be more responsive and effective, making them the preferred choice for efficient precision site-specific pesticide applications. Future research should evaluate the influence of other operational parameters such as look-ahead time and ground speed variations on the performance of both systems in actual field applications.

HighlightsComparison of PC system and PWM system in-field performance indicated that the PWM system made sensor-based N applications more accurately than the PC system.The turndown ratio calculated from the aggregate application instances was 6.2:1.For both the PWM system and the PC system, applications were made more accurately when 28% UAN was applied rather than 32% UAN. Abstract. Sensor-based nitrogen (N) applications have shown promise for improving N use efficiency, but present significant challenges for application rate control due to highly variable and frequently changing target rates. If applications are to be made precisely, equipment systems used for sensor-based N applications must be designed to meet system demands. Pulse-width modulation (PWM) equipped systems have emerged as a technological advancement over traditional pressure-controlled (PC) systems for improving variable rate N application accuracy. Little research, however, has been done to assess the performance of PWM systems during sensor-based N applications in-field. This work analyzed as-applied data collected from in-field sensor-based N applications with pressure-controlled (PC) and PWM systems in Nebraska between 2015 and 2017 to quantify system requirements, assess system performance, and determine performance impacting operational variables. It was found that systems should be capable of 1-s rate changes of ±71.1 L ha-1 (7.6 gpa), 1-s flow rate changes of ±11.4 L min-1 (3 gpm), and turndown ratios of at least 6:1. PWM systems achieved application rates within 10% of the target rate 10% more often than PC systems, and showed less variability in application error. However, PWM systems still demonstrated significant application errors with an observed RMSE of 44.9 L ha-1 (4.8 gpa). Speed change magnitude was found to be most associated with increases in percent application error. These findings substantiate that PWM systems effectively improve sensor-based N application accuracy versus traditional PC systems. However, collaborative efforts toward greater cohesion between sensor-based application expectations and application equipment capabilities are necessary for maximizing the effectiveness of sensor-based N applications. Keywords: Precision agriculture, Rate controllers, Site-specific crop management, Sprayer, Turndown ratio.

Chemical application is an integral part of crop care. Today, advanced sprayers automatically control individual boom sections and nozzles to accommodate increased machine sizes and travel speeds, yet automatic control of flow-based systems raises concerns regarding coverage accuracy and uniformity during changes in travel speed and spray swath width. New commercial systems apply product at a constant pressure using varied duty cycles of pulse width modulated (PWM) solenoids to maintain a constant application rate. However, concerns exist regarding the dynamic effect of solenoid on/off latency on spray fan pattern and spray coverage. The objectives of this study were to investigate the on/off latency in PWM nozzles, determine if active nozzles affect spray fan pattern latency, and develop flow characteristics to simulate dynamic spray coverage. A PWM system and flow rate controller were installed on a 6.6 m three-section boom sprayer with 13 nozzles. A Raven Viper 4 controller regulated the product flow rate and pressure, while a Capstan Pinpoint controller was used to set the system pressure, nozzle on/off configuration, and duty cycle. The results indicated that the PWM spray system maintained the pressure within ±5% of the target value and applied an accurate amount of flow per pulse regardless of the number of nozzles activated. There was a 20 ms delay in nozzle pressure development during each cycle, and the delay was constant regardless of the number of nozzles activated. After de-energizing the solenoid, the nozzle continued spraying at system pressure for 10 ms. Static spray droplet distribution proved that the system applied the correct volume per pulse. In addition, PWM duty cycles of 100%, 80%, 60%, and 40% provided spray coverage within ±10% of the target rate for 100%, 94%, 77%, and 67% of the time, respectively. Greater signal overlap between odd and even nozzles increased the application coverage. Dynamic spray simulations showed that as-applied application error may vary beyond ±10% of the target rate. As such, while the PWM system provided the desired amount of product per pulse, the spray coverage results indicated that the on-ground coverage could result in areas with under- or over-application.

Droplet size and nozzle tip pressure from a pulse-width modulation sprayer

<b><sc>Abstract.</sc></b> Pulse width modulation (PWM) technology manages the flowrate by varying the duty cycle. However, application errors might still occur while the system manages to maintain the target pressure resulting in pesticide resistance and product loss. Field tests were performed to assess the pressure and droplet size uniformity of the PWM technology. Boom pressure and duty cycle data from selected nozzles across the sprayer boom were recorded using a custom data acquisition system when applying product at a rate of 140.3 l L ha^-1 at 275.8 kPa application pressure (field 1) and 112.2 L ha^-1 application rate at 413.7 kPa application pressure ( field 2). Results showed that the pressure was within ±10% of the target for 84.4% on field 1 and 89.8% on field 2 when using a PWM system. Pressure coefficient of variations were less than 10.0% for 98.0% of the time in both fields. In a flow-based system, the pressure was below ±10.0% of the target for the majority of the time in both fields. The droplet size varies from coarse (73.0%) to medium (27.0%) for field 1 while medium (65.9%) to fine (34.1%) on field 2 when using a PWM system. In a flow-based system, the droplet size was at the coarse category for field 1, while it varies from coarse (24.0%), medium (60.8%) to fine (1.6%) for field 2. The PWM technology may provide an application pressure within the acceptable range thereby providing a better droplet size and application uniformity than a flow-based system.

HighlightsEffectiveness of four nozzle types was evaluated to deliver spray droplets inside soybean canopy in a wind tunnel.Spray deposition at the bottom part of canopies was significantly lower than the upper part across the test section.Nozzles generating medium and coarse droplet sizes improved spray coverage on the top and middle part of the canopy.Abstract. Adequate spray deposition and penetration of pesticides reaching the lower part of soybean canopy can increase the chance of success to protect plants from diseases and insects, especially when soybean foliage is matured. Therefore, selecting the nozzle type with the most appropriate droplet size plays a significant role in providing the right amount of spray deposition to the right place in plant canopy. The objective of this study was to evaluate the most effective spray nozzle and droplet size distribution to achieve more spray coverage within the soybean canopy under a 2 ms-1 wind-tunnel-controlled wind speed at 0.38 m row spacing. An open circuit wind tunnel with laminar airflow was used to avoid the uncontrollable outdoor weather conditions that often vary when similar experiments are conducted in the field. Four commercial spray nozzles (droplet size): XR11004 (medium), TTJ6011004 (coarse), AITTJ6011004 (very coarse), and AI11004 (extremely coarse) were operated at 275 kPa pressure and sprayed for 3 s to increase the spray droplet density to detect their effects in the soybean canopy. Eleven pots of soybean plants were placed in the wind tunnel test section in three rows along the direction of airflow to simulate the 0.38 m soybean row spacing. For each test run, water sensitive papers (WSP) were placed at three different heights of the soybean canopy (top, middle, and bottom) within 5 soybean plants located 0.15, 0.70, 1.25, 1.80, and 2.40 m downwind from the spray boom. After plants were sprayed, WSP samples were collected to determine the spray coverage. The top of the canopy received the greatest amount of spray coverage, followed by the middle position. Regardless of the nozzle and droplet size, significantly lower amounts of spray deposition were found at the bottom part of the canopy at all the sample collection points along the wind tunnel test section. Overall, the nozzles that generated medium and coarse droplet sizes provided higher levels of spray coverage on the top and middle part of the soybean canopy. Providing adequate coverage in the bottom part of the canopy remained a challenge, which must be addressed in future studies to evaluate additional nozzle types with different droplet size classes under different wind speed and row spacing settings. Keywords: Droplet size spectrum, Nozzle type, Soybean plants, Spray coverage, Spray deposition.

Abstract. Chemical application is an integral part of crop care replacing mechanical operations. Applications usually occur multiple times to address crop stress from weed competition, fungus, nutrient deficiency, and neighboring crop. Today, advanced sprayers automatically control individual sections and nozzles to accommodate increased machine size and travel speeds. Yet, automatic control raise concerns for flow based systems regarding coverage accuracy and uniformity during speed changes. New commercial systems apply product at constant pressure using varied duty cycles of Pulse Width Modulated (PWM) solenoids to maintain a constant application rate. However, concerns exist in terms of dynamic spray coverage. This study combined a full-system audit and high speed imagery to study the dynamic effect of solenoid On/Off latency on spray fan pattern and product distribution. Study objectives were to investigate the On/Off time latency in PWM nozzles, determine if active nozzles affect spray fan pattern latency, and develop flow characteristics to simulate dynamic spray coverage. . A PWM system along with rate controller was installed on a 21.5 ft boom-section sprayer with 13 nozzles. A Raven Viper 4 system regulates sprayer system pressure and flow while the Capstan Pinpoint™ controller controls the system pressure and active nozzle configuration while adjusting the duty cycle. Results indicate the pressure latency remained constant regardless of active nozzles. On/off-time latency was found to be 20 ms to reach system pressure after energizing and de-energizing a nozzle solenoid. However, after de-energizing a nozzle solenoid, the nozzle continued spraying at system pressure for 10 ms. Static spray fan pattern deposit prove the system applies the correct rate per pulse; however, on/off-time latency create varying coverage as quantified in the dynamic simulation. As found with high-speed images, deposit time was consistently found to be 65 ms from when the nozzle solenoid is energized with an average droplet speed of 467 in/s. Fast travel speed result in a higher duty cycle and longer on-time with increased coverage efficiency. To conclude, PWM spray systems apply an accurate amount of flow per pulse regardless of active nozzles with uniform coverage occurring from higher duty cycles.

Effective management of greenhouse whiteflies (Trialeurodes vaporariorum) is critical due to their high potential for crop damage and relative susceptibility to insecticidal control. This study was conducted to evaluate the impact of spray nozzle orientation, application volume, droplet size, and insecticide deposition on whitefly mortality and foliar spray coverage in tomato crops. Two insecticidal formulations viz. emamectin benzoate 5% and beta-cyfluthrin 5% EW were applied using three nozzle orientations and two spray volume rates. Results indicated a negative correlation between insect mortality in the upper plant canopy and increased spray application volume. At the same canopy level, spray droplet size was positively correlated with deposition (R2 = 0.97), with small droplets depositing significantly less insecticide compared to medium and large droplets. However, droplet size did not have a significant effect on nymphal mortality. Furthermore, increasing the spray volume to 858.4 L · ha-1 did not enhance insecticide deposition or improve spray coverage. Canopy penetration by spray droplets was also unaffected by application volume but was significantly influenced by nozzle orientation. Overall, increasing spray application volume beyond 858.4 L · ha-1 is not recommended. Instead, reducing spray droplet size to approximately 128.53 µm may enhance whitefly control efficacy by improving canopy penetration and insecticide coverage within tomato crops..

Pulse width modulation (PWM) allows for the real-time flow rate adjustment of spray nozzles without changing system pressure, indicating that PWM is a promising technology for improving the quality of pesticide applications. However, its effect on the droplet formation process is not yet fully understood. In this study, the effects of a PWM system on the droplet spectrum and velocity generated by different flat fan hydraulic nozzles were evaluated. The experiment was conducted via a spray simulator to test the impact of PWM technology under various operational conditions and flat fan nozzle types (standard, pre-orifice, and air inclusion). With the aid of a real-time particle analyzer and high-resolution imaging, the following variables were analyzed: volume median diameter (VMD), relative span, droplet velocity, and the percentage of volume composed of droplets with a diameter smaller than 100 µm. Four simulated working speeds (1.1, 1.7, 2.8, and 3.9 m s−1), which were equivalent to four PWM valve duty cycles (35%, 42%, 71%, and 100%), respectively, were evaluated. The PWM system altered the droplet size, generally reducing the VMD in comparison to the conventional system. The relative span was not influenced by the PWM system’s duty cycle, although system activation increased droplet size heterogeneity in some nozzle types. The droplet velocity was generally slower using the PWM system in comparison with the conventional system, but higher duty cycles increased this parameter. Overall, the results of this study suggest that spray patterns are altered by PWM activation, and the traits of this behaviour depend on the spray nozzle type.

Evaluation of unmanned aerial vehicle for effective spraying application in coconut plantations

Highlights The effectiveness of four nozzles with flat-fan spray pattern types was evaluated to assess their ability to deliver spray droplets inside the soybean canopy in a wind tunnel equipped with a moving boom. The effect of wind speed on the spray coverage, deposition, and airborne drift of droplets discharged from the four evaluated nozzles was investigated under the wind speeds of 0, 2.4, and 5.1 m s-1. Spray deposition at the bottom part of canopies was significantly lower than at the upper part. Nozzles that produced ultra-coarse droplets reduced airborne spray drift risks. The dense soybean canopies and overlapping foliage of crops limit the spray droplet penetration capability of the hydraulic nozzles. ABSTRACT. Adequate spray deposits and coverage in the middle and lower parts of the canopy are essential to protect soybean crops from disease and insect attacks. Additionally, uncontrollable weather conditions can influence the effectiveness of spray applications. Thus, the objective of this research was to evaluate the effect of the wind speeds of 0, 2.4, and 5.1 m s -1 on the spray coverage and deposition discharged from travelling nozzles with different droplet sizes under wind tunnel-controlled conditions. An open-circuit wind tunnel, equipped with a moving spray boom placed 0.5 m above the top of the soybean canopy and operating at a speed of 0.9 m s -1 , was used in this study. To achieve the application rate of 150 L ha -1 , pulse width modulation solenoid valves were coupled with the nozzles at a duty cycle of 19% and an operating pressure of 276 kPa. Four types of same color-coded 110° flat-fan spray nozzles (XR11004, TTJ6011004, AITTJ6011004, and AIXR11004) were used to determine the effects of spray droplet size spectra Keywords: Controllable weather conditions, Open circuit wind tunnel, Spray drift, Spray penetration.

Highlights The effectiveness of four nozzles with flat-fan spray pattern types was evaluated to assess their ability to deliver spray droplets inside the soybean canopy in a wind tunnel equipped with a moving boom. The effect of wind speed on the spray coverage, deposition, and airborne drift of droplets discharged from the four evaluated nozzles was investigated under the wind speeds of 0, 2.4, and 5.1 m s-1. Spray deposition at the bottom part of canopies was significantly lower than at the upper part. Nozzles that produced ultra-coarse droplets reduced airborne spray drift risks. The dense soybean canopies and overlapping foliage of crops limit the spray droplet penetration capability of the hydraulic nozzles. ABSTRACT. Adequate spray deposits and coverage in the middle and lower parts of the canopy are essential to protect soybean crops from disease and insect attacks. Additionally, uncontrollable weather conditions can influence the effectiveness of spray applications. Thus, the objective of this research was to evaluate the effect of the wind speeds of 0, 2.4, and 5.1 m s -1 on the spray coverage and deposition discharged from travelling nozzles with different droplet sizes under wind tunnel-controlled conditions. An open-circuit wind tunnel, equipped with a moving spray boom placed 0.5 m above the top of the soybean canopy and operating at a speed of 0.9 m s -1 , was used in this study. To achieve the application rate of 150 L ha -1 , pulse width modulation solenoid valves were coupled with the nozzles at a duty cycle of 19% and an operating pressure of 276 kPa. Four types of same color-coded 110° flat-fan spray nozzles (XR11004, TTJ6011004, AITTJ6011004, and AIXR11004) were used to determine the effects of spray droplet size spectra Keywords: Centrifugal fan, Laminar flow, PWM nozzle, Spray deposition, Spray drift, Traveling boom, Turbulence.

Input to state set stability for pulse width modulated control systems with disturbances

Nozzle pressure uniformity and expected droplet size of a pulse width modulation (PWM) spray technology