The GreenStar 2™ Spray Control System for TwinFluid™ sprayers incorporates two regulation systems. The automatic rate control system ensures that the desired application rate (in liters per hectare) is adjusted and regulated. Furthermore, there is a droplet size regulation system available on the TwinFluid ¹ sprayers. The object of the droplet size regulation system is to keep the drop size constant when driving speed and/or liquid pressure fluctuates. The driver can choose between four different droplet sizes, adapted to the type of crop spraying and the weather conditions. The required droplet size can be chosen on the GreenStar 2 ² display. An on-board wind speed sensor can measure the prevailing weather conditions (wind speed) in order to allow for optimal adjustment, thus minimising drift and guaranteeing optimal spraying results.

Example:

If a medium spray quality (M) has been chosen, the droplet size control system regulates the air pressure in such a way that a medium sized droplet will always be sprayed, even when the liquid pressure fluctuates. The driver simply chooses the droplet size prior to spraying (based on the wind speed measured) and the controller will then regulate the air pressure in such a manner that the required droplet size is sprayed. The TwinFluid Control System even keeps the droplet size constant when the driving speed and/or liquid pressure changes. The controller measures both the liquid pressure and the air pressure, because the droplet

The ratio between the required air pressure in keeping with a given liquid pressure has been programmed in the memory of the controller for certain droplet sizes. This ratio is different for each of the four droplet sizes. At a liquid pressure of 4 bar, for example, an air pressure of 1.25 bar is required for a fine spray quality, while an air pressure of 0.74 bar is required for a coarse spray quality (according to the British Crop Protection Council classification).

Due to there being four droplet size settings, there are also four graphs showing the ratio of the air pressure and liquid pressure. All these graphs have been programmed into the controller at the factory (depending on the type of insert). Each graph (droplet size) has a minimum and maximum liquid pressure. This means that, at a constant application rate in l/ha (set on the GreenStar display), the liquid pressure can vary within these limits. The driving speed can therefore also be varied within these limits without there being any effect on the droplet size and the output. As soon as the liquid pressure exceeds the set limits, the display gives a speed alarm.

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While the droplet size regulation system regulates the air pressure, the rate control system regulates the liquid output, depending on the target application rate, driving speed and position of the sectional valves. The machine is also fitted with a wind speed meter. This device allows for measurement of the prevailing wind speed on the field and, on the basis of this measurement, advice is given to the driver on the best setting for the droplet size, with regard to drift and effectiveness. Wind speed measurement must take place when the machine is stationary, for example during or before filling of the tank. When the main shut-off valve is open, the droplet size control system will begin regulating the air pressure which corresponds to the chosen droplet size. The display shows the liquid pressure, the air pressure and the set droplet size.

Each droplet size selection corresponds to a specific graph for the TwinFluid nozzle. Each graph gives the ratio of liquid pressure and air pressure. The controller constantly measures the liquid pressure and calculates the required air pressure on the basis of the set droplet size (graph). The controller then regulates the air pressure regulator valve in such a manner that the required air pressure is realised. During the regulation, the controller also checks whether the liquid pressure (controlled by the rate control system) is within the limits of the graph (min/max pressure).

If the liquid pressure threatens to exceed the limits, the controller will show an alarm message on the GreenStar 2 display to the driver, that he must increase his driving speed if the liquid pressure is too low or must drive more slowly if the liquid pressure is too high. If the driver adjusts his driving speed, the spraying computer will adapt the liquid pressure in order to keep the required output as consistent as possible.

When the liquid pressure exceeds the limits, the air pressure will be regulated to correspond with the

The following parameters have been programmed per droplet size setting:

• maximum wind speed : The maximum wind speed with which spraying can taken place at this droplet size setting (for example 4 m/s), used as advice for the driver. These values are used to determine which setting (position VF, F, M or C) is most suitable for the prevailing conditions, after measurement of the wind speed. The measured wind speed is compared with the four maximum wind speeds for the four droplet size settings, after which the best setting is determined. The setting with the smallest droplet size will be advised, whereby the measured wind speed is under the maximum admissible wind speed.
• droplet size classification : VF, F, M or C
• three points of the droplet size graph , which give the ratio between the air pressure and liquid pressure required in order to achieve a certain droplet size. For a droplet size with code F, the following table gives an example of the ratio of the liquid pressure and the air pressure.

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The pressure sensors used give a current signal (e.g. 0-20 mA or 4-20 mA) which corresponds with a certain pressure (e.g. 0 - 25 bar or 0 - 2.0 bar). The analogue current signal is converted into a digital value by an A/D Converter before being further processed by the

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