Most rate controllers will come with a range of standard features that allow the operator to customise when warnings or alarms register. The sensitivity of regulating valves and settings will ensure the nozzles can function correctly at low speeds (minimum setting).

Alarms

Alarms can be set up to be audible or visual, or both. There are many different alarm settings in each brand of controller. Always consult the controller manual to determine which functions are available on the model you have.

Common examples of alarms that may be set or adjusted by the operator include:

• low tank level reached;

• outside the programmed application rate;

• maximum speed or pressure reached; and

• minimum setting reached.

Tip

• Don’t assume that the tank capacity is exactly as stated by the manufacturer. Calibrating spray tanks is very important. Markings or graduations on the tank are often not correct, and most manufacturers state they are only a guide. Too many spray operators change the flow meter calibration figure to match the perceived tank capacity, which may impact on the accuracy of all future applications.

Minimum settings

For Standard pressure based sprayers (not PWM), setting a minimum pressure, speed or flow (total flow or litres per minute per nozzle) at which the rate controller will not drop below when you reduce your spraying speed can be very useful to ensure nozzles continue to work effectively (with PWM systems setting a minimum duty cycle will have the same effect).

If you are not sure if the minimum setting has been programmed into your controller, you should see the L/ha on the screen increase above the programmed L/ha as you slow down; generally this will indicate that the minimum hold has been engaged.

When determining what the appropriate minimum setting should be, be aware that once the controller engages the minimum hold, further reducing the spraying speed will result in overdosing.

It is a good idea to match the minimum setting to the type of nozzle being used and to allow large enough headlands to minimise overdosing. A spray plan will help to identify suitable settings for different nozzle types.

A number of manufacturers identify the minimum settings in the controller by different names, three examples are shown below.

Tip

• Check that the controller can go down to zero output by putting the controller in manual with the spray system running, then turning the boom section on and pushing switch/button to lower pressure/flow.

Tip

• Caution needs to be exercised when determining where to set the minimum hold function when applying residual herbicides or other products at the maximum label rate. Operators should carefully plan spraying speed and the size of headlands to minimise the amount of time that the minimum hold function will engage to avoid possible overdosing. Preparing a spray plan to work out appropriate speeds and pressures is critical for minimising overdosing.