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6. CALIBRATION
As with any mistblower, an AU8000 sprayer must be calibrated before use. This involves setting the correct output rate of chemical and adjusting the sprayhead to produce the appropriate droplet size for the chemical and application technique being used.
The following sections describe the calibration of a standard Micronair AU8000 sprayer. Some details of the procedures may differ if the sprayhead is used with a different model of mistblower.
6.1.Output Rate of Chemical
The output rate of chemical from the sprayer will be determined by the required application rate (in litres/hectare) and the area sprayed per minute (in hectares/minute).
The flow of chemical from the atomiser is controlled by the interchangeable restrictor tube attached to the on/off valve and by the chemical pressure. Chemical is pressurised by air from the blower fan and by the optional boost pump (if fitted).
The following steps describe the calibration procedure in detail:
1.Establish the average walking speed of the operator. This will depend upon, for example, the target being sprayed, the evenness or slope of the ground, the amount of chemical carried and the temperature.
The most accurate means of assessing walking speed is for the operator to spray the actual crop or target in a 'trial run' with clean water. The speed can then be calculated from the time to cover a measured distance.
2.Establish the width of the swath of spray on the target. In row crops or orchard spraying this can often be determined by the number of rows sprayed at a time. In public health or pest control spraying using a drift technique over open ground the swath width must be determined by the use of sensitive cards or paper. These should be placed both horizontally and vertically. The cards should be mounted downwind of the spray line. The sprayer must be used under typical conditions of wind and temperature.
When spraying field crops or open areas (e.g. for locust control), the distance between successive passes of the sprayer should be less than the measured maximum swath width to ensure adequate overlap of the spray and allow for variations in the wind and terrain. For the purposes of calibration, the distance between passes should be regarded as the swath width.
