Hardi AutoHeight, Instruction Book

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3 - Description
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Areas of "No Crop" in CROP Mode
If, while operating in CROP mode, the sensor encounters an area where there is no crop, the system will behave as follows.
The sensor will track the soil (A) because only one target is available. The boom will lower (B) as no crop is detected. Areas
like this may include missed areas during seeding, alkaline areas, and so on. When the problem area ends (C), it may not be
possible for the sensor to see the crop again unless the operator raises the boom manually. The sensor may be closer than
required 25 cm from heads of the crop (D), thus blanking out the desired target.
Figure 8 - Area of "No Crop" When Operating CROP Mode
Thin Crop
The AutoHeight ultrasonic sensors operate by bouncing sound waves off the desired target. A minimum signal level is
required from the crop in order to use it for control purposes. This is no different than the fact that your radio must be at a
certain minimum volume level before you can physically hear it. Different types of crop and crops at different stages of
development return varying levels of sound. The following are some general guidelines.
• Crops in growing stages are relatively good sonic targets.
• Bearded crops are relatively poor sonic targets.
• In row crops, the sensor must be positioned over the row to use the crop signal, or between the rows to use the
ground signal.
• The desired target must cover roughly 60 percent of the area to be tracked consistently. That is, when looking at the
ground, the heads should cover about 60 percent of the ground. Otherwise, you can use SOIL mode.
• If the sensor runs too close to the heads, they may not return enough signal to be seen, or they may be blanked out.
The nozzles must be at least 55 cm from the crop. Slightly higher target height settings will work better in thin crop.
Boom Lift Sensor in Wheel Track
The required location for the centre section sensor is determined by the AutoHeight Installation Manual for your sprayer and
by the options you have installed. Special attention is necessary when mounting the centre section sensor. Mounting the
centre section sensor directly behind a sprayer tire may impair boom lift control when operating in CROP mode. Height
readings from crop that is flattened by the sprayer wheel do not provide an accurate measurement of canopy height,
resulting in poor performance.
Sensing Further Ahead of the Boom
A common misconception is moving the sensor further ahead of the boom will increase performance. Moving the sensor
further ahead of the boom increases the distance between the nozzle and sensor. This puts the sensor at a different location
within the field than the nozzles, which introduces a height error at the nozzles. In severe terrain this height error can bring
the nozzles close to the ground as the sensor reads over the crest of the hill or down a ditch.
Similarly, aiming the sensors ahead (rather than pointing straight down) will reduce sensor performance by providing
inaccurate height readings.