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Wind speed is wrong when moving, though it is correct when stationary
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Last Updated
10th of January, 2012

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For the WatchDog Sprayer Station, there are two probable causes for the wind to be radically wrong when the sprayer is moving, although it is accurate when the sprayer is standing still.

1. If the tab on the Sprayer Station sensor head is not pointed exactly straight ahead, the true wind computations will be wrong.  If the station points slightly to the side, it will assume that the wind caused by motion, which it now detects coming in not from the front, but instead to the side, is partly due to motion, and partly due to a strong wind from the side of the vehicle.  As a result, it computes a stronger wind, at a completely different angle than it should.

2. If the station is not fully in the wind flow as the sprayer moves, the station cannot compute wind properly.  If, for example, the station is mounted near the side of the cab roof, the wind over the roof is likely flowing at an angle to the side (like a bow wave from a boat).  This causes the same miscalculation as reason 1.  In a worst case, the wind flows up and over the station, without passing through it.  Basically, when moving, the station is in an area of dead air.  This appears on the display as a relatively low wind speed, often from different directions each reading.  The station thinks that since there is no detected wind, but the sprayer is moving at for example, 10 miles/hour, that there must be a 10 mile/hour tailwind.

In either case, the problem is resolved by relocating the Sprayer Station sensor.  If the problem recurs, it can be helpful to tape a length of string or yarn to the top of the station, and have another person observe the string as the sprayer moves.

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