Vaisala WMT700 - Manual (Page 42)

User's Guide ______________________________________________________________________
Wind Speed and Direction Averaging
WMT700 provides average values for wind speed and direction
using either scalar or vector averaging. With both methods, the
average is determined according to the user-configurable
averaging time. The averaging time affects serial communication
and analog output similarly.
You can also configure the gust averaging time for calculating
wind extreme values. The default gust averaging interval is 3
seconds, as recommended by World Meteorological Organization
(WMO).
If scalar averaging is selected, you can also enable wind direction
coasting to ensure consistent direction measurement results at low
wind speeds.
Scalar Averaging
When scalar averaging is selected, WMT700 calculates wind
speed and direction averages by adding up each wind
measurement from the averaging time and dividing the sum by
the number of measurements. The time between each consecutive
wind speed and wind direction measurement is 0.25 seconds.
Wind direction is a circular function with a discontinuity at the
north, where 360 degrees is equal to zero degrees. For example:
359° + 5° = + 4°
0° - 5° = 355°
WMT700 translates wind direction to a linear function to
determine the wind direction average. For instance:
359° + 5° is translated to 364°, which is then further converted to
+4° for output.
0° - 5° is translated to 355°.
This ensures that the wind direction average stays representative
of the true situation even if individual samples occur on both sides
of the zero direction.
If the data acquisition system requests data before the initial
averaging time completes, the sensor returns the most recent
complete measurement data.
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