The time required for a measuring sequence is approx. 2.5 msec at +20°C at the maximum
measuring speed.
2.1
Measuring principle: Wind velocity and direction
The speed of propagation of the sound in calm air is superposed by the velocity components of an
air flow in the direction of the wind.
A wind velocity component in the propagation direction of the sound supports the speed of
propagation; i.e. it increases it while a wind velocity component against the propagation direction
reduces the speed of propagation.
The propagation speed resulting from superposition leads to different propagation times of the
sound at different wind velocities and directions over a fixed measurement path.
As the speed of sound greatly depends on the temperature of the air, the propagation time of the
sound is measured on each of the two measurement paths in
both
directions. This rules out the
influence of temperature on the measurement result.
By combining the two measurement paths which are at right angles to each other, the
measurement results of the sum and the angle of the wind velocity vector are obtained in the form
of perpendicular components.
After the perpendicular velocity components have been measured, they are then converted to polar
coordinates by the
µ
processor of the anemometer and output as a sum and angle of wind velocity.
Wind from NNE
Y-component
X-component
E
N
W
S
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