User's Guide _______________________________________________________________________
12 ___________________________________________________________________ M210470EN-B
CHAPTER 3
FUNCTIONAL DESCRIPTION
Wind measurement principle
The WXT510 uses Vaisala WINDCAP
â
sensor technology in wind
measurement.
The wind sensor has an array of three equally spaced ultrasonic
transducers on a horizontal plane. Wind speed and wind directions are
determined by measuring the time it takes the ultrasound to travel
from each transducer to the other two.
The wind sensor measures the transit time (in both directions) along
the three paths established by the array of transducers. This transit
time depends on the wind speed along the ultrasonic path. For zero
wind speed, both the forward and reverse transit times are the same.
With wind along the sound path, the up-wind direction transit time
increases and the down-wind transit time decreases.
The wind speed is calculated from the measured transit times using
the following formula:
)
/
1
/
1
(
5
.
0
r
f
w
t
t
L
V
−
×
×
=
where:
V
w
=
Wind speed
L
=
Distance between the two transducers
t
f
=
Transit time in forward direction
t
r
=
Transit time in reverse direction
Measuring the six transit times allows V
w
to be computed for each of
the three ultrasonic paths. The computed wind speeds are independent
of altitude, temperature and humidity, which are cancelled out when
the transit times are measured in both directions, although the
individual transit times depend on these parameters.
