9windtrdNX2.doc Page 1 Latest update: 29 Jan -03
9. WIND TRANSDUCER - MAST TOP UNIT -
The basic principle of the windtransducer is to measure the angle and rotation
speed of a black and white ball with two opto sensors. In order to be able to
transmit the analog value of an angle there is a need of two channels (a sinus
and a cosinus) in order not to get some jumps/skips. Thise skips should
otherwise happen at the changeover from 359° to 0°.
On the otherhand a sinuscurve hasn’t any skips.
The two opto sensors are displaced in an fixed angle of 90° against eachothers.
The ball with a special design (see figure) is fixed on the propeller-shaft.
When the propeller is rotating the ball is rotating. When wind angle changes the
shaft is turning. The light from the opto sensors LED’s is reflected from white area
but not from the black on the ball to the sensors. This gives the origin for the
pulses with different quota high/low signals out from the transducer.
The shape of the black and white area is designed so that pulse quotas from
respective channel describes a sinus curve.
The
turning angle (wind angle) is transmitted via two signals A and B (sinus and
cosinus). One period corresponds to one turn for the propeller. The wind speed is
given by the formula:
h
v
= ( f/3,4 ) + 0,3
Where f = frequency for channel A or B. Because of friction there is an offset
error of 0,3 m/s, i.e. if we measure 3,4 Hz the wind speed is 1 + 0,3 (1,3 m/s),
6,4 Hz gives 2 + 0,3 (2,3 m/s), 34 Hz gives 10 + 0,3 (10,3 m/s) and so on.
Pulsequotas (quota time high/frequency) in percent (Q
A%
, Q
B%
) is given by the
formula:
Q
A%
= 50 % + 30 % x sinus (α)
Q
B%
= 50 % + 30 % x cosinus (α) (cosinus (α) = sinus (α + 90°))
α = wind angle
The two outputs are of the type open collector, i.e. there is a demand of a pull-up
resistor to get out an output signal.
Recommended value: 5 - 10 kΩ
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