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Appendix D. Wind direction
measurement theory
It is not necessary to understand the concepts in this section for the general operation of the
05103 with a Campbell Scientific data logger.
FIGURE D-1. 05103 potentiometer in a half bridge circuit
The
BRHalf
CRBasic instruction outputs a precise excitation voltage (V
), and measures the
x
voltage between the wiper and ground (V
). The resistance between the wiper and ground (R
),
s
s
and V
vary with wind direction. The measurement result is the ratio of the measured voltage to
s
the excitation voltage (V
/V
). This ratio is related to the resistance as shown in this equation:
s
x
The maximum value that R
will reach is R
, just before it crosses over from the west side of north
s
f
to the east side of north (at this point R
= 0). V
/ V
reaches its maximum value of 1.0 mV/mV at
t
s
x
355 degrees. The multiplier to convert V
/V
to degrees is 355 degrees / 1.0 V
/V
= 355. Refer to
s
x
s
x
the data logger manual for more information on the bridge measurements.
Wind Monitor Series
24
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