D-1
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 Campbell Scientific’s datalogger.
FIGURE D-1. 05103 potentiometer in a half bridge circuit
The
BRHalf
CRBasic instruction outputs a precise excitation voltage (V
x
), and
measures the voltage between the wiper and ground (V
s
). The resistance
between the wiper and ground, R
s
, and V
s
varies with wind direction. The
measurement result is the ratio of the measured voltage to the excitation
voltage (V
s
/V
x
). This ratio is related to the resistance as shown below:
(
)
s
t
s
x
s
R
R
R
V
V
+
=
The maximum value that R
s
will reach is R
f
, just before it crosses over from the
west side of north to the east side of north (at this point R
t
= 0). V
s
/
V
x
reaches
its maximum value of 1.0 mV/mV at 355 degrees. The multiplier to convert
V
s
/V
x
to degrees is 355 degrees / 1.0 V
s
/V
x
= 355. Since the datalogger outputs
the ratio V
s
/
V
x
, the multiplier is the same for the CR3000, even though it uses
a different excitation voltage. See Section 13.5 in the datalogger manual from
more information on the bridge measurements.
Summary of Contents for Wind Monitor Series
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Page 24: ...Wind Monitor Series 16...
Page 26: ...Appendix A Importing Short Cut Code Into CRBasic Editor A 2...
Page 30: ...Appendix B Example Programs B 4...
Page 34: ...Appendix C Wind Direction Sensor Orientation C 4...
Page 36: ...Appendix D Wind Direction Measurement Theory D 2...
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