Campbell Scientific CR200/CR200X-series Dataloggers - Manual (Page 132)

Section 11. Programming Resource Library
For most applications, total power usage of 318 mA for 15 seconds is not
excessive, but if 16 probes were wired to the same SDI-12 port, the resulting
power draw would be excessive. Spreading sensors over several SDI-12
terminals will help reduce power consumption.
11.5 Wind Vector
11.5.1 OutputOpt Parameters
In the CR200(X) WindVector () instruction, the OutputOpt parameter is used to
define the values which are stored. All output options result in an array of
values, the elements of which have "_WVc(n)" as a suffix, where n is the
element number. The array uses the name of the Speed/East variable as its base.
TABLE. OutputOpt Options (p. 120) lists and describes OutputOpt options.
Table 16. OutputOpt Options
Option Description (WVc() is the Output Array)
0
WVc(1): Mean horizontal wind speed (S)
WVc(2): Unit vector mean wind direction (Θ1)
WVc(3): Standard deviation of wind direction σ(Θ1). Standard deviation is calculated using the Yamartino
algorithm. This option complies with EPA guidelines for use with straight-line Gaussian dispersion models
to model plume transport.
1 WVc(1): Mean horizontal wind speed (S)
WVc(2): Unit vector mean wind direction (Θ1)
2 WVc(1):Resultant Mean horizontal wind speed (Ū)
WVc(2): Resultant mean wind direction (Θu)
WVc(3): Standard deviation of wind direction σ(Θu). This standard deviation is calculated using Campbell
Scientific's wind speed weighted algorithm. Use of the resultant mean horizontal wind direction is not
recommended for straight-line Gaussian dispersion models, but may be used to model transport direction in
a variable-trajectory model.
11.5.2 Wind Vector Processing
WindVector () processes wind speed and direction measurements to calculate
mean speed, mean vector magnitude, and mean vector direction over a data
storage interval. Measurements from polar (wind speed and direction) or
orthogonal (fixed East and North propellers) sensors are accommodated. Vector
direction and standard deviation of vector direction can be calculated weighted
or unweighted for wind speed.
When a wind speed measurement is zero, WindVector () uses the measurement
to process scalar or resultant vector wind speed and standard deviation, but not
the computation of wind direction.
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