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Section 11. Programming Resource Library

Note Cup anemometers typically have a mechanical offset which is added to

each measurement. A numeric offset is usually encoded in the CRBASIC

program to compensate for the mechanical offset. When this is done, a

measurement will equal the offset only when wind speed is zero; consequently,

additional code is often included to zero the measurement when it equals the

offset so that WindVector () can reject measurements when wind speed is zero.

11.5.2.1 Measured Raw Data

• S

: horizontal wind speed

• Θ

: horizontal wind direction

• Ue

: east-west component of wind

• Un

: north-south component of wind

• N: number of samples

11.5.2.2 Calculations

11.5.2.2.1 Input Sample Vectors

Figure 45: Input Sample Vectors

In FIGURE. Input Sample Vectors (p. 121) the short, head-to-tail vectors are the

input sample vectors described by s

and Θ

, the sample speed and direction, or

by Ue

and Un

, the east and north components of the sample vector. At the end

of data storage interval T, the sum of the sample vectors is described by a vector

of magnitude U and direction Θu. If the input sample interval is t, the number of

samples in data storage interval T is N = T / t. The mean vector magnitude is Ū

= U / N.

121

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Campbell CR200 Betreibershandbuch Seite 135