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Appendix d. theory of operation, D.1 mechanical, D.2 calibration – Campbell Scientific 014A Met One Wind Speed Sensor User Manual

Page 33

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Appendix D. Theory of Operation

D.1 Mechanical

The sensor’s cup assembly consists of three aluminum cups mounted on a cup

assembly hub. A stainless steel shaft, which rotates on precision-sealed ball

bearings, connects the cup assembly to a magnet assembly. When the shaft is

rotated, the turning magnet assembly causes a reed switch to close. There are

two contacts (reed switch closures) per revolution. The frequency of closures

is linear from threshold to 45 m s

–1

.

D.2 Calibration

The 014A sensor has a threshold speed of 0.447 m s

–1

and follows the equation:

V = 0.447 + f/1.250 where

V = wind speed (m s

–1

), and

f = output frequency (hz,)

or,

V = 1.0 + f/0.5589

where V = wind speed (mph), and

f = output frequency (hz.)

D-1