Campbell Scientific 014A Met One Wind Speed Sensor - Manual (Page 33)

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