Meteorological instruments -- Measurement of Surface Wind
Cup Anemometer and Wind Vane
A cup generator and wind vane are used to measure the wind speed and wind direction respectively. The cup generator normally has three cups mounted symmetrically about a vertical axis so that the diametric plane of each cup is vertical. As the force on the concave side of the cup, due to the wind, is greater than on the convex side, the cup wheel rotates. The wind speed is determined by the rotation rate of the cups.
Wind direction is indicated by means of a wind vane. It consists basically of an asymmetrically-shaped object mounted at its center of gravity about a vertical axis. The end which offers the greater resistance to the motion of air moves to the downwind position.