Anemometer

Abstract

An anemometer includes a rotor mounted to spin about a vertical axis in response to wind being directed against it, and a cage having a plurality of circumferentially spaced apart, vertically disposed vanes surrounding the rotor. The vanes deflect the normal flow of air to produce an asymmetrical airflow pattern across the face of the rotor to cause the rotor to spin about its axis. A transducer senses the rotational speed of the rotor and converts it into a signal proportional to airspeed. In one form of the invention, the cage is fixed, and in another embodiment the cage is attached to a windvane to rotate with the windvane relative to the rotor. The windvane senses the direction of the wind, and a second transducer converts the rotational motion of the windvane into a signal proportional to wind direction. Preferably, the windvane includes a horizontally disposed, planar airfoil surface for deflecting the normal flow of air to increase the velocity of the air directed against the cage and rotor in proportion to increases in the angular deviation between the rotor axis and the general direction of the wind. Preferably, the rotor is a paddle wheel of relatively low mass on a shaft which is engaged with a pair of journal bearings. A low friction thrust bearing held in contact with a pointed end of the rotor shaft handles the weight of the rotor, while the journal bearings handle the aerodynamic loads on the rotor.