An anemometer is an instrument for measuring the rate of flow of air or other gases. It is used primarily to measure wind speed in order to provide data for aircraft flights, weather forecasts, and weather records. A wind direction vane generally is used with the anemometer so that the wind velocity (both speed and direction) is measured.
Several types are in use, including rotating-cup and propeller anemometers. Each type has specific advantages in cost or performance that make it suitable for particular applications.
The rotating-cup anemometer in general use has three conical-shaped cups mounted on radial arms supported by a common hub. Energy from the rotation of the cups can be used to drive a mechanical counter to show wind speed.
The propeller anemometer usually has three blades mounted on a common hub; the blades move in a vertical plane. A vane is required to keep the blades facing directly into the wind. Small propeller anemometers often are used as flow-measuring instruments in ventilation ducts.
Less commonly used types include pressure-tube anemometers (or Dines) and hot-wire, bridled-cup, pressure-plate, drag-sphere, and sonic anemometers.