An anemometer is a meteorological device used to measure aspects of wind. An anemometer is a device typically found in a weather station, although the devices can be used as a stand-alone as well. The name is derived from the Greek word "anemos," which means wind.
Anemometers measure several aspects of wind:
Typically, anemometers are categorized into these two categories: velocity and pressure anemometers. However, because there is such a close connection between these two aspects of wind (velocity and pressure), either anemometer will usually give adequate information about both.
Velocity anemometers are divided into two classes: those that require some sort of wind vane and those that do not.
- Cup anemometers are perhaps the most widely used and recognized of all anemometers. Constructed of four hemispherical cups that form a cross if viewed from above, the wind is captured in the cups, causing the anemometer to spin.
A mechanism at the axis records and calculates the number of revolutions, which then allows wind velocity to be observed. Cup anemometers are simple and do not require intricacies such as a weather vane, but they do not record velocity at any given moment as accurately as other types do. For example, a sudden gust of wind may pass by unrecorded.
- Windmill anemometers are based on the design of wind vanes, which simply illustrate wind direction. A windmill anemometer is more accurately described as an aerovane, which is essentially a wind vane with a propeller on it. The tailfin of the wind vane accurately displays wind direction, while the propeller at the front can record wind velocity by calculating revolutions per minute.
Plate anemometers are typically divided into two classes: plate and tube anemometers.
- Plate anemometers are constructed of a square or circular flat plate with a precision spring resting behind it. A wind vane keeps the plate directed against the wind, and the force of the plate against the spring can accurately measure the pressure of the wind. The majority of plate anemometers are not suited to record abrupt fluctuations in wind pressure, mainly because the fundamental design prohibits it. They are generally used to record average wind pressures.
- Tube anemometers are of slightly more complex design than plate anemometers. These devices use a vessel with an opening at the top to record wind pressure. The pressure exerted through the mouth of the opening causes changes to the internal pressure of the chamber, which then allows calculations to be made concerning wind pressure. One advantage of tube anemometers is their self-sufficiency; they can be mounted atop a high pole and left unattended for long periods.