A cup anemometer is a scientific instrument used to measure wind speed. This device is named for the cups used to capture and measure wind. They are able to measure wind speed quite accurately, but most versions cannot measure wind direction. They are standard features in most modern weather stations, and simple versions can easily be built or purchased for use in home weather stations.
Irish scientist, John Thomas Romney Robinson, invented the cup anemometer in the 19th century. The British were very interested in meteorological research, as this information was used by the Royal Navy in addition to the scientific community. Britain moved swiftly to establish a regular network of meteorological stations and included cup anemometers to measure wind speed.
This scientific instrument has changed little from its earliest days. The construction of a cup anemometer is simple. Three or four cups, typically made of metal or rugged plastic, are spaced symmetrically at the ends of arms, which are affixed to a central pivot point. Each cup is positioned so that its hollow interior is parallel to the length of the support arm. Such a configuration ensures that the cups will catch wind from any direction.
Wind spins the cups in an anemometer, and stronger winds spin the instrument more rapidly. The specific ratio between wind speed and the speed of cup rotation varies based on the particular specifications of a given instrument. A standard cup anemometer is unable to determine the direction of wind, and is usually paired with a second instrument, which can be as simple as a weather vane, to take this measurement. Newer versions of the cup anemometer employ cups with different shapes, and can use the different drag on different cups to determine which direction the wind is blowing, but most still use the older design.
A rotating cup anemometer can accurately measure winds up to at least 60 miles per hour (roughly 100 kilometers per hour). Faster winds, however reduce the accuracy of wind speed readings to a modest extent. Extremely powerful winds can damage a cup anemometer, but modern models can survive even most hurricane conditions, and still produce useful data.
Residential anemometers are widely available for purchase, but enterprising aspiring meteorologists can also construct these instruments. An improvised anemometer can be made from paper cups. A small mounted wheel can serve as the base for a paper cup anemometer. The paper cups can then be mounted to the wheel with dowels or any other lightweight materials that happen to be handy. Such an instrument is surprisingly accurate in measuring wind speed but is best kept out of hurricane-force winds.