anemometer

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Device for measuring wind speed and liquid flow. The most basic form, the cup-type anemometer, consists of cups at the ends of arms, which rotate when the wind blows. The speed of rotation indicates the wind speed.

Vane-type anemometers have vanes, like a small windmill or propeller, that rotate when the wind blows. Pressure-tube anemometers use the pressure generated by the wind to indicate speed. The wind blowing into or across a tube develops a pressure increase or decrease, proportional to the wind speed, that is measured by a manometer or pressure gauge. Hot-wire anemometers work on the principle that the rate at which heat is transferred from a hot wire to the surrounding air is a measure of the air speed. Wind speed is determined by measuring either the electric current required to maintain a hot wire at a constant temperature, or the variation of resistance (and hence of temperature) while a constant current is maintained.

The red, white, and black tricolour formed the basis of the flags of both North and South Yemen. Effective date: 22 May 1990. >>