Anemometer is an instrument for measuring air speed or pressure. There are three types: the Robinson cup, which is in general use, particularly in the work of weather bureaus; the vane type, suitable for determining velocities of directed air streams in ventilation; and the Fitot tube, which measures velocity pressures and static pressures of fluids at the same time, these being translatable into velocities. While the last may be classed as an anemometer, giving readings least likely to error, its operation function will be found under Pitot Tube.
The cup anemometer consists of three or four hemispherical cups attached to the ends of rods or spokes which have their hub on a vertical spindle. This wheel of cups rotates in the wind because of the air forced into the cups, which rotate without regard to wind direction. The spindle, driven by the cups, may connect, through gears, to a dial or counter. Or the spindle may drive a small electric generator which indicates just what the velocity is by its fluctuation of output. This anemometer is very efficient when correction has been made by comparisons with standards in the various ranges of wind velocities. In the Gurley electronic anemometer for recording low wind speeds and gusts, the rotation of the cups is made to introduce pulses in an electronic circuit that controls the amount of direct current flowing through the recording mechanism.
Vane anemometers are like small windmills, which can be held in the hand, measuring air motion on dials by means of clock-like hands which arc driven by means of gears from the vane spindle. This type, when held at the face of a ventilating grille, can measure low speeds.
The Dines pressure-tube anemometer, designed for recording both average wind speeds and gusts near the ground, has a vane that keeps a tube pointed into the wind. Several different devices can be used to measure and record the pressure in this tube, which depends upon the wind speed. In the Friez bridled anemometer, a wheel carrying 32 cups is restrained by springs from rotating in the wind. I’he restraining force, which is a measure of the wind speed, is transmitted to the recording device by self-synchronous motors.
There are other types of anemometers. In aircraft, anemometers equipped with a nickel or platinum wire that is is used electronically.A device is also called an anemometer, in airplanes, which is used to calculate the speed of displacement. In this case, the anemometer has a different appearance and design, and allows to compare the dynamic pressure (that is, the pressure of the air) and the static pressure by means of a Pitot tube.
