Anemometers are devices used to measure wind speed. Anemometers which are used at weather stations., were thought to come into existence around the year 1450.There are two major classes of anemometers; one which measures the winds velocity, the other which measures wind pressure. However, because the velocity and pressure of wind are so closely connected a particular instrument usually is used to measure both.
A cup anemometer is one type of velocity anemometer. Cup anemometers were invented in 1846 by Dr. John Robinson. This type of anemometer was made up of four cups mounted at the end of four horizontal arms. Air flowed past these cups in such a way that the flow was related to the speed of the wind. The average speed was determined by counting how many times the cups turned. Later discoveries found that the size of the cups and the length of the arms holding the cups were important in determining the actual speed of the wind.
Robinson’s four cup anemometer was modified by John Paterson in 1926 into a three cup model which proved to be more efficient. This model had only a three percent error up to wind speeds that didn’t exceed sixty miles per hour. The three cup anemometer was again perfected upon in 1991 by Derek Weston, with his model measuring both wind speed and pressure.
Another form of anemometer is the hot wire anemometer which uses a fine wire heated to a particular temperature. When wind passes this anemometer, its speed is determined by the degree of cooling the wire undergoes. While this type of anemometer is delicate, it is also very accurate.
More recently developed velocity anemometers are called Laser Doppler anemometers. Also known as laser doppler veolocimetry,these anemometers use a light beam from a laser to measure wind speed. Particles which come in contact with the beam produce what’s known as the Doppler affect which in turns allows for the measurement of wind speed.
A windmill anemometer also known as a propeller anemometer is another type of velocity anemometer. This mechanical anemometer must be placed so that it is parallel to the wind in order for an accurate measurement. Therefore, it is set up so that the axis of rotation is set up horizontally.
The earliest pressure anemometer was known as the Plate Anemometer. These simple anemometers were plates that were suspended from the top so that wind could deflect the plate. Invented by Italian architect Leon Alberti, these anemometers were later modified with a wind vane so that they were not moving when there was no wind.
In 1775 James Lind invented the tube anemometer to measure wind pressure.Lind’s anemometer consisted of a glass U tube which contained a liquid. This tube was bent in such a way so that it was facing the wind and so its one vertical end was parallel to the way wind flowed.
In 1892 William Dines invented a metal pressure tube anemometer which measured the pressure differences between two sections of the instrument. This anemometer turned out to be very accurate with only a one percent error.
This is a broad overview of the wind anemometer. There are many types of anemometers and they are able to measure wind speed in miles per hour or in knots. While the most basic anemometer can measure wind speed, the more complex ones can measure speed, pressure and wind direction.