The term anemometer is derived from the Greek word anemos which means ‘wind’ and metros which means ‘measure’. These devices were first developed in the 15th century to measure wind speeds. For safety reasons, planning a trip or simple curiosity, knowing the direction of wind is important. Wind is an element that can cause catastrophic damage to any settlement, therefor it is crucial to have some idea of its direction. For example, sailors boarding a ship should know of any incoming storms otherwise they can get into mortal peril. Anemometers are designed specifically to cater to this need and adopt clever methods to decipher the next turn of unfortunate weather events.
Wind rotates around our planet in streams which are not different than rivers. Experts classify winds on the basis of their origin like gradient winds or geostrophic winds. For Anemometer units, wind is recorded in miles per hour or MPH, SI unit is m/s. Converting from MPH to m/s can be easy with this formula:(1 mi/hr) = (mi/1,609 m)(3600 s/hr) = 0.447 m/s.
The commonest kind of anemometer is a kind of horizontal three-armed windmill, with a hollow hemispherical cup on the end of each arm. Useful range of an anemometer is from 5 to 100 knots. The hot wire anemometer is one of the most popular temperature anemometers. It has an electrically heated wire supported by needles.
The pressure on the inside of a cup when it is back to wind overcomes the pressure on the rounded front of the cup on the opposite arm, and the cups revolve at rather more than two-fifths the speed of the wind. The mill moves a pointer round a graduated dial. By timing a given number of revolutions, as shown by the pointer, the speed of the wind is easily calculated.
There is a huge range of anemometers for measuring wind and velocity. The most common four types of anemometers include vane, thermal, cup and velocity/temperature profiling ones. Usually, anemometers are classified as constant temperature or constant power anemometers.
Constant Temperature anemometers have a high frequency response, low noise and are compatible with hotfilm sensors. They are immune from burnout when the airflow drops suddenly.
Constant Power anemometers have temperature proportional to flowrate. Constant-power anemometers are not stable in zeroflow reading and their temperature compensation is also limited.
1 Vane Anemometers
Rotating velocity anemometers are classified in the Vane class. In cases where direction of air motion is same, vane anemometers give the most satisfactory results. Additional points like temperature and humidity can be added to modify vane anemometers.
2 Thermal Anemometers
These devices use a wire or heated up element which helps measure the resistance of wire and air flow velocity. Thermal anemometers are very delicate, have high frequency can be modified with additional features.
3. Thermal Anemometers with Velocit/Temperature Profiles
Thermal anemometer profiling systems have sensors to measure both velocity and temperature. This type is commonly used in wind tunnels for heat sink analysis.
4 Cup Anemometers
Cup anemometer is the simplest type of anemometers. It has 3 to 4 cups mounted on arms. Air flow moving past the cups moves them to a particular direction. Three cup anemometer was designed by John Patterson in 1926 and modified by Derek Weston in 1991. Three cup anemometers are used as industry standard for wind assessment studies around the world.
Anemometers are widely used in all weather stations, be it the Arctic or equatorial regions. This is because wind speed is checked to determine change in weather patterns like an incoming storm. Wind speed and storm predictions are the most important for pilots, engineers and climatologists. Aerospace engineers use a modified anemometer to perform velocity experiments. These modified anemometers calculate the wind speed around fast moving cars, planes and spacecraft. These calculations help in making vehicles more aerodynamic.
Running events around the world, especially international track competitions can get distracted because of wind as the runners have to move in one direction. Anemometers are places trackside in such competitions to record wind directions. Anything above 2.0 m/s makes the track ineligible for running. Modern timing and speed recording equipment try to set ideal conditions so that the competition can land accurate results.