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How does an anemometer work?

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Quick answer

An anemometer measures wind speed by letting the wind spin a set of cups or a propeller. The wind pushes harder on the concave side of each cup than on the rounded back, creating a turning force. The faster the wind, the faster the spin, and a sensor converts that rotation into a speed reading.

An anemometer measures wind speed by converting the wind's push on rotating cups or a spinning propeller into a rotation rate. The faster the wind, the faster the cups spin, and the instrument translates that spin into a speed reading.

Step by step

  1. Wind blows against the cups of the anemometer.
  2. The concave side of each cup catches more wind force than the convex side.
  3. This unequal push creates a torque that rotates the cups around a central axis.
  4. A magnet and reed switch or an optical sensor counts each rotation.
  5. The rotation count per second is converted into wind speed using a calibration factor.

Key things to understand

  1. The most common type has three or four cups mounted on a vertical axis.
  2. Wind pushes the cups; the concave side catches more force than the convex side.
  3. This difference in drag makes the cups rotate around the axis.
  4. The rotation rate is proportional to the wind speed.
  5. A sensor counts rotations per second and converts that to metres per second or kilometres per hour.

Labelled diagram

  1. Wind flow

    Moving air approaches the anemometer from one direction.

  2. Cups

    Three or four hemispherical cups catch the wind on their concave sides.

  3. Rotation

    Unequal drag forces make the cups spin around a vertical axis.

  4. Sensor

    A magnet and switch or optical counter detects each full rotation.

  5. Display

    Electronics convert rotation rate into a wind speed reading.

How a cup anemometer measures wind speed

Real-world examples

  • At airports, cup anemometers on masts provide real-time wind speed for pilots during takeoff and landing.
  • Meteorological stations use anemometers to record wind data for weather forecasts and climate studies.
  • On a sailboat, a small propeller anemometer at the masthead helps sailors adjust sails to the wind.
  • In a science classroom, a handheld anemometer measures wind speed during a field trip to study local weather.

Common mistake

✗ Myth: An anemometer measures wind direction as well as speed.

✓ Fact: A cup anemometer measures only wind speed; direction usually comes from a separate wind vane. Some designs, such as ultrasonic anemometers and propeller-vane aerovanes, measure both speed and direction.

People also ask

What is an anemometer used for?
An anemometer is used to measure wind speed. Meteorologists use it for weather forecasts, pilots use it for safe takeoff and landing, sailors use it to set sails, and engineers use it to assess wind loads on buildings and wind turbine performance.
How does a cup anemometer measure wind speed?
A cup anemometer measures wind speed by counting how fast its cups spin. The wind pushes harder on the concave side of each cup than on the convex side, creating rotation. The rotation rate is proportional to wind speed, so a sensor converts it into a speed reading.
Who invented the anemometer?
The first known anemometer was described by Leon Battista Alberti around 1450. The cup anemometer, the most common type today, was invented by John Thomas Romney Robinson in 1846. Since then, many variations have been developed for different applications.
What units do anemometers use?
Anemometers typically report wind speed in metres per second (m/s), kilometres per hour (km/h), miles per hour (mph), or knots. Meteorologists often use knots because they are convenient for aviation and marine forecasts. Many devices let you switch between units.
Can an anemometer measure wind direction too?
No, a standard anemometer only measures speed. Wind direction is measured by a separate instrument called a wind vane, which points into the wind. Together, they form a complete wind sensor called an aerovane or wind vane and anemometer set.
How accurate are cup anemometers?
Cup anemometers are accurate to within about 1–2% of the true wind speed when calibrated. However, they can overshoot in gusty conditions because the cups have inertia and take time to speed up or slow down. Regular calibration maintains accuracy.
What are other types of anemometers?
Besides cup anemometers, there are propeller anemometers, hot-wire anemometers (which measure cooling of a heated wire), ultrasonic anemometers (which use sound waves), and laser Doppler anemometers. Each works best in different conditions, such as low speeds or turbulent flows.

Part of the guide: Water & Weather Phenomena →