Anemometer – Definition and Effects on Icing

Anemometer

What is an anemometer? An anemometer is a device used to measure the speed of the wind and its pressure. Anemometers are vital instruments for meteorologists as they help them to study weather patterns. They are also useful to physicists as they help them understand how the air moves.

What does an anemometer measure?

Anemometers are commonly found in weather stations. The wind causes the air to move, resulting in a difference in air pressure. A traditional anemometer contains four cups to measure the speed of the wind. These four cups are linked to a horizontal arm. The cups spin faster on their axis, depending on how fast the wind is. The revolutions in one minute give the wind speed in rpm units. 

The measurement of the speed of the wind helps in forecasting weather like storms, hurricanes, and tornadoes. Presently, modern anemometers are available that have a unique appearance. Even pocket-sized anemometers are available nowadays. 

What does an anemometer measure? If you want to measure the speed of the wind, you can take an anemometer outdoors. Then, you can count the number of times the cup moves to the front in 30 seconds. Multiply that number by two to obtain the value for rotations per minute or revolutions per minute. This way, the speed of wind is expressed in rpm. You can also count the number of times the cup rotates for 60 seconds to obtain the revolutions per minute directly.

How to Make an Anemometer

What is an anemometer method of construction? An anemometer can be easily constructed using a few basic materials. Anemometers are of different types depending on the situation, ecosystems, and measurements. An anemometer also employs laser and ultrasonic techniques to measure the wind accurately. 

Let us prepare an anemometer using disposable cups. The anemometer prepared this way is known as the Robinson Anemometer. The disposable cups are used to catch the wind that causes it to spin. The number of spins in a certain time interval is measured to calculate the speed of the wind. This will reveal how fast the wind is moving. 

Materials Required for the Experiment

• Five small paper cups
• Three thin wooden dowels
• An empty bottle made of plastic 
• Hole punch
• Scissors
• Stopwatch
• Duct tape

Procedure

• By using the hole punch, make a hole on the side of each of the four paper cups.
• The last paper cup will form the center of the anemometer. So, four evenly spaced holes should be made around its rim.
• Now, pass two wooden dowels through the holes you made in the center of the cup.
• Insert the wooden dowels’ other end into the holes of the other cup. Take them using duct tape. Ensure that all the cups face the same direction.
• Attach the last wooden dowel to the bottom of the center cup.
• Place the wooden dowel at the center into the empty bottle made of plastic. 

Observation

The cup anemometer made this way cannot display the speed of the wind, but it can provide an idea about how fast the wind is blowing. You can only record the wind speed with this anemometer when you measure the revolutions per minute. What does an anemometer measure? The anemometer that is used for forecasting weather is of a higher capacity. It measures the speed of the wind in terms of miles per hour or kilometers per hour.

A record of the wind by revolution per minute can be kept for a few days, after which the average wind speed in a week can be calculated. Also, the wind speed can be checked at different times of the day, like the morning, evening, afternoon, and night. 

History of Anemometers

The anemometers were first developed in the 15th century and have been changed slightly since then. These were first invented by a scientist named Alberti in 1450. In the subsequent centuries, several other scientists, including Robert Hooke, developed their own versions of anemometers. John Romney, in the year 1846, used four hemispherical cups and mechanical wheels to improve the design of the existing anemometers.

 A Canadian meteorologist named John Patterson in 1926 developed a three-cup anemometer which was later improved in design by Joiner and Brevoort. Another scientist named Derek Weston, in 1991, enhanced the functioning of the pre-existing anemometers by adding the ability to measure the direction of the wind. The sonic anemometer was invented by Andreas Pflitsch in 1994. 

Effect of Icing on Anemometers

What is anemometer icing? It is important to have an accurate measurement of the wind parameters at airports under all conditions, including freezing precipitation weather conditions. The operation of wind turbines is also monitored and controlled using the concept of anemometry. These wind turbines are prone to in-cloud icing in cold environments. 

This icing affects the aerodynamics of an anemometer and can even make it out of service. This is why anemometers used in such settings must be heated internally. The present heated versions of anemometers are the sonic anemometers and the cup anemometers.

Types of Anemometers

Anemometers are classified based on the measurement of the pressure of wind and the velocity of the wind. There are five main types of anemometers:

• Cup anemometer definition: This type of anemometer comprises four hemispherical cups mounted at equal angles on one end of the horizontal arms on a vertical shaft. The cups are positioned in such a way that the air crosses them in a horizontal direction, making them rotate so that it is proportional to the wind speed. The average wind speed is determined by calculating the turns of the cup over a period of time. These anemometers are employed by meteorologists, researchers, and educational institutes for commercial purposes and research activities.
• Hot Wire anemometer definition: This type of anemometer comprises a thin wire which is heated up to a temperature slightly higher than the atmospheric temperature. As the air flows across the wire, it cools down. To determine the velocity, the relationship between the wire’s resistance and the wind velocity must be established because most metals’ resistance depends on the temperature of the metal. The types of anemometers are used in heating, air conditioning, and ventilation businesses to measure the airflow through the building ducts.
• Windmill anemometer definition: This type of anemometer is similar to the normal windmill employed to calculate the wind velocity. It has an axis of rotation that runs parallel to the wind’s direction. It also consists of an aerovane as the wind direction is variable, helping the axis to change its direction. The aerovane comprises a propeller and a tail to attain the precise value of the wind speed and direction.
• Laser doppler anemometer definition: This anemometer uses a light beam so that it is split into two beams. Calculation of the amount of light reflected off by moving air particles when one of the two parts of the split beam enters the anemometer gives the velocity. These types of anemometers are used in scientific wind turbines and aircraft.

Uses of Anemometer

Besides measuring the wind speed, an anemometer has the following uses:

• To measure the wind flow.
• To measure the pressure of the wind.
• To determine the wind direction.
• To measure the air speed in aerodynamics.
• It is employed to check the weather conditions before using drones or RC planes.
• Anemometers are also utilized by pilots and long-range shooters.
• Employed by skydivers to assess the velocity of the wind before leaping into the abyss.

Conclusion

An anemometer is a useful mechanical instrument to measure the velocity or speed of gasses or the air. Its flow may either be contained like airflow in a duct or uncontained, such as the atmospheric wind. An anemometer can detect the alterations in some physical properties of fluids to find out the velocity of air. An anemometer performs by counting the number of rotations. It is also used to measure the speed of the wind. Additionally, anemometers are used by physicists to study air movements. 

Frequently Asked Questions (FAQ’s)

1.How does the commonest type of anemometer work?

The commonest anemometers have three to four cups attached to their horizontal arms, which are in turn attached to a vertical arm. The cups rotate as the wind blows, making it spin. The rod spins faster if the wind is stronger. The number of rotations is counted by the anemometer, which is then used to measure the speed of the wind. Because the wind has gusts and lulls and is not consistent, wind speed is averaged over a time period

2.What is a cup anemometer?

A cup anemometer is also called a rotational anemometer. It comprises cups that are placed on its vertical axis. Because of the pressure of the wind against these cups, they rotate. The speed of the wind depends on how fast the cups rotate and vice versa. These are commonly used by researchers, meteorologists, and educational institutions for study purposes.

3.What is a laser doppler anemometer?

A laser doppler anemometer works on the concept of the doppler effect to find out the flow of the wind. It uses a light beam that is further cleaved into a pair of beams. The speed is found by estimating the amount of light reflected off by the wind particles. Its application is mostly in river hydrology and high-tech jet engines.