First and foremost, we should thank Leon Battista Alberti for his contribution to civilization for inventing the anemometer in 1450.
What he did was that he had secured a disc and had placed it perpendicularly to the direction of the wind so as to use the angle of inclination for his calculations.
Later on, more people came and altered the design and functions slowly to bring us even more anemometers. Now, anemometers are generally grouped into two major categories: to measure wind speed and to measure wind pressure.
First, let’s talk about the anemometers for measuring wind speed.
7 Different Types Of Anemometers
1. Cup Anemometers
John Thomas Romney Robinson, an Irish astronomer and physicist, entered the scene in 1846 to redesign the original anemometer by adding cups and wheels.
Specifically, he had attached four cups, and each of them was clamped vertically and connected to a wheel. The wind put force on each cup to make the instrument spin.
So, the theory was that wind speed would be proportional to the rate at which the cups will be spinning. As a result, the number of rotations made by the cups had to be noted down. This number obtained for wind speeds was needed as well to form a data set, for which each value corresponds to their respective wind speeds.
But matters like air resistance, cup size, and others were found to influence the result and give us false readings.
Later on, John Patterson in 1926 redesigned Robinson’s anemometer by removing a cup. He also found that the cups needed to be at an angle of 45 degrees to the direction of the wind.
Patterson’s model brought down the error percentage to less than 3 percent. The three-cup idea was used henceforth.
2. Vane Anemometers
It’s another simple anemometer that can help you to find out the wind direction and the wind speed as well.
Compared with the cup anemometer, they have their axes parallel to the wind direction instead of being perpendicular. You would find a fan attached to the end of a pointed body, and each of the blades is tilted slightly so that when the wind forces them to move, the fan ends up rotating.
The other end of the body extends outwards, forming a thin, arrow-like shape, called the tail. Meanwhile, the body rests on a vertical shaft but is free to rotate about. After rotating, the body will settle, and the direction the tail will point towards will be the direction of the traveling wind.
Measurements are much more precise and accurate with vane anemometers. The speed is measured by an already installed counter and evaluated by electronic chips.
You can find compact and portable ones as well as bigger vane anemometers in the market.
3. Hot-Wired Anemometers
This one is a bit expensive but worth the money.
They use a very fine piece of wire, held by metal coated supporters. You need to connect the whole thing to a circuit to let current flow in, and eventually heat up the wire. For such heating purposes, tungsten or platinum metals are usually used.
The fluid flow (in most cases air) cools down the wire as it travels against it. As a result, the wire’s resistance changes. The wire is connected to a separate circuit to give us proportional readings for air flow.
Usually, two types of these devices exist. One tries to maintain a constant temperature for the wire and the other tries for a constant current flow.
Warning: constant current configured anemometers are subjected to having higher chances of burning out.
They can come really compact to lessen flow disturbance. And they can be very sensitive, hence the higher precision and accuracy.
But these can be useless if the flow pressure is too high as the wire might get cooled down too fast.
Meanwhile, the other special hot-wired anemometers come with insulated wires and are usually built for heavy duty use.
4. Laser Doppler Anemometers
LDA in short, these anemometers use laser light. Rather than a single device, they’re more like machinery set ups.
The laser light is first divided to form two beams, both having the same frequency. Also, the two beams are made to converge with one another.
Next, particles are let in the medium whose flow needs to be measured through the probe volume. What they do is that they scatter the laser light into different directions, all with different frequencies.
They create a Doppler effect. Some of the scattered laser light rays reach the detector, if traveling in the right direction. They give the detector two types of frequencies: the initial and the scattered one. These values are directly proportional to the medium’s flow changes.
Laser Doppler anemometers are advantageous because they don’t disturb the fluid’s path, nor do they need to be calibrated. They can even work and measure in contaminated or reversed flow environments.
Obviously, bump up the functions, and you bump up the price too.
5. Sonic Anemometer
These anemometers use ultrasonic sound waves, to be exact.
You need to have a transmitter and a receiver. The time taken for the sound waves to generate from the transmitter are sent to be detected by the receiver. And disturbances due to wind flow can give us proportional readings for different wind speeds.
Ultrasonic waves are used to avert noise pollution since us humans can’t pick up waves outside our hearing range.
Erroneous result can occur if the air is contaminated or due to noise disturbances. Weather conditions such as humidity and temperature have an effect as well.
But the biggest problem of all is the speed difference between the sound waves and wind speed. A significant change in the wave speed is needed to get proper readings.
They can lighten your wallet since they are pretty expensive.
Ultrasound anemometers can be either two-dimensional or three-dimensional, both used in different cases. The two-dimensional ones are used in navigation and aviation, while the three-dimensional ones are used in measuring emissions, like in the industry power plants.
Now, let’s move on to the anemometers that are used for measuring wind pressure.
6. Plate Anemometers
Recall good old Alberti? Both types of anemometers have one thing in common; plates.
But here, springs are used. The plate restricts the air flow, gaining force to be pushed backwards. Moreover, the spring is compressed, and the length of compression is used to find values for pressure.
These anemometers are intended for gusty winds.
7. Tube Anemometers
The very first design was like of a manometer. While one end faced the wind directly, the other end’s surface only grazed it.
The end which faces the wind has a pressure increase due to receiving a force from the wind, and the other end of the u-tube has a decrease in pressure because a suction force is created.
Keep in mind that the difference in the water levels corresponds both to speed and wind pressure.
Just like plate anemometers, they’re inadequate instruments for rapidly changing winds and better results can be obtained only at the right angle.
So, you see, anemometers have lots of types, and those types can be further classified.
None offers results satisfactory enough for everyone, as of yet. But science is growing, and we’re still hoping to achieve better result in the future.