An anemometer is a valuable mechanical device for measuring the speed or velocity of gasses. It can do this in a contained flow, such as airflow in a duct, and in unconfined flows, such as atmospheric wind.
You can find various kinds of anemometers that are on the market and each type features a unique style and functionality.
To choose the right one, you must consider certain factors and aspects. The commonly used one is the cup anemometer. It is made from cups that rotate as the wind flows. The stronger the speed of the wind, the faster it rotates. The total number of cups rotated can be used for measuring the wind speed.
Other anemometers estimate wind speed in different ways. A hot-wire anemometer operates based on the fact that air cools a heated object when it flows over it. An electrically heated thin wire is located in the wind in a hot-wire anemometer.
The amount of power required to hold the wire hot is used to measure the wind speed. The higher the wind speed, the more power is needed to keep the wire at a constant temperature.
Also, the wind speed can be calculated by measuring air pressure. A tube anemometer determines the wind pressure or speed by using air pressure. It measures the air pressure inside a glass tube closed at one end. The wind speed can be measured by comparing the air pressure within the tube to the outside air pressure.
Other types of anemometers calculate the speed of sound waves by using laser beams and measuring their effect.
Usually, anemometers are classified as constant-temperature or constant-power anemometers.
An anemometer is utilized in weather stations, airports, agricultural sectors, etc. It is beneficial for meteorologists to study the pattern of winds.
Considerations To Make When Selecting An Anemometer
Every type of anemometer operates differently and is better at certain purposes than others. For example, if you need a portable handheld wind speed instrument, a vane anemometer or a hot wire anemometer may meet your requirements. A cup anemometer is maybe difficult to carry due to its being bulky.
Some anemometers are easily portable. You can carry them everywhere you go. Others are part of wireless weather stations. You can install them in your backyard and read from an indoor display.
In addition, some handheld anemometers are easy to use, have a compact and lightweight design, and others have long installation cables. Some types are suitable for installing or repairing HVAC applications. Others, like hot-wire anemometers, are well suited for measuring airflow through a door or window that can enter from an opening.
Accuracy rating is the most important factor to consider when evaluating the quality of an anemometer. It indicates the accuracy of the reading provided by a particular anemometer. Anemometers with accuracy ranging from ± 5% or better always offer better results.
Response Time And Wind Speed
Another essential factor you must consider is the wind speed reported by the device. A good anemometer generally provides a wind speed reporting range from 0 to 100 mph or higher. It should provide quick responses. Since the wind speed fluctuates fast, the device must be able to produce intelligent and updated wind speed readings.
Size And Design
Anemometers come with varieties of sizes and designs—for example, some vane anemometers with larger vanes and some smaller ones. Also, there are cup anemometers with different numbers of cups. Vane anemometers with big vanes are more desirable than smaller ones.
Also, the 3-cup anemometer is more accurate than the 4-cup. The anemometer with longer cables is ideal because if the wind sensor is located higher, you can achieve a more accurate reading. You should notice little things while selecting an anemometer.
The device's durability depends on the anemometer's material and construction. These are necessary factors to consider when choosing an anemometer.
You must ensure that the anemometer you select is rugged and can resist the worst climates. It will constantly be prone to the outdoor environment and face the harshest weather conditions.
Usually, icing effects can disrupt the operation of cup and vane anemometers and cause failure. But today, some high-end heated versions of cup anemometers are available that can also operate even during the freezing climate.
Moreover, with new technologies, some cup and vane anemometers are designed with rotating parts with long operation life compared to the normal ones.
The color of the anemometer is somewhat important for places often affected by ice. Anemometers come up in two colors, black and white. Both are sensitive to icing, but black ones get warm and melt faster than white anemometers.
There are many other features that you can search for, such as electrical and mechanical components, accessibility for clean-up and maintenance, and digital pulse data that help avoid electrical interference from different sources like a radio transmission.
All types of anemometers do not fit your needs. You have to choose the style that meets your requirements and conditions. Does it respond to elevated or low temperatures? How long does the system warranty last? How reliable is that brand?
Once you think of buying an anemometer, firstly, you should decide which device is more appropriate to meet your needs. You should take the price into account based on your requirements. Because the cost can be different due to the features and comfort of the anemometer, choose the device that has excellent quality and best suits your budget.
Probe selection for anemometers
The flow velocity measurements ranging from 0 to 100 m/s are available in 3 segments:
- Low speed: 0 to 5m/s.
- Medium speed: 5 to 40m/s.
- High speed: 40 to 100m/s.
The thermal probe of the anemometer is suitable for precise measurements from 0 to 5m/s.
The rotor probe of the anemometer measures the flow velocity of 5 to 40m/s.
In the high-speed range, pitot tubes provide the best results.
Temperature is an added criterion for the correct selection of the flow probe of an anemometer. Normally, the temperature of the thermal sensor of an anemometer is about +-70C. Also, the rotor probe of a specific anemometer can get 350C. Pitot tubes are suitable for temperatures above +350C.
Thermal Probes For Anemometers
The thermal probe of the anemometer works based on the working principle that the airflow cools down the heating element. An adjustment switch maintains the temperature constant. The adjustment current corresponds to the flow rate.
By using thermal probes in turbulent flow, airflow simultaneously hits the thermal element from all directions. So, it can affect the accuracy of the measurement results. When measuring a turbulent flow, thermal anemometer flow sensors demand higher indications than rotor probes.
The above phenomena can occur during pipeline measurement. It can be observed even at low speeds based on the design that controls the turbulence in the pipe.
So, an anemometer must measure the flow on the straight section of the pipeline. The starting point of the straight line should be at least 10×D before the measurement point:
D=pipe diameter, in CM
The endpoint should be at least 4×D behind the measurement point. The fluid section must not have obstacles such as edges, re-suspensions, objects, etc.
Rotor Probe For Anemometer
The rotator probe of the anemometer works based on converting the revolution into an electrical signal.
First, the rotation of the runner is counted through a proximity induction head, and a pulse series is produced, then converted by the detector. So, we have the speed value.
The large-diameter probe (60mm, 100mm) of the anemometer fits the need to measure turbulent flow with the medium and small flow velocity.
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