- 2Velocity anemometers
- 3Pressure anemometers
In today’s guide you’re going to learn everything you need to know about ultrasonic anemometer.
What Is Ultrasonic Anemometer
Maybe you have heard of sonic anemometers. But in our experiments at schools or science and technology museums, you probably know that sound travels by making air molecules move back and forth. It’s fairly obvious that the speed of the wind affects the speed at which sounds travels. If you’re shouting to a friend who’s down-wind of where’re standing, you’ll hear their voice s slightly sooner than would have if they had t travels. Here are no wind at all. Similarly, if they shout back, you’ll hear their voice slightly later – because the sound waves they generate have to fight against the wind to reach you. The same idea is used in an ingenious way in ultrasonic anemometers, which measures wind speed using high-frequency sound (generally above the range of humans can hear).
Anemometer, derived from greek word anemos(wind), is a device used for measuring the wind speed. While the first known description, we encounter dates far back to 1450, the widely used, cup anemometer was created in 1845 by Dr.John Thomas and hasn’t changed much since then in its fundamental concept. Since the cup anemometer consist of mechanical moving parts, it is adversely affected by various environmental factors like salty air or dust. To counter these affects, a better alternative was developed known as, Sonic Anemometers, and it uses ultrasonic sound waves to measure wind velocity.
An ultrasonic anemometer has two or three pairs of sound transmitters and receivers mounted at right angles to one another. Stand it in the wind and each transmitter constantly beams high-frequency sound to its respective receiver. Electronic circuits inside measure the time it takes for the sound to make its journey from each transmitter to the corresponding receiver. Depending on how the wind blows, it will affect some of the sound beams more than the others, slowing it down or speeding it up very slightly. The circuits measure the difference in speeds of the beams and use that to figure out how fast the wind is blowing.
Sonic Anemometer Working Principle
The basic principle used in sonic anemometer is that when the wind flows in the same direction as sound, the velocity of sound increases and when is in opposite direction, the velocity gets reduced accordingly.Therefore along a axis two transducers are placed and Time of Flight is calculated in both directions as explained by equations. This pair of transducers act alternately as transmitters and receivers, exchanging high-frequency ultrasound pulses between themselves. The times of flight in each direction t1 and t2, are measured. If c is the speed of sound in air, and L ,is the distance between the transducers and there is an airflow of velocity v along the line of the transducers, the following relationship is readily derived:
By combining Eqns (1) and (2) and solving for ` v`, the following equation is obtained:
Above calculations were only for one axis, but we can add more axis making devices 2D anemometer or 3D anemometer.This proposal, aims first for 2D sonic anemometer, which measures the time taken for an ultrasonic pulse of sound to travel from the North transducer to the South transducer, and compares it with the time for a pulse to travel from S to N transducer. Likewise times are compared between West and East, and East and West transducers.
The projected horizontal wind vector,`u `,specified by its magnitude in m/s and direction in degrees (0° is the direction of the north, the angle was counted positively in an easterly direction and negatively in a westerly direction) Now following Equations are involved here,
Now from above equations it is clear that speed of sound calculated this way is independent of factors such as temperatures.
Now with this device we can calculate the wind speed as well as temperature as described below-
here R is the universal gas constant (8314.34 mJ/mol K), C is speed of sound, M is the molecular weight (grams/mol) of the gas, and γ is the ratio of heat capacities Cp and Cv; Cp and Cv are the specific heats at constant pressure and constant volume of the gas, respectively.
The sonic temperature, Tv (in Kelvin), may differ from the absolute temperature by an amount equal to the water vapor content in the air measured. This difference amounts to ±1°C at 20°C and decreases as the temperature decreases.
Pros & Cons Of Ultrasonic Anemometer
|Volume & Weight||Small size and light weight|
|Temperature Effect||Considering temperature calibration and interference to ultrasonic probe|
|Accuracy||High accuracy and sensitivity|
|Starting Velocity||Start-up wind speed is small, 0.1m/s|
|Electromagnetic Interference||Electromagnetic interference is large and should be treated separately.|
|Life||No moving parts, long life|
|Price||High cost performance||More expensive than mechanical ones.|
Application Of Ultrasonic Anemometer
1. Ultrasonic Anemometer for Wind Power Industry.
In recent years, with the development of wind power technology, wind power sensors are constantly innovating. As a kind of weather measurement equipment, the mechanical wind speed and direction sensor used to measure the direction of wind slowly exposes many problems in the use, affecting the efficiency of wind power. Mechanical anemometer depends on the rotation of bearings to complete the measurement, so its accuracy and life basically depends on the bearings.
For example, in the case of severe sand and dust and corrosive coastal occasions, the bearing will be stuck prematurely due to foreign bodies and corrosion, and its service life will not exceed one and a half years.
When the environment is relatively good, the damp of the bearing will change after the anemometer is used for a certain time at any time. The error of the measured data will increase with the passage of time. Generally, its service life is about 3 years. Data error is too large, not only the power generation efficiency is low, but also will affect the life of other equipment.
For example, if the wind speed error is large, the generator may not start or stop when the wind is strong. The former only affects the efficiency of power generation, while the latter may cause production accidents. For example, the wind direction error is large: it may cause frequent windmill yaw and inaccurate wind, increase the fault of yaw system and reduce the life of blades, while inaccurate wind may directly cause the damage of blades in strong wind. When the wind direction is erroneous, the whole power generation efficiency will inevitably decrease.
Ultrasound anemometer is measured by ultrasonic sensor, so its accuracy and life basically depend on the ultrasonic sensor module. The surface of each sensor is coated with rubber. The whole sensor is mounted in a stainless steel sensor seat. The seat and the sensor bracket are welded seamlessly by laser. This prevents the sensor from being exposed directly, reduces the interference of sand and dust, and enhances its ability of resisting wind and sand, corrosion and rainwater. The signals collected by the sensor of the ultrasonic anemometer are identified and processed by CUP, which can reflect the wind speed, direction and ambient temperature more truthfully and reliably. Usually the service life of the ultrasonic wind speed and direction indicator is not less than 5 years.
2. Ultrasonic Anemometer for Tower Crane industry
It’s a simple but profound statement for crane operators today. The fact is wind is the second most common cause for crane accidents worldwide. The American National Standards Institute (ANSI) reports that, “Between 2000 and 2010, there were 1,125 tower crane accidents reported worldwide, resulting in over 780 deaths. One of the main culprits behind these tragedies was exposure to wind, which caused 23 percent of all accidents.”
At present, in the case of wind measurement of tower crane, the mechanical three-cup anemometer is mainly used. Costs vary greatly from high to low. Because there is no strict industry standard, the product quality is uneven.
In field visits, the anemometer life is as short as 1-3 months. The main reason is that the tower crane engineers are not professionals in the field of meteorology. They are too blind in the selection of wind direction and speed sensors.
Because the environment of the tower crane is very bad, generally the dust is bigger, and the mechanical vibration is more. If it is used in the Port Tower crane, the salt fog erosion of the sea water is very serious. If the conventional mechanical cup anemometer is used, there is a problem that requires regular manual maintenance, and foreign bodies in bearings need to be cleaned regularly.
At the same time, because the wind direction and wind speed are independent, it also needs to connect multiple cables, which also creates uncertainty for the stability of the system.
At present, ultrasonic anemometer is widely used in tower crane industry. Because of its fast response frequency, it can record real-time wind speed, ultra-low start wind speed, record the total wind process and maximum wind speed value.
This provides a theoretical guarantee for the operation safety of tower crane, and the long life of its equipment also provides support for the stability of the system, which gradually becomes the preferred scheme for engineers.
3. Ultrasonic Anemometer for UAV
At present, UAVs are widely used, and there are more and more kinds of instruments on board. Monitoring meteorological information is also one of their main uses.
Because of the small size and limited load of UAV, the conventional three-cup anemometer can not be selected, so the ultrasonic anemometer is a very suitable choice, the lightest can be 50-100g, because of its low power consumption of ultrasound itself, it should be the first choice for UAV wind measurement.
Unmanned aerial vehicle (UAV) is mainly used in the field of detection: environmental measurement, atmospheric monitoring, geological exploration, but also can be used for its own flight safety monitoring.
Find More About Sonic Anemometer
Three measurement campaigns and the use of sonic anemometry under specific conditions are described in this work. EBEX2000 was an international energy balance field experiment in San Joaquin Valley USA, were different sonic anemometer types, and heat and momentum flux measurements, were analyzed and compared. The second case was a complex coastal flow at Madeira Island, Portugal.
ISO 16622:2002 defines test methods of the performance of sonic anemometers/thermometers which employ the inverse time measurement for velocity of sound along differently oriented paths. It is applicable to designs measuring two or three components of the wind vector within an unlimited azimuthal acceptance angle.
|How It Works||WindSonic Ultrasonic Anemometers||FT Technologies – Ultrasonic wind sensors|
|GSoC-2017: Sonic Anemometer||3 Axis Ultrasonic Anemometer Market Insights, Forecast to 2025||FT7 Series wind sensors – Powered by Acoustic Resonance Technology|
How To Buy Sonic Anemometer
|Characteristic||Accuracy, Authority||Wind Power||Scientific Research||Accuracy, Cost-Effective|
|Main Application||Meteorological||Industry||Industry||Meteorological, IoT|
Future Ultrasonic Anemometer
The application of different ultrasonic anemometer, the only choice for scenarios of the product is the best.
1. Home ultrasonic anemometer and field application is different.
2. Such as used in the machine without anemometer and wind speed in the fan on the requirements are different,
These should be treated differently, and should not be to meet all needs in a way.
Compared with the traditional anemometer, the ultrasonic anemometer has no moving parts. But separate power
supply and communication are also needed. I think in the future scenarios, it should be able to integrate, users only
need a simple installation to upload data.
At present, sensor data are directly output, and there is no separate algorithm. Later, when it comes to equipment
data, there should be a cloud processing platform, including AI, which automatically identifies alarm information
and gives trend information of monitoring data.
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