How does anemometer measure wind speed

A rather cheaper type is the propeller anemometer, but to get an accurate measure of speed it has to be kept facing into the wind — whose direction changes from one moment to the next, so this can sometimes be tricky. A cup anemometer just has to be held vertically and it will measure wind from any direction.

Depending on the use the wind data is to be put, the speed is either averaged over a few minutes or the maximum speed is taken - known as a gust.

In addition, because wind speed increases with height above the ground, a standard measurement height of 10 metres is adopted. Most amateurs with weather stations cannot keep to these rules and neither can some Met Office stations so the general guidance is to make measurements as high as possible in an area which is as open as possible.

The highest officially-recognised gust at a low level weather station was mph at Fraserburgh, Scotland, on 13 Feb , but on the top of mountains wind is generally much stronger — gusts of mph were recorded on Cairngorm on 20 March Halloween can be a scary time of year when it comes to the weather.

From ghost-grey fogs to howling gales, just about anything is possible. Types of anemometers There is a wide range of anemometers models for directly measuring wind and air velocity.

Anemometers are usually classified as constant-temperature, or constant-power anemometers. Constant-temperature anemometers are popular because of their high-frequency response, low electronic noise level, immunity from sensor burnout when airflow suddenly drops, compatibility with hotfilm sensors, and their applicability to liquid or gas flows. Constant-power anemometers do not have a feedback system.

Temperature is simply proportional to flowrate. They are less popular because their zero-flow reading is not stable, temperature and velocity response is slow, and temperature compensation is limited. Most common anemometer applications An anemometer usually measures gas flows that are in turbulent flow conditions. The vane anemometer, thermal anemometer and cup anemometer typically used in weather stations are mostly used to measure the mean velocity, while the hot wire anemometers are usually used when turbulence characteristics are being measured, such as transverse measurements in a cross-section.

The term "thermal anemometer" is often used to mean any anemometer that uses a relationship between heat transfer and velocity to determine velocity.

Anemometers for weather stations The cup anemometer used in weather stations measures the velocity in a plane perpendicular to the axis of its rotation cups.

If the cup anemometer is mounted with the shaft perpendicular to the horizontal, it will measure only the component of the wind that is parallel to the ground. Other anemometers, such as vane anemometers, are used with the tip aligned with the total velocity vector. Before using an anemometer, it is important to determine how it should be positioned and what component of the total velocity its measurement represents.

Vane Anemometers Forms of rotating mechanical velocity anemometers may be described as belonging to the vane or propeller class.

With this style of anemometer, the axis of rotation must be parallel to the direction of the wind and therefore typically horizontal. In open spaces the wind varies in direction and the axis has to follow its changes.

In cases where the direction of the air motion is always the same, as in the ventilating shafts of mines and buildings for instance, wind vanes, known as air meters are employed, and give most satisfactory results. Vane anemometers are available with additional functions such as temperature, humidity and dew point measurements, volumetric conversion and data logging ability. Thermal Anemometers Thermal anemometers use a very fine wire on the order of several micrometers or element heated up to some temperature above the ambient.

Air flowing past over has a cooling effect. As the electrical resistance of most metals is dependent upon the temperature of the metal tungsten is a popular choice for hot wires , a relationship can be obtained between the resistance of the wire and the flow velocity. The voltage output from these anemometers is thus the result of some sort of circuit within the device trying to maintain the specific variable current, voltage or temperature constant. Additionally, PWM Pulse Width Modulation anemometers are also used, wherein the velocity is inferred by the time length of a repeating pulse of current that brings the wire up to a specified resistance and then stops until a threshold "floor" is reached, at which time the pulse is sent again.

Hot-wire anemometers, while extremely delicate, have extremely high frequency-response and fine spatial resolution compared to other measurement methods, and as such are almost universally employed for the detailed study of turbulent flows, or any flow in which rapid velocity fluctuations are of interest.

Thermal anemometers are available with additional functions such as temperature measurement, data logging ability. The sensors measure both velocity and temperature. Without a complicated calibration of the instrument t. Make sure the students understand the purpose of an anemometer. Initiate a discussion on the different things wind speed affects helps or hurts in the world.

Discuss the importance of making accurate measurements in predicting weather. Discuss the fact that the wind in the upper atmosphere moves at a different speed than the wind on the surface of the earth. Discuss some of the factors that might affect the speed of the wind. Details on all these subjects can be found by entering key words on google.

Toggle navigation. Home » Make Your Own Anemometer. Without a complicated calibration of the instrument t hey build, they will not be able to accurately convert their measurements to miles per hour.

We recommend wooden rulers because they are a good size, they have a hold in the center, and they are inexpensive. You may substitute any other materials you have available, just be sure that both spinning arms are the same length.