An anemometer is a device that measures the speed of gases, either in confined or unconfined flows, such as airflow in a duct or wind in the atmosphere. The anemometer determines the velocity of a flow by measuring changes in the flow’s physical properties or by detecting an effect of the flow on a mechanical device.
Hot wire anemometers are the most popular constant-temperature anemometers. It has an electrically heated, fine-wire element (0.016 inches in diameter and 0.05 inches in length) with needles at its ends. The hot wire anemometer is best suited to measuring gases with low velocities, however, venturi meters may also be useful for measuring liquid flow applications (for instance, slurry).
An overview of anemometers
Anemometers are used for what?
In addition to measuring total velocity magnitude and velocity magnitude on a horizontal plane, an anemometer can also measure velocity component in a specific direction.
There are many types of anemometers available for measuring air velocity and wind speed directly. Vane anemometers, Thermal anemometers, Velocity/Temperature profiling thermal anemometers and Cup anemometers are the most popular anemometer models. In general, anemometers are divided into constant-temperature and constant-power types.
A constant-temperature anemometer is popular because of its high-frequency response, low electronic noise level, immunity to sensor burnout when airflow suddenly drops, compatibility with hot-film sensors, and application to liquid or gas flows.
A constant-power anemometer lacks a feedback system. The temperature is simply proportional to the flowrate. Since their zero-flow readings aren’t stable, temperature and velocity responses are slow, and temperature compensation is limited, they are smaller and less popular.
Anemometer applications most commonly used
Gas flows are usually measured by an anemometer under turbulent conditions. The vane anemometer, thermometer, and cup anemometer (typically used in weather stations) are used to measure mean air velocity, while hot wire anemometers are used to measure turbulence characteristics in cross-sections. “Thermal anemometers” refer to any anemometers which use a relationship between temperature and velocity to calculate velocity.
In a cup anemometer (used at weather stations), the velocity is measured perpendicular to the rotation axis. An anemometer mounted with the shaft perpendicular to the horizontal will only measure the air motion parallel to the ground when it is mounted that way.
In other anemometers, such as vane anemometers, the tip is aligned with the total velocity. Anemometers are very useful equipment for measuring velocity; however, it is important to understand how they should be positioned and what components of total velocity they measure.