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. 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. 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. Several ways of implementing this exist, and hot-wire devices can be further classified as CCA (Constant-Current Anemometer), CVA (Constant-Voltage Anemometer) and CTA (Constant-Temperature Anemometer). 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. Air flowing past over has a cooling effect. Thermal anemometers use a very fine wire (on the order of several micrometers) or element heated up to some temperature above the ambient. Before using an anemometer, it is important to determine how it should be positioned and what component of the total velocity its measurement represents. Other anemometers, such as vane anemometers, are used with the tip aligned with the total velocity vector. 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. The cup anemometer (used in weather stations) measures the velocity in a plane perpendicular to the axis of its rotation cups.

The term anemometer was derived from the Greek words anemos, “wind,” and metron, “measure.” Mechanical anemometers were first developed back in the 15th century to measure wind speed. The term 'thermal anemometer' is often used to mean any anemometer that uses a relationship between heat transfer and velocity to determine velocity. 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. They are less popular because their zero-flow reading is not stable, temperature and velocity response is slow, and temperature compensation is limited.Īn anemometer usually measures gas flows that are in turbulent flow conditions. Temperature is simply proportional to flowrate. Anemometers are usually classified as constant-temperature, or constant-power anemometers.Ĭonstant-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.Ĭonstant-power anemometers do not have a feedback system. The four most popular anemometer models are: Vane Anemometers, Thermal Anemometers, Thermal Anemometers with Velocity / Temperature Profiling and Cup Anemometers.

There is a wide range of anemometers models for directly measuring wind and air velocity.

While hot wire anemometers are best suited for clean gases at low velocities, venturi meters can also be considered for some liquid (including slurry) flow applications.Īn anemometer can measure the total velocity magnitude, the velocity magnitude on a horizontal plane, or the velocity component in a particular direction. It consists of an electrically heated, fine-wire element (0.00016 inch in diameter and 0.05 inch long) supported by needles at its ends. The hot wire anemometer is the most popular kind of constant-temperature anemometers. To determine the velocity, an anemometer detects change in some physical property of the fluid or the effect of the fluid on a mechanical device inserted into the flow. An anemometer is an instrument used to measure the speed or velocity of gases either in a contained flow, such as airflow in a duct, or in unconfined flows, such as atmospheric wind.

Velometer vs anemometer