UKAS Air Velocity Calibration Update Jan 2019

6th January 2019

Anemometer Calibration, Latest news for customers requiring ISO 17025 UKAS accredited calibration with our recently improved measurement calibration uncertainty for all types of air velocity, wind speed or anemometer instruments.

Cup Anemometer, being one of the oldest types of anemometer, commonly referred to as a rotating cup anemometer, as the wind blows, the cup rotates and outputs a frequency. The faster the cup rotates the higher the frequency and a calibration of frequency against air velocity is derived. Due to their large size these types of anemometers cannot be calibrated in 90% of the UKs wind tunnels. There are only a handful of UK commercial laboratories that can undertake rotating cup anemometer calibration. Young Calibration offer a 75 kW, 1m x 1m test section and can offer a UKAS accredited CMC of 0.23% of reading across an air velocity range of 1 24 m/s on rotating cups up to rotational diameter of 480 mm.

Vane anemometer, or more correctly named a rotating vane anemometer, can either be a fixed or remote measuring head. Generally smaller in physical size than the cup anemometers but work on a similar principle of the higher the rotational speed of the vane gives a higher frequency output. As a mechanical device the air velocity range is generally limited to wind speeds between 0.2 and 40 m/s. Our ISO 17025 accredited calibration uncertainty CMC is 0.20% +0.001 m/s.

Hot wire anemometers, or often known as thermal anemometers use the air velocity to cool a heated wire or film, where the higher the air velocity the more power is required to keep the wire at a constant temperature. Thermal anemometers have extremely high frequency response and fine spatial resolution and are often used for detailed study of turbulent flows in which rapid velocity fluctuations are of interest. High grade instruments are known as CTAs or constant temperature anemometers and can be manufactured in 1, 2 or 3 axes of measurement. Accredited calibration range is from 0.05 to 80 m/s with an air velocity CMC of 0.19% + 0.001 m/s.

Pitot tubes, yaw probes, S type and L type probes can be calibrated over a wide range of air velocities and results can also be derived for pitot head coefficients. Accredited calibration covers the range of 0.05 80 m/s with a CMC of 0.18% + 0.001 m/s.

Sonic anemometers, or ultrasonic anemometers have pairs of transducers for each axis of measurement and work on the time response of the ultrasonic wave from the transmit transducer to the capture of the wave at the receiving transducer. They have no moving parts and have quick response. They are often used in weather monitoring stations. Accredited calibrations can be undertaken across 0.05 40 m/s with a CMC of 0.20% + 0.001 m/s.

Laser doppler anemometer, or often shortened to LDA, uses a continuous wave laser source which is divided into two beams using a Bragg cell, the two beams are aimed to the focal point in the air flow stream, where the scattered light produced in the fringe volume made possible by tiny seeding material produces a doppler shift which proportional to the air velocity, by use of optics, lens, filtering, photo detector and signal conditioning the air velocity can be accurately determined. These types of anemometers are extremely accurate and can measure even the slightest changes in air velocity. We use both 1D and 2D laser doppler anemometers as our reference instruments for our anemometer calibration work. Measurement uncertainty of the reference device is around 0.08% of reading