Probe Selection and Measurement Applications of Anemometers
The flow velocity measuring range of 0 to 100 m/s is divided into three intervals: low speed from 0 to 5 m/s, medium speed from 5 to 40 m/s, and high speed from 40 to 100 m/s. Thermal anemometer probes are designed for low‑velocity measurement of 0 to 5 m/s; rotary vane probes deliver optimal performance at 5 to 40 m/s; and pitot tubes provide the most accurate results for high‑speed measurement.
Ambient temperature is another important factor for probe selection. Standard thermal sensors typically operate within a range of ±7 °C. Specialized rotary vane probes can withstand temperatures up to 35 °C, while pitot tubes are suitable for operating temperatures above 35 °C.
Thermal Probes for Anemometers
The operating principle of a thermal probe relies on cool airflow removing heat from a heated sensing element. A control circuit maintains a constant temperature, making the adjustment current directly proportional to the flow velocity.
When thermal probes are used in turbulent flow, airflow impacting the sensing element from all directions reduces measurement accuracy. In turbulent conditions, readings from thermal sensors are generally higher than those from rotary vane probes. This situation is commonly encountered during duct testing and may occur even at low velocities depending on duct structure and turbulence characteristics.
Measurements should therefore be carried out on straight duct sections. The measuring point must be located at least 10×D downstream from any upstream fitting and at least 4×D upstream from downstream obstructions, where D represents the duct diameter in centimeters. The entire flow cross‑section must remain clear of barriers such as sharp corners, suspended components and other obstacles.
Recommended thermal anemometer: DT‑8880 manufactured by Guangzhou Hongcheng. Equipped with a high‑sensitivity thermal probe, it measures duct wind speed, air temperature and airflow volume with superior precision and responsiveness, especially for low‑velocity conditions.
Rotary Vane Probes for Anemometers
Rotary vane probes convert mechanical rotation into electrical signals. A proximity sensor records vane revolutions and outputs a pulse sequence, which is processed by the instrument to calculate rotational speed and flow velocity.
Large‑diameter probes (60 mm, 100 mm) are suitable for measuring turbulent flow at medium and low velocities, such as at duct outlets. Small‑diameter probes are ideal for ducts whose cross‑sectional area is more than 100 times that of the probe.
Anemometer Positioning in Airflow
For accurate readings, the rotary vane axis must be aligned parallel to the airflow direction. Rotating the probe slightly will change the displayed value; the correct orientation is confirmed when the reading reaches its maximum.
Sufficient straight duct length upstream of the test point minimizes the influence of turbulence on thermal probes and pitot tubes.
Duct Air Velocity Measurement
Field experience proves that the 16 mm anemometer probe offers the widest range of practical applications. Its structural design ensures low flow resistance while withstanding flow velocities up to 60 m/s. Duct velocity testing is a mature and reliable detection method, and indirect measurement procedures such as the grid traversal method are widely applied to air duct inspection.
