The FloXact air flow volume probes are designed to measure air velocity / air volume in HVAC systems together with the DPT-3500 FS air volume transmitter, for example. FloXact probe is also easy to install to the existing ducts.
The measurement is done over several measuring points inside the probe. The number of measurement points depends on the duct size and shape. The DPT 3500 FS can determine the average air flow volume on the basis of the measurements.