Vane anemometers
Vane anemometers rely on air flowing through them to spin the vane proportionally to the velocity of the flow. They offer good averaging (damping) and can be used in sweep mode to determine average flow across a duct that may have a varying velocity profile. Somewhat tolerant to turbulence compared to other forms of anemometer. Greatest accuracy of the three forms of anemometers.
Can sample, log, record temperature, and calculate volumetric flow given duct dimensions.
They store data internally for download to PC in fixed format or editable in Excel.
Hotwire anemometers
Hotwire anemometers use the cooling effect of air passing over a heated element. They monitor the power required to maintain the temperature of the element, and this is proportional to the air flow.
Hotwire anemometers are commonly used to insert perpendicularly into ducts, being ~7mm diameter they can be used where vane anemometers can not. With an articulated head they can also be inserted longitudinally into large ducts.
Hotwire anemometers calculate air flow (volumetric rate) given duct dimensions, and temperature. They will log sample figures. Advanced versions will log periodically, measure humidity, and calculate dewpoint and wet bulb temperature.
Data is stored internally for download to PC in fixed format or editable.
Pitot tubes / Pitot matrix
Measuring air flow by pitot principal relies on the precise measurement of the differential pressure of air on the tip of the pitot (the dynamic pressure) compared to that at the reference holes (the static pressure). The measurement and subsequent calculation is performed by precision micro manometer and units of measure may include dp (Pa/mBar, kPa) velocity, and volumetric flow.
Pitot tubes are very directional so can be adversely affected by turbulence or misalignment. They do however offer extended flow measurement band (100m/s) and may be used at elevated temperatures and within ducting, making them ideal for exhaust flue measurement or measurement where hotwires would be considered dangerous (volatile gas).
The Pitot matrix works on the same principal but employs an array of static and dynamic pressure holes to allow exceptional averaging of multiple readings as is the case with an accubalance balometer.