Figure 4-5. Applications of a commercially available swinging vane anemometer.
(3) Heated thermocouple anemometer. The heated thermocouple
anemometer operates on the principle that air moving past a heated object will remove
heat. The amount of heat removed is proportional to the quantity of air passing, which
is a function of velocity. These instruments have one or more thermocouples as
sensing elements that are heated by either alternating or direct current. A change in
airflow causes a change in temperature of the thermocouples, resulting in a change of
direct current output. Another unheated thermocouple is in the direct current circuit to a
meter. As a result of the changes in temperature, a change in voltage is developed
which is read as air velocity. These instruments are usually comprised of a single probe
MD0165
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