A simple anemometer consists of a small piece of wire which is heated with the help of an electric current passing through it and this material is placed in the air or gas stream whose velocity is to be measured. When the stream passing through it the wire cools it,
the rate of cooling being dependent on the flow velocity.
There are few various procedures to
achieve it.
(i) If a constant current is passed through the wire, the variation in flow results in a change of temperature of the wire and hence a change in resistance
which may be measured by a Wheatstone bridge arrangement. The change in resistance may be related to fluid flow.
(ii) If the wire’s resistance, and hence temperature, is kept constant, a change in fluid flow results in a corresponding change in current which can be
calibrated as an indication of the flow rate.
(iii) A thermocouple may be incorporated in the assembly, monitoring the hot wire and recording the temperature which is an indication of the air
or gas velocity.
