The hot-wire anemometer is a widely used transducer in velocity measurements and for this reason, salient features involved in its operation are discussed below:

1. Wire temperature is usually in the range - C and is limited by the strength between the wire and the prongs. The corresponding wire resistances at room temperature and at are 3.5 and 6.5 ohms, respectively. The ratio of these resistances, called the overheat ratio is between 1.5 and 2.

2. The hot wire output is non-zero even when This is because a non-zero current must flow through the wire to compensate for heat transfer to the prongs by conduction, buoyancy driven motion of the fluid around the wire and heat transfer by radiation.

3. Mode of operation of the hot-wire probe described above wherein it is kept at a constant temperature results in a constant temperature anemometer (CTA). It is possible to use the probe in a constant current mode (CCA) as well. In the CCA mode the change in resistance of the wire is measured by passing a small current mA) through it and this change is related to the local velocity. It can be shown that a hot wire working in the CTA mode has a high frequency response kHz) in comparison to the CCA mode Hz). However, the CCA mode is useful in the measurement of local temperature and temperature fluctuations when the wire operates as a resistance thermometer.