The hot-wire anemometer, principally used in gas flow measurement, consists of an electrically
heated, fine platinum wire which is immersed into the flow.
As the fluid velocity increases, the rate of heat flow from the heated wire to the flow stream increases. Thus, a cooling effect on the wire electrode occurs, causing its electrical resistance to change.
In a constant-current anemometer, the fluid velocity is determined from a measurement of the resulting change in wire resistance.
In a constant-resistance anemometer, fluid velocity is determined from the current needed to maintain a constant wire temperature and, thus, the resistance constant…