The Signal-to-Noise Ratios of Constant-Current and Constant-Temperature Hot-Wire Anemometers

Expressions are derived for the signal-to-noise ratios of transistorized constant-current anemometers and constant-temperature anemometers. It is shown that the respective signal-to-noise ratios (in the same bandwidth) are not equal, but do not differ appreciably in a practical case. The minimum detectable signal (defined on the basis of unity signal-to-noise ratio and expressed in terms of equivalent turbulence intensity) of a constant-temperature anemometer, operated with a typical 5 micron diameter tungsten hot-wire transducer at a mean air flow velocity of 50 m/s, is shown to be 0.3 percent turbulence, in a direct current to 100 kHz frequency range.