Improvement of the signal-to-noise ratio of the constant-temperature hot-wire anemometer using the transfer function

In the present paper, a compact low-noise constant-temperature hot-wire anemometer (CTA) was developed to improve the signal-to-noise (S/N) ratio in hot-wire measurements. The CTA circuit was small enough to be attached to the support stem directly, which minimized the reactance of the sensor cable, maximized the electromagnetic shielding effect and simplified the circuit's transfer function. White noise as well as a square wave were used to examine the dynamic responses of the CTA in detail. Three parameters in the transfer function were successfully determined by the square-wave test. The transfer function with experimentally determined parameters was found to describe the CTA responses quite well over the wide frequency range, from 1 Hz to 250 kHz. It was demonstrated for residual free-stream turbulence in a wind tunnel that the established transfer function allowed the separation of electric noise from the measured data, improving the S/N ratio in the power spectrum of the velocity fluctuations. (paper)