Electronic noise in a constant voltage anemometer

Abstract

The electronic noise and the signal-to-noise ratio in a constant voltage anemometer (CVA) are analyzed in terms of the main constitutive elements of the circuit. It is shown that the output voltage due to electronic noise decreases with the wire resistance, permitting one to know the noise upper limit by using the results of the unheated wire. The noise power spectrum increases at high frequencies as f2, like in other anemometers, because of the need to compensate for the thermal lag of the hot wire, thus leading to a reduced signal-to-noise ratio at high frequencies. Explicit formulas are given in terms of wire, CVA, and flow quantities. Measurements of electronic noise in a CVA prototype confirm the theoretical analysis and illustrate some interesting issues concerning measurements of noise and low levels of flow fluctuations.