Drift compensation in thermal anemometry

Abstract

The drift of the resistance of sensors used in thermal (such as hot-wire and hot-film) anemometry remains a perpetual concern for users of constant-temperature anemometers (CTAs). Even small changes in the resistance of such sensors result in error if the sensor was calibrated prior to the occurrence of the drift. In the present work, modified forms of the relationship between the output voltage of a constant-temperature anemometer and the fluid velocity, which take into account the sensor resistance as well as other resistances involved in the Wheatstone bridge (top resistance, operating resistance, cable and probe resistances), are used to minimize the sensitivity of the CTA to changes in the sensor resistance. These new relationships are tested using (i) two different CTAs and (ii) three hot-wires of differing resistances (3–), and are shown to collapse the calibration data, even though the sensor resistances had drifted. It is expected that use of this method would reduce the frequency of calibrations needed to maintain satisfactory degrees of accuracy and repeatability in experimental measurements of fluid flows made using CTAs.