Effect of bridge imbalance on the estimation of sensitivity coefficients for constant-temperature hot-wire anemometers

The Wheatstone bridge in which the hot wire is embedded in normal constant-temperature hot-wire anemometers is never perfectly balanced, due to the finite value of the amplifier offset. In this paper we investigate the influence of this imbalance on the estimation of sensitivity coefficients for velocity and temperature fluctuations. The analysis is made using the anemometer model developed by Perry and Morrison (1971 J. Fluid Mech. 47 577). It is shown that the absolute value of both non-dimensional sensitivity coefficients is always lower than in the ideal case of an anemometer which maintains the bridge perfectly balanced. The degree of discrepancy increases with increasing offset voltage and decreasing overheat ratio. However, it is shown that a direct calibration procedure takes this effect into account, thus ensuring an accurate determination of the sensitivity coefficients of the anemometer in practice. Experimental evidence confirming the theoretical results is presented.