A new approach to enhance the sensitivity of a hot-wire anemometer and static response analysis of a variable-temperature anemometer

A new hot-wire anemometer which has greater sensitivity than that of a conventional constant-temperature anemometer (CTA) was proposed. Sensitivity differences between a recently developed constant-voltage anemometer (CVA) and a CTA provided a direct motivation of the present study. To derive a factor which made the difference in sensitivity, static response analyses of a CTA and CVA were performed first by calculations and experiments. It was found that the major factor which is responsible for the sensitivity of an anemometer is not the working resistance of a hot wire itself, but the change in the wire resistance with velocity. Based on this analysis, a new anemometer circuit, Where the wire working resistance increases with velocity - that is, the operating mode of the wire becomes variable-temperature - was proposed and named a variable-temperature anemometer (VTA). The VTA was made by substituting a voltage-controlled variable resistor such as a photoconductive cell or a transistor for one arm of the bridge. By positively feeding back the bridge-top signal to the input side of these electronic components, the wire resistance could be increased with velocity automatically. The enhanced sensitivity of the VTA was validated by comparing experiment with the CTA.