A digital anemometer

A digital anemometer has been developed for air flow measurements in home and office environments. The principle is based on hot-wire anemometry. The probe consists of a cold thermistor for flow temperature detection and a hot thermistor for flow rate detection. The latter is self-heated by a thermal bridge. Its unbalance voltage due to the air flow is compared with the reference response transformed into the time domain by direct digital synthesizing. This pulse-width modulation provides the linear digital representation of the flow rate under measurement. The unbalance component due to flow temperature is compensated by scaling the reference response depending on temperature detected by a cold thermistor. These linearization and compensation techniques make accurate measurements possible with a simple configuration. Performances of a prototype anemometer built using a one-chip 4-bit microcomputer are also presented to demonstrate the validity of these techniques