A digital anemometer

A digital anemometer is presented for air flow measurements in house 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 velocity detection. The latter is self-heated by a thermal bridge. Its imbalance voltage due to the air flow is compared with the reference response transformed to the time domain by direct digital synthesizing. This pulse-width modulation provides the linear digital representation of the flow velocity under measurement. The imbalance component due to flow temperature is compensated for 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. The performance of a prototype anemometer built using a one-chip 4-b microcomputer is also presented to demonstrate the validity of these techniques