An anemometer with PWM excitation

An experimental prototype of an anemometer with PWM excitation is described. The instrument employs a thermistor as a flow detection sensor heated by a PWM voltage. An electronic negative feedback circuit substitutes the thermal power absorbed by the fluid from the heated sensor, and maintains it at a constant temperature. The pulse width contains the information about the fluid velocity and using a timer counter, the velocity information can be available in the digital form, without the use of a conventional A/D converter. Test results are also presented.