Patent ID: 7072776

Claim:
An anemometer comprising: a bridge circuit having a hot wire sensing resistor, a pair of input terminals, and a pair of output terminals, the hot wire sensing resistor operational to change its resistance in response to air flowing past it, unbalancing the bridge circuit and causing a differential signal to appear across the bridge circuit output terminals; a first differential amplifier coupled to the output terminals of the bridge circuit, the first differential amplifier configured to generate an output signal in response to the differential signal at the bridge circuit output terminals; a switching circuit operational to cycle a supply voltage to the input terminals in response to the first differential amplifier output signal and further in response to a discontinuous time control signal, such that current does not flow continuously through the hot wire sensing resistor; wherein the switching circuit comprises: a switching transistor; a second differential amplifier responsive to the first differential amplifier output signal and the discontinuous time control signal to turn the switching transistor on and off such that the supply voltage is intermittently connected to the bridge circuit; further comprising an intermediate output voltage circuit connected to the bridge circuit and operational to generate an anemometer output voltage V O = ( R 1 R 1 + R H ) ⁢ ( K V BAT ) , where V O is the anemometer output voltage, R H is the hot wire sensing resistor, R 1 is a bridge circuit resistor in the same arm as hot wire sensing resistor R H , K is constant determined at a given air flow rate, and V BAT is the anemometer supply voltage.