Air Flow Meter/Sensor: Description and Operation

DESCRIPTION
The mass air flow sensor measures the mass flow rate of intake air. Measurements are made so that the control circuit will emit an electrical output signal corresponding to the amount of heat dissipated from a hot wire placed in the stream of intake air.
The airflow past the hot wire removes the heat from the hot wire. The temperature of the hot wire is very sensitive to the mass flow rate. The higher the temperature of the hot wire, the greater its resistance value. This temperature change (resistance) is determined by the mass air flow rate. The control circuit accurately regulates current (I) in relation to the varying resistance value (RH) so that VA always equals VB. The mass air flow sensor transmits a voltage value VA to the ECM where the output is converted into an intake air signal.