Air Flow Meter/Sensor: Description and Operation

Fig. 21 Air Flow Meter Operation:

The air flow meter measures the mass air flow rate of intake air. A heated wire is subjected to the air flow, corresponding to the amount of heat dissipated by the wire, an electrical signal is sent to the ECU. The higher the temperature of the wire, the higher the resistance is.
The more air that the wire is subjected to, the lower the resistance (temperature). The control circuit regulates current I in relation to the varying resistance value RH so that VA always equals VB. The ECU receives the voltage value from VA and converts it into an air flow rate.