Air Flow Meter/Sensor: Description and Operation

OPERATION:
The hotwire airflow sensor is based on a concept in which a heated resistance element within the air current is maintained at a constant temperature. The system monitors the heating element's temperature.
The amount of electrical current that the heater element needs to maintain a constant temperature varies according to the amount and temperature of the air flowing past the mass air-flow sensor.
The heater element's current draw thus provides a direct index of the amount of air entering the system.

Mass Air-Flow Sensor G70:

Electrical Circuit - Mass Air-Flow Sensor G70:

Mass Air-Flow Sensor G7O:
The Hitachi MP1 has a mass airflow sensor using a hotwire and temperature sensor.
The temperature sensor measures the intake air temperature. The regulating electronics in the mass airflow sensor measures the heat current for the hot wire, so that the temperature lies at a constant value via the intake air temperature. Thereby the hotwire current is a direct measurement for mass airflow current and for the engine load.
During signal failure the engine runs with replacement values (independent of throttle Position and rpm). An adjustment is Possible via oxygen sensor control.