Hot Film Mass Air Flow Sensor (B2/5), Function

Schematic Veiw Of Mass Air Flow Sensor:

The electronic control in hot film mass air flow sensor controls the temperature of the heating resistor (RH) by means of a variable voltage, so that its temperature is 160 °C above the intake air temperature detected by the temperature resistor (RL). The temperature of the heating resistor (RH) is detected by the sensor resistor (RS).

If a temperature change occurs as a result of an increased or reduced air flow, the electronic control corrects the voltage at the heating resistor (RH) until the temperature difference is again achieved. This control voltage is used by the engine control module as a measure for the metered air mass.
The intake air temperature is detected by a further NTC resistor.