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A mass air flow sensor (MAF) sensor measure the volume of air entering an engine. A sensitive constant-current series/parallel resistance circuit is used in this device to produce feedback voltage to the microprosessor. This circuit is contructed so that it will emit an electrical output signal corresponding to the amount of heat dissipated from a hot wire or metal foil placed in the stream of intake air.

The air flow past the 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 wire, the greater its resistance. This temperature change and result resistance change is used to determine the MAF rate. The circuit accurately reguates current (I) in relation to the veryig resistance value (Rh) so that Va always equal Vb. Voltage Vais fed back to microcomputer, whice uses this information to compute the MAF rate. Typical MAF output voltage ranges from 0.5V to 4.5V, white the voltage going up as the MAF rate increases.

The MAF sensor can be checked in circuit by measuring the input and output voltage with a digital voltmeter for different air flow conditions.

Use Airflow Calculator, easy Stuff  to calculate Air Flow..