A
mass air flow sensor is used to find out the
mass of
air entering a fuel-injected engine. The air mass information is necessary for the
engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Air changes its density as it expands and contracts with temperature and pressure. In automotive applications, air
density varies with the ambient
temperature and
altitude, and this is an ideal application for a mass sensor. (See
stoichiometry and
ideal gas law.)
There are two common types of mass airflow sensors in usage on gasoline engines. These are the vane meter and the hot wire. Neither design employs technology that measures air mass directly. However, with an additional sensor or two, the engine's air mass flow rate can be accurately determined.
Both approaches are used almost exclusively on electronic
fuel injection (EFI) engines. Both sensor designs output a 0 - 5.0 volt or a
PWM signal that is proportional to the air mass flow rate, and both sensors have an intake air temperature (IAT) sensor incorporated into their housings.
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