Автор: Series (212.57.188.---)
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http://www.wellsmfgcorp.com/counterpoints/Counterpoint3_2.pdf
In a hot-wire MAF, a platinum wire is heated 212 degrees F above the incoming air temperature. In a hot-film MAF, a foil grid is heated 167 degrees F above ambient air temperature.
The output signal produced by the MAF sensor varies according to the application. The hot-wire Bosch MAF sensors, which are found on some import cars with LHJetronic fuel injection dating back to 1979
as well as 1985-89 GM 5.0L and 5.7L Tuned Port Injection (TPI) engines,
generate an analog voltage signal that varies from 0 to 5 volts. Output at idle is usually 0.4 to 0.8 volts increasing up to 4.5 to 5.0 volts at wide-open throttle.
The hot-film MAFs, which AC Rochester introduced in 1984 on the Buick turbo 3.8L V6 and were also used on Chevrolet 2.8L
engines and GM 3.0L and 3.8L V6 engines, produce a square-wave variable frequency output. The frequency range varies from 32
to 150 Hz, with 32 Hz being average for idle and 150 Hz for wide-open throttle. In 1990, GM switched most of its engines back to
speed-density fuel injection systems, except for the Buick 3.3L and 3.8L which changed to a Hitachi MAF sensor.
Another difference between the hot-wire and hot-film sensors is that the Bosch hot-wire units have a self-cleaning cycle where the
platinum wire is heated to 1,000 degrees C (1,832 F) for one second after the engine is shut down. The momentary surge in current is controlled by the onboard computer through a relay to burn off contaminants
that might otherwise foul the wire and interfere with the sensor’s ability to read incoming air mass accurately.
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