8-VALVE 1.4
ENGINE
FIAT PUNTO TRAINING OUTLINE
Fiat Auto S.p.A.
After Sales Training
Operation
The air temperature sensor is made up of a NTC (Negative Temperature Coefficient)
thermistor.
The resistance exhibited by the sensor decreases as the temperature increases.
The control unit input circuit distributes the 5 V reference voltage between the sensor
resistance and a fixed reference value, thus obtaining a voltage proportional to the resistance
(and, therefore, to the temperature).
The pressure sensor sensitive element is made up of a Wheatstone bridge silk-screen printed
on a ceramic membrane.
The absolute reference vacuum is found on one face of the membrane; the vacuum found in
the inlet manifold acts on the opposite face.
The signal (of a piezoresistive nature) resulting from the distortion suffered by the membrane
is amplified by an electronic circuit contained in the support that houses the ceramic
membrane and is then conveyed to the engine management control unit.
The diaphragm bends, with the engine off, depending on the atmospheric pressure value;
thus, the exact altitude information is obtained, with the key inserted.
During the engine operation, the effect of the vacuum causes a mechanic action on the sensor
membrane: the latter bends, thus making the resistance value to change.
Since the power supply is strictly kept constant (5 V) by the control unit, the resistance value
variation causes the output voltage value to vary, too.
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