Mass flow sensor
In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder.
However, with additional sensors and inputs, an engine's ECU can determine the mass flow rate of intake air.
A voltage is applied to the potentiometer and a voltage appears on the output terminal of the potentiometer proportional to the angle the vane rotates, or the movement of the vane may directly regulate the amount of fuel injected, as in the K-Jetronic system.
The vane moves because of the drag force of the air flow against it; it does not measure volume or mass directly.
The current increase or decrease is proportional to the mass of air flowing past the wire.
Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density.
The GM LS engine series (as well as others) use a coldwire MAF system (produced by AC Delco) that works similarly to the hot-wire MAF system; however, it uses an additional "cold" resistor to measure the ambient air and provide a reference for the "hot" resistor element used to measure the air flow.
[5] The mesh on the MAF is used to smooth out airflow to ensure the sensors have the best chance of a steady reading.
In situations where owners use oiled-gauze air filters, it is possible for excess oil to coat the MAF sensor and skew its readings.
Indeed, General Motors has issued a Technical Service Bulletin, indicating problems from rough idle all the way to possible transmission damage resulting from the contaminated sensors.
The sensors should be gently sprayed from a careful distance to avoid physically damaging them and then allowed to thoroughly dry before reinstalling.
Manufacturers claim that a simple but extremely reliable test to ensure correct functionality is to tap the unit with the back of a screwdriver while the car is running, and if this causes any changes in the output frequency then the unit should be discarded and an OEM replacement installed.
A Kármán vortex sensor works by disrupting the air stream with a perpendicular bow.
Providing that the incoming flow is laminar, the wake consists of an oscillatory pattern of Kármán vortices.
A heater is integrated in the center of the membrane which maintains a constant temperature similar to the hot-wire approach.
The thermal membrane sensor is also capable of measuring flow in both directions, which sometimes occur in pulsating situations.
Such a microsensor reaches a significantly higher speed and sensitivity compared with macroscopic approaches.
