Air Flow Transducer
An air flow transducer is an apparatus for measuring the quantity or the flow rate of any type of moving gas. Transducers of this type can be categorized into four groups, namely, true mass, differential pressure, velocity, and positive displacement.
Four Basic Types
The most direct measurement of air flow is done by a true mass air flow transducer using, for instance, a thermal meter. Differential pressure air flow transducers, like rotameters and Venturi tubes, gauge the flow rate by calculating the square root of the discrepancies in pressure.
With velocity meters, on the other hand, square root relationships are not extracted, making the equation completely linear. Electromagnetic meters and sonar-based devices are examples of velocity meters. Oval gear meters are an example of positive displacement devices. Measurement is done by mechanically counting the increments of air flow.
Automotive Application
One of the common types of air flow transducers is used in fuel-injected engines of automobiles. This sensor determines the mass of air that enters the engine. Air density can change and air expands because the temperature rises and as the heat subsides, it contracts. Pressure, brought about by changes in altitude also contributes to changes in density.
Pressure is measured to ascertain balance within the engine. As long as air flow is identified, the control unit, which delivers fuel to the engine, can determine the right amount of fuel needed at any given time. The air flow transducer feeds the engine control unit electrical signals that represent the measurement.
While the air flow transducer measures the volume of incoming air, it does not control it. Regulation of the air flow is done by another component, the engine throttle plates.
Vane Air Flow Sensor
Gasoline engines use any of a few types of air flow transducers. The Vane Air Flow sensor is perhaps the most common kind. It measures air volume rather than air mass. It has an air flap that rotates when incoming air pushes against it.
The rotation of the Vane Air Flow sensor causes contact with signal-producing resistors. The resulting voltage output is therefore directly proportional to the air volume. Some vane air flow transducers are also equipped with heat sensors which make them more useful.