Air Flow Sensors

Basic Description

Air flow sensors measure the volume or the mass of air flowing in a channel. In an automobile, the primary use of an air flow sensor is to determine the amount of air drawn into the engine through the intake manifold. There are two main types of air flow sensors: volume air flow sensors (that measure the effect of the moving air on a pin wheel or deflecting plate) and mass air flow sensors. As the load on an internal combustion engine varies, it is necessary to determine how much air (by mass) is entering the cylinders in order to determine how much fuel to inject and how to adjust the engine timing. The mass flow sensor (MAF) is located in the air stream, between the air cleaner and throttle where it measures the amount of incoming air. The mass airflow sensor uses a hot wire to sense the airflow. As the air moving through the sensor cools the hot wire, the current flow through the wire changes. The sensor's internal circuitry converts this change in current to an output voltage. Three or four wires are normally used. The sensing wires are normally a thin platinum wire wound on a ceramic bobbin and coated with glass. This wire is maintained at 392°F (200°C) above the ambient temperature as measured relative to a constant "cold wire''.

Mass Air Flow Sensor

Manufacturers

Bosch, Continental, Delphi, Denso, Honeywell

For More Information

[1] Mass Flow Meter, Wikipedia.

[2] Air Flow Sensors, A Toyota document located at Autoshop101.com.

[3] Mass Air Flow Sensor (MAF), Automotive Illustrated Glossary at Samarins.com.

[4] Mass Air Flow (MAF) Sensor, freeautomechanic.com.

[5] Mass Air Flow Sensor (PID) , Youtube.com, Jan. 2008.