Air Flow Meter/Sensor: Description and Operation

CIRCUIT DESCRIPTION
As shown in the figure, when a pillar (Vortex generating body) is placed in the path of a uniform flow, vortices called Karman-Vortex are generated downstream of the object. Using this principle, a vortex generator is placed inside the volume air flow meter. By measuring the frequency of the vortices generated, the Engine Control Module (ECM) can determine the volume of air flowing through the volume air flow meter. The vortices are detected by their exerting pressure on thin metal foil (mirror) surfaces and a light emitting element and light receptor (LED and photo transistor) positioned opposite the mirror which optically senses the vibrations in the mirror. The ECM uses these signals mainly for calculation of the basic injection volume and the basic ignition advance angle.