Karman Vortex Air Flow Meter Terminal Identification

Constant Control

Regulated 5 volt reference


Karman Signal

Digital frequency signal representing air flow


Earth Ground

Sensor ground return

Air Flow Sensor Karman Vortex

The Karman vortex air flow meter and ECU are wired as shown in the diagram. Signal characteristics are represented by the illustration of the variable frequency square wave. Because of the pull-up resistor wired between the Vcc and Ks circuit, the Ks signal will go to 5 volts if the circuit is opened.

When air passes through the air flow meter, the vortex generator creates a swirling of the air downstream. This swirling effect is referred to as a "Karman vortex." The frequency of this Karman vortex varies with the velocity of the air entering the air flow meter and other variables. The photocoupler and metal foil mirror are used to detect changes in these vortices.

Karman Vortex Air Flow Sensor

The metal foil mirror is used to reflect light from the LED to the photo transistor. The foil is positioned directly above a pressure directing hole which causes it to oscillate with the changes in vortex frequency. As the mirror oscillates, the 5 volt Vcc reference is switched to ground by a photo transistor within the sensor. The resulting digital signal is a 5 volt square wave which increases in frequency in proportion to increases in intake air flow.

Vortex Hho

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