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Mass air flow sensor Karman Vortex
A Kármán vortex sensor works by setting up a swirling air stream. The air stream is
disrupted by a vertical bow in the sensor. This causes a wake in the air stream and
subsequently the wake will collapse repeatedly and cause Kármán vortexes.
The frequency of the resulting air pressure oscillation is proportional to the air
velocity. These vortexes can read by making then to collide with a mirror which will
then interrupt or transmit a reflected light beam to generate the pulses in response
to the vortexes.
Instead of outputting a constant voltage modified by a resistance factor, this type
of mass air flow sensor outputs a frequency which must then be interpreted by the ECU.
This type of mass air flow sensor can be found on Mitsubishi Eclipse, Eagle Talon,
Plymouth Laser, some Toyotas and Lexus, and some BMWs, among others.
To analyze this diagram, you can see at the far left a photo transistor and light
emitting diode, also called L E D. This two components form the heart of the sensing
circuit. You can also see at the upper middle a voltage regulated reference voltage
used to supply a stable power feed. The two triangle components are operational
amplifyers, used to condition the signal, which is output and fed to the E C M.
The circuit itself, in this simplified diagram is easy to understand. Current flows
through the photo transistor and L E D, is regulated by the zener diode next to it,
the incoming air air vortex is detected by the L E D transistor pair, and the output
is fed to the operational amplifiers. These sensors normally output a frequency and
not a voltage output, which is a funtion of the oprational amplifiers.