Air Flow Meter discussion (WAS: "I'm missing something...)

[Jesse Ruppel]

> Karmann Vortex MAS: I don't know how the Toyota sensor works, but the
> Mitsubishi uses the honeycomb to straighten out the flow of air,
> remove the
> turbulence (kinda like GM sensors, I believe). I believe that the
> honeycomb
> was put in there mainly for low-flow situations, I.E. idle and
> light cruise
> (to produce a laminar flow). After the honeycomb, it has a small "wing" in
> the airstream, designed to introduce little ultrasonic "whorls" into the
> airstream. Just past that, there are 2 Piezo microphones that listen for
> these whorls, counting them. The sensor then outputs a square-wave signal
> directly proportional to the number of whorls - more whorls = more air
> flowing throught the MAS. The earlier Mitsu designs would start to lose
> count somewhere near 1600hz, while the newer style is supposed to
> be good to
> over 2200hz. The Mitsu MAS also uses a seperate Barometric Pressure sensor
> and an Ambient Air Temp sensor, mounted on the outside of the MAS body, in
> the airfilter can.
>
> Scott C.

The Toyota Karmann vortex AFM works in a very similar way.  I have been told
the Karmann vortices are detected via a LED and photodetector system though
it looks a lot more like a strain gauge to me.  I need to find a junk one to
take apart and test.  The description that made Karmann vortices much more
clear to me is to picture a flag flapping in the wind - the higher the
velocity of the air the higher the frequency it flaps at.

Did you ever do enough testing with the Mitsu. meter to tell if the
frequency was linearly proportional to the velocity or not?  I am currently
trying to determine this for a project.

Thank you,

Jesse Ruppel
ruppeljw at capital.net

87T Supra
87T 4x4 Pickup

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