Air flow measurement

[Peter Wales]

The air mass meter was a proprietary product from Mtisubishi. It worked by
having the usual pair of ultrasonic transducers across the air flow and a
triangular shaped piece of plastic just in fromt of the transducers. The
point was in the air stream and the principle was that the edges would shed
vortices into the air stream which would have a swirl component at right
angles to the air stream. This was in the ultrasonic beam and generated a
doppler shift which was then amplified and sent out as the pulse stream

I believe it was called the karmann vortex principle

It did give a very good measure of air flow into the engine, but made no
allowances for any other variables so they added a diode in the stream as
well which was used to generate a signal for air temperature. I'm not sure
how that worked, except that I expect the voltage acrross the diode at very
low currents must have varied with temperature, but I would have thought it
would have been better to use a thermistor.

I remember trying to calibrate the air meter to see when it ran out of
capacity and I strapped it to the hood of a car and drove around with a
frequency meter attatched to it. It was still linear at 130 MPH which was as
fast as I could get my 2.6 liter Lonsdale to go. 

Those were the days....what pioneers we were.....boldly going...mutter mutter

Peter