Air flow measurement

[Matthew Lee Franklin]

Peter commented:
>Below boost, the air flow rate was measure by an ultrasonic flow meter which
>gave out a pulse train, of a frequency proportional to the air velocity. The

I had heard only of the hot wire or hot film made by Hitachi and others.  
If it really is ultrasonic I'd be curious to hear who makes it and if there 
are any good SAE papers on it.

Later,
Matt