Forwarded: Re: Airflow measurement - again...

[Mazda Ebrahimi]

adt1 wrote:
> 
> >Someone else on this list posted a message suggesting use of a strain
> >gauge for flow measurement.  I've been thinking about that some more from
> >time to time and it seems like a good idea.  His idea was basically based
> >on mounting a small object in the air flow path via an arm that has a
> >strain gauge.  Increased air flow equates to change in the load cell
> >reading.  To cancel out vehicle dynamics an identical setup outside the
> >flow path is used and the signals are subtracted.  The resulting reading
> >needs to be corrected based on air temp since the drag force is a
> >function of air density, viscosity, velocity ^ 2.  Knowing density (by
> >temp) and viscosity, we can calculate or look-up velocity, and knowing
> >velocity, area, and density, we can determine mass flow rate.
> >
> >Not too many people commented about his message unfortunately, and I
> >can't find the original posting.  What are your thoughts?
> 
> This approach to air flow measurement sounds very similar to
> a vane meter.  Both the strain gauged arm and the vane meter
> rely on an aerodynamic drag force to deflect a spring.  The
> deflection is measured (by a strain gauge in the first case
> and a potentiometer in the second) and then converted to mass
> flow rate.
> 
> I'm not saying it's good or bad, just pointing out the
> similarity I see.  It makes me wonder how big the sphere
> would have to be to get a good magnitude of deflection.
> 
> Anthony Tsakiris


That's a good question.  Also, I don't know much about the vane meters 
(I have never actually seen one on an engine), but are they not a little 
restrictive?

Best Regards, Mazda