Forwarded: Re: Airflow measurement - again...

[adt1]

>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