AFM measuring pressure or mass?

[Greg Hermann]

>Hi,
>
>I feel silly even asking this one.
>
>My ongoing assumption had been that a flap-type AFM did actually
>measure air *mass*, flow velocity times air density. This going on
>the theory that denser air would produce more force against the
>flap than less dense air flowing at the same speed. Obviously when
>it comes to *static* pressure, you can have a high temperature and
>a high pressure, even with a low density, but the air flow meter
>is working from dynamic pressure, right?
>
>Anyway this begs the question of why flap type AFMs have intake
>air temperature sensors. Are they really measuring flow *volume*,
>and you need to correct for density? What sort of temperature-based
>correction is applied to the flap meter reading? The usual sort of
>linear correction based on absolute temperature? (Taking into
>account the logarithmic reading of the AFM of course.)
>
>So now you can all tell that I should have taken more than one
>semester of fluid dynamics in college, and/or paid attention as
>well. But if someone can come up with detailed info on a flap-type
>AFM (any one!) I'd really appreciate it.
>
>   TIA,
>   Chris C.
>
>p.s. at least I paid attention in my major ;)

I believe that they are like a venturi--and measure volume flow, which must
be corrected for abs. temp, abs. pressure, and (average) molecular weight
to get to mass flow. The last of these is constant, since none of us is
driving on Mars or Venus yet :-) <ducking!!>

And, hey--fluids was the best mid-morning nap/hangover cure in memory!!!
Not even anyone pretty around to interupt the snoozing with nice dreams!!
<ducking lower!!>

Regards, Greg