AFM measuring pressure or mass?

[Chris Conlon]

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 ;)