Air Flow Measurement

[Dave Zug]

tom cloud wrote:
> 
> >>      Specifically, I am wondering if anyone has looked into using a
> >differential-pressure manometer to calculate air flow.  This manometer
> >could be located in the same location as GM puts its heated-wire
> >mass-air-flow sensor.  Any thoughts/comments?
> >
> >>(FYI - Air flow could be calculated from a differential pressure manometer

(.....)

> >You still need a measure of density to determine mass flow rate, even
> >if you know the
> >
> >begin 600 WINMAIL.DAT
> >M>)\^(@,2`0:0" `$```````!``$``0>0!@`(````Y 0```````#H``$(@ <`
> >M& ```$E032Y-:6-R;W-O9G0 at 36%I;"Y.;W1E`#$(`0V ! `"`````@`"``$$
> >MD 8`9 $```$````,`````P``, (````+``\.``````(!_P\!````8P``````
> 
> Anthony, can't you speak English ?  I'd like to read this ... it's
> like watching 'X' files and having it TO BE CONTINUED !!
> 
> Tom Cloud <cloud at peaches.ph.utexas.edu>


c'mon, you can't read that?, thats the first message i CAN read and 
understand!  after having 68hc11 code burned into the back of my brain, 
this is REAL easy on the eye...

Our experience in the HVAC CONTROLS industry is that a cost effective 
air flow measuring station (one that low-bidder can sell), using 
hot-wire, or static and total pressure, becomes REAL inaccurate at the 
low end, as was mentioned in a previous responce.  mass of air must be 
assumed, and the duct runs must be of a certain minimum STRAIGHT 
distance before and after the flow station (no turbulance?). as the 
price of these stations goes up, honey-comb inserts can be included to 
mix and straighten the air out as it comes around a bend in the duct. 
(try that in a 4"dia twisting steel tube). with more cash, you can 
matrix anamometers or combo pressure pickups in a duct in a grid that 
samples the pressures at 9,12,16... points. granted, HVAC doesnt have to 
be as exacting, but a blade-position sensor produces such a non-linear 
percent open-to-flow relationship, that to use it, you have to FLOW the 
setup to get a curve to track. (ie 10% open=35%flow). as you add "fixes" 
to a simple manometer setup to correct for ??? the price goes up and up 
and you've lost the bid and your broke cause you spent all your wad on 
the blueprints and lunch for the engineer and your jobs on the 
line...... 
sorry, i drifted out of EFI and into rat race there. just another 
airflow view from another airflow angle.

lucky ECM designers get decent budgets for the controllers or we'd still 
be cranking that spark-retard knob.  

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~Dave.   @:-)-I--<
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