More silly ideas-MAP2

[Pat Ford]

Previously, you (Todd....!!) wrote:
> HOW EERY!!
> 
> About the A/C pressurizing the interior of the car...
> 
> I asked my Dad how many pounds of pressure he thought the A/C
> pressurized his Riviera when we were cruisin around a while back... Like
> when I was 8 yrs old or so!!  I'm now 30... Haven't EVER heard of anyone
> else ever mentioning this or anything until NOW!
> 
> He said it may pressurize the cabin by up to about 5 lbs. or so!  Anyone
> have a different guess?

I find that number hard to believe, a windshield is what ~2' by 4' ( around
1152 sq inches) multiply that by 5PSI and you get 5760 pounds force pushing
outwards on the glass. Or in another light that is 11.2245 feet of fresh 
water, I've seen an eardrum pop at 5', you can pop your lungs if you hold 
your breath after breathing from scuba gear and rising from 4' to the surface.
( can you tell I taught scuba diving)

generaly I feel my ears pop outwards when I slow down, I think that the pressure 
drops inside the car when moving.  

> 
> I'm SURE the presures vary with engine rpm or vehicle make etc... Wonder
> how hi these A/C pressures get in the fuel injected cars?

at a standstill maybe 1/4 psi

> 
> LATER!
> 
> Todd....
> 
> ------------
> 
> Ward wrote:
> > 
> > Has anyone cosidered how hare it is to get a reliable BARO reading in a
> > moving car, If you sens outside the interior it will turn ito an airspeed
> > sensor, If you sense inside, your testing the A/C systems ability to
> > pressurise the car's interior.

don't airplane have a baro. I know there are high pressure areas on a car,
so there most be low pressure areas. given that shouldn't it follow that there
most be a neutral pressure area?


> > 
> > Ward
> > 
> > On Tue, 08 Jun 1999 07:47:08 -0500, Matt S Bower wrote:
> > 
> > >
> > >
> > > Dave Z wrote:
> > > >
> > > > I too am curious about the MAP "bubble" pocket.. someone take one
> > > > apart and check it out! seems if there were a pocket, wouldnt it be
> > > > pretty expensive to have such a room or whatever instruments to make
> > > > the reference pocket exact? I skipped a couple of posts forgive if
> > > > the subject is over.
> > >
> > > Actually the value would not be that critical.  Experiences I have seen
> > > with some of the sensors we currently use at the engine works here have
> > > the manufacturer build the circuit with carbon deposit resistors on
> > > there filtering and tuning boards that are built into the sensors
> > > today.  On these sensors they just put them onto a calibrated supply and
> > > do some laser trimming of the resistor deposits to tune them in for the
> > > specs they want.  On an absolute sensor the pocket is just a reference
> > > so that it always reacts to the same value the same way no matter what
> > > that value is so that value is an absolute.  In a guage the value is
> > > alway referenced to whatever baro happens to be when the measurement is
> > > taken, nothing constant.  My question on the MAP sensor is what is the
> > > margin of error over time.  I wonder more if GM is less concerned about
> > > how exact there baro reading is because they know that the map sensor
> > > will continue to give adequate readings after say 5 years but not
> > > accurate enough to make continous updates of baro worthwile.  To get
> > > this accurate over the long haul the best approach would probably be to
> > > use a sensor or a driver that can be calibrated.  With no way of
> > > calibrating the sensor they can drift a lot.  Our test cells calibrate
> > > all of there tranducers every 6 mo. and still have a fair amount of
> > > drift every six months.  The diaphrams change shape a little bit or a
> > > multitude of different things and your readings are off  so how accurate
> > > are readings really going to be anyway.
> > >
> > > Sorry for the rambling.  Got on a tangent and just had to follow it to
> > > the end.
> > >
> > > Matt
> > 
> > _______________________________________________________
> > Get your free, private email at http://mail.excite.com/
> 

--
Pat Ford                           email: pford at qnx.com
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