More silly ideas-MAP2

[Matt S Bower]

If you put the sensor opening into a box under the hood that shrouded it
from the moving air and put the box some place out of the airs path that
should get you pretty close to baro.  But are you looking for true
baro?  Aren't we interested in the air pressure right outside the intake
compared to the air pressure inside the intake.  So any air moving in
the engine compartment that would cause a relative baro change at the
point of air entry would result in the same effect of a different baro
effect to the opperation of the engine.

Does this sound right?

Matt


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.
> 
> 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
> 
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