More silly ideas-MAP2

[Ward]

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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