More silly ideas-MAP2

[Matt S Bower]

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