I'm measuring vacuum and boost in my car, and I've used the AP
for this, with a calibration mode to record ambient pressure w/o the
car running.  Vac/boost is determined by using that cal as a reference.

Cheers.


----- Original Message -----
From: "Douglas Butler" <dbutler@IMETRIX.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, March 11, 2002 9:52 AM
Subject: Re: [EE]: Motorola MPX pressure sensors -- AP vs GP


> I would point out that both of these have very good uses.  If you want
> to measure the water level in a tank by measuring the pressure at the
> bottom, you want a gauge sensor.  If you are in a submarine and want to
> measure how deep you are, you want an absolute sensor (plus a weather
> report).
>
> If you used an absolute sensor to measure the tank level, the result
> would depend on the local barometric pressure.
>
> If you used a gauge sensor to measure depth of a submarine your results
> would be influenced by the pressure of the air in the submarine cabin
> which, depending on the ventillation system used and cabin temperature,
> could vary widely.  Of course either senser will be affected by the
> barometric pressure above so you also need a weather report.
>
> Sherpa Doug
>
> > -----Original Message-----
> > From: Chris Loiacono [mailto:chris@MAIL2ASI.COM]
> > Sent: Monday, March 11, 2002 10:05 AM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: [EE]: Motorola MPX pressure sensors -- AP vs GP
> >
> >
> > I believe these designations are for Gauge & Absolute
> > sensing. Gauge refers
> > to a sensor that will measure the pressure relative to 1 ATM,
> > so a gauge
> > sensor will report 14.7 psi as zero, and 15.7 psi as 1. The
> > motorola gauge
> > sensors are differential sensors with the second port open to
> > the ambient
> > pressure. It will only give predictable results when that
> > port is at a known
> > pressure, such as at sea level (1 ATM) or 14.7 psi.
> >
> > The Absolute Sensor will provide an output that is == the
> > absolute pressure.
> > At 1 ATM the unit should provide output for 14.7 psi. These
> > can be made
> > several ways: by reducing the pressure on and sealing the
> > second port so
> > that it offsets the 1 ATM pressure, or by offsetting the output
> > electronically to obtain the same output.
> >
> >
> >
> > Chris
> >
> >
> > > Anyone know what the diffs are between the AP and GP versions
> > > of the motorola MPX4250, MPX5700, etc sensors?  The datasheet
> > > doesn't seem to be too clear on this.  What exactly does "gauge"
> > > mean on the GP versions and how would the output differ from
> > > that of the AP versions?
> > >
> > > Thanks.
> > >
> >
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