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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