I'm not terribly concerned with the actual altitude, nor with terrible
accuracy.  As long as I can get an idea of how far up I am from
where I started, and only over, say, twenty minutes, which is
probably too short a time for changes in the barometer to make a
huge impact on the results.

Thanks for the input!

Mike H.

On Thu, 16 Sep 2004 10:50:55 -0500, Bob J <rocketbob@gmail.com> wrote:
> > Basically what I want to know is this:  can I use a pressure
> > sensor with an absolute range of up to 30 PSI to measure within
> > 10 to 20 feet the difference in altitude between the current position
> > of a sensor package and the position at which the package was
> > initialized?  At altitudes of 1000 feet or less?
> 
> Yes you can get resolution of 10-20 feet with an absolute pressure
> sensor using something like a Motorola MPX series sensor.  However,
> you also need to know barometric pressure, and to get barometric
> pressure the user needs to input that number (either in millibars or
> inches Hg).  If you don't know the barometric pressure, a weather
> change will fool the device into thinking it has climbed or descended.
> 
> If you were using a GPS to get altitude information, the variation is
> +-300 feet, not good enough for your application.
> 
> In aircraft, when landing at an airport there are two ways to set the
> altimeter: 1., set it to the airport's elevation (which whill change
> the barometer setting in the altimeter) or change the barometer
> setting in the altimeter which will change the altitude, and that
> altitude should agree with the field elevation.  Some airports have
> radio frequencies to dial in to receive automated current altimeter
> setting in barometric pressure, so you can listen in and adjust the
> altimeter.
> 
> Regards,
> Bob
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