Re: [Paparazzi-devel] distance measurement for landing.

[David Carlson]

I can confirm that as a pilot, you definitely only use the altimeter as 
a reference.

I can also confirm that pressure sensors for altitude drift, and a lot.  
I cut my teeth with autopilots using a Procerus Kestrel and we would see 
drifting anywhere from +/- 5-10m in a 30 minute flight.  One thing you 
could _always_ count on was that when you landed, you would not "be" at 
0m AGL.

Hope that helps.

Buzz

antoine drouin wrote:
> ola
>
> On Tue, Nov 10, 2009 at 8:26 AM, gisela.noci
> <address@hidden> wrote:
>   
> > What 'Baro' sensor?
> >     
>
> freescale MPX6115
>
>   
> > The maths does not lie.
> >  [...]
> > limited. This is often done, since most of our applications do not go to
> > 10,000meters,(I suspect this is what they have done in the sensor in the
> > quadrotor) .....
> >     
>
>  yep, x100 gain amplifier with variable offset driven by the lpc DAC
>
>   
> > But, there is no free lunch here - you have to use
> > amplifiers that have very low input and output noise, very low DC offset,
> > and good temp stability. If you have access to a high accuracy pressure
> > calibration system, you could put the sensor pack in the environmental
> > chamber, and cycle the temp from 0 to whatever, and vary the pressure to the
> > sensor at each temp, and generate a calibration curve to eliminate all the
> > errors,ie, temp, offset, drift, etc but the cost.....(takes many hours to
> > do)
> >
> >     
>
> no doubt about drift. I don't have experience with baros on fixed
> wings, but I fear that the static pressure intake would need to be
> quite perfect to achieve that kind of accuracy.
>
> Regards
>
> Poine
>
>
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