Re: IBM HDAPS, I need a tip.

[Vojtech Pavlik <vojtech@suse.cz>]

On Mon, Aug 01, 2005 at 08:55:53AM -0400, linux-os (Dick Johnson) wrote:

> > Jan Engelhardt wrote:
> >>> So in order to calibrate it you need a readily available source of
> >>> constant acceleration, preferably with a known value.
> >>>
> >>> Hint: -9.8 m/sec^2.
> >>
> >> Drop it out of the window? :)
> >
> > No, no. Constant gravity (like having the laptop sitting on the desk)
> > "feels like" constant acceleration.
> >
> > Dropping it out of the window should measure 0 m/sec^2, because the
> > accelerometer is not working on an inertial referential (I hope this is
> > the correct term in english...). For the accelerometer, this is just
> > like the feeling of free falling inside an elevator: no gravity :)
> >
> > --
> > Paulo Marques - www.grupopie.com
> 
> You need a centrifuge or something that works like one. You can
> make one and you can calibrate it using simple techniques.

Not at all. It's enough to let the laptop lie on the table for [0,0]G
calibration, then put sequentially it on all the four sides for [-1,0]G,
[1,0]G, [0,1]G, [0,-1]G calibration.

>From these five measurements you have both the zero point and the
slopes, including a good error estimate.

I've done that before when toying with IMUs.

-- 
Vojtech Pavlik
SuSE Labs, SuSE CR