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I have briefly looked at the preliminary technical datasheet for the
ADIS16209 device and found the following information:

1)  The tilt sensing system uses gravity as its only stimulus, and
a MEMS accelerometer as the sensing element.  This results in
responses to dynamic forces associated with acceleration and static
forces, such as gravity.

2)  Corrections are included for several error sources so that
high accuracy is maintained.  Although the device is factory
calibrated, user offsets may be applied for calibrated acceleration
data and accurate incline angles.

3)  Claims are made that dual-axis tilt error is not more than
0.1 degree across a +/- 30 degree range in a horizontally mounted
setup..  14 bit inclination resolution is  0.025 degree.  14 bit
acceleration data is 0.244 mg resolution (gravity = 1 g).

4)  Applications include platform control, stabilization, and tilt
sensing, inclinometers, leveling motion/alarm devices (security,
medical, safety), navigation and surveying equipment, satellite-
antenna-stabilization systems, automotive-wheel alignment and
autonomously piloted farm equipment, etc.

I would of course like more technical data and even several
application notes describing useage but it is early for such
documents since this device hasn't been around long.  In fact, some
of the data sheets indicate "TBD" for the perfomance charactistics
portion.  I have not been able to discern just how fast the data
throughput is since it will be dependent upon the chosen
clock/sample rate but it is very likely a matter of milliseconds.
Usually, sample rate, serial transfer rate and power dissipation are
related and the designer has to determine what combination will
best do the job.

This device might be a key item in the electronics package of any
futuristic sextant.

Frank J
Rochester, NY


=================================================
From:               "George Huxtable" 
To:                 
Subject:            [NavList 4240] Re: automatic celestial navigation
Date sent:          Thu, 6 Dec 2007 15:45:07 -0000
Send reply to:      NavList@fer3.com

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Frank Jones wrote-

| I recently noted in the November 22, 2007 issue of EDN (Electronic
|
Design News - <>), page 19 a brief announcement
|
regarding a MEMS-based (microelectromechanical-system) |
inclinometer
apparently capable of accurately measuring the | deviation from
vertical by sensing the downward G force.  The | device/s is
described
as an Analog Devices (<>) | ADIS16209. | | All
the key
elements are obviously available to designers for | construction of an
advanced sextant now, even one that | automatically tracks objects
day
or night.  I suspect a gimballed | arrangement would make the
software
engineering easier although | it might be avoided at the expense of
much more complicated | tracking schemes.  I recently saw optical
sensors for similar | systems go for several hundred dollars each on
eBay.  The cost of a | 'new' sensor like these in small quantities
would be much pricer. ====================

Comment from George-

If they have somehow succeeded in disentangling the "downward G
force"
from all the other accelerations that apply to a sextant in a vessel
in waves on the sea, then there may be a future in it. But I doubt if
they have. In which case, it would suffer from all the defects of a
pendulum or spirit level or other form of artificial horizon, that
render them all unusable at sea.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.




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