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Accelerometers
An accelerometer is
a sensor for testing the acceleration along a given axis. When a physical body
accelerates at a certain direction, it becomes subject to a force equal to:
F=ma
in accordance with Newton's Second Law. In this formula, m is the
mass, a is the acceleration. Therefore, accelerometers are built on the principle of measuring
the force exerted on a test body of a known mass along a given axis.
The following drawing schematically shows the
structure of an accelerometer.

In Newton's day, accelerometers where built using
a test mass (shown in red) held at rest with springs and having a scale showing
the acceleration along the sensitivity axis. Note that the unit g is equal to
the acceleration subject to all bodies at the surface of the earth due to
gravity, and is equal to about 9.8 meter/second². The same gravity is the acceleration that translates our body mass
to a weight we can measure when we stand on a scale.
In the early 1950s, accelerometers were used in
inertial navigation systems, and their structure has been modernized to include
an easy electronic interface, and to replace the springs with magnetic forces.
In the early 1990s, a new generation of MEMS devices integrated the
accelerometer into a single silicon structure.
With modern MEMS technology, the sensors are
easily included in miniature electronic boards, like in
RotoView.
The accelerometer can detect movement based on
double integration of the measured acceleration and addition of the initial
position and speed. However, since the Earth exerts a gravity acceleration on
all bodies, we can also use the accelerometer to measure tilt.

When the sensitivity axis points directly to the
center of the Earth, it measures 1g (assuming no additional hand acceleration
in this direction). When the accelerometer sensitivity axis lies parallel to
the surface of the Earth, it measures 0 acceleration.
The actual tilt angle may be inferred with the following formula:
Tilt Angle=ArcSin
(measured acceleration / 1g).
When using an accelerometer to measure the tilt of an hand-held device, the
movements of the hand create additional accelerations components which distort
the exact calculation of the tilts. Therefore, RotoView
NLDR algorithms are used to allow easy and intuitive view navigation,
as you can experiment with this development system.
For further questions, please
contact us at 1+ (281) 879-6226, fax 1+ (281) 879-6415, e-mail
sales@innoventions.com.
INNOVENTIONS® Inc.
"INNOVATIVE PRODUCTS FROM INVENTIVE MINDS" ©2010 INNOVENTIONS,
INC.
All rights reserved. RotoView and INNOVENTIONS are registered trademarks of
INNOVENTIONS, Inc.
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