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# accelerometer

Posted on 1999-07-14
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what is accelerometer
how is it used
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Question by:team
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Expert Comment

ID: 1159238
You doing a school assignment or something? Remember that your user agreement for this forum forbids using this forum to do your homework.

Accelerometer measures acceleration.

Say you hold one of these sensors in your hand, sensing axis pointed to the sides. Now move your hand to the right. The accelerometer will measure a force moving to the right, then when velocity is constant, measure nothing. Then when you hand slows down to stop, it measures acceleration to the left until your hand stops.

With three of these mounted on different axes, you can measure an object's 3D movement.

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Accepted Solution

mark2150 earned 20 total points
ID: 1159239
You can buy the chips from National Semi. They have a little mechanical contrivance in the IC that allows a comb-like arm to swing over another comb-pattern on the fixed part of the IC. Both parts are mettalized and therefore act as the plates of a capacitor. As the free arm moves, the capacatance between it and the fixed plate changes. By careful design of the mechanical components G ranges from .001 up to 200G's can be accomodated. They have gotten quite cheap as they are in high volume production due to their use in automotive air bags. They are how the airbag knows to deploy. Typically each sensor only measures accelleration along one axis. If you want to control motion in free space you need three of them mounted at right angles to each other as kschang said.

Other accellerometers are based on gyroscopic principles where a spinning mass in a gimbal is allowed to freely rotate when the outer frame of the gimbal is turned. These are older, expensive, difficult to maintain/calibrate and are generally considered obsolete for all but specialty applications.

A third type uses a coil of fiber optic cable and circularly polarized light. As the system is rotated the polarization of the light will change slightly. These are the most advanced and accurate sensors out there. They are very sensitive, highly accurate and *very* expensive. Typically you'll find them in military aircraft and space borne systems.

Enough info for a 10 pt Q?

M

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