Tuesday, March 03, 2009

Accelerometer: From Wikipedia, the free encyclopedia

An accelerometer is a device that measures non-gravitational accelerations[1]. These are accelerations produced by mechanically accelerating the accelerometer via its casing.

Single- and multi-axis models are vertical to detect magnitude and direction of the acceleration as a vector quantity,[2] and can be used to sense orientation, vibration and shocks. Accelerometers are present in numerous portable electronic devices and video game controllers, including the Nokia N95, Nokia 5800, Sony Ericsson W910i, Blackberry Storm, Apple iPhone[3], the Apple iPod Nano 4G and Nintendo's Wii Remote[4] and the Google G1.

Accelerometers may be used in some cases to measure acceleration produced by gravity forces, but only indirectly. This is done by assessing the device's output in situations where gravity forces are known not to vary in time (for example, with the device is at rest at a given altitude), and then inferring from the overall zero vertical acceleration of the device, that the measured non-gravitational forces must be equal (but opposite) to any gravitational fields which are present (see gravimeter).

Accelerometers are also used in inertial navigation systems where the exact gravity is unknown, and then an estimate of the gravity based on the position/altitude is used. This allows the output to be integrated to convert it into changes in vertical velocity and to calculate distance (with respect to the center of the Earth) via essentially dead reckoning.