An accelerometer is an instrument that measures acceleration or the gravitational force capable of imparting acceleration. It
usually employs a concentrated mass that resists
movement because of its inertia; acceleration
is measured in terms of the displacement of this mass relative to its supporting
frame or container.
|A linear accelerometer. If the device is moving at
constant velocity, the mass (1), supported on a bar by springs (2),
remains static and an intermediate reading is registered on the potentiometer
(3). On acceleration in the direction of the bar (4), i.e., along
the accelerometer's sensitive axis, inertia causes the mass to lag
behind, compressing the spring behind it (5) and stretching the spring
ahead of it (6): a high voltage is registered. On deceleration, inertia
causes the mass to compress the spring ahead of it and stretch that
behind it, and thus a low voltage is registered on the potentiometer.
|Developed by Steve Arms and his colleagues at MicroStrain,
the G-LINK Wireless Accelerometer nodes monitored vibration and shock
loads within the Liberty Bell during its relocation. Image credit:
MiocroStrain, Inc. Caption text: NSF
The simplest example of an accelerometer is a plumb
bob suspended from the object being accelerated. The angle of the plumb
bob is proportional to the acceleration. A more sophisticated version, used
in ballistic missiles, is an electromechanical
device that translates the acceleration into electric current.
Modern accelerometers are typically micro-machined silicon sensors that
are based on the capacitive, piezo-resistive or optical detection of the
deflection a small mass experiences when the sensors is subjected to acceleration.