What is an accelerometer?

Fundamentals
Today’s tiny accelerometers are used to measure force, shock, vibration, and changes in velocity and direction (Getty Images)

An accelerometer is an electronic sensor that measures the acceleration forces acting on an object, in order to determine the object’s position in space and monitor the object’s movement. Acceleration, which is a vector quantity, is the rate of change of an object’s velocity (velocity being the displacement of the object divided by the change in time).

There are two types of acceleration forces: static forces and dynamic forces. Static forces are forces that are constantly being applied to the object (such as friction or gravity). Dynamic forces are “moving” forces applied to the object at various rates (such as vibration, or the force exerted on a cue ball in a game of pool). This is why accelerometers are used in automobile collision safety systems, for example. When a car is acted on by a powerful dynamic force, the accelerometer (sensing a rapid deceleration) sends an electronic signal to an embedded computer, which in turn deploys the airbags.  

MEMS Capacitive Accelerometer Diagram
MEMS Capacitive Accelerometer Diagram. (HowToMechatronics)

There are three different types of accelerometers, and they are each designed to efficiently function in their intended environments. The three types are: piezoelectric, piezoresistance and capacitive.

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A piezoelectric accelerometer utilizes the piezoelectric effect (piezoelectric materials produce electricity when put under physical stress) to sense change in acceleration. Piezoelectric accelerometers are most commonly used in vibration and shock measurement.

Piezoresistance accelerometers are much less sensitive than piezoelectric accelerometers, and they are better suited to vehicle crash testing. A piezoresistance accelerometer increases its resistance in proportion to the amount of pressure applied to it.

The third and most commonly used type of accelerometer is the capacitive accelerometer. Capacitive accelerometers use change in electrical capacitance to determine an object’s acceleration. When the sensor undergoes acceleration, the distance between its capacitor plates changes as the diaphragm of the sensor moves. 

Most accelerometers are miniscule, and they are often referred to as Micro-Electro-Mechanical Systems (MEMS) accelerometers. Because of their size and affordability, they are embedded in a myriad of hand-held electronic devices (such as phones, tablets, and video game controllers). In phones and tablets, the accelerometer is responsible for “flipping” the screen when the device is rotated. Accelerometers are also used by zoologists (to track the movement of animals in the wild), engineers (especially in collision experiments) and factories (to monitor the vibration of machinery).

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