Many applications, such as smartphones, fitness equipment and cameras rely on accelerometers to determine movement and orientation. Accelerometers are used to better understand the surroundings of an item, as they measure physical acceleration relative to free-fall along one dimension. A dynamic accelerometer measures gravitational pull to determine the angle at which a device is tilted with respect to the earth. Typically accelerometers operate on three axes (x, y, z), each is measured separately, and an algorithm processes the data that is used by the application to carry out an action.
The Technology
Accelerometers can gauge the orientation of a stationary item in relation to the earth’s surface. Because we know that the vertical component of the acceleration value of a stationary object must be 1-g (9.8m/s^2), we can compute the tilt angle of the unit (hence the object to which the unit is attached) by simple trigonometry.
Most accelerometers on the market use a technology called Microelectromechanical Systems (MEMS) Devices. MEMS are very small systems or devices, composed of micro-components ranging from 0.001 mm to 0.1 mm in size. These components are made up of silicon, polymers metals and/or ceramics to create electromechanical devices that measure physical value, in this case acceleration. These electromechanical devices are usually combined with a microprocessor to interact easily with the product’s system. MEMS technology is used in such devices as an accelerometer, gyroscope, magnetometer and others.
The MEMS accelerometer measures acceleration by measuring change in capacitance. Its microstructure has two parts, fixed outer plates and a mass attached to a spring which allows it to move according to external movements in one direction. So when acceleration in a particular direction is applied, the two parts will be moved closer together, changing the capacitance between them. This change in capacitance is measured and processed by the microprocessor to produce the acceleration value.
Limitations of Accelerometers
An accelerometer measures proper acceleration (according to the theory of relativity). This is the acceleration commonly experienced by people and objects and can be defined as the acceleration an object experiences relative to free-fall. An accelerometer will have a reading of zero during any type of freefall, therefore it cannot be used alone to assist in keeping aircrafts properly oriented, and are used in conjunction with a gyroscope and magnetometer in this case. An accelerometer does not indicate lateral orientation, because it only has a vertical reference (gravitational direction) and not a horizontal reference.
Applications of Accelerometers
Accelerometers are used in multiple disciplines, although the most well known application of accelerometers is as an orientation sensor, commonly used in smartphones and tablets. Accelerometers used in laptops protect the hard drive from damage, by detecting the sudden free-fall of a laptop and immediately turn off the hard drive to prevent the reading heads colliding with the hard drive platter, which can destroy the hard drive. Accelerometers are also used in cars as way to detect a car crash and deploy an airbag almost immediately.
