Information about Accelerometer

An accelerometer is a measuring device for specific external force. Specific external force is the sum total of external forces acting on an object divided by the mass. Accelerometers do not measure internal forces such as gravity. An accelerometer sitting still on a table top will read one g of specific force due to the table pushing up on the accelerometer equal to its weight. If dropped in a vacuum it will read zero. For computation of position, the Inertial Navigation System adds in the estimate of the local gravity acceleration to the signal coming off of the accelerometers. Accelerometers may be part of an Inertial Navigation System, used to detect and measure vibrations, or for measuring acceleration due to gravity (inclination). An accelerometer inherently measures its own motion (locomotion), in contrast to a device based on remote sensing.

Accelerometers are perhaps the simplest micro electro-mechanical system (MEMS) device possible, sometimes consisting of little more than a suspended cantilever beam or proof mass (also known as seismic mass) with some type of deflection sensing and circuitry. MEMS Accelerometers are available in a wide variety of ranges up to thousands of g's. Single-axis, dual-axis, and three-axis models are available.

Accelerometers can be used to measure vibration on cars, machines, buildings, process control systems and safety installations. They can also be used to measure seismic activity, inclination, machine vibration, dynamic distance and speed with or without the influence of gravity. Applications for accelerometers that measure gravity, wherein an accelerometer is specifically configured for use in gravimetry, are called gravimeters.

Accelerometers are being incorporated into more and more personal electronic devices such as media players and gaming devices, like the Nintendo Wii, which has multiple accelerometers in the controller to add another element of gameplay. In particular, more and more smartphones (such as Apple's iPhone) are incorporating accelerometers for step counters, user interface control, and switching between portrait and landscape modes.

Accelerometers are used along with gyroscopes in inertial guidance systems, as well as in many other scientific and engineering systems. One of the most common uses for MEMS accelerometers is in airbag deployment systems for modern automobiles. In this case the accelerometers are used to detect the rapid negative acceleration of the vehicle to determine when a collision has occurred and the severity of the collision.

The widespread use of accelerometers in the automotive industry has pushed their cost down dramatically.

Types of accelerometers

• Piezo-film or piezoelectric sensor - PCB Piezotronics, IMI Sensors http://www.imi-sensors.com
• Shear Mode Accelerometer — Connection Technology Center, PCB Piezotronics, IMI Sensors http://www.imi-sensors.com
• Surface Micromachined Capacitive (MEMS) — Analog Devices, Freescale, Honeywell, PCB Piezotronics, Systron Donner Inertial (BEI)
• Thermal (submicrometre CMOS process) — MEMSIC
• Bulk Micromachined Capacitive — VTI Technologies, Colibrys
• Bulk Micromachined Piezo Resistive
• Capacitive Spring Mass Based - Rieker Inc
• Electromechanical Servo (Servo Force Balance)
• Null-balance
• Strain gauge - PCB Piezotronics
• Resonance
• Magnetic induction
• Optical
• Surface acoustic wave (SAW)
• Laser accelerometer
• [DC Response] - PCB Piezotronics
• High Temperature - Connection Technology Center, PCB Piezotronics
• Low Frequency - Connection Technology Center
• High Gravity - Connection Technology Center
• 4-20 mA Loop Power - Connection Technology Center
• Triaxial - Connection Technology Center
• Modally Tuned Impact Hammers - PCB Piezotronics, IMI Sensorshttp://www.imi-sensors.com
• Seat Pad Accelerometers - PCB Piezotronics, Larson Davis

Applications

Zoll's AED Plus uses CPR-D•padz which contain an accelerometer to measure the depth of CPR chest compressions.

The Wii Remote for the Nintendo Wii video game console contains accelerometers for measuring movement and tilt to complement its pointer functionality.

Within the last several years, Nike, Polar and other companies have produced and marketed sports watches for runners that include footpods, containing accelerometers to help determine the speed and distance for the runner wearing the unit.

More recently, Apple Inc and Nike have combined the footpod with Apple's iPod nano to provide real-time audio feedback to the runner on his/her pace and distance. It is known as the Nike + iPod Sports kit [1]. Apple Inc also uses an LIS302DL accelerometer in the iPhone allowing the device to know when it is tilted on its side. Third-party developers have expanded its use to the realm of absurdity, to produce applications such as electronic bobbleheads.

The Nokia 5500 sport features a 3D accelerometer that can be accessed from software. It is used for step recognition (counting) in a sport application, and for tap gesture recognition in the user interface. Tap gestures can be used for controlling the music player and the sport application, for example to change to next song by tapping through clothing when the device is in a pocket. The Nokia N95 and Nokia N70 has an accelerometer embedded inside it, but it is only used as a tilt sensor for tagging the orientation to photos taken with the built-in camera. Some other devices provide the tilt sensing feature with a cheaper component, which is not a real accelerometer.

The Sony Ericsson W580 and W910 also has an accelerometer built inside the phone that enables Track Switching on music player known by users as the Shaker Feature but the W910 along with K850 can use the motion sensor feature in gaming, Picture UI AutoRotation and many other applications that require the feature and can be accessible via J2ME application. The first phone from the company to feature an accelerometer was the Sony Ericsson W710.

A small number of modern notebook computers feature accelerometers to automatically align the screen depending on the direction the device is held. This feature is only relevant in Tablet PCs and some smartphones.

Some laptops' hard drives utilize an accelerometer to detect when falling occurs. When low-g condition is detected, indicating a free-fall and an expected shock, the write current is turned off so that data on other tracks is not corrupted. When the free-fall and shock ends, the data can be rewritten to the desired track, thus negating the effects of the shock.

Camcorders use accelerometers for image stabilization. Still cameras use accelerometers for anti-blur capturing. The camera holds off snapping the CCD "shutter" when the camera is moving. When the camera is still (if only for a millisecond, as could be the case for vibration), the CCD is "snapped". Some digital cameras contain accelerometers to determine the orientation of the photo being taken and some also for rotating the current picture when viewing.

Accelerometers are used in rocketry to detect apogee.

Herman Digital Trainer uses accelerometers to measure strike force in physical training (The Contender 3 Episode 1 SPARQ testing ESPN).