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An accelerometer is a tool that measures
proper acceleration In relativity theory, proper acceleration is the physical acceleration (i.e., measurable acceleration as by an accelerometer) experienced by an object. It is thus acceleration relative to a free-fall, or inertial, observer who is momentarily at r ...
.Extract of page 33
/ref> Proper acceleration is the
acceleration In mechanics Mechanics (Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approx ...

acceleration
(the rate of change of
velocity The velocity of an object is the Time derivative, rate of change of its Position (vector), position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction ...

velocity
) of a body in its own instantaneous
rest frameIn special relativity the rest frame of a particle is the coordinate system (frame of reference) in which the particle is at rest. The rest frame of compound objects (such as a fluid, or a solid made of many vibrating atoms) is taken to be the frame ...
;Extract of page 61
/ref> this is different from coordinate acceleration, which is acceleration in a fixed
coordinate system In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space t ...

coordinate system
. For example, an accelerometer at rest on the surface of the Earth will measure an acceleration due to Earth's gravity, straight upwards (by definition) of g ≈ 9.81 m/s2. By contrast, accelerometers in
free fall #REDIRECT Free fall In Newtonian physics, free fall is any motion of a body where gravity Gravity (), or gravitation, is a list of natural phenomena, natural phenomenon by which all things with mass or energy—including planets, star ...

free fall
(falling toward the center of the Earth at a rate of about 9.81 m/s2) will measure zero. Accelerometers have many uses in industry and science. Highly sensitive accelerometers are used in
inertial navigation system An inertial navigation system (INS) is a navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation ...
s for aircraft and missiles. Vibration in rotating machines is monitored by accelerometers. They are used in
tablet computer A tablet computer, commonly shortened to tablet, is a mobile device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations aut ...
s and digital cameras so that images on screens are always displayed upright. In
unmanned aerial vehicles being tested in California California is a U.S. state, state in the Western United States. With over 39.3million residents across a total area of approximately , it is the List of states and territories of the United States by population ...
, accelerometers help to stabilise flight. When two or more accelerometers are coordinated with one another, they can measure differences in proper acceleration, particularly gravity, over their separation in space—that is, the gradient of the
gravitational field In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...

gravitational field
.
Gravity gradiometry Gravity gradiometry is the study and measurement of variations ( anomalies) in the Earth's gravitational field In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis ...
is useful because absolute gravity is a weak effect and depends on the local density of the Earth, which is quite variable. Single- and multi-axis accelerometers can detect both the magnitude and the direction of the proper acceleration, as a
vector Vector may refer to: Biology *Vector (epidemiology) In epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and risk factor, determinants of health and disease conditions in defined pop ...
quantity, and can be used to sense orientation (because the direction of weight changes), coordinate acceleration, vibration, shock, and falling in a resistive medium (a case in which the proper acceleration changes, increasing from zero). Micromachined
microelectromechanical systems Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, p ...
(MEMS) accelerometers are increasingly present in portable electronic devices and video-game controllers, to detect changes in the positions of these devices.


Physical principles

An accelerometer measures
proper acceleration In relativity theory, proper acceleration is the physical acceleration (i.e., measurable acceleration as by an accelerometer) experienced by an object. It is thus acceleration relative to a free-fall, or inertial, observer who is momentarily at r ...
, which is the acceleration it experiences relative to freefall and is the acceleration felt by people and objects. Put another way, at any point in spacetime the
equivalence principle In the theory A theory is a rational Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously making sense of things, applying logic Logic (fr ...
guarantees the existence of a local
inertial frame In classical physics and special relativity, an inertial frame of reference is a frame of reference that is not undergoing acceleration. In an inertial frame of reference, a physical object with zero net force acting on it moves with a const ...
, and an accelerometer measures the acceleration relative to that frame. Such accelerations are popularly denoted
g-force The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight In science Science () is a systematic ente ...

g-force
; i.e., in comparison to
standard gravity The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by or , is the nominal gravitational acceleration In physics, gravitational acceleration is the accel ...
. An accelerometer at rest relative to the Earth's surface will indicate approximately 1 g ''upwards'' because the Earth's surface exerts a normal force upwards relative to the local inertial frame (the frame of a freely falling object near the surface). To obtain the acceleration due to motion with respect to the Earth, this "gravity offset" must be subtracted and corrections made for effects caused by the Earth's rotation relative to the inertial frame. The reason for the appearance of a gravitational offset is Einstein's
equivalence principle In the theory A theory is a rational Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously making sense of things, applying logic Logic (fr ...
, which states that the effects of gravity on an object are indistinguishable from acceleration. When held fixed in a gravitational field by, for example, applying a ground reaction force or an equivalent upward thrust, the reference frame for an accelerometer (its own casing) accelerates upwards with respect to a free-falling reference frame. The effects of this acceleration are indistinguishable from any other acceleration experienced by the instrument so that an accelerometer cannot detect the difference between sitting in a rocket on the launch pad, and being in the same rocket in deep space while it uses its engines to accelerate at 1 g. For similar reasons, an accelerometer will read ''zero'' during any type of
free fall #REDIRECT Free fall In Newtonian physics, free fall is any motion of a body where gravity Gravity (), or gravitation, is a list of natural phenomena, natural phenomenon by which all things with mass or energy—including planets, star ...

free fall
. This includes use in a coasting spaceship in deep space far from any mass, a spaceship orbiting the Earth, an airplane in a parabolic "zero-g" arc, or any free-fall in a vacuum. Another example is free-fall at a sufficiently high altitude that atmospheric effects can be neglected. However, this does not include a (non-free) fall in which air resistance produces drag forces that reduce the acceleration until constant
terminal velocity Terminal velocity is the maximum velocity (speed) attainable by an object as it falls through a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external fo ...

terminal velocity
is reached. At terminal velocity, the accelerometer will indicate 1 g acceleration upwards. For the same reason a skydiver, upon reaching terminal velocity, does not feel as though he or she were in "free-fall", but rather experiences a feeling similar to being supported (at 1 g) on a "bed" of uprushing air. Acceleration is quantified in the SI unit metres per second per second (m/s2), in the cgs unit gal (Gal), or popularly in terms of
standard gravity The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by or , is the nominal gravitational acceleration In physics, gravitational acceleration is the accel ...
(''g''). For the practical purpose of finding the acceleration of objects with respect to the Earth, such as for use in an
inertial navigation system An inertial navigation system (INS) is a navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation ...
, a knowledge of local gravity is required. This can be obtained either by calibrating the device at rest, or from a known model of gravity at the approximate current position.


Structure

Conceptually, an accelerometer is a damped mass, a
proof massA proof mass or test mass is a known quantity of mass Mass is both a property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or with something, whether as an attribute or as a component of said t ...
, on a spring. When the accelerometer experiences an acceleration, the mass is moved to the point that the spring can push (accelerate) the mass at the same speed as the casing. The measurement of the spring's compression measures the acceleration. The system is damped so that oscillations (wiggles) of the mass and spring do not affect the needed measurements. Because of the damping, accelerometers always respond in different ways to different frequencies of acceleration. This is called the "frequency response." Many animals have sensory organs to detect acceleration, especially gravity. In these, the proof mass is usually one or more crystals of calcium carbonate
otolith An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as th ...
s (Latin for "ear stone") or
statoconia An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as th ...
, acting against a bed of hairs connected to neurons. The hairs form the springs, with the neurons as sensors. The damping is usually by a fluid. Many vertebrates, including humans, have these structures in their inner ears. Most invertebrates have similar organs, but not as part of their hearing organs. These are called
statocysts The statocyst is a Equilibrioception, balance sensory receptor present in some aquatic invertebrates, including molluscs, bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, and crustaceans. A similar structure is also found in ''Xenotur ...
. Mechanical accelerometers are often designed so that an electronic circuit senses a small amount of motion, then pushes on the proof mass with some type of
linear motor Synchronous linear motors are straightened versions of permanent magnet rotor motors A linear motor is an electric motor that has had its stator The stator is the stationary part of a rotary system, found in electric generators, electric mo ...

linear motor
to keep the proof mass from moving far. The motor might be an
electromagnet An electromagnet is a type of magnet A magnet is a material or object that produces a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector field is an assignment of a vector to each poin ...

electromagnet
or in very small accelerometers,
electrostatic Electrostatics is a branch of physics that studies electric charges at Rest (physics), rest (static electricity). Since classical antiquity, classical times, it has been known that some materials, such as amber, attract lightweight particles af ...
. Since the circuit's electronic behavior can be carefully designed, and the proof mass does not move far, these designs can be very stable (i.e. they do not
oscillate Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparently irreversible process, irreversible succession from the pas ...
), very linear with a controlled frequency response. (This is called
servo Servo may refer to: Mechanisms * Servomechanism In control engineering Control engineering or control systems engineering is an engineering discipline that applies control theory to design equipment and systems with desired behaviors in Cont ...
mode design.) In mechanical accelerometers, measurement is often electrical,
piezoelectric Piezoelectricity (, ) is the electric charge Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried ...

piezoelectric
, piezoresistive or
capacitive A capacitor is a device that stores electric charge in an electric field An electric field (sometimes E-field) is the physical field that surrounds electrically-charged particle In physics Physics (from grc, φυσική (ἐπ ...
. Piezoelectric accelerometers use piezoceramic sensors (e.g.
lead zirconate titanate Lead zirconate titanate is an with the (0≤''x''≤1). Also called lead zirconium titanate, it is a ceramic material that shows a marked , meaning that the compound changes shape when an electric field is applied. It is used in a number of ...
) or single crystals (e.g.
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...

quartz
,
tourmaline Tourmaline ( ) is a crystalline boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone can be found in a wide variety of colors. Etymology The term is derived from th ...

tourmaline
). They are unmatched in high frequency measurements, low packaged weight, and resistance to high temperatures. Piezoresistive accelerometers resist shock (very high accelerations) better. Capacitive accelerometers typically use a silicon micro-machined sensing element. They measure low frequencies well. Modern mechanical accelerometers are often small ''micro-electro-mechanical systems'' (
MEMS Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
), and are often very simple MEMS devices, consisting of little more than a with a
proof massA proof mass or test mass is a known quantity of mass Mass is both a property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or with something, whether as an attribute or as a component of said t ...
(also known as ''seismic mass''). Damping results from the residual gas sealed in the device. As long as the
Q-factor In physics and engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engine ...
is not too low, damping does not result in a lower sensitivity. Under the influence of external accelerations, the proof mass deflects from its neutral position. This deflection is measured in an analog or digital manner. Most commonly, the capacitance between a set of fixed beams and a set of beams attached to the proof mass is measured. This method is simple, reliable, and inexpensive. Integrating piezoresistors in the springs to detect spring deformation, and thus deflection, is a good alternative, although a few more process steps are needed during the fabrication sequence. For very high sensitivities
quantum tunnelling Quantum tunnelling or tunneling (US) is the quantum mechanical Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The proce ...
is also used; this requires a dedicated process making it very expensive. Optical measurement has been demonstrated in laboratory devices. Another MEMS-based accelerometer is a thermal (or
convective Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity Homogeneity and heterogeneity are concepts often used in the sciences and statistics Statistics ...

convective
) accelerometer. It contains a small heater in a very small dome. This heats the air or other fluid inside the dome. The thermal bubble acts as the
proof massA proof mass or test mass is a known quantity of mass Mass is both a property Property (''latin: Res Privata'') in the Abstract and concrete, abstract is what belongs to or with something, whether as an attribute or as a component of said t ...
. An accompanying temperature sensor (like a
thermistor A thermistor is a type of resistor whose resistance is strongly dependent on temperature Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter, which is the source ...

thermistor
; or
thermopile A thermopile is an electronic device that converts thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concepts, such as the internal energy of a system; heat ...

thermopile
) in the dome measures the temperature in one location of the dome. This measures the location of the heated bubble within the dome. When the dome is accelerated, the colder, higher density fluid pushes the heated bubble. The measured temperature changes. The temperature measurement is interpreted as acceleration. The fluid provides the damping. Gravity acting on the fluid provides the spring. Since the proof mass is very lightweight gas, and not held by a beam or lever, thermal accelerometers can survive high shocks. Another variation uses a wire to both heat the gas and detect the change in temperature. The change of temperature changes the resistance of the wire. A two dimensional accelerometer can be economically constructed with one dome, one bubble and two measurement devices. Most micromechanical accelerometers operate ''in-plane'', that is, they are designed to be sensitive only to a direction in the plane of the
die Die, as a verb, refers to death, the cessation of life. Die may also refer to: Games * Die, singular of dice, small throwable objects used for producing random numbers Manufacturing * Die (integrated circuit), a rectangular piece of a semiconduct ...
. By integrating two devices perpendicularly on a single die a two-axis accelerometer can be made. By adding another ''out-of-plane'' device, three axes can be measured. Such a combination may have much lower misalignment error than three discrete models combined after packaging. Micromechanical accelerometers are available in a wide variety of measuring ranges, reaching up to thousands of ''g''s. The designer must compromise between sensitivity and the maximum acceleration that can be measured.


Applications


Engineering

Accelerometers can be used to measure vehicle acceleration. Accelerometers can be used to measure
vibration Vibration is a mechanical phenomenon whereby oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparentl ...

vibration
on cars, machines, buildings,
process control An industrial process control in continuous production processes is a discipline that uses industrial control system#REDIRECT Industrial control system Industrial control system (ICS) is a general term that encompasses several types of control ...
systems and safety installations. They can also be used to measure
seismic activity An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that ...
, 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 undulations based on satellite gravimetry. Gravimetry is the measurement of the strength of a gravitational field In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''ph ...
, are called
gravimeter undulations based on satellite gravimetry. Gravimetry is the measurement of the strength of a gravitational field In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Mot ...
s. Notebook computers equipped with accelerometers can contribute to the '' Quake-Catcher Network'' (QCN), a BOINC project aimed at scientific research of earthquakes.


Biology

Accelerometers are also increasingly used in the biological sciences. High frequency recordings of bi-axial or tri-axial acceleration allows the discrimination of behavioral patterns while animals are out of sight. Furthermore, recordings of acceleration allow researchers to quantify the rate at which an animal is expending energy in the wild, by either determination of limb-stroke frequency or measures such as overall dynamic body acceleration Such approaches have mostly been adopted by marine scientists due to an inability to study animals in the wild using visual observations, however an increasing number of terrestrial biologists are adopting similar approaches. For example, accelerometers have been used to study flight energy expenditure of
Harris's Hawk Harris's hawk (''Parabuteo unicinctus''), formerly known as the bay-winged hawk or dusky hawk, and known in Latin America as peuco, is a medium-large bird of prey that breeds from the southwestern United States south to Chile Chile (, ; ) ...
(''Parabuteo unicinctus'').. Researchers are also using smartphone accelerometers to collect and extract mechano-biological descriptors of resistance exercise .


Industry

Accelerometers are also used for machinery health monitoring to report the vibration and its changes in time of shafts at the bearings of rotating equipment such as turbines,
pump A pump is a device that moves fluids (liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which the ...

pump
s, fans, rollers,
compressor A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
s, or bearing fault which, if not attended to promptly, can lead to costly repairs. Accelerometer vibration data allows the user to monitor machines and detect these faults before the rotating equipment fails completely.


Building and structural monitoring

Accelerometers are used to measure the motion and vibration of a structure that is exposed to dynamic loads. Dynamic loads originate from a variety of sources including: * Human activities – walking, running, dancing or skipping * Working machines – inside a building or in the surrounding area * Construction work – driving piles, demolition, drilling and excavating * Moving loads on bridges * Vehicle collisions * Impact loads – falling debris * Concussion loads – internal and external explosions * Collapse of structural elements * Wind loads and wind gusts * Air blast pressure * Loss of support because of ground failure * Earthquakes and aftershocks Under structural applications, measuring and recording how a structure dynamically responds to these inputs is critical for assessing the safety and viability of a structure. This type of monitoring is called Health Monitoring, which usually involves other types of instruments, such as displacement sensors -Potentiometers, LVDTs, etc.- deformation sensors -Strain Gauges, Extensometers-, load sensors -Load Cells, Piezo-Electric Sensors- among others.


Medical applications

Zoll's Plus uses CPR-D•padz which contain an accelerometer to measure the depth of CPR chest compressions. Within the last several years, several 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. In Belgium, accelerometer-based step counters are promoted by the government to encourage people to walk a few thousand steps each day. Herman Digital Trainer uses accelerometers to measure strike force in physical training. It has been suggested to build
football Football is a family of s that involve, to varying degrees, a to score a . Unqualified, normally means the form of football that is the most popular where the word is used. Sports commonly called ''football'' include (known as ''soccer'' ...

football
helmets with accelerometers in order to measure the impact of head collisions. Accelerometers have been used to calculate gait parameters, such as stance and swing phase. This kind of sensor can be used to measure or monitor people.


Navigation

An inertial navigation system is a
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

navigation
aid that uses a computer and motion sensors (accelerometers) to continuously calculate via
dead reckoning In navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: ...
the position, orientation, and
velocity The velocity of an object is the Time derivative, rate of change of its Position (vector), position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction ...

velocity
(direction and speed of movement) of a moving object without the need for external references. Other terms used to refer to inertial navigation systems or closely related devices include inertial guidance system, inertial reference platform, and many other variations. An accelerometer alone is unsuitable to determine changes in altitude over distances where the vertical decrease of gravity is significant, such as for aircraft and rockets. In the presence of a gravitational gradient, the calibration and data reduction process is numerically unstable.


Transport

Accelerometers are used to detect
apogee Apsis ( el, ἀψίς; plural apsides , Greek: ἀψῖδες; "orbit") denotes either of the two extreme points (i.e., the farthest or nearest point) in the of a about its (or simply, "the primary"). The plural term, "apsides," usuall ...

apogee
in both professional and in amateur rocketry. Accelerometers are also being used in Intelligent Compaction rollers. Accelerometers are used alongside
gyroscope A gyroscope (from Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). ...

gyroscope
s in inertial navigation systems. One of the most common uses for
MEMS Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
accelerometers is in
airbag An airbag is a vehicle occupant-restraint system using a bag designed to inflate extremely quickly, then quickly deflate during a collision In physics Physics is the natural science that studies matter, its Elementary particle, funda ...

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. Another common automotive use is in
electronic stability control Electronic stability control (ESC), also referred to as electronic stability program (ESP) or dynamic stability control (DSC), is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction ( skiddi ...
systems, which use a lateral accelerometer to measure cornering forces. The widespread use of accelerometers in the automotive industry has dramatically. Another automotive application is the monitoring of
noise, vibration, and harshness Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, ha ...
(NVH), conditions that cause discomfort for drivers and passengers and may also be indicators of mechanical faults.
Tilting train A tilting train is a train that has a mechanism enabling increased speed on regular rail tracks A railway track (British English and International Union of Railways, UIC terminology) or railroad track (American English), also known as pe ...
s use accelerometers and gyroscopes to calculate the required tilt.


Volcanology

Modern electronic accelerometers are used in remote sensing devices intended for the monitoring of active
volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet a ...

volcano
es to detect the motion of
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
.


Consumer electronics

Accelerometers are increasingly being incorporated into personal electronic devices to detect the orientation of the device, for example, a display screen. A ''free-fall sensor'' (FFS) is an accelerometer used to detect if a system has been dropped and is falling. It can then apply safety measures such as parking the head of a
hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data stora ...

hard disk
to prevent a
head crash A head crash is a hard-disk failure that occurs when a read–write head of a hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device On a reel-to-reel tape recorde ...
and resulting data loss upon impact. This device is included in the many common computer and consumer electronic products that are produced by a variety of manufacturers. It is also used in some
data logger A data logger (also datalogger or data recorder) is an electronic device that records data over time or in relation to location either with a built in instrument Instrument may refer to: Science and technology * Flight instruments two-seat ...

data logger
s to monitor handling operations for
shipping container A shipping container is a container A container is any receptacle or enclosure for holding a product used in storage, packaging, and transportation, including shipping. Things kept inside of a container are protected by being inside of its ...

shipping container
s. The length of time in free fall is used to calculate the height of drop and to estimate the shock to the package.


Motion input

Some
smartphone A smartphone is a portable device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can per ...

smartphone
s, digital audio players and
personal digital assistant#REDIRECT Personal digital assistant The Palm TX A personal digital assistant (PDA), also known as a handheld PC, is a variety mobile device which functions as a personal information manager. PDAs have been mostly displaced by the widesprea ...
s contain accelerometers for user interface control; often the accelerometer is used to present landscape or portrait views of the device's screen, based on the way the device is being held.
Apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...
has included an accelerometer in every generation of
iPhone {{Infobox information appliance , name = iPhone , logo = , image = , caption = The front face of an iPhone 13 Pro The iPhone 13 Pro and iPhone 13 Pro Max are smartphones designed and marketed by Apple Inc. They are the flagship smart ...

iPhone
,
iPad iPad is a line of tablet computer A tablet computer, commonly shortened to tablet, is a mobile device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequenc ...

iPad
, and
iPod touch The iPod Touch is a line of iOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, includ ...

iPod touch
, as well as in every
iPod nano The iPod Nano (stylised and marketed as iPod nano) is a discontinued portable media player designed and formerly marketed by Apple Inc. The first generation model was introduced on September 7, 2005, as a replacement for the iPod Mini, using ...

iPod nano
since the 4th generation. Along with orientation view adjustment, accelerometers in mobile devices can also be used as
pedometer A pedometer is a device, usually portable and electronic or electromechanical In engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bri ...

pedometer
s, in conjunction with specialized
applications Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a co ...
. Automatic Collision Notification (ACN) systems also use accelerometers in a system to call for help in event of a vehicle crash. Prominent ACN systems include
OnStar OnStar Corporation is a subsidiary A subsidiary, subsidiary company or daughter company is a company (law), company owned or controlled by another company, which is called the parent company or holding company. Two subsidiaries that belong to t ...

OnStar
AACN service, Ford Link's 911 Assist, Toyota's Safety Connect, Lexus Link, or BMW Assist. Many accelerometer-equipped smartphones also have ACN software available for download. ACN systems are activated by detecting crash-strength accelerations. Accelerometers are used in vehicle
Electronic stability control Electronic stability control (ESC), also referred to as electronic stability program (ESP) or dynamic stability control (DSC), is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction ( skiddi ...
systems to measure the vehicle's actual movement. A computer compares the vehicle's actual movement to the driver's steering and throttle input. The stability control computer can selectively brake individual wheels and/or reduce engine power to minimize the difference between driver input and the vehicle's actual movement. This can help prevent the vehicle from spinning or rolling over. Some
pedometer A pedometer is a device, usually portable and electronic or electromechanical In engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bri ...

pedometer
s use an accelerometer to more accurately measure the number of steps taken and distance traveled than a mechanical sensor can provide. Nintendo's
Wii The Wii ( ) is a developed and marketed by . It was first released on November 19, 2006, in North America and in December 2006 for most other of the world. It is Nintendo's fifth major home game console, following the and is a alongsid ...

Wii
video game console uses a controller called a
Wii Remote The Wii Remote, also known colloquially Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom normally employe ...

Wii Remote
that contains a three-axis accelerometer and was designed primarily for motion input. Users also have the option of buying an additional motion-sensitive attachment, the
Nunchuk (Chinese: ) is a traditional Okinawan martial arts weapon consisting of two sticks connected at one end by a short chain or rope. The two sections of the weapon are commonly made out of wood, while the link is a cord or a metal chain. The person ...

Nunchuk
, so that motion input could be recorded from both of the user's hands independently. Is also used on the
Nintendo 3DS The is a handheld game console produced by Nintendo. It was announced in March 2010 and unveiled at E3 2010 as the successor to the Nintendo DS. The system features backward compatibility with older Nintendo DS video games. As an eighth-gener ...
system. The Sony
PlayStation 3 The PlayStation 3 (PS3) is a home video game console A home video game console is a video game console that is designed to be connected to a display device, such as a television, and an external power source as to play video games. Home c ...
uses the
DualShock 3 The DualShock (originally Dual Shock; trademarked as DUALSHOCK or DUAL SHOCK; later named DualSense) is a line of gamepads with vibration-feedback and analog controls developed by Sony Interactive Entertainment for the PlayStation family of syste ...

DualShock 3
remote which uses a three axis accelerometer that can be used to make steering more realistic in racing games, such as '' MotorStorm'' and ''
Burnout Paradise ''Burnout Paradise'' is a 2008 open world racing video game developed by Criterion Games and published by Electronic Arts for PlayStation 3, Xbox 360 and Microsoft Windows. It was also released on the PlayStation Store and via Xbox Live Marketplac ...
''. The 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. Other uses for accelerometer in Nokia phones include Pedometer functionality in Nokia Sports Tracker. Some other devices provide the tilt sensing feature with a cheaper component, which is not a true accelerometer. Sleep phase alarm clocks use accelerometric sensors to detect movement of a sleeper, so that it can wake the person when he/she is not in REM phase, in order to awaken the person more easily.


Sound recording

A microphone or eardrum is a membrane that responds to oscillations in air pressure. These oscillations cause acceleration, so accelerometers can be used to record sound. A 2012 study found that voices can be detected by smartphone accelerometers in 93% of typical daily situations. Conversely, carefully designed sounds can cause accelerometers to report false data. One study tested 20 models of (MEMS) smartphone accelerometers and found that a majority were susceptible to this attack.


Orientation sensing

A number of 21st-century devices use accelerometers to align the screen depending on the direction the device is held (e.g., switching between Page orientation, portrait and landscape modes). Such devices include many tablet computer, tablet PCs and some
smartphone A smartphone is a portable device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can per ...

smartphone
s and digital cameras. The Amida Simputer, a handheld Linux device launched in 2004, was the first commercial handheld to have a built-in accelerometer. It incorporated many gesture-based interactions using this accelerometer, including page-turning, zoom-in and zoom-out of images, change of portrait to landscape mode, and many simple gesture-based games. As of January 2009, almost all new mobile phones and digital cameras contain at least a tilt sensor and sometimes an accelerometer for the purpose of auto image rotation, motion-sensitive mini-games, and correcting shake when taking photographs.


Image stabilization

Camcorders use accelerometers for image stabilization, either by moving optical elements to adjust the light path to the sensor to cancel out unintended motions or digitally shifting the image to smooth out detected motion. Some stills cameras use accelerometers for anti-blur capturing. The camera holds off capturing the image when the camera is moving. When the camera is still (if only for a millisecond, as could be the case for vibration), the image is captured. An example of the application of this technology is the Glogger VS2, a phone application which runs on Symbian based phones with accelerometers such as the Nokia N96. Some digital cameras contain accelerometers to determine the orientation of the photo being taken and also for rotating the current picture when viewing.


Device integrity

Many laptops feature an accelerometer which is used to detect drops. If a drop is detected, the heads of the Hard disk drive, hard disk are parked to avoid data loss and possible head or disk damage by the ensuing Shock (mechanics), shock.


Gravimetry

A gravimeter or gravitometer, is an instrument used in
gravimetry undulations based on satellite gravimetry. Gravimetry is the measurement of the strength of a gravitational field In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''ph ...
for measuring the local
gravitational field In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...

gravitational field
. A gravimeter is a type of accelerometer, except that accelerometers are susceptible to all
vibration Vibration is a mechanical phenomenon whereby oscillation Oscillation is the repetitive variation, typically in time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparentl ...

vibration
s including noise, that cause oscillatory accelerations. This is counteracted in the gravimeter by integral vibration isolation and signal processing. Though the essential principle of design is the same as in accelerometers, gravimeters are typically designed to be much more sensitive than accelerometers in order to measure very tiny changes within the Gravity of Earth, Earth's gravity, of 1 ''g''. In contrast, other accelerometers are often designed to measure 1000 ''g'' or more, and many perform multi-axial measurements. The constraints on temporal resolution are usually less for gravimeters, so that resolution can be increased by processing the output with a longer "time constant".


Types of accelerometer

* Bulk micromachined capacitive * Bulk micromachined piezoelectric resistive * Capacitive spring mass system base * DC response * Electromechanical
servo Servo may refer to: Mechanisms * Servomechanism In control engineering Control engineering or control systems engineering is an engineering discipline that applies control theory to design equipment and systems with desired behaviors in Cont ...
(Servo Force Balance) * High gravity * High temperature * Laser accelerometer * Low frequency * Magnetic induction * Modally tuned impact hammers * Null-balance * Optical * PIGA accelerometer, Pendulous integrating gyroscopic accelerometer (PIGA) * Piezoelectric accelerometer * Quantum (Rubidium atom cloud, laser cooled) * Resonance * Seat pad accelerometers * Shear mode accelerometer * Strain gauge * Surface acoustic wave (SAW) * Surface micromachined capacitive (
MEMS Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
) * Thermal (submicrometre CMOS process) * Triaxial * List of vacuum tubes#DDR, Vacuum diode with flexible anode * potentiometric type * LVDT type accelerometer


Exploits

Millions of smartphones could be vulnerable to software cracking via accelerometers.


See also

* Accelerograph * Degrees of freedom *
g-force The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight In science Science () is a systematic ente ...

g-force
* Geophone * Gyroscope * Inclinometer * Inertial measurement unit * Inertial navigation system * Magnetometer * Seismometer * Vibration Calibrator


References

{{Reflist, 30em Accelerometers, Acceleration