# Accelerometer

An accelerometer is a device that measures proper acceleration.[1] Proper acceleration, being the acceleration (or rate of change of velocity) of a body in its own instantaneous rest frame,[2] is not the same as coordinate acceleration, being the acceleration in a fixed 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 (falling toward the center of the Earth at a rate of about 9.81 m/s2) will measure zero.

Accelerometers have multiple applications in industry and science. Highly sensitive accelerometers are components of inertial navigation systems for aircraft and missiles. Accelerometers are used to detect and monitor vibration in rotating machinery. Accelerometers are used in tablet computers and digital cameras so that images on screens are always displayed upright. Accelerometers are used in drones for flight stabilisation. Coordinated accelerometers can be used to measure differences in proper acceleration, particularly gravity, over their separation in space; i.e., gradient of the gravitational field. This gravity gradiometry is useful because absolute gravity is a weak effect and depends on local density of the Earth which is quite variable.

Single- and multi-axis models of accelerometer are available to detect magnitude and direction of the proper acceleration, as a vector quantity, and can be used to sense orientation (because direction of weight changes), coordinate acceleration, vibration, shock, and falling in a resistive medium (a case where the proper acceleration changes, since it starts at zero, then increases). Micromachined microelectromechanical systems (MEMS) accelerometers are increasingly present in portable electronic devices and video game controllers, to detect the position of the device or provide for game input.

## Physical principles

An accelerometer measures proper acceleration, which is the acceleration it experiences relative to freefall and is the acceleration felt by people and objects.[2] Put another way, at any point in spacetime the equivalence principle guarantees the existence of a local inertial frame, and an accelerometer measures the acceleration relative to that frame.[3] Such accelerations are popularly denoted g-force; i.e., in comparison to standard gravity.

An accelerometer at rest relative to the Earth's surface will indicate approximately 1 g upwards, because any point on the Earth's surface is accelerating 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,[4] 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. 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 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 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 (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, a knowledge of local gravity is required. This can be obtained either by calibrating the device at rest,[5] or from a known model of gravity at the approximate current position.

## Structure

Conceptually, an accelerometer behaves as a damped mass on a spring. When the accelerometer experiences an acceleration, the mass is displaced to the point that the spring is able to accelerate the mass at the same rate as the casing. The displacement is then measured to give the acceleration.

In commercial devices, piezoelectric, piezoresistive and capacitive components are commonly used to convert the mechanical motion into an electrical signal. Piezoelectric accelerometers rely on piezoceramics (e.g. lead zirconate titanate) or single crystals (e.g. quartz, tourmaline). They are unmatched in terms of their upper frequency range, low packaged weight and high temperature range. Piezoresistive accelerometers are preferred in high shock applications. Capacitive accelerometers typically use a silicon micro-machined sensing element. Their performance is superior in the low frequency range and they can be operated in servo mode to achieve high stability and linearity.

Modern accelerometers are often small micro electro-mechanical systems (MEMS), and are indeed the simplest MEMS devices possible, consisting of little more than a cantilever beam with a proof mass (also known as seismic mass). Damping results from the residual gas sealed in the device. As long as the Q-factor 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 tunneling is also used; this requires a dedicated process making it very expensive. Optical measurement has been demonstrated on laboratory scale.

Another, relatively new type of MEMS-based accelerometer is a thermal (or convective) accelerometer[6] that contains a small heater at the bottom of a very small dome, which heats the air/fluid inside the dome, producing a thermal bubble that acts as the proof mass. An accompanying temperature sensor (like thermistor; or thermopile) in the dome is used to determine the temperature profile inside the dome, hence, letting us know the location of the heated bubble within the dome. Now, due to any applied acceleration, there occurs a physical displacement of the thermal bubble and it gets deflected off its center position within the dome. Measuring this displacement, the acceleration applied to the sensor can be measured. Due to the absence of solid proof mass, thermal accelerometers yields high shock survival rating.

Most micromechanical accelerometers operate in-plane, that is, they are designed to be sensitive only to a direction in the plane of the die. 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 make a 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 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.

Notebook computers equipped with accelerometers can contribute to the Quake-Catcher Network (QCN), a BOINC project aimed at scientific research of earthquakes.[7]

### Biology

Accelerometers are also increasingly used in the biological sciences. High frequency recordings of bi-axial[8] or tri-axial acceleration[9] 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[10] or measures such as overall dynamic body acceleration[11] 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. This device can be connected to an amplifier to amplify the signal.

### 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, pumps,[12] fans,[13] rollers,[14] compressors,[15][16] or bearing fault[17] 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.[18] 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 AED 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.[19][20]

It has been suggested to build football helmets with accelerometers in order to measure the impact of head collisions.[21]

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.[22][23]

### Navigation

An inertial navigation system is a navigation aid that uses a computer and motion sensors (accelerometers) to continuously calculate via dead reckoning the position, orientation, and 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.[24][25]

### Transport

Accelerometers are used to detect apogee in both professional[26] and in amateur[27] rocketry.

Accelerometers are also being used in Intelligent Compaction rollers. Accelerometers are used alongside gyroscopes in inertial navigation systems.[28]

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. Another common automotive use is in electronic stability control systems, which use a lateral accelerometer to measure cornering forces. The widespread use of accelerometers in the automotive industry has pushed their cost down dramatically.[29] Another automotive application is the monitoring of noise, vibration, and harshness (NVH), conditions that cause discomfort for drivers and passengers and may also be indicators of mechanical faults.

Tilting trains use accelerometers and gyroscopes to calculate the required tilt.[30]

### Volcanology

Modern electronic accelerometers are used in remote sensing devices intended for the monitoring of active volcanoes to detect the motion of magma.[31]

### 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 to prevent a head crash 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 loggers to monitor handling operations for shipping containers. 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

Tri-axis Digital Accelerometer by Kionix, inside Motorola Xoom

Some smartphones, digital audio players and personal digital assistants 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 has included an accelerometer in every generation of iPhone, iPad, and iPod touch, as well as in every iPod nano since the 4th generation. Along with orientation view adjustment, accelerometers in mobile devices can also be used as pedometers, in conjunction with specialized applications.[32]

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 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 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 pedometers use an accelerometer to more accurately measure the number of steps taken and distance traveled than a mechanical sensor can provide.

Nintendo's Wii video game console uses a controller called a 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, so that motion input could be recorded from both of the user's hands independently. Is also used on the Nintendo 3DS system.

The Sony PlayStation 3 uses the 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.

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. 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.[33]. A 2012 study found that voices can be detected by smartphone accelerometers in 93% of typical daily situations.[34].

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. [35]

#### 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 portrait and landscape modes). Such devices include many tablet PCs and some smartphones 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,[36] 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 are parked to avoid data loss and possible head or disk damage by the ensuing shock.

### Gravimetry

A gravimeter or gravitometer, is an instrument used in gravimetry for measuring the local gravitational field. A gravimeter is a type of accelerometer, except that accelerometers are susceptible to all vibrations 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 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".

## References

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Comparison of smartphones

This is a comparison of the various internal components and features of many smartphones.

Digital pen

A digital pen or smart pen is an input device which captures the handwriting or brush strokes of a user and converts handwritten analog information created using "pen and paper" into digital data, enabling the data to be utilized in various applications. This type of pen is usually used in conjunction with a digital notebook, although the data can also be used for different applications or simply as a graphic.

A digital pen is generally larger and has more features than an active pen. Digital pens typically contain internal electronics and have features such as touch sensitivity, input buttons, memory for storing handwriting data and transmission capabilities.

Doodle Jump

Doodle Jump is a platforming video game developed and published by American studio Lima Sky, for Windows Phone, iPhone OS, BlackBerry, Android, Java Mobile (J2ME), Nokia Symbian, and Xbox 360 for the Kinect platform. It was released worldwide for iPhone OS on March 15, 2009, and was later released for Android and Blackberry on March 2, 2010, Symbian on May 1, 2010, and Windows Phone 7 on June 1, 2011 (Re-Released August 21, 2013 Windows Phone 8). It was released for the iPad on September 1, 2011. Since its release, the game has been generally well received. The game PapiJump by Sunflat Games inspired the gameplay of Doodle Jump, and characters featured in Doodle Jump were based on Elise Gravel's illustrations. The game is currently available on nine platforms.

Doodle Jump was renowned for its selling rate by App Store standards, which counted 25,000 copies sold daily for 4 consecutive months (later overtaken by Angry Birds). As of December, 2011, the game sold 10 million copies over iTunes and Google Play and reached 15 million downloads across all platforms. The game has been developed into a video redemption game for play at video arcades. Croats Igor and Marko Pušenjak are authors of Doodle Jump, where Igor works from a New York-based address and Marko resides in Croatia. In July 2016, Lima Sky announced partnership with Skillz to develop a tournament-playable version of the game.

G-force

The gravitational force, or more commonly, g-force, is a measurement of the type of acceleration that causes a perception of weight. Despite the name, it is incorrect to consider g-force a fundamental force, as "g-force" is a type of acceleration that can be measured with an accelerometer. Since g-force accelerations indirectly produce weight, any g-force can be described as a "weight per unit mass" (see the synonym specific weight). When the g-force acceleration is produced by the surface of one object being pushed by the surface of another object, the reaction force to this push produces an equal and opposite weight for every unit of an object's mass. The types of forces involved are transmitted through objects by interior mechanical stresses. The g-force acceleration (except certain electromagnetic force influences) is the cause of an object's acceleration in relation to free fall.The g-force acceleration experienced by an object is due to the vector sum of all non-gravitational and non-electromagnetic forces acting on an object's freedom to move. In practice, as noted, these are surface-contact forces between objects. Such forces cause stresses and strains on objects, since they must be transmitted from an object surface. Because of these strains, large g-forces may be destructive.

Gravitation acting alone does not produce a g-force, even though g-forces are expressed in multiples of the acceleration of a standard gravity. Thus, the standard gravitational acceleration at the Earth's surface produces g-force only indirectly, as a result of resistance to it by mechanical forces. These mechanical forces actually produce the g-force acceleration on a mass. For example, the 1 g force on an object sitting on the Earth's surface is caused by mechanical force exerted in the upward direction by the ground, keeping the object from going into free fall. The upward contact force from the ground ensures that an object at rest on the Earth's surface is accelerating relative to the free-fall condition. (Free fall is the path that the object would follow when falling freely toward the Earth's center). Stress inside the object is ensured from the fact that the ground contact forces are transmitted only from the point of contact with the ground.

Objects allowed to free-fall in an inertial trajectory under the influence of gravitation only, feel no g-force acceleration, a condition known as zero-g (which means zero g-force). This is demonstrated by the "zero-g" conditions inside an elevator falling freely toward the Earth's center (in vacuum), or (to good approximation) conditions inside a spacecraft in Earth orbit. These are examples of coordinate acceleration (a change in velocity) without a sensation of weight. The experience of no g-force (zero-g), however it is produced, is synonymous with weightlessness.

In the absence of gravitational fields, or in directions at right angles to them, proper and coordinate accelerations are the same, and any coordinate acceleration must be produced by a corresponding g-force acceleration. An example here is a rocket in free space, in which simple changes in velocity are produced by the engines and produce g-forces on the rocket and passengers..

Gyroscope

A gyroscope (from Ancient Greek γῦρος gûros, "circle" and σκοπέω skopéō, "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotation (spin axis) is free to assume any orientation by itself. When rotating, the orientation of this axis is unaffected by tilting or rotation of the mounting, according to the conservation of angular momentum.

Gyroscopes based on other operating principles also exist, such as the microchip-packaged MEMS gyroscopes found in electronic devices, solid-state ring lasers, fibre optic gyroscopes, and the extremely sensitive quantum gyroscope. Applications of gyroscopes include inertial navigation systems, such as in the Hubble Telescope, or inside the steel hull of a submerged submarine. Due to their precision, gyroscopes are also used in gyrotheodolites to maintain direction in tunnel mining. Gyroscopes can be used to construct gyrocompasses, which complement or replace magnetic compasses (in ships, aircraft and spacecraft, vehicles in general), to assist in stability (bicycles, motorcycles, and ships) or be used as part of an inertial guidance system.

MEMS gyroscopes are popular in some consumer electronics, such as smartphones.

Huawei Ascend (phone)

Huawei Ascend is the first phone in the Huawei Ascend series. It ran Android OS 2.1 by default. It has been released in the United States for Cricket Wireless and MetroPCS unsubsidized. As of the summer of 2012, the model is also available on the market in Europe.The device features a 3.5-inch HVGA capacitive touch screen, 2.5 mm headphone jack, 3.2-megapixel camera, as well as an accelerometer and a compass. The HVGA capacitive touch screen is not multitouch capable.

First model is Huawei Ascend M860.

Inclinometer

An inclinometer or clinometer is an instrument used for measuring angles of slope (or tilt), elevation, or depression of an object with respect to gravity's direction. It is also known as a tilt indicator, tilt sensor, tilt meter, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, declinometer, and pitch & roll indicator. Clinometers measure both inclines (positive slopes, as seen by an observer looking upwards) and declines (negative slopes, as seen by an observer looking downward) using three different units of measure: degrees, percent, and topo (see Grade (slope) for details). Astrolabes are inclinometers that were used for navigation and locating astronomical objects from ancient times to the Renaissance.

A tilt sensor can measure the tilting in often two axes of a reference plane in two axes.

In contrast, a full motion would use at least three axes and often additional sensors. One way to measure tilt angle with reference to the earth's ground plane, is to use an accelerometer. Typical applications can be found in the industry and in game controllers. In aircraft, the "ball" in turn coordinators or turn and bank indicators is sometimes referred to as an inclinometer.

Inertial navigation system

An inertial navigation system (INS) is a navigation device that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate by dead reckoning the position, the orientation, and the velocity (direction and speed of movement) of a moving object without the need for external references. Often the inertial sensors are supplemented by a barometric altimeter and occasionally by magnetic sensors (magnetometers) and/or speed measuring devices. INSs are used on vehicles such as ships, aircraft, submarines, guided missiles, and spacecraft. Other terms used to refer to inertial navigation systems or closely related devices include inertial guidance system, inertial instrument, inertial measurement unit (IMU) and many other variations. Older INS systems generally used an inertial platform as their mounting point to the vehicle and the terms are sometimes considered synonymous.

Integrated Electronics Piezo-Electric

The abbreviation IEPE stands for Integrated Electronics Piezo-Electric. It characterises a technical standard for piezoelectric sensors which contain built-in impedance conversion electronics. IEPE sensors are used to measure acceleration, force or pressure. Measurement microphones also apply the IEPE standard.

Other proprietary names for the same principle are ICP, CCLD, IsoTron or DeltaTron.

The electronics of the IEPE sensor (typically implemented as FET circuit) converts the high impedance signal of the piezoelectric material into a voltage signal with a low impedance of typically 100 Ω. A low impedance signal is advantageous because it can be transmitted across long cable lengths without a loss of signal quality. In addition, special low noise cables, which are otherwise required for use with piezoelectric sensors, are no longer necessary.

The sensor circuit is supplied with constant current. A distinguishing feature of the IEPE principle is that the power supply and the sensor signal are transmitted via one shielded wire.

Most IEPE sensors work at a constant current between 2 and 20 mA. A common value is 4 mA. The higher the constant current the longer the possible cable length. Cables of several hundred meters length can be used without a loss of signal quality. Supplying the IEPE sensor with constant current, results in a positive bias voltage, typically between 8 and 12 volts, at the output. The actual measuring signal of the sensor is added to this bias voltage. The supply or compliance voltage of the constant current source should be 24 to 30 V which is about two times the bias voltage. This ensures maximum amplitudes in positive and negative direction.

A typical IEPE sensor supply with 4 mA constant current and 25 V compliance voltage has a power consumption of 100 mW. This can be a drawback in battery powered systems. For such applications low-power IEPE sensors exist which can be operated at only 0.1 mA constant current from a 12 V supply. This may save up to 90 % power.

Many measuring instruments designed for piezoelectric sensors or measurement microphones have an IEPE constant current source integrated at the input.

In measuring instruments with IEPE input the bias voltage is often used for sensor detection.

If the signal lies close to the constant current supply voltage, there is no sensor present or the cable path has been interrupted. A signal close to the saturation voltage, indicates a short-circuit in the sensor or cable. In between these two limits a functional sensor has been detected.

The bias voltage is cut off by a coupling capacitor at the instrument input and only the AC signal is processed further.

Piezoelectric sensors which do not possess IEPE electronics, meaning with charge output, remain reserved for applications where lowest frequencies, high operating temperatures, an extremely large dynamic range, very energy saving operation or extremely small design is required.

Motorola Flipout

The Motorola Flipout (Model Number MB511, also styled FLIPOUT) is a phone made by Motorola and released in June 2010. Its touchscreen is 2.8 inches in size. It also has a 3.2-megapixel camera and comes in a wide variety of colors such as "Poppy Red", "Brilliant Blue″, "Licorice Black", "White", and "Saffron". However, in Australia, only "Poppy Red" and "Licorice Black" are available. The Flipout runs on Android 2.1 (codenamed Eclair). Its square-shaped body has two parts that rotate near the bottom-right corner to reveal a five-row QWERTY keyboard below the screen. It has an accelerometer and includes a web browser with Adobe Flash Lite 3.0. It also has a 720 MHz processor with a QVGA 320x240 pixel display.

Nokia 6210 Navigator

The Nokia 6210 Navigator is a smartphone made by Nokia that is a successor to Nokia 6110 Navigator. It was announced on February 11, 2008 and had been available from July 2008. It runs on Symbian OS v9.3 with a S60 3rd Edition FP2 user interface.

The Nokia 6210 Navigator is the third phone in the Navigator series to be released by Nokia. The Nokia 6210 Navigator includes pre-loaded navigation maps with a free navigation license for 6 months. It is also the company's first device with a built-in magnetic compass.

It should not be confused with the Nokia 6210 from 2000.

It was succeeded by the Nokia 6710 Navigator.

Nokia E66

The Nokia E66 is a slider smartphone in the Nokia Eseries range, a S60 platform third edition device with slide action targeting business users. It is a successor to the Nokia E65 with which it shares many features.E66 has similar features to the Nokia E71 handset, but lacks sufficient battery capacity for all day use and does not have the full QWERTY, however the E66 is smaller in size and weighs less. The E66 also includes an accelerometer and new animations and transition effects, which are lacking in the E71.

Nokia N93i

The Nokia N93i (also known as the N93i-1) is a smartphone produced by Nokia, announced on 8 January 2007 and released the same month. It is part of the Nseries line and is a redesign of the Nokia N93. The N93i runs on Symbian OS version 9.1, with the S60 3rd Edition user interface. Like the N93, it is a clamshell and swivel design with a camera and landscape position.

The N95's improved camera capabilities have led to it being seldom called the N93i's successor, though Nokia have never made another swivel-style phone since.

Nokia N95

The Nokia N95 (N95-1, internally known as RM-159) is a smartphone that was produced by Nokia as part of their Nseries line of portable devices. Announced in September 2006, it was released to the market in March 2007. The N95 ran S60 3rd Edition, on Symbian OS v9.2. It has a two-way sliding mechanism, which can be used to access either media playback buttons or a numeric keypad. It was first released in silver and later on in black, with limited edition quantities in gold and purple. The launch price of the N95 was around €550 (about US\$730, GB£370).

The N95 was a high-end model that was marketed as a "multimedia computer", much like other Nseries devices. It featured a then-high 5 megapixel resolution digital camera with Carl Zeiss optics and with a flash, as well as a then-large display measuring 2.6 inches. It was also Nokia's first device with a built-in Global Positioning System (GPS) receiver, used for maps or turn-by-turn navigation, and their first with an accelerometer. It was also one of the earliest devices in the market supporting HSDPA (3.5G) signals.

After the introduction of the original model (technically named N95-1), several updated versions were released, most notably the N95 8GB with 8 gigabytes of internal storage, a larger display and improved battery. The 'classic' N95 and its upgraded variant N95 8GB are widely considered as breakthrough technologies of its time. It was well noted for its camera, GPS and mapping capabilities, and its innovative dual-slider, and some have hailed it as one of the best mobile devices to have been released.

Piezoelectric accelerometer

A piezoelectric accelerometer is an accelerometer that employs the piezoelectric effect of certain materials to measure dynamic changes in mechanical variables (e.g., acceleration, vibration, and mechanical shock).

As with all transducers, piezoelectric convert one form of energy into another and provide an electrical signal in response to a quantity, property, or condition that is being measured. Using the general sensing method upon which all accelerometers are based, acceleration acts upon a seismic mass that is restrained by a spring or suspended on a cantilever beam, and converts a physical force into an electrical signal. Before the acceleration can be converted into an electrical quantity it must first be converted into either a force or displacement. This conversion is done via the mass spring system shown in the figure to the right.

Steel (web browser)

Steel is a discontinued freeware web browser developed by Michael Kolb under the name kolbysoft. It is a fork of the default browser for Android, taking its WebKit-based layout engine and providing what is intended to be an easier and more "touch friendly" user interface.

Steel was one of the first Android applications to support automatic rotation based on the hardware's accelerometer and a virtual keyboard. This feature is now more common among Android applications.

In 2010 Skyfire purchased kolbysoft and the Steel browser.

Sudden Motion Sensor

The Sudden Motion Sensor (SMS) is Apple's motion-based data protection system used in their notebook computer systems. Apple introduced the system January 1, 2005 in its refreshed PowerBook line, and included it in the iBook line July 26, 2005. Since that time, Apple has included the system in all of their non-SSD portable systems (since October 2006), now the MacBook Pro and MacBook Air.

With a triaxial accelerometer, the shock detector detects sudden acceleration, such as when the computer is dropped, and prepares the relatively fragile hard disk drive mechanism for impact. The system disengages the disk drive heads from the hard disk platters, preventing data loss and drive damage from a disk head crash. When the computer is stable, the drive operates normally again. A clicking noise can be heard when the sudden motion sensor activates.

Broadly speaking, there have been two types of Sudden Motion Sensor. The sensor used in the G4-based laptops resolved shifts of 1/52 g (e.g. the dynamic range was close to 6-bit), while the sensor used in the current Intel-based laptops have an 8-bit resolution (250 scale divisions). In at least one model of Intel-based laptop, the MacBook Pro 15", Apple uses the Kionix KXM52-1050 three-axis accelerometer chip, with dynamic range of +/- 2g and bandwidth up to 1.5 kHz.

Swarm (spacecraft)

Swarm is a European Space Agency (ESA) mission to study the Earth's magnetic field. High-precision and high-resolution measurements of the strength, direction and variations of the Earth's magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide data for modelling the geomagnetic field and its interaction with other physical aspects of the Earth system. The results offer a view of the inside of the Earth from space, enabling the composition and processes of the interior to be studied in detail and increase our knowledge of atmospheric processes and ocean circulation patterns that affect climate and weather.

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