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58-462: The instruments used in the seismic array are CUSP-3Clp accelerometers manufactured by Canterbury Seismic Instruments Ltd. based in New Zealand. The instruments record three components of ground motion, i.e. one vertical and two horizontal components, over a high dynamic range. The instruments are connected to a GPS clock, ensuring a uniform time over the network. The instruments communicate via

116-408: 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

174-520: A body near the surface of the Earth is due to the combined effects of gravity and centrifugal acceleration from the rotation of the Earth (but the latter is small enough to be negligible for most purposes); the total (the apparent gravity) is about 0.5% greater at the poles than at the Equator . Although the symbol ɡ is sometimes used for standard gravity, ɡ (without a suffix) can also mean

232-668: 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. Standard gravity The standard acceleration of gravity or standard acceleration of free fall , often called simply standard gravity and denoted by ɡ 0 or ɡ n ,

290-544: A column of mercury of 760 mm. But since that weight depends on the local gravity, they now also needed a standard gravity. The 1887 CIPM meeting decided as follows: The value of this standard acceleration due to gravity is equal to the acceleration due to gravity at the International Bureau (alongside the Pavillon de Breteuil ) divided by 1.0003322, the theoretical coefficient required to convert to

348-654: 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. 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

406-506: 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 . 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 to keep the proof mass from moving far. The motor might be an electromagnet or in very small accelerometers, electrostatic . Since

464-673: A latitude of 45° at sea level. All that was needed to obtain a numerical value for standard gravity was now to measure the gravitational strength at the International Bureau . This task was given to Gilbert Étienne Defforges of the Geographic Service of the French Army. The value he found, based on measurements taken in March and April 1888, was 9.80991(5) m⋅s . This result formed the basis for determining

522-413: A majority were susceptible to this attack. 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

580-410: 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

638-415: 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 is reached. At terminal velocity, the accelerometer will indicate 1 g acceleration upwards. For

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696-455: A silicon micro-machined sensing element. They measure low frequencies well. Modern mechanical accelerometers are often small micro-electro-mechanical systems ( MEMS ), and are often very simple MEMS devices, 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

754-407: 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 mass . An accompanying temperature sensor (like a thermistor ; or 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

812-400: A wireless permanent GPRS connection. This enables remote configuration of individual units and near real-time alerts and data uploading. An important feature that has been developed during the establishment of the array is a common triggering scheme. This feature was designed in collaboration with the manufacturers of the units. In the event of two or more units receiving an earthquake trigger,

870-495: Is a key aspect when designing infrastructure. It can have a dramatic effect on the response of structures and the extent of damage. In order to estimate the effects, it is necessary to develop models from data recorded on a seismograph array. This is the reason why the ICEARRAY was created. The models developed from the data recorded on the ICEARRAY have enabled the first reliable assessment of earthquake effects on infrastructure in

928-441: Is a weak effect and depends on the local density of the Earth, which is quite variable. A single-axis accelerometer measures acceleration along a specified axis. A multi-axis accelerometer detects both the magnitude and the direction of the proper acceleration, as a vector quantity, and is usually implemented as several single-axis accelerometers oriented along different axes. An accelerometer measures proper acceleration , which

986-413: 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

1044-556: Is in free fall will measure zero acceleration. Accelerometers have many uses in industry, consumer products, and science. Highly sensitive accelerometers are used in inertial navigation systems for aircraft and missiles. In unmanned aerial vehicles , accelerometers help to stabilize flight. Micromachined micro-electromechanical systems (MEMS) accelerometers are used in handheld electronic devices such as smartphones , cameras and video-game controllers to detect movement and orientation of these devices. Vibration in industrial machinery

1102-410: Is monitored by accelerometers. Seismometers are sensitive accelerometers for monitoring ground movement such as earthquakes. 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 . Gravity gradiometry is useful because absolute gravity

1160-425: 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

1218-439: 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 guarantees the existence of a local inertial frame , and an accelerometer measures the acceleration relative to that frame. Such accelerations are popularly denoted g-force ; i.e., in comparison to standard gravity . An accelerometer at rest relative to

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1276-486: Is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth . It is a constant defined by standard as 9.806 65  m/s (about 32.174 05  ft/s ). This value was established by the third General Conference on Weights and Measures (1901, CR 70) and used to define the standard weight of an object as the product of its mass and this nominal acceleration . The acceleration of

1334-896: The Iceland hotspot , which causes dynamic uplift of the Iceland Plateau , with associated volcanism and seismicity . The line of the Mid-Atlantic Ridge is offset by two transform zones in Iceland, the South Iceland Seismic Zone (SISZ) in the south and the Tjornes Fracture Zone in the north. The town of Hveragerdi is located at the western end of the SISZ, an area of considerable seismicity. The South Iceland Seismic Zone (SISZ) has been

1392-781: The Nintendo 3DS system. 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. 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

1450-534: The newton , two units of force . Already in the early days of its existence, the International Committee for Weights and Measures (CIPM) proceeded to define a standard thermometric scale, using the boiling point of water. Since the boiling point varies with the atmospheric pressure , the CIPM needed to define a standard atmospheric pressure. The definition they chose was based on the weight of

1508-688: The 4th generation. Along with orientation view adjustment, accelerometers in mobile devices can also be used as pedometers , in conjunction with specialized applications . 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

1566-435: 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

1624-436: The SISZ. The data also provides a physically realistic description of fault rupture. The models and simulations developed can be applied in other regions and the methods used provide a link between seismology and earthquake engineering Accelerometers An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change of velocity ) of

1682-416: The acceleration of a body in free fall at sea level at a geodetic latitude of 45°. Although the actual acceleration of free fall on Earth varies according to location, the above standard figure is always used for metrological purposes. In particular, since it is the ratio of the kilogram-force and the kilogram , its numeric value when expressed in coherent SI units is the ratio of the kilogram-force and

1740-439: 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, or from a known model of gravity at the approximate current position. A basic mechanical accelerometer is a damped proof mass on a spring . When the accelerometer experiences an acceleration, Newton's third law causes

1798-522: The appearance of a gravitational offset is Einstein's equivalence principle , 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

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1856-438: The automotive industry has pushed their cost down dramatically. 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. Modern electronic accelerometers are used in remote sensing devices intended for

1914-732: 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 ), very linear with a controlled frequency response. (This is called servo mode design.) In mechanical accelerometers, measurement is often electrical, piezoelectric , piezoresistive or capacitive . Piezoelectric accelerometers use piezoceramic sensors (e.g. lead zirconate titanate ) or single crystals (e.g. quartz , 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

1972-613: The common triggering feature activates the entire array to start recording. This scheme ensures complete data coverage and greatly reduces the need to filter out noise and manmade disturbances. Iceland is located on the Mid-Atlantic Ridge , the extensional tectonic plate boundary between the North American Plate and the Eurasian Plate . It is also located over a deep-seated mantle plume known as

2030-409: The damping causes accelerometers to have a 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 otoliths (Latin for "ear stone") or statoconia , acting against a bed of hairs connected to neurons. The hairs form the springs, with the neurons as sensors. The damping is usually by

2088-445: 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

2146-428: 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. 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

2204-471: 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 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

2262-420: 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

2320-543: 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 helmets with accelerometers in order to measure

2378-453: The local acceleration due to local gravity and centrifugal acceleration, which varies depending on one's position on Earth (see Earth's gravity ). The symbol ɡ should not be confused with G , the gravitational constant , or g, the symbol for gram . The ɡ is also used as a unit for any form of acceleration, with the value defined as above. The value of ɡ 0 defined above is a nominal midrange value on Earth, originally based on

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2436-458: The location of numerous large destructive earthquakes in the past. The SISZ is an east-west trending transform zone approximately 70 km long and 10–20 km wide. Destructive earthquake sequences in this region usually consist of several earthquakes exceeding a magnitude of 6.5 and with their epicentres located on north-south trending faults . Such a sequence started on 17 June 2000 at 15:40 local time with an earthquake of magnitude 6.5. It

2494-399: The monitoring of active volcanoes to detect the motion of magma . 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

2552-498: 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

2610-488: The object relative to an observer who is in free fall (that is, relative to an inertial frame of reference ). Proper acceleration is different from coordinate acceleration, which is acceleration with respect to a given coordinate system , which may or may not be accelerating. For example, an accelerometer at rest on the surface of the Earth will measure an acceleration due to Earth's gravity straight upwards of about g ≈ 9.81 m/s . By contrast, an accelerometer that

2668-416: The package. 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

2726-487: The presence of a gravitational gradient, the calibration and data reduction process is numerically unstable. Accelerometers are used to detect apogee in both professional and in amateur rocketry. Accelerometers are also being used in Intelligent Compaction rollers. Accelerometers are used alongside gyroscopes in inertial navigation systems. One of the most common uses for MEMS accelerometers

2784-803: 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 ( Parabuteo unicinctus ). Researchers are also using smartphone accelerometers to collect and extract mechano-biological descriptors of resistance exercise. Increasingly, researchers are deploying accelerometers with additional technology, such as cameras or microphones, to better understand animal behaviour in

2842-465: 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 . 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

2900-496: 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. Zoll's AED Plus uses CPR-D•padz which contain an accelerometer to measure the depth of CPR chest compressions. Within

2958-468: 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/s ), in the cgs unit gal (Gal), or popularly in terms of standard gravity ( g ). For the practical purpose of finding

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3016-457: The spring's compression to adjust to exert an equivalent force on the mass to counteract the acceleration. Since the spring's force scales linearly with amount of compression (according to Hooke's law ) and because the spring constant and mass are known constants, a measurement of the spring's compression is also a measurement of acceleration. The system is damped to prevent oscillations of the mass and spring interfering with measurements. However,

3074-445: 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 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 ) accelerometer. It contains

3132-408: The user to monitor machines and detect these faults before the rotating equipment fails completely. 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: Under structural applications, measuring and recording how a structure dynamically responds to these inputs is critical for assessing

3190-502: The value still used today for standard gravity. The third General Conference on Weights and Measures , held in 1901, adopted a resolution declaring as follows: The value adopted in the International Service of Weights and Measures for the standard acceleration due to Earth's gravity is 980.665 cm/s , value already stated in the laws of some countries. The numeric value adopted for ɡ 0 was, in accordance with

3248-439: 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

3306-399: The wild (for example, hunting behaviour of Canada lynx ). 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 , fans, rollers, compressors , or bearing fault which, if not attended to promptly, can lead to costly repairs. Accelerometer vibration data allows

3364-433: Was followed on 21 June 2000 at 00:51 by a magnitude 6.4 event. Earthquake-induced damage was widespread, although fortunately there was no loss of life and no serious injuries. The potential of these large destructive earthquakes occurring is a constant threat to local and national infrastructure , such as pipelines, electrical power transmission, roads, dams and bridges. The spatial variability of earthquake ground motions

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