Overview of the Accelerometer Sensor

Accelerometer sensors measure static and dynamic acceleration forces. Static forces are exemplified by the pull of gravity, which exerts a steady force on objects, while dynamic forces are set in play when the accelerometer is moved, for example, by being shaken or rotated.

Some of these sensors function by means of miniscule crystals that generate voltages whenever they are stressed by accelerative movements (the piezoelectric effect). Others harness alterations in electrical capacitance between two microstructures – if accelerative movements cause these structures to minutely alter position relative to one another, there will be a corresponding alteration in capacitance. This electrical change in capacitance is converted into voltage by means of some additional electrical circuitry.

Still other accelerometer sensors employ piezoresistive technology, light, and even heated bubbles of air.

Accelerometers can detect changes in static acceleration, such as when a smartphone’s screen automatically rotates to be the right way up when the phone’s position is altered. Effectively, the sensor detects changes in the device’s angle in relation to the earth.

IBM and Apple have recently utilised the dynamic acceleration detection feature of accelerometers to protect mobile computers, such as laptops, from mechanical impact damage: in dynamic mode, the sensor detects how an object is moving. If a laptop is accidentally dropped, for example, the sensor detects a sudden dynamic acceleration and trips a switch instantly to close down the hard drive, safeguarding it against impact damage caused when the normally moving heads are slammed against the drive’s platters. This is similar to the functioning of accelerometer sensors in vehicles, which activate airbags at precisely the right moment when a collision or emergency deceleration occurs.

History

Accelerometers preceded the multitude of uses to which they have been put in the twenty first century by more than 250 years: the first was designed to validate the theoretical constructs of Newtonian physics by Newton’s fellow physicist, the Englishman George Atwood, in 1783. Atwood’s ingenious invention lay practically dormant until the rise of the automobile industry: as more people began using cars, the manufacturers became more preoccupied with safety. Accelerometers began to be placed by automakers inside test vehicles in numerous places to determine the dispersal of the engine’s power. Interest in the dynamics of collisions – front, side and rear – developed alongside measures to minimise their destructive effects. Today, human crash dummies are fitted with multiple accelerometers; when these are placed in a moving vehicle, researchers can work out how the human body is affected by forces in normal motion and emergency/accident conditions, such as collisions and skids.

Technical aspects

The majority of accelerometer sensors in use today are classified as “MEMS” (Micro-Electro-Mechanical Systems), which utilise the displacement of a minute mass suspended on a cantilever arm (known as a seismic or proof mass) in response to movement. Whenever an external force is applied to the proof mass, such as in acceleration, it moves from a neutral to an active position, with the degree of deflection being measured by either digital or analogue readouts.

Single spring mechanisms of this sort can be inaccurate, largely because the mechanism can deform with repeated use over time, with the result that higher-spec MEMS utilise a series of springs incorporating piezoresistors that accurately measure the extent of deformity.

The vast majority of MEMS devices measure deformity along a single axis but two-and three-axis alternatives are available (at greater expense) and are considerably more accurate for measuring accelerative motion.

Where the Accelerometer sensor is used in manufacturing

In industrial settings, accelerometers can monitor the condition of heavy rotating machinery such as industrial fans, pumps, cooling towers and turbines, by detecting changes in the extent of vibration in their shafts across time. They are usually located at the bearings that facilitate the rotation or movement. The advantages of these vibration monitoring programmes are multiple; they can alert personnel to the risk of imminent machine failure, make work environments around potentially dangerous moving machinery considerably safer, minimise downtime and reduce costs. They do this by identifying serious issues before they have become critical, such as the early wearing of bearings, the early signs of a shaft becoming misaligned, failing gears and imbalances in the rotors: early rectification of these inevitable problems is considerably less expensive than repairing a completely failed machine

Vibration monitoring programmes are widely used in the manufacture of motor vehicles, the manufacture of steel, the manufacture of paper and pulp and in the production of a huge range of products, from foods and beverages to pharmaceuticals. They can also be found in plants as diverse as sugar mills and power generators, and are widely integrated into machinery in industries such as petrochemicals and hydropower.

Examples of where the Accelerometer sensor is used

Not only are accelerometers widely used in military and aviation equipment (exceptionally sensitive ones are integral components of the navigation systems of missiles and aeroplanes), they are also routinely used in considerably less martial settings. Digital cameras, tablets and smartphones employ accelerometer sensors for their “auto-rotate” functions, which ensure that display images are always the right way up whether the device is held horizontally, vertically or upside down.

In medicine, accelerometers have been developed to measure the depth of chest compression during CPR, and several prominent health sector manufacturers have devised sensors to be contained in watches to enable athletes to monitor their speed and how far they have travelled while running.

How the Accelerometer sensor differs from other sensors

Like all sensors, accelerometers use alterations in a physical component in response to an external influence and convert it into a readable measurement. However, they are unique in that the external influence they measure is acceleration (as opposed to, say, heat, light or chemical toxicity) and they now have a vast range of applications in the modern world as a result.