Need an accelerometer? Faced with a variety of technologies, shapes, sizes, measurement ranges, innovations, even the most experienced engineers can face the problem of choosing the right model. We hope that this article will help you quickly navigate the wide range of accelerometers.

Measuring principle

The first step to choosing the right accelerometer is to determine the most appropriate measurement parameter. Today, three technologies for building an accelerometer are used:
- piezoelectric accelerometers - the most common type of accelerometers today, which are widely used to solve testing and measurement problems. These accelerometers have a very wide frequency range (a few Hz to 30 kHz) and sensitivity range, and are available in a variety of sizes and shapes. The output signal of piezoelectric accelerometers can be charge (C) or voltage. The sensors can be used for both shock and vibration measurements.
- Piezoresistive accelerometers usually have a small sensitivity range, so they are more suitable for shock detection than vibration detection. Another area of ​​their application is crash safety testing. For the most part, piezoresistive accelerometers have a wide frequency range (from several hundred Hz to 130 kHz or more), while the frequency response can reach 0 Hz (so-called DC sensors) or remain unchanged, which makes it possible to measure signals of a long duration.
- variable capacitor accelerometers are among the latest technology components. Like piezoresistive accelerometers, they have a DC response. These accelerometers are characterized by high sensitivity, narrow bandwidth (from 15 to 3000 Hz) and excellent temperature stability. The sensitivity error in the full temperature range up to 180°C does not exceed 1.5%. Variable capacitor accelerometers are used to measure low frequency vibration, motion and fixed acceleration.

Measured parameters

Schematically, the parameters measured by accelerometers can be grouped into the following classes:

• Vibration measurement: An object vibrates if it oscillates about its equilibrium position. Vibration is measured in the transport and aerospace industries, as well as in industrial production.
• measurement of shock accelerations: sudden excitation of the structure, creating a resonance. The impact impulse can be generated by an explosion, by a hammer hitting an object, or by a collision with another object.
• motion measurement: slow movement at a fraction of a second to several minutes, such as the movement of a robot arm or the suspension of a car.
• seismic surveys: measurements of small displacements and low-frequency vibrations. Such measurements require specialized, low-noise, high-resolution accelerometers. Seismic accelerometers monitor the movements of bridges, floors, and also detect earthquakes.

General concepts

Before discussing the technology and application features, it is necessary to make a few general remarks.
The frequency response is the dependence of the electrical output signal of the accelerometer on external mechanical action in the frequency range with a fixed amplitude. This is one of the main parameters on which the choice of a particular component depends. The frequency range is usually determined by a series of experiments and specified in the specification. Typically, this parameter is specified with an accuracy of ±5% of the reference frequency (typically 100 Hz).

Many components are specified at ±1dB or ±3dB. These values ​​indicate the accuracy of the accelerometer in the specified frequency range. Many data sheets contain typical frequency response graphs that illustrate the fluctuation in component accuracy over different frequency ranges.

Another important parameter of the accelerometer is the number of measurement axes. Today there are components with one and three measuring axes. Another possibility of building a complex system is the organization of three accelerometers into one measuring unit.

Vibration

Piezoelectric accelerometers are the best choice for vibration measurement due to their wide frequency response, good sensitivity and high resolution. Depending on the type of output signal, they can be either charge output or voltage output (IEPE).

Recently, accelerometers with a voltage output signal have been widely used because they are convenient to use. Despite the variety of brands and modifications, all manufacturers of components in this group adhere to a single pseudo-standard, therefore they are easily interchangeable with each other. Typically, such accelerometers have a charge amplifier in their structure, so they do not require additional external components. All that is needed to connect the accelerometer is a DC source. Thus, to measure vibrations in a known range and within the temperature range of -55…125°C (up to 175°C for high-temperature models), it is recommended to use piezoelectric accelerometers with a voltage output signal.

The advantages of charge-output accelerometers are the ability to operate at high temperatures and in a wide amplitude range, which is determined by the settings of the charge amplifier (note that voltage accelerometers have a fixed amplitude range). The typical operating temperature range is -55...288°C, and specialized components can operate in the range -269...760°C.

However, unlike IEPE accelerometers, capacitive sensors require the use of special low-noise cables, which cost significantly more than standard coaxial cables. To connect the sensors, charge amplifiers and linear converters are also required. Summing up, we can conclude that capacitive accelerometers are preferable for high-temperature measurements of accelerations unknown in advance.

In applications where very low frequency vibration needs to be measured, variable capacitor (VC) accelerometers are recommended. Their frequency response is from 0 Hz to 1 kHz, depending on the required sensitivity. When making low frequency VC vibration measurements, an accelerometer with a frequency response of 0-15 Hz will have a sensitivity of 1 V/g. Such sensors are indispensable in electrohydraulic shakers, in the automotive industry, in testing machines and structures, in suspension systems, and in railway transport.

Impact acceleration

Two technologies are used to measure shock accelerations, the model range is represented by components for different levels of impact force and with different output characteristics. The choice of accelerometer for shock accelerations primarily depends on the expected level of shock acceleration.

• Low level<500 г
• clash<2000 г
• Far-field field 500-1000 g, sensor 2 meters from impact point
• Near field >5000 g, sensor less than 1 meter from point of impact

General purpose accelerometers can be used to measure small shock accelerations. The accelerometer should have a linear range of up to 500 g and a shock resistance of 500 g. Typically, voltage output sensors are used for this, as they are not sensitive to cable vibrations. It is recommended to use an amplifier with a low-pass filter to attenuate the resonance.

Piezoresistive accelerometers are used for safety testing of machines. For impact measurements in the far field, specialized accelerometers with a built-in filter and a shear mode are used. An electronic filter reduces the natural resonant frequency of the accelerometer to prevent equipment overload.

Accelerometers for near field measurements have a working range up to 20,000 g. Here the choice depends on the specifics of the test being carried out, so both piezoelectric and piezoresistive sensors are used. Typically, such devices have a built-in mechanical filter.

As with vibration measurements, frequency response is the most important parameter of shock acceleration sensors. It is desirable that such sensors have a wide frequency range (about 10 kHz).

Measurement of motion, fixed acceleration and low frequency vibration

For such purposes, variable capacitance accelerometers are the most suitable choice. They allow you to measure slow acceleration changes and low frequency vibration, while their output level is quite high. Also, such sensors provide high stability over a wide range of operating temperatures.
When the VC accelerometer is set to a position where its axis of sensitivity is parallel to the axis of gravity of the earth, the output signal of the sensor will be equal to a force of 1 g. This pattern is known as DC response. Due to this feature, variable capacitor accelerometers are often used to measure centrifugal force or accelerations and decelerations of lifting devices.

Operating conditions

After selecting an accelerometer of the appropriate technology and that meets the requirements of the intended application, a number of factors need to be considered. First of all, these are the environmental conditions where the sensor will be used. This includes operating temperature, maximum acceleration level and humidity.

The measurement range of the accelerometer is specified twice in the specification, which can confuse the application engineer. The actual range is indicated in the dynamic characteristics. For example, an IEPE accelerometer may have a range of 500 g, but under certain environmental conditions it can withstand shocks up to 1000 g and 2000 g. 500 g is the maximum linear range of the accelerometer. The parameters specified for specific operating conditions indicate the maximum allowable impact level.

In the case of charge-type accelerometers, the dynamic characteristics do not include an operating range, since it largely depends on the charge amplifier. Here it is better to refer to the linearity of the amplitude characteristic, which is indicated in the dynamic parameters section. As in the previous case, the maximum measurement range indicated under certain operating conditions indicates the maximum load capacity of the accelerometer.

The possibilities of sensors operation in a humid environment are indicated by various indicators of the tightness of the housing design. It should be noted that a continuous change in temperature conditions can damage the epoxy insulation of the sensor housing.

Since current accelerometer technologies use non-magnetic materials, magnetic sensitivity is rarely specified in the component data sheet. If the sensor is intended for installation on flexible surfaces, the parameters of the base bending take the lead. Bending the surface causes the base of the accelerometer to bend, which can cause the sensor to erroneously trigger due to vibration. Therefore, the use of compression accelerometers on flexible surfaces should be avoided.

Accelerometer Weight

When the accelerometer touches the object, the measured acceleration will change. This effect can be avoided if you do not forget about the weight of the sensor itself. It can be taken as a rule of thumb that the weight of the accelerometer should exceed the weight of the object by no more than 10%.

Sensitivity and Resolution

When transducers with low output or wide dynamic range are needed, resolution and sensitivity should be considered.

The accelerometer converts mechanical energy into an electrical output signal. This signal can be expressed in mV/g or pC/g (for sensors with charge output). Typically, the line of accelerometers contains several models with different sensitivity, the optimal value of which depends on the level of the measured signal. For example, measurements of strong shock vibrations require sensors with low sensitivity.

For applications requiring low acceleration measurements, the best solution is to use a high sensitivity accelerometer where the output signal is above the noise level of the amplifier. For example, if a vibration level of 0.1g is expected and the sensitivity of the sensor is 10mV/g, the output signal voltage will be 1mV and an accelerometer with a higher sensitivity will be required.

Resolution is related to the minimum significant accelerometer signal. This parameter is based on the noise floor of the accelerometer (and if the IEPE accelerometer is selected, on the internal electronics) and is expressed in g rms.

The term "accelerometer" comes from the Latin accelero, which means "I accelerate." An accelerometer is a device that measures apparent acceleration. In other words, it is designed to help the smartphone software determine the position, as well as the distance of movement of the mobile device in space.

Often this sensor is confused with a gyroscope. However, these are different sensors, although they complement each other, and can even perform the same functions. Their difference lies in the principle of work, as well as in the efficiency of performing specific tasks. Can be used together to achieve the most accurate results.

The sensor greatly expands the capabilities of the smartphone. The main functions for which it is responsible are listed below.

• Automatic change of screen orientation when turning the device.
• Management of the gameplay with the help of slopes.
• Reacting the device to certain gestures, and performing appropriate actions (change the music track, turn off the alarm or reject the call). Examples of gestures: tapping or shaking the case, flipping the smartphone screen down.
• Determination and visual demonstration of changes in the position of a person in space through navigation applications (Google Maps, etc.).
• The ability to track physical activity. A classic example is counting the distance traveled using a pedometer.

How the accelerometer works, the principle of its structure

The picture below shows a schematic design of the simplest accelerometer.

It consists of an inert mass (in this example, its role is played by a small weight), which is attached to a movable, elastic element (for example, to a spring). The spring, in turn, is fixed on a fixed part. A damper is used to suppress vibrations of the weight. When there is a shake, tilt or rotation of the object in which the accelerometer is embedded, the inertial mass reacts to the force of inertia. With an increase in the intensity and force of tilt, turn or shock, the radius of deformation of the spring increases.

Then the weight takes its previous position, thanks to the spring. A special sensor records the level of displacement of the inertial mass from its position in the "rest" state. Then this data is converted into an electrical signal and transferred to electronics and software for processing. Thanks to the received data, the program can "calculate" changes in the physical changes in the location of the object.

There is also such a thing as the sensitivity axis of the device. If there is only one axis, the sensor will be able to transmit data on the change in the position of the object in space only within the sensitivity of the axis. To increase the sensitivity of the sensor, and to obtain accurate data on the strength and direction of the object's inclination, two, or even better, three axes are needed. By combining three axes at once into one device, it is possible to calculate the position of an object in three-dimensional space.

Accelerometer in smartphones

For technical and other reasons, the sensor design described above is not applicable in mobile devices. It is replaced by a miniature chip containing an inert mass.

The principle of operation of the chip is similar to a classic sensor: an inertial mass changes its position during acceleration. Thanks to this, the smartphone receives data on the position in space. But between classical devices and chips there is a huge difference not only in design, but also in the method of production.

The manufacture of such sensors is a fully automated process. To get a working copy, a chemical reaction is used between silicone and other elements. The process requires the highest precision in calculations and proportions. Manually, with the help of physical impact on materials, it is virtually impossible to do this.

Output

The accelerometer in a mobile device, which is only a tiny chip, has a significant impact on the interaction between a person and a smartphone. With its help, the control of the device moves to a new, more comfortable level. And games and applications get a lot of additional features that can be implemented using the accelerometer.

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The accelerometer is a rather complicated mechanism, but you don’t need to understand the essence of its work. This is a device in the phone for measuring gravitational acceleration. In the phone, this thing is used to determine the position of the smartphone relative to its axis. That is, thanks to the accelerometer, the system understands what position the smartphone is in - horizontal or vertical.

Take any modern smartphone and turn it 90 degrees. The accelerometer will understand this, and the image on the screen will also flip 90 degrees relative to the X and Y axes. Also, the accelerometer can be used by different programs. For example, PlayMarket and AppStore have programs for measuring the number of steps taken. The calculation is based on the data collected by the accelerometer. A small vibration of this sensor with certain parameters is equal to one step for a person. Approximately so the program thinks and will count the number of steps that a person takes during the day.

Some phones can be shaken, and this or that action will occur from this. For example, you can program the system to open the Camera app when shaken. The accelerometer understands the shake easily and the system launches the application. True, this can be done in phones that provide functionality for programming actions.

Many modern games are based on the use of an accelerometer. The popular races, in which the phone must be tilted to move the car to the right or left, will definitely use the accelerometer. In general, it is difficult to overestimate the usefulness of this sensor inside a smartphone. This is a convenient and versatile thing, which today is even in cheap smartphones.

Modern technologies make life much easier, and if earlier a smartphone allowed you to just call, today, thanks to the accelerometer, its functionality has expanded greatly. In general, today such a sensor as an accelerometer is obsolete. This is something like a simple ballpoint pen, which you will not surprise anyone, but which is indispensable in the modern world.

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(the difference between the absolute acceleration of an object and the gravitational acceleration, more precisely the acceleration of free fall). There are three-component (three-axis) accelerometers that allow you to measure acceleration along three axes at once.

Some accelerometers also have built-in data acquisition and processing systems. This allows you to create complete systems for measuring acceleration and vibration with all the necessary elements.

Application

The accelerometer can be used both for measuring projections of absolute linear acceleration and for indirect measurements of projections of gravitational acceleration. The latter property is used to create inertial navigation systems, where the measurements obtained with their help are integrated, obtaining the inertial velocity and coordinates of the carrier, when registering amplitudes above its own resonant frequency, you can directly measure the own speed of the accelerometer.

Electronic In the control devices of game consoles, the accelerometer together with the gyroscope is used to control games without using buttons - by turning in space, shaking, etc. For example, the Wii Remote and Playstation Move controllers have an accelerometer.

Accelerometers are used in hard drives to activate the protection mechanism against damage caused by shocks, shocks and falls. The accelerometer reacts to a sudden change in device position and parks the hard disk heads, which helps prevent disk damage and data loss. This protection technology is used mainly in laptops, netbooks and external drives.

An accelerometer in industrial vibration diagnostics is a vibration transducer that measures vibration acceleration in non-destructive control and protection systems.

Parameters

The main parameters of the accelerometer are

• Threshold sensitivity (resolution) - the value of the minimum change in apparent acceleration that the device is able to determine.
• Zero offset - instrument readings at zero apparent acceleration.
• Random walk is the standard deviation from zero offset.
• Nonlinearity - changes in the relationship between the output signal and the apparent acceleration when the apparent acceleration changes.

Notes

Links

• Using an analog accelerometer as an inclinometer

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Synonyms:

See what "Accelerometer" is in other dictionaries:

Accelerometer ... Spelling Dictionary

- (from Latin accelero I accelerate and ... meter) a device for measuring accelerations (overloads) of aircraft, etc ... Big Encyclopedic Dictionary

ACCELEROMETER, a device used to measure acceleration. The simplest example is a lead weight suspended from an object falling with acceleration, the angle of its deviation from the vertical is proportional to the acceleration. A more complex device, ... ... Scientific and technical encyclopedic dictionary

- (from the Latin accelero I accelerate and the Greek metreo I measure) a device for measuring the acceleration of moving objects. A. is widely used on aircraft. The principle of operation of A. is based on the use of the laws of inertia. Distinguish A. for measuring ... Encyclopedia of technology

Exist., number of synonyms: 5 accelerograph (3) accelerometer (1) gyroaccelerometer ... Synonym dictionary

Device for measuring accelerations. On aircraft, surface ships and submarines, it is used in EdwART inertial navigation systems. Explanatory Naval Dictionary, 2010 ... Marine Dictionary

accelerometer- a, m. accéléromètre lat. 1888. Lexis. tech. A device for measuring the accelerations occurring on aircraft. spacecraft, rockets, etc., as well as when testing machines, engines, etc. Krysin 1998. Lex. TSB 3: accelero/meter… Historical Dictionary of Gallicisms of the Russian Language

accelerometer- A measuring device designed to measure accelerations. [GOST 18955 73] Topics accelerometers EN accelerometer … Technical Translator's Handbook

- (from lat. accelero I accelerate and ... meter), a device for measuring accelerations (g-forces) of aircraft, etc. * * * ACCELEROMETER ACCELEROMETER (from lat. accelero I accelerate and Greek. acceleration... ... encyclopedic Dictionary

- (Latin accelerare accelerate + ... meter) a device for measuring accelerations (overloads) that occur on airplanes, spacecraft, rockets and other moving objects, as well as for testing machines, engines, etc. New dictionary ... ... Dictionary of foreign words of the Russian language