Accelerometersdevices that look deceptively simple but are complex electromechanical systems. But there are numerous mechanical, environmental, electronic, and application-related factors to consider when using an accelerometer.
This FAQ reviews a few subtleties to consider when using accelerometers as vibration sensors and concludes with a look at the ISO/IEC/IEEE 21451-4:2010 standard for Transducer Electronic Data Sheet (TEDS) formats and how it can be used in setting the accelerometer.
Frequency range and resonance errors
The vibration energy of accelerometers is often higher in the frequency range between 10 Hz and 1 kHz. There are two primary factors that can limit accelerometer performance at lower frequencies. One may be low-frequency cutoff of the amplifier, but this is only a problem in extreme circumstances when measuring vibrations below 1 Hz. Another is the effect of ambient temperature fluctuations, which can be particularly problematic at low frequencies. The use of shear-type accelerometers can reduce the influence of temperature variations at low frequencies.
Some applications may require measurements up to 10 kHz or more and may require special treatment. The upper limit is determined by the resonant frequency of the accelerometer. As a general rule, setting the upper frequency limit to approximately one-third of the resonant frequency of the accelerometer will eliminate concerns about resonance-induced measurement errors. This is less of a problem with small accelerometers that can have resonant frequencies up to 175 kHz.
For larger general-purpose accelerometers with higher outputs, resonant frequencies may be lower than 20 kHz. These accelerometers may be subject to resonant errors at high frequency due to the inherent resonance of the accelerometer. This can result in measurement errors when taking a broadband reading. Choosing a device with a wide frequency range and adding a low-pass filter, often included in vibration sensors and preamplifiers, can reduce problems caused by accelerometer resonance (Picture 1). Alternatively, when measurements are made at low frequencies, the effects of high-frequency resonance can be mitigated by mechanical filters such as a rubber layer placed between the accelerometer and the mounting surface.
Sensitivity
Sensitivity is a key specification for accelerometers. It quantifies the conversion between vibration and voltage at a reference frequency and is specified in mV/g and is often frequency dependent. For example, if an accelerometer has a sensitivity of 100 mV/g, it produces an output of 1 V when measuring an acceleration of 10 g. The sensitivity of individual accelerometers is measured during calibration. Since it can be frequency dependent, a full sensitivity calibration over the entire usable frequency range may be required. Low-sensitivity accelerometers are generally used to measure high-amplitude vibrations, and high-sensitivity units are used for low-amplitude applications.
Residual noise
The residual noise level determines the lowest amplitude that the sensor can measure. It is important to use an accelerometer with an optimal measurement range. Accelerometers with a wider measurement range will also be subject to higher levels of residual noise. The internal electronics in integrated electronics piezoelectric (IEPE) accelerometers can provide very high effective dynamic ranges. Charge sensors can offer similar dynamic ranges, but can be susceptible to noise issues related to cables and other factors. Capacitive and MEMS accelerometers often have a narrower dynamic range.
Weight
The weight of the accelerometer can be a significant factor due to the effect of mass loading. Each mass added to a structure increases the total mass of the combined structure and changes its dynamic (vibrational) behavior. In general, the weight of the accelerometer should not exceed 10% of the weight of the vibrating element on which it is mounted.
Assembly
The way the accelerometer is mounted can affect its operation, especially its frequency limit. There are many mounting options, four of the most common are:
- Manual or probe tips
- Magnetic
- Glue
- Kid
Manual, magnetic, and adhesive measurements are generally reserved for short-term or spot acceleration measurements. The less secure the connection, the lower the limit of the measurable frequency. Additionally, adding mass such as an adhesive or magnetic mounting pad lowers the resonant frequency, limits the usable frequency range, and can reduce the accuracy of the accelerometer. Most accelerometers that are designed for different mounting styles include information in the datasheet about how the mounting affects performance. Stud mounting is the strongest and gives the best overall performance, but requires drilling a hole in the mounting surface and is generally used for permanent installations. Examples of frequency limits for a 100 mV/g accelerometer using different mounting methods are summarized intable 1.
Environmental restrictions
Environmental factors such as operating temperature range, humidity, and exposure to chemicals can affect accelerometer performance. In demanding industrial environments, accelerometers are available packaged in stainless steel that can handle corrosion and chemicals.
The piezoelectric materials used in many accelerometers are temperature dependent and changes in ambient temperature will cause a change in the sensitivity of the device. The output of piezoelectric accelerometers can vary when subjected to temperature fluctuations. These temperature transitions can be particularly problematic with low-frequency vibrations or low-level sensor output. Shear-type accelerometers where the sensing element is attached between the central post and the seismic mass usually have less sensitivity to temperature transients.
Accelerometers with charging mode without integrated electronics are best suited for working at high temperatures. Their operating temperature range is limited only by sensor technology and packaging materials. But the lack of integrated electronics means these units may require an external amplifier or charge converter, and quiet cabling is required to reduce susceptibility to noise. IEPE accelerometers can eliminate the need for a silent cable, but have lower maximum operating temperatures due to the integrated amplifier.
Thermal management can be important when accelerometers are attached to high temperature surfaces. For example, a heat sink with thermal grease and a cinder block can be attached between the base and the accelerometer to keep the sensor at around 250 °C, even when the measuring surface is above 350 °C. Forced air flow can provide additional cooling. MEMS and IEPE operating temperatures are limited by the internal electronics, typically -40 to 125 °C.
Cabling
Cables can be a problem with accelerometers, especially piezoelectric accelerometers with high output impedance. For example, when a coaxial cable is bent, twisted, or compressed, local changes in capacitance can produce charge transfer due to the triboelectric effect. Induced charge transfer interferes with low vibration measurements with charge transducers. Low noise cables such as graphitized accelerometer cables can be used to alleviate this problem. In addition, the cable should be secured with clamps, tape or glue to reduce the possibility of movement.
Strong electromagnetic fields can also result in error signals, especially with charge converters. The cable should be placed away from sources of electromagnetic interference such as generators, motors and switchgear converters.
IEPE accelerometers generally do not require special low-noise cables and can be used with standard coaxial cables. The third option is to use a probe to measure the distance. Unlike conventional accelerometers, these probes are non-contact devices. They measure the distance to the target and can be used to track vibrations. Proximity probes are often used to measure vibrations in structures such as rotating shafts, where it is not possible to attach a conventional accelerometer.
TEDS compatibility
Smart sensors may use the technology specified in ISO/IEC/IEEE 21451-4:2010 "Information technology — Smart probe interface for sensors and actuators — Part 4: Mixed-mode communication protocols and probe electronic data table (TEDS) formats." This standard is based on the IEEE 1451 series of open standards for smart sensor communications.
TEDS enables the use of sensors such as accelerometers in a plug-and-play manner, eliminating the need for manual setup and installation. A typical TEDS chip is a small EEPROM that includes data such as:
- Sensor type
- Serial number
- Model name
- Calibration data
- Manufacturer's name
The standard defines two classes of TEDS devices (Figure 2):
1st gradedevices use the same wires for both analog signals and TEDS digital communication. When TEDS data is read, the sensor output is reverse-biased to prevent any interference.
class 2devices use separate wires for analog signal and TEDS digital communication. This is common in retrofit situations where the TEDS chip was added after the sensor was manufactured.
Abstract
Using an accelerometer as a vibration sensor requires careful attention to numerous details related to the environment, mechanical assembly, cabling, signal conditioning electronics, and other factors to ensure reliable and accurate operation. The incorporation of TEDS technology can accelerate the deployment of these sensors.
Reference
5 rules for installation and assembly of piezoelectric force transducers, HBM
Accelerometer cabling, Metra measurement and frequency technology
Accelerometer signal cable basics, The Modal Shop
Differences between Class 1 and Class 2 TEDS sensors, JE
Shock and vibration measurement using the accelerometer sensor, DEWEsoft
Vibration measurement using accelerometers, JE
sensors, VibraSens
Piezoelectric accelerometers, Brüel & Kjær
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FAQs
Can accelerometer be used as vibration sensor? ›
Accelerometers are versatile sensors used for high or low frequency vibration as well as shock measurements.
What is the use of accelerometer in vibration measurement? ›Accelerometers measure vibration by monitoring acceleration and converting it into voltage. They are usually mounted on equipment to measure vibration on machines operating at greater than 60 Hz. On machines at 60 Hz or less an accelerometer integrated to velocity is usually used to identify any irregularities.
What is the difference between a vibration sensor and an accelerometer sensor? ›An accelerometer measures a quality of acceleration, not necessarily vibration. But vibration sensors, which measure a quantity of acceleration and are therefore a type of accelerometer, are by definition accelerometers. A vibration sensor typically contains a piezoelectric crystal element bonded to a mass.
What is the function of the accelerometer sensor? ›An accelerometer sensor is a tool that measures the acceleration of any body or object in its instantaneous rest frame. It is not a coordinate acceleration. Accelerometer sensors are used in many ways, such as in many electronic devices, smartphones, and wearable devices, etc.
What type of accelerometer is a vibration sensor? ›An accelerometer is a device that measures the vibration, or acceleration of motion of a structure. The force caused by vibration or a change in motion (acceleration) causes the mass to "squeeze" the piezoelectric material which produces an electrical charge that is proportional to the force exerted upon it.
What is the sensitivity of vibration accelerometer? ›Accelerometer Sensitivity
The most common sensitivities for accelerometers in vibration testing applications are 100mV/G and 10mV/G. Common IEPE accelerometers can output a ±5V excitation signal.
Vibration analysis is one of the most important and effective methods of detecting the health of machinery. Vibration data can help us identify faults or detect warning signs of potential failures. It can also aid in the detection of misalignment or unbalance of assets such as bearings and rotating pieces of equipment.
Why are vibration sensors important? ›Vibration sensors allow engineers or technicians to monitor the vibration frequency resulting from the compressor elements, bearings, and shafts.
What are the disadvantages of accelerometer sensor? ›The disadvantage of low impedance accelerometers is that the sensor has an internally fixed range and time constant, potentially limiting their uses in some applications. Operation at higher temperatures, up to 185°C for test and measurement accelerometers.
What is the best sensor to measure vibration? ›Accelerometers. Accelerometers are the most commonly used sensors for detecting and measuring vibrations. When mounted on or in a vibrating structure, accelerometers proportionally convert mechanical energy into electrical energy.
What type of sensor is most commonly used in vibration measurement? ›
Accelerometers
By far the most common types of vibration sensors, accelerometers measure the changes of velocity of a given component. When attached to a piece of equipment, any vibration will reflect a change in velocity, which will cause the accelerometer to produce an electrical signal.
The accelerometer has an advantage over the pedometer by its ability to distinguish between walking and running on level terrain. Also, many of the newer accelerometer can separate human movement from movement outside of the human range such as mechanical vibration which may result from riding in a car.
What are the advantages of accelerometer? ›Benefits or advantages of Accelerometer sensor
➨It has high impedance. ➨It offers higher sensitivity. ➨It has high frequency response. ➨It uses built-in signal conditioning circuit to measure capacitance.
Accelerometers are widely used to measure sedentary time, physical activity, physical activity energy expenditure (PAEE), and sleep-related behaviors, with the ActiGraph being the most frequently used brand by researchers.
What sensor is used to detect vibration? ›Accelerometers: An accelerometer measures changes in velocity and converts them to electronic signals. The most popular type of vibration sensor.
How does a vibration sensor work? ›The vibration sensor consists of a piezoelectric crystal that has a seismic mass attached to it. When the equipment/machine under study experiences vibrations, the crystal is subjected to stress, and an electric signal is generated, which is then converted to valuable data.
What are the alternatives to vibration sensors? ›Microphone or Acoustic Pressure Sensor. Laser Displacement Sensor. Eddy Current or Capacitive Displacement Sensors.
What are the characteristics of a vibration sensor? ›Five main features must be considered when selecting vibration sensors: measuring range, frequency range, accuracy, transverse sensitivity and ambient conditions.
What is the accuracy of accelerometer sensor? ›| Parameter | Calibration under well-controlled laboratory conditions | Calibration with reduced accuracy requirements (e.g. with portable calibrators) |
|---|---|---|
| accelerometers 0.4 - 1000 Hz | 1 % | 3 % |
| accelerometers 1- 2 kHz | 2 % | 5 % |
| accelerometers 2 - 10 kHz | 3 % | 10 % |
| velocity and displacement sensors (20 - 1000 Hz) | 4 % | 6 % |
The Sensitivity of the accelerometer should produce an electrical output compatible with existing instrumentation. Use a low sensitivity accelerometer to measure high amplitude vibrations and conversely use a high sensitivity accelerometer to measure low amplitude vibrations.
What are the 3 basic characteristics measured in vibration? ›
The terms used to describe this movement are frequency, amplitude and acceleration.
What are the 3 important parameters used to measure vibration? ›There are three main parameters that are measured to evaluate the vibration characteristics of any dynamic system as: acceleration, displacement and velocity.
What is one of the most important aspects of vibration analysis? ›Velocity: Velocity is related to the destructive force of vibration, making it the most important parameter. It places equal importance on both high and low frequencies. Usually, the RMS value of velocity (measured in the range of 10 to 10,000 Hz) shows the best sign of vibration severity.
What are the limitations of vibration sensors? ›Drawbacks or disadvantages of Vibration sensor
➨Accelerometer: It is sensitive to higher frequency noise, requires external power. ➨Velocity sensor: It has lower resonant frequency, bigger in size and higher in weight, cross noise etc.
Sensitivity and Frequency
Industrial vibration sensors are suitable for measuring vibrations at medium strengths. These sensors have a sensitivity of 100 mV/g and their typical frequency band ranges from 1 Hz to 8000 Hz.
- See gains up to two times faster.
- Improves muscle strength.
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Accelerometers do not inform on body posture; thus, they cannot distinguish between sitting and standing still.
Are accelerometers effective? ›Accelerometers offer the benefit of quantifying sedentary behavior in free-living conditions but most, especially with wrist placement, cannot differentiate well between various sedentary behaviors such as lying, reclining, or sitting.
What are the main advantages and disadvantages of using sensors? ›Sensors have many advantages, including their ability to provide real-time data, their precision and accuracy, and their ability to work in harsh environments. However, they also have some disadvantages, including cost, susceptibility to interference and damage, and limited lifespan.
What is the most sensitive vibration sensor? ›Piezoelectric Accelerometer Sensor
Perhaps the most preferred vibration sensor type is piezoelectric accelerometer sensors. Versatile, wide dynamic range, with support for many potential applications such as vibration sensor alarm, security systems, industrial usages, etc.
What two types of measurement does vibration have? ›
Acceleration and displacement are the most common methods of vibration measurement. Accelerometers are small devices that are installed directly on the surface of (or within) the vibrating object.
What is the accuracy of vibration sensor? ›The sensitivity varies and can vary up to 5 to 10% both ways (plus and minus). This variation is also called the Accuracy of the Sensor. A more accurate sensor will have a lesser variation of say +/- 5%, whereas normally used vibration sensors will have a variation or Accuracy of +/- 10%.
What are the real life applications of accelerometer? ›Accelerometer is one of the most widely used types of motion sensors, which is used for a variety of applications such as device orientation detection, game controlling, shock protection, and activity discovery.
What are the three types of accelerometer? ›- Capacitive MEMS Accelerometer. Micro-Electro-Mechanical Systems (MEMS) is a fabrication technology that can be used to manufacture accelerometers. ...
- Piezoresistive Accelerometer. ...
- Piezoelectric Accelerometer.
- Microphone or Acoustic Pressure Sensor. Microphones offer a cost-effective way to measure high-frequency vibration and are especially useful to determine how a system's vibration changes with time. ...
- Laser Displacement Sensor. ...
- Eddy Current or Capacitive Displacement Sensors.
Accelerometers: An accelerometer measures changes in velocity and converts them to electronic signals. The most popular type of vibration sensor.
Which sensor is best for vibration? ›Accelerometers. Accelerometers are the most commonly used sensors for detecting and measuring vibrations.
Is accelerometer can be used for sensing mechanical vibration True or false? ›Explanation: Accelerometers can be used for sensing mechanical vibrations. They can detect even very precise vibrations in the machine. Since the vibration is in single plane a two axis accelerometer is best suited for the measurement.
What are the advantages of vibration sensor? ›It helps to avoid unplanned downtime, reduce maintenance costs, increase production levels and provide predictive maintenance. Condition monitoring uses vibration monitoring because vibration sensors give you the ability to record speed, acceleration, temperature and bearing condition characteristics.
What are the limits of vibration sensor? ›Sensitivity and Frequency
Industrial vibration sensors are suitable for measuring vibrations at medium strengths. These sensors have a sensitivity of 100 mV/g and their typical frequency band ranges from 1 Hz to 8000 Hz.
What are the disadvantages of vibration sensor? ›
Wired vibration sensors take time to install. The installation process is costly, which is a drawback if you're operating on a lean budget. Because of the installation process, it can also be difficult to scale your wired vibration monitoring system.
What device reduces vibration? ›Anti-vibration mounts, commonly known as AV mounts, act as a low-cost vibration dampener, noise reducer or shock absorber in many machine applications. Anti-vibration mounts have male and female threads and are often made from stainless steel and natural rubber.
How accurate is accelerometer sensor? ›Accelerometer: Basic error 2 % Frequency error (band limits at 5 % deviation) 5 %
What is an accelerometer sensor also known as? ›Most accelerometers are miniscule, and they are often referred to as Micro-Electro-Mechanical Systems (MEMS) accelerometers.
Can accelerometer detect velocity? ›An accelerometer is a device that measures the change in velocity over time of a reference mass. Using Newton's Law, mass times acceleration equals force (F = m x a). Accelerometers can measure both the magnitude and direction of this force. They come in various shapes, sizes, sensitivity levels, and technologies.