Accelerometers are essential transducers used to measure vibration and acceleration in various applications, including automotive safety, consumer electronics, and industrial machinery. This guide covers the selection, mounting, calibration, data collection, and analysis techniques necessary to effectively use accelerometers for precise vibration measurements.

What is an accelerometer?

An accelerometer is a transducer that measures vibration by detecting the acceleration of motion in a structure. It converts the vibration into a proportional electrical signal, following Newton’s Second Law of Motion, which states that acceleration (m/s²) is directly proportional to the net force (Newton) acting on a body and inversely proportional to its mass (kilograms). Accelerometers typically measure acceleration indirectly by detecting the force applied to one of their axes. A common sensing approach is capacitance sensing, where the acceleration is related to changes in capacitance caused by the movement of a mass. Different types of accelerometers, such as piezoelectric and MEMS, use varying mechanical constructions for transduction.

What are the types of accelerometers?

The main types of accelerometers include:

• Piezoelectric accelerometers: Use a sensing crystal to which a seismic mass is attached. When the sensor experiences acceleration, the mass exerts force on the crystal, generating an electrical charge proportional to the acceleration. This high-impedance signal can be measured directly or conditioned by electronic circuits. Piezoelectric accelerometers are commonly used in industrial vibration measurements and high-frequency applications.
• MEMS (Microelectromechanical systems) accelerometers: Built using microfabrication technology, these accelerometers consist of tiny mechanical components on a silicon chip. They detect acceleration by sensing changes in capacitance caused by the movement of a micro-machined mass. MEMS accelerometers are widely used in consumer electronics, automotive safety, and low-frequency vibration measurements.
• Piezoresistive accelerometers: These accelerometers use materials that change electrical resistance under mechanical stress. They are similar to strain gauges and are often used in high-bandwidth applications, such as crash testing, where they measure short-duration, high-frequency events.
• Strain gauge accelerometers: These devices use strain gauges attached to a structure that deforms under acceleration. This deformation changes the resistance of the strain gauges, which is measured using a bridge circuit. Strain gauge accelerometers are ideal for measuring static and low-frequency accelerations and are commonly used in automotive safety systems like ABS and traction control.

What are the main applications of accelerometers?

Accelerometers are crucial in designing, operating, and maintaining systems across various industries. Different types of accelerometers are selected based on their specific capabilities and the requirements of the application:

• Designing: In the R&D phase, accelerometers are used to test and validate designs. For automotive safety systems, MEMS and piezoresistive accelerometers test components like airbags, anti-lock braking systems (ABS), and traction control systems. Piezoresistive accelerometers handle high-frequency impacts in crash testing. In consumer electronics, MEMS accelerometers enable features like screen rotation, motion gaming, and fitness tracking, providing critical data for designing user interfaces. In aerospace and defense, piezoelectric and MEMS accelerometers help design navigation systems, stability control, and structural health monitoring by measuring high-frequency vibrations and inertial navigation parameters.
• Operation: During operation, accelerometers provide real-time functionality and safety features. In automotive applications, MEMS accelerometers detect rapid deceleration to deploy airbags. In consumer electronics, MEMS accelerometers rotate screens in smartphones and tablets, and measure body vibrations for health and ergonomic assessments. For seismic activity monitoring, MEMS and capacitive accelerometers detect and record ground movements, providing high sensitivity and wide frequency range measurements. In industrial machinery, piezoelectric accelerometers monitor and analyze vibrations for operational stability, detecting imbalances and potential failures.
• Maintenance: For ongoing maintenance, accelerometers monitor the health and performance of systems. In predictive maintenance, piezoelectric and strain gauge accelerometers analyze vibrations to predict and prevent equipment failures, scheduling maintenance before catastrophic failures occur. In structural health monitoring, strain gauge and capacitive accelerometers assess the integrity of structures like bridges, buildings, and dams by measuring low-frequency vibrations and deformations. In vehicle health monitoring, MEMS and piezoresistive accelerometers continuously monitor vibrations and shocks, identifying issues requiring maintenance, such as imbalances or worn-out components.

How to use accelerometers for vibration measurements?

Using accelerometers for vibration measurements requires specific expertise. Engineers, technicians, and researchers must ensure proper mounting, calibration, and data collection methods. The accelerometer is connected to a vibration meter, and environmental factors like temperature and humidity must be considered to ensure accurate readings.

What devices use accelerometers?

Accelerometers are part of a measurement chain of vibration meters that includes powering, cables, and connectors. Proper powering of the accelerometer is essential to obtain accurate readings. The use of appropriate cables and connectors ensures reliable signal transmission and minimizes data loss. Vibration meters can be single or multichannel, and therefore, accelerometers are available in single and three-axis versions.

How to choose the right accelerometer?

When selecting an accelerometer for a given application, consider the following key characteristics:

1. Frequency Range (Hz): Indicates the range of vibration frequencies to which the accelerometer responds. For example, the measurement frequency range of the vibration severity measuring instrument shall be from 10 Hz to 1,000 Hz, but can include other ranges. (In some parts of ISO 20816, a lower cut-off frequency of 2 Hz or even lower is used.)
2. Dynamic Range (g): The range between the smallest detectable amplitude and the largest amplitude before distorting or clipping the output signal.
3. Sensitivity (mV/g or mV/ms²): Defines the minimum detectable signal or the change in output electrical signal per change in input mechanical change. Usually provided at one frequency; the sensitivity is related to the operating range.
4. Temperature: The operational temperature range the accelerometer can withstand.
5. Mass: The weight of the accelerometer, which can affect its mounting and the measurement accuracy.
6. Mounting Type: The method by which the accelerometer is attached to the measurement surface.
7. Compatibility with the vibration meter: Ensuring the accelerometer works seamlessly with the vibration meter being used.

How to collect vibration data from the accelerometers?

Setting up a data acquisition system involves configuring the equipment (vibration meter) to record vibration data accurately. Selecting the appropriate sampling rate and data logging parameters is crucial for capturing the necessary details and avoiding data loss. It’s essential to select results like PEAK, RMS, MAX, PEAK-PEAK, VDV, or frequency spectrum analyses such as FFT or 1/3 octaves, and recording raw data (WAV recording).

Data processing and analysis

Once data is collected, it needs to be processed and analyzed. Specialized software, such as SvanPC++ tools, apply filters and algorithms to the raw data, extracting meaningful information about vibration patterns, frequencies, and amplitudes.

Interpreting data and making adjustments

The final step involves interpreting the processed data to understand the condition of the machinery or structure. Based on this analysis, engineers and technicians can make necessary adjustments to improve performance, prevent failures, and ensure safety.

Key Takeaways

1. Accelerometers are versatile transducers that measure vibration and acceleration across a wide range of industries, including automotive, aerospace, and structural health monitoring.
2. Types of accelerometers include piezoelectric, MEMS, piezoresistive, and strain gauge accelerometers, with each type suited for specific applications.
3. Proper use of accelerometers involves mounting techniques, calibration, and data acquisition expertise. Accurate measurements require proper installation and calibration, as well as advanced data processing methods.
4. Accelerometers enhance safety and efficiency in applications such as predictive maintenance and structural monitoring, while also enabling quick detection of rapid motion changes in safety-critical systems like automotive airbags.
5. Accurate vibration measurements depend on a comprehensive measurement chain, which includes the right powering methods, cables, connectors, and robust data acquisition systems. Regular calibration and in-situ checks are crucial for maintaining measurement accuracy and reliability.