Accelerometers and Vibration Sensors in NVH Testing

What is an Accelerometer?

An accelerometer is a sensor that measures acceleration – the rate of change of velocity over time – at a specific point on a structure being tested. In NVH testing, it is the most widely used measuring device, as almost every test – from modal analysis to operational vibration measurement – ​​requires acceleration data as a foundation.

Every vibration source in a vehicle, from the engine and transmission to the electric motor, creates a unique "fingerprint" of vibrations in terms of frequency and amplitude. The accelerometer accurately captures this fingerprint, transforming these invisible vibrations into data that can be analyzed, compared, and improved.

Basic Operating Principles

Most accelerometers used in NVH testing operate on the piezoelectric principle: when a structure vibrates, a piezoelectric crystal inside the sensor is compressed or stretched, generating an electrical charge proportional to the acceleration. This electrical signal is then amplified and converted into digital data via a data acquisition system (DAQ).

Some modern accelerometers utilize MEMS (Micro-Electro-Mechanical Systems) technology – smaller, lighter, and more cost-effective, making them suitable for large-scale multi-point measurement applications.

Classification of Accelerometers According to Measurement Axis

Uniaxial accelerometer

Measuring acceleration in only one direction is typically used when the direction of vibration is predetermined, for example, measuring vertical vibration on the vehicle floor or axial vibration on the cardan shaft.

Triaxial accelerometer

Simultaneously measuring acceleration in three directions (X, Y, Z) is the most common choice in modern NVH testing because:

• - Reduces the number of sensors that need to be installed compared to using multiple single-axis accelerometers.
• - Obtaining complete spatial vibration information is crucial when analyzing complex vibration modes.
• - Suitable for modal testing on asymmetrical structures.

Key Technical Specifications to Consider When Choosing an Accelerometer

Choosing the wrong accelerometer is one of the most common mistakes that causes NVH data to be skewed from the start:

• - Sensitivity: Measured in mV/g or pC/g - highly sensitive sensors are suitable for measuring small oscillations, but easily saturate when measuring large vibrations.
• - Frequency range: Must cover the entire frequency range of the phenomenon being measured - for example, measuring engine vibration requires a low frequency range (below 500 Hz), while measuring brake squeal requires a frequency range up to tens of kHz.
• - Measurement range: In grams - it is necessary to select a measurement range that matches the actual oscillation amplitude to avoid signal clipping or loss of resolution.
• - Sensor mass (mass loading effect): A sensor that is too heavy for a lightweight structure will alter the true vibration characteristics of the object - this is a classic technical error in modal measurement.
• - Heat and environmental resistance: For measurements near engines or braking systems, sensors need to withstand high temperatures and oily environments.

Accelerometer Applications by Source Group NVH

The Role of Accelerometers in Modal Analysis

In experimental modal analysis (EMA) tests, the accelerometer plays a role in collecting feedback signals at multiple points on the structure, combined with the excitation signal from the impact hammer or shaker. This data is processed to determine:

• - The natural frequency of the structure
• - Damping ratio at each oscillation mode
• - Mode shape - a visual representation of how the structure deforms at each resonant frequency.

The number and placement of accelerometers in a modal test directly affect the detail of the obtained modal shape – too few points will miss complex modes, while too many will increase unnecessary processing costs and time.

Common Mistakes When Using an Accelerometer

• - Incorrect installation technique: Using wax mounting for high-frequency measurement is wrong, as it reduces the sensor's actual frequency response range.
• - Neglecting periodic calibration: Sensor sensitivity can shift over time if not calibrated, leading to accumulated errors throughout the measurement series.
• - The effect of mass loading is not taken into account: This is especially serious when measuring on plastic or thin sheet materials in the car's interior.
• - Electromagnetic signal interference: Particularly important when measuring near electric motors or inverters in EVs - shielded cables and sensors with good interference rejection capabilities are necessary.

GPower Vietnam - Partner Supplying Specialized Accelerometers for NVH Testing

Choosing the right accelerometer – from sensitivity and frequency range to installation technique – requires practical experience, not just catalog specifications. GPower Vietnam accompanies customers throughout this entire journey.

• - Sensor selection advice: Determine the correct type of accelerometer suitable for each specific measurement location and testing objective.
• - Supplier consultation: Connect with reputable accelerometer brands within our international partnership network.
• - Integrated solution consulting: Ensuring the sensor operates seamlessly with the customer's existing DAQ system and analysis software.
• - Calibration, warranty, and maintenance: Regular calibration services help the accelerometer maintain its accuracy over time.

Contact GPower Vietnam today for advice on the most suitable NVH sensor solution for your project - Hotline: 0936093289 | Email: info@gpower.com.vn