ISO 7626-5:2019

Overview

ISO 7626-5:2019 specifies procedures for experimental determination of mechanical mobility (and related frequency-response functions such as accelerance and dynamic compliance) using impact excitation with an exciter that is not attached to the structure under test. The standard focuses on accurate mobility measurements using impulse (impact) forces and signal-analysis methods based on the discrete Fourier transform (DFT), typically implemented via FFT. It clarifies the method’s advantages, limitations and best practices for reliable frequency-response function (FRF) data.

Key technical topics and requirements

• Scope and limitations
  • Applies only to impact excitation with a non-attached exciter; attached exciters and other excitation methods (step relaxation, transient random) are outside the scope.
  • Signal processing restricted to DFT/FFT-based methods (wide availability and established practice).
• Measurement fundamentals
  • Definitions and relationships among mobility, accelerance, and dynamic compliance; conversion of accelerometer data to velocity when needed.
• Test setup
  • Guidance on support conditions (grounded vs ungrounded), and how the exciter not being attached enables efficient transfer-mobility mapping.
• Excitation and impactor design
  • Recommendations on impactor design, force spectrum characteristics, control of excitation frequency range, and avoidance of double hits.
• Transducers and calibration
  • Requirements for force transducers, impactor calibration, and response transducer selection to minimize measurement error.
• Signal processing
  • Filtering, sampling, transient capture, windowing techniques (force and response), averaging, and avoidance of saturation (clipping).
• Validation and quality checks
  • Use of coherence functions, repeatability, reciprocity, linearity checks, and comparison with attached-exciter measurements.
• Informative guidance
  • Annexes such as correction for exponential windowing and bibliography for further reading.

Practical applications

ISO 7626-5:2019 is used to:

• Obtain mobility/FRF data for modal analysis and to estimate natural frequencies, damping ratios and mode shapes.
• Predict dynamic response and interaction of connected structures.
• Validate and improve numerical models (FE model correlation).
• Support NVH (noise, vibration, harshness) testing, structural dynamics research, and material dynamic-property characterization.
• Rapid, low-cost screening tests to plan more detailed random or steady-state excitation.

Who should use this standard

• Structural dynamics engineers and vibration test specialists
• Modal analysts and NVH engineers
• Test laboratories, R&D centers, and quality assurance teams performing FRF or mobility measurements
• Researchers developing test methods or validating simulation models

Related standards

• ISO 7626-1 - basic definitions and transducers (series overview)
• ISO 7626-2 - mobility measurements using attached exciters

Keywords: ISO 7626-5:2019, mechanical mobility, impact excitation, frequency-response function, DFT, FFT, accelerance, dynamic compliance, modal analysis, vibration testing.