Overview
ISO 18431-3:2014 - Mechanical vibration and shock - Signal processing - Part 3: Methods of time‑frequency analysis - specifies digital methods for calculating time‑frequency (and time‑scale) representations from sampled measurements of physical or engineering quantities (for example acceleration, force, displacement). The standard provides mathematical formulations of several time‑frequency transforms, specifies the measurement and processing parameters to record, and gives recommendations to enable quantitative, reproducible analysis of vibration and shock data.
Keywords: ISO 18431-3:2014, time-frequency analysis, mechanical vibration, signal processing, Wigner-Ville, short-time Fourier transform, wavelet transform, Choi-Williams
Key topics and technical requirements
- Scope of data: Applies to both experimentally measured and numerically simulated sampled signals over a time interval (broad applicability from microscopic instruments to vehicles and buildings).
- Time‑frequency transforms specified:
- Short‑Time Fourier Transform (STFT) - requirements for window length K, window function w(k) and time increment Δn; units reported (e.g., u/Hz).
- Wigner‑Ville distribution - quadratic time‑frequency method based on autocorrelation; notes on high resolution and potential spurious cross‑terms; sampling/time indexing considerations.
- Generalized Wigner‑Ville / Choi‑Williams transform - filtered/autocorrelation forms and the dimensionless sigma parameter (σ) to reduce spurious components.
- Wavelet transform (continuous) - definition, requirement to state the chosen mother wavelet (e.g., Gaussian‑enveloped sinusoid), and the inherent time/scale resolution trade‑offs.
- Parameters and documentation: The standard requires recording of processing parameters (window type/length, Δt, Δn, transform-specific parameters such as σ or mother wavelet choice) and recommends how to report units and plots so results are quantitative and comparable.
- Units and plotting: Guidance on which quantity to plot (e.g., |STFT|^2, |Wigner|, |Wavelet|^2) and their units (u/Hz, u·s, etc.).
Practical applications and users
- Applications:
- Condition monitoring and fault diagnosis (e.g., gearbox/gear tooth fault detection)
- Analysis of impulsive events and shock responses (impact duration and frequency content)
- Vibration analysis of variable‑speed machinery (engines, turbines) where spectral content changes with time or RPM
- Structural vibration and civil/industrial testing
- Who should use this standard:
- Vibration and condition‑monitoring engineers
- Test laboratories and OEM validation teams
- Research scientists in signal processing and mechanical diagnostics
- Software developers of vibration analysis and condition monitoring tools
Related standards
- ISO 18431-1 - Signal processing: General introduction
- ISO 18431-2 - Time domain windows for Fourier transform analysis
- ISO 2041 - Mechanical vibration, shock and condition monitoring - Vocabulary
ISO 18431-3 provides the mathematical basis and practical parameter reporting that make time‑frequency methods reliable and interoperable across test labs, diagnostic systems and research, improving reproducibility and the quality of vibration and shock analysis.