VectoraLab Lab

What is Kurtosis? Kurtosis is a statistical measure of the "tailedness" of the signal distribution. In vibration analysis, it quantifies the impulsivity of the signal. Formula: K = (1/N Σ (x-μ)⁴) / σ⁴ For a Gaussian (normal) distribution: K = 3 Interpretation: • K ≈ 3: Normal healthy signal (Gaussian) • K > 4: Impulsive signal — possible bearing/gear impacts • K > 6: Significant impulsivity — investigate immediately • K > 10: Severe impacts — critical fault likely Why Kurtosis for Bearing Detection? • Early bearing defects produce random impact pulses • These create heavy tails in the amplitude distribution • Kurtosis is very sensitive to these short-duration impacts • Works well in early stages when RMS is still normal Limitations: • Kurtosis decreases as fault severity grows (more continuous damage) • Sensitive to signal processing and filtering choices • Can be elevated by non-fault impulsive events (e.g., knocks) • Always combine with frequency analysis (envelope) for confirmation Kurtogram: A Kurtogram finds the bandpass filter settings that maximize kurtosis — useful for finding the best envelope analysis band. Important: Kurtosis > 4 indicates possible impulsivity — not a confirmed fault. Further analysis is always required.