VectoraLab Lab

What is a Spectrogram? A spectrogram is a time-frequency representation of a vibration signal. It shows how the frequency content changes over time, revealing transient events, run-up/coast-down behavior, and non-stationary fault signatures. How to Read a Spectrogram: • X-axis: Time • Y-axis: Frequency • Color/intensity: Amplitude (bright = high energy) When to Use: • Run-up or coast-down analysis (resonance identification) • Intermittent faults that appear and disappear • Tracking order frequencies as RPM changes • Detecting sidebands that shift with load Common Patterns: • Horizontal bright lines: Constant-frequency sources (structural) • Diagonal lines: Order-related (RPM-dependent) frequencies • Bright spots: Transient events • Broadband energy bursts: Impact events Short-Time Fourier Transform (STFT): The spectrogram is computed using STFT — applying FFT to short overlapping windows. Shorter windows give better time resolution but worse frequency resolution (and vice versa). Important: The spectrogram is an analysis tool for visualization and exploration. It does not automatically diagnose faults; interpretation requires engineering judgment.