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What does a machinery fault look like in a spectrum?
Pick a fault, set the shaft speed, and read the result. The spectrum below is a real FFT of a signal built from that fault's model — not a stored animation — so the peaks move where the physics puts them.
Live fault simulator static unbalance
1490 rpm
1x
24.8 Hz
RMS
4.7 mm/s
Dominant
1.0x
Real FFT — computed, not a stored animation.
What to look for
Each fault leaves a different fingerprint. These describe the signature the simulator above produces.
- Healthy
- A modest 1x peak and very little else. The floor is low and flat. This is the reference every other pattern is read against.
- Static unbalance
- One dominant peak at 1x that grows with speed, and almost nothing at 2x. If a single peak at running speed towers over the rest of the spectrum, unbalance is the first suspect.
- Misalignment
- Energy at 1x AND 2x, often with 3x present. A 2x comparable to or larger than 1x is the classic tell — and the reason a spectrum alone is not enough: phase across the coupling is what confirms it.
- Looseness
- A long harmonic series — 1x, 2x, 3x and onward — with half-order content between the harmonics. The spectrum looks crowded rather than peaked.
- Bearing outer race
- Non-synchronous peaks that do not line up with whole orders of running speed, sitting on a raised noise floor. Early defects show in the envelope long before they show here.
- Blade / vane pass
- A peak at the blade count times running speed. It is normal for it to exist; what matters is whether it is growing, and whether sidebands appear around it.
Questions about reading a spectrum
- Is this a real FFT or an animation?
- A real one. Choosing a fault synthesises a time signal from that fault's model at the speed on the slider, takes a radix-2 FFT of it, and plots both the waveform and the spectrum. The RMS and dominant-order readouts are computed from that same signal, so they cannot disagree with the picture.
- What does unbalance look like in a vibration spectrum?
- A single dominant peak at 1x running speed that grows with speed, with little energy at 2x. Select 'static unbalance' above and move the speed slider — the 1x peak rises while the rest of the spectrum stays where it is.
- How do I tell misalignment from unbalance?
- In the spectrum, misalignment puts significant energy at 2x — often comparable to 1x — and frequently at 3x, where unbalance is dominated by 1x alone. The spectrum narrows it down; phase measurements across the coupling are what settle it.
- Can I practise on real hardware rather than a simulation?
- That is what TMFSS is. The simulator on this page reproduces the signature; the TMFSS bench reproduces the fault itself on a real rotor, so the measurement chain, the mounting and the analysis are all exercised the way they are in a plant.
- Does it work on a phone?
- Yes. The fault buttons, the speed slider and both plots work on a touch screen — the FFT is computed in the browser, so nothing is downloaded or sent anywhere.