Free Engineering Tool #033
Vibration Source Identifier
Interactive diagnostic tool — enter vibration frequency as order of running speed to identify likely fault sources for rotating machinery.
Diagnostic Results
Complete Frequency–Fault Reference
Vibration Frequency Analysis
Every mechanical fault produces vibration at characteristic frequencies related to the shaft rotational speed. By identifying the dominant frequency in a vibration spectrum and expressing it as an order (multiple) of the shaft speed, the most probable fault source can be determined.
Order Calculation
Where f_vibration is the measured dominant frequency in Hz and RPM is the shaft rotational speed.
Common Fault Frequencies
| Order | Frequency | Primary Source | Additional Indicators |
|---|---|---|---|
| 1x | Shaft speed | Unbalance | Stable phase, proportional to speed squared |
| 1x | Shaft speed | Bent shaft | High axial vibration, phase stable |
| 2x | 2 x shaft speed | Misalignment | High axial, 180° phase across coupling |
| 3x | 3 x shaft speed | Severe misalignment | Multiple harmonics present |
| 0.42–0.48x | Sub-synchronous | Oil whirl | Journal bearings, speed-dependent |
| 0.5x | Half shaft speed | Looseness / rub | Fractional sub-harmonics |
| Multiple harmonics | 1x, 2x, 3x… | Mechanical looseness | Many harmonics of running speed |
| Non-synchronous | BPFO, BPFI, BSF | Bearing defects | Modulated by running speed |
| Z x RPM | Blade pass | Flow issues | Pulsation, cavitation |
| Z x RPM | Gear mesh | Gear problems | Sidebands indicate which gear |
| 2x line (100/120 Hz) | Fixed frequency | Electrical | Disappears when power removed |
Phase Angle Guide
Phase analysis is critical for distinguishing faults at the same frequency. At 1x: stable phase = unbalance, 180° across coupling = misalignment, unstable phase = looseness. Always use a tachometer reference.
Practical Example
Given: Running speed = 1500 RPM, Dominant frequency = 75 Hz
Running speed frequency = 1500 / 60 = 25 Hz
Order = 75 / 25 = 3.0x
Primary suspect: Severe misalignment or mechanical looseness
Recommended: Check coupling alignment, inspect mounting bolts, verify foundation
⚠️ Note: This tool provides guidance based on common fault-frequency relationships. Definitive diagnosis requires correlation with phase data, time waveform, orbit plots, operating conditions, and machine history. Always verify with additional measurements.
Most mechanical faults produce vibration at characteristic frequencies related to shaft speed:
- 1× RPM: Unbalance (most common), bent shaft, looseness
- 2× RPM: Misalignment (primary indicator)
- 0.42–0.48×: Oil whirl in journal bearings
- Non-synchronous: Bearing defects
Express the vibration frequency as a multiple (order) of the shaft speed, then match to known fault patterns. Always correlate with phase, amplitude trend, and operating conditions.
1× (or synchronous) vibration occurs at exactly the shaft rotational frequency. For a 3000 RPM machine, 1× = 50 Hz.
1× vibration is always present to some degree due to residual unbalance. It becomes concerning when amplitude exceeds acceptable limits per ISO 10816/20816.
Primary causes: mass unbalance, bent shaft, eccentricity, resonance. Phase angle analysis helps distinguish between these causes.
Sub-synchronous vibration (below 1× RPM) causes include:
- Oil whirl (0.42–0.48×): Journal bearing instability, frequency tracks with speed
- Oil whip: More severe — frequency locks at rotor natural frequency, does not track speed
- Rub (0.5×, fractional): Rotor-stator contact creates sub-harmonics
- Looseness (0.5×): Mechanical looseness at mounting points
- Belt resonance: Belt natural frequency in belt-driven systems
Sub-synchronous vibration is often more dangerous than synchronous because it can lead to catastrophic instability.
High-frequency vibration (above 10× RPM) sources:
- Rolling element bearing defects: BPFO (outer race), BPFI (inner race), BSF (ball spin), FTF (cage)
- Gear mesh: Number of teeth × RPM, with sidebands
- Blade/vane pass: Number of blades × RPM
- Electrical noise: Slot pass frequency, commutation
- Cavitation: Random high-frequency broadband
- Structural resonance: Natural frequencies of components
Phase angle is the angular relationship between the vibration peak and a shaft reference mark (measured with a tachometer).
Key diagnostic uses:
- Unbalance: Stable, repeatable phase at 1×
- Misalignment: ~180° phase difference across coupling at 1× and/or 2×
- Looseness: Unstable, drifting phase
- Resonance: ~90° phase shift at natural frequency, high amplification
- Bent shaft: 1× phase shift of ~180° from inboard to outboard bearing
Without phase data, it is often impossible to distinguish between faults that produce the same frequency (e.g., unbalance vs. misalignment at 1×).
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional vibration analyzers with spectrum analysis, order tracking, and fault diagnosis. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
