वाइब्रेशन सोर्स आइडेंटिफायर

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×).