What is Diagnosis in Vibration Analysis? Fault Identification • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors What is Diagnosis in Vibration Analysis? Fault Identification • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors

What is Diagnosis in Vibration Analysis? Fault Identification

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Understanding Diagnosis in Vibration Analysis

Definition: What is Diagnosis?

Diagnosis in vibration analysis is the process of identifying the specific type of fault causing abnormal vibration, determining which component is defective, and understanding the root cause. Diagnosis goes beyond fault detection (knowing a problem exists) to answer: What specific defect? Which component? Why did it occur? Accurate diagnosis is essential because different faults require different corrective actions—unbalance requires balancing, bearing defects need bearing replacement, misalignment requires alignment correction.

Diagnosis is the analytical and interpretive core of vibration analysis, transforming measurement data into specific, actionable maintenance directives through systematic evaluation of frequency content, amplitude patterns, phase relationships, and correlation with equipment design and operating conditions.

Diagnostic Process

Step 1: Data Collection

Step 2: Pattern Recognition

  • Identify dominant frequency components
  • Match to fault frequency database
  • 1× = unbalance or eccentricity
  • 2× = misalignment or crack
  • BPFO/BPFI/BSF/FTF = bearing defects
  • Gear mesh frequency = gear problems

Step 3: Confirmation

  • Verify fault signature complete (harmonics, sidebands expected?)
  • Check consistency across measurement points
  • Compare to known fault signatures
  • Correlation with other parameters (temperature, performance)

Step 4: Root Cause Analysis

  • Why did fault develop?
  • Operating conditions, maintenance history, design
  • Contributing factors
  • Preventive measures identification

Step 5: Recommendation

  • Specific corrective actions
  • Timeline based on severity and progression
  • Root cause corrections to prevent recurrence

Common Diagnostic Patterns

Unbalance

  • Signature: High 1× vibration, radial
  • Confirmation: Stable phase, responds to balancing
  • Cause: Material loss/buildup, manufacturing tolerance
  • Action: Balance rotor

Misalignment

  • Signature: High 2× (and 1×), high axial component
  • Confirmation: Phase relationships, responds to alignment
  • Cause: Installation error, thermal growth, settling
  • Action: Precision alignment

Bearing Defects

  • Signature: Bearing fault frequencies, harmonics, sidebands
  • Confirmation: Envelope analysis, match to calculated frequencies
  • Cause: Fatigue, lubrication failure, contamination
  • Action: Replace bearing, address root cause

Mechanical Looseness

  • Signature: Multiple harmonics (1×, 2×, 3×+), erratic
  • Confirmation: Unstable phase, non-linear response
  • Cause: Loose bolts, worn fits, cracks
  • Action: Tighten, repair, replace components

Diagnostic Confidence

High Confidence

  • Classic fault signature present
  • Multiple confirming indicators
  • Matches known patterns
  • Can recommend specific action

Moderate Confidence

  • Most indicators point to specific fault
  • Some ambiguity remains
  • May recommend inspection to confirm before major repair

Low Confidence

  • Abnormal vibration but unclear cause
  • Multiple possible faults
  • Recommend additional testing or investigation
  • List differential diagnosis possibilities

Tools and Aids

Fault Frequency Databases

  • Bearing databases with calculated frequencies
  • Equipment-specific frequency lists
  • Quick reference for pattern matching

Diagnostic Charts and Tables

  • Fault type vs. vibration signature
  • Decision trees for diagnosis
  • Reference guides

Expert Systems

  • Software with diagnostic rules
  • Automated fault identification
  • Confidence scoring
  • Assists but doesn’t replace human expertise

Diagnostic Skills

Required Knowledge

  • Machinery design and operation
  • Vibration theory and analysis
  • Fault mechanisms and signatures
  • Measurement techniques

Development

  • Formal training (ISO 18436 certification)
  • Practical experience
  • Mentoring from experienced analysts
  • Feedback from repair verifications
  • Continuous learning

Diagnosis is the interpretive art and science of vibration analysis that identifies specific faults from vibration signatures. Combining systematic analysis procedures, pattern recognition skills, equipment knowledge, and diagnostic reasoning, effective diagnosis transforms condition monitoring data into specific, actionable maintenance directives that enable targeted repairs and root cause corrections.

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