What is Spike Energy? Impact Detection Parameter • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors What is Spike Energy? Impact Detection Parameter • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors

What is Spike Energy? Impact Detection Parameter

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Understanding Spike Energy

Definition: What is Spike Energy?

Spike energy (also called impact energy or shock pulse energy) is a vibration measurement parameter that quantifies the energy content of high-frequency impact events, particularly those generated by rolling element bearing defects. Spike energy is measured by detecting the peak high-frequency acceleration response when rolling elements strike defects on bearing races, providing an early warning indicator of bearing damage that is more sensitive than overall vibration levels or even standard frequency analysis.

The spike energy technique, related to the Shock Pulse Method (SPM), focuses on the brief, high-amplitude acceleration spikes created when balls or rollers impact spalls, cracks, or pits, enabling bearing defect detection months earlier than conventional vibration monitoring methods.

Physical Basis

Impact Generation in Bearings

When a rolling element strikes a bearing defect:

  1. Brief, high-force impact occurs (microseconds duration)
  2. Impact excites high-frequency resonances in bearing structure (typically 5-40 kHz)
  3. High-frequency ringing created
  4. Energy concentrated in short-duration spike
  5. Spike energy measures this impact energy content

Why High-Frequency Focus?

  • Bearing impacts create energy primarily at high frequencies
  • Low-frequency vibration (unbalance, etc.) doesn’t contribute to spikes
  • High-frequency measurement isolates bearing-generated events
  • Better signal-to-noise for bearing defects

Measurement Method

Instrumentation

  • High-Frequency Accelerometer: Wide bandwidth sensor (>30 kHz)
  • Resonant Sensor: Some systems use accelerometer resonance (~32 kHz) to amplify impacts
  • Bandpass Filter: Typically 5-40 kHz to isolate impact frequencies
  • Peak Detector: Captures maximum acceleration within each impact
  • Energy Calculation: Integral of squared acceleration over impact duration

Units and Scaling

  • Expressed in dB (decibels) relative to reference level
  • Typical scale: 0-60 dB
  • Sometimes expressed as gSE (spike energy in g units)
  • Logarithmic scale accommodates wide dynamic range

Interpretation and Severity Criteria

Typical Severity Levels

Good Condition (< 20 dB)

  • Minimal impact energy
  • Bearing in good condition
  • Normal lubrication
  • No corrective action needed

Fair Condition (20-35 dB)

  • Some impact activity detected
  • Early-stage bearing wear or defect initiation
  • Monitor more frequently
  • Plan maintenance within 3-6 months

Poor Condition (35-50 dB)

  • Significant impact energy
  • Active bearing defects present
  • Increase monitoring to weekly/daily
  • Plan replacement within weeks

Critical Condition (> 50 dB)

  • Very high impact energy
  • Advanced bearing damage
  • Immediate replacement recommended
  • Risk of sudden failure

Bearing Life Stages and Spike Energy

  • New Bearing: Low spike energy (10-15 dB)
  • Normal Wear: Gradual increase (15-25 dB)
  • Defect Initiation: Spike energy begins rising (25-35 dB)
  • Active Defect: Rapid increase (35-50 dB)
  • Advanced Failure: Very high (> 50 dB) then may decrease as bearing disintegrates

Advantages

Early Detection

  • Detects bearing defects 6-18 months before FFT methods
  • Sensitive to micro-spalls and incipient damage
  • Rises early in defect development
  • Provides maximum lead time for maintenance planning

Simplicity

  • Single numerical value (dB)
  • Easy to trend over time
  • Simple threshold-based alarming
  • Minimal training required for data collection

Low-Speed Effectiveness

  • Works well at low speeds where velocity measurements weak
  • Impacts still generate high-frequency spikes regardless of shaft speed
  • Good for slow-speed equipment (< 500 RPM)

Limitations

Bearing-Specific

  • Primarily detects bearing defects
  • Not diagnostic for unbalance, misalignment, or most other faults
  • Must complement with other techniques for comprehensive monitoring

No Fault Identification

  • Indicates bearing problem but doesn’t specify which component (outer race, inner race, etc.)
  • Requires spectral analysis for specific fault identification
  • Single number lacks diagnostic detail

Sensor and Mounting Sensitivity

  • Requires good high-frequency sensor
  • Mounting method critical (stud mount best, magnet acceptable, handheld poor)
  • Transmission path affects reading

Practical Application

Route-Based Monitoring

  • Quick spike energy measurement at each bearing
  • Identify bearings with elevated readings
  • Flag for detailed FFT or envelope analysis
  • Efficient screening of many bearings

Trending

  • Plot spike energy vs. time
  • Look for upward trends
  • Rapid increases indicate accelerating damage
  • Trigger detailed analysis or maintenance

Complementary with Other Methods

  • Use spike energy for screening and trending
  • When elevated, perform envelope analysis for specific fault identification
  • Combine with crest factor and kurtosis for comprehensive bearing assessment

Spike energy is a valuable bearing condition indicator that provides early warning of developing defects through simple, single-value measurements. While it lacks the diagnostic detail of frequency analysis, spike energy’s simplicity, early detection capability, and effectiveness at low speeds make it a useful component of comprehensive bearing monitoring programs, particularly for screening large numbers of bearings and triggering more detailed analysis when problems are detected.

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