Top 12 Vibration Metrics to Monitor
& How to Calculate Them

Top 12 Vibration Metrics Webinar Recording




What are the Top 12 Vibration Metrics to Monitor?

  1. Acceleration Peak
  2. Acceleration RMS
  3. Crest Factor
  4. Standard Deviation of Acceleration
  5. Velocity RMS
  6. Displacement RMS
  7. Peak Frequency
  8. Acceleration RMS below 65 Hz
  9. Acceleration RMS from 65 to 300 Hz
  10. Acceleration RMS above 300 Hz
  11. Peak Pseudo Velocity
  12. Frequency of Peak Pseudo Velocity

For a detailed analysis and example of each metric, please see Steve's blog post: Top 12 Vibration Metrics to Monitor & How to Calculate Them

Vibration Data from a Bearing




Data from Case Western Introduced Bearing Faults How to Quantify?

 

Easy Metrics

Data Set Acceleration Peak (g) Acceleration RMS (g) Crest Factor Standard Deviation (g)
Fault_021 1.038 0.199 5.222 0.198
Fault_014 1.339 0.158 8.484 0.158
Fault_007 0.650 0.121 5.361 0.121
Normal 0.269 0.066 4.081 0.065


Peak is Peaky Clear Trend with RMS RMS & Std Dev

 

Simple Sine Wave

 

Sine Wave Table

Data Set Acceleration Peak (g) Acceleration RMS (g) Crest Factor Standard Deviation (g)
100 Hz, 0g Bias 1.000 0.705 1.418 0.707
29 Hz, 0g Bias 0.999 0.701 1.424 0.707
29 Hz, 1g Bias 1.999 1.221 1.636 0.707
15 Hz, 0g Bias 0.995 0.696 1.430 0.707


Look at Standard Deviation!

 

Integrating Velocity and Displacement





 

Integrating Velocity and Displacement





Tapers Fix Offset Noise Requires Filters

 

Integrating Velocity and Displacement






 

Integrating Velocity and Displacement





Less Velocity with Faults? Different Frequency Components

 

Integrating Velocity and Displacement





 

FFT





 

FFT





FFT Looks Right

 

FFT





Same Signal But Very Different FFTs

 

FFT





PSD to the Rescue!

 

FFT





FFTs Are Even Worse with Real Vibration Data

 

FFT





PSD to the Rescue (Again)!

 

PSD





Motor RPM High Frequency Need to Further Simplify

 

RMS from PSD





Easy to Compare Multiple Signals Opportunity to Define Ranges

 

Velocity and Displacement from PSD

  Vel From PSD (in/s) Vel From Time (in/s) Disp From PSD (in) Disp From Time (in) Vel Error % Disp Error %
Fault_021 0.0086 0.0080 0.000054 0.000054 7.8 -0.5
Fault_014 0.0090 0.0084 0.000007 0.000010 7.2 -26.3
Fault_007 0.0069 0.0067 0.000010 0.000011 3.7 -5.3
Normal 0.0272 0.0264 0.000087 0.000083 3.2 4.8


Integrate to Velocity Easily Good Agreement with Calculations in Time Domain

 

Octave PSD





Log Spaced Bins Clear Comparison

 

RMS within Range





Faults Introduce High Frequency Oscillations

 

PVSS





Used for Shock Testing Quantifies Damage Potential Frequency of Peak

 

Summary of All Metrics





High Frequency RMS is Best Specifically High Frequency Just 1 Example - Different Per Application

 

Conclusion

  1. Go Get Some Data!
  2. Summarize into Quantifiable Metrics
  1. Monitor Over Time
enDAQ Shock and Vibration Sensor

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