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Vibration Analysis
________________________
Timken Gears & Services Inc.
FFT or Fast Fourier Transformer
Vibration Analysis
● Uses a FFT to pull data from the
time waveform then inputs to a
discr...
Time record
Time window
Signal from Transducer
Machine Vibration
RMS
peak
peak to peak
RMS is 0.707 ofpeak
RMS vs. Peak or Peak to Peak
0
0.5
1
1.5
2
2.5
0 20 40 60 80 100 120 140 160 180 200
Vibration Analysis
~99% ~1% ~0.1%
Rotational Impacts Friction
Forces Causing Vibration
Frequency domain
Time domain
IMPACTS / SHOCKS
Periodic / non-periodic
transients
CREST KURT SKEW
Crest Kurtosis Skewness
factor
FRICTION
Periodic / non...
Velocity (VEL)
Rotational Forces
Definition
● RMS amplitude of the vibration velocity over the
measured frequency range
Mo...
Acceleration (ACC)
Rotational Forces
Definition
● RMS amplitude of the vibration acceleration over the
measured frequency ...
Crest
Impacts / Shocks
Definition
● The ratio (difference) between vibration peak
amplitude and RMS amplitude
Monitors
● R...
Kurtosis (KURT)
Impacts / Shocks
Definition
● 4th statistical moment of the vibration signal
● Describes how a signal is g...
Skewness (SKEW)
Impacts / Shocks
Definition
● 3rd statistical moment of the vibration signal
● Describes the symmetry of t...
Noise Level (NL1-4)
Friction
Definition
● Random noise in one quarter of the measured
frequency range
Monitors
● Rotationa...
Frequency
domain
Time
domain
Extremely important to verify the speed with strobe or
laser due to vibration Analysis is bas...
Fault Frequencies
Used for fault recognition:
● Moving parts in a rotating machine contribute to the
vibration at specific...
Fault or Forcing Frequencies
Examples
● Unbalance, misalignment,
looseness, resonance, gear
damage, belt / chain drive
fau...
Output Shaft
Bearing: Torrington 110TDO456
(BPFO, BPFI, FTF, BSF)
63 Gear Teeth * RPM
Input Shaft
Bearing: Torrington 2232...
Fault Frequencies Calculations
Fault Frequencies Matches
Analysis in the Time Waveform
Analysis in the Time Waveform
Analysis in the Time Waveform
Phase readings
Used for fault recognition:
● Moving parts in a rotating machine contribute to the
vibration which can be v...
Misalignment has two types, Angular
& Parallel Offset. Below is Angular
Vibration Analysis is extremely helpful to
detect machine condition and when
conducting readings make sure to take
vertica...
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Vibration Analysis

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Vibration Analysis

  1. 1. Vibration Analysis ________________________ Timken Gears & Services Inc.
  2. 2. FFT or Fast Fourier Transformer Vibration Analysis ● Uses a FFT to pull data from the time waveform then inputs to a discrete Fourier transform (DFT), a mathematical process or algorithm that transforms a waveform into the components to a frequency spectrum of the input signal from the time waveform.
  3. 3. Time record Time window Signal from Transducer Machine Vibration
  4. 4. RMS peak peak to peak RMS is 0.707 ofpeak RMS vs. Peak or Peak to Peak
  5. 5. 0 0.5 1 1.5 2 2.5 0 20 40 60 80 100 120 140 160 180 200 Vibration Analysis
  6. 6. ~99% ~1% ~0.1% Rotational Impacts Friction Forces Causing Vibration
  7. 7. Frequency domain Time domain
  8. 8. IMPACTS / SHOCKS Periodic / non-periodic transients CREST KURT SKEW Crest Kurtosis Skewness factor FRICTION Periodic / non-periodic random noise NL1 NL2 NL3 NL4 ROTATIONAL Vibration Forces ACCELERATION ACC Total RMS-value of acceleration VELOCITY VEL Total RMS-value of velocity Condition Parameters - Time Domain Calculations • Unbalance • Misalignment • Looseness • Wear • Gear damage • Coupling damage • Other shocks/ impacts • Scraping parts • Journal bearing Used to detect and monitor
  9. 9. Velocity (VEL) Rotational Forces Definition ● RMS amplitude of the vibration velocity over the measured frequency range Monitors ● Rotational forces Well ● Impacts/Shocks Acceptable ● Friction Unsatisfactory Comments ● Best used for frequency range < 1,000 Hz
  10. 10. Acceleration (ACC) Rotational Forces Definition ● RMS amplitude of the vibration acceleration over the measured frequency range Monitors ● Rotational forces Well ● Impacts/Shocks Acceptable ● Friction Unsatisfactory Comments ● Best used for frequency range > 1,000 Hz
  11. 11. Crest Impacts / Shocks Definition ● The ratio (difference) between vibration peak amplitude and RMS amplitude Monitors ● Rotational forces Unsatisfactory ● Impacts/Shocks Well ● Friction Unsatisfactory Comments ● A sine wave has CREST = 1.414 ● Normal values is 1.4 - 3.0
  12. 12. Kurtosis (KURT) Impacts / Shocks Definition ● 4th statistical moment of the vibration signal ● Describes how a signal is grouped around its mean value Monitors ● Rotational forces Unsatisfactory ● Impacts/Shocks Well ● Friction Unsatisfactory Comments ● A sine wave has KURT = -1.5 ● A signal with transients has KURT > 0.
  13. 13. Skewness (SKEW) Impacts / Shocks Definition ● 3rd statistical moment of the vibration signal ● Describes the symmetry of the signal around its mean Monitors ● Rotational forces Unsatisfactory ● Impacts/Shocks Well ● Friction Unsatisfactory Comments ● A sine wave has SKEW = 0 ● Positive transients give SKEW > 0 ● Negative transients give SKEW < 0.
  14. 14. Noise Level (NL1-4) Friction Definition ● Random noise in one quarter of the measured frequency range Monitors ● Rotational forces Unsatisfactory ● Impacts/Shocks Unsatisfactory ● Friction Well Comments ● Describes the broad band noise floor in the spectrum
  15. 15. Frequency domain Time domain Extremely important to verify the speed with strobe or laser due to vibration Analysis is based on knowing the speed then using rpm to calculate the fault frequencies
  16. 16. Fault Frequencies Used for fault recognition: ● Moving parts in a rotating machine contribute to the vibration at specific frequencies ● Most symptoms are shown under normal conditions (like gear mesh) but increase with damage ● Some symptoms appear only when the component is damaged (like rotor bar fault)
  17. 17. Fault or Forcing Frequencies Examples ● Unbalance, misalignment, looseness, resonance, gear damage, belt / chain drive faults, fan / blade faults, oil whirl, bearing faults, rotor bars, etc. ● Or, define your own faults if you know what your looking for as to certain Characteristics.
  18. 18. Output Shaft Bearing: Torrington 110TDO456 (BPFO, BPFI, FTF, BSF) 63 Gear Teeth * RPM Input Shaft Bearing: Torrington 22320 (BPFO, BPFI, FTF, BSF) 23 Gear Teeth * RPM Intermediate Shaft Bearing: Torrington 22332 (BPFO, BPFI, FTF, BSF) 13/43 Gear Teeth *RPM Fault Frequency Selection Example of frequency domain inputs
  19. 19. Fault Frequencies Calculations
  20. 20. Fault Frequencies Matches
  21. 21. Analysis in the Time Waveform
  22. 22. Analysis in the Time Waveform
  23. 23. Analysis in the Time Waveform
  24. 24. Phase readings Used for fault recognition: ● Moving parts in a rotating machine contribute to the vibration which can be verified by taking phase readings. ● Unbalance will show phase readings with a 90 degree phase shift from the vertical reading to the horizontal reading. ● Misalignment will show a phase shift of 180 degrees across the shaft in the axial direction between machine components.
  25. 25. Misalignment has two types, Angular & Parallel Offset. Below is Angular
  26. 26. Vibration Analysis is extremely helpful to detect machine condition and when conducting readings make sure to take vertical, horizontal and axial readings. Readings should never be taken on guards or false housing as well again verify rpm. When conducting readings on roller bearings ensure the axial reading is in the load zone.

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