Rotating Machinery Analysis Outline

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Rotating Machinery Analysis - Outline

• Analysis techniques for diagnosis in steady
  state condition
• Analysis techniques for non-stationary signals
• run-up/down tests
• transient phenomena

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Rotating Machinery Analysis

• Analysis tools for diagnosis in steady state
  condition
• narrow-band FFT analysis
• high resolution FFT using zoom or large
  transforms
• order tracking for machines with varying speed
• signal enhancement, also combined with order
  tracking
• tachometers for one or more shafts
• phase-assigned autospectrum for ODS, balancing
  etc.
• data export to modal programs for ODS animation
  etc.
• cepstrum of weighted spectrum for identification
  of harmonic- and sideband-families
• orbit plot (time x versus time y)

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Transmission of Vibration
System Response (Mobility)
Input Forces


Vibration

• Forces caused by
• Imbalance
• Shock
• Friction
• Acoustic

• Structural
• Parameters
• Mass
• Stiffness
• Damping

• Vibration
• Parameters
• Acceleration
• Velocity
• Displacement

891875
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High Resolution spectrum based on large Fourier
Transform
Identification of narrow spaced components over a
wide frequency span

• 6400 line Fourier Spectrum
• (? f 62.5mHz
• span 400Hz)

Detailed view around the fundamental rotational
frequencies (Display of 240 lines out of the 6400
lines)
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Analysis without and with Tracking
a) Original signal
Time
b) Fixed sampling frequency
Spectrum without tracking
fs 2,56 ? fmax
Samples analysed
fmax
Time
Frequency
c) Sampling according to frequency variation
Spectrum with tracking
Example fs 8 ? ffundamental
Samples analysed
4
3
2
1
Orders
Revolutions (periods)
810110/1
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Signal Enhancement combined with Order Tracking
FFT without signal enhancement Time
Frequency Spectrum

• Signal Enhancement and Order Tracking
• Time Enhanced Time Enhanced Order
  Spectrum

7
Cepstrum for identification of harmonic- and
sideband- families

• Frequency spectrum

Cepstrum
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Rotating Machinery Analysis

• Analysis tools for run-up/down tests
• FFT with short time records (few no. of lines)
• order tracking for
• a) avoiding smearing
• b) wide RPM, order ranges
• time capture for fast run-ups/downs using Short
  Time Fourier Transform (STFT)
• speed tags from one or more tacho signals
• more independent multibuffers for f.ex run-up and
  run-down in the same measurement session
• Vold-Kalman Order Tracking Filter

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Storage in Multi-buffers(storage based upon
speed interval, time,..)

• Four multi-buffers with individual setup
• Separate analysis of run-up and run-down in a
  single test
• Spectra
• Slices (order, frequency band)
• Speed values from Tachometer
• Average speed values from Analyzer(s)
• Time

FFT, Order, 1/3 oct. Spectra
Order, Freq.Band Overall Slices
Tags
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Coast-down test - Before After Repair

• Waterfall plots before and after repair
• Notice changes in the 2nd and 4th orders due to
  misalignment

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Short Time Fourier Transform of fast run-up of
spin drier

• Short Time Fourier Transform (STFT) of fast spin
  drier run-up
• span 800Hz
• 200 lines, ? f 4Hz
• Radial response
• 1st and 22th order dominating

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Tacho Processing
Tacho inputs

• Speed
• Use
• Speedometer
• Speed trigger
• Speed interval trigger

Tacho- meter

• Trigger
• Use
• Start of FFT record
• Syncronous analysis

• Tracking Reference
• Use
• Order Analyzer

Accuracy!!
Frequency Analysis Reference is sec
Order Tracking Reference is rev