Download - Key Setup Parameters
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Key Setup Parametersfor
Meaningful Vibration DataAnalysis
Dennis H. Shreve
Commtest Inc.
Knoxville, TN
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Meaningful Vibration Data Analysis
Lots of tools and techniques available.
Sometimes can be a bit intimidating and
burdensome.
Need to take away some of the mystery.
Make the best of the situation.
Examine scientific terminology and industryjargon.
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Getting Down to Basics
Vibration is a leading indicator of machinery health.
Accelerometer is like a doctors stethoscope.
Capture the raw data. Convert to a signature for comparison.
Know the equipment make-up.
Watch for patterns, amplitudes, and changes over
time.(Interpret information relative to PF curve)
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Predictive Maintenance (PdM)
(an evolution from Breakdown to Preventive)
4 Key Elements to the process:
Detection
Analysis
Correction
Verification
Pinpoint a problem, get to the root cause, take action,and verify effectiveness.
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DETECTION
Capture details on equipment and application.
Choose the right sensor.
Set up the right measurement parameters. Obtain good, solid data also, repeatable.
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ANALYSIS
Examine trends, changes, patterns, and
amplitudes. (The Signature.)
Compare to known acceptable standards orbaselines.
(Note: Signature, Spectrum, and FFT (FastFourier Transform) are used synonymously.)
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CORRECTION
Take actions against offending vibrationlevels:
Balancing.
Alignment.
Replacing defective bearings.
Tying down loose components.
Avoiding resonance.
The BIG 5!
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VERIFICATION
Perform a Before and After assessment.
Did the follow-up action make the situation
better? If the problem has been addressed, set a new
measurement baseline for the future.
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Primary Goals of the PdM Program
Ensure convenient rework.
Avoid panic.
Avoid secondary damage. Promote safety.
Reduce repair time.
Avoid any unnecessary downtime.
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12 Steps for Success
Survey the plantin terms of critical, essential, balance of plant
categories.
Choose the machinesto put into the program.
Optimize measurementsin terms of parameters and timing.
Choose the methodand educate participants.
Set criteria(alarms) for assessment.
Baselinethe machine under consideration.
thru 10, Setup, Measure, Store, Present(detection).
Problem assessment(analysis). Correct the fault(correction).
(After step 12, the process can be re-entered at step 6.)
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Establishing the Program
Put equipment into categories of critical,essential, and balance of plant.
Start with the critical machinery.
Get into the physical make-up of theequipment and the application.
Decide the kinds of measurements and sensors
to be used. Look for vibration presence, patterns, and
severity.
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Vibration measurement
Choose the best location.
Choose the proper sensor.
Make the proper placement firm mounting and
direction. (similar to sensitive directionalmicrophone).
Measure in several axes.
Set measurement parameters to get tell-tale data.
Set alarm limits for proper assessment. (typically
warning, alert, and danger).
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Other Key Considerations
Know the make-up of the machine in terms ofbearings, gearbox, pulleys, couplings, coolingfans (# of blades) and pumps (# of impellor
blades).
Know the 1X (i.e., running speed) of themachine being measured.
Know the relative phase readings on keypositions of the machine. (This will showrelative motion.)
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Key Measurement Parameters
Time or frequency data to be captured.
Sample time.
Number of samples. Number of averages.
Frequency range.
Frequency resolution.
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Data Interpretation
Examining presence, patterns, and severitywill lead to correction.
There are typically 5 main causes for thevibration:
Unbalance.
Misalignment.
Bearing defects. Looseness.
Resonance.
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Getting Good Data
Avoid the GIGO (garbage in, garbage out) principle.
Make certain to have a good sensor, cabling, andconnections.
Ensure proper (solid) mounting (no rocking).
Set up instrument parameters to get the rightmeasurements.
Make sure that the equipment is running.
Be sure that it is the right location.
Recognize bad data before moving on. Utilize auxiliary tools available to build confidence in the
assessment. (Examples here include bump tests,coastdown, cross-channel phase, and demodulation.)
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Measurement Considerations
Right place, right time.
Minimize outside influences.
Time or frequency?
Frequency band, Fmin and Fmax.
Resolution.
Windowing.
Sampling time.
Number of samples. Number of averages
Accompanying speed and phase information?
Additional simultaneous channel?
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Measurement Relationships
Highest frequency (Fmax)Fmax (Hz) = # of samples / (2.56 * sample time)
(corollary: sample time = # lines of resolution / Fmax (Hz))
Lines of resolution
# Lines = samples / 2.56(corollary: samples = 2.56 * # lines)
Time for collection
Time = (# averages * # lines) / Fmax (in Hz)
Frequency resolutionResolution = Fmax / # lines
(Keep in mind the specifications for the sensor andinstrumentation.)
4 averages, no overlap
4 averages, 50% overlap
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Measurement Considerations
Shannon (Nyquist) Sampling Theorem: Sampled
signal can be completely reproduced if sampling
frequency is at least twice the highest frequency
content. (We use the factor 2.56 in digitizing.)
Any attempt to do less results in aliasing.
There is an inverse relationship between time sample
and highest frequency content.
More samples, less time results in higher frequency.
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Digital Sampling Example
Two very different signals with same sampling.
The more samples, the better reconstruction.
2.56X is a nice sampling factor in digitizing.
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Further considerations
Product(s) specifications and limitations.
Measurement capture.
Measurement processing. Measurement unit (acceleration, velocity,
displacement).
Measurement scaling (rms, average, peak, pk-pk).
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Windowing for sampling
Comparison of non-periodic sine wave and FFT with
leakage (left) to windowed sine wave and FFT showing
no leakage (right).
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Overlapping Averages
Overlap processing shortens the acquisition time by recovering a
portion of each previous frame that otherwise is lost due to the
effect of the FFT window,
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Example at instrument side
Key settings to address
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Example at instrument sideMost commonly used
On routine data collection
Advanced analysis
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FFT (Spectrum) Measurement
Typical Settings Menu
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TWF (Time Waveform) Measurement
Typical Settings Menu
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Measurements at Instrument
Time Waveform
FFT
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Zoomed FFT on Instrument
Shows more precise frequency and resolution
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Viewed at PC
Wet End - Breast Roll - Tending Side Axial - Vel Time 400 ms1/16/2008 10:14:34 AM
secs
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
in/s
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.075 in/s0.037 secsCursor A:
0.074 in/s0.061 secsCursor B:
-0.001 in/s0.025 secsDiff:
2435.714 CPMDiff:
O/All 0.079 in/s 0-pk
Location Note (9/5/2007 12:34:27 PM)
1/16/2008 10:14:34 AM O/All 0.079 in/s 0-pk
Note delta cursors to determine approximate frequency
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Viewed at PC
Wet End - Breast Roll - Tending Side Axial - Vel Freq 60000 CPM1/16/2008 10:40:31 AM
CPM
0 10,000 20,000 30,000 40,000 50,000 60,0
in/s
0-pk
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08 0.081 in/s2417.776 CPMCursor A:
O/All 0.083 in/s 0-pk
Location Note (9/5/2007 12:34:27 PM)
1/16/2008 10:40:31 AM O/All 0.083 in/s 0-pk
Interpolated running frequency
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Setup Parameters - TWF
Note the settings
and calculated
equivalent Fmaxvalue and estimated
time.
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Setup Parameters - FFT
Note the settings
and estimated time.
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Examples of Field Problems
Ski-Slope- PoorConnection- Horizontal - VelSpec60000 CPM8/30/2005 9:09:04PM
CPM
0 10,000 20,000 30,000 40,000 50,000 60,0
in/s0-pk
0
0.002
0.004
0.006
0.008
0.01
0.012O/All 0.015in/s 0-pk
Ski-Slope due to poor connection across sensor/cable/vb.
Inspect theconnections.
Notethelowamplitude of all other frequencies
8/30/2005 9:09:04 PM O/All 0.015in/s0-pk
Loose or faulty connections
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Examples of Field Problems
Ski-Slope - Saturation- Horizontal- Vel Spec60000 CPM9/12/2005 9:29:25PM
CPM
0 10,000 20,000 30,000 40,000 50,000 60,0
in/s0-pk
0
0.1
0.2
0.3
0.4
0.5
O/All 2.156in/s 0-pk
Ski-Slopedueto signal saturation(impactingof sensor)
Note thehighO/All magnitudecompared to the lowamplitudeof all other frequencies
9/12/2005 9:29:25 PM O/All 2.156in/s0-pk
Impacting and saturation
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Example of Setup IssuesResolution- Low - Horizontal - Vel Freq 60000 CPM
7/24/2005 6:31:06 PM
CPM
0 10,000 20,000 30,000 40,000 50,000 60,0
in/s
0-pk
0
0.5
1
1.5
2
2.5
3
3.5 3.339 in/s1 orders5999.574 CPMCursor A:
O/All 3.34 in/s 0-pk
Resolution of 400 lines showing a broad based spectral element
7/24/2005 6:31:06 PM O/All 3.34 in/s0-pk 5999.574 RPM
Resolution - High - Horizontal - Vel Freq 60000 CPM7/24/2005 6:31:17 PM
CPM
0 10,000 20,000 30,000 40,000 50,000 60,0
in/s
0-pk
0
0.5
1
1.5
2
2.5
3
3.5 3.339 in/s5999.579 CPMCursor A:
O/All 3.339 in/s 0-pk
Resolution of 3200 lines showing a narrow based spectral element.
7/24/2005 6:31:17 PM O/All 3.339 in/s0-pk
Improved frequency resolution
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StructLooseness - 3-Pmp-DE - Vertical- Vel Spec60000CPM"hi res."9/7/20053:58:28PM
CPM
0 10,000 20,000 30,000 40,000 50,000 60,000
in/s0-pk
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18 0.126in/s1.018 orders1495.739 CPMCursor A:
O/All 0.264 in/s 0-pk
Runningspeed
9/7/20053:58:28PM O/All 0.264in/s0-pk 1470RPM
Power(in/s0-pk)
0.46
0
Example of Good Data for Analysis
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Summary Key Considerations
Know the equipment and application.
Recognize changing conditions.
Choose the best shot at capturing the event.
Choose the best sensor for the job.
Choose the best location for the measurement.
Make appropriate settings for the measurement.
Capture good quality data.
Transform data to information.
Identify tell-tale signs of trouble.
Decide a course of action.
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Concluding Remarks
Vibration is a primary measurement for an effective PdMprogram.
Education and experience in the technology and techniques areessential for success.
Get management buy-in on the process.
Know the equipment in terms of physical make-up andintended operation.
Know standards for acceptable operation.
Know the tell-tale signs for potential problems.
Know the tools available for the program. Perform the proper setup for acquiring data.
Be confident in assessing the situation.
Have confidence in making the call for action.
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Questions and/or Comments?
Dennis [email protected]