key setup parameters

8/13/2019 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:


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:


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:


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:


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]

key setup parameters

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