Vibration Basics 2

8/2/2019 Vibration Basics 2

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VIBRATION ANALYSIS

BASICS

Presented by : H.S.A


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Topics:

Introduction to Vibration Theory


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Topics:

Introduction to Vibration TheoryBasic Terminology & Practices


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Topics:


Basic Fault Identification


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Topics:


Basic Fault IdentificationCase History Examples (show from MT)


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Topics:


Basic Fault IdentificationCase History Examples (Show from MT)Advanced Topics


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Topics:


Basic Fault IdentificationCase History ExamplesAdvanced TopicsRequested Topics ???


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WHAT IS VIBRATION?

MOTION OF A BODY ABOUT AREFERENCE POINT

CAUSED BY AN UNDESIRABLE

MECHANICAL FORCE

For example,SHAFT VIBRATION


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VIBRATIONSOURCE

TRANSDUCER

ELECTRICALSIGNALTIME

WAVEFORM

SIGNALPROCESSINGSPECTRUMPROBLEM

DETECTIONAUTOMATED

DIAGNOSTICSMANUAL

DIAGNOSTICS

INFORMATIONNEEDED FOR

ANALYSIS

It's helpful to understand a littleabout the signal processingstep in order to get the mostbenefit from the Analyzer


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COLLECTION OF VIBRATION

MEASUREMENTS


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Compare Across Points

5.3 mils

1.2 mils

2.3 mils

3.1 mils

Directional vibration on outboard bearing


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Signal Processing Flow

FFT

Waveform

Spectrum

Transducer

Ampl

itude

A

mplitude

Time

FrequencyData Collector/Analyzer


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Rotation

Heavy Spot


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Rotation

Heavy Spot

1 revolution

Time

Amplitude

0

+

-

Time Waveform


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Rotation

Heavy Spot

1 revolution

Time

Amplitude

0

+

-

Time Waveform

3600 rpm = 3600 cycles per minute60 Hz = 60 cycles per second

1 order = one times turning speed

360 degrees


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1000 rpm 1 revolution

Time

Amplitude

0

+

-

Time Waveform


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Time

Amplitude

0

+

-

Time Waveform

4 blades = vibration occurs 4 times per revolution4 x 1000 rpm = vibration occurs at 4000 cycles per minute

= 4000 cpm


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12 tooth

gear


Time

Amplitude

0

+

-

Time Waveform


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12 tooth

gear


Time

Amplitude

0

+

-

Time Waveform

12 teeth are meshing every revolution of the gear12 x 1000 rpm = vibration occurs at 12,000 cycles per minute

= 12,000 cpm = 200 Hz


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Time0+

-

Time0+

Time0+-

-


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Time0

-

+

Time Waveform contains all the differentfrequencies mixed together


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TIME WAVEFORM

AMPLITUDE VS TIME


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We are now entering the

Frequency Domain

FFT - Fast Fourier Transform


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Frequency Domain

FFT - Fast Fourier TransformSeparates individual frequencies


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Frequency Domain

FFT - Fast Fourier TransformSeparates individual frequencies

Detects how much vibration at eachfrequency


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Amplitude

Amplitude

Amplitude

Time

Amplitude

TimeFrequency


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Time0-

Time0+

Time0+-

-

Time

Frequency

Frequency

Frequency

1x

4x

12x


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FREQUENCY SPECTRUM (or

FFT)

AMPLITUDE VS FREQUENCY

0.30.60.91.21.51.8

1000 2000 3000 4000Frequency

Amplitude


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VIBRATION TERMINOLOGY

AMPLITUDE HOW BAD IS IT?DISPLACEMENT (MOVEMENT)VELOCITY (SPEED)

ACCELERATION (FORCE)

FREQUENCY WHERE IS ITHERTZ (CYCLES / SECOND)CPM (CYCLES / MINUTE)ORDERS (MULTIPLES OF RUN SPEED)

PHASE (LAG) TIME BETWEEN EVENTSDEGREES (ROTATIONAL MEASUREMENT)

Amplitu

de

Frequency

Spectrum


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What's an Fmax,

and why does it matter?


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What's an Fmax,


Maximum Frequency of the Spectrum


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What's an Fmax,


Maximum Frequency of the Spectrum If you don't collect it, you can't analyze it

Fmax = low frequency

Fmax = high frequency


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What's an Fmax,


Maximum Frequency of the Spectrum If you don't collect it, you can't analyze itWhy not always collect the highest Fmaxpossible? Limitations of the analyzer Takes extra data storage space

Reduces the Resolution of the Spectrum


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Why should I be concerned about resolution?

Because you can't analyze it if you can't see it....


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What's the difference between

Acceleration, Velocity, &Displacement ?


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What's the difference between

Acceleration, Velocity, &Displacement ?The frequency range of interest

Acceleration(high freq.)

Velocity(general purpose)Displacement

(low freq)


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And let's not forgetPhase Analysis


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Phase Comparison

In Phase: 180 Out of Phase:o


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Phase Comparison


A lit d A A lit d A


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TimeAmplitude - A

0+

-Time

Amplitude - A0+

-

Time

Amplitude - B

0

+

- Time

Amplitude - B

0

+

-

A ABB


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Time0

+

-

Tach Pulse

Vibration Signal

Phase Measuredbetween the two

360 degrees


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Rotor kit / Strobedata collection tipsTime for a demonstration:


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Spectrum Analysis

0.30.60.91.21.51.8 1xRPM - BALANCE

2xRPM - ALIGNMENT3-6xRPM - LOOSENESS

1000 2000 3000 4000Frequency

6-30xRPM 30-50xRPMGEARS & ANTI FRICTION BEARINGS


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Vibration Spectrum andParameter Bands

Trend ofBalance

Trend ofBearings

Alarm

Amplitude

Sub-Harmonic 1X 2X Bearing Bearing Gears Bearing

1x 2x 50x

5mm/sec

1mm/secTime

(Days) Time(Days)


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SELECTED FREQUENCYBAND ALARMING

Trend ofBalance

Trend ofBearings

Alarm

Amplitude

Sub-Harmonic 1X 2X Bearing Bearing Gears Bearing

1x 2x 50x

5mm/sec

1mm/secTime

(Days) Time(Days)


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OVERALL ALARMAREA (ENERGY) UNDER THE SPECTRUM

'SHOTGUN' METHOD, NO DIAGNOSTIC INFORMATION

ALARM LEVEL = 0.1 IN/SEC

PEAK - RMSOVERALL VALUE

BEARING AND GEAR PROBLEMS WILL NOT GIVE EARLYWARNING WITH OVERALL ALARMS


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ENVELOPE ALARMING CONSTRUCTED FROM BASELINE SPECTRA "VARIABLE SHAPE ENVELOPING" EFFECTIVE IN FINDING SMALL CHANGES

0.1 in/secIncrease

200 % riseover Reference

0.3 in/sec

AbsoluteValue.02 in/sec

MinimumValue


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Diagnosing Machine Faults Imbalance


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Diagnosing Machine Faults ImbalanceMisalignment


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General Looseness or Wear


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General Looseness or WearBearing Defects


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General Looseness or WearBearing DefectsGear Defects


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General Looseness or WearBearing DefectsGear Defectsand many more...


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What is Imbalance?

Rotation

Heavy SpotCenter of Mass Center of Shaft

Center of Shaft = Center of Mass


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Imbalance can be separated into twocomponents:Types of Imbalance

Static Imbalance: Couple Imbalance:o

(constant across rotor) (opposite across rotor)


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IMBALANCECHARACTERISTICS


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IMBALANCECHARACTERISTICS HIGH RADIAL PEAKS AT 1 X SHAFT RPM


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IMBALANCECHARACTERISTICS HIGH RADIAL PEAKS AT 1 X SHAFT RPM LOW AXIAL VIBRATION AT 1 X SHAFT RPM


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IMBALANCECHARACTERISTICS HIGH RADIAL PEAKS AT 1 X SHAFT RPM LOW AXIAL VIBRATION AT 1 X SHAFT RPM LOW HARMONICS OF SHAFT RPM


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IMBALANCECHARACTERISTICS HIGH RADIAL PEAKS AT 1 X SHAFT RPM LOW AXIAL VIBRATION AT 1 X SHAFT RPM LOW HARMONICS OF SHAFT RPM 1 X RPM SINUSOIDAL PATTERN IN THE TIME WAVEFORM


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IMBALANCECHARACTERISTICS HIGH RADIAL PEAKS AT 1 X SHAFT RPM LOW AXIAL VIBRATION AT 1 X SHAFT RPM LOW HARMONICS OF SHAFT RPM 1 X RPM SINUSOIDAL PATTERN IN THE TIME WAVEFORM CAN CAUSE OTHER FAULTS TO SHOW UP, ESPECIALLY

LOOSENESS


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RADIAL VIBRATIONAT 1 X TURNING

SPEED IS MUCHMORE SIGNIFICANTTHAN IN THE AXIAL

DIRECTION

IMBALANCE

Freq: 60.04Order: 1.010Spec: .390


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What is misalignment?Deviation from a common centerlineduring operation.

BEFORE AFTER

GRRR! hmmm!


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Types of MisalignmentOffset

Angular

Both


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MISALIGNMENTCHARACTERISTICS


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MISALIGNMENTCHARACTERISTICS 2 X SHAFT RPM MAY DOMINATE


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MISALIGNMENTCHARACTERISTICS 2 X SHAFT RPM AXIAL DOMINATES HIGH AXIAL AT 1, 2 AND 3 X SHAFT RPM


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MISALIGNMENTCHARACTERISTICS 2 X SHAFT RPM AXIAL DOMINATES HIGH AXIAL AT 1, 2 AND 3 X SHAFT RPM HIGH RADIAL AT 1, 2 AND 3 X SHAFT RPM


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MISALIGNMENTCHARACTERISTICS 2 X SHAFT RPM AXIAL DOMINATES HIGH AXIAL AT 1, 2 AND 3 X SHAFT RPM HIGH RADIAL AT 1, 2 AND 3 X SHAFT RPM HARMONICS OF SHAFT RPM ABOVE 4 X ARE

USUALLY LOW


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MISALIGNMENTCHARACTERISTICS 2 X SHAFT RPM AXIAL DOMINATES HIGH AXIAL AT 1, 2 AND 3 X SHAFT RPM HIGH RADIAL AT 1, 2 AND 3 X SHAFT RPM HARMONICS OF SHAFT RPM ABOVE 4 X ARE

USUALLY LOW PHASE READINGS SHOW A 180 DEGREE SHIFT

ACROSS THE COUPLING


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2X IS DOMINANTLOCATION OF

VIBRATIONS

VANE PASS IS DUE TO 11BLADE PUMP IMPELLER

MISALIGNMENT

VANE PASSFreq: 59.50Order: 2.010Spec: .640


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Using Phase to distinguish

Imbalance from Misalignment

GRRR!

Cross Coupling PhaseIn Phase180 deg out


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MECHANICAL LOOSENESSMULTIPLE HARMONICS OF RUN SPEED

RUN SPEED HARMONICS1X, 2X, 3X, 4X, 5X, 6X, 7X, 8X

1X2X

3X

4X5X6X

7X8X


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Discuss "Harmonics"


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Bearing Fault Frequencies Function of the Geometry of the Bearing

Outer Race(BPFO)

Inner Race(BPFI)

Ball Spin(BSF)

Cage(FTF)


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ROLLER BEARING EXAMPLE

Freq: 441.03Order: 7.390Spec: .180


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Discussion Topics:Fault frequencies Inner -vs- Outer race defects "Side-band" analysisSeverity stages


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GEARMESH FAULT

Freq: 106.89Order: 21.00

Spec: .062


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RESONANCESo much to say and so little time (lead in to advanced topics)

Typical Periodic Vibration Survey Flow


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Typical Periodic Vibration Survey Flow

DatabaseData

CollectorRoute

ExceptionReport

DataAnalysis

AutomatedDiagnosisReportGeneration& Machine

MaintenanceAction

Documents

Vibration Basics 2