Vibration Analysis Ppt

5/24/2018 Vibration Analysis Ppt

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Vibrat ion Analys is


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" Of al l the parameters that can be measu red

non-in t rus ively in industry today,

the one contain ing the mos t informat ionis the vib rat ion signature."

Art Crawford


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What is Vibration?

Vibration is the motion of a body about

a reference point caused by anundesirable mechanical force.

Shaft vibration caused by the shaftmoving about the centerline of a

journal bearing.


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Basic Term ino logy in Vib rat ion

Vibration is a continuous,random or periodic motionof an object

or transient impact event ofshort time duration

Caused by either a man-made, natural excitation of astructure, and mechanicalfaults . Vibration institute


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Basic Term ino logy in Vib rat ion

AmplitudeHow big/severe is the

vibration?

Time Waveform How does the vibration

change over time

Frequency How rapidly does the

vibration change?

Phase What is the delay

between events?

Displacement

Velocity

Acceleration


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D = max

V = 0

A = max

D = 0

V = maxA = 0

D = max

V = 0

A = max1 period, T

Frequency (f) = 1 / T


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How Vib rat ion is measu red &

descr ibed

Displacement (mils, micron) distance of an object from its reference position

Velocity (ips, mm/s) the rate of change of displacement with time

Acceleration (g, mm/s2, Inch/s2) the rate of change of velocity with time

g= 9.807m/ s2


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Disp lacement, Veloc i ty and Accelerat ion

on a Same Vib rat ing Mach ine

Peaks of graphs are atincrements of 30Hz

(i.e.. 0, 30Hz, 60Hz,90Hz) Displacement (mm)

Proximity Probe

Velocity (mm/s)

Velocity Pickup

Acceleration (m/s2)

Accelerometer


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Relat ion between Disp lacement,

Veloc i ty, Accelerat ion

Displacement A sin(wt)

Velocity A wcos(wt)

Acceleration

-A w2sin(wt)

Where w=radian frequency=2pf

H ib t i i d &


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How vibrat ion is measu red &

descr ibed

Peak to Peak

Commonly used for

displacement measurement

Equal to 2x Peak

Peak (zero to peak)

Can be used to express

Velocity & Acceleration (US)

RMS (root mean square)

Equal to 0.707 x peak

Can be use to expressVelocity & Acceleration

(Europe)


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Vibrat ion Transducer

Displacement transducers: typically used for shaft relative movement at low frequencies

Velocity transducers commonly used for low to intermediate frequency

applications, where velocity believed to give best guide tovibration severity

best to measure velocity with an accelerometer usingelectronic integration

Accelerometers:

best for high frequency, such as bearing impacting, highspeed gear & blading problems

transducer of choice for industrial applications


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Measures relative displacementbetween probe tip and rotatingshaft

Useful on machines with highcase to rotor weight ratio (e.g.steam turbines)

Usually already installed as OEM

equipment Limited frequency range due to

run-out

0 to 1000 Hz(0 to 60,000 CPM)

typical Requires special power

supply/signal conditioner andcables

Proximity Probe

Radial X & Y Installation


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-9V DC

-18V DC

-24V DC

Driver

CL

Shaft

Probe Tip Near Shaft

Probe Tip Far Away From Shaft

Bias or DC

Gap Voltage AC Signal plus theDC gap voltage formachine spin-up

ProximityProbe

Proximity Probe,

also known as an eddy current probe, has

both AC and DC signal components.

AC signal represents vibration;

DC average clearance, plus offset.

App l icat ion & Data Representat ionProximity Probe


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Seismic transducer works well wherethere is significant casing vibration

Gives velocity signal directly

Self-generating, no power required May have good signal-to-noise ratio,

but limited frequency range (10 - 2000Hz)

Tend to be relatively large, heavy &expensive.

Transducers must be mountedhorizontally to obtain the best results

Calibration may shift due to wear andtemperature fluctuations (due todamping)

Velocity Pick-up

Transducer Connector

Transducer Case

Spring

Transducer Coil

Permanent Magnet

Damping Fluid


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The transducer of choice in industrytoday

Very wide frequency range possible

from 0 to 20,000 Hz (differenttransducers!)

typically 2 to 15 kHz(120 to900,000 CPM)

Extremely rugged, no moving parts Relatively small and lightweight

Easy mount for permanent orintermittentuse(stud, adhesive,magnet, hand-held)

Requires constant current powersupply for built-in amplifier(someneed external amps)

Signal output is acceleration

Accelerometer

Transducer Connector

Built-in Amplifier

Pre-loaded Ref. Mass

Mica Insulator

Piezoelectric CrystalConductive Plate

Base

Electrical Insulator


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Signal Data Acqu is i t ion

Transducer

OverallEnergy

FFT

Waveform

Spectrum

Am

plitude

Am

plitude

Time

FrequencyOff-line On-line


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FFT Signal Process ing

Freq

uency

Amplitude

Time

Amplitude

Time

Am

plitude


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Sing le Channel Vibrat ion

Machine Fault Diagnosis


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Three Rules o f Diagnos is

Each machine fault generates a specific

vibration pattern

The frequency of the vibration is determined

by the machine geometry and operatingspeed

A single vibration measurement providesinformation about multiple components


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A Typ ical FFT Spectrum

Many distinct peaks


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Specificpeaks typically correlate to

Specificmachine faults

Relatedto machine speed


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Typ ical Mach inery Prob lems

Unbalance 40%

Misalignment 20%

Resonance 20%

RE Bearing

Sleeve Bearing Gear Problem 20%

Motor Electrical

Cavitations

Vane pass

Etc.

Ralph T Buscarello

Update International

U b l


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Unbalance

Imbalance

Imbalance typically appears at

the turning speed of the machineOnly in Radial Direction

Mi l i t


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Misal ignment

Misalignment

Misalignment typically shows up

at either 1 or 2 x turning speedsOn Axial and Horizontal direction

L


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Looseness

Looseness

Looseness shows up asmultiples of turning speed

G M h F lt


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Gear Mesh Fau lt

Many distinct peaksSidebandsincrease with

gear wear

Gear Wear

A T i l FFT S t


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Bearing wear shows up at

specific peaks related to the

geometry of the bearing

Bearing Wear

Roller Bearing Fau lts


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Roller Bearing Fau lts

Ball Spin Frequency

(BSF)

Fundamental Train

Frequency

(FTF)

Ball Pass Frequency

Inner Race

(BPFI)

Ball Pass Frequency

Outer Race

(BPFO)

Four different bearing frequencies

How Bearing Fau lts Generate


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g

Vibrat ion

Outer Race

Impacting

Inner RaceImpacting

How Bearing Fau lts Generate


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Vibrat ion

Outer Race

Impacting

Inner RaceImpacting

Inner race signal

with modulation

Actual Ou ter Race Defec t


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Actual Outer Race Defec t

Advanced bearing wear shows

up clearly in spectrum

Onset o f Ou ter Race Defec t


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Onset o f Outer Race Defec t

Early bearing wear frequently

cant be detected with

standard vibration measurements

Standard Wavefo rm of Bad Bearing


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Standard Wavefo rm of Bad Bearing

Standard Waveform

some level ofimpacting visible

Standard FFT of Bad Bearing


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Standard FFT of Bad Bearing

Standard FFT

high frequency signalsno clear indication

PeakVue Wavefo rm of Bad Bearing


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PeakVue Wavefo rm o f Bad Bearing

PeakVue Waveform

focuses on

bearing impacting

clear indication

of bearing wear

PeakVue FFT of Bad Bearing


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PeakVue FFT of Bad Bearing

PeakVue Spectrum

high frequency signals

brought to low

frequency

clear indication ofbearing fault

Demodu lat ion vs PeakVue


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Demodu lat ion vs . PeakVue

Demodulation

Amplitude 0.003 gDemodulation and

PeakVue eachdetect early

bearing wear

PeakVue shows:

!fault more clearly!less signal noise

!actual amplitude

PeakVue

Amplitude 0.05 g


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Detec t ing Fau l ts Au tomatical ly

Vibration Alarming Methods

Overal l A larm


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Overal l A larm

Total vibration on machine

May detect imbalance vibration (typically higher amplitudes)

ALARM LEVEL = 0.11 IN/SEC

PEAK - RMS

OVERALL VALUE

Overal l A larm


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Overal l A larm

Total vibration on machine

ALARM LEVEL = 0.11 IN/SEC

PEAK - RMS

OVERALL VALUE

Not sensitive enough for even advanced bearing faults

(typically low amplitude signals)

Frequency Bands


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eque cy a ds

Divide spectrum in frequency bands based on the

types of mechanical faults that might appear on the machine

1X

2X3X- 6X

BEARING BAND 1BEARING BAND 2

9-30X RPM30-50X RPM

Imbalance

Misalignment

LoosenessBearing Band 1

Bearing Band 2

Frequency Bands


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q y



1X

2X3X- 6X


9-30X RPM30-50X RPM

Imbalance

Misalignment


Bearing Band 2

Frequency Bands


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q y



1X

2X3X- 6X


9-30X RPM30-50X RPM

Imbalance

Misalignment


Bearing Band 2

Frequency Bands


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q y



1X

2X3X- 6X


9-30X RPM30-50X RPM

Imbalance

Misalignment


Bearing Band 2

Frequency Bands


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q y



1X

2X3X- 6X


9-30X RPM30-50X RPM

Imbalance

Misalignment


Bearing Band 2

Frequency Bands


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q y



1X

2X3X- 6X


9-30X RPM30-50X RPM

Imbalance

Misalignment


Bearing Band 2

Frequency Bands w ith Trend


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Trend of

Imbalance

Alarm

Amplitude

Sub-

Harmonic

1X 2X Bearing Bearing Gears Bearing

1xRPM 2xRPM

.3in/sec

.1in/secTime

(Days)

Time(Days)

Trend of

Bearing Wear

10-20xRPM

Estab l ish ing a Vib rat ion Program


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Define program focus

Document business and maintenance implications

TECHNICAL STEPS

Determine collection method(s)

Create database

Collect data

Detect developing faults

Diagnose nature and extent of fault

BUSINESS

STEPS

Step 1: Def ine program focus


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Identify Critical Machines

Effect on production

Availability of back-up machine

Cost to repair

Time to repair

Step 2: Determ ine Co l lec t ion Method(s )


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Route-based

periodic

general plant equipment walk around survey

manual measurement

monthly reading typical readily accessible

Online monitoring critical equipment

installed sensors automatic monitoring

define measurement

interval

inaccessible or

hazardous area

Sing le vs . Dual Channel Analys is


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g y

Single ChannelAnalysis

Dual ChannelAnalysis

Implementation Lower cost, reducedtraining Higher cost,Increased training

Focus Detect developingmachine faults

Analyze machinestructure

Purpose Identify componentwear (fault type)

Indentify wearmechanism root cause

Application General applicationacross most equipment

Typically only forproblem machines

On-l ine vs . Off-l ine Mon ito r ing


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Periodic measurement(route-based survey)

Continuous(on-line monitoring)

Implementation Lower capital cost,increased labor cost

Higher capital cost,minimal labor cost

Focus Monthly measurement(Detect prior to failure)

Continuous update(Detect at on-set)

Purpose Maximize plantavailability

Protect assets, ensuresafety & availability

ApplicationGeneral applicationacross most equipment

Most applicable tocritical plant equipment

Step 3: Create database


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Enter machines information Machine ID (asset code)

Description Operating speed (RPM)

Define measurement points Point ID (identification)

Description

Sensor type (accelerometer)

Analysis Parameters (how to analyze signal)

Alarm Limits (allowable amount of vibration)

Measu rement Po int Locations


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MOAPOA

POH

POV

PIH

PIV

MIH

MIV

MOH

MOV

2 per bearing + 1 axial measurement per shaft

Automated Database Set-up


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Selection of

component types

Automatically assigns

measurement points,

parameters and alarm limits

Step 4: Collec t Data


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2) Smart sensor

with periodic data transfer

1) Periodic walk-

around survey

3) Continuous

and on-line

Step 5: Detec t Develop ing Fau lts


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****************************

* SUSPECT MACHINE LIST * ****************************

MEASUREMENT ANALYSIS PARAMETER ALARM/FAULT ALARM DAYS TO

POINT PARAMETER VALUE LEVELS CODE ALARM

---------------------- ---------------- --------------- ----------- ----- -------

Alignment Fault ( 11-DEC-96 )

ALIGNMENT - (RPM = 3550.) (LOAD = 100.0)

M1H --- 2xTS .055 In/Sec . 035 .081 C 62

M1H 36-65xTS .0067 In/Sec .0050 .024 Br 78

M1V --- 36-65xTS .012 In/Sec .010 .024 C 26

M1V 1. - 10. kHz .328 G-s .394 .773 A 66

M2H --- 2xTS .041 In/Sec .035 .081 C 121

M2H 36-65xTS .015 In/Sec .010 .024 C 280

M2V --- 36-65xTS .013 In/Sec .010 .024 C 25

M2V 1. - 10. kHz .432 G-s .394 .773 C 64 M2A --- 36-65xTS .012 In/Sec .010 .024 C 68

M2A 1. - 10. kHz .326 G-s .301 .773 Br 234

P2A --- 3-8xTS .083 In/Sec .080 .300 Br 257

P2A 36-65xTS .023 In/Sec .021 .175 Br 198

P2A 1. - 10. kHz 1.289 G- s 1.149 5.414 Br 123

P2H --- 9-35xTS .035 In/Sec .027 .150 Br 310

Measurement Point List showing

alarm conditions



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Visual detection using

color and shape

Entire Machine Train

on one screen

Motor Gearbox Pump

Vibration

divided

into

frequency

bands

Step 5: Detec t Fau lts On-l ine


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Color coding

at machine level

Color coding by frequency

band identifies specific

developing fault types

On-line trend indicates

rate of change

Point

statistics

Advantages o f On-l ine Approach


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Continuous monitoring of critical equipment

Automatic scan for developing machine faults

Immediate notification of alarm conditions

Extensive data history available for diagnosis

Screen ing Vib rat ion Data


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500 Total

Machines

200 FromScreening

Step 6: Diagnose Natu re of Fau lt


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Multiple

Analysis

Options

Fault frequenciesto identify specific

nature of fault

Multiple

Plot

Options

Report

Link

Fast

Indexing

Expert System Program Documentation

Step 6: Diagnose Natu re of Fau lt


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Trend shows

rate of

advancement

for fault

in questionIndividual

trend

parametercovering

suspect

frequency

range

Step 6: Au tomated Diagnos is


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AutomaticallyDetermine RPM

across machine train

StatisticalAnalysis

of RPM

Flag SuspectReadings



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Multiple

Diagnoses

Calculates

Problem

Severity

CalculatesCertainty

Calculates Overall Severity

Diagnosis

Across

Entire

MachineTrain



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View Logic Tree for Diagnosis in Tutorial Mode



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Purpose of Expert System is:

NOT to replace analyst, but

to screen data to identify developing problems



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500 TotalMachines

200 FromScreening

100 FromExpert System

Need more Inpu t?


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Periodic and on-line systems should provide the

ability

to collect additional diagnostic data:

increased resolution and/or frequency range

peak/phase measurement

order based analysis

time synchronous averaging

Advanced Analys is


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Transient Analysis

Dual Channel Analysis

Cross Channel Analysis

Structural Analysis

Step 6: Gett ing to the Real Prob lem


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500 TotalMachines

200 FromScreening

100 FromExpert System

50 RealProblems

7) DocumentBus iness & Maintenance Impl icat ions


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Document:

diagnoses

recommendations

accuracy

reoccurring faults

production gains

cost savings

financial impact

Vibrat ion Sys tem Check l is t


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Periodic

Fast data collection

Analysis on Demand

Dual channel capability

Advanced gearbox &bearing analysis

Expandability

Expert System Software

On-line Parameter band alarming

Analysis on Demand

Dual channel capability

Connectivity - acrossnetwork & other systems

Expandability

Expert System Software

Integration of On-line & off-line system


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Vibration Analysis Ppt

Documents

shaft vibration

vib rat ion vibration

relat ion

accelerat ion displacement

peak peak

vib rat ion signature

sinwt velocity

hz displacement