Vibration Analysis Ppt
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Transcript of Vibration Analysis Ppt
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Vibrat ion Analys is
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Vibrat ion Analys is
" 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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Vibrat ion Transducer
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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Vibrat ion Transducer
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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Vibrat ion Transducer
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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A Typ ical FFT Spectrum
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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A Typ ical FFT Spectrum
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
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
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
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
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
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 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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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
Step 5: Detec t Develop ing Fau lts
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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
Step 6: Au tomated Diagnos is
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Multiple
Diagnoses
Calculates
Problem
Severity
CalculatesCertainty
Calculates Overall Severity
Diagnosis
Across
Entire
MachineTrain
Step 6: Au tomated Diagnos is
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View Logic Tree for Diagnosis in Tutorial Mode
Step 6: Au tomated Diagnos is
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Purpose of Expert System is:
NOT to replace analyst, but
to screen data to identify developing problems
Step 6: Au tomated Diagnos is
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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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Vibrat ion Analys is