Vibration Monitoring

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• Vibration Monitoring Analysis

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Vibration Monitoring
What is Vibration ? It is motion of
mechanical parts back and forth from its position
of rest /neutral position.
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Vibration Monitoring
What causes Vibration ? Induced Force
Freedom for Movement
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Vibration Monitoring

• Harmful Effects of Excess vibration
• Increased load on BRGs Reduced BRG Life
• Higher Forces on Mountings
• Foundation Loosening and Damage of Support
  Structure
• Increased Stresses of M/c Risk of fatigue
• components

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Vibration Monitoring

• Harmful Effects of Excess vibration
• Decreased Equipment efficiency.
• Reduced Output Quality.
• Increased Maintenance Cost due to more Component
  Failures and Unplanned Operations
• Unsafe Operating Environment

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Vibration MonitoringProblem Identifications

• Unbalance
• Misalignment
• Mechanical Looseness
• Antifriction / Sleeve Bearing Defects
• Gear Defects

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Vibration MonitoringProblem Identifications

• Belt Defects
• Impeller / Blade Defects
• Bent Shaft
• Electrical Problems
• Resonance

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Vibration Monitoring

• Fundamental Realities
• All Machines vibrate.
• An increase in vibration level is a sign of
  trouble amplitude of Vibration depends on the
  extent of defect in the machinery components
• Each trouble will create vibration with different
  characteristics

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VIBRATION FUNDAMENTALS
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Upper Limit
Neutral Position
180
TIME
Lower Limit
270
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Characteristics of Vibration

• Vibration characteristics are
• Amplitude
• Frequency Hz or CPM
• Phase Angle or clock face

Displacement
Velocity
Acceleration
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Parameter Selection

• Frequency sensitivity

Displacement lt600CPM
Velocity 600-60,000CPM
Acceleration gt60,000CPM
Spike Energy/SEE Ultrasonic range
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Frequency sensitivity
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Vibration Monitoring
Displacement
Velocity
Acceleration
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FFT FAST FOURIER TRANSFORM.

• THE PROCESS OF TRANSFORMING TIME DOMAIN SIGNAL TO
  FREQUENCY DOMAIN.
• THE TIME DOMAIN SIGNAL MUST
• FIRST BE SAMPLED AND
• DIGITIZED.

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Time Domain - overall data is the sum of all
exciting and reacting forces
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Spectrum Analysis
Enables precise evaluation of machinery condition
and prediction
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Fmax, LINES, AVERAGES.

• Fmax REPRESENTS THE MAXIMUM FREQUENCY RANGE IN
  CPM OR HZ TO BE SCANNED BY THE INSTRUMENT.
• Fmax SHOULD NOT BE SET TOO HIGH SO THAT THE
  RESOLUTION AND ACCURACY SUFFERS OR IT SHOULD NOT
  BE TOO LOW SO THAT WE MISS SOME IMPORTANT HIGH
  FREQUENCIES.

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GUIDELINES FOR SETTING Fmax.

• FOR MACHINES HAVING ANTI-FRICTION BEARINGS- Fmax
  60 x RPM
• FOR MACHINES HAVING SLEEVE BEARINGS- Fmax 20 x
  RPM
• FOR GEAR BOXES- Fmax 3.25 x GMF

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LINES OF RESOLUTION

• THE RESOLUTION IS THE NUMBER OF LINES
• OR CELLS WHICH ARE USED TO CALCULATE AND
  DISPLAY THE FREQUENCY SPECTRUM.
• THE BANDWIDTH CAN BE CALCULATED BY DIVIDING Fmax
  BY THE LINES OF RESOLUTION.
• THE GREATER THE NUMBER OF LINES , THE BETTER IS
  THE ACCURACY.

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FREQUENCY RESOLUTION
F max
Bandwidth

total lines of resolution
total lines of resolution
lines or bins or cells of resolution
Amplitude
Fmax
Frequency
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Spectrum Data Collection Time

• FFT Calculation Time Time to calculate FFT from
  Time Waveform assuming no overlap processing

(60) ( FFT Lines) (Averages)
FFT Calculation Time
Frequency Span
Where FFT Number of FFT Lines
or Bins in Spectrum
Averages Number of Averages
Frequency Span measured in CPM
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FFT SPECTRUM
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OVERALL VIBRATION
Total summation of all the vibration,with no
regard to any particular frequency.
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OVERALL VIBRATION Overall vibration is the total
vibration energy measured within a frequency
range. Measuring the overall vibration of a
machine or component, a rotor in relation to a
machine, or the structure of a machine, and
comparing the overall measurement to its normal
value (norm) indicates the current health of the
machine. A higher than normal overall vibration
reading indicates that something is causing the
machine or component to vibrate more.
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Overall Vibration
Total summation of all the vibration,with no
regard to any particular frequency. OA
OAOverall level of Vibration Spectrum , Ai
Amplitude of each FFT line n No. of FFT
Lines of resolution , NBF Noise Bandwidth for
Window chosen
2
2
2
A1 A2 An
NBF
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NOTE Dont be concerned about the math, the
condition monitoring instrument calculates the
value. Whats important to remember is when
comparing overall vibration signals, it is
imperative that both signals be measured on the
same frequency range and with the same scale
factors.
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What is Phase?

• The position of a vibrating part at a given
  instant with reference to a fixed point or
  another vibrating part.
• The part of a vibration cycle through which one
  part or object has moved relative to another
  part.
• The unit of phase is degree where one complete
  cycle of vibration is 360 degrees.

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Phase is a measurement, not a processing method.
Phase measures the angular difference between a
known mark on a rotating shaft and the shafts
vibration signal. This relationship provides
valuable information on vibration amplitude
levels,shaft orbit, and shaft position and is
very useful for balancing and analysis purposes.
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Vibration Phase
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Additional Illustration on Phase
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PHASE AN ILLUSTRATION
32 Micron 10 degrees
30 Micron 10 degrees
Shaft centre line moves up and down in a planer
fashion
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PHASE AN ILLUSTRATION
32 Micron 190 degrees
30 Micron 10 degrees
Shaft center line moves up and down in a rocking
fashion
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MACHINE TRAIN MISALIGNMENT
TURBINE
G/B
HP COMP
LP COMP
AXIAL PHASE (degrees)
0 5 15 18
198 215 10 12 22
24 210 220 12
10 20 22 208
218 8 6 16
20 200 210
Note All phase readings corrected for pickup
direction
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Comparing Overall Levels Across Mounting
Interfaces
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Phase application
C
B
A
A 5 Microns, 10 degrees
B 7 Microns, 12 degrees
C 25 Microns, 175 degrees
Bolt at C is loose
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Vibration Analysis of

• Common Problems

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Vibration AnalysisUnbalance

• Amplitude proportional to the amount of unbalance
• Vibration high normally in radial direction (may
  be also in axial direction incase of overhung
  and flexible rotors ).
• 1 RPM vibration is greater than 80 (normally)
  of the overall reading.

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Vibration AnalysisUnbalance

• Horizontal and vertical 1 RPM amplitude should
  be nearly same, although it also depends on
  system rigidity on the particular direction.
• Other frequency peaks may be less than 5 of the
  1RPM amplitude
• Phase shift of 90 deg. When sensor moves from
  horizontal to vertical.

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UNBALANCE

• Operating conditions such as load, flow condition
  and temperature effect unbalance
• Balance under normal operating conditions
• Changes in track and pitch angle of fan blades
  can result in Aerodynamic Unbalance

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Typical Spectrum For Unbalance
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MISALIGNMENT

• BIGGEST PROBLEM INITIALLY
• Operating temperature can affect alignment
• Machines aligned cold can go out when warm
• Bases or foundations can settle
• Grouting can shrink or deteriorate
• Increases energy demands

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MISALIGNMENT

• Forces shared by driver and driven (not
  localized)
• Level of misalignment severity is determined by
  the machines ability to withstand the
  misalignment
• If coupling is stronger than bearing the bearing
  can fail with little damage to the coupling

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Three Types of Misalignment

• Combination (most common)
• Angular
• Parallel or Offset

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General Characteristics Of Misalignment

• Radial vibration is highly directional
• 1X, 2x, and 3x running speed depending on type
  and extent of misalignment
• Angular 1x rpm axial
• Parallel 2x rpm radial (H V)
• Combination 1,2,3x rpm radial and axial

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Typical Spectrum for Misalignment
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Vibration AnalysisMisalignment

• Angular Misalignment
• High axial vibration
• ( Greater than 50 of the radial vibration)
• 1 , 2, 3 RPM normally high.
• 180 deg. Out of phase across the coupling

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Angular Misalignment

• Produces predominant 1x rpm component
• Marked by 180 degree phase shift across the
  coupling in the axial direction

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Vibration AnalysisMisalignment

• Off-Set Misalignment
• High Axial vibration. Also shows high radial
  vibrations.
• 1, 2, 3 RPM high. 2 often larger than 1
• In case of severe misalignment, much high
  harmonics (4 - 8) or even a whole series of
  high frequency harmonics will be generated.
• 180 deg. Out of phase across coupling

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Parallel Or Offset Misalignment

• Produces a predominant 2x rpm peak in the
  spectrum
• Marked by 180 degree phase shift across the
  coupling in the radial direction.

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Typical Spectrum for Misalignment
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Axial Phase Showing Misalignment
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Other Types Of Misalignment
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Vibration AnalysisMechanical Looseness

• Caused by structured looseness / weakness of
  machine feet, base plate or foundation also by
  deteriorated grouting, loose base bolts and
  distortion of the frame or base.
• Radial vibration high
• 2 RPM 1 RPM dominant
• 180 deg. Phase differences between mating
  surfaces which have looseness between them.

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Vibration AnalysisMechanical Looseness

• Caused by structured looseness / weakness of
  machine feet, base plate or foundation also by
  deteriorated grouting, loose base bolts and
  distortion of the frame or base.
• Radial vibration high
• 2 RPM 1 RPM dominant
• 180 deg. Phase differences between mating
  surfaces which have looseness between them.

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Looseness

• Looseness produces
• 2X RPM Freq.

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Vibration AnalysisMechanical Looseness

• Caused by looseness in bearing housing bolts and
  cracks in the frame structure.
• Radial vibration high
• 2 RPM normally dominant. 0.5, 1 and 3 RPM may
  also be present
• Substantial Phase difference between mating
  surfaces which have looseness between them

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LOOSENESS

• Not an exciting force
• Allows exciting frequencies already present to
  exhibit much higher amplitudes
• Loss or reduction in normal stiffness
• Caused by
• loose mounting bolts
• deterioration of grouting
• cracked welds

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Two Types Of Looseness

• Looseness of Rotating Components
• Loose Rotors
• Bearings Loose on the Shaft or in Housing
• Excessive Sleeve Bearing Clearances
• Looseness of Support System
• Loose Mounting Bolts
• Grouting Deterioration
• Cracks
• Poor Support
• Frame Distortion

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Looseness Of Rotating System

• Rattling condition cause impacts due to excessive
  clearance in a rolling element or sleeve bearing
• Impacts cause multiple running speed harmonics to
  appear in the spectra
• Identified by
• multiple harmonics
• unstable phase
• highly directional radial vibration

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Typical Spectrum for Looseness of Rotating System
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Looseness Of Support System

• FFT readings show 1x rpm, 2x rpm, and 3x rpm
  components
• Structural looseness / weakness will cause high
  1xrpm peak in FFT
• Identified by
• Highly directional radial vibration
• Bouncing
• Taking comparative phase readings across
  interfaces and look for amplitude variation
• Typically loose in vertical direction

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Looseness Of Support System
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Modern Trend in Vibration Technology
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Condition MonitoringSystem Integration
NETWORK
DCS
SOFTWARE
CMMS
PdM TECHNOLOGIES
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Overall Data Acquistion
4-20mA
MONITOR
THE DCS
DCS OUTPUT
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Overall Data Trends- this is what the DCS records
The limitation is that it does not adequately
reflect changes at higher frequencies which can
increase by 100 but only add 1 to the overall
energy level
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Vibration Analysis
Protection Monitor and / or
Data Collector
Vibration Spectrum
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Band Alarms, associate with each rotating element
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Band Trending, the new way forward

• Trend and alarm the
• Machine unbalance
• Alignment
• Gear mesh
• Bearings etc

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Emonitor Odyssey spectrum band alarming though
its diagnostic tools feature for both On Off
line gives advanced machinery analysis and
reduces False Alarms
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EMONITOR Odyssey Frequency Band Trends
Frequency Trend of Single Measurement
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DIAGNOSTICS - the advantage of frequency band
trending

• Root cause analysis is a complex machine specific
  exercise considering all eventualities
• Expert systems are a one off diagnosis and do not
  show a trend
• Frequency band trending is specific to root cause
  analysis
• Band alarming also indicates vibration signals
  that are outside the established norms
• Trending alignment, unbalance, gear meshing and
  bearing condition condition is more specific
• A complex issue simplified without the need of
  specialist customisation and regular updates

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DCS Limitations - Summary

• We have shown that putting total belief in the
  DCS vibration trend is highly risky
• Machinery failures still happen with on-line
  vibration monitoring with 4-20mA data to the DCS.
  Most causes are due to higher frequency signals
  swamped by the overall levels.
• Advanced machinery protection through Frequency
  Band Trending and Alarming - more specific than
  an Expert system.
• The latest S/w based Analysers incorporates
  Narrow Band Alarming. They offer machinery
  protection and narrow band alarming.
• A lower cost solution is periodic manual Data
  Collection.

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ESHAPE Modal analysis using phase for advanced
diagnosis and better understanding of system
response
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On line Vibration and othermonitors

• Innovative, fully-digital design
• Exceeds API 670 specification
• Widely-used system
• Fully field programmable
• Low installation cost
• ModBus protocol

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TYPICAL APPLICATION
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POWER PLANT INTEGRATION
ENGINEERING
OPERATIONS
DCS
ODYSSEY SERVER
VIBRATION ANALYSER
DATA LOGGER
BFP
ID
BFP
FD
CWP
PA
TURBINE SUPERVISORY
STATOR END WINDING
GATEWAY TO CMMS
AUXILIARIES
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Plant Integration with LAN or WAN
ENGINEERING
DCS
ODYSSEY CLIENT SERVER
VIBRATION ANALYSER
ETHERNET
GATEWAY TO CMMS ANURAKSHAN
TG 1
TG 2
TG 3
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NETWORKING THE INFORATION - LAN / WAN e.g.
RIHAND
TALCHER
PLANTOPERATIONS
VINDHYACHAL
NOIDA HQ CM CELL
GATEWAY TO CMMS ANURAKSHAN
KAYAMKULAM
UNCHAHAR
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Using PlantLink
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Information however you want it !
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X-Window Screen Captures
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Scenario of Instruments Sensors Probes

• Velocity sensors are made in India
• Accelerometers range over 150 types
• standard
• Low frequency
• High temperature (Gas Turbines)
• Special application

• Eddy current probes - comprehensive range
• Others available for process measurement

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Vibration Datacollectors

• Many vendors
• Select on Fitness for Purpose
• Intrinsic Safety
• Dust Moisture proof
• Diagnostic Capability

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