Vibration analysis

1. Vibration Monitoring &Vibration Monitoring &
AnalysisAnalysis

2. What is Vibration ?
It is motion of mechanical parts back and
forth from its position of rest /neutral
position.
Vibration MonitoringVibration Monitoring

3. Vibration MonitoringVibration Monitoring
What causes
Vibration ?
Induced Force
&
Freedom for Movement

4. Vibration MonitoringVibration 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

5. Vibration MonitoringVibration 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

6. Vibration MonitoringVibration Monitoring
Problem Identifications
• Unbalance
• Misalignment
• Mechanical Looseness
• Antifriction / Sleeve Bearing Defects
• Gear Defects

7. Vibration MonitoringVibration Monitoring
Problem Identifications
• Belt Defects
• Impeller / Blade Defects
• Bent Shaft
• Electrical Problems
• Resonance

8. Vibration MonitoringVibration 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

9. VIBRATION FUNDAMENTALS
TIME
Period(T)
(1 complete cycle)
Neutral Position
Upper Limit
Lower Limit
90
180
270

10. Characteristics of VibrationCharacteristics of Vibration
• Vibration characteristics are
Amplitude
Frequency Hz or CPM
Phase Angle or clock face
Displacement
Velocity
Acceleration

11. Parameter SelectionParameter Selection
• Frequency sensitivity
Displacement <600CPM
Velocity 600-60,000CPM
Acceleration >60,000CPM
Spike
Energy/SEE
Ultrasonic range

12. Frequency sensitivity

13. Vibration MonitoringVibration Monitoring
Displacement
Velocity
Acceleration

14. FFT
FAST FOURIER TRANSFORM.
• THE PROCESS OF TRANSFORMING TIME
DOMAIN SIGNAL TO FREQUENCY
DOMAIN.
• THE TIME DOMAIN SIGNAL MUST
FIRST BE SAMPLED AND
DIGITIZED.

15. Indian Institute For Production Management
FFT SPECTRUM ANALYSIS
A method of viewing the vibration signal in a way that is more useful for analysis
is to apply a Fast Fourier Transformation (FFT). In non-mathematical terms, this
means that the signal is broken down into specific amplitudes at various
component frequencies.

16. Time Domain - overall data is the sum of
all exciting and reacting forces
Imbalance
Rolling
Element
Bearing
Coupling
chatter
Gearmesh
Time
Resultant Complex
Waveform

17. Spectrum Analysis
Enables precise evaluation of
machinery condition and prediction

18. 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.

19. 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

20. 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.

21. FREQUENCY
RESOLUTION Bandwidth =
FF maxmax
total lines of resolutiontotal lines of resolution
total lines of resolutiontotal lines of resolution
Amplitud
e
Frequency FFmaxmax
lines or bins or cellslines or bins or cells
of resolutionof resolution

22. • FFT Calculation Time = Time to calculate
FFT from Time Waveform [assuming no
overlap processing]
Spectrum Data Collection
Time
FFT Calculation Time =FFT Calculation Time =
(60) ( #FFT Lines) (#Averages)(60) ( #FFT Lines) (#Averages)
Frequency SpanFrequency Span
Where: #FFT = Number of FFT Lines or Bins in Spectrum
# Averages = Number of Averages
Frequency Span measured in CPM

23. FFT SPECTRUM

24. OVERALLOVERALL
VIBRATIONVIBRATION
Total summation of all the vibration,with no
regard to any particular frequency.

25. 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.

26. Overall VibrationOverall Vibration
Total summation of all the vibration,with no
regard to any particular frequency.
OA =
OA=Overall level of Vibration Spectrum , Ai = Amplitude of each FFT line
n = No. of FFT Lines of resolution , NBF= Noise Bandwidth for Window chosen
A1 + A2 + ………………………+AnA1 + A2 + ………………………+An22 22 22
NNBFBF

27. NOTE: Don’t be concerned about the math,
the condition monitoring instrument
calculates the value. What’s 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.

28. What is Phase?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.

29. PhasePhase is a measurement, not a processing
method. Phase measures the angular
difference between a known mark on a rotating
shaft and the shaft’s 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.

30. Vibration PhaseVibration Phase

31. Additional
Illustration on
Phase

32. PHASE AN ILLUSTRATIONPHASE AN ILLUSTRATION
30 Micron
10 degrees
32 Micron
10 degrees
Shaft centre line moves up and down in a planer fashion

33. PHASE AN ILLUSTRATIONPHASE AN ILLUSTRATION
30 Micron
10 degrees
32 Micron
190 degrees
Shaft center line moves up and down in a rocking fashion

34. MACHINE TRAIN MISALIGNMENTMACHINE TRAIN MISALIGNMENT
Note: All phase readings corrected for pickup direction
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

35. Comparing Overall LevelsComparing Overall Levels
Across Mounting InterfacesAcross Mounting Interfaces

36. Phase applicationPhase application
A
B
C
A 5 Microns, 10 degrees
B 7 Microns, 12 degrees
C 25 Microns, 175 degrees
Bolt at C is loose

37. Vibration Analysis of
Common ProblemsCommon Problems

38. Vibration Analysis
Unbalance
• 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.

39. Vibration Analysis
Unbalance
• 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 1*RPM amplitude
• Phase shift of 90 deg. When sensor
moves from horizontal to vertical.

40. 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”

41. Typical Spectrum For
Unbalance

42. 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

43. 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

44. Three Types of Misalignment
• Combination (most common)
• Angular
• Parallel or Offset

45. 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

46. Typical Spectrum for
Misalignment

47. Vibration Analysis
Misalignment
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

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

49. Vibration Analysis
Misalignment
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

50. 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.

51. Typical Spectrum for
Misalignment

52. Axial Phase Showing
Misalignment

53. Other Types Of Misalignment

54. Vibration Analysis
Mechanical 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.

55. Vibration Analysis
Mechanical 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.

56. Looseness
• Looseness produces
2X RPM Freq.

57. Vibration Analysis
Mechanical 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

58. 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

59. 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

60. 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

61. Typical Spectrum for Looseness
of Rotating System

62. 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

63. Looseness Of Support System

64. Modern Trend
in
Vibration Technology

65. Condition Monitoring
System Integration
SOFTWARE DCS
CMMS
NETWORK
PdM TECHNOLOGIES
ON-LINE
ANALYSIS
SURVEILLANCE
ON - LINE
PERIODIC
WALKAROUND
OFF- LINE
CENTRALISED
PROTECTION
DISTRIBUTED
PROTECTION
CONTINUOUS
PROTECTION

66. Overall Data Acquistion
time waveform
THE DCS
MONITOR
DCS OUTPUT
4-20mA

67. current value
Overall Data Trends-
this is what the DCS records
lo alarm
hi alarm
changes over time
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

68. Vibration Analysis
time waveform
transducer
Vibration Spectrum
Data Collector
Protection Monitor
and / or

69. Band Alarms, associate with each rotating element
frequency bands
hi alarm
lo alarm

70. Band Trending, the new way forward
lo alarm
hi alarm
changes over time
Trend and alarm the:
•Machine unbalance
•Alignment
•Gear mesh
•Bearings etc

71. Emonitor Odyssey: spectrum band alarming though its
diagnostic tools feature for both On & Off line gives advanced
machinery analysis and reduces False Alarms

72. EMONITOR Odyssey: Frequency Band
Trends
Frequency Trend of Single Measurement

73. 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

74. 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.

75. ESHAPE: Modal analysis using phase for
advanced diagnosis and better understanding of
system response

76. On line Vibration and other
monitors
• Innovative, fully-digital design
• Exceeds API 670 specification
• Widely-used system
• Fully field programmable
• Low installation cost
• ModBus protocol

77. TYPICAL APPLICATION
TACHO
TACHO
MONITOR
VIBRATION
IRD
VIBRATION
MONITOR
IRD
TACHO TACHO TACHO TACHO
VIBRATION
MONITOR
CH.1 CH.2
IRD
VIBRATION
MONITOR
IRD
CH.1 CH.1CH.2 CH.2CH.1
VIBRATION
MONITOR
IRD
MONITOR
VIBRATION
CH.2 CH.1
IRD
TACHOTACHO TACHO TACHO
CH.2
MONITOR
VIBRATION
CH.1
IRD
MONITOR
VIBRATION
IRD
CH.1
VIBRATION
MONITOR
VIBRATION
CH.2 CH.1 CH.2 CH.1 CH.1CH.2
MONITOR
IRD IRD
HP
DRIVERSDRIVERS DRIVERS DRIVERS
IP
TACHO TACHO
MONITOR
VIBRATION
IRD
CH.1CH.2 CH.2
VIBRATION
MONITOR
CH.1 CH.2
IRD
TACHO
VIBRATION
MONITOR
IRD
CH.1CH.2
TACHO
CH.2 CH.1 CH.2
VIBRATION
MONITOR
IRD
DRIVERSDRIVERS
LP
DRIVERS
ALT.

78. FS HP LP GEN EX
TURBINE
SUPERVISORY
STATOR END
WINDING
CWP
BFP
BFP ID
FD
PA
AUXILIARIES
ENGINEERINGOPERATIONSDCS ODYSSEY
SERVER
POWER PLANT INTEGRATION
GATEWAY
TO CMMS
VIBRATION
ANALYSER
DATA
LOGGER

79. ENGINEERINGDCS ODYSSEY
CLIENT SERVER
GATEWAY
TO CMMS
ANURAKSHAN
VIBRATION
ANALYSER
Plant Integration with LAN or WAN
FS HP LP GEN EX FS HP LP GEN EX FS HP LP GEN EX
CONTROL ROOM No 1 CONTROL ROOM No 2 CONTROL ROOM No 3
TG 1 TG 2 TG 3
ETHERNET

80. NETWORKING THE INFORATION - LAN
/ WAN e.g.
NOIDA HQ
CM CELL
VINDHYACHAL
RIHAND
TALCHER
UNCHAHAR
KAYAMKULAM
PLANT
OPERATIO
NS
GATEWAY
TO CMMS
ANURAKSHAN

81. Using PlantLink
Vibration Trend Plot
Digital Picture of Plant
Hyperlink to
equipment
Hierarchy
Automatic E-Mail notification on
Equipment Alarm Status
Click on Measurement
Label to link to plots or
other views.

82. Information however you want it !

83. X-Window Screen Captures

84. 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

85. Vibration Datacollectors
Many vendors
Select on ‘Fitness
for Purpose’
Intrinsic Safety
Dust & Moisture proof
Diagnostic Capability