Introduction to Vibration system & basic information

Vibration system

1. Introduction to
Vibration Theory
(Waveform & Spectrum)

2. What is Vibration?
The cyclic or pulsating motion of a
machine or machine component
from its point of rest.
Stiffness
Mass
Damping
Dynamic
Resistance

3. What causes vibration ?
•A force changing in direction
•A force changing in magnitude
•Friction (rub)
•Any combination of the above

4. VIBRATION REPRESENTS...
•The SYMPTOM of a problem
•A destructive mechanism
promoting fatigue or wear

5. The vibration’s“unique characteristics”
will be determined by the nature of the
developing fault
(unbalance, electrical, random forces,
impacts)

6. •AMPLITUDE. HOW
MUCH.
•FREQUENCY. HOW OFTEN.
•PHASE. WHEN.
VIBRATION
CHARACTERISTICS

7. Characteristics of Vibration
•Amplitude = Quantity
•Frequency = # of Events
•Phase = Relative Timing Between Events
–comparative of two measurements or measurement &
shaft position (during balancing)
–lost when waveforms are transposed to spectra

8. Reminder
•Amplitude Response = Dynamic Force
Dynamic Resistance
•More force yields more vibration
•More resistance (mass, stiffness, damping at
resonance) means less vibration

9. F
M
Peak Acceleration
Peak Velocity
Period T (time) 1 Cycle
Time

10. •DISPLACEMENT
WAVEFORM
TIME
Period(T)
(1 complete cycle)
Neutral Position
Upper Limit
Lower Limit
90
18
0
270
VIBRATION AMPLITUDE
Minimum Velocity
Maximum
Velocity
Minimum
Velocity
Maximum Acceleration
Minimum
Acceleration
Maximum
Acceleration
DISPLACEMENT

11. DISPLACEMENT
VELOCITY
ACCELERATION
TIME
TIME
TIME

12. CALCULATION OF VIBRATION DISPLACEMENT,
VELOCITY AND ACCELERATION
•Where:
A = Acceleration (g
pk), V = Velocity (mm/s
pk), D = Displacement (um
pk-pk)
•D = 2 V x 10
3
D = 2 g x A x 10
6
= 19.10 x 10
3
V / RPM (um
pk-pk) = 1.79 x 10
9
A / (RPM)
2
(um
pk-pk)
•V = 0.5 D x 10
-3
V = g x A x 10
3
= 52.36 x 10
-6
D x RPM (mm/s
pk) = 93.68 x 10
3
A / RPM (mm/s
pk)
•A = 0.5 D x 10
-6
A = V x 10
-3
= 0.559 x 10
-9
D x (RPM)
2
(g
pk) = 10.67 x 10
-6
V x RPM (g
pk)
2pRPM
60
60
2pRPM
60
2pRPM
2
2pRPM
60
60
2pRPM
2pRPM
60
2
g g

13. Amplitude Units
•Magnitude of the vibration signal / Quantity
–Displacement (Mils)>
–Velocity (in/s) > RELATED
–Acceleration (g’s) >
–Spike Energy (g/SE)> STAND ALONE

14. Cyclic Motion Studies

15. Cyclic Motion relative to
repetitively applied force

16. Concept of a Simple Time
Waveform
•Paper feeds as the
block oscillates up
and down

17. Time Domain

18. Time Domain
T
Time (SEC)
A
WHERE
A = Amplitude
T = Period of vibration cycle

19. Vibration Characteristics’
Parameters
•Frequency -
•Amplitude -
•Phase -
•CPM or Hertz
•Displacement
•Velocity
•Acceleration
•Spike Energy
–dissimilar parameter
•Relative Motion
–angle

20. WHICH MEASUREMENT PARAMETER
SHOULD WE USE?
•Stress = Displacement
0-600 CPM
•Fatigue = Velocity
600-120,000 CPM
•Force = Acceleration
Above 120,000 CPM
Vibration Institute
recommendation

21. •DISPLACEMENT -How far it moves
(Microns or Mils)
•VELOCITY -How fast it moves
(mm/sec or in/sec)
•ACCELERATION -How quickly velocity
changes
(g or mm/sec
2
or in/sec
2
)
MEASUREMENT PARAMETERS,
WHAT DO THEY MEASURE?

22. WHICH MEASUREMENT PARAMETER
SHOULD WE USE ?
•The measurement parameter that will give the
greatest response to any change in machinery
condition whatever the cause
•DISPLACEMENT : 0 cpm -600 cpm
(STRESS)
•VELOCITY : 600 cpm -120 Kcpm
(FATIGUE)
•ACCELERATION : >120 Kcpm
(FORCE)

23. •For the time waveform shown in Figure 1,
what is the “PEAK AMPLITUDE” ?
A) 2.0 in/s
B) 0.2 in/s
C) 3.0 in/s
D) 4.0 in/s
Amplitude
(in/s)
.1
Time
(m Sec)
.2 .3 .4.5.6 .7
Figure 1
2
1
0
-1
-2

24. Real Vibration is Complex

25. FFT
•Fourier Transform
–Developed in the late 18th / early 19th century
by Baron Joseph Jean Baptiste Fourier, French
Mathematician and high level civil servant
(under Napoleon)
–Mathematical algorithm to decompose a
complex function into a series of simple sine
and cosine waves

26. FFT = Fast Fourier Transform
•Further development to rapidly calculate a
spectrum’s frequency contents
–Bell Labs, circa 1965

27. COMPARISON OF FREQUENCY AND
TIME DOMAINS
Time Domain
(Sec or Min) Frequency Domain
(CPM or Hertz)
Amplitude
Complex Waveform
Simple Wave forms
Frequency
Spectrum
Plot
T
MAX
F
MAX
1X
3X
5X
9X

28. The time required to complete one full cycle of vibration
is called THE PERIOD. i.e.:-
If one period is completed in one fifth of a second, the
vibration frequency would be 5 cycles per second
(5 hz) or 300 cycles per minute (300 cpm).
FREQUENCY IS THUS
THE RECIPROCAL OF THE PERIOD.
VIBRATION FREQUENCY.

29. FREQUENCY
•DISPLACEMENT AND FREQUENCY
FROM THE TIME WAVEFORM
DISPLACEMENT
TIME
Period(T)
(1 complete cycle)
Neutral Position
Upper Limit
Lower Limit
Frequency =
1
T
=
Cycles
Second
1
Period
=

30. Frequency : Events per Unit of Time
•Measure of the number of cycles of
vibration that occur in a specific period of
time
•Tells us at what rate the vibration is
occurring
•Reciprocal of the Period (T)
•Measured in Hz /CPM
–Converted by a factor of 60
•CPM relates directly to machine RPM

31. Period
•The time required to
complete one full
cycle of vibration
•Measured in seconds,
msecs or microsecs
(msec)
FREQUENCY =
1
/PERIOD

32. •From the time waveform below, calculate
the frequency of the vibration in CPM
A) 100
B) 333
C) 2,000
D) 20,000
Amplitude
(in/s)
0 3 6 9 12
Time
(m Sec)

33. 3
One cycle (period) = 3 msec
= .003 sec/cycle
= 333.3333 cycles/sec
333.333 x 60 = 19999.998 cycles/minute
Answer = 20,000 cpm
1
.003
Calculation of Frequency from
Time Waveform
1000

34. Significance of Frequency
•Essential to pinpoint the cause of a machine
problem
•Most vibration problems exhibit frequencies
DIRECTLY related to the rotational speed(s) of
the machine
•Process of elimination to narrow down the exact
machine fault
•Problems are NOT always exact multiple of rpm

35. WHY IS VELOCITY THE PARAMETER
NORMALLY USED.
•IT GIVES EQUAL AMPLITUDE WEIGHTING TO
ALL VIBRATION FREQUENCIES.
•MOST ROTATING MACHINES PRODUCE
FREQUENCIES BETWEEN 6OOCPM TO 120KCPM
WHERE VELOCITY IS THE MOST RESPONSIVE
•IT IS THE ONLY MEASUREMENT PARAMETER
WHERE THE OVERALL VIBRATION LEVEL CAN
BE APPLIED DIRECTLY TO A STANDARD OF
VIBRATION SEVERITY.IE:-WHEN THE
FREQUENCIES OF THE VIBRATION ARE
UNKNOWN.

36. Overall Vibration
•Is a total summation of the amplitudes of all the
vibration frequencies at a point. There are two types
:-
Analog Overall Level -
•Frequency range is limited only by the Transducer & Instrument
performance
•When available, use in preference to RSS to assess machinery
condition.
Digital Overall Level -
•Usually uses the Root Sum Squared (RSS) Calculated over a user
defined frequency range.
•Does not see vibration above F
MAX orbelow F
MIN
•Comparing the Analog to Spectral RSS will reveal if
your chosen spectrum (0-F
MAX) is high enough to
see all necessary information

37. RMS (root-mean-square) of a sinusoidal vibration
T =
1
__
f
Where T = period of one cycle of the vibration
v = instantaneous velocity
t = the variable time
Peak
= 0.707 Peak
v
i
t
Veff
i

41. Typical Spectrum

42. Terminology
•Dominant peak : highest in the
spectrum
•Synchronous : 1X RPM
•Asynchronous or Non-synchronous :
not a whole (integer) multiplier of
RPM
CRITICAL in Rolling Element
Bearings

43. Terminology
•Fundamental : the lowest frequency associated
to a problem or phenomenon
•Harmonic : orders of a fundamental (1x
fundamental, 2x, 3x, etc)
•Subsynchronous : BELOW 1X

44. Severity Tables
Applicable to spectral peaks which are
considered normal (i.e. NOT defects)

45. FOR
DISPLACEMENT
&
VELOCITY

46. FOR
ACCELERATION

47. Contours of Equal Severity

48. COMPARISON OF VIBRATION DISPLACEMENT, VELOCITY AND
ACCELERATION -CONTOURS OF EQUAL SEVERITY
F (cpm)
60
600
6,000
60,000
600,000
D (um)
100.00
10.00
1.00
0.10
0.01
V (mm/s)
0.314
0.314
0.314
0.314
0.314
A (g)
0.0002
0.002
0.020
0.201
2.012
LOG
AMPLITUDE
(um, mm/s, g)
LOG FREQUENCY (CPM)
Displacement
Velocity
Acceleration
Force Indicator
Fatigue Indicator
Stress Indicator
60 600 6K 60K 600K
10 um
.314 mm/s
.002 g
.20 g
.314 mm/s
.1 um

49. Parameter (Units) Review
•Velocity preferred
–linear severity over a wide frequency range
•600 to 60 000 CPM
•Acceleration preferred for HIGH freq.
•Displacement gives a good measurement for
LOW frequency

50. PHASEPHASE
WHEN?WHEN?

51. WHAT IS PHASE ?.
•The angular reference --at a given
instance in time --of a moving part--to a
fixed point.
•The angular reference--at a given
instance in time --of two moving parts
to each other.

52. In-phase

53. 90
0
Out-of-phase

54. 180
0
Out-of-phase

55. Simply

56. METHODS OF OBTAINING A
PHASE READING
•STROBE LIGHT
•REFERENCE PICKUP

57. STROBE LIGHT

58. OBTAINING PHASE
WITH A STROBE
Totally un-damped-Real time display.
No Reference Pickup required.
Can positively identify the source of a
vibration.
Poor in bright sunlight & slow speeds.
Rotating parts must be visible
Close access required.
Needs accurately marked Angular Reference

59. REFERENCE PICKUP (REMOTE PHASE)

60. OBTAINING PHASE
WITH A REFERENCE PICKUP
No angular marking required.
Phase readings at remote locations.
Shafts can be totally enclosed.
Good for low speeds (Not E/Mag PU)
Digital readings not real time
Pulse reference required on shaft.
Reference pickup requires mounting.

61. METHODS OF OBTAINING PHASE
REFERENCE PICKUPS
•PHOTOCELL REFLECTIVE TAPE
BAD :-CLEAN AIR OPERATION ONLY
–GOOD :-LOW SPEED-EASY SET UP.
TEMPERATURE SENSITIVE
•FIBRE OPTIC REFLECTIVE TAPE
–SAME AS FOR PHOTOCELL BUT NOT TEMPERATURE
SENSITIVE
•ELECTRO MAGNETIC CONDUCTIVE PROTRUSION OR RECESS
–GOOD:-ENCLOSED & OIL WASHED COMPONENTS
BAD :-OUTPUT DEPENDENT ON SPEED & GAP
•NON CONTACT PICKUP CONDUCTIVE PROTRUSION OR RECESS
REQUIRES SPECIAL MOUNTING BRACKETS AND POWER
SUPPLY
•LASETACH ANY SIGNIFICANT CHANGE IN TEXTURE OR
COLOUR
–GOOD :-CAN BE USED UP TO 15 METERS FROM TARGET
BAD :-SAFETY (EARLIER TYPES-CLASS B LASER)
CLEAN AIR SPACE

62. Phase Measurements
In addition to Phase measurements at IX reference
input, the analyser can easily display phase up to
10X referenceinput

63. PHASE
•PHASE readings enable you to
differentiate between defects with similar
frequency characteristics i.e..
–Phase Direction -Relative between points.
–Phase Separation. -At one point.
–Phase Instability
–Phase With Respect to Amplitude & Speed
–Phase With Respect to Time
–Phase With Respect to Time and Position.

64. PHASE INSTABILITY
•Erratic :- Impact -Looseness
•Changing :-Resonance
•Changing between runs :-Components
slipping on initial torque. Loose objects
in hollow components. Plastic shafts etc..
•Swinging :-Phasing -Beating
•Rotating :-Slipping components
Severe phasing

65. RECAP
VIBRATION
TECHNOLOGY

66. Machines
Everywhere-
In the home -
Air Conditioners,
Washing machines,
At work -
Presses,
Motors,
Pumps

67. When they breakdown -
I get annoyed because & I couldn't
get a good night’s sleep!
The one-man company goes bust
since he can’t produce his products
and the customers go elsewhere!
The large multi-nationals just put in
a new machine!

68. Some of the
consequences :-
Annoyance!
Financial Disaster!
Personal Injury!
Loss of life!

69. Do you ever walk past a machine and
put your hand on the casing?
We do this to “Feel” if it is running the
way it normally should.
An inexperienced driver will know that
something is wrong when the steering
wheel begins to shake.
Therefore, it is natural for us to relate
the condition of our machines to the
amount of vibration that they are giving
off.

70. SEEMS BAD. LET’S
SHUT IT DOWN
I THINK IT’S
MISALIGNED
I DON’T THINK IT’S TOO
BAD! LEAVE IT ALONE
Subjective Experience

71. Objective Technology
The vibration
analysis says it’s
out of balance.
At 7 mm/sec it’s
only slightly rough.
That’s good!
We can
continue
operations but
plan
maintenance.

72. What is Vibration?
We can define vibration as -
The back and forth motion of a
machine, or one of it’s components,
from its normal position of rest.
This back and forth motion is called
an Oscillation.
Any motion that repeats itself after
an interval of time is called an
oscillation.

73. VIBRATION DEFINITION
M
Lower limit
Neutral position
Upper limit
Vibration is simply a
motion back and forth
from a position of rest.

74. WHY USE VIBRATION?.
All machines vibrate.
Developing problems are
usually accompanied by an
increase in vibration.
The vibration’s unique
characteristics will be
determined by the nature of the
developing fault.

75. Causes of Vibration:
Vibrations are caused by forces that are
generated within the machinery. These forces
may be ones that:
Change in direction over time -rotating unbalance.
Change in amplitude, or intensity, over time -
unbalanced magnetic forces in induction motors.
Cause friction between rotating and stationary parts.
Cause impacts -gear tooth contacts -rolling elements
in bearings.
Cause randomly generated forces -flow turbulence.

76. Common Causes of Vibration are:
Misalignment of couplings, bearings & gears.
Unbalance of rotating components.
Looseness of bolts, grouting or excessive clearance.
Deteriorating rolling elements in bearings.
Gear wear.
Rubbing.
Aerodynamic / Hydraulic Forces.
Electrical problems such as unbalance in motors.
Resonance.
Eccentricity of rotating components.

77. What Causes the Vibratory Condition
of a Machine to Deteriorate?
•Dynamic forces increase
–Wear, corrosion, or build up of deposits
increases imbalance
–Settling of foundations may increase
misalignment forces
•The stiffness of the machine reduces
–Loosening or stretching of mounting
bolts
–Broken weld
–Crack in the foundation
–Deterioration of grouting

78. Reasons to Minimize Vibration -
Plant Reliability
–Reduction in Outage & Maintenance Cost
More Productivity
Precision machine tools
–Quality products require
Good dimensional tolerances
Human Annoyance
–Residences
Low vibration in heating, ventilation, air
conditioning. machinery, etc...

79. Maintenance Philosophies
Breakdown Maintenance
Preventative (Scheduled) Maintenance
Predictive Maintenance

80. Breakdown Maintenance
No maintenance (Run to failure mode).
Results in lost production and/or poor
quality production.
Causes untimely failure.
Catastrophic failure may lead to
extensive damage (complete machine
replacement).
Safety related concerns.
Up to three times the cost.

81. Scheduled or Preventive Maintenance
Regularly stop the equipment and inspect for
defects, lubricate etc.
Advantages of periodic disassembly and
inspection
–Lessens frequency of breakdown repairs
–Allows for scheduling parts, labour,
processes
Disadvantages
–Periodic disassembly of every critical
machine (and non-critical) is expensive
and time consuming
–Period or interval is difficult to
determine

82. PREDICTIVE MAINTENANCE.
THE USE OF GRAPHIC TRENDS OF
SELECTED MEASUREMENT
PARAMETERS AGAINST KNOWN
ENGINEERING LIMITS FOR THE PURPOSE
OF:-
DETECTING, ANALYSING &
CORRECTING
MACHINERY DEFECTS,
BEFORE FAILURE OCCURS

83. Predictive Maintenance Advantages:
Minimizes machine damage and allows
scheduling of downtime, labour,
materials
Helps eliminate costly trial and error
approaches to solving problems
Allows machines in good operating
condition to continue to run
Eliminates unnecessary overhauls
Improves safety and quality performance

84. Predictive Maintenance
Involves the trending and analysis of
machinery performance parameters.
Condition Monitoring
The assessment on a continuous or
periodic basis of the mechanical
condition of machinery, equipment and
systems from the observations and / or
recordings of selected measurement
parameters.

85. MEASUREMENT PARAMETERS
•NOISE
•TEMPERATURE.
•PRESSURE.
•CURRENT FLOW.
•MOVEMENT:- EXPANSION -VIBRATION.
•INFRA RED :- THERMOGRAPHY.
•OIL CONDITION / CONTAMINATION
•WEAR ANALYSIS:-FEROGRAPHY.
SPECTROMETRIC OIL
ANALYSIS.

86. WHY DO WE WANT TO DO THIS?
We want the machines to
run for as long as possible,
in their normal operating
conditions.
We want as much warning
of impending failure as we
can possibly get, so that we
can avoid breakdowns.

87. MACHINE OPERATING CONDITIONS
Bathtub Curve
RUNNING
IN
NORMAL OPERATIONS
FAILURE
SHUT DOWN
WARNING
LEAD
TIME
OIL
DEBRIS

88. PREDICTIVE MAINTENANCE
•DETECTION
•ANALYSIS
•CORRECTION
•VERIFICATION
An effective
PREDICTIVE MAINTENANCE PROGRAMME (PMP)
consists of four logical steps-

89. The Four Logical Steps of an Effective
Predictive Maintenance Program.
Detection
Trending a machines vibration level to detect and quantify any
changes from the norm.
Analysis
When a significant change is detected the vibration is analyzed
to determine the nature of the problem
Correction .
The advanced warning provided by the detection and analysis
enables corrective action to be prepared and scheduled.
Verification.
After correction new readings are obtained to ensure that all
defects have been eliminated and to establish new baseline
characteristics.

90. Fifth Stage
Most companies now add a fifth stage
to their Predictive Maintenance
Program
Root Cause Analysis
When the defect is confirmed, the fault
and/or defective components are
analyzed to prevent re-occurrence of
the problem.