Basics of Vibration Analysis which will useful to find out fault in machines

1. Contents
Vibration Analysis to find out fault in machines
1
1. Maintenance philosophy
2. Predictive and Preventive maintenance
3. What is Vibration ?
4. Fundamental facts behind vibration monitoring
5. Characteristic of Vibration
6. Organizing vibration monitoring program
7. Vibration sensors and selection
8. Recommended locations of shaft vibration measurements as per
ISO
9. How Vibration is analyzed?
10. Vibration severity chart
11. Vibration identification chart
12. Common causes of Vibration- unbalance, Misalignment,
Mechanical Looseness, bent shaft, gear defects. bearing defect etc.
13. Vibration Measurement

2. Maintenance Definition
2
Maintenance philosophy
• Organised activities carried out to keep an machine in its best
operational condition with minimum cost.
• The combination of all
• technical actions like repair or replacement activities and
• administrative actions like supervision,
• which are necessary for an equipment to reach its acceptable
productivity condition
• Maintenance is
• an art of Preservation and
• an act of Restoration
• To ensure Maximum Availability of Plant and Equipment at
optimizing Cost and Resources
What is Maintenance?

3. Types of maintenance
3
Advantage Disadvantage
Breakdown Maintenance: Do the job when job appears to you
• Advisable for inexpensive, non
critical equipment
• Where stand by is available
• High down time and high inventory
• Frequent failure and high cost
• Destruction of machine, Safety hazard
• Disaster and Crude method
Preventive Maintenance: Do the job when you appears to the job
• Enables planning
• Reduces breakdowns
• Useful in large expensive,
continuous plant. .
• If period of frequency is too short cost is
high; If too long chances of failure in-
between. Good machines also opened
• Misapplied sometimes
• Increases incidence of human error in
machine
• Replacement of component regardless of
condition

4. Types of maintenance
4
Advantage Disadvantage
Predictive Maintenance: Do the job when job is going to appear to you
• Most economical
• Best planning is possible
• Higher safety
• Minimum loss of output
• Required components are
replaced based on condition
• Hi-tech/high cost measuring
instruments are required
• Perfect prediction, extra efforts and
skill is required
Proactive Maintenance: Do something where job will not appear to you
• Life of equipment will be
increased.
• Equipment will not be allowed
to fail.
• Failure analysis and design
change can be introduced
• Failure data is required
• Analytical skill is required

5. Predictive maintenance
5
Time
DegreeofFailure
Breakdown Range
Predictive Maintenance Range
Carryout maintenance here
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On condition check interval

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• Also called as Condition based maintenance or Condition monitoring
• Preventive maintenance is done many a times before required and
many a times failure occurs before schedule maintenance done
• To decide frequency of inspection is difficult and people do mistake
during overhaul hence having few drawback
• Best option is to predict or measure the condition of machine and do
the maintenance when it is required
• This require base line data, instruments, knowledge and skill
• Visual Monitoring
• Vibration Monitoring
• Bearing Monitoring
• Corrosion Monitoring
• Temperature Monitoring
Predictive maintenance
• Noise Monitoring
• Lubrication Monitoring
• Wear debris analysis
• Performance Monitoring
• Leakage monitoring
Some of the major condition monitoring methods are:

7. What is Vibration?
7
Vibration Monitoring
• It is the motion of a mechanical part back and forth
from its position of rest/neutral position at certain
frequency
• Vibration is the physical movement or oscillation of a
mechanical part about a reference position
What is Vibration analysis?
• It is a non-destructive technique which helps early detection of
machine problems by measuring vibration.

8. Fundamental facts behind vibration monitoring
8
All rotating and reciprocating machines vibrate; may be to
a smaller extent to a higher extent; because there is no
perfect machine.
Machine vibrates because of defects in the system.
The characteristic of vibration produced by different
defects are different.
As vibration increases, mechanical trouble develops and
also trouble increases
• Therefore changes in vibration reveal the condition of machine.
• Vibration characteristic reveal the cause of vibration.

9. Fundamental facts behind vibration monitoring
9
Vibration is a major cause of premature failure of
component of machines
Vibration analysis and diagnostic study has gained
considerable progress in monitoring machine health
condition
Vibration is the language of machine if one can
listen and understand, is enough to diagnose their
complaints and ailment.
Vibration monitoring has gained considerable
importance because of the above fundamental facts.

10. Characteristic of Vibration
10
• What causes vibration?
• As the shaft turns, there are frictional and rotational forces.
• (Exciting force = Stiffness force + Inertia force + Damping force)
• That vibration created by those forces is transferred via the bearings
to the machine housing
In simple terms vibration analysis can answer following three questions.
1) How much vibration (in amplitude) is present in the machine?
2) What defect are causing this vibration ?
3) Which parts of machinery are having these defects?
Let us understand ….
• What vibration is
• Characteristic of vibration
• What vibration analysis can tell us.

11. Characteristic of Vibration
11
• Vibration: Motion of a machine or part of a machine, back and forth
from its position of rest.
• Consider that a weight is suspended on a spring, which is allowed to
vibrate up and down under some influential cyclic force.
• A plot of this movement against time will give basic information of
vibration characteristic.
• The motion of the weight from the neutral position to the top limit of
travel, back through the neutral position to the bottom limit of travel
and its return to the neutral position represent one cycle of motion.
• This one cycle of motion is plotted against time as shown in figure.

12. Characteristic of Vibration
12
Displacement
Velocity
Acceleration
Frequency
Phase
Vibration can be fully identified by five characteristics.
• Displacement, velocity and acceleration
called as amplitudes and indicate how
much vibration is present in terms of the
condition of machine, how bad or good is
its condition i.e. it gives reply to our first
question.
• Amplitude is an indicator of the severity of
a vibration
Amplitude (How much is it vibrating?)
Indicates size of the problem
• Displacement
• Velocity
• Acceleration
Each characteristic tells something of significance about the vibration.

13. Characteristic of Vibration
13
Displacement
Velocity
Acceleration
Frequency
Phase
Vibration can be fully identified by five characteristics.
Phase ( which part and how is it
vibrating?).. Help in replying third
question.. Indicates cause of the vibration
and position of the vibrating path with
certain reference
Vibration frequency indicate what is
causing the vibration and gives reply to our
second and third question. What defect
and which part is causing vibration?
Each characteristic tells something of significance about the vibration.

14. Characteristic of Vibration
14
Vibration analysis can answer following three questions.
1) How much vibration (in amplitude) is present in the machine?
2) What defect are causing this vibration ?
3) Which parts of machinery are having these defects . with reference?
What defect? 2- Frequency
*
Peak velocity & displacementHow much? -1
Which? -3 - Phase -

15. Vibration Displacement
15
• Displacement is a measure of the actual distance an object is moving
from a reference point.
• The total distance traveled by the vibrating path from one extreme
limit of travel to other extreme is called "peak to peak"
displacement.
• Displacement is expressed in microns (μm) or in mills (1 mill=.001
inch) (measured in mm or inch)
• Displacement is also frequency related, in that 10 mils @ 1000 rpm is
not the same as 10 mils @ 10000 rpm

16. Vibration Velocity
16
• Since the movement of the vibrating path is with certain speed or
velocity and this is measured in terms of mm/sec. or in inches/sec.
• The velocity is greatest as the machine passes through its neutral
position and it is this velocity known as peak velocity.
• Velocity is the rate of change in position
• Velocity is the most accurate measure of vibration because it is not
frequency related. 0.5 mm/sec @ 1000 rpm is the same as 0.5 mm/sec
@ 10000 rpm.

17. Vibration Acceleration
17
• The acceleration is a rate of change of velocity and is usually
expressed in terms of g's peak value 1g = 980.665 cm/sec./sec.
• It is the measurement of the force being produced. ( in m/s2 or g)
• Expressed in gravitational forces or “G’s”, (1G = 32.17 ft/sec/sec)
• Acceleration is frequency related, in that 1 g @ 1000 rpm is not the
same as 1 g @ 10000 rpm.
Units of Measurement:
Displacement : microns or mm (How far it moves)
Velocity : mm/sec (How fast it moves)
Acceleration : g (mm/sec2) (How quickly Velocity changes)
Parameter Selection:
Displacement: <600 CPM
Velocity : 600 – 60,000 CPM
Acceleration : >60,000 CPM

18. Vibration frequency
18
• Frequency is equal to the number of cycles completed in unit time and it is
indicated in terms of Hertz'. (Cycles/sec.) 1 HZ = 60 CPM
• The rate of mechanical oscillation in a period of time. Frequency can be
expressed in one of the following units:
• RPM - Revolutions per Minute
• CPM - Cycles per Minute
• CPS - Cycles per Second
• Hz - Hertz, 1 Hz - 1 cycle per second .. 10 Hz= 10 cycle per second
(to convert from Hz to RPM or CPM, apply the following formula: Hz x 60 =
RPM = CPM)

19. Vibration Phase
19
• Vibration phase defined as the instantaneous position of the vibrating
path with certain 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.
• It measures the angular difference between a known mark on a
rotating shaft and the shaft’s vibrating signal.
• Phase is a measure of relative time difference between two sine
waves.
• 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

20. 20
Vibration Phase

21. Frequency and Phase
21
• Vibration frequency indicate what is causing the vibration.
• The particular part causing the vibration or what is the trouble of the
part, can be pinpointed by comparing the frequency with the rotating
speed and multiple of rotating speeds.
• Frequency is the most important characteristic in vibration monitoring
• Vibration phase is useful in balancing and will help in identifying the
defective location in the system.
• Two or more vibrating motion can be compared by measurement of
phase
Importance of Phase:
• Phase is a relative measurement. Provides information how one part
of a machine is vibrating compared to other.
• To judge problems like - Unbalance, Misalignment, Eccentric Rotor,
Bent Shaft, Mechanical Looseness, Structural Weakness, Soft Foot,
Resonance.

22. Unit of Vibration
22
(A) Displacement
• microns, peak to
peak
• microns, 0 to peak
• microns, RMS
Period, T
RMS
Unit Circle
Peak-to-Peak
0 to Peak
0
(b) Velocity
• mm/sec, 0 to peak
• mm/sec, RMS
(c) Acceleration
• m/sec2, peak
• m/sec2, RMS
• g, peak
• g, RMS

23. Average RMS Peak
Peak - Peak
RMS = 0.707 x Peak
Average = 0.637 x Peak
Peak to Peak = 2 x Peak
Unit of Vibration
• Peak to Peak: the distance from the top of the positive peak to bottom of the
negative peak.
• Peak: the measurement from the zero line to the top of the positive peak.
• Average: 0.637 of peak.
• Root Mean Square (RMS): 0.707 of peak. =
• RMS is the square root of the average of the squared value of amplitude

24. Vibration Measurement – How?
24
• Electronic instruments are available for vibration measurement .
• Classified as meters, monitors, analyzers, data collectors etc.
• The heart of the vibration measurement system is vibration pick-up or
transducer.
• The vibration transducer is a device which converts mechanical
vibration into an electrical signal.
• The most commonly used pick-up are velocity type, accelerometer and
non contact type.
• Accelerometers are specially sensitive to high frequency vibration.

25. 25
Vibration Measurement – How?
• To measure vibration, pick up should be placed at various points onto
the machine. These measurement points should be carefully chosen to
give most useful information.
• In general the pick up should be placed on or as near as possible to the
bearings because vibration forces are getting transmitted through the
bearings.
• Vibration readings are usually taken with the pick up in the horizontal,
vertical and axial direction.
• Apart from bearing locations, fixing points, mounting blades, meeting
areas, machine casing, foundation etc. may also have to be selected for
vibration measurement depending upon the nature of the problem.
• Vibro meter
• Vibration Analyzer
• FFT Analyzer

26. 26
1 • List the critical machines to be included in the program
2 • Establish acceptable vibration levels
3 • Determine each machine's condition and normal vibration level
4 • Select periodic vibration check points
5 • Start a data recording system
6 • Select the interval for periodic vibration checks
7 • Evaluate condition of the machine from data and decide action
8 • Train personnel to carry out the program:
Organizing vibration monitoring program
Eight basic steps to establish vibration monitoring program.

27. 27
Organizing vibration monitoring program
Instruments : Portable and on line
Portable Monitoring Online, Continuous

28. Vibration Sensors
28
• A transducer or sensor
that converts mechanical
motion into electronic
signals.
• Three categories:
• Displacement
• Velocity
• Accelerometer
Which parameter
to use?

29. Recommended locations of shaft vibration measurements as per ISO
29

30. 30
Class Class Class Class Class Class
Limits
1 Step
Class I: Motor KW < 15 KW, Class II: Motor KW : (15-75 KW)
Class III: Motor KW > 75 KW , Class IV: Machine with soft foundation + TG sets
with light weight structure, Class V: Machines with inbuilt unbalance (Crusher) +
strong foundation Class VI: Machines with inbuilt unbalance (Crusher) + soft
foundation /weak
ISO 2372: Vibration criteria A = Good
B = Acceptable
C = Still acceptable
D = Not acceptable

31. Main Causes
Common causes of Vibration
31
• Machine vibration can be
attributed to the various
mechanical defects within the
machine.
• Here are some of the common
causes of vibration and how
they can be identified.
• Unbalance
• Misalignment
• Mechanical Looseness
• Bad antifriction bearing
• Bad Gears
• Belt Defects
• Electrical trouble
• Aerodynamic and Hydraulic forces
• Oil whirl
• Bent shaft- Eccentric rotor
The vibration identification chart
The vibration identification chart (Table) indicates the amplitude,
frequency and phase characteristic of the most common defects that
creates vibration in rotating machinery.

32. Vibration Identification Chart
32
Probable Defects Frequency
Dominant
Plane
Amplitude
Phase
relationship
Unbalance 1 x RPM Radial Steady In phase or out of
phase 90
Misalignment Usually 1 x RPM
often 2 x RPM
Axial Steady Out of phase 180
Mechanical
Looseness
2 x RPM Radial Steady Unstable
Defective Antifriction
Bearing
Several time x RPM Radial Increase as bearing
degrades
N.A.
Bad gears Gear RPM x no. of
teeth
Radial or
Axial
Depends on load,
speed
N.A.
Belt defects 1 x RPM, 2 x RPM Radial Steady In-phase
Oil Whirl 42 to 46% of RPM Radial Steady N.A.
Electrical Troubles 1 x RPM
1 x Synchro
Radial Steady N.A.
Resonance Whole range of
frequency
Radial or
Axial
Steady Unstable
Aerodynamic &
Hydraulic forces
Several times x RPM Radial Fluctuating N. A.

33. Vibration Identification Chart
33
Sr. Frequency Most likely Cause Other possible causes
1 1 x RPM Unbalance • Eccentric journal, gear or pulley;
• Misalignment or bent shaft (high Axial)
• Bad belts if rpm of belt
• Resonance
• Reciprocating forces
• Electrical problems
2 2 x RPM Mechanical
Looseness
• Misalignment (if high axial)
• Reciprocating forces
• Resonance
• Bad belts if 2 x RPM of belts
3 2 x RPM Misalignment • Usually a combination of misalignment
and excess axial clearance
4 Less than 1 x
RPM
Oil whirl • Bad belts
• Background vibration
• Subharmonic resonance
• Beat vibration

34. Vibration Identification Chart
34
Sr.
No.
Frequency Most likely Cause Other possible causes
5 Synchronous
(AC line
Frequency)
Electrical problems • Electrical problems in a squirrel cage
rotor (such as broken rotor bar)are
separated from powerline frequency
by slip frequency.
6 Many times
RPM
(harmonics
related)
Bad Gears
Aerodynamic forces,
Hydraulic forces,
Mechanical
looseness
Reciprocating forces
• Gear teeth times RPM of bad gears
• Nos. of fan blades times RPM
• Nos. of impeller vanes times RPM
• May occur at 2, 3, 4 and sometimes
higher harmonics of severe looseness
7 Higher
Frequency
(Non
harmonically
related)
Bad Antifriction
bearings
• Bearing vibration may be unsteady-
amplitude and frequency
• Cavitation, recirculation and flow
turbulence cause random high
frequency vibration
• Improper lubrication of jounal bearing
• Rubbing

35. Unbalance
35
• The most common cause of vibration and is caused when the centre of
mass of component does not coincide with its centre of vibration.
• It is usually be corrected in-situ without major machinery disassembly.
• Amplitude proportional to the amount of unbalance
• Vibration high normally in radial direction- in either a horizontal or
vertical direction-(also in axial direction incase of overhung rotors)
• Frequency equal to the rotating speed (1 x RPM) of the part.
• 1 x RPM vibration is greater than 80% of the overall reading.
• 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.
• Operating conditions such as load, flow condition and temperature
affect unbalance
• Changes in track and pitch angle of fan blades can result in
“Aerodynamic Unbalance”

36. Misalignment
36
Misalignment is a condition where the
centerlines of coupled shafts do not coincide.
• Classified as the second major source of vibration. Misalignment can
be of the bearing with shaft, between the bearings or because of bent
shaft.
Causes:
• Thermal expansion - Most machines align when they are cold.
• Machine vibrations.
• Forces transmitted to the machine by pipe or support structure.
• Soft foot.
• Direct coupled machines are not properly aligned.
• Poor workmanship

37. Misalignment
37
• Biggest problem initially
• Operating temperature can affect alignment
• Machines aligned at cold condition, can go out when warm
• Bases or foundations can settle it
• Grouting can shrink or deteriorate
• Increases energy demands
• 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
• Radial vibration is highly directional
• Misalignment will show up a high axial vibration usually at 1 x RPM,
sometimes 3 x RPM & 4 x RPM depending on type and extent of misalignment
• Angular misalignment: 1 x rpm axial
• Parallel misalignment: 2 x rpm radial (H & V)
• Combination misalignment: 1, 2, 3 x rpm radial and axial

38. Mechanical looseness
38
• Loose mechanical parts are a common cause of vibration and are
detected at twice rotational speed i.e. 2 x RPM in the radial direction.
• Vibration contain higher harmonics because the sinusoidal vibration
caused by unbalance or other defects are truncated when mechanical
looseness is taken up.
• It alone can not create vibration but in the influence of Unbalance,
Misalignment, Bearing problems it amplify the amplitude.
• It should be corrected first.
Types of Mechanical Looseness
1) Structural frame/base looseness (1 x RPM)
2) Cracked structure/looseness in bearing pedestal (2 x RPM)
3) Rotating looseness - Loose bearing/improper fit between component
parts. (Multiple x RPM)

39. 39
• A symptom peculiar for journal bearings is oil whirl.
• It shows up as a vibration of approx. 0.42 x - 0.48 x RPM.
• Oil whirl can be diagnosed by increasing the load which will decrease
the sub synchronous vibration
Oil Whirl - Journal bearings
frequency
mm/srms