Vibration analysis of equipments

1. 1
PG
INSTRUMENTATION
REFRESHER COURCE
TOPIC:
VIBRATION MEASUREMENT IN
ROTATING EQUIPMENT

2. 2
VIBRATION MEASUREMENT
THE KEY TOOL TO DIAGNOSE
ROTARY EQUIPMENT
HEALTH

3. 3
VIBRATION
• MECHANICAL OSCILLATIONS ABOUT AN
EQUILIBRIUM POINT.
• A REGULAR PERIODIC VARIATION IN VALUE
ABOUT A MEAN
•VIBRATION IS RESPONSE OF A SYSTEM TO AN
INTERNAL AND EXTERNAL STIMULUS (EITHER IMPACT
OR PERIODIC FORCE) CAUSING IT TO OSCILLATE OR
PULSATE

4. 4
VIBRATION
PHYSICS TERMINOLOGY
•MOTION THAT REPEATS ITSELF OVER AND OVER IS
PERIODIC MOTION
•THE TIME REQUIRED FOR ONE REPETITION IS CALLED
THE PERIOD.
• ONE COMPLETE REPETITION OF THE MOTION IS
CALLED A CYCLE.
THE NUMBER OF TIMES A COMPLETE MOTION CYCLE TAKES
PLACE DURING THE PERIOD OF ONE SECOND IS CALLED THE
FREQUENCY AND IS MEASURED IN HERTZ (HZ).

5. 5
VIBRATION
TWO TYPES OF VIBRATION
•FREE VIBRATION
Free vibration takes place when a system oscillates under the action of
forces inherent in the system itself, and when external impressed forces are
absent. the system under free vibration will vibrate at one or more of its natural
frequencies, which are properties of the dynamic system established by its mass
and stiffness distribution.
•FORCED VIBRATION
Vibration that takes place under the excitation of external forces is called
forced vibration. When the excitation is oscillatory, the system is forced to vibrate
at the excitation frequency. If the frequency of excitation coincides with one of the
natural frequencies of the system, a condition of resonance is encountered, and
dangerously large oscillations may result.

6. 6
QUANTIFY THE VIBRATION LEVEL
VIBRATION AMPLITUDE,THE CHARACTERISTIC WHICH
DESCRIBES THE SEVERITY OF THE VIBRATION, IS
QUANTIFIED IN FOLLOWING WAYS..
PEAK TO PEAK_ PEAK VALUE _AVERAGE VALUE
RMS VALUE
TIME
PEAK TO
PEAK
PEAK LEVEL RMS
LEVEL
AVERAGE
LEVEL
T

7. 7
VIBRATION
DYNAMIC EFFECT OF
• MANUFACTURING TOLERENCES
•CLEARENCES
•ROLLING & RUBBING CONTACT BETWEEN M/C
PARTS
•OUT OF BALANCE FORCES IN ROTATING &
RECIPROCATING MEMBERS
OFTEN, SMALL INSIGNIFICANT VIBRATIONS CAN EXCITE THE RESONANT
FREQUENCIES OF SOME OTHER STRUCTURAL PARTS AND BE AMPLIFIED
INTO MAJOR VIBRATION AND NOISE SOURCES.

8. 8
VIBRATION
PARAMETERS
•ACCELARATION
•VELOCITY
•DISPLACEMENT

9. 9
VIBRATION
.
•DISPLACEMENT
AN INDICATOR OF UNBALANCE IN ROTATING MACHINE PARTS.
MEASUREEMNT OF DISPALCEMENT WILL GIVE MORE WEIGHT TO
LOW FREQUENCY COMPONENTS.
•ACCELARATION
MEASUREEMNT OF ACCELARATION WILL GIVE MORE WEIGHT TO
HIGH FREQUENCY COMPONENTS.
•VELOCITY
VIBRATION VELOCITY BETWEEN 10 TO 1KHz GIVES A GOOD
INDICATION OF VIBRATION SEVEARITY.
CHOICE OF PARAMETER IS IMPORTANT IF THE SIGNAL HAS
COMPONENTS AT MANY FREQUENCIES

10. 10
VELOCITY
90º PHASE LEAD
DISPLACEMENT
ACCELARATION
180º PHASE LEAD
0.1 1 10 Hz 100 1KHz 10 100
ACCELARATION
VELOCITY
DISPLACEMENT
ATTENUATION
db
V = A
2πF
D = A
2π²F²
FOR SINUSOIDAL SIGNALS, DISPLACEMENT, VELOCITY AND
ACCELERATION AMPLITUDES ARE RELATED
MATHEMATICALLY BY A FUNCTION OF FREQUENCY AND TIME

11. 11
VIBRATION
IT IS ADVANTAGEOUS TO SELECT THE PARAMETER
WHICH GIVES THE FLATTEST FREQUENCY SPECTRUM IN
ORDER TO UTILISE THE DYNAMIC RANGE
FOR THIS REASON THE VELOCITY OR
ACCELERATION PARAMETER IS NORMALLY
SELECTED FOR FREQUENCY ANALYSIS PURPOSES.

12. 12
VIBRATION
MEASUREMENT
BASIC VIBRATION SENSOR
•DISPLACEMENT NON CONTACT
•VELOCITY VELOMETER
•ACCELARATION ACCELEROMETER

13. 13
VIBRATION
MEASUREMENT (DISPLACEMENT)
SS BODY
POTTING
MATERIAL
EDDY CURRENT SENSOR
NON CONDUCTIVE
PLASTIC
SILVER WIRE COIL

14. 14
VIBRATION
MEASUREMENT (DISPLACEMENT)
WORKING PRINCIPLE EDDY CURRENT TRANSDUCER
•THREE MATCHED COMPONENTS
DRIVER,PROBE & EXTENSION CABLE
•VOLTAGE APPLIED TO DRIVER
GENERATE RF SIGNAL
•SIGNAL TRANSMITTED TO PROBE
THROUGH EXTENSION CABLE

15. 15
VIBRATION
MEASUREMENT (DISPLACEMENT)
WORKING PRINCPLE EDDY CURRENT TRANSDUCER
•PROBE TIP SERVES AS AN ANTENA
RADIATES HIGH FREQUENCY ENERGY INTO FREE
SPACE
•CONDUCTIVE MATERIAL WHITHIN FIELD ABSORB
ENERGY
RESULTED OUTPUT OF PROBE TO DECREASE
PROPORTIONAL TO GAP VOLTAGE

16. 16
EDDY CURRENT PROBE
ALSO KNOWN AS PROXIMITY
PROBE
MODULATOR/ DEMODULATOR
ALSO KNOWN AS PROXIMITER
EXTENSION CABLE
ELECTROMAGNETIC FIELD
SYSTEM OVERVIEW
VIBRATION

17. 17
VIBRATION
ADVANTAGES OF EDDY CURRENT PROBE
•LOW FREQUENCY RESPONSE (TO 0 Hz)
•CAN MEASURE RELATIVE DISPLACEMENT
•USEFUL AS A KEY PHASOR FOR DYNAMIC
BALANCING & ANALYSIS
•RELIABLE IF PROPERLY INSTALLED & MAINTAINED

18. 18
VIBRATION
DISADVANTAGE OF EDDY CURRENT PROBE
•DIFFICULT TO INSTALL
•PRACTICAL LIMITS OF HIGH FREQUENCY
DISPLACEMENT MEASUREMENT
•CALIBRATION DEPENDENT ON SHAFT MATERIAL
•SHAFT RUN OUT / GLITCHES PRODUCES FALSE
SIGNAL

19. 19
1 PICK-UP , 2 WIRE COIL, 3 DAMPER 4 MASS 5 SPRING 6 MAGNET
•HOUSING VIBRATES WHILE THE SPRING SUSPENDED COIL
REMAINS STATIONARY
•AMPLITUDE OF THE OUTPUT VOLTAGE IS PRAPORTIONAL TO
THE VELOCITY OF THE VIBRATION
VIBRATION
ELECTRODYNAMIC VELOCITY SENSOR

20. 20
VIBRATION
ADVANTAGES OF ELECTRODYNAMIC VELOCITY SENSOR
•NO EXTERNAL POWER
•POWERFUL SIGNAL OUTPUT
•EASY TO USE
•ABILITY TO OPERATE AT HIGH TEMEPERATURE

21. 21
VIBRATION
DISADVANTAGE OF ELECTRODYNAMIC VELOCITY
SENSOR
• NOT USEFUL FOR VERY LOW FREQUENCY
• NOT USEFUL FOR VERY HIGH FREQUENCY
• MOVING PARTS WEAR
• MOUNTING ORIENTATION IMPORTANT
• SIZE
• ACCURACY

22. 22
VIBRATION
MEASUREMENT ACCELARATION
TYPES OF ACCELEROMETER
•PIEZOELECTRIC
•STRAIN GAGE
•PIEZORE SISTIVE
•VARIABLE CAPACITENCE
•OTHERS

23. 23
•MEASURES ACCELARATION
•VERY SENSITIVE
•CONTACTING
•MEASURES ABSOLUTE CASING MOTION
•MEASURES VERY LOW FREQUENCY
•MEASURES VERY HIGH FREQUENCY
VIBRATION
PIEZOELECTRIC ACCELEROMETER

24. 24
VIBRATION
WORKING PRINCIPLE OF PIEZOELECTRIC SENSOR
•PIEZOELECTRIC MATERIAL (SENSING ELEMENT)
PLACED UNDER LOAD USING MASS
•AS STACK VIBRATES
CRYSTAL IS SQUEEZED OR RELEASED
•CHARGE OUTPUT
PROPORTIONAL TO FORCE
•CONVERT
CHARGE OUTPUT INTO VOLTAGE OUTPUT

25. 25
.1 1 10 100 1000 Hz
.6 60 600 6,000 60,000 cp m
FREQUENCY
1,000
100
10
1
0.1
0.01
0.001
0.0001
EU
(mils pp)
(ips)
(g)
VIBRATION V/S FREQUENCY
•VERY LITTLE AMPLITUDE IN TERMS OF ACCELERATION IS
PRODUCED AT LOW FREQUENCY
•MUCH LARGER AMPLITUDE ARE PRODUCED IN TERMS OF
DISPLACEMENT
VIBRATION
DISPLACEMENT (mils pp)
VELOCITY (ips)
ACCELERATION (g)

26. 26
VIBRATION
CAUSES
•UNBALANCE
•MISALIGNMENT
•ECENTRICITY FORCES
•BENT SHAFT

27. 27
VIBRATION
CAUSES
•FAULTY ANTI FRICTION BEARING
•FAULTY JOURNAL BEARING
•MECAHNICAL LOOSENESS
•ELETRICAL PROBLEM

28. 28
VIBRATION
CAUSES
•BAD GEARS
•RESONENCE
•AERODYNAMIC/ HYDRAULIC FORCES
•RECIPROCATING FORCES

29. 29
VIBRATION
CAUSES
•RUBBING
•ROTOR FLEXIBILITY
•BEATS OR PULSATION

30. 30
VIBRATION
EQUATION FOR SINUSOIDAL MOTION
DISPLACEMENT (D),VELOCITY (V), ACCELERATION (A), AND FREQUENCY (F)
D =
V
πF =
G
2π²F²
=
2V²
GA
V = πFD = 2πF = √ 2
GAD
A =
2π²F²D
G
=
2πFV
G
=
2V²
GD
F =
2π²D
GA
√ =
V
πD
=
GA
2πV

31. 31
VIBRATION
FREQUENCY ANALYSIS
WHY?
•FREQUENCY SPECTRUM GIVES DETAIL INFORMATION
ABOUT SIGNAL SOURCE, CAN NOT BE OBTAIN FROM
TIME SIGNAL
•GIVES INFORMATION ABOUT VIBRATION LEVEL
CAUSED BY ROTATING PARTS
AMPLITUDE
TIME
AMPLITUDE
FREQUENCY

32. 32
START
SHAFT DISPLACEMENT FROM
JOURNAL CENTRELINE, Xf
Xf = sin ℓ
2L
PEDESTAL / BEARING
STIFFNESS RATIO, α
α = {Z2 / Z1}
PEDESTAL
VIBRATION
MEASUREMENT
SHAFT ABSOLUTE
VIBRATION
MEASUREMENT
SHAFT RELATIVE
VIBRATION
MEASUREMENT
ISO 10816 ISO 7919
Xr ≥ 0.1
α > 1
Xr < .01
α < 1
1/5 < α < 5
FLOW DIAGRAM FOR SELECTION OF MEASUREMENTS & EVALUATION OF VIBRATION SEVERITY

33. 33
VIBRATION
ISO STANDERED

34. 34
2
1
0
-1
-2
Transducer
output
voltage
Distance µ
Target Shaft
Ds + 200µ
Ds
Standard set gap
Measuring range
Zero Point
PROBE
With Zero
With gain
TYPICAL RESPONSE CURVE & MEASURING RANGE VIBRATION PROBE
SHIN NIPPON VIBRATION PROBE
( IHI AIR COMPRESSOR )

35. 35
BENTLEY NEWADA 7200 SYSTEM REPLACED WITH SHINKAWA
VM15 DUE TO OBSOLENCE

36. 36
TK3-2 VIBRATION CALIBRATION INSTRUMENT

37. 37
TK3-2 SPECIFICATIONS

38. 38
EXCIT
VIBRATION
TYPICAL TURBINE MEASUREMENTS

39. 39
EXCIT
VIBRATION
TYPICAL TURBINE MEASUREMENT

40. 40
VIBRATION
SHOCK PULSE METHOD
•IS A SIGNAL PROCESSING TECHNIQUE USED TO
MEASURE METAL IMPACT AND ROLLING NOISE.
•THIS TECHNUICQUE USED WHERE METAL TO METAL
CONTACT IS SOURCE OF WEAR.
•UNIQUE FEATURE OF TECHNOLOGY IS THE
SEPERATION AND ANALYSIS OF VIBRATION
FREQUENCY.

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VIBRATION
VIBRATION MEASUREMENT / ANALYSIS INSTRUMENTS

42. 42
Axial Vibrations:
Axial vibrations are the most commonly measured and
are typically measured in a three axis (x.y,z) orthogonal
arrangement. These are the “up/down”, “sideways” and
“front/back” directions. Ingenious setup of uniaxial
and triaxial vibration sensors around equipment and
structures permits the measurement of different
vibration modes.
VIBRATION

43. 43
Torsional Vibrations:
Torsional vibrations typically occur in rotating
equipment such as shafts driven by motors, engines and
turbines. Torsional vibration can be detrimental to rotating
equipment and is typically superimposed on the static torque
already experienced by power transmission shafts. This
may result in extremely high stresses leading to catastrophic
failure. Strain gages and telemetry equipment are used to
measure torsional vibration and stresses in rotating
equipment.
Torsional vibrations can also occur in cantilevered
equipment or Structures with offset centers of gravity. For
non-rotating equipment vibrating in a torsional mode, two
axial accelerometers may be used to obtain frequency and
phase information

44. 44
WHEN IT COMES TO YOUR MACHINES,YOU CANT
AFFORD TO MISS
ALWAYS FOR ACCURATE VIBRATION
MEASUREMENTS