1.
VIBRATION ANALYSIS FOR CBM
BASIC CONCEPTS – UNIT 1
BY DIBYENDU DE

2.
ALL MACHINES VIBRATE
Because of:
Inertia
Stiffness
Imposed forces

3.
VIBRATION MONITORING
What causes Vibration ?
INDUCED FORCE
&
FREEDOM FOR MOVEMENT

4.
VIBRATION MONITORING
Types of Forces ?
Inertia Forces
Acceleration & Deceleration
Looseness & Impacts

5.
MACHINE VIBRATION IS COMPLEX
• Behaviour of each component creates their
own frequencies
• Frequency tells us about a possible problem.
• Amplitude tells us about the severity of the
problem.
• Multiple frequencies combine to produce the
overall vibration
• Vibration from 1 Hz to 1000 Hz captures
overall amplitude

6.
ONE CYCLE OF VIBRATION
• Movement of weight from neutral
position to upper limit
• Upper limit back through neutral
position to lower limit
• Lower limit to neutral position
• The movement of the weight
plotted against time is a sine wave
•

7.
FREE & FORCED VIBRATION
• With sudden impulse the system will
vibrate at its natural frequency
• Free vibrations die out with time if the
system is stable. (Bump test)
• Forced vibration are periodically imposed
on the system (like motor). The response is
also periodic

8.
FORCE, MOBILITY & VIBRATION
• Response to forced
vibration is not uniform at
all frequencies.
• Response depends on the
mobility of the structure
• Mobility varies with
frequencies. High at
resonance. Low where
damping is present.

9.
MEASUREMENT OF AMPLITUDE & FREQUENCY
Peak  for velocity and
acceleration (used for algorithms)
Peak to Peak  Displacement
RMS  Velocity & acceleration
(Europe) Energy content (only for
sine wave)
Average  Not used in vibration
analysis
Frequency = 1/Period (Hz/CPM)

10.
MEASUREMENT OF AMPLITUDE
Peak  for velocity and
acceleration
Peak to Peak  Displacement
RMS  Velocity & acceleration
(Europe) Energy content (only for
sine wave)
Average  Not used in vibration
analysis

11.
DISPLACEMENT, VELOCITY & ACCELERATION
What?
• Displacement = d = x = A sin (wt)
• Velocity = v = dx / dt = Aw cos wt = Aw sin
(wt + 90o)
• Acceleration = a = dv /dt = - Aw2 sin wt =
Aw2 sin (wt + 180o)
Why?
• Strain Energy ∝ to d2
• Kinetic Energy ∝ to v2
• Acoustic Pressure ∝ to a2
• Force

12.
VIBRATION - CAR ANALOGY
Low Frequency
Long period (T)
High displacement
Average Velocity
Low Acceleration
Medium Frequency
Medium period (T)
Average displacement
Average Velocity
Average Acceleration
High Frequency
Short period (T)
Low displacement
Average Velocity
High Acceleration

13.
THANK YOU FOR COMPLETING UNIT 1
CONTACT: FOR FACILITATED TRAINING
DIBYENDU DE, EMAIL ID: DDE337@GMAIL.COM