Vibration:
It is the response of a system to an internal or external force which causes the
system to oscillate.
Vibration
Analysis: Vibration analysis is a non-destructive technique
which helps early detection of machine problems by measuring vibration.
Basic
Theory of Vibration: It follows sine curve.
Frequency:
How
many times oscillation is occurring for a given time period?
Units:
CPS
(Hz), CPM
Amplitude:
It
is the magnitude of vibration signal.
Units:
Micron,
Mm/Sec, M/Sec2
Physical
Significance of Vibration Characteristics:
Frequency - What is vibrating?
Source
of the vibration.
Amplitude - How much is it vibrating?
Size
(severity) of the problem.
Phase
Angle - How is it vibrating?
Cause
of the vibration.
Frequency
Measurement:
60
RPM = 1 Rev / s = 1 Hz
Amplitude
Measurement:
1.
Displacement: Total distance traveled by the mass.
Unit:
Microns
2.
Velocity : Rate
of change of displacement. It is the measure of the speed at which the mass is vibrating during its oscillation.
Unit:
Mm/Sec,
Inch/sec
3.
Acceleration: It is the rate of change of velocity.
The greater the rate of change of velocity the greater the forces (P=mf) on the
machines.
Unit:
M/Sec2,
Inch/sec2
Physical
Significance of Vibration Amplitude:
Displacement: Stress Indicator
Velocity :
Fatigue Indicator
Acceleration: Force
Indicator
Advantages
of Using Velocity:
• Flat
frequency range compared to displacement & acceleration.
• Almost
all machines generate fault frequency between 600CPM to 60KCPM
• Velocity
indicates fatigue.
• Velocity
is the best indicator of vibration severity.
Scales
of Amplitude:
Peak - a
Peak
to Peak - 2a
RMS - 0.707 a
Average - 0.637 a
