INTRODUCTION TO

VIBRATION MONITORING

KEVIN

CIM05

WHAT IS VIBRATION?

• When a body is displaced from its equilibrium

position by the application of external force and

then released, it commences to vibrate.

Causes of vibration

• Unbalanced rotating parts

• Eccentric rotor

• Bent shafts

• Misalignment

• Mechanical looseness

• Excess wear

INTRODUCTION

• All operating machines gives rise to vibration.

• As the condition of machine starts deteriorating, the

corresponding vibration level also increases.

• By monitoring this vibration, it is possible to obtain

information about the machines condition

• Mechanical vibration is used as the reliable parameter to

measure vibration.

Machinery signatures.

• When the complex waveforms of machinery vibration are

broken down into spectral components, it may be defined

as the sum of harmonic functions of discrete amplitudes

and frequency, this is called as machinery signature.

Complex waveform

Machinery signatures in unbalanced shaft.

Broken spectral components

Selection of transducers

WHAT IS TRANSDUCER?

• A transducer is a device which transforms a non-electrical

physical quantity (i.e. temperature, sound or light) into an

electrical signal (i.e. voltage, current, capacity…)

• In other word it is a device that is capable of converting

the physical quantity into a proportional electrical quantity

such as voltage or current.

Selection of transducers.

• Sensitivity: The transducer must be sensitive enough to

produce detectable output.

• Operating Range: The transducer should maintain the range

requirement and have a good resolution over the entire range.

• Accuracy: it is defined as how close the output of the

transducer is to the expected value. High accuracy is required.

• Response time

It is also defined as the time required to observe the change

in output as a result of a change in input .

• Reliability:

Reliability is the ratio of how many times a system operates

properly, divided by how many times it is used.

• Size: Depending on the application of the transducer, the

size may be of primary importance

• Operating Principle: The transducer are many times

selected on the basis of operating principle used by them.

The operating principle used may be resistive, inductive,

capacitive , optoelectronic, piezo electric etc

• Environmental Compatibility: the transducer is selected

based on the various environmental conditions it can

work.

• Insensitivity to unwanted signals: The transducer

should be minimally sensitive to unwanted signals and

highly sensitive to desired signals.

• Cost: The cost of a transducer is an important

consideration, especially when many sensors are needed

for one machine

Based on vibration pickups

• Three important vibration pickups are

• Displacement

• Velocity

• Acceleration

DISPLACEMENT PICKUP

• Here the coil is excited by

the high frequency

oscillator.

• Varying the distance

between coil and shaft

produces change in

inductance and output

voltage proportional to

displacement.

Velocity pickup

• This probe is mounted on

vibrating surface.

• Relative motion between

coil and core produces

output voltage proportional

to velocity.

Acceleration pickup• The spring mass system

converts acceleration to

force, that force when

applied to piezoelectric

material produces change

in voltage proportional to

acceleration

Thank you