INTRODUCTION TO VIBRATION MONITORING

INTRODUCTION TO VIBRATION MONITORINGKEVINCIM05WHAT 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 vibrationUnbalanced rotating partsEccentric rotorBent shaftsMisalignmentMechanical loosenessExcess wear

INTRODUCTIONAll 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 pickupsThree important vibration pickups areDisplacementVelocityAcceleration

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 accelerationThank you