Vibration analysis

Vibration analysis

Vibration analysis is a very powerful condition monitoring technique which is becoming more popular and a common practice in industry. As a general rule, machines do not breakdown or fail without some form of warning, which is indicated by an increased vibration level. Here we explain in details about:

  • Machine vibration,
  • Causes of vibration,
  • What is vibration analysis,
  • Why it helps to reduce vibrations, and
  • How to carry out vibration analysis.


Machine vibration

Machine vibration can be described as the oscillation of a machine and its components relative to a reference plane of measurement. Vibration in industrial equipment can be a symptom, or cause, of a problem, or it can be associated with normal operation.

For the most part, mechanical equipment is engineered to avoid vibration rather than produce it. Vibration can indicate a problem and if left unchecked can cause damage or expedited deterioration.


Most common causes of machine vibration

Imbalance, misalignment, wear and looseness are common factors to generate vibration.


Vibration due to the machine being more flexible in the horizontal plane. Also, imbalance is one of the most common machinery problems and imbalance produces a radial vibration, that is, part vertical and part horizontal. Because the machine is usually more flexible in the horizontal plane, excessive horizontal.

Imbalance could be caused by manufacturing defects (machining errors, casting flaws) or maintenance issues (deformed or dirty fan blades, missing balance weights). As machine speed increases the effects of imbalance become greater. Imbalance can severely reduce bearing life as well as cause undue machine vibration.

Misalignment /shaft runout

Vibration can result when machine shafts are out of line. Angular misalignment occurs when the axes of (for example) a motor and pump are not parallel. When the axes are parallel but not exactly aligned, the condition is known as parallel misalignment. Misalignment can be caused during assembly or develop over time, due to thermal expansion, components shifting or improper reassembly after maintenance. The resulting vibration can be radial or axial (in line with the axis of the machine) or both.

  1. Parallel misalignment happens when the two shafts to be aligned have centrelines parallel to each other, but the centrelines are offset.
  2. Vertical angle misalignment is a misalignment of two shafts in the vertical plane.
  3. Horizontal angle misalignment is a misalignment of two shafts in the horizontal plane.
  4. A combination of a vertical angular and offset misalignment occurs when one shaft is at an angle with another shaft, but both shafts still operate in the same vertical plane.
  5. A combination of a horizontal angular and offset misalignment occurs when one shaft is at an angle with another shaft, but both shafts still operate in the same horizontal plane.


As components such as ball or roller bearings, drive belts or gears become worn, they might cause vibration. When a roller bearing race becomes pitted, for instance, the bearing rollers will cause a vibration each time they travel over the damaged area. A gear tooth that is heavily chipped or worn, or a drive belt that is breaking down, can also produce vibration.


Vibration that might otherwise go unnoticed can become obvious and destructive if the component that is vibrating has loose bearings or is loosely attached to its mounts. Such looseness might or might not be caused by the underlying vibration. Whatever its cause, looseness can allow any vibration present to cause damage, such as further bearing wear, wear and fatigue in equipment mounts and other components.


What is Vibration Monitoring and Analysis?

Vibration monitoring and analysis is the process of capturing and analysing the vibration levels and frequencies of a machine and then using that data to analyse the machine’s health and its components.

Vibration monitoring is nothing but the diagnostic of a problem with the machine/equipment.


Where is Vibration Analysis Used?

Usually, Vibration analysis is carried out for condition monitoring on components of machinery and their critical rotating parts. These include:

  • Bearings, gears, shafts, freewheels
  • Gearboxes, motors, fans and drive-trains
  • Piston engines, reciprocate compressors, pumps

Apart from machinery and rotating parts, it’s also used to monitor vibrations in bridges, pipes, turbine blades, etc.


How to Measure Motor Vibration

Various form of equipment to measure Motor Vibration:

  • Sensor tags
  • Vibration recorders
  • Shaft sticks
  • Vibration meters
  • Proximity probes
  • Vibration data loggers
  • Accelerometers
  • Vibration measurement systems


Why Vibration Analysis?

Vibration analysis can be used to determine whether bearings have been properly installed. It also can be used to determine how well a machine is assembled. It can detect misalignment in a pump, for example, determining whether the rotating elements are binding, if the base is uneven, or if torsion exists between motor and pump.


Vibration Analysis Methodologies

There are two approaches to analyze vibration:

Time-domain analysis

The time-domain analysis refers to the waveform when the amplitude is plotted against time. As it measures the amplitude, it can monitor vibration levels. So, when vibration levels go beyond the pre-defined limit, it means that the machine is not in good health, and there’s an underlying issue.

Frequency domain vibration analysis

Frequency domain analysis helps detect abnormal vibrating patterns. The waveform (amplitude vs. time) is subjected to spectrum analysis or FFT (Fast Fourier Transform)/ HFFT (Hexagonal Fast Fourier Transform) to do the frequency vibration analysis. This results in frequency vs. amplitude and can help discover the periodicity of the collisions.

There are several types of asset classes that are ideal for vibration monitoring programs.

  • Fans and Blower Motor Vibration Monitoring
  • Pump Vibration Monitoring
  • Cooling Tower Vibration Monitoring
  • Conveyor Motor Vibration Monitoring
  • Dust Collector and Air Handler Vibration Monitoring
  • Crane and Hoist Motor Vibration Monitoring

A vibration Analysis Equipment is an instrument used to measure, store and diagnose the vibration produced by your machines. Vibration analysis equipments use FFT based tools to measure frequencies and identify the causes that originate them.

Digivibe M30

Vibration Analysis Equipment is an advanced and portable system designed to analyse machinery vibrations individually. On site balancing for 1 and 2 planes.

  • Frequency range: 1 Hz – 14 kHz
  • Resolution lines: 1,638,400
  • Simultaneous input channels: 4
  • Balancing capability: Yes
  • 3D simulations (ODS)


The Wiser 3X triaxial accelerometer also has the Wiser Vibe and Digivibe application compatibility.

  • Frequency range: 1 Hz – 14 kHz
  • Resolution lines: 1,638,400
  • Simultaneous input channels: 4

Phantom EPH-V11 (Permanent Vibration Analysis Equipment)

Phantom EPH-V11 is a wireless vibration sensor designed for permanent mounting. Phantom records 3 Axes vibration FFT. Long Life replaceable battery of 2 to 3 years.

  • Frequency range: 1 Hz – 10 kHz
  • Amplitude range: 32g
  • Resolution lines: 6,400

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