A Simple Step-by-step Guide To Bearing Vibration Analysis

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Generally. when developing and testing bearings a simple step by step procedure should be followed.

A simple roller bearing
A simple roller bearing

For the even the simplest of tests bearing vibration analysis must measure vibration along with rotational speed in revolutions per minute (RPM).

Therefore, at least two sensors are required – an accelerometer to measure the acceleration or vibration and a tachometer sensor to measure the rotary position.

Generally, we would suggest an IEPE accelerometer with a suitable frequency range and amplitude range for the bearing in question and the speeds involved.

An IEPE accelerometer
An IEPE accelerometer

It is important to note that the shaft speed in RPM divided by sixty is not the maximum frequency of interest. The maximum frequency of interest could well be the rotation speed multiplied by the number of rollers or a number of phenomena in the race. Or, in the case of a fault, it would be the number of occurrences per revolution. The point to stress here is that there is no simple rule for the maximum desired frequency range. Only with experience & knowledge of the bearing can final test specifications be decided.

Roller thrust bearing
Roller thrust bearing

As a guide, the technology for the tachometer sensor is quite open. Many types of sensors are available including lasers, infra red sensors, magnetic or hall effect sensors and many others.

Tachometer sensor
Tachometer sensor

Generally, one ‘pulse per revolution’ (PPR) is enough in most cases. However, up to, say, 30 PPR would not be overdoing it. More than that is not required for this type of test.

Tachometer sensor
Tachometer sensor

With the sensors prepared the shaft should be run through a range of speeds. Typically, we might go from zero to the maximum operating speed.

Then with the data from the sensors the analysis can be completed.

The analysis would consist of a speed based waterfall. This is simply a series of FFT spectra shown at different operating speeds. This would be followed by order extraction.

A waterfall plot
A waterfall plot shown as a colour map

The order curves of the vibration signal can be used to find faults and identify good and bad bearings.

A typical set of overlaid order traces
A typical set of overlaid order traces

Further testing would have to be carried out to find the statistical average of a good or bad bearing or a particular faulty bearing.

Fundamentally it would be necessary to study the bearings dynamics to find the definition for a good or bad bearing and or what a fault looks like.

With regards to fault finding this can be a simple process of introducing a fault in a race, cage or even a roller itself.

Then by studying how these faults change the order curves it is possible to test new bearings and understand their internal state.

The following articles offer a more in-depth look at bearing analysis…

How Do I Analyze Bearings & Gearbox Vibration Using Demodulation Techniques?

How Do I Analyze Bearings & Gearbox Vibration Using Demodulation Techniques? (Part 1)http://blog.prosig.com/2014/05/01/bearings-gearbox-analysis-using-demodulation-techniques/Bearings and Gearboxes are fundamental components of rotating machines and are used in many industrial applications. These are critical components and as such any failure can prove expensive in bot…
Analyzing Bearing & Gearbox Vibration Using Demodulation Techniques? (Part 2)

Analyzing Bearing & Gearbox Vibration Using Demodulation Techniques? (Part 2)http://blog.prosig.com/2014/05/02/bearing-gearbox-vibration-analysis-using-demodulation-techniques-part-2/Understanding that modulation of primary fault frequencies may occur when analysing vibration spectra from bearings and gearboxes is important when diagnosing faults. However,…
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James Wren

Former Sales & Marketing Manager at Prosig
James Wren was Sales & Marketing Manager for Prosig Ltd until 2019. James graduated from Portsmouth University in 2001, with a Masters degree in Electronic Engineering. He is a Chartered Engineer and a registered Eur Ing. He has been involved with motorsport from a very early age with a special interest in data acquisition. James is a founder member of the Dalmeny Racing team.

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