How to analyse vibration measurements

And which softwares can and should be used in the process?

I've recorded vibrations, how to analyse them?

How to analyse vibrations is great question to ask yourself. But first of all, let us congratulate you on doing a great job in acquiring the vibration measurements! But, as you have found this article you are most likely thinking about what the next step can be to understand the vibrations that you have just measured. And we are here to help! When we started, we were in the same position as you are know – so let us share our knowledge with you! 

When you have recorded the vibrations you are interested in, it is time to start analysing! Jump down to the section “Which type of analysis can I perform?” and we will tell you more! 

PS! If you have found this article but wondering how you actually can record vibrations, you can take a look at the ReLog (which is our vibration data logger), and this article where we compare the ReLog with a few of our competitors. 

How can I use my vibrations measurements?

Definitely a good question! We do have to assume that by ending up on this page, you have drawn the conclusion that you could benefit from measuring vibrations in some way. And it is a bit tricky to provide accurate advice without knowing too much about your specific situation. But, we have put together the most normal reasons that our customers purchases the ReLog to measure vibrations in the article “How to use vibration measurements?” and what info it provides them with. 

Engineers inspecting industrial asset
A team of engineers inspecting an industrial asset after having performed vibration measurements

Which type of analysis can I perform?

Once you have recorded vibrations, there is a multitude of analysis that you can perform depending on what it is that you would like to analyse. We have written a longer piece on how to analyse vibrations (link) where you can dive deeper into the world of analysing vibrations. 

But, to cover the basics within frequency domain vibration analysis (which is what we used most of the time), let us give you an overview of FFT, PSD, and Spectrogram analysis. 

FFT” – Calculates the discrete Fourier transform of the signal. This provides information about the average spectral content in the signal. The resolution of the FFT is directly proportional to the length of the measurement and the sample rate used. 

PSD” – The PSD is based on the FFT algorithm, but normalizes the values to frequency bin width. Practically, this reduces the influence of sampling duration on the spectrum. If a random signal is sampled for 10 seconds, or 100 seconds, the spectral content will appear to be different if using FFT, although the signal is similar throughout the measurement. With the PSD however, they will be similar, despite the difference in signal length.

Spectrogram” – A spectrogram is computed by calculating several FFTs, each for an individual segment of the time-domain signal. The segments together span the entire signal, and may be overlapping. This gives insight into how the frequency content changes over time in the signal. It may be useful for e.g. tracking how the operating speed of a motor changes throughout the measurement.

If a machine or assets start showing sign of wear, performing a vibration analysis is a great starting point for a root cause analysis to try to determine what have made the machine to start to act abnormally. A good read on how to get started is to head over to Wikipedia and set up your structure on how to perform the analysis. We recommend including a step where you measure vibrations at different spots on the machine and compare the vibration levels and ask yourself, is there a logical reason why the vibration is/isn’t different? And simply start working your way towards the root cause.
PSD analysis of vibration signal

Example: A PSD analysis carried out in the software VibInspect offered by us a ReVibe Energy

Which software can I use to get started?

When it’s time to perform the actual analysis there are many different softwares out there that you can use. Depending on how advanced your skills are when it comes to vibrations and programming, you should consider if you do best in using less complex, easier and often free software or if you would like to go for the bulkier softwares that has more capabilities but more often than not requires programming skills on your part. In this article, we have gone through the different available options on the market to make things easier for you. But to give you a quick hint of which softwares that we think you should consider using, we have listed the different softwares below: