Learning how to interpret a vibration signal from rotating machinery25 June 2021

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Vibration analysis is a powerful way of looking at rotating machinery, not just for one-off diagnosis of a problem but for ongoing machine condition monitoring. There are recognised routes to learn how to do this. By Toby Clark

A number of companies and organisations offer training, most of it accredited by two main bodies: BINDT (the British Institute of Non-Destructive Testing) and Mobius Institute, a private company which also provides training materials. Both organisations offer courses related to the ISO 18436-2 standard (see box below). Among the companies that have accredited training programmes in the UK are PCMS Eng Group, Baseline-RTS and RMS.

Another provider is consultancy AVT Reliability, which offers courses accredited by Mobius Institute as well as undertaking vibration analysis – whether by collecting its own data, or analysing data collected by customers. Graham Scrogham, principal consultant and external training manager, says: “We do courses ranging from a one-day ‘Introduction to Vibration Analysis’ – that is just a basic overview – to a more comprehensive two-day introduction, and then we have our ISO 18436 courses.” These courses are:

  • Category 1: basic vibration analysis training
  • Category 2: intermediate
  • Category 3: advanced

Each course is similar in content to ISO 18436 courses offered by other training providers. He continues: “ISO courses tend to be more academically-based. There are practical simulators and equipment on the course to get a feel of the subject, but we are based in a classroom for the entirety of those courses.

“For the introductions, there tends to be a bit of hands-on experience, but courses can be tailor-made depending on client needs”. For instance, Scrogham says the course “can be on how to use the vibration monitoring equipment rather than analysing the data – we have clients where they have staff collecting the data, but we analyse the data remotely.”

“We can also do lubrication analysis for rotating equipment; that’s another key part of condition monitoring which should not be forgotten about."

“We have staff at clients’ sites collecting data and analysing data, but we see the benefit of training, and we need to know that our staff are trained to a recognised standard. We were originally an asset management firm and the training has grown out of that. Clients were asking for training and it’s developed from there.

“We recently signed a partnership with Mobius Institute. It produces its own training materials in accordance with ISO 18436, and it has also been able to develop an examination body.”

Incidentally, Mobius Institute has a good range of introductory videos about vibration analysis available for free on its YouTube channel: www.is.gd/tupage.

The format of training courses – whether from AVT or other providers – is pretty flexible: “We have the option to do a public course; normally we use a hotel or conference facility, or we do have some dedicated training facilities. Or if a client is after exclusive training, we can go to a client site.”

But with COVID restrictions, in-person training is not always possible: “We can also do it online. There are a couple of options: we can either offer a video-based online course where you get access to the materials for six months: you can watch the videos as many times as you like as you’re working your way through the course. Students can work at their own pace, and their company doesn’t have to release them for a full week in one go.” The course can involve up to 35 hours’ teaching, depending on the level.

“Or there is live instructor-led teaching: it’s just like being in a classroom, only you have the instructor at the end of a Microsoft Teams setup,” says Scrogham.

Vibration analysis does need an understanding of how the machine works, says Scrogham, and this means that “You do need to pace the training to the students’ abilities”.

Much of the course is taken up with using the equipment: “We talk about accelerometers, how they function, and how the data is collected – how the data collector processes the readings and gives you something that’s worthwhile.”

While AVT has its own brand of monitoring equipment, Machine Sentry, it trains clients on equipment from the whole range of suppliers: SKF, Pruftechnik, Erbessd Instruments and many others. “It all depends what the client wants,” says Scrogham. “A lot of clients want an integrated system – not just vibration analysis but also lube analysis, thermography, action notes etc. – but what you find is 99% of the time they are used as basic data collectors.

“The data collector can only do what you tell it to do, and if your set-up is looking at the wrong parameters, you’re not going to see the full picture of what’s going on in the machine. It’s not just about sticking the accelerometer on the machine and pressing go.”

BOX: ISO 18436

Vibration analysis training and compliance comes under an ISO (and BS) standard: ‘Condition monitoring and diagnostics of machines. Requirements for qualification and assessment of personnel’. Of particular relevance is ISO 18436-2: ‘Vibration condition monitoring and diagnostics’.


Vibration analysis using accelerometers (and sometimes velocity and displacement sensors) is a well-established discipline. But it has really come into its own in the last few years with the development of sophisticated software tools and the powerful computer hardware to run them. The instruments themselves have become more compact and rugged (almost every mobile phone contains a microscopic three-axis accelerometer these days, and some wireless models claim to have a battery life of up to 10 years) while data recording and analysis is easier and cheaper than ever before.

Straightforward single-axis measurements can be used to diagnose an out-of-balance component, while an experienced operator can spot a lack of lubrication in a bearing, or fluid cavitation in a pump.

Measuring in two or three axes provides more to work from: depending on the type of fault, the vibration changes differently across the axes, and all of this can be seen on a graph of vibration amplitude against time – a time waveform chart.

Vibration from additional components (for example, a fan) adds more frequencies of vibration, as well as harmonics: that is, multiples of the original frequency. All of this can be viewed easily on a frequency spectrum graph (such as the waterfall plot from the Digivibe MX M30 vibration analyser, top).

More information comes from a phase reading, when a rotation sensor is used to locate the timing of the vibration precisely in relation to the motion. This can identify how components relate to each other and pinpoint a vibration.

More sophisticated techniques include demodulation and enveloping, which can be used to detect problems such as bearing damage, and to even diagnose whether problems are in the bearing’s inner race, outer race or the rolling elements.

Orbit analysis is another technique suited to larger rotating machinery. This uses multiple proximity probes to determine the behaviour of components on a shaft. Finally, it is important to point out that vibration analysis complements other inspection techniques such as thermography and oil analysis.

Toby Clark

Related Companies
AVT International
Baseline Ltd
Pruftechnik Ltd
RMS Engineering
SKF (UK) Ltd

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