[An Introduction To Vibration Analysis – Part 5] Welcome to Part 5 of our ongoing introduction to the world of vibration and acoustic measurement and analysis. Here, we look specifically…
[An Introduction To Vibration Analysis – Part 4] Welcome to the fourth part of our ongoing introduction to the world of vibration and acoustic measurement and analysis. In this post,…
[An Introduction To Vibration Analysis - Part 3] Modal analysis is one of the most widely adopted vibration measurement techniques for studying the dynamic behaviour of structures and mechanical components.…
[An Introduction To Vibration Analysis - Part 2] Introduction This post on vibration measurement techniques is the second in our series, introducing vibration analysis. Future posts will continue the exploration…
The following post on Joseph Fourier is our second in the On The Shoulders of Giants series. It is hard to overstate Joseph Fourier's importance in the field of sound…
[An Introduction To Vibration Analysis - Part 1] Introduction For professionals delving into the worlds of automotive, aerospace, or industrial engineering, vibrations are not just mere oscillations; they're a symphony…
This article will look at the basic steps needed to measure noise & vibration in rotating machines. We won’t look in great detail at some of the techniques involved – we deal with these elsewhere on the blog. This material is suitable for a newcomer to the field who understands the basic concepts of noise & vibration analysis but has not dealt with rotating machinery before.
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When using vibration data, especially in conjunction with modelling systems, the measured data is often needed as an acceleration, as a velocity and as a displacement. Sometimes different analysis groups require the measured signals in a different form. Clearly, it is impractical to measure all three at once even if we could. Physically it is nigh on impossible to put three different types of transducer in the same place.
The 2013 Annual Prosig Prize for Engineering at Portsmouth University has been awarded to Peter Thompson for his project “Vibration Analysis of Aircraft Structures (Airframe)”. Peter completed his study at the…
The use of a vibration condition monitoring system for monitoring vibration from large rotating machines fitted with fluid-filled journal bearings such as steam or gas turbines is well understood. Vibration from these components generally falls within the main harmonics or orders of the shaft rotational speed such as 1st, 2nd 3rd or 4th harmonic. Some energy may also exist below the 1st order, called the sub-synchronous component. Most energy exists below 1KHz and so standard displacement probes or velocity transducers are generally fitted. The Prosig PROTOR system collects this data in amplitude and phase form, relative to a ‘once-per-revolution’ phase reference signal, as standard and allows data to be displayed in real-time as mimic diagrams, trend plots, orbit and vector displays.
Creating a good quality tachometer signal is one of the hardest parts of analyzing rotating machinery. So what happens if we have missing tachometer pulses? The data looked great until we tried to perform some in-depth torsional vibration analysis. And now we no longer have the component or vehicle to retest it. Do we have to scrap the whole test? Was all that time wasted? Not necessarily…
It sometimes occurs that signals are captured with A-weighting applied to the data by the acquisition device. This can be a problem if, for example, you wish to use the data in a hearing test or to use it for a structural vibration analysis. Now, A-weighting allegedly mimics what the ear does to a signal. If we play back an A weighted sound then we perceive a double A-weighted signal which is clearly not intended. When doing structural work it is usually the lower frequencies, say 2kHz or less, that is generally required. A-weighting seriously attenuates the low frequencies and also applies gain above 1kHz.
A common requirement to measure overall level vibration (or noise) as a function of time. Now, the overall level is a measure of the total dynamic energy in the signal. That is it does not contain the energy due to the DC level, which is the same as the mean value. The overall level is often loosely referred to as the signal RMS value. However the formal definition of the RMS level is that it contains the DC level as well as the dynamic energy level. If only the dynamic contribution is required then the measure needed is, strictly speaking, the Standard Deviation (SD). Sometimes it is useful to refer to the SD as the Dynamic RMS.
