Various human body vibration measurements and assessments are defined in the ISO2631, ISO5349, ISO6954 standards and also in the EEC vibration directive 2002/44/EC. These assessments are based on the analysis…
By power spectrum we are talking about an ASD (Auto Spectral Density) or PSD (Power Spectral Density). In fact PSD is often used when really ASD would be more correct.
Taking any signal and performing a frequency analysis using an ASD or a PSD will give the energy over a range of frequencies. (more…)
When engineers talk about the ‘Load Spectrum’ what do they mean?
There is no simple answer, simple terms like load and spectrum can be used in different situations and therefore to mean different things. However the most common definition of load spectrum is as follows… (more…)
Much confusion revolves around linear and non-linear numbers. The following outlines the mathematical process to convert from a number expressed in dB to a linear quantity. How do we convert to decibels and back again? (more…)
In our previous post on this subject we briefly looked at how we can use the detailed design information of bearings and gearboxes to look for specific fault conditions by collecting vibration information and analysing their frequency spectra. Amplitude modulation of the vibration signatures is common and we have seen how this causes side-bands to be present in the frequency domain.
The video below shows some examples of structural animation using Prosig's DATS software. https://www.youtube.com/watch?v=QsVzk0wwcR0
After finding the natural frequency of a system, what could be done to stop or reduce the systems resonance being excited? Basically put, how do we avoid resonance This is…
The Auto Spectral Density or Auto RMS spectrum analyses uses Fourier Transforms to process optionally overlapped sections of the input data. The result of each Fourier analysed section is called a periodogram. We then process all the resulting periodograms to produce a spectral result. (more…)
In this post we will first look at how to process data from rotating machinery. Then we will focus on shaft or gear train twist. Let's look at 3 different…
What sample rate should I use if I am measuring whole body vibration? Strict ISO8041 compliance imposes a minimum sample rate of 900 samples per second. This ensures the amplitude…
In the process of looking at some order data, a question about the accuracy of the measurement of the signal level of discrete frequency signals which were close to the general noise level. To answer this question, a small DATS worksheet was created which generated 2 signals. The first signal was a 35 Hz sinusoid which, by itself the spectrum level was measured to be approximately -9 dB (ref 1 V) as seen in Figure 1.
A method to identify subjectively objectionable disturbances (e.g. piston slap, valve tick,… etc) in internal combustion engines
The Prominence Ratio is a technique designed to see if there are any aurally prominent tones in a signal. Primarily, it is applicable where we have a noise source with…
When working in the synchronous/angle domain, how many samples per revolution are required to study a particular order.
To study the nth order we need 
Picture the scenario; you have captured some noise & vibration data from a rotating machine. Typically, this might be noise in a vehicle cabin, but could have been anything from…
When performing frequency analysis of vibration data for any application the resultant spectrum has both amplitude and phase components, therefore the phase component represents half of the information available and…
One of the most searched for and read topics on the Noise & Vibration Measurement Blog is that of converting between measurements of acceleration, velocity and displacement. To help anyone…
In the previous two articles (What Is Resonance? (Part 1) & What Is Resonance (Part 2)) in this series we have looked at how we can identify a resonant frequency.…
Understanding filters is actually simpler than it may first seem. Creating a filter is another story; it’s like being able to drive a car without having to know the intricate…
There are a number of ways to find the natural frequency (resonance) of a part like an automotive inlet manifold. Here are three different types of popular test techniques. But which one should you use and why?
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We were asked the following question…
I want to perform some cylinder head and inlet manifold vibration analysis, what should I do?
First we need to consider sensor selection (more…)
Assuming one wants a frequency spectrum from an acquired time measurement, it is generally accepted that averaging of a signal in the time domain is not very useful due to…
The relationship between sample rate and maximum frequency that can be analysed (called bandwidth) is a factor of 0.4. Or to look at it another way the sampling rate is…
Anytime you measure something which is changing with time, there are multiple ways to quantify the signal. For the purpose of this discussion, we will be talking about how to describe the…
Whether you call them spikes, glitches, anomalies or data dropouts, these phenomena have been a problem to engineers ever since they started recording data. There are any number of reasons…
