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. Contine reading
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… Contine reading
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? Contine reading
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. Contine reading
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 and phase characteristics of the applied weightings meet the required criteria. To take account of the anti alias hardware filter we would recommend 1200 samples/second. If non-strict compliance is used the minimum sample rate is 300 samples/second.
ISO2631-1 recommends a minimum data duration of 227 seconds. However, for greater reliability, 600 seconds is now considered essential. That is, a 600 second or longer signal will be more representative and will provide better quality results.
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.
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 samples per revolution. Contine reading
There are a number of ways to find a resonant frequency of a part like an automotive inlet manifold. Here are three different types of popular test technique. But which one should you use and why? Contine reading
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 Contine reading