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…)
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…)
An investigation was made of a sample of automotive components where some were exhibiting a high frequency “tick” or rattle during each operating cycle. This feature could be heard above the normal operating noise. The problem this posed was to measure and analyze components in an objective fashion and classify components as “good” or “bad”.
The following article will attempt to explain the basic theory of the frequency response function (FRF). This basic theory will then be used to calculate the frequency response function between two points on a structure using an accelerometer to measure the response and a force gauge hammer to measure the excitation.
Fundamentally a FRF is a mathematical representation of the relationship between the input and the output of a system.
(more…)
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