Category Archive: signal processing

Mar 19

What is the maximum analysis frequency for a waterfall in DATS?

The maximum analysis frequency is always half the sample rate of the input signal. So if your data is captured at 50kHz the maximum analysis frequency will be 25kHz.

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Aug 28

What is waterfall frequency spacing? And how does the DATS parameter ‘Requested Frequency Spacing’ work?

Let us try to understand what waterfall frequency spacing is. Waterfall frequency spacing is the gap between spectral lines in an FFT plot. For example, if you had an analysis frequency of 0Hz to 100Hz and 100 spectral lines, then Frequency Spacing is 1Hz. So why is there a ‘Requested Frequency Spacing’ and an ‘Actual Frequency …

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Aug 20

What is “waterfall smearing”?

Waterfall created using a suitable frequency resolution

When analysing a waterfall or performing order analysis it is important to consider the frequency resolution or the frequency spacing. There is often a desire to increase the resolution to finer and finer detail. But that is a process of diminishing returns, and actually fraught with danger. And that danger is waterfall smearing.

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Jul 28

Multiplane Balancing – Zero Imbalance or Specified Imbalance

In the DATS Multiplane Balancing Software, there are two options, optimise for ‘Zero imbalance’ or optimise for ‘Specified imbalance’, but what is the objective of these two options?

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May 13

What engineering decisions are made by measuring a power spectrum?

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.

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May 09

What Is A Load Spectrum?

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…

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May 06

How Do I Convert To Decibels?

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?

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Mar 12

What is Auto Spectral Density?

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.

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Feb 05

What Sample Rate Do I Use To Measure Whole Body Vibration?

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. …

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Nov 11

Relative signal levels of a sinusoid with and without background noise

Spectrum level of 35Hz sinusoid

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 …

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