Example of performing a Moving Average

This tutorial guides a DATS user through the steps required to perform a moving average on a given signal. The tutorial explains the concept of the ‘Integration Length’ and the ‘Output Interval Step’.

Initially a signal is required to perform the moving average on. In this tutorial a sine wave will be generated. A sine wave is generated using the parameters shown in Figure 1.

Averaging Frequency Response Functions From A Structure

The following was written by Adrian Lincoln in response to a customer asking about averaging Frequency Response Functions (FRFs)

Further to your reply it should be noted that there is no such mathematical or physical quantity corresponding to an averaged structural FRF except in those special cases where you are testing a symmetric structure comprised of nominally identical components (such as turbine blades). For symmetric structures, where you can impact at a similar position on each component and measure the corresponding acceleration at a similar response position, then the individual FRF’s should have the same characteristics and therefore can be averaged.

For structures that don’t have multiple symmetric components then you should not perform any sort of averaging because the FRF’s will not have the same characteristics. For example, if you have beam-like structure and are measuring the FRF’s between different locations along the beam, then these FRF’s should only be averaged as moduli and not with respect to phase and coherence.

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.

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

What is “waterfall smearing”?

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. Continue reading What is “waterfall smearing”?