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How Do I Get An XYZ Resultant Waterfall

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A user has three signals captured using a triaxial accelerometer and asked “What is the simplest way to get the XYZ resultant from run-up file?” He had tried forming a resultant of the raw time histories, but didn’t fully understand the resultant time history.

Of course, the correct way of processing the data is to calculate the individual waterfalls from the x, y & z data and then calculate a resultant waterfall.

The Calculate X,Y Z resultant module calculates the resultant modulus of the X,Y and Z input signals. It squares each value, sums them and takes the square root. Consequently the result is always positive (as it is a square root). So performing this analysis on time histories (with positive and negative amplitudes)  gives you the modulus result which is always positive and looks completely different from the input time histories.

Example worksheet calculating a resultant waterfall from x, y & z measurements from a triaxial accelerometer
Example worksheet calculating a resultant waterfall from x, y & z measurements from a triaxial accelerometer

The example worksheet above does the following:

  1. Takes the dataset AutomotiveImpactStrip.dac from the examples\data\General Data folder
  2. Selects the signals Seat Track X, Seat Track Y and Seat Track Z. You can change it if you want to analyse other signals.
  3. Performs a waterfall on each of these
  4. Takes the 3 waterfall results and performs a resultant calculation on them.
  5. The result shows rms (square root of the sum of the squares) waterfall.

Click here to download the worksheet

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Dr Mike Donegan

Senior Software Engineer at Prosig
Mike graduated from the University of Southampton in 1979 and then went on to complete a PhD in Seismic Refraction Studies in 1982. Mike joined Prosig as a special applications engineer. He now researches & develops new algorithms for Prosig's DATS software and assists customers with data analysis issues.

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