The Gaussian Probability Density: Part 4 of 4 of Understanding Random Vibration Signals

If an experimental measurement matches the Gaussian PDF model, the Gaussian model can then be used to draw many important inferences about the measurement. Many statistical curve-matching tests are available to establish if a measurement is Gaussian. These include the Kolmogorov-Smirnov (KS), Shapiro-Wilk and Anderson-Darling tests. For practical purposes, most well-fixtured and well-conducted random shake tests will produce data that pass any of these model-matching statistical tests for Gaussian behavior.

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Histograms and The Amplitude Domain: Part 3 of 4 of Understanding Random Vibration Signals

The mean and variance dominate statistical measurements in both the time and frequency domains. They are also reflected by so-called amplitude domain measurements. The most basic of these is called a histogram. To measure a histogram, break a signal’s potential amplitude range into a contiguous series of N amplitude categories (i.e. x is between a and b) and associate a counter with each category.

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Control of a Random Vibration Signals: Part 2 of 4 of Understanding Random Vibration Signals

One statistical description measured during a random shake test is the Control Spectrum. Specifically, this variable is often the output of an accelerometer mounted to the shaker table. The sensor’s voltage output is scaled to engineering units of acceleration, typically gravitational units (g’s) sampled at a fixed interval, Δt. This time-sampled history is transformed to the frequency domain using the Fast Fourier Transform (FFT). In this process, a series of “snapshots” from the continuous time waveform are taken and dealt with sequentially.

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Terms of Probability Statistics: Part 1 of 4 of Understanding Random Vibration Signals

Verifying the robustness of products (or their packaging) by subjecting them to shaker-induced vibration is an accepted method of “improving the breed”. While shock bumps and sine sweeps are intuitively obvious, random shakes with their jumps and hissing are anything but. Even the language of a random test is confusing at encounter. Let’s try to improve upon that first introduction to random signals!

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Crystal Instruments Receives US Patent for Kurtosis Control

This patent protects an important contribution to CI’s Vibration Control System (VCS) business, its unique means of controlling the kurtosis of a random vibration signal. A conventional (Gaussian) random signal has a peak-to-rms ratio (the crest factor) of about 3. In contrast, a high kurtosis random signal of the same RMS intensity, with identical spectrum shape, can have a significantly higher crest factor.

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