Technical Papers

Vibration Testing Technical Papers


Improving SRTD With Resonance Phase Settings

Author: Philip Van Baren
Appeared in: Sound & Vibration Magazine, October 2013 pp 13-15.

Traditionally, when test engineers performed "sine resonance track and dwell" tests they have controlled the frequency of the resonance with little concern for the phase of the resonance. There is some good reasoning to this. Since a resonance occurs when a material's vibrations are reinforced (constructive interference) by the "reflected" waves in the material, it can be assumed that the ideal phase value for a resonance is 90 degrees. However, in reality this theoretical phase value of 90 degrees could be different. The phase value may be affected by the location of the accelerometer or due to a lag in the reading of instrumentation. When these real-life factors are considered, the test engineer should be concerned about the phase value of the resonance... Read Full Article


Using Kurtosion® to Accelerate Structural Life Testing

Authors: Joel Minderhoud, Philip Van Baren
Appeared in: Sound & Vibration Magazine, October 2010 pp 2-6.

Life testing using controlled random excitation is a long- accepted means of fnding design and/or assembly faws. Class- general broadband spectra, such as the NAVMAT profle, permit testing without initially knowing the specifc resonances of a new package. Now kurtosis control allows such tests to be conducted in a fraction of the time required for a Gaussian drive signal to precipitate failures. However, the kurtosis control needs to be properly implemented to circumvent interference from the Central Limit Theorem. A unique feature within the Vibration Research Corporation (VRC) Kurtosion® process allows resonant fatigue as well as simple static failure tests to be accelerated... Read Full Article


Does your Controller Square with Chi?

Authors: George Fox Lang, Philip Van Baren
Appeared in: Sound & Vibration Magazine, October 2009 pp 8-16.

"Why does the random test spectrum look ragged?" is a frequently asked question. It is actually a far deeper question than most interrogators realize. This article reviews the statistical nature of a random test's spectra. We will provide an answer to this nagging question; provide some valuable test planning information and present methods to evaluate your controller's statistical performance... Read Full Article

Spreadsheet



How Well Does 3 Approximate Infinity - Understanding 3 Sigma Clipping in Random Shake Tests

Authors: George Fox Lang, John Van Baren
Appeared in: Sound & Vibration Magazine, March 2009 pp 9-16.

Random vibration testing presents a host of new and often confusing concepts to the test engineer. Among these, the notion of 'clipping' or 'limiting' the excitation signal to "±3 Standard Deviations" has caused undo confusion. This paper attempts to explain what 3 σ clipping is all about and how it came to haunt us. Given the erosion of written history with time, we will do better at the former objective than the latter.

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The Fatigue Damage Spectrum and Kurtosis Control

Authors: John Van Baren, Philip Van Baren
Appeared in: Sound & Vibration Magazine, October 2012 pp 10-13.

The accumulated damage that a product experiences on the field due to the variety of stresses placed upon it will eventually cause a failure in the product. These failure modes can be replicated in the laboratory using random vibration testing. During the past several years, the vibration industry has been introduced to Kurtosis Control - a new technique that brings about these failure modes in the laboratory in a more realistic and speedy fashion. The Fatigue Damage Spectrum (FDS) is an effective tool that can show the damage a product will experience at a particular frequency and the effect Kurtosis Control has on the random vibration test. Kurtosis Control is a more effective method than traditional random vibration tests because it brings products to failure more quickly. The Fatigue Damage Spectrum shows the increasing fatigue damage across all frequencies that accompany the increased kurtosis levels that cause the faster product failure. The FDS is another great tool that clearly illustrates the effectiveness of Kurtosis Control.

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Accelerometer Calibration Using the VR9500

Author: Kevin Van Popering
To be presented at: NCSL International Workshop & Symposium 2015

This paper describes back-to-back accelerometers and the process of using these accelerometers to calibrate other sensors. The process is described using a step-by-step tutorial including customizable test setup, required equipment for calibration, and the other considerations that need to be made when conducting calibration procedures. The paper logically walks the reader through the calibration process as if they were using a VR9500 vibration controller and VibrationVIEW software from Vibration Research Corporation. Other topics include basic accelerometer properties and definitions, piezoelectric sensor limitations and miscellaneous pitfalls associated with accelerometer calibration.

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Improving Transportation Industry Random Vibration Tests - Kurtosion and SRS

Authors: John Van Baren, Philip Van Baren
Appeared in: Sound & Vibration Magazine, September 2012 pp 18-19.

The transportation industry historically has used Gaussian random vibration tests to simulate real-world transportation data. However, examination of real-world transportation data reveals that transportation data is Non-Gaussian in nature. Consequently, transportation test engineers should simulate the real-world data using Non-Gaussian random vibration. Non-Gaussian random vibration (Kurtosis control) increases the number of large peak accelerations (that arise in field data due, in part, to the pot-holes of transportation) that the Gaussian random vibration tests "average-away" with their averaging techniques. By implementing Kurtosis control, the transportation industry would be well on its way to making their laboratory simulation tests much more realistic. And this, in turn, would result in better packaging - putting more products in the customer's hand without damage.

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Statistical Properties of the Random PSD

Author: Philip Van Baren
Appeared in: Sound & Vibration Magazine, March 2012 pp 12-13.

This document describes the statistical properties of the PSD of a Gaussian Random waveform, including tolerance bands, confidence intervals, and degrees of freedom (DOF).

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Fulfilling MIL-STD-1540D-Tolerance

Author: John Van Baren

Is your Random Vibration Testing fulfilling MIL-STD-1540D-Tolerance on Vibration Controllers

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MIL-HDBK-340A, Vol. 1, Table III


KURTOSION® - GETTING THE KURTOSIS INTO THE RESONANCES

Author: Philip Van Baren, John Van Baren
Presented at: SAVIAC 2007.

Traditional random tests, using a Gaussian distribution, have not satisfactorily tested products in a realistic manner because the Gaussian distribution method fails to bring into the test the large peak accelerations which cause product failure. The key to bringing those large peak accelerations into the random vibration test is to use a kurtosis control method. Kurtosion® , the patented technique developed by Vibration Research Corporation, is a kurtosis control method that can effectively bring large peak accelerations into the random vibration test. This technique has been criticized by some who appeal to the Papoulis Rule a rule that indicates that all systems tend towards Gaussian distribution. However, while the Papoulis Rule indicates the output of highly filtered systems tend towards a Gaussian distribution, it does not claim they actually are Gaussian. Test results obtained at VRC with their newly developed kurtosis control technique clearly show that non-Gaussian distributions can indeed be created at product resonances, regardless of the Papoulis Rule.

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Examining the Dynamic Range of Your Controller

Author: George Fox Lang, Philip Van Baren
Appeared in: Sound & Vibration Magazine, August 2007 pp 12-20.

Dynamic range is one of the fundamental metrics describing the capability of a shaker controller. We all know that dynamic range describes the span of small-to-large acceleration amplitude that can be properly controlled during a test. Since modern controllers are digital instruments, we also know the dynamic range to be six times the number of bits in the analog/digital converter. But what do we really know? Let's examine the dynamic range of a vibration controller more scientifically.

Read Article (as PDF) - VR8500
*Updated* Read Article (as PDF) - VR9500


The Missing Knob on Your Random Vibration Controller

Author: Philip Van Baren
Appeared in: Sound & Vibration Magazine, October 2005 pp 2-7.

Random vibration testing is the industry workhorse for simulating the environment for a broad range of products. Tests are typically specified by defining a spectrum shape and overall RMS amplitude. The test controller then causes a measured reference acceleration to match these specified parameters. The controller forces a shaped-random response with a normal or Gaussian amplitude distribution. However, experience has shown that such tests may be too conservative for some product/environment combinations. The test does not produce the same damage statistics observed in the field. Adding a third control dimension provides more realistic random vibration tests that better match the damage potential of the actual environment. That third dimension is kurtosis control, which matches the amplitude distribution of the test to that of the environment.

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The Third Dimension of Random Vibration Control

Author: Philip Van Baren

Random vibration testing is the industry workhorse for simulating the environment for a broad range of products. Tests are typically specified by defining a spectrum shape and overall RMS amplitude. The test controller then causes a measured reference acceleration to match these specified parameters. The controller forces a shaped-random response with a normal or Gaussian amplitude distribution. However, experience has shown that such tests may be too conservative for some product/environment combinations; the test does not produce the same damage statistics observed in the field. Adding a third control dimension provides more realistic random vibration tests that better match the damage potential of the actual environment. That third dimension is Kurtosis control, which matches the amplitude distribution of the test to that of the environment.

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Kurtosis - The missing dashboard knob.

Author: John Van Baren
Appeared in: Test Engineering & Management Magazine, October/November 2005 pp 14-16.

Many test personnel have recognized that random testing, while good, has shortcomings when it comes to simulating the real-world environment. As a result, over the years, there have been many vibration testing method modifications to address these shortcomings. In the automotive world, technicians often see that random tests do not find product faults that should show up when vibration testing. To make random testing more effective, they sometimes take the random spectrum, and increase the level accoreding to their own internal, home-cooked formula. The level may be increased so the random peak g levels match the real world.

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Computing Random Acceleration, Velocity, and Displacement Values from a Breakpoint Table

A helpful guide for calculating acceleration, velocity, and diplacement RMS from a breakpoint table.

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Test your product using sine or random?

Authors: John Van Baren, Philip Van Baren
Appeared in: Test Engineering & Management Magazine, June/July 2004.

As you know, in the vibration world, there are quite a few test "types" to which you can expose your product. The major choices are Sine, Random, Classical Shock, Transient Shock, Field Recorded Time History, Sine-on-Random, Random-on-Random and Sine-and-Random-on-Random. Frequently, our customers will request advice on which of these types of test to run on their product, and in particular, how to choose between the two most common test types: sine or random. Their desire is to know which test, sine or random, is best to most quickly pinpoint flaws in their product. If they can only run one test, either sine or random, which should it be? Recently, we received an even more specific request from a customer. This customer (Don) presented both a sine test and a random test and wanted to know, given both a sine test and a random test, how he could determine which is the most severe? Read Full Article


What Is Random Vibration Testing?

Author: John Van Baren
Appeared in: Sound & Vibration Magazine, February 2012 pp 9-12.

There is a degree of confusion about the different kinds of vibration tests available to the vibration testing engineer. Difficulties encountered usually center on the difference between sinusoidal vibration (sine testing) and random vibration testing

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Ask the IEST Testing Experts

Author: John Van Baren
Appeared in: Test & Management Magazine, August/September 2007

How do I get the peak levels back up to 120 G peaks when running my random profile? There are several solutions implemented in the real world to "solve" this issue...Read Full Article


A Comparison of Simultaneous and Sequential Single-axis Durability Testing

This article appeared in Experimental Techniques
Volume 30 Issue 5 Page 32 - September/October 2006
Authors: R.M. French, R. Handy, H.L. Cooper (2006)
Experimental Techniques 30 (5), 32–37.

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Slide Decks

  1. Kurtosion 2008 NoVI TestExpo.pdf
  2. Saviac 2007
  3. Original Kurtosion Power Point.pdf
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