A digital control system which is completely under computer command has been constructed to make possible fully automated control of random-noise vibration tests. The system is capable of providing real-time analysis with a continuously improving confidence level, and because the computer-controlled system can be preprogramed, it is possible to verify spectral test patterns prior to actual testing and to avoid operator error in setting up test parameters. The digital control system includes a Fourier processor, which is a special-purpose computer with a hard-wired, built-in algorithm for effecting a fast Fourier transform of time samples of the acceleration signal. During the test, the spectral response is displayed on a cathode ray tube which is integral with the Fourier processor, and a digital plotter is interfaced with the computer to plot results upon completion of the test. Test results are expressed as a power spectrum and in spectral ratios. Some of the attractive features of the vibration testing are: the short time required to reach a steady state, the increased accuracy of spectrum definition (there are no gaps as in the conventional noise sources), and a true Gaussian amplitude distribution of the resulting signals. The computer-controlled vibration testing system possibly can be used for controlled shock-tests; for example, with the described system, it is possible to introduce initially the response characteristics of the total test system, and then to devise an input pulse which can produce the desired acceleration transient. Such a test would be operated as a semi-closed loop system.

  • Supplemental Notes:
    • This article appeared in a publication Analytical Techniques: A Compilation.
  • Corporate Authors:

    National Aeronautics and Space Administration

    400 Maryland Avenue, SW
    Washington, DC  United States  20546
  • Authors:
    • Chapman, C P
    • Sotomayor, B
  • Publication Date: 1975-1

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Filing Info

  • Accession Number: 00128507
  • Record Type: Publication
  • Report/Paper Numbers: NASA CR-2028
  • Contract Numbers: MFS-24402, NPO-11612, MFS-16968
  • Files: TRIS
  • Created Date: Apr 21 1976 12:00AM