Index of Files 
    This is an index of the files available here for download.  Click on the filename to download it with your Web browser.  Some browsers provide more options if you right-click.

    Check back often, as I intend to add new files and updates as work progresses.  (Use your browser's refresh/reload to see the latest changes.) 
       
  • sts1solve.zip   Updated October 5, 2004 - 622k

    • An analysis of a fixed-end astatic leaf spring vertical seismometer, using the STS-1 vertical as a model.  Requires Excel 97 or later. With documentation in .rtf format.  May be modified to analyze similar designs. 
    Unzips to sts1solve.xls (642k) and sts1solve.rtf (2,878k).
  • sts1docs.zip  Updated October 5, 2004 - 365k

    • The documentation only, for the the above system.  Identical contents to the sts1docs.rtf file contained in sts1solve.zip, above.
    Unzips to sts1docs.pdf (928k)
     
  • feedback.pdf  Updated November 4, 1998 - 9k

    • A short tutorial on feedback system analysis and design.  Previously part of loop2.pdf.
    Part I of a series.
     
  •  complex.pdf   Updated November 23, 1998 - 15k

    • This is a short tutorial on complex variables, as needed for the analysis of the STM-8 loop.
    Part II of a series.
     
  •  loop3.pdf     Updated November 28, 1998 - 91k

    • This is an ongoing mathematical analysis of the feedback loop properties of a force-feedback seismograph.  Part III of a series.

    STM-8 block diagram and definitions of the blocks.  Both forward and feedback paths analyzed and results graphed along with loop-gain and response curves for velocity input only.  Includes asymptote and corner-frequency formulas and evaluation of  how some individual components are affecting the system.  Matches S-T Morrissey's data quite well. Considerable explanatory detail added to mathematics sections.  Short section on design approach for seismometer loops in general.  Work still in progress.  Plan to take a look at how the loop deals with noise and large signals.
     

  • driver2.pdf     Updated May 20, 2000 - 46k

    • Suggestions for modifying the STM-8 driver circuit and P/I/D branches in order to improve DC stability and resistance to spring creep and other slowly-varying forces.  Incorporates suggestions received from several sources on the previously proposed design modifications.  Addendum added to address noise issues raised by S-T Morrissey.
     
  • lpmeas2.pdf       Updated October 5, 2004 - 179k

    • How to measure the loop gain of a force feedback seismometer using an oscillator and oscilloscope.  This is packed with real world advice on how to measure and interpret the system loop gain.  Added info on using an audio transformer for voltage injection, also on the use of current injection.  Added explanations to unclear areas.
     
  •  zerohng2.pdf  Updated October 5, 2004 - 35k

    • The revised and corrected "zero force" hinge. A design for a vertical seismometer beam hinge having extremely low restoring force.
     
  •  bbab-028.pdf  Updated November 13, 1998 - 109k

    • Burr-Brown Corporation Application Bulletin 28 - "Feedback plots define op-amp performance"  This was written for operational amplifier designers, but is an excellent tutorial on all aspects of feedback design. Downloaded from the old Burr-Brown Web site.
     
  •  bbab-045.pdf   Updated November 13, 1998 - 73k

    • Burr-Brown Corporation Application Bulletin 45 - "Op-amp performance analysis"  Another excellent article for op-amp designers that contains much wisdom about feedback systems in general.
     
  • vertgeom.pdf   Updated October 5, 2004 - 141k

    • Comparison of the geometries of the LaCoste infinite-period vertical sensor design and a leaf spring vertical such as the STM-8. Includes graphs demonstrating infinite-period behavior.  When complete, I hope to also include some procedures to derive the physical design for an infinite-period leaf spring vertical.
     
  • vertgeom.dxf   Updated February 19, 1999 - 154k

    • CAD file of vertical seismo geometry.  Used to make two images in the above doc file.  (Use scale of 2.5" per inch.)
     
  • spring2.pdf    Updated October 5, 2004 - 60k

    • Previously updated to correct error in "Maximum Stress " values, also corrected one formula.  This is the result of a spreadsheet analysis of a strongly bent flat spring as used in the STM-8 vertical seismograph.  It contains data and graphs of the force-deflection curves of a 12"x3.5"x0.018" spring and measured data on a 0.5"-wide spring as a test of the theory.  Included is a discussion of the equations, which were derived from a section in  reddick.pdf .
     
  •  spring.txt   Updated October 27, 1998 - 83k

    • For those who would like to re-create the spreadsheet analysis, this is a tab-delimited text file which should import successfully into most any spreadsheet program.  Column widths and number formats will have to be re-entered, but all formulas are included.  Includes a short table of elliptic integrals which are required for the computation.  Results are in both pounds/inches and Newtons/meters.
     
  •  reddick.pdf     Updated October 23, 1998 - 169k

    • Three pages scanned from Reddick & Miller "Advanced Mathematics for Engineers" - 2nd edition, New York, John Wiley and Sons, 1938
    This is a (rather challenging) mathematical analysis of the curve taken by flat springs when loaded at the ends via hinges, known as the Elastica.  The results of this article were used to derive the formulas for computing force vs length for the STM-8 vertical seismometer spring in  spring.pdf .
     
  •  tempco.pdf     Updated October 5, 2004 - 24k

    • A short analysis of the temperature coefficient of the STM-8 leaf spring.


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