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Subject: new style vertical seismometer
From: Randall Peters PETERS_RD@..........
Date: Thu, 14 Feb 2008 13:56:00 -0500

Those of you who like to build things might want to try your hand at a new design for the old
LaCoste spring vertical seismometer.  Internal friction that limits performance has with
previous designs been mainly concentrated in both (i) spring, and (ii) axis.  My design can
radically reduce the hinge force influence, which should improve performance. A prototype is
pictured at
     The key to the smaller reaction forces at the hinge (pair of ball-point pens) is to add an angled
boom appendage that allows the zero-length spring itself to be vertical, as opposced to the usual
orientation (inclined)--and to place the inertial masses such that the center of mass is close to where the
spring passes through the split region of the horizontal segment of the boom.
    Although the prototype is shown with an SDC array to sense displacement, the instrument can be
configured to operate with a magnet/coil (Faraday-law) velocity sensor.


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