PSN-L Email List Message

Subject: further magnet ideas
From: Randall Peters PETERS_RD@..........
Date: Fri, 09 Nov 2007 07:53:07 -0500

    Don't know whether we qualify as 'great minds', but at least we're 'on the same sheet of music'.  The first thing I thought about following the 'obvious standard pendulum' was whether the idea could be extended to verticals--just as Meredith suggested.  Also, Chris alluded to another element of the
idea--rolling cylinders.
    Before the 'dangling pen' I had noticed that two cylindrical rare earth magnets roll together nicely.  If you make one stationary and 'ping' the other it oscillates nicely.  What's the primary source of damping?   Some is the rolling friction, and some derive from induced eddy current in earch.  If
we reduce the rolling part, who cares about the eddy current parts?  After all, they are part of the desired Q-reduction that has become standard to eliminate transient response of the instrument.  Thus an arrangement I think could have promise is the following.
    A few years ago, now retired Georgia Tech seismologist Tim Long (very highly honored in our state) sent me a picture of a vertical he designed.  Unlike with most instruments that use Lucien LaCoste's famous zero-length spring, Tim put the 'approximate' zero-length spring (probably a screen door
type) below the boom.  This is accomplished by flex-pivot elastic strips at the short end (top) of the U-shaped steel iron strip that serves as the 'backbone' of the instrument.
    I believe that Tim's flex-pivot strips could be replaced with two rare-earth magnets, one 'stuck' to the top of the frame and the other glued to the non-sensor end of the required non-ferrous boom.  The boom magnet would roll on the frame magnet, with the contact force being made small (the two
trying to pull apart) by 'proper' placement of each of the magnets.
   You amateurs are 'like a fresh cool wind' on a 'hot-as-hell Georgia August afternoon' and I love your enthusiam toward what might to the 'pro's' look like hare-brained ideas.  I look forward to additional brainstorming on these thoughts.

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