PSN-L Email List Message
Subject: A simpler Shackleford-Gundersen frame
From: meredithlamb meredithlamb@.............
Date: Sun, 22 Sep 2002 21:07:22 -0600
For a "down and dirty & cheap S-G frame":
A concrete paver and or about 5 ceramic bricks could also
be used as a S-G "frame" (one could use more bricks laid
flat of course). The concrete paver could be the base. Two
pairs of bricks end on end atop the paver, with the fifth brick
being the crossover piece. Most (U.S.) bricks have 3 holes in
them, likely two of the outside holes downward could suspend
the S-G hinges/boom/mass. Probably a concrete drill
and using a old threaded tap size, could give the 3 "setcrews"
action for adjustments....but even here, simple wedges could
be subsituted. Epoxy or even cement could be used for glueing
the thing together.
One might not even need a "boom", if another brick is used as
the "mass".....as two thin spaced magnet wires are likely strong
enough to support it. One could adjust the wire lengths for
the period somewhat. I use 0.001" thick by 0.0250 wide by
1.5" length brass strips as the hinges in my S-G's with a ~ 3
pound mass as its needed for the normal period and tilt
sensitivity of a Hall sensor....none have broken yet over
acouple years or so since installation.
Most bricks are electrical insulators and that helps. There
is probably some iron oxide in some bricks, but I doubt its
sufficient to have much influence over its mass weight inertia
versus any introduced magnets. Probably the lighter in color
the brick; the less the iron or other magnetic contaminants
Yes; one could attach a coil....or other wires for whatever sensor
arrangement is desired. What the heck....its going to be set up in a
vault or basement anyway and theres NO known "spiffy" seismo
fashion appearance magazine reporters around (ha) and this
possible ultimate in simplicity will get you recording alot faster.
One thing for sure, it will be quite sturdy (and heavy) which
Damping could be via a oil van/tank or a eddy current damping
add-on on the "paver" base itself. The damping aspect maybe
the most time consuming aspect overall.
Have to admit, I have no such "critter" here though...ha.
OK.....you could paint it "professional" white, if its
appearance is more "critical".....to your personal ego
standards....on the other hand...auto "chrome" paint could
somewhat mask the true nature of the "critter"....ha. The
primer and paint helps prevent water absorption expansion
and contraction problems around the cement joints...apply
any paint after a sufficient cementing drying time has expired.
Take care, Meredith Lamb
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