David Lamb's "H" seismometer setup
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The above two photos are of Davids "H" PG seismometer
which uses a laser (red dot) and a photodiode sensor. The 3
magnets rest on a flat steel plate, and inbetween the two magnet channels,
are placed two steel spacers; the surface of which has been filed down
to create a slightly rounded shape to levitate and contain the "H" graphite
assembly in stable levitation for two directions. To prevent the
"H" assembly from touching the magnet walls, the weight of the assembly
must be balanced. The magnets polarity is such that the broadest
faces are the poles;
i.e., the top views of the magnet/s are one same pole,
while the bottom attached to the steel is the other pole. The seismometer
also acts like a "S-G", or a hanging pendulum.
Following Chris Chapmans idea of putting additional
sheet metal atop the outline of the magnets, the levitation is greatly
enhanced for this instrument; and has been incorporated a short time later
into this design that David operates.
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The above two photos are of Davids "H" actual PG assembly, including the damping silver plate and a partially painted mica sheet "flag", which partially interupts a part of the laser diode light, while part of the light goes to a photodiode sensor. The PG graphite is roughly 1.25" in length for the channels. The crossbar is ~ 1.25" across. Circa ~ early 2002.