Seismometer built by James Lehman and
modified by Joseph J.
Gerencher, Moravian College, PA
Explanatory notes by J. Gerencher
Pictures by David Skoupil.
The vertical seismometer is
kept at the rear of the Earth Science classroom within a Plexiglas
enclosure to minimize the effects of air currents. Its frame
consists of soldered copper plumbing pipes that are attached to a
particle-board base with threaded steel connectors. A spring is
hung from the center of the pipe frame via a threaded bolt so the
vertical distance between the top of the suspended portion can be
adjusted to maintain an optimal separation relative to the coil below.
This is a view from above showing the
suspended magnets inside the copper plumbing fixture for the magnetic
damping.
This close up shows details of the
magnetic damping system. Super magnets are sandwiched between
steel washers that fit within the copper plumbing fixture. Note
that the spring is attached to the vertical brass threaded rod via a
small hole that has been drilled through the rod near its upper end.
This photograph shows the two super
magnets that are sandwiched between the steel washers. In normal
operation, the sandwiched magnets and the washers fit closely within the
copper plumbing fixture without touching it. The original
design by Jim Lehman used a copper plate that was suspended below the
spring and two magnets that were attached to the copper frame by the
brass bolts and brass nuts. These bolts and nuts are now used to
hold the copper plumbing fixture.
The bottom of the unit shows the pick-up
coil on the base and the suspended horseshoe magnet above it. Also
easily seen is the super magnet "sandwich" within the copper plumbing
fixture. Between them are aluminum weights to increase the
suspended mass in order to achieve a period of one second. The
horseshoe magnet, the aluminum weights, and the damping magnet
"sandwich" are all mounted on a threaded brass rod using brass nuts and
brass washers.
The pick-up coil fits within the
suspended horseshoe magnet without touching it.
This is another view of the damping
magnet and copper plumbing fixture assembly. The brass nuts were
soldered onto the copper plumbing fixture so the threaded bolts could
hold the plumbing fixture rigidly.
The damping magnets are sandwiched
between the heavy steel washers. These magnets are super magnets
that were probably originally used in old computer drives.
The connection of the spring to the
copper pipe frame is accomplished by a threaded bolt. Nuts on the
bolt allow it to be adjusted vertically and rotated in the horizontal
plane. When the nuts are tightened, the bolt is fixed in both
directions. The bottom of the bolt is drilled with a small hole to
hold the top portion of the spring. The bottom nut secures the
spring to the bolt.
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Last modification
22.09.2005 20:57:33
