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CD-ROM Aktief 1995 #3
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CDA3.iso
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LEHMAN3.MOD
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1992-11-02
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Lehman Seismometer Modifications
By Terry Frost
1. Coil-Magnet: Horseshoe magnets from Edmund Scientific were $46.95 each.
Dairy Supply stores sell a 1/2" dia. 3" long, rounded end
"cow magnet" for about $3.00 (they are placed in cows stomachs
to pick up bailing wire). Use a solenoid type coil that has a
large number of turns of fine wire. Hole in center should be
about 1" in diameter. Magnet should be inserted only half
way into coil.
2. Knife Edge: Cut slot in end of Boom with a hack saw. Crimp slot slightly
closed in a vise. Break off a 1/2" section of an X-Acto knife
blade and insert it in the slot. While setting period of the
seismometer, tap back of blade above and below boom to assure
flush contact with bolt head. Epoxy blade and slot with 5
minute expoxy after final adjustment.
3. Weight: Melt 5-6 lbs of lead. Pour into 3/4" dia tin can. Cut can
Magnet away when cold. Drill 1/2" hole about 3/4" deep on the
Mount circumference of lead slug. Place magnet in hole. Peen to
hold tight. Drill boom mounting hole slightly off center to
balance system.
4. Nichrome: Use a guitar string obtained from a Music Store. The smallest
Wire metal one.
5. Damper: To eliminate cost of horseshoe magnets, use an oil dampening
system. Cut top off a plastic oil container (l qt. size).
Cut a paddle out of thin aluminum. Bend around boom and pop
rivet in place. Dimensions depend on container size and dis-
tance from boom to base. Dampening is varied by changing oil
depth. Container also acts as a boom stop.