From: SFPhysics@aol.com
Date: Fri, 21 May 1999 20:54:18 EDT
Subject: Simple Seismograph?
To: pinhole@exploratorium.edu
I was involved in setting up the mechanical (antique) seismograph at the
Randall Junior Museum in San Francisco. In order to do mechanical
amplification to make a mark on the smoked drum the weight was massive. Most
seismic movement is very small and thus either mechanical or electronic
amplification is needed. With its' low sensitivity I was soon asked to make
an electronic seismograph amplifier and Stan Oliver of the Sidewalk
Astronomers made the transducer.
The Radio Shack Science Project book by Forrest Mims (#276-5018) has a very
simple magnet hung on fishing line over a wire coil which provides the
induced EMF when any horizontal motion occurs. A circuit with an OP Amp does
have to be built. If you are one of the few enlightened schools with an
Electronics Lab (Electric Shop), ask the teacher to throw the circuit
together. The output can go to a strip chart recorder, an oscilloscope, or
just an LED that lights for a quake. The small Neodymium magnets given out
at a recent PTRA make the unit work with extra sensitivity. In fact, you
will grow to hate streetcars, prestressed concrete floors which give under
changing weight loads, heavy lab carts being moved, etc. ..... ;-)
Have fun,
Al Sefl
Physics is finding out how God made the universe, wound it up, and made it
tick. A.S.