The Amateur Scientist column in the January 2000 issue of Scientific American describes a magnetic gravimeter/seismometer.
The instrument was designed by Roger Baker and the article was writen up by Shawn Carlson, regular Amateur Scientist column writer and the founder of the Society of Amateur Scientists (SAS).
SAS maintains a web site that includes a forum for discussing Amateur Scientist projects.
Scientific American article
(a local copy).
Roger Baker's gravimeter web page
Society for Amateur Scientists (SAS),
SAS Gravimeter Forum.
Developing The Model
A good mathematical model that captures
the physics of the device is essential to understanding the instrument's
sensitivity to gravity and temperature.
The expected sensitivity to gravity of this device is very poor
and much smaller than its sensitivity to temperature or air pressure.
physical data about magnets.
Building The Probe
The probe, as described in the original Sci. Am. article, is a magnetic
floater held in suspension between two magnetic stacks.
The rigid framework of the device is made of cut glass held together by
silicone cement. A very pleasant combination of materials to work with.
The front end detector uses a paper flag attached to the floater and oscillating between a bright diode and a phototransistor.
The front end signal is amplified and controlled by a differential amplifier and feedback through a magnetic coil.
The device is very temperature sensitive so temperature monitoring and temperature control are essential.