Modified magnetic damping on vertical seismometer.
I used two super magnets that were removed from computer hard drives. I sandwiched these two magnets between two large steel washers that are bolted onto a brass rod with brass bolts, and suspended this assembly from the spring within a brass plumbing fixture. An Edmund horseshoe magnet is attached to the end of the brass rod that holds the washer/magnet sandwich. Non-magnetic weights are added to the rod between the washers and the horseshoe magnet to adjust the period of the whole unit to one second. Vertical motions of the entire rigid assembly below the spring are damped by an induced electric current that is set up within the plumbing fixture. Additional images of this seiemometer can be found on our SIMA2 software web site: http://www.netquake.org/seismometers/vertical.htm.