Illustrated History of the Seismomeer Project, 1991 - 1998:
Long- and Short-Period Systems of 4 Seismometers, Each Using Apple IIe.
About 1991, I had the opportunity to use, on an indefinite loan basis, a one-second period vertical seismometer which was supplied by Penn State University. Although I had the ability to connect this unit to the Apple IIe and run it as a fourth input, my experience was that the three long-period units and the new short-period unit could not be integrated on the same system without compromising the output signals of one or the other. Because I had sufficient hardware for a second computer system, I decided to create a separate short-period system using a second Apple IIe and the SAS software. A one-second period horizontal seismometer then became available on the used equipment market, so I had Moravian College purchased it for $250. Unfortunately, it did not have an amplifier for its output, so I constructed one for it. At about this time, Jim Lehman of James Madison University made a tall home-made vertical unit of about a one-second period, which he loaned to me, also on an indefinite loan basis, for integration into my short-period seismograph system. He subsequently made a second vertical unit of about a one-second period, but with a much shorter design. Both his units used magnetic damping by having a copper plate suspended between strong magnets. I modified his damping mechanism on the smaller vertical unit to use a moving magnet within a brass plumbing fixture which is installed permanently onto the frame of the apparatus. This smaller unit, as modified, resided in the back of my classroom, along with the original long-period horizontal unit. I built amplifiers for both vertical units. Jim and I cooperated on a workshop, "Seismology in the Classroom: Sensor Design and How to Do It," which he presented to the National Science Teachers Association Global Summit on Science and Science Education in San Francisco, December 27 - 29, 1996.
At this point I had two independent seismic systems running on two Apple IIe's, and each system had one seismometer in the classroom and two others in the basement. Because the software could handle four inputs for each system, and because the desired outcome is to have three orthogonal orientations (N - S, E - W, and U - D), I decided to construct one more unit for each system to have all three orientations in the basement, where the noise level is less than the classroom, and to have one redundant direction for each system in the classroom. In building the needed new horizontal seismometer for each system, I decided to use a common frame and a common enclosure for both the short-period and long-period horizontal systems. Thus, by about 1998, I had finally achieved my objective of having a complete 3-axis system in the basement for both the short- and long-periods, and having one redundant seismometer for each system in the classroom.