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Additional Information – Moravian CollegeThe seismic signals available via the SIMA2 software from Moravian College include output from four seismometers that all operate with home made amplifiers and, consequently, tend to be less than perfect. Their outputs tend to drift with humidity changes, in particular when the building goes from the heating season to the cooling season, and vice-versa.
Here is a description of the output of each of the four devices on the Moravian College system, organized by channel of transmitted data.
First Channel (Channel 0)
This home-made seismometer of the Lehman design is a twin of the one that is in the Earth Science laboratory. It is oriented to sense the N - S horizontal component of the ground motions. Its pipe frame is mounted on a base made of wood chip particles. The seismometer boom is adjusted to have a period of 18 seconds. The whole device is kept within a Plexiglas case. The home-made amplifier is the follower-with-gain design using the dual 741 IC’s.
Horizontal N-S seismometer in basement location.
Second Channel (Channel 1)
As of 19 February 2003, the vertical seismometer was changed to a Kinemetrics, Model SV-1, which has a 5-second period. I purchased this unit on auction from e-Bay approximately a year previous. I constructed an amplifier for the SV-1 that is similar to those used for the horizontal units. This seismometer was originally sited in the Science Division laboratory, but in July, 2003, was moved into the basement with the other two horizontal seismometers.
Some of the example seismograms posted on this web site were made prior to 19 February 2003, so they used a different vertical seismometer then above than the SV-1 above.
Third Channel (Channel 2)
This seismometer is oriented to sense E – W motions in the horizontal plane. It is kept in the basement of the science building immediately beneath the Earth Science classroom. It is adjusted to have a period of 18 seconds. The amplifier is home made, using two 741 IC’s in the follower-with-gain configuration. The seismometer is also home made, is of the Lehman design, and has a pipe frame that is mounted to a base made of wood-chip board. The pipe frame supports the long period (18 second) seismometer on one side and a short period (1 second) on the other side, with both enclosed under a common Plexiglas cabinet to keep air currents from affecting the units. Both use motor oil damping. The basement floor on which the seismometer rests is made of concrete poured onto excavated, compacted soil. Unfortunately, we have no access to bedrock at our science building site.
E-W horizontal long-period unit (right)
and short period unit (left)
on a common frame in basement
Fourth Channel (Channel 3)
This home-made seismometer of the Lehman design is kept in the Earth Science classroom/laboratory, on a metal table that is located along a wall that separates an equipment area from the classroom. It is oriented to sense the N-S ground motions. Persons walking in the classroom, or in the equipment area on the other side of the wall, disturb this seismometer. A television screen in the front of the room shows the output from all four units, but students can see the effects of their motions around the room on the trace from this particular unit. The gain is set higher on the amplifier for this unit than the others so the motions of people in the room are more apparent and more impressive.
N-S horizontal unit in classroom.
The outputs from the four devices are shown on the display below, which is portrayed by the original SIMA software (not the newer SIMA2 software). Notice that students walking in the classroom have disturbed that unit (the white trace), but not the traces of the other units. The identities of the traces are as follows:<>
First Channel (Channel 0) Red 18 second period N – S
Second Channel (Channel 1) Green 05 second period vertical
Third Channel (Channel 2) Blue 18 second period E – W
Fourth Channel (Channel 3) White 18 second period N - S <>
<>On the display screen, the direction toward the top of the screen corresponds to the following: North, East, and Up.
Seismometer display showing four seismometers in SIMA (not SIMA2) software.
Scroll bar at bottom of screen allows traces made previously to be viewed.
Note time stamp (date and time) on bottom of screen.
|Last Updated: July 5, 2005
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