The machine needs to have a stable surface and it needs to be mounted properly so that it does not tip over when the earth begins to shake. When the earth moves, the instrument case will move, and the seismometer, which is inside of the case, stays still. The case will move around the seismometer, and this is what helps to record the magnitude of the shaking.
In the past, a pendulum was utilized as the seismometer. However, today, they make use of electromagnetism via a large magnet permanently affixed inside of the case. It is the movements of the magnet that will generate small electrical pulses, which are then sent to a computer and recoded in a seismogram. This is the readout that can provide specialists with an indication of just how strong the earth movement was. They are sensitive enough to record quakes that are too minor to be felt by people.
A seismograph is a specialized instrument that can measure and record details about ground motion. They are used to measure earthquakes, eruption of volcanos, and other types of seismic activity. They are useful to those who study these movements and those who perform environmental tests.
Seismographs are available from many manufacturers around the world today. Some of the options available include those from companies such as Nanometrics, Green Globe Line, Co., NOMIS, Geostuff, GeoSonics/Vibra-Tech, Heritage Group, Inc., Seistronix, and ESS Earth Sciences. With all of the options available, it should be possible to find a quality seismograph that will work for your needs.