This seismometer was built from a Dave Nelson and Brett Nordgren design. The model is named “Inyo” and is one of a series of broadband Force-Balance Vertical (FBV) seismometers by the designers. What makes this particular family of seismometers attractive for the amateur is that their designs achieve levels of sensitivity previously only available with high-level commercial instruments. The models are intended for construction by advanced amateurs and the designers make available CAD drawings, schematics, and all necessary technical information. Brett Nordgren maintains a website that includes a wealth of seismometer design information in general, and the team-designed force balance seismometers in particular. Of value to the amateur are Nordgren’s analytical tools that provide quantitative modeling of the feedback loop for those builders who want to modify their seismometer to achieve a particular response. Built as originally designed, the seismometer response is flat through the frequency range of 0.01 to 30 Hz.
The mechanical design is relatively simple and rugged and all components are easily constructed by anyone having basic metalworking and electronic skills. The electronics are contained on a single PC board yielding excellent performance.
This instrument is deployed within a pressure container to isolate it from barometric and temperature changes. It's signal is run into a Webtronics 16 bit A/D board (PSN-ADC-USB Version III) and analyzed using Webtronics WinSDR and WinQuake software.
If the energy propagation direction of an earthquake is favorable, this seismograph can pick up a magnitude 5.5 quake anywhere in the world.