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Below 2 images are horizontal Lehman Seismometers with 25 second resonant periods with Chapman magnet and sensor design using NdFeB magnet material. See here for design details.

Lehman East-West Seismometer

Lehman North-South Seismometer

Below are image files for a Force-Balance-Horizontal seismometer built along the design of Dave Nelson's and Brett Nordgren's Force-Balance_Vertical Inyo seismometer. The seismometer has both a low and high sensitivity over a frequency range of 76 seconds to 20 Hz. The low-gain sensitivity is 7.50 volts/cm/sec. The high-gain sensitivity is 375 volts/cm/sec. See here for sensor construction details.

Force Balance Horizontal E-W Low Gain Seismometer

Force Balance Horizontal E-W High Gain Seismometer

Below are image files for a Force-Balance-Vertical seismometer built along the design of Dave Nelson and Brett Nordgren. The seismometer has both a low and high sensitivity over a frequency range of 100 seconds to 20 Hz. The low-gain sensitivity is 7.50 volts/cm/sec. The high-gain sensitivity is 375 volts/cm/sec. See here for construction details.

Force Balance Vertical Low Gain Seismometer

Force Balance Vertical High Gain Seismometer

Infra-Sonic Atmospheric Pressure vs. Time

The above display is a plot of differential atmospheric air pressure recorded by comparing at moment of measuring and that of a 470 ml reference volume with a calibrated leak. The time-constant of the reference volume and calibrated leak is 220 seconds. See here for sensor construction details.

The seismometer data is updated every 10 minutes. Send an e-mail if you have any questions.