Broadband Seismometer Observer

Built-in mass zero-position adjusting mechanism to perform automatic mass adjustment


The 151B series Broadband Seismometer, “Observer”, is a force-balance feedback sensor available with frequency bandwidth 0.0083 Hz (120 sec) – 50 Hz, and 0.016 Hz (60 sec) – 50 Hz flat to velocity. The 151B Observer contains three independent sensors (one vertical and two horizontal) with built-in electronic feedback circuit, control and power conversion circuits, featuring low noise, large dynamic range and easy installation and use.

The 151B Observer has built-in leveling and mass lock/unlock facilities. The leveling mechanism includes two bubble levels, three adjustable feet and three locknuts which are located on the seismometer’s chassis.

The 151B Observer has a built-in mass zero-position adjusting mechanism to perform automatic mass adjustment. As soon as the seismometer is powered it checks the zero position of each component’s mass and automatically adjusts the zero position if needed.

The 151B Observer is a low noise seismometer (see next tab for Power Spectral Density plot). The low self noise performance makes the 151B-120 an ideal seismometer for local, regional, and global seismicity studies in different installation configurations, including observatory and portable, surface and posthole applications.


  • High performance broadband seismometer
  • Low self-noise over a wide bandwidth
  • Portable design
  • Low power consumption
  • Force-balance electronic feedback
  • Robust mass locking mechanism
  • Easy installation

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