GEOfba200 Force Balance Accelerometer

  • Low noise accelerometer for high precision and high dynamic range
  • Selectable full scale range +/-4g to +/-0.25g standard, higher gain set custom available
  • Wide passband DC to 215Hz, higher corner frequency custom available
  • Simple installation using a central fix bolt
  • Electronically adjustable DC offset
  • Power 9-18Vdc, 1.2W
  • Waterproof IP68 aluminum or stainless-steel casing

The GEOfba200 is a very low-noise triaxial force-balance accelerometer with a large dynamic range, suitable for seismology, hazard mitigation and civil engineering applications. The instrument has both a flat response to ground acceleration from DC to 215 Hz and a stable phase response within the passband. Output range is 40Vpp differentially and supports variety range of gain sets from +/-4g to +/-0.25g in the standard configuration and availability for higher gain set under request.

Due to it’s high dynamic range which exceeds 155dB the sensor provides from on-scale recording of earthquake motions to structural seismic noise monitoring and allows engineers to study motions at higher frequencies. The sensor allows easy field calibration through its calibration line.

GEOfba200 sensing element mechanism

Inside the GEOfba200 there are three similar accelerometers, orthogonally placed. The sensor is operating according to the force-balance principle as closed-loop sensor (servo accelerometer).

The motion of the seismic mass is monitored from a very sensitive capacitive transducer and a very low noise VHF preamplifier. The demodulator generates in-phase and low noise seismic signal which is fed back to the seismic mass through a phase compensator, a power amplifier and a fully symmetrical force actuator consisting of a double coil-magnet system. This design eliminates any non-linearity due to lack of symmetry. The output amplifier sets the selectable acceleration gain between +/-4g to +/-0.25g.

GEOfba200 block diagram

GEOfba200 self-noise

Red: 4g, Orange: 2g, Yellow 1g, Green 0.5g, Blue 0.25g

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