Introduction to FBAs

Force Balance Accelerometers (FBAs), like Tilia T130, are precision instruments used for measuring acceleration in applications where accuracy, stability, and dynamic range are critical. Unlike open-loop accelerometers, FBAs operate on a closed-loop feedback mechanism that maintains the proof mass in a null (zero displacement) position, allowing for highly accurate and low-drift measurements over extended periods. These accelerometers are essential in fields such as seismology and structural monitoring.

Operating Principle of FBAs

At the heart of an FBA is a proof mass suspended in a spring within a housing, capable of moving under the influence of inertial forces. When the system experiences acceleration, the proof mass tends to move relative to the housing. In a force balance configuration, this displacement is detected by a position sensor (typically capacitive), which triggers a feedback control loop. This feedback loop applies a restoring force via an electromagnetic actuator (such as a coil-magnet), counteracting the motion of the mass and keeping it at the null position. The current required to maintain the null position is directly proportional to the input acceleration, making it the primary output signal.

How FBA compare to MEMS

A force-balance accelerometer and a MEMS accelerometer differ significantly in performance. Force-balance accelerometers use a feedback mechanism to maintain the position of a proof mass, offering high precision, unmatched dynamic range and stability, making them ideal for seismic applications. In contrast, MEMS (Micro-Electro-Mechanical Systems) accelerometers are miniaturized chip devices commonly used in applications with lower requirements to sensitivity and stability and where cost is a bigger factor. While MEMS sensors provide adequate accuracy for many applications, they lack the sensitivity and low noise performance of force-balance types, which can offer a dynamic range several hundreds of times better than MEMS types. FBAs are typically required for scientific seismic measurements and for dynamic modal analysis.

Seisodin offers both FBA-based (Tilia T130) and MEMS-based (Tilia T100) accelerographs.

	Tilia T130 (FBA)	Tilia T100 (MEMS)
Dynamic Range	155dB	105dB