A multi-orientation low-frequency rotational accelerometer

We present a low frequency rotational accelerometer coined ALFRA with a few nrad/Hz readout sensitivity above 20 mHz and 0.1 nrad/Hz above 50 mHz. The ALFRA is a beam-balance style rotation sensor, which pivots about a cross flexure designed to allow mounting with any orientation, the axis of the pivot determining which rotational component is measured. The high sensitivity is achieved through the use of a walk-off sensor readout used in a feedback loop with an electromagnetic coil to keep the beam dynamically locked. The ALFRA is relatively compact for a ground rotation sensor, measuring at 780 × 240 × 55 mm³.