Vibration Rectification and Thermal Disturbances in Ultra Precision Inertial Sensors

Advanced inertial MEMS sensors facilitate achieving superb precision and resolution in measuring translational and rotational displacements, down to femtometers and milli-arcseconds. At present such performance is possible only in measurements of a very short duration, typically below 1 second. As this duration increases, the precision rapidly deteriorates. However, experimental accelerometers indicate the possibility of measurements with sub-micron precision for up to 30 seconds. For longer measurements, e.g., up to 5 minutes, the errors increase. However they still remain below 100 μm. The main cause of errors is a strong amplification of low frequency disturbances and distortions introduced by the sensors. It occurs when acceleration and angular rate are converted to the translational and angular displacement, i.e., during the integration. Thus, the key to maximizing the performance of inertial displacement sensors is a reduction of their low frequency disturbances. In the top tier sensors the key components of the disturbances include (1) the inherent thermodynamic and electrical noise, (2) chaotic mechanical phenomena, and (3) nonlinear distortion. The presented research is concerned with these three areas. It focuses on the identification and correction of errors which deteriorate a stability of the sensors’ bias, in particular on the vibration rectification error (VRE) and temperature variations due to the actuation in servo accelerometers. The investigated accelerometers are high performance sensors, digital and analog, whose total harmonic distortion is in the range from 1% down to a few parts-per-million (i.e., <0.001%). The objective is to develop on-line corrective filters capable of reducing the overall low frequency distortion below 0.00001%.