We present a mechanical rotation sensor consisting of a balance pivoting on a tungsten carbide knife edge. These sensors are important for precision seismic isolation systems, as employed in land-based gravitational wave interferometers and for the new field of rotational seismology. The position sensor used is an air-core linear variable differential transformer with a demonstrated noise floor of \documentclass[12pt]{minimal}\begin{document}${1}{\,\times\, 10^{-11}}\textrm { m}/\sqrt{\textrm {Hz}}$\end{document}1×10−11m/ Hz . We describe the instrument construction and demonstrate low noise operation with a noise floor upper bound of \documentclass[12pt]{minimal}\begin{document}${5.7}{\,\times\, 10^{-9}}\textrm { rad}/\sqrt{\textrm {Hz}}$\end{document}5.7×10−9 rad / Hz at 10 mHz and \documentclass[12pt]{minimal}\begin{document}${6.4}{\,\times\, 10^{-10}}\textrm { rad}/\sqrt{\textrm {Hz}}$\end{document}6.4×10−10 rad / Hz at 0.1 Hz. The performance of the knife edge hinge is compatible with a behaviorur free of noise from dislocation self-organized criticality.

A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems.