Nano-Torque Induction System based on Watch's Hands Rotation in Gravity Field
(2024) 20TH INTERNATIONAL SYMPOSIUM ON GEODYNAMICS AND EARTH TIDES — Location: Strasbourg, France (25.August.2024)
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- Abstract
- Generation, detection, and calibration of narrow torques are crucial in establishing the scale factor of many instruments, including tidal tiltmeters, gravimeters, or micro-strain gauges. In this study, we investigate the calibration of a nano-torque inductor relying directly on the Earth’s local gravitational field which serves as a secondary reference to the SI fundamental standards. In the first part, we describe the sensing device, consisting of a horizontal two-plate balance equipped with a capacitance bridge transducer. Its symmetry effectively mitigates undesired effects by inherently rejecting common mode uncertainties. Secondly, the establishment of the scale factor of the system was determined with repetitive cycles of a lever-arm modulated known torque, establishing the correspondence between variations in signal output frequency and sensed torque. As each capacitance’s signal is recorded independently, we access common thermal effects by adding the two signals. Conversely, the output signal is produced by subtracting the two frequency-modulated signals. A quartz watch was placed on the device, and the tilt caused by the shifting center of mass of the movable electrode as the hands rotate was monitored, and we showed that it could serve as a portable calibrated torque inducer. Employing continuous signal acquisition, the effects of the watch were isolated by stacking, leveraging its known periodicities (minute, hour, mid-day). The sinusoidal motion (122.5 nNm peak to peak for the smallest periodicity) intrinsic to the watch’s operation was then extracted thanks to the signal processing method’s effective attenuation of random noise which scales inversely with the square root of the number of the aggregated sample size. Calibration of a gravimeter was then experimented with the calibrated watch and allowed continuous calibration with long term stability as the order of magnitude of the torque induced is the same as the gravitational effect measured.
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Citations
Lebrun, J., & et al. (2024). Nano-Torque Induction System based on Watch’s Hands Rotation in Gravity Field. 20TH INTERNATIONAL SYMPOSIUM ON GEODYNAMICS AND EARTH TIDES, Strasbourg, France. https://hdl.handle.net/2078.5/218178