Design of an electrostatic feedback for an experiment to measure G

Published

June 20, 2022

Author(s)

Stephan Schlamminger, Leon Chao, Vincent Lee, David B. Newell, Clive Speake

Abstract

The torsion pendulum at the heart of the BIPM apparatus to measure the gravitational constant, $G$, is used to measure the gravitational torque between source and test-mass assemblies with two methods. In the Cavendish method, the pendulum moves freely. In the electrostatic-servo method, the pendulum is maintained at a constant angle by applying an electrostatic torque equal and opposite to any gravitational torque on the pendulum. The electrostatic torque is generated by a servo. This article describes the design and implementation of this servo at the National Institute of Standards and Technology. We use a digital servo loop with a Kalman filter to achieve measurement performance comparable to the one in an open loop. We show that it is possible to achieve small measurement uncertainty with an experiment that uses three sets of electrodes for feedback control.

Citation

Review of Scientific Instruments

Volume

1

Pub Type

Journals

Download Paper

https://doi.org/10.1109/OJIM.2022.3182391

Local Download

Keywords

control system, electrostatic forces, gravitational constant, precision measurement

Citation

Schlamminger, S. , Chao, L. , Lee, V. , Newell, D. and Speake, C. (2022), Design of an electrostatic feedback for an experiment to measure G, Review of Scientific Instruments, [online], https://doi.org/10.1109/OJIM.2022.3182391, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=934716 (Accessed October 8, 2025)