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Design of an electrostatic feedback for an experiment to measure G



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


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.
Review of Scientific Instruments


control system, electrostatic forces, gravitational constant, precision measurement


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],, (Accessed July 18, 2024)


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Created June 20, 2022, Updated November 29, 2022