Capacitive force-balance system for measuring small forces and p

Details Capacitive force-balance system for measuring small forces and p Capacitive force-balance system for measuring small forces and p

1990-02-07

1992-02-04

Raevis, Robert

Measuring and testing

Surface and cutting edge testing

Roughness

73724, G01B 528

Patent

active

050850709

ABSTRACT:
A force balancing method and apparatus detects small changes in force or pressure. An LC tuned circuit having a capacitor with at least one movable plate senses force or pressure changes. Deviations in the phase of the response of the tuned circuit are compared to the phase of a driving reference oscillator to generate an error signal. The error signal is used to control the oscillator to increase or decrease its output amplitude for driving the tuned circuit. As a result the electrostatic force across the capacitor plates tends to change in such a way as to precisely balance the effect of external force or pressure changes. The system therefore operates in a force-balance mode and in such a way as to provide a high sensitivity together with a precisely controlled stiffness. This system is particularly applicable to high sensitivity microphones, micro-topography, and atomic force microscopy.

REFERENCES:
patent: 3076870 (1963-02-01), Jones, Jr.
patent: 4227419 (1980-10-01), Park
patent: 4359892 (1982-11-01), Schnell et al.
patent: 4644798 (1987-02-01), Tamura et al.
patent: 4665739 (1987-05-01), Mizuno
"The Application of Capacitive Transducers to Sound Velocity Measurements in TTF-TCNO", by T. Tiedje et al., J. Acoust. Soc. Am., vol. 65, No. 5, May 1979, pp. 1171-1180.
"The Precise Measurement of Small Capacitances", by A. M. Thompson IRE Transactions on Instrumentation, Dec. 1958, pp. 245-253.
"The Design and Some Applications of Sensitive Capacitance Micrometers", by R. V. Jones et al., Review Article, Journal of Physics E: Scientific Instruments, 1973, vol. 6, Printed in Great Britain, pp. 589-600.

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