Electrostatic accelerometer

• US 4,345,474 A
• Filed: 04/09/1980
• Issued: 08/24/1982
• Est. Priority Date: 04/11/1979
• Status: Expired due to Term

• Current Assignee: Societe D'Applications Generales D'Electricite et de Mecanique Sagem
• Original Assignee: Societe D'Applications Generales D'Electricite et de Mecanique Sagem
• Inventors: Deval, Alain
• Primary Examiner(s): Gill, James J.
• Application Number:
  US06/138,731
• Time in Patent Office: 867 Days
• Field of Search: 73/516 R, 73/517 B, 318/636, 318/648, 318/651, 318/662, 318/676
• US Class Current: 73/514.18
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A pendulous accelerometer comprises a stator defining a cavity having two nfronting surfaces which constitute two electrodes.

It also comprises a pendulum consisting of a disc connected to the stator by a hinge. A servo-circuit applies DC forces to the capacitors, each comprising a surface of the cavity and the confronting electrically conductor surface of the pendulum for creating an electrostatic torque which balances the acceleration torque.

Claims

1. An electrostatic pendulous accelerometer for measuring acceleration along a sensing axis, comprising:

a stator defining an internal cavity;

a pendulum consisting of an electrically insulating disc connected to the stator by hinge means allowing the pendulum to oscillate under the action of accelerations along said sensing axis;

a pair of first electrodes formed on the opposite surfaces of said cavity perpendicular to said sensing axis;

a pair of second electrodes disposed on the opposite sides of said disc, each confronting one of said first electrodes and in capacitive relation therewith;

a detection circuit for detecting unbalance between the capacities of two measurement capacitors each comprising one of the first electrodes and the confronting second electrode, said detection circuit comprising two legs, each leg having a reference capacitor connected to constitute a capacitor bridge with one of said measurement capacitors and a charge amplifier connected to charge said reference and measurement capactors with a constant current;

a servo-control circuit which comprises integrating amplifier means connected to receive an electric signal representative of the unbalance of the capacities of said two measurement capacitors and supplying two channels constructed and connected to cause delivery of square voltage pulses to each of the capacitive bridges by the associated charge amplifier depending on the direction of acceleration for rebalance of the pendulum, and a pulse counter connected to count the difference between the number of square pulses applied to the capacitive bridges; and

a sequencer alternately supplying pulses for simultaneous energization of both charge amplifiers and pulses for selectively opening one of two gates each transmitting the outputs signals of one of said comparators to a corresponding one of said charge amplifiers, as charge controlled signals.

2. A rebalance electrostatic pendulous accelerometer for measuring acceleration along a sensing axis, comprising:

a stator defining an electromagnetically shielded internal cavity;

a pendulum consisting of an electrically insulating disc connected to the stator by hinge means allowing the pendulum to oscillate under the action of accelerations along said sending axis in a predetermined range about a centered position;

a pair of first electrodes formed on the opposite surfaces of said cavity perpendicular to said sensing axis;

a pair of second electrodes disposed on the opposite sides of said disc and electrically interconnected to be at the same potential, each confronting one of said first electrodes and in capacative relation therewith;

a detection circuit for detecting unbalance between the capacities of two capacitors each comprising one of the first electrodes and the confronting second electrode, said detection circuit comprising an AC generator for applying AC voltages whose frequency is orders of magnitude greater than the frequency band of the accelerations to be detected, having the same amplitude and out of phase by 180°

to the first electrodes and comprising capacitor means connected to said second electrodes;

and a servo-control circuit connected to said capacitor means to receive an unbalance representative voltage therefrom, said servo-control circuit having first means for continuously applying D.C. bias voltages of equal values and opposite polarities to said first electrodes, and second means for phase lock demodulating and filtering of said unbalance voltage and delivery of a D.C. analog voltage which is in direct proportion to the filtered voltage and representative of the amount of acceleration impressed on the pendulum for rebalance thereof and which is applied to said second electrodes for rebalancing said capacitors, said first means being constructed for delivering D.C. bias voltages sufficient for linearization of the response.

3. An electrostatic pendulous accelerometer for measuring acceleration along a sensing axis, comprising:

a stator defining an internal cavity;

a pendulum consisting of an electrically insulating disc connected to the stator by hinge means allowing the pendulum to oscillate under the action of accelerations along said sensing axis;

a pair of first electrodes formed on the opposite surfaces of said cavity perpendicular to said sensing axis;

a pair of electrically connected second electrodes disposed on the opposite sides of said disc, each confronting one of said first electrodes and in capacitive relation therewith;

a detection circuit for detecting unbalance between the capacities of two capacitors each comprising one of the first electrodes and the confronting second electrode, said detection circuit having a high impedance amplifier whose input is electrically connected to said second electrodes, a processing circuit for comparing the output of said amplifier with predetermined limits and delivering an output depending on the result of such comparison;

a digital servo-control circuit comprising a reference voltage generator, for delivering voltages of the same values and opposed polarities for supplying respective ones of two channels each connected through first switch means and an amplifier to a respective one of said first electrode; and

sequencer means connected to receive the output signal of said processing means and for alternately supplying pulses for opening additional switch means for connecting said second electrodes to earth and one or the other of the switch means of said two channels depending upon the signal received from said processing means; and

a pulse counter connected to count the difference between the numbers of pulses applied to the first electrodes by the associated channels.