Force balance instrument with electrostatic charge control
First Claim
1. For use with a forced balanced instrument having a sensing member which is displaced from a null position in response to an input condition to be measured, and first and second electrostatic plates mounted adjacent to and on opposite sides of said sensing member and cooperating with said sensing member to form first and second capacitors, a method of controlling position of said sensing member comprising the steps of:
- generating a pickoff signal indicative of displacement of said sensing member from a said null position;
repetitively applying to said sensing member a constant magnitude force, independent of displacement of said sensing member, alternately for first and second periods of time to respectively opposite sides of said sensing member in respective ones of first and second opposite directions; and
varying said first and second periods of time in response to said pickoff signal and to effect a difference in said first and second periods that is indicative of said input condition.
1 Assignment
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Accused Products
Abstract
A force balanced instrument, such as an accelerometer, employs a pendulous mass having combined electrostatic pickoff and forcing plates on opposite sides thereof. The plates provide a constant attractive force in successive periods acting alternatively on opposing sides of the sensitive element. Force balance is achieved by controlling the duty cycle so that the difference in duration between each of the parts of a full cycle is a linear measure of acceleration. Voltage on each of the forcing plates is sensed independently immediately after each is charged with a fixed charging pulse which provides a fixed force level over the duration of the part cycle. The two successive voltage samples are stored, and the difference between them integrated to control the duty cycle of a pulse width modulator, which itself controls the duration of application of the alternately directed forces applied by the respective plates to the pendulous mass.
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Citations
32 Claims
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1. For use with a forced balanced instrument having a sensing member which is displaced from a null position in response to an input condition to be measured, and first and second electrostatic plates mounted adjacent to and on opposite sides of said sensing member and cooperating with said sensing member to form first and second capacitors, a method of controlling position of said sensing member comprising the steps of:
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generating a pickoff signal indicative of displacement of said sensing member from a said null position; repetitively applying to said sensing member a constant magnitude force, independent of displacement of said sensing member, alternately for first and second periods of time to respectively opposite sides of said sensing member in respective ones of first and second opposite directions; and varying said first and second periods of time in response to said pickoff signal and to effect a difference in said first and second periods that is indicative of said input condition. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 20, 21)
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15. A force balanced instrument comprising:
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a sensing member mounted for movement in response to an input to be measured; first and second electrostatic plates mounted on opposite sides of said sensing member and cooperating with said sensing member to form first and second capacitors having first and second gaps, respectively, that vary as said sensing member moves in response to an input thereto; means for applying equal charges to said first and second capacitors for first and second successive time intervals to produce first and second voltages on said capacitors respectively; and means for generating a pickoff signal indicative of the difference between said first and second voltages. - View Dependent Claims (16, 17, 18, 19, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32)
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Specification