Control circuit for electro-static accelerometer
First Claim
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1. A control circuit for an electro-static capacitive accelerometer which includes two fixed plates and a movable intermediary plate, the circuits comprising:
- a reference source of DC power;
a plurality of interconnected resistive means connected at their outer terminals across the output of the power source for generating DC voltages thereacross;
phase sensitive demodulator means having a first input connected to a reference AC voltage source and a second input connected in circuit with the accelerometer to detect capacitive imbalances thereof;
integrating means connected to the output of the demodulator means for generating a signal corresponding to the integral of the capacitive imbalance;
feedback means connecting the integral signal to a junction between the resistive means;
means connecting the fixed plates of the accelerometer to outer terminals of the resistive means;
terminal means connected to the output of the integrating means for permitting measurement of the integral signal;
wherein the reference AC voltage is derived from a terminal of a transformer, a secondary winding of the transformer being connected in circuit with fixed plates of the accelerometer, and further wherein means are connected between a center tap of the secondary winding and the second input of the phase sensitive demodulator; and
wherein a resistor is connected at a first terminal thereof to the output of the integrating means and at a second terminal thereof to both the resistive means junction and the second input of the demodulator means.
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Abstract
An electro-static capacitive accelerometer is a square law device and includes two fixed plates and an intermediary movable plate. A control circuit detects unbalances in the accelerometer, due to acceleration, and generates a signal which induces a corresponding electro-static corrective torque on the accelerometer thus forcing it toward a null condition. The signal is proportional to the acceleration. The invention eliminates prior art summing amplifiers in the control circuit for linearizing the torque of the accelerometer.
9 Citations
6 Claims
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1. A control circuit for an electro-static capacitive accelerometer which includes two fixed plates and a movable intermediary plate, the circuits comprising:
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a reference source of DC power; a plurality of interconnected resistive means connected at their outer terminals across the output of the power source for generating DC voltages thereacross; phase sensitive demodulator means having a first input connected to a reference AC voltage source and a second input connected in circuit with the accelerometer to detect capacitive imbalances thereof; integrating means connected to the output of the demodulator means for generating a signal corresponding to the integral of the capacitive imbalance; feedback means connecting the integral signal to a junction between the resistive means; means connecting the fixed plates of the accelerometer to outer terminals of the resistive means; terminal means connected to the output of the integrating means for permitting measurement of the integral signal; wherein the reference AC voltage is derived from a terminal of a transformer, a secondary winding of the transformer being connected in circuit with fixed plates of the accelerometer, and further wherein means are connected between a center tap of the secondary winding and the second input of the phase sensitive demodulator; and wherein a resistor is connected at a first terminal thereof to the output of the integrating means and at a second terminal thereof to both the resistive means junction and the second input of the demodulator means. - View Dependent Claims (2)
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3. A control circuit for an electro-static capacitive accelerometer which includes two fixed plates and an intermediary movable plate, the circuit comprising:
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a reference source of DC power; a pair of resistors of substantially equal resistance connected together at a junction, the outward terminals of the resistors connected across the power source; a transformer having a reference AC signal at the primary winding thereof; the secondary winding of the transformer connected across the accelerometer via respective DC blocking capacitors; means connecting outward terminals of the resistors across the accelerometer; a phase sensitive demodulator having a first input thereof connected to the transformer primary and a second input thereof connected to a center tap of the secondary winding for detecting capacitive imbalances; means connected at the output of the phase sensitive demodulator for integrating output signals corresponding to a signal associated with the integral of capacitive imbalance; feedback means connecting the integral signal to the junction between resistors; a terminal connected to the output of the integrating means for permitting measurement of the integral signals; a preamplifier connected between the center tap and the input of the demodulator; together with inverter means inductively coupled to the reference source of DC power for providing DC isolation at the input of the reference source.
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4. A control circuit for an electro-static capacitive accelerometer which includes two fixed plates and an intermediary movable plate, the circuit comprising:
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a reference source of DC power; inverter means inductively coupled to the reference source for providing DC isolation at the input of the source; a pair of resistors of substantially equal resistance connected together at a junction, the outward terminals of the resistors connected across the power supply; means connecting the outward resistor terminals in parallel with the fixed accelerometer plate; a phase sensitive demodulator having a first input thereof connected in circuit with the junction and a second input thereof connected to the inverter means, the demodulator detecting capacitive imbalance in the accelerometer; means connected at the output of the phase sensitive demodulator for integrating output signals corresponding to a signal associated with capacitive imbalances; a feedback resistor connected between the output of the integrating means and the junction; and a terminal connected to the output of the integrating means for allowing measurement of the integral signal. - View Dependent Claims (5)
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6. A control signal for an electro-static capacitive accelerometer which includes two fixed plates and a movable intermediary plate, the circuits comprising:
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a reference source of DC power; means connected at the inputs thereof to the source for generating positive and negative potentials at outputs thereof; phase sensitive demodulator means having a first input connected to a reference AC voltage source and a second input connected in circuit with the accelerometer to detect capacitive imbalances thereof; integrating means connected to the output of the demodulator means for generating a signal corresponding to the integral of the capacitive imbalance; feedback means connecting the integral signal to the movable plate; means connecting the fixed plates of the accelerometer to corresponding positive and negative potentials; and terminal means connected to the output of the integrating means for permitting measurement of the integral signal; wherein the reference AC voltage is derived from a terminal of a transformer, a secondary winding of the transformer being connected in circuit with fixed plates of the accelerometer.
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Specification