Capacitive measurement system
First Claim
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1. A sensor for the measurement of small variations in a value of a sensing capacitor comprising:
- A) means for exciting said sensing capacitor with an alternating voltage at a predetermined frequency whereby the voltage on the sensing capacitor reverses polarity,B) means for sampling the voltage on the sensing capacitor each time the voltage reverses polarity,C) means for accumulating the charge on the sensing capacitor from the sampling means during each sampling,D) means for generating an output signal that represents the charge in the charge accumulating means.
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Abstract
Sensor circuits for the measurement of small variations in the value of a sensing capacitor. An alternating voltage excites the sensing capacitor a predetermined frequency whereby the voltage on the sensing capacitor reverses polarity. This voltage on the sensing capacitor is sampled each time the voltage reverses polarity. An accumulator accumulates the sampled charges from the sensing capacitor. An output signal that represents the charge in the charge accumulating means indicates the measured capacitance.
117 Citations
29 Claims
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1. A sensor for the measurement of small variations in a value of a sensing capacitor comprising:
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A) means for exciting said sensing capacitor with an alternating voltage at a predetermined frequency whereby the voltage on the sensing capacitor reverses polarity, B) means for sampling the voltage on the sensing capacitor each time the voltage reverses polarity, C) means for accumulating the charge on the sensing capacitor from the sampling means during each sampling, D) means for generating an output signal that represents the charge in the charge accumulating means. - View Dependent Claims (2, 3, 4, 5, 6, 10, 11, 12, 13, 14, 15)
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7. A sensor as recited in 1 for making linear measurements of small values of capacitive impedance including a reference capacitor in series connection with sensing capacitor and connected to said exciting means wherein said exciting means includes:
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i) a variable-amplitude alternating-current excitation voltage source connected to said sensing capacitor with its waveform in phase opposition to said fixed alternating-current excitation voltage, and ii) amplification-demodulation means with a gain substantially greater than one having an input connected to the junction of said reference and sensing capacitors, and an output with a direct-current level responsive to the difference of said reference capacitor'"'"'s charge and said sensing capacitor'"'"'s charge, whereby the output of said amplification-demodulation means assumes a value to null the difference of said reference capacitor'"'"'s charge and said sensing capacitor'"'"'s charge and whereby said output is related to the ratio of the sensing and reference capacitors. - View Dependent Claims (8, 9)
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16. A method for measuring small variations in a value of a sensing capacitor comprising:
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A) exciting the sensing capacitor from a voltage source with an alternating voltage at a predetermined frequency whereby the voltage on the sensing capacitor reverses polarity, B) sampling the voltage on the sensing capacitor each time the voltage reverses polarity, C) accumulating the charge on the sensing capacitor during each said sampling, D) generating an output signal that represents the accumulated charge. - View Dependent Claims (17, 18, 19, 20, 21, 25, 26, 27, 28, 29)
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22. A method as recited in 16 for making linear measurements of small values of capacitive impedance including connecting a reference capacitor in series between the sensing capacitor and the exciting means and said exciting of the sensing capacitor includes:
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i) applying a variable-amplitude alternating-current excitation signal to said sensing capacitor with its waveform in phase opposition to said predetermined frequency excitation voltage, and ii) amplifying with a gain substantially greater than one and demodulating the signal produced the junction of the reference and sensing capacitors thereby to generate a direct-current level output signal responsive to the difference between the charges on the reference capacitor and sensing capacitor whereby the output resulting from the amplification-demodulation assumes a value to null the difference between the charges on the reference capacitor and sensing capacitor and is related to the ratio of the capacitances of the sensing and reference capacitors. - View Dependent Claims (23, 24)
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Specification