Apparatus and method for measuring capacitance from the duration of a charge-discharge charge cycle
First Claim
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1. A device for measuring capacitance, comprising:
- charging means for subjecting the capacitance to a charge-discharge-charge cycle, wherein the capacitance is linearly charged to a first predetermined voltage, then linearly charged to a second predetermined voltage that is opposite in polarity from the first predetermined voltage, and then linearly charged to a reference voltage that is intermediate the first and second predetermined voltages; and
output means electrically coupled and responsive to said charging means for generating an output signal indicative of capacitance that varies in accordance with the duration of the charge-discharge-charge cycle, said duration being proportional to the measured capacitance.
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Abstract
A highly accurate system to measure the value of a capacitor using proportionality against a time base reference. The capacitor under test is linearly sequentially charged in three discrete steps yielding integrated net neutral charge as well as a delay for discharging dielectric absorption during each measurement cycle.
87 Citations
20 Claims
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1. A device for measuring capacitance, comprising:
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charging means for subjecting the capacitance to a charge-discharge-charge cycle, wherein the capacitance is linearly charged to a first predetermined voltage, then linearly charged to a second predetermined voltage that is opposite in polarity from the first predetermined voltage, and then linearly charged to a reference voltage that is intermediate the first and second predetermined voltages; and output means electrically coupled and responsive to said charging means for generating an output signal indicative of capacitance that varies in accordance with the duration of the charge-discharge-charge cycle, said duration being proportional to the measured capacitance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A capacitance measuring device for generating an output signal that has a time duration that is a function of the capacitance of two conductors separated by a dielectric, comprising:
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(a) first and second constant current sources each having opposite polarities; (b) a ground reference voltage; (c) first and second leads, the first lead adapted for connection to one of the conductors, the second lead adapted for connection to the other one of the conductors and coupled to the ground reference; (d) control means coupled to the first lead for; commencing generation of the output signal; initially coupling the first lead to the first current source to linearly charge the capacitance to a first predetermined voltage; detecting when the capacitance is charged to the first predetermined voltage, and then coupling the first lead to the second current source to linearly charge the capacitance to a second predetermined voltage that is opposite in polarity to the first predetermined voltage; detecting when the capacitance is charged to the second predetermined voltage, and then coupling the first lead to the first current source to linearly charge the capacitance to the ground reference voltage; detecting when the capacitance is charged to the ground reference voltage, and then coupling the first lead to the ground reference voltage and terminating generation of the output signal. - View Dependent Claims (11, 12, 13, 14)
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15. A method for measuring the capacitance of two conductors separated by a dielectric that is initially at a reference ground, comprising the steps of:
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(a) initially linearly charging the capacitance to a first predetermined voltage; (b) linearly charging the capacitance to a second predetermined voltage that is opposite in polarity to the first predetermined voltage; (c) linearly charging the capacitance to the reference ground; (d) measuring the amount of time required to sequentially perform steps (a) through (c); and (e) comparing the amount of time measured in step (d) to a predetermined reference time that is longer in duration than the measured time, wherein the ratio of said measured time to said reference time is indicative of capacitance. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification