Capacitive measurement system
First Claim
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1. A system for measuring the capacitance C of a capacitor independently of the resistance R of a resistor connected in parallel with said capacitor, which comprises:
- a first source of alternating sinusoidal voltage of a first frequency W0 ;
a second source of alternating sinusoidal voltage of a different second frequency W1 ;
switch means for alternatively connecting said capacitor and parallel resistor to said first and second sources during successive intervals;
current measurement means for providing average values of current supplied to said capacitor and parallel resistor, said current measurement means providing an average current value N0 during an interval with said capacitor and parallel resistor is connected to said first source and providing an average current value N1 during an interval when said capacitor and parallel resistor are connected to said second source; and
computer means for calculating said capacitance in accordance with an equation ##EQU8## where K0 is a multiplier constant for converting the current value N0 to an admittance value (W0 C)2 +1/R2, and K1 is a multiplier constant for converting the current value N1 to an admittance value (W1 C)2 +1/R2.
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Abstract
A system for independently determining the capacitance and resistance of a capacitive sensor, in which the sensor and a reference capacitor are sequentially energized from two alternating voltage sources of different frequencies, and average sensor and reference capacitor current valves at the two frequencies are measured and supplied to a computer which periodically calculates the sensor capacitance and resistance.
42 Citations
7 Claims
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1. A system for measuring the capacitance C of a capacitor independently of the resistance R of a resistor connected in parallel with said capacitor, which comprises:
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a first source of alternating sinusoidal voltage of a first frequency W0 ; a second source of alternating sinusoidal voltage of a different second frequency W1 ; switch means for alternatively connecting said capacitor and parallel resistor to said first and second sources during successive intervals; current measurement means for providing average values of current supplied to said capacitor and parallel resistor, said current measurement means providing an average current value N0 during an interval with said capacitor and parallel resistor is connected to said first source and providing an average current value N1 during an interval when said capacitor and parallel resistor are connected to said second source; and
computer means for calculating said capacitance in accordance with an equation ##EQU8## where K0 is a multiplier constant for converting the current value N0 to an admittance value (W0 C)2 +1/R2, and K1 is a multiplier constant for converting the current value N1 to an admittance value (W1 C)2 +1/R2. - View Dependent Claims (2)
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3. A system for measuring the capacitance C of a capacitor independently of a resistance R of a resistor connected in parallel with said capacitor, which comprises:
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a first source of alternating sinusoidal voltage of a first frequency W0 ; a second source of alternating sinusoidal voltage of a different second frequency W1 ; a measurement circuit; first switch means for alternatively energizing said measurement circuit from said first and second sources, respectfully; a reference capacitor of known capacitance Cref ; second switch means for alternatively energizing said reference capacitor and said capacitor and parallel resistor combination from said measurement circuit; switch control means for operating said first and second switch means, to dispose these switch means in four arrangements during respective time intervals of a measurement sequence, said four arrangements including; a first arrangement wherein said reference capacitor is energized by said first source, a second arrangement wherein said reference capacitor is energized by said second source, a third arrangement wherein said capacitor and parallel resistor is energized from said first source, and a fourth arrangement wherein said capacitor and parallel resistor is energized from said second source; current measurement means for determining average current values of the measurement circuit, including; an average current value Nref0, during a time interval when said first and second switch means are disposed in said first arrangement, an average current value Nref1, during a time interval when said first and second switch means are disposed in said second arrangement, an average current value N0, during a time interval when said first and second switch means are disposed in said third arrangement, and an average current value N1, during a time interval when said first and second switch means are disposed in said fourth arrangement; and a computer which includes; storage means for including and storing said current values, and calculating means for calculating said capacitance C in accordance with the equation ##EQU10## - View Dependent Claims (4)
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5. A system for measuring the capacitance C of a capacitor independently of a resistance R of a resistor connected in parallel with said capacitor, which comprises:
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a first source of alternating sinusoidal voltage of a first frequency W0 ; a second source of alternating sinusoidal voltage of a different second frequency W1 ; a measurement circuit which comprises; a first branch including a reference capacitor of known capacitance Cref, and a second branch connected in parallel with said first branch and including said capacitor and parallel resistor; a first switch means for alternately energizing said measurement circuit from said first and second source, respectively; a second switch means, disposed in series with said reference capacitor in said first branch, for alternatively energizing or de-energizing said reference capacitor; a third switch means, disposed in series with said capacitor and parallel resistor or de-energizing said capacitor and parallel resistor; a switch control timer means for operating said first, second, and third switch means to define a plurality of measurement circuit arrangements which occur sequentially in any selected order of occurrence during respective time intervals of a measurement sequence, said circuit arrangements including; a first arrangement wherein said measurement circuit is energized from said first source and said second and third switch means are open, a second arrangement wherein said measurement circuit is energized from said second source and said second and third switch means are open, a third arrangement wherein said measurement circuit is energized from said first source, said second switch means is closed and said third switch means is open, a fourth arrangement wherein said measurement circuit is energized from said second source, said second switch means is closed and said third switch means is open, a fifth arrangement wherein said measurement circuit is energized from said first source, said second switch means is open, and said third switch means is closed, and a sixth arrangement wherein said measurement circuit is energized from said second source, said second switch means is open, and said third switch means is closed; current measurement means for generating a plurality of digitized average current values of the measurement circuit current during respective time intervals of said measurement sequence, said digitized average current value including; a value NO.sbsb.0 which occurs during an interval when said measurement circuit is disposed in said first arrangement, a value O.sbsb.1 which occurs during an interval when said measurement circuit is disposed in said second arrangement, a value ND.sbsb.ref0 which occurs during an interval when said measurement circuit is disposed in said third arrangement, a value ND.sbsb.ref1 which occurs during an interval when said measurement circuit is disposed in said fourth arrangement, a value ND.sbsb.0 which occurs during an interval when said measurement circuit is disposed in said fifth arrangement, and a value ND.sbsb.1 which occurs during an interval when said measurement circuit is disposed in said sixth arrangement; and a computer which includes; storage means for securing and storing said plurality of digitized current values, and calculating means for periodically calculating said capacitance C in accordance with the equation ##EQU12## - View Dependent Claims (6, 7)
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Specification