Distributed impedance sensor
First Claim
1. An apparatus for measuring at least one parameter of a variable physical structure, comprising:
- a sensing element placed in proximity to the variable physical structure, the sensing element having a length, the sensing element formed of at least two electrically conductive members, at least two of the conductive members electrically insulated from one another, forming first and second sensing electrodes;
the sensing element having a sensing capacitance between at least the first and second sensing electrodes, the sensing capacitance approximately distributed along the length of the sensing element;
a variation in at least one of the measured parameters causing a variation of the sensing capacitance, the variation of the sensing capacitance being representative of the variation in the measured parameter;
the first sensing electrode forming a first inductance, the second sensing electrode forming a second inductance, the first and second inductances approximately distributed along the length of the sensing element;
at least two of the sensing electrodes excited with an alternating current at an operating frequency, first and second inductances having first and second inductive reactances, respectively, at the operating frequency, the sensing capacitance having a capacitive reactance at the operating frequency;
the first inductive reactance being at least ten percent of the capacitive reactance, and the second inductive reactance being at least ten percent of the capacitive reactance.
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Accused Products
Abstract
An apparatus is disclosed for measuring one or more parameters of a variable physical structure, at least one of the parameters being fluid level, position, velocity or acceleration. The apparatus includes an electromagnetic sensing element comprising at least two electrically conductive members that are electrically insulated from one another. A distributed capacitance and a distributed inductance are each formed along a length of the sensing element. The inductive reactance is at least ten percent of the capacitive reactance, thereby allowing the capacitance to be distributed, rather than acting as a “lump capacitance”. The distributed capacitance enables shaping of the electric and magnetic fields around the electromagnetic sensing element so that disturbance by nearby electromagnetic fields, conductors, and dielectrics is minimized.
When the apparatus is configured as a fluid level sensor, the capacitance is affected by the permittivity and the level of the measured fluid. A reference sensor can be used to compensate for changes in the permittivity of the fluid.
When the apparatus is configured as a position sensor, the capacitance and/or inductance are affected by the position of an electrically conductive or dielectric target. The position measurement can be differentiated to obtain measurements of velocity or acceleration. Electronic circuits for operating the sensing element are also shown.
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Citations
19 Claims
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1. An apparatus for measuring at least one parameter of a variable physical structure, comprising:
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a sensing element placed in proximity to the variable physical structure, the sensing element having a length, the sensing element formed of at least two electrically conductive members, at least two of the conductive members electrically insulated from one another, forming first and second sensing electrodes; the sensing element having a sensing capacitance between at least the first and second sensing electrodes, the sensing capacitance approximately distributed along the length of the sensing element; a variation in at least one of the measured parameters causing a variation of the sensing capacitance, the variation of the sensing capacitance being representative of the variation in the measured parameter; the first sensing electrode forming a first inductance, the second sensing electrode forming a second inductance, the first and second inductances approximately distributed along the length of the sensing element; at least two of the sensing electrodes excited with an alternating current at an operating frequency, first and second inductances having first and second inductive reactances, respectively, at the operating frequency, the sensing capacitance having a capacitive reactance at the operating frequency; the first inductive reactance being at least ten percent of the capacitive reactance, and the second inductive reactance being at least ten percent of the capacitive reactance. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A capacitive sensing apparatus for measuring one or more parameters of a variable physical structure, comprising:
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a sensing element formed of at least two electrically conductive members, the conductive members electrically insulated from one another, the sensing element having a length; the sensing element positioned proximate the variable physical structure; the sensing element having a sensing capacitance, the sensing capacitance approximately distributed along the length of the sensing element; variation of at least one measured parameter causing a variation in the sensing capacitance that is representative of the variation in the parameter; at least two of the conductive members forming first and second inductances which are approximately distributed along the length of the sensing element; the sensing element excited with an alternating current; the electrically conductive members supported at least partially by a dielectric support structure.
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19. An apparatus for measuring one or more parameters of a variable physical structure, comprising:
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a sensing element positioned proximate the variable physical structure; the sensing element having a length; the sensing element formed of at least two electrically conductive members, the conductive members electrically insulated from one another; the sensing element having a sensing element capacitance between at least two of the conductive members, the capacitance approximately distributed along the length of the sensing element; at least two of the conductive members forming first and second inductances which are approximately distributed along the length of the sensing element; variation in at least one measured parameter causing a variation in at least one of the first and second inductances representative of the variation in the parameter; at least two of the conductive members excited with an alternating current at a frequency whereby inductive reactance of the first inductance is at least ten percent of capacitive reactance of the sensing element capacitance, and inductive reactance of the second inductance is at least ten percent of capacitive reactance of the sensing element capacitance.
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Specification