Liquid level sensor
First Claim
1. A capacitive sensor insertable into a reservoir containing a liquid wherein said liquid undergoes indeterminable variation in contamination and electrical conductivity, said sensor comprising:
- a first electrically conductive member having a first face region and a second face region elevationally displaced from said first region;
a second member of unitary construction including an electrically conductive portion and an electrically insulative portion to isolate electrically said conductive portion from said liquid when said sensor is immersed therein, said second member being in a facting relationship to said first face region to form a first capacitor having a first gap communicating externally of said sensor; and
a third member of unitary construction including an electrically conductive portion and an electrically insulative portion to isolate electricaly said conductive portion of said third member from said liquid when said sensor is immersed therein, said third member being in a facing relationship to said second face region to form a second capacitor having a second gap communicating externally of said sensor;
said sensor being adapted for positioning within said reservoir wherein said liquid entirely fills said first gap and said liquid elevationally varies in said second gap commensurately with said level of said liquid in said reservoir thereby varying capacitance of said second capacitor, such that said level of said liquid in said reservoir may be determined as a function of capacitance of said first capacitor and said second capacitor, said insulative portion of each of said second member and said third member electrically isolating said conductive portion of each of said second member and said third member from electrical conduction through said liquid between said second member and said third member.
1 Assignment
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Accused Products
Abstract
A capacitive sensor is constructed to eliminate electrical conduction through a liquid being measured. The electrical conduction in the liquid occurs between the plates of the reference and measuring capacitors. The capacitive plates which are spaced from the common capacitive plate to form the reference and measuring capacitors are of unitary construction and formed from anodized aluminum. The anodization forms an insulated surface which prevents conduction between the electrodes through the liquid. A ratio taken between the measuring capacitor and reference capacitor is therefore indicative of the level of the liquid within the gap of the measuring capacitor and is independent of the conductance of the liquid and its dielectric constant. Such a probe is particularly useful in applications where the liquid undergoes indeterminable changes in conductivity such as a lubricant which becomes contaminated by metallic particulates.
64 Citations
22 Claims
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1. A capacitive sensor insertable into a reservoir containing a liquid wherein said liquid undergoes indeterminable variation in contamination and electrical conductivity, said sensor comprising:
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a first electrically conductive member having a first face region and a second face region elevationally displaced from said first region; a second member of unitary construction including an electrically conductive portion and an electrically insulative portion to isolate electrically said conductive portion from said liquid when said sensor is immersed therein, said second member being in a facting relationship to said first face region to form a first capacitor having a first gap communicating externally of said sensor; and a third member of unitary construction including an electrically conductive portion and an electrically insulative portion to isolate electricaly said conductive portion of said third member from said liquid when said sensor is immersed therein, said third member being in a facing relationship to said second face region to form a second capacitor having a second gap communicating externally of said sensor; said sensor being adapted for positioning within said reservoir wherein said liquid entirely fills said first gap and said liquid elevationally varies in said second gap commensurately with said level of said liquid in said reservoir thereby varying capacitance of said second capacitor, such that said level of said liquid in said reservoir may be determined as a function of capacitance of said first capacitor and said second capacitor, said insulative portion of each of said second member and said third member electrically isolating said conductive portion of each of said second member and said third member from electrical conduction through said liquid between said second member and said third member. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A capacitive prode sensor comprising:
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an electrically conductive first tube having an inner surface, an outer surface, a first axially extending face region, a second axially extending face region, and a plurality of openings extending between said inner surface and said outer surface, each of said first face region and said second face region being disposed on said inner surface; a second tube having an insulative outer portion and a conductive inner portion, said second tube being coaxially disposed within said first tube in a facing relationship to first face region, said first face region and said second tube forming a first capacitor having a first gap; a third tube having an insulative outer portion and a conductive inner portion, said third tube being coaxially disposed within said first tube in a facing relationship to said second face region, said second face region and said third tube forming a second capacitor having a second gap; means for mounting said second tube and said third tube within said first tube, said openings communicating said first gap and said second gap externally of said first tube; and means for electrically contacting said first tube and said conductive inner portion of each said of said second tube and said third tube to electrically determine a vaue of capacitance to each of said first capacitor and said second capacitor. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification