METHODS AND APPARATUS FOR A CAPACITIVE SENSOR
Various embodiments of the present technology may provide methods and apparatus for a capacitive sensor. The methods and apparatus may provide a pair of capacitive sensors formed along at least one plane of a container to create dual sensing fields. The capacitive sensor provides a first electrode affixed to the container and extending from a lower portion of the container to an upper portion of the container, a second electrode affixed to an upper portion of the container, and a third electrode affixed to a lower portion of the container and spaced a predetermined distance apart from the second electrode.
1 . A capacitance sensor for detecting a level of a substance within a container, comprising:
a first electrode extending upwardly along a first vertical sidewall of the container between a bottom of the container and a top of the container;
a second electrode disposed along an upper portion of the container; and
a third electrode disposed along lower portion of the container, wherein:
the second and thirds electrodes are separated from each other by a predetermined vertical distance;
a first capacitance is formed between the first electrode and the second electrode; and
a second capacitance is formed between the first electrode and the third electrode.
2 . A capacitance sensor according to claim 1 , wherein an inflection point in a rate of change in the first and second capacitances occurs when the level of the substance in the container drops below a lowermost edge of the second electrode.
3 . A capacitance sensor according to claim 1 , wherein the first electrode comprises a constant width between the bottom of the container and the top of the container.
4 . A capacitance sensor according to claim 1 , wherein the third electrode is disposed along an entire bottom surface of the container perpendicular to the first electrode.
5 . A capacitance sensor according to claim 4 , wherein the second electrode is disposed along at least two vertical sidewalls of the container.
6 . A capacitance sensor according to claim 5 , wherein:
the first electrode extends along a middle portion of the first vertical sidewall; and
the second electrode extends along opposing upper side edge portions of the first vertical wall.
7 . A capacitance sensor according to claim 4 , wherein the second electrode is disposed along a second vertical sidewall of the container that is opposite the first vertical sidewall.
8 . A capacitance sensor according to claim 1 , wherein:
the first electrode extends along a middle portion of the first vertical sidewall;
the second electrode comprises two electrode segments, wherein each segment is:
positioned in opposing upper side edge portions of the first vertical wall; and
separated from the first electrode by a first gap;
the third electrode comprises two electrode segments, wherein each segment is:
positioned in opposing lower side edge portions of the first vertical wall; and
separated from the first electrode by a second gap.
9 . A capacitance sensor according to claim 8 , wherein each segment of the second electrode comprises an extension section that extends from a bottom edge of the segment downwardly to the bottom of the first vertical wall in the second gap formed between the first electrode and the third electrode.
10 . A capacitance sensor according to claim 8 , wherein each segment of the third electrode comprises an extension section that extends from a top edge of the segment upwardly to the top of the first vertical wall in the first gap formed between the first electrode and the second electrode.
11 . A method for detecting a level of a substance in a container using a capacitive sensor, comprising:
positioning a first electrode along a first vertical sidewall of the container wherein the first electrode extends upwardly between a bottom of the container and a top of the container;
positioning a second electrode along an upper portion of the container;
positioning a third electrode disposed along lower portion of the container, wherein the second and thirds electrodes are separated from each other by a predetermined vertical distance;
forming first capacitance between the first electrode and the second electrode;
forming a second capacitance between the first electrode and the third electrode; and
detecting an inflection point in a rate of change in the first and second capacitances according to a height of a surface of the substance.
12 . A method according to claim 11 , wherein the first electrode comprises a constant width between the bottom of the container and the top of the container.
13 . A method according to claim 11 , wherein the third electrode is disposed along an entire bottom surface of the container perpendicular to the first electrode.
14 . A method according to claim 13 , wherein the second electrode is disposed along at least two vertical sidewalls of the container.
15 . A method according to claim 14 , wherein:
the first electrode extends along a middle portion of the first vertical sidewall; and
the second electrode extends along opposing upper side edge portions of the first vertical wall.
16 . A method according to claim 13 , wherein the second electrode is disposed along a second vertical sidewall of the container that is opposite the first vertical sidewall.
17 . A method according to claim 11 , wherein:
the first electrode extends along a middle portion of the first vertical sidewall;
the second electrode comprises two electrode segments, wherein each segment is:
positioned in opposing upper side edge portions of the first vertical wall; and
separated from the first electrode by a first gap;
the third electrode comprises two electrode segments, wherein each segment is:
positioned in opposing lower side edge portions of the first vertical wall; and
separated from the first electrode by a second gap.
18 . A method according to claim 17 , wherein each segment of the second electrode comprises an extension section that extends from a bottom edge of the segment downwardly to the bottom of the first vertical wall in the second gap formed between the first electrode and the third electrode.
19 . A method according to claim 17 , wherein each segment of the third electrode comprises an extension section that extends from a top edge of the segment upwardly to the top of the first vertical wall in the first gap formed between the first electrode and the second electrode.
20 . A method according to claim 11 , wherein the inflection point occurs when the level of the substance in the container drops below a lowermost edge of the second electrode.