Miscible liquid capacitive sensing system

• US 6,351,132 B1
• Filed: 09/03/1999
• Issued: 02/26/2002
• Est. Priority Date: 09/03/1999
• Status: Expired due to Fees

• Current Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Original Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Inventors: Park, Kyong M.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Sundaram, T R
• Application Number:
  US09/389,703
• Time in Patent Office: 907 Days
• Field of Search: 324/664, 324/676, 324/677, 324/681, 324/686, 324/689, 324/444, 324/666, 324/665, 73/614.3, 733/04.C
• US Class Current: 324/664
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/2829 mixtures of fuels, e.g. determining the RON-number
• CPC Class Codes: G05D 11/138 by sensing the concentration of the mixture, e.g. measuring pH value

Abstract

A capacitive sensor is employed to measure the dielectric constant of miscible liquids, and thereby determine the relative concentration of the two liquids. Further, a feedback circuit may be provided to change the operation of the system in accordance with the relative concentration of the liquids. Further, circuit arrangements may be provided to adjust the sensitivity and offset of the electrical circuit included in the system to match the output of the sensor with the dielectric constants being measured.

Claims

1. A sensing and control system comprising:

a container;

first and second miscible liquids in said container, said liquids having significantly different first and second dielectric constants, respectively;

a capacitive sensor mounted to extend into said container;

said sensor having spaced electrodes exposed to said liquids, wherein the capacitance between said electrodes varies with the dielectric constant of said miscible liquids, and the concentration thereof;

said sensor having an electrical output which varies with the sensed capacitance;

said system including adjustable operational controls for varying flow conditions of said liquids into the container; and

feedback circuitry coupled to said sensor for varying said adjustable operational controls in accordance with the output of said sensor.

2. A system as defined in claim 1 wherein said sensor is mounted in said container near the bottom thereof so that it is normally submerged in said liquids.

8. A capacitive sensor system as defined in claim 1 including a source of one of said liquids, and an electrically operated valve coupling said source to said container, a second source of the other of said liquids and an electrically operated valve coupling said second source to said container, and said feedback circuitry being coupled to control said valves to provide the desired concentration of said liquids.

9. A capacitive sensor system as defined in claim 1 wherein said sensor is mounted in said container near the bottom thereof so that it is normally submerged in said liquid.

10. A capacitive sensor system as defined in claim 1 wherein said sensor includes a threaded housing for securing said sensor to said housing, with a pair of closely spaced capacitive plates extending into said container.

11. A capacitive sensor system as defined in claim 10 wherein said capacitive plates are concentric.

12. A capacitive sensor system as defined in claim 10 wherein said housing includes electronic circuitry for converting variations in the capacitance sensed by said plates into corresponding variations in output signal from said circuitry.

13. A capacitive sensor system as defined in claim 1 wherein said system includes a microprocessor coupled to receive signals from said sensor and to implement desired operating conditions of the system.

3. A capacitive sensing system comprising:

a tank;

first and second miscible liquids in said tank, said liquids having significantly different first and second dielectric constants, respectively;

a capacitive sensor mounted to extend into said tank, said sensor having spaced electrodes to said liquids, wherein the capacitance between said electrodes varies with the dielectric constant of said miscible liquids, and the concentration thereof;

said sensor having an electrical output extending over a predetermined range;

said sensor including arrangements for adjusting the offset and the gain of said sensor so that varying concentrations of said miscible liquids correspond substantially to the range of said sensor;

feedback circuitry coupled to said sensor for varying operating conditions of said system in accordance with the output of said sensor; and

a source of one of said liquids, and an electrically operated valve coupling said source to said tank, a second source of the other of said liquids and an electrically operated valve coupling said second source to said tank, and said feedback circuitry being coupled to control said valves to provide the desired concentration of said liquids.

4. A capacitive sensing system comprising:

a container;

first and second miscible liquids in said container, said liquids having significantly different first and second dielectric constants, respectively;

a capacitive sensor mounted to extend into said container;

said sensor having spaced electrodes exposed to said liquids, wherein the capacitance between said electrodes varies with the dielectric constant of said miscible liquids, and the concentration thereof;

said sensor having an electrical output which varies with the sensed capacitance;

feedback circuitry coupled to said sensor for varying operating conditions of said system in accordance with the output of said sensor; and

a source of one of said liquids, and an electrically operated valve coupling said source to said tank, a second source of the other of said liquids and an electrically operated valve coupling said second source to said container, and said feedback circuitry being coupled to control said valves to provide the desired concentration of said liquids.

14. A capacitive sensor system as defined in claim 4 wherein the output of said sensor normally extends over a predetermined range, and wherein said system includes circuitry associated with said sensor for adjusting the offset and the gain of said sensor so that varying concentrations of said miscible liquids correspond substantially to the range of said sensor.

15. A capacitive sensor system as defined in claim 4 wherein said sensor includes a threaded housing for securing said sensor to said housing, with a pair of closely spaced capacitive plates extending into said container.

16. A capacitive sensor system as defined in claim 15 wherein said capacitive plates are concentric.

17. A capacitive sensor system as defined in claim 4 wherein said system includes a microprocessor coupled to receive signals from said sensor and to implement desired operating conditions of the system.

5. A capacitive sensing system comprising:

a container;

first and second miscible liquids in said container, said liquids having significantly different first and second dielectric constants, respectively;

a capacitive sensor mounted to extend into said container;

said sensor having spaced electrodes exposed to said liquids, wherein the capacitance between said electrodes varies with the dielectric constant of said liquids, and the concentration thereof;

said sensor including electronic circuitry providing a normal electrical output which varies with the sensed capacitance;

said system further including at least one variable liquid control component; and

feedback arrangements coupled to said sensor for varying the operating conditions of said system by changing the state of said liquid control component in accordance with the output of said sensor.

6. A capacitive sensing system comprising:

a container;

first and second miscible liquids in said container, said liquids having significantly different first and second dielectric constants, respectively;

a capacitive sensor mounted to extend into said container;

said sensor having spaced electrodes exposed to said liquids, wherein the capacitance between said electrodes varies with the dielectric constant of said liquids, and the concentration thereof;

said sensor including electronic circuitry providing a normal electrical output which varies with the sensed capacitance;

said system further including at least one variable physical component for variably controlling said liquids, in addition to said electronic circuitry; and

feedback arrangements coupled to said sensor for varying the operating conditions of said system by changing the state of said physical component in accordance with the output of said sensor.

7. A system as defined in claim 6 wherein said variable physical component includes at least one valve.