Capacitive liquid level indicator

• US 6,164,132 A
• Filed: 09/02/1998
• Issued: 12/26/2000
• Est. Priority Date: 06/12/1997
• Status: Expired due to Fees

• Current Assignee: GDM SPA (Is Company SRL)
• Original Assignee: GDM Incorporated
• Inventors: Matulek, Andrew M.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WORTH, WILLIE M
• Application Number:
  US09/145,675
• Time in Patent Office: 846 Days
• Field of Search: 73/304 C
• US Class Current: 73/304.00C
• CPC Class Codes: G01F 23/265 for discrete levels
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01F 23/268 mounting arrangements of probes

Abstract

A capacitive liquid level indicator having a capacitive sensor array superposed on each side of a dielectric substrate, wherein the sensor signal detection electronics are located immediately adjacent each capacitive sensor. These provisions result in high sensitivity of detection of submergence in the liquid, as well as essentially eliminating parasitic electric fields. The preferred capacitive sensors are interdigitated capacitors, and the preferred sensor signal detection circuit is an RC bridge and a comparator, wherein the comparator senses a voltage difference in the RC bridge between a sensor resistor and sensor capacitor of a first leg thereof and a reference resistor and reference capacitor of a second leg thereof. It is preferred for the capacitive liquid level indicator to be coated with a low dielectric conformal coating to thereby insulate the electronic components (inclusive of the capacitive sensors) thereof with respect to the liquid into which it is submerged. The sensitivity of the capacitive liquid level sensor according to the present invention is extremely high; as a result, a reference capacitive sensor is obviated, and there are no false indications of liquid due to any film of the liquid clinging to an exposed portion of the capacitive liquid level sensor.

Claims

1. A capacitive liquid level indicator comprising:

a dielectric substrate having a first side and an opposite second side;

a dual capacitive sensor array comprising a first capacitive sensor array located at said first side of said substrate and a second capacitive sensor array located at said second side of said substrate, said first and second capacitive sensor arrays comprising a plurality of capacitive sensor pairs; and

electronic means for sensing capacitance of said dual capacitive sensor array in response to fluids contacting said dual capacitive sensor array;

wherein said electronic means comprises;

oscillator means for providing an oscillating voltage; and

sensor signal detection circuit means connected with said oscillator means and each said capacitive sensor pair for providing an electronic signal responsive to the capacitance of each respective capacitive sensor pair;

wherein said sensor signal detection circuit means comprises a sensor signal detection circuit for each said capacitive sensor pair comprising;

an RC bridge comprising;

a first leg comprising a sensor resistor and a respective capacitive sensor pair; and

second leg comprising a reference resistor and a reference capacitor;

a first connection to said first leg located between said sensor resistor and said respective capacitive sensor pair;

a second connection to said second leg located between said reference resistor and said reference capacitor; and

comparator means connected with said first and second connections for switching between an on state and an off state responsive to voltage differences between said first and second connections.

2. The capacitive liquid level indicator of claim 1, wherein said first capacitive sensor array comprises a plurality of mutually spaced first capacitive sensors;

and wherein said second capacitive sensor array comprises a plurality of mutually spaced second capacitive sensors, wherein said plurality of first capacitive sensors is superposed in relation to said plurality of second capacitive sensors.

3. The capacitive liquid level indicator of claim 2, wherein each respectively superposed first and second capacitive sensors are mutually connected in parallel to form each said capacitive sensor pair.

4. The capacitive liquid level indicator of claim 3, wherein the first capacitive sensor of each capacitive sensor pair has a polarization like that of the superposed second capacitive sensor thereof.

5. The capacitive liquid level indicator of claim 4, wherein each respective sensor signal detection circuit is located substantially immediately adjacent its respective capacitive sensor pair.

6. The capacitive liquid level indicator of claim 5, wherein said electronic means further comprises signal conditioning means connected with said sensor signal detection circuit means for driving a preselected liquid level indicator.

7. The capacitive liquid level indicator of claim 6, wherein said electronic means is coated with a low dielectric conformal coating.

8. A capacitive liquid level indicator comprising:

a dielectric substrate;

at least one capacitive sensor array connected with said substrate, said at least one capacitive sensor array comprising a plurality of capacitive sensors; and

electronic means for sensing capacitance of said plurality of capacitive sensors in response to fluids contacting said at least one capacitive sensor array, said electronic means comprising;

oscillator means for providing an oscillating voltage; and

sensor signal detection circuit means connected with said oscillator means and each said capacitive sensor for providing an electronic signal responsive to the capacitance of each respective capacitive sensor;

wherein said sensor signal detection circuit means comprises a sensor signal detection circuit for each said capacitive sensor comprising;

an RC bridge comprising;

a first leg comprising a sensor resistor and a respective capacitive sensor; and

a second leg comprising a reference resistor and a reference capacitor;

a first connection to said first leg located between said sensor resistor and said respective capacitive sensor;

a second connection to said second leg located between said reference resistor and said reference capacitor; and

comparator means connected with said first and second connections for switching between an on state and an off state responsive to voltage differences between said first and second connections.

9. The capacitive hissed level indicator of claim 8, wherein each respective sensor signal detection circuit is located substantially Immediately adjacent its respective capacitive sensor.

10. The capacitive liquid level indicator of claim 9, wherein said electronic means further comprises signal conditioning means connected with said sensor signal detection circuit means for driving a preselected liquid level indicator.

11. The capacitive liquid level indicator of claim 10, wherein said electronic means is coated with a low dielectric conformal coating.

12. A capacitive liquid level indicator comprising:

a dielectric substrate having a first side and an opposite second side;

a dual capacitive sensor array comprising a first capacitive sensor array located at said first side of said substrate, wherein said first capacitive sensor array is arranged in a predetermined spaced relation such that said first capacitive sensor array has a predetermined lend and a second capacitive sensor array located at said second side of said substrate wherein said second capacitive sensor array is arranged in a predetermined spaced relation such that said second capacitive sensor array has substantially said predetermined length, said first and second capacitive sensor arrays comprising a plurality of capacitive sensor pairs; and

electronic means for sensing capacitance of said dual capacitive sensor array in response to fluids contacting said dual capacitive sensor array, said electronic means comprising;

oscillator means for providing an oscillating voltage; and

sensor signal detection circuit means connected with said oscillator means and each said capacitive sensor pair for providing an electronic signal responsive to the capacitance of each respective capacitive sensor pair, wherein said signal detection circuit means comprises a sensor signal detection circuit for each said capacitive sensor pair;

wherein each respective sensor signal detection circuit is entirely located on said substrate within three-quarters of said predetermined length from its respective capacitive sensor pair such that each respective sensor signal detection circuit is entirely disposed closely adjacent its respective capacitive sensor pair;

wherein each respectively superposed first and second capacitive sensors are mutually connected in parallel to form a capacitive sensor pair;

wherein the first capacitive sensor of each capacitive sensor pair has a polarization like that of the superposed second capacitive sensor thereof;

wherein said first capacitive sensor array comprises a plurality of mutually spaced first capacitive sensors; and

wherein said second capacitive sensor array comprises a plurality of mutually spaced second capacitive sensors, wherein said plurality of first capacitive sensors is superposed in relation to said plurality of second capacitive sensors.

13. The capacitive liquid level indicator of claim 12, wherein each respectively superposed first and second capacitive sensors are mutually connected in parallel to form a capacitive sensor pair.

14. The capacitive liquid level indicator of claim 13, wherein the first capacitive sensor of each capacitive sensor pair has a polarization like that of the superposed second capacitive sensor thereof.