Sensor for levels of conductive liquids

• US 20060021432A1
• Filed: 07/28/2004
• Published: 02/02/2006
• Est. Priority Date: 07/28/2004
• Status: Active Grant

• Current Assignee: Vertex Pharmaceuticals Incorporated
• Original Assignee: Vertex Pharmaceuticals Incorporated
• Inventors: Emery, Michael P., Vuong, Minh, Flores, Javier H., Salzmann, Philip E., Harootunian, Alec T., Bennett, Todd N.
• Granted Patent: US 7,219,545 B2
• Time in Patent Office: Days
• US Class Current: 73/304.R
• CPC Class Codes: G01F 23/242 Mounting arrangements for electrodes
• CPC Class Codes: G01F 23/243 Schematic arrangements of probes combined with measuring circuits

Abstract

A liquid level sensor comprises a plurality of electrodes arranged in a defined relationship with respect to a container filling trajectory, a signal generator coupled to one or more of the plurality of electrodes, a signal receiver coupled to one or more of the plurality of electrodes, and a sensing circuit coupled to at least one of the signal generator and signal receiver. The sensing circuit is configured to produce an output indicative of electrical resistance between at least one pair of the plurality of electrodes. The sensing circuit may be associated with the signal receiver and/or with the signal generator.

Claims

1. A liquid level sensor comprising:

a plurality of electrodes arranged in a defined relationship with respect to a container filling trajectory;

a signal generator coupled to one or more of said plurality of electrodes;

a signal receiver coupled to one or more of said plurality of electrodes; and

a sensing circuit coupled to at least one of said signal generator and signal receiver, wherein said sensing circuit is configured to produce an output indicative of electrical resistance between at least one pair of said plurality of electrodes.

2. The sensor of claim 1, wherein said sensing circuit is associated with said signal receiver.

3. The sensor of claim 1, wherein said sensing circuit is associated with said signal generator.

4. The sensor of claim 1, wherein said signal receiver and said sensing circuit comprise a resistor coupled between one of said electrodes and a circuit common.

5. The sensor of claim 4, wherein said resistor forms a voltage divider with an electrical resistance of said liquid.

6. The sensor of claim 4, wherein said resistor is coupled to an electrode proximate to a bottom of said container.

7. The sensor of claim 6, wherein said generator comprises a voltage source.

8. The sensor of claim 1, wherein said generator comprises a voltage source.

9. A method of sensing liquid level comprising:

energizing a first electrode with an applied electrical signal for a period of less than one second;

sensing said applied electrical signal with a second electrode when some or all of said first electrode is in contact with said liquid.

10. The method of claim 9, wherein said applied electrical signal is sensed if all or some of said first electrode is in contact with a meniscus formed by said liquid.

11. The method of claim 9, wherein said first electrode is energized for less than one millisecond.

12. The method of claim 9, additionally comprising serially energizing a set of electrodes with an applied electrical signal.

13. The method of claim 12, wherein said serially energizing comprises energizing electrodes from a first electrode proximate to a top of a container holding liquid.

14. A method of estimating a liquid level comprising:

passing a current from a first electrode in at least partial contact with said liquid to a second electrode in at least partial contact with said liquid; and

outputting a signal dependent on an amount of resistance to said current between said electrodes.

15. The method of claim 14, comprising passing said current through a resistor to a circuit common.

16. The method of claim 14, additionally comprising discriminating said output signal.

17. A system for measuring the level of liquid in a container, said system comprising:

a container;

a plurality of transmitter electrodes arranged sequentially from a lower portion of said container to an upper portion of said container;

at least one receiver electrode positioned beneath said plurality of transmitter electrodes;

a control circuit comprising an output for each of said plurality of transmitter electrodes, wherein said control circuit is configured to apply a voltage individually to each of said plurality of transmitter electrodes;

a threshold detector coupled to said receiver electrode, wherein said threshold detector is configured to detect current flow between said transmitter electrodes and said receiver electrode when liquid is in contact with at least a portion of a transmitter electrode that is energized with a voltage.

18. The system of claim 17, wherein said threshold detector comprises a resistor coupled to a circuit common.

19. The system of claim 17, wherein said threshold detector comprises at least one comparator, and wherein said at least one comparator has a first input coupled to said receiver electrode and a second input coupled to a predetermined threshold voltage.

20. The system of claim 19, comprising two comparators having their second inputs coupled to different predetermined threshold voltages.