Self-Calibrating Capacitive Transducer for Determining Level of Fluent Materials

• US 20090301188A1
• Filed: 06/09/2008
• Published: 12/10/2009
• Est. Priority Date: 06/09/2008
• Status: Active Grant

• Current Assignee: Rochester Gauges LLC
• Original Assignee: Luna Labs, Inc.
• Inventors: Calcote, Clyde
• Granted Patent: US 8,161,814 B2
• Time in Patent Office: Days
• US Class Current: 73/304.C
• CPC Class Codes: G01F 23/265 for discrete levels
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01F 25/20 of apparatus for measuring liquid level

Abstract

A capacitive transducer for detecting the level of liquids and other materials has one or more antenna probes connected to an integrated chip normally associated with touch-screen displays. Each antenna probe operates independently and senses the level condition of wet or dry flowable materials such as water, oil, fuel, grain, and so on. The antenna probes may be formed as insulated conductive wires or conductive traces between layers of a stiff or flexible substrate, such as a PCB, with the substrate material serving as the insulating layers. Each antenna probe has a different length representing different depths of the material being measured to provide dynamic calibration of the level condition independent of the material type and ambient conditions.

Claims

1. A transducer for measuring a level of fluent material in a container, the transducer comprising:

an electronics section having a touch-sensitive module with at least one port that normally receives and processing signals from a capacitive touch device; and

a probe section having at least one antenna probe connected to the at least one port, the antenna probe including an elongate electrical conductor and an insulating layer covering at least a portion of the electrical conductor;

wherein a change in detected capacitance of the at least one antenna probe is reflective of a change in level of the fluent material.

2. A transducer according to claim 1, wherein the touch-sensitive module comprises a programmable System on Chip (SoC) device having a processor, a memory operably associated with the processor, and at least one oscillator circuit connected between the at least one port and the processor such that a measured capacitance of the at least one antenna probe is translated into count values that are received by the processor for determining level.

3. A transducer according to claim 2, wherein the oscillator circuit is a relaxation oscillator circuit.

4. A transducer according to claim 2, wherein the SoC device comprises a plurality of I/O ports and the at least one antenna probe comprises a plurality of independently functioning antenna probes connected to the I/O ports.

5. A transducer according to claim 4, wherein the antenna probes are of different lengths and include offset tip portions representing discrete measurement levels.

6. A transducer according to claim 5, wherein the longest antenna probe is adapted for continuous measurement of level and the shorter antenna probes are adapted to modify a measurement reading at the different discrete levels to thereby dynamically calibrate the longest antenna probe.

7. A transducer according to claim 1, wherein the touch-sensitive module comprises a plurality of ports and the at least one antenna probe comprises a plurality of antenna probes connected to the ports.

8. A transducer according to claim 7, wherein the antenna probes are of different lengths and include offset tip portions representing discrete measurement levels.

9. A transducer according to claim 8, wherein the longest antenna probe is adapted for continuous measurement of level and the shorter antenna probes are adapted to modify a measurement reading at the different discrete levels to thereby dynamically calibrate the longest antenna probe.

10. A transducer according to claim 8, wherein the probe section further comprises an insulating substrate with the antenna probes being formed as conductive traces between layers of the substrate.

11. A capacitive transducer for measuring a level of fluent material in a container, the transducer comprising:

a primary capacitive antenna probe comprising a first elongate electrical conductor having a first length and adapted to continuously measure material level;

a secondary capacitive antenna probe comprising a second elongate electrical conductor having a second length shorter than the first length and an end tip positioned at a discrete measurement level, the end tip representing a trip point when reached by the material at the discrete measurement level to thereby dynamically calibrate the primary antenna probe.

12. A capacitive transducer according to claim 11, and further comprising an electronics section that receives signals from the primary and secondary capacitive antenna probes in the form of count values to thereby calculate material level;

the electronics section being adapted to modify the calculated level when the count value of the secondary capacitive probe is greater than a predetermined value.

13. A method of determining material level comprising:

providing a plurality of capacitive antenna probes with end tips at discrete positions representing different predetermined material levels;

establishing a pre-calibrated capacitive reference value for each probe;

reading a present capacitive value for each probe;

determining the material level based on the present probe values and probe reference values; and

performing a dynamic calibration after each reading to automatically compensate for variations in material properties and ambient conditions.

14. A method according to claim 13, wherein the step of establishing a pre-calibrated reference value for each probe comprises determining an optimal threshold voltage and scan speed to be applied to each probe during the reading step.

15. A method according to claim 14, wherein the step of establishing a pre-calibrated reference value for each probe further comprises reading a dry value for each probe based on the optimal threshold voltage and scan speed.

16. A method according to claim 13, wherein the step of determining the material level comprises:

establishing a primary probe and at least one secondary probe from the plurality of probes;

determining a coarse material level by counting the number of end tips activated by the presence of the material; and

determining a fine material level by

     1) calculating a delta value of the primary probe between the last end tip activated and an adjacent tip that has not been activated, and

     2) adding the delta value to the coarse material level.

17. A method according to claim 16, wherein the step of calculating the delta value comprises:

determining one or more space values between activated probe tips; and

calculating a difference between the primary probe value and a summation of the one or more space values.

18. A method according to claim 17, wherein the step of performing a dynamic calibration comprises:

detecting activation of an end tip for determining a predefined material level that has been reached;

reading the primary probe value upon activation of the end tip; and

associating the primary probe value with the predefined material level.