Self-calibrating liquid level transmitter

• US 7,284,427 B2
• Filed: 06/08/2006
• Issued: 10/23/2007
• Est. Priority Date: 06/08/2005
• Status: Active Grant

• Current Assignee: Lumenite Control Technology Incorporated
• Original Assignee: Lumenite Control Technology Incorporated
• Inventors: Calabrese, Ronald V.
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): FRANK, RODNEY T
• Application Number:
  US11/423,090
• Publication Number:
  US 20060277992A1
• Time in Patent Office: 502 Days
• Field of Search: 733/04.R, 733/04.C, 732/90.R
• US Class Current: 73/304.00R
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01F 23/268 mounting arrangements of probes

Abstract

The present disclosure generally relates to a capacitance sensing apparatus equipped with self-calibrating capacity and method of use thereof. The disclosure contemplates the determination using a secondary means of precise fluid levels according to five possible embodiments, and the use of the determined fluid level to recalibrate the capacitance sensing apparatus along its continuous analog level, namely, a variation of the thickness of the insulation of a capacitance sensing apparatus, the variation of the surface geometry of the capacitance sensing apparatus, the use of a dual-probe sensor including a probe with a varied surface geometry, the use of an electromagnetic sensor adjoining the capacitance sensor, and the variation of the electromechanical sensor to serve as a capacitance sensing apparatus. The disclosure also contemplates methods for using the sensing apparatus previously disclosed to measure a fluid level using a self-calibrating capacitance sensing apparatus. Finally, the present disclosure contemplates the use of an improved mathematical method associated with a variability measurement, such as an exponential smoothing method, to determining locally discrete changes in the variability measurement of the capacitance in order to determine a fixed fluid level.

Claims

1. A fluid level sensing apparatus for placement in a container comprising:

a sensor further comprising an electrically conductive first body having a first surface contact area, an electrically conductive third body having a third surface contact area, an electrically conductive second body having a second surface contact area disposed in opposition to the first and the third bodies;

a container progressively filled with a fluid in order to change a fluid level, wherein the fluid electrically couples a first fraction of the first surface contact area and a third fraction of the third surface contact area with a second fraction of the second surface contact area;

a means for energizing the first body and the third body at a voltage compared to the second body;

a first means for detecting the variability in voltage as the fluid level in the container changes as the first fraction of the first surface contact area and the second fraction of the second surface contact area changes;

a second means for detecting the variability of voltage as the fluid level in the container changes as the third fraction of the third surface contact area and the second fraction of the second surface contact area changes,

wherein a surface geometry of the third body varies along the first surface contact area as the fluid level in the container changes to create forced variations in the voltage detected by the means for detecting the variability of the voltage for both the first and the second means for detecting the variability of both voltage.

2. The fluid level sensing apparatus of claim 1, wherein the variation of the surface geometry of the first body varies along a vertical step function.

3. The fluid level sensing apparatus of claim 2, wherein the step function is made of 4-inch sections of a first contact area separated by 7/16-inch sections of a second contact area.

4. The fluid level sensing apparatus of claim 1, wherein the second body is the container and the second surface contact area is the inside wall of the container.

5. The fluid level sensing apparatus of claim 1, wherein the fluid is water.

6. The fluid level sensing apparatus of claim 1, wherein the first body and the third body are probes made of stainless steel.

7. The fluid level sensing apparatus of claim 1, wherein the first body and the third body are two semicircular probes made of stainless steel separated by insulation.

8. The fluid level sensing apparatus of claim 7, wherein the insulation is a layer of phenolic insulation.

9. The fluid level sensing apparatus of claim 1, wherein the variation of the surface geometry of the first body is a semicylinder with regularly spaced notches.

10. The fluid level sensing apparatus of claim 1, wherein the means for detecting the variability in voltage comprises the use of an exponential smoothing method to determine the changes associated with a fixed fluid level, wherein the fixed level is used to calibrate the fluid level sensing apparatus.

11. A method for measuring a fluid level in a container using a dual-probe capacitance sensor, the sensor comprising a first body, a third body having an irregular geometry, and a second body, where the first and third bodies are energized by a voltage and disposed in opposition to the second body, and a fluid electrically couples the opposed first, second and third bodies, the capacitance sensor further comprising a means for detecting the variability in voltage of each of the two probes as the level of the fluid in the container changes and a means for producing a output range and a variability for each probe, wherein the irregular geometry includes notches, the method comprising the steps of:

disposing the dual probe capacitance sensor in the container where a lower measure point of each probe is in contact with a low fluid level to be measured and the higher measure point of each probe is in contact with a high fluid level to be measured;

calibrating each of the two capacitance sensors to the desired output range so the lower measure point is a first extremity of the output range and the high measure point is a second extremity of the output range;

calibrating the means for detecting the variability of the voltage in the third body using a determination method to recognize irregularities in voltage associated with the irregularities in the geometry and associating a fixed fluid level with the irregularities in geometry;

determining a first fluid level based on the measured output voltage of the first capacitance sensor probe;

correcting the first fluid level associated with the measured output voltage of the first probe of the capacitance sensor based on the fluid level associated with the selected irregularities of the second probe.

12. The method of claim 11, wherein the first body of the capacitance sensor is a cylindrical sensor probe.

13. The method of claim 11, wherein the third body of the capacitance sensor is a cylindrical sensor probe with regular notches.

14. The method of claim 11, wherein the regular notches are separated by 4 inches.

15. The method of claim 11, wherein the second body is the fluid container.

16. The method of claim 11, wherein the capacitance sensor output range is 4-20 mA for each of the two probes.

17. The method of claim 11, wherein the determination method is an exponential smoothing method.