SELF-CALIBRATING LIQUID LEVEL TRANSMITTER

• US 20090064757A1
• Filed: 11/14/2008
• Published: 03/12/2009
• 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.
• Granted Patent: US 7,665,358 B2
• Time in Patent Office: Days
• US Class Current: 73/1.730
• 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, an insulating layer having a thickness disposed over the first body to cover a first surface contact area, an electrically conductive second body having a second surface contact area disposed in opposition to the first body;

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 second fraction of the second surface contact area;

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

a means for detecting the variability in voltage as the fluid level changes, wherein the thickness of the insulating layer varies along the first surface contact area as the level fluid changes to create forced variations in the voltage detected by the means for detecting the variability of the voltage.

2. The fluid level sensing apparatus of claim 1, wherein the thickness is varied vertically along a step function.

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

4. The fluid level sensing apparatus of claim 1, wherein the insulating material is polytetrafluoethylene.

5. 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.

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

7. The fluid level sensing apparatus of claim 1, wherein the first body is a cylindrical rod of stainless steel.

8. The fluid level sensing apparatus of claim 1, wherein the means for detecting the variability in voltage comprises the use of 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.

10. The fluid level sensing apparatus of claim 1, wherein the first body geometry is varied vertically along a step function.

11. The fluid level sensing apparatus of claim 2, wherein the step function is made of 4-inch sections separated by 7/16-inch sections.

12. The fluid level sensing apparatus of claim 1, wherein the insulating material is Polytetrafluoethylene.

13. 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.

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

15. The fluid level sensing apparatus of claim 1, wherein the means for detecting the variability in voltage comprises the use of 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.

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

a sensor further comprising an electrically conductive first body having an irregular surface geometry, an insulating layer disposed placed over the first body to cover a first surface contact area, an electrically conductive second body having a second surface contact area disposed in opposition to the first body;

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 second fraction of the second surface contact area;

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

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

16-36. -36. (canceled)

37. A method for measuring a fluid level in a container using a capacitance sensor, the sensor comprising a first body having an insulation layer having an irregular thickness, and a second body, where the first body is energized by a voltage and disposed in opposition to the second body, a fluid electrically coupling the opposed first and second bodies, and a means for detecting the variability in voltage of the sensor as a fluid level changes to produce a output range, wherein the irregular thickness includes successive levels in a step function, the method comprising the steps of:

disposing the capacitance sensor in the container so that a lower measure point is in contact with a low fluid level to be measured and the higher measure point is in contact with a high fluid level to be measured;

calibrating the capacitance sensor to the desired output range so that 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;

further calibrating the capacitance sensor and means for detecting the variability of the voltage using a determination method to recognize variation associated with the successive levels in the step function associated with the irregular thickness of the insulation in order to determine a precise fluid level for recalibration associated with each successive level in the step function;

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

recalibrating the first fluid level associated with the measured output voltage based on the precise fluid level.

38. The method of claim 37, wherein the first body of the capacitance sensor is a cylindrical stainless sensor.

39. The method of claim 37, wherein the insulation is polytetrafluoethylene.

40. The method of claim 37, wherein the regular steps in the step function are separated by 4 inches.

41. The method of claim 37, wherein the second body is the fluid container.

42. The method of claim 37, wherein the capacitance sensor output range is 4-20 mA.

43. The method of claim 37, wherein the capacitance sensor output range is 0-5 volts.

44. A method for measuring a fluid level in a container using a capacitance sensor, the sensor comprising a first insulated body having an irregular geometry, and a second body, where the first body is energized by a voltage and disposed in opposition of the second body, a fluid electrically coupling the opposed bodies, and a means for detecting the variability in voltage of the sensor as the fluid level changes to produce a output range, wherein the irregular geometry is made of successive levels in a step function, the method comprising the steps of:

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

calibrating the capacitance sensor to the desired output range so that 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;

further calibrating the capacitance sensor and means for detecting the variability of the voltage using a determination method to recognize variation associated with the successive levels in the step function associated with the irregular geometry in order to determine a precise fluid level for recalibration associated with each successive level in the step function;

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

recalibrating the first level of fluid associated with the measured output voltage based with the precise fluid level.

45. The method of claim 44, wherein the first body of the capacitance sensor is a cylindrical stainless sensor.

46. The method of claim 44, wherein the insulation is polytetrafluoethylene.

47. The method of claim 44, wherein the regular steps in the step function are separated by 4 inches.

48. The method of claim 44, wherein the second body is the fluid container.

49. The method of claim 44, wherein the capacitance sensor output range is 4-20 mA.

50. The method of claim 44, wherein the capacitance sensor output range is 0-5 volts.

51-63. -63. (canceled)

64. A determination method for recognition and quantification of irregularities associated with fixed fluid levels using a capacitance fluid level sensing apparatus, the determination method comprising the steps of:

determining a variability in capacitance by measuring and comparing the capacitance over a fixed interval of time;

associating the variability of capacitance with a data point;

storing the data points and the quantity of data points in two arithmetic sums;

determining a new data point to be quantified as a possible irregularity;

adding the data point to the arithmetic sums;

reviewing the evolution of a derivative function of the arithmetic sums to determine if a change in slope is observed over a fixed number of sum intervals; and

comparing the change in the derivative function with a predetermined value to determine if a slope change is observed and if a fixed fluid level is calculated.