Self-calibrating liquid level transmitter

• US 7,461,550 B2
• Filed: 09/07/2007
• Issued: 12/09/2008
• 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 E.
• Assistant Examiner(s): Frank; Rodney T
• Application Number:
  US11/851,835
• Publication Number:
  US 20070295056A1
• Time in Patent Office: 459 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 capacitance sensor further comprising an electrically conductive first body having a first surface contact area, an electrically conductive second body having a second surface contact area disposed in opposition to the first body;

an electromechanical sensor further comprising a guide positioned in a fluid to be measured disposed in the container, a float movably connected to the guide to rise and fall with a fluid level, a series of reed switches disposed at pre-selected intervals along the guide, and a means for establishing a magnetic field across the reed switches,

a container progressively filled with the fluid in order to change the 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, and wherein the change in the fluid level changes the float position along the guide in order to move the means for establishing a magnetic field and close a reed switch associated with a pre-determined fluid level,

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

a 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; and

a means for determining which reed switch is closed as the fluid level in the container changes, wherein the determination of the fluid level based on the means for determining which reed switch is closed is used to correct the determination of the fluid level based on the means for detecting the variability of the voltage by fixing known level steps, wherein the circular vertical probe is covered by a polytetrafluoethylene insulation.

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

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

an electromechanical sensor further comprising a guide positioned in a fluid to be measured disposed in the container, a float movably connected to the guide to rise and fall with a fluid level, a series of reed switches disposed at pre-selected intervals along the guide, and a means for establishing a magnetic field across the reed switches,

a container progressively filled with the fluid in order to change the 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, and wherein the change in the fluid level changes the float position along the guide in order to move the means for establishing a magnetic field and close a reed switch associated with a pre-determined fluid level,

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

a 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; and

a means for determining which reed switch is closed as the fluid level in the container changes, wherein the determination of the fluid level based on the means for determining which reed switch is closed is used to correct the determination of the fluid level based on the means for detecting the variability of the voltage by fixing known level steps,

wherein the guide of the electromechanical sensor serves as the first body of the capacitance sensor.

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

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

an electromechanical sensor further comprising a guide positioned in a fluid to be measured disposed in the container, a float movably connected to the guide to rise and fall with a fluid level, a series of reed switches disposed at pre-selected intervals along the guide, and a means for establishing a magnetic field across the reed switches,

a container progressively filled with the fluid in order to change the 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, and wherein the change in the fluid level changes the float position along the guide in order to move the means for establishing a magnetic field and close a reed switch associated with a pre-determined fluid level,

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

a 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; and

a means for determining which reed switch is closed as the fluid level in the container changes, wherein the determination of the fluid level based on the means for determining which reed switch is closed is used to correct the determination of the fluid level based on the means for detecting the variability of the voltage by fixing known level steps,

wherein the second body is the container and the second surface contact area is the inside wall of the container.

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

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

an electromechanical sensor further comprising a guide positioned in a fluid to be measured disposed in the container, a float movably connected to the guide to rise and fall with a fluid level, a series of reed switches disposed at pre-selected intervals along the guide, and a means for establishing a magnetic field across the reed switches,

a container progressively filled with the fluid in order to change the 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, and wherein the change in the fluid level changes the float position along the guide in order to move the means for establishing a magnetic field and close a reed switch associated with a pre-determined fluid level,

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

a 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; and

a means for determining which reed switch is closed as the fluid level in the container changes, wherein the determination of the fluid level based on the means for determining which reed switch is closed is used to correct the determination of the fluid level based on the means for detecting the variability of the voltage by fixing known level steps,

wherein the means of establishing a magnetic field is a ring magnet, and

wherein the reed switches are located inside a polytetrafluoethylene-encapsulated guide.

5. A method for measuring a fluid level in a container using a capacitance sensor and an electromechanical sensor, the capacitance sensor comprising a first conductive body and a second conductive body energized by a voltage disposed in position, and a fluid electrically coupling the first body and second body, a means for detecting the variability in voltage as the fluid level in the container changes and producing a output range, and the electromechanical sensor extending in the container comprising a guide, a float movably connected to the guide including a means for establishing a magnetic field on a reed switch disposed on the guide at a fixed fluid level and producing a fixed voltage output associated with the reed switch within a output voltage range, the method comprising the steps of:

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

calibrating the capacitance sensor 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 electromechanical sensor to the desired output range so the reed switch corresponds to a fixed output voltage within the output voltage range;

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

correcting the first fluid level associated with the measured output voltage of the capacitance sensor to the fluid level associated with the reed switch, once the fluid level of the reed switch is reached.

6. The method of claim 5, wherein the first body of the capacitance sensor is a cylindrical sensor probe.

7. The method of claim 5, wherein the second body of the capacitance sensor is the fluid container.

8. The method of claim 5, wherein the guide of the electromechanical sensor is covered with insulation, and wherein the first body of the capacitance sensor is the guide.

9. The method of claim 5, wherein the capacitance sensor output range is 4-20 mA.

10. The method of claim 5, wherein a plurality of reed switches is located inside the guide.