Liquid level and weight sensor

• US 20030033871A1
• Filed: 08/15/2001
• Published: 02/20/2003
• Est. Priority Date: 08/15/2001
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litton Marine Systems Inc.
• Inventors: Klein, A. David, Carroll, Carlton W.
• Granted Patent: US 6,606,905 B2
• Time in Patent Office: Days
• US Class Current: 73/299
• CPC Class Codes: G01F 23/14 by measurement of pressure
• CPC Class Codes: G01G 17/04 for weighing fluids, e.g. gases, pastes
• CPC Class Codes: G01G 3/12 wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing

Abstract

A liquid level and weight sensor utilizes a pressure sensor of any type positioned at the base of the liquid or weight. A second pressure sensor is positioned external to the liquid or weight to measure the ambient pressure. Ambient pressure is subtracted from the total pressure indicated by the base positioned pressure sensor to determine the actual pressure exerted by the liquid or weight on the base positioned sensor. The actual pressure is then utilized in the calculation of liquid level or weight.

The determination of liquid level requires that both the pressure and density of the liquid be known. When the density of the liquid is not known, a third pressure sensor is inserted in the tank at a known level above the first. The differential pressure and differential level are determinative of the liquid'"'"'s density.

Claims

1. An apparatus for sensing a level of a liquid, the liquid having a density, a liquid base, and a liquid surface, the level being the height of the liquid surface above the liquid base, comprising:

at least one base pressure sensor positioned at said base, whereby pressure at said base due said height of said liquid is determined;

at least one external pressure sensor positioned above said liquid surface, whereby pressure external to said liquid surface is determined; and

a level indicator coupled to said base pressure sensor and said external pressure sensor wherein said level of said liquid is determined from pressure values provided by said at least one base pressure sensor and said at least one external pressure sensor.

2. An apparatus in accordance with claim 1 in which said level indicator includes a calculator wherein a pressure value P_E, determined by said at least one external pressure sensor, is subtracted from a pressure value P, determined by said at least base pressure sensor, to obtain a pressure difference P−

P_E and divides this pressure difference by said density to establish said liquid level.

3. An apparatus in accordance with claim 1 further including at least one intermediate sensor coupled to said level indicator and positioned below said surface at a predetermined height above said at least one base sensor, said level indicator utilizing pressure values provided by said at least one base pressure sensor and said at least one intermediate pressure sensor to determine said density of said liquid.

4. An apparatus in accordance with claim 3 wherein a pressure value P_E, determined by said at least one external pressure sensor is subtracted in said level indicator from a pressure value P, determined by said at least one base pressure sensor, to obtain a pressure difference P−

P_E, said pressure difference divided in said level indicator by said liquid density to establish said liquid level.

5. An apparatus in accordance with claim 4 wherein a pressure value P_I, determined by said at least one intermediate pressure sensor, is subtracted in said level indicator from said pressure value P to obtain a second pressure difference P−

P_I, and said pressure difference is divided by said predetermined height to establish said liquid density.

6. An apparatus for determining the weight of an object comprising:

a first pressure sensor having a surface with a surface area on which said object is positioned, said weight of said object causing a pressure to be applied to said surface;

a second pressure sensor positioned external to said object to determine ambient pressure; and

a weight indicator coupled to said first and second pressure sensors wherein said ambient pressure is subtracted from said surface pressure to provide a pressure difference and wherein said pressure difference is multiplied by said surface area to obtain said weight.

7. An apparatus in accordance with claim 6 wherein said first pressure sensor comprises a plurality of pressure sensors each with a surface having a surface area, a sum of each surface area being a total surface area, and wherein said weight indicator multiplies said pressure difference by said total surface area to obtain said weight.

8. A method for sensing a level of a liquid, the liquid having a density, a liquid base, and a liquid surface, the level being the height of the liquid surface above the liquid base, comprising the steps of:

positioning at least one base pressure sensor at said base, whereby pressure at said base due said height of said liquid is determined;

locating at least one external pressure sensor above said liquid surface, whereby pressure external to said liquid surface is determined; and

coupling said base pressure sensor and said external pressure sensor to a level indicator wherein said level of said liquid is determined from pressure values provided by said at least one base pressure sensor and said at least one external pressure sensor.

9. A method in accordance with claim 8 wherein said level indicator further performs the steps of:

subtracting a pressure value P_E, determined by said at least one external pressure sensor, from a pressure value P, determined by said at least one base pressure sensor, to obtain a difference P−

P_E; and

dividing this difference by said density to establish said liquid level.

10. A method in accordance with claim 8 further including the steps of:

positioning at least one intermediate pressure sensor below said surface at a predetermined height above said at least one base sensor;

coupling said at least one intermediate pressure sensor to said level indicator; and

determining liquid density from pressure values provided by said at least one base pressure sensor and said at least one intermediate pressure sensor.

11. A method in accordance with claim 10 further including the steps of:

determining a pressure value P_E at said at least one external pressure sensor;

subtracting said pressure value P_E from said pressure value P to obtain a pressure difference P−

P_E,;

dividing said pressure difference P−

P_E by said predetermined height to establish said liquid density.

12. A method in accordance with claim 11 further including the steps of:

determining a pressure value P_I at said at least one intermediate pressure sensor;

subtracting said pressure value P_I from said pressure value P to obtain a second pressure difference P−

P_I; and

dividing said second pressure difference P−

P_I by said predetermined height to establish said liquid density.

13. A method in accordance with claim 12 further including the step of subtracting a pressure value provided by said at least one external pressure sensor from a pressure value provided by said at least one base pressure sensor when no liquid is present, thereby providing a calibration for subsequent liquid level and density determinations.

14. A method for determining weight of an object comprising the steps of:

providing a first pressure sensor having a surface and a surface area;

locating a second pressure sensor to measure ambient pressure;

positioning said object on said surface, thereby establishing an applied pressure to said first pressure sensor;

subtracting said ambient pressure from said applied pressure, thereby providing a pressure difference; and

multiplying said pressure difference by said surface area to obtain said weight of said object.

15. A method in accordance with claim 14 wherein said first pressure sensor comprises a plurality of pressure sensors each with a surface having a surface area, a sum of each surface area being a total surface area and wherein said pressure difference is multiplied, in said multiplying step, by said total surface area to obtain said weight.

16. A method in accordance with claim 15 further including the step of subtracting a pressure value provided by said second pressure sensor from a pressure value provided by said first sensor when said object is not positioned on said surface, thereby providing a calibration for subsequent weight determinations.