Liquid storage gauging method and apparatus

• US 4,553,216 A
• Filed: 12/27/1982
• Issued: 11/12/1985
• Est. Priority Date: 12/27/1982
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Stevens, Glenn G., Kennedy, Roger C.
• Primary Examiner(s): Wise, Edward J.
• Application Number:
  US06/452,966
• Time in Patent Office: 1,051 Days
• Field of Search: 364/558, 364/509, 364/424, 73/301, 73/304 C, 73/149
• US Class Current: 702/55
• CPC Class Codes: G01F 23/18 Indicating, recording or alarm devices actuated electrically
• CPC Class Codes: G01F 23/802 Particular electronic circuits for digital processing equipment

Abstract

The density, volume and mass of fuel held in an aircraft tank are measured by a system of four pressure sensors interfaced with an associated microcomputer. The sensors are disposed in a predetermined array at unequal depths below the surface plane of the contained fuel. Electrical transducers associated with the pressure sensors develop electrical signals representing the associated pressures P1, P2, P3, and P4 and these signals are processed by the microcomputer which is programmed to correlate the individual pressure signals and known coordinate locations of the sensors with certain unknown parameters including the fuel density ρ, and the orientation and distance of the fuel surface plane relative to each pressure sensor. These relationships establish four simultaneous equations that are processed by the programmed microcomputer to yield simultaneous solutions for the density ρ, and for the position of the fuel surface plane. Further processing by the programmed microcomputer of the signals representing the position of the surface plane yields output data signals representing the volume of the fuel, i.e., that which fills the tank up to the now-determined plane of the fuel surface level. Thereafter the previously measured density ρ is automatically multiplied in the microcomputer by the determined volume of fuel to yield data signals representing the fuel mass. The resulting signals for the density ρ, volume V and mass M of the fuel are displayed on readout devices responsive to output signals from the microcomputer. In an alternative embodiment, a system of three pressure sensors is employed in a similar manner to produce information signals representing volume V and mass M of the fuel when the density ρ is either known or assumed.

Claims

1. A method of measuring density ρ

of a liquid from a plurality of pressure measurements, comprising the steps of;

sensing the liquid pressure P_i at a plurality of at least four separate sensing locations, said sensing locations defined relative to a selected coordinate system by vectors r_i. where i=1, 2, 3, and 4, and disposed at different depths relative to the surface plane of the contained liquid that is being measured;

converting the sensed pressures P_i, corresponding to the sensing locations into representative first, second, third, and fourth electrical signals;

inputting the first, second, third, and fourth electrical signals along with signals representative of vectors r_i into a computing device;

setting up in a computing device a formula relating an unknown density ρ

of the liquid as a function of the first, second, third, and fourth electrical signals representing pressures P_i that is based on a series of simultaneously solvable equations relating such liquid pressures to the unknown density ρ

of the liquid, the unknown depth of such sensor locations defined by vectors r_i and said surface plane of the liquid which is common to all of the sensor locations, and computing in the computing device an electrical signal representing density ρ

as a function of the first, second, third, and fourth electrical signals representing pressures P_i ; and

outputting from said computing device the density ρ

.

2. The method of claim 1 wherein said step of computing includes the substep of:

computing the orientation and distance of said surface plane of the liquid with respect to said sensing locations whereat said pressures P_i are sensed.

3. The method of claim 1 for measuring a volume of the liquid when confined in a container of predetermined configuration, wherein said step of computing further comprises the substeps of computing the orientation and distance of said surface plane of the liquid within said container as a function of the electrical signals representing the pressures P_i and the measured density ρ

of the liquid, wherein said orientation and distance of said surface plane are computed relative to said pressure sensing locations;

computing the volume V of the liquid as a function of a predetermined relationship between said orientation and distance of the surface plane relative to said pressure sensing locations and said fixed configuration of said container; and

said outputting step comprising the substep of outputting the computed volume of the liquid.

4. The method of claim 3 for measuring, in addition to density ρ

and volume V of the liquid, a mass M, further including the step of;

computing the mass M of the liquid confined in said container as a function of the measure density ρ and

volume V; and

,

said outputting step further including outputting the computed mass M.

8. The apparatus as set forth in claim 1 wherein said computing means further comprises means for producing electrical signals representing the orientation of said surface plane relative to said point of origin with respect to which said predetermined locations of said first, second, third and fourth pressure sensor means are defined.

5. An apparatus for measuring density ρ

of a liqud from a plurality of pressure measurements, comprising;

first, second, third and fourth pressure sensor means adapted to be disposed at known, spaced-apart locations beneath a surface plane of the liquid, wherein said locations are defined by position vectors r_i (i=1,2,3,4) and are disposed at different, unknown distances from said surface plane, said position vectors r_i (i=1,2,3,4) being related to a coordinate system and defined by associated coordinates x_i,y_i z_i (i=1,2,3,4);

electrical means associated with said pressure sensor means for producing first, second, third and fourth electrical signals representing pressures P₁, P₂, P₃, and P₄ existing within the liquid respectively at said associated locations defined by position vectors r_i (i=1,2,3,4), said density ρ

being a function of said first, second, third and fourth electrical signals representing pressures P₁, P₂, P₃, and P₄ and said coordinates x_i, y_i, z_i (i=1,2,3,4);

computing means for computing density ρ

as a function of said first, second, third and fourth electrical signals and said coordinates x_i, y_i, z_i (i=1,2,3,4); and

output means connected to said computing means for indicating the density ρ

.

6. The apparatus of claim 5 wherein said pressure sensor means further includes means for detecting said liquid pressure while communicating with ambient pressure.

7. The apparatus of claim 5 wherein said computing means further includes means for computing the orientation and distance of said surface plane of the liquid with respect ot said predetermined locations of said first, second, third, and fourth pressure sensor means.

9. The apparatus set forth in claim 5 in which said first, second, third and fourth pressure sensor means are disposed in a liquid container of predetermined configuration, and wherein said computing means comprises first submeans for computing an orientation and distance of the surface plane of a liquid within said container as a function of the determined density ρ

of the liquid; and

second submeans for producing electrical signals that represent a liquid volume as a function of a predetermined relationship between an orientation and distance of the surface plane of the liquid relative to the point of origin of said coordinate system and said predetermined configuration of said container.

10. An apparatus for determining the position of a surface plane of a liquid from a plurality of subsurface pressure measurements comprising:

first, second and third pressure sensor means adapted to be disposed beneath the surface plane of a liquid having a given density ρ and

at predetermined locations of nonequal depths below such surface plane, said predetermined locations being defined by a coordinate system referenced to a predetermined point of origin;

electrical signal-producing means associated with said first, second and third pressure sensor means for producing electrical signals representing liquid pressures P₁, P₂, and P₃ respectively at said first, second and third pressure sensor means;

signal-processing means for receiving said signals representing pressures P₁, P₂, and P₃ and for producing electrical signals representing the orientation and distance of the surface plane referenced by said coordinate system to said point of origin.

11. The apparatus of claim 10 further comprising a container of known configuration and in which said first, second and third pressure sensor means and said liquid are disposed, and wherein signal-processing means comprises submeans for producing electrical signals representing the volume of said liquid that is present in said container as a function of the relationship between said orientation and distance of the surface plane relative to said point of origin and said known configuration of said container.

12. A method of measuring density ρ

of a liquid from a plurality of pressure measurements, comprising the steps of;

sensing the liquid pressure at a plurality of at least four separate sensing locations, said locations defined relative to a selected coordinate system by associated position vectors r_i (i=1,2,3,4), wherein said sensing locations are disposed at different depths relative to the surface plane of the liquid that is being measured and the distance from the origin of said coordinate system to said surface plane along a line perpendicular to that plane is symbolized as d, and wherein n symbolizes a unit vector relative to the coordinate system that is normal to said surface plane;

converting the sensed pressures corresponding to the sensing locations into representative first, second, third and fourth electrical signals symbolized by P_i (i=1,2,3,4);

inputting the first, second, third and fourth electrical signals along with electrical signals representative of said vectors r_i and n and electrical signals representative of distance d into a computer;

setting up within said computer formulas equating distance d with the sum of the product of vector n and vectors r_i and the quotient of pressure P_i over density ρ

for i=1,2,3,4;

simultaneously solving said formulas within said computer to determine the value of density ρ

; and

outputting from said computer said value of density ρ

for display or recordation.

13. The method of claim 12 wherein said step of simultaneously solving said formulas includes solving said formulas to determine the values of the vector n and the values of distances d for defining the surface plane of the liquid with respect to said coordinate system

14. The method of claim 13 for measuring, in addition to the density ρ

, volume V of the liquid, wherein the liquid is confined in a container of predetermined configuration, said inputting step including the substep of storing in the computer a multitude of values for vector n and d that define a multitude of possible positions of said surface plane and an associated multitude of possible volumes defined by said surface plane with respect to said container;

wherein after said simultaneously solving step the method further includes the steps of comparing said solved value of vector n and d with each stored value of vector n and d to determine which stored value of vector n and d most closely correspond to the solved value of vector n and d; and

said outputting step further including outputting the value of the stored volume corresponding to the stored value of vector n and d determined to most closely correspond to the solved value of vector n and d.