Load sensing system

• US 5,900,592 A
• Filed: 08/29/1997
• Issued: 05/04/1999
• Est. Priority Date: 08/29/1997
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Energy Research Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Energy Research Corporation (Martin Marietta Corporation)
• Inventors: Wallace, Steven Allen, Sohns, Carl W., Nodine, Robert N.
• Primary Examiner(s): Gibson, Randy W.
• Application Number:
  US08/919,949
• Time in Patent Office: 613 Days
• Field of Search: 177/210 R, 177/210 C, 177/210 FP, 177/212, 177/210 EM, 177/45, 73/862.68, 361/277, 361/280
• US Class Current: 177/210.00R
• CPC Class Codes: G01G 7/06 by electrostatic action

Abstract

A load sensing system inexpensively monitors the weight and temperature of stored nuclear material for long periods of time in widely variable environments. The system can include an electrostatic load cell that encodes weight and temperature into a digital signal which is sent to a remote monitor via a coaxial cable. The same cable is used to supply the load cell with power. When multiple load cells are used, vast inventories of stored nuclear material can be continuously monitored and inventoried of minimal cost.

Claims

1. A load sensing system, comprising:

a load bearing platform providing a first conductive surface;

a base providing a second conductive surface, said first and second conductive surfaces being relatively movable toward and away from one another as a function of a load applied to said load bearing platform;

a sensor plate disposed between said first and second conductive surfaces and at a fixed distance from one of said first and second conductive surfaces, said system being subject to varying ambient conditions causing variation of a dielectric constant between said first and second conductive surfaces;

a time-varying voltage generator connected between said first and second conductive surfaces for establishing an electric field between said first and second conductive surfaces;

said sensor plate providing a signal representative of varying electrical field strength as said first and second conductive surfaces move toward and away from one another; and

,

a processor responsive to said signal from said sensor plate representative of varying electrical field strength between the first and second conductive surfaces, independently of said varying dielectric constant, for generating load value information.

2. The system of claim 1, wherein said processor determines a ratio of electrical field strength between said sensor and said first conductive surfaces and electrical field strength between said first and second conductive surfaces in accordance with said signal, said ratio being independent of said dielectric constant.

3. The system of claim 1, wherein said voltage generator successively applies a first set of time varying voltage signals across said first and second conductive surfaces, said sensor generating a second set of time varying voltage signals responsive to said first set of time varying voltage signals.

4. The system of claim 3, wherein said first and second surfaces are substantially flat.

5. The system of claim 3, further comprising posts for slidingly connecting the load bearing platform and the base, and springs mounted on the posts for urging the load bearing platform and the base apart.

6. The system of claim 3, wherein the base is stationary and the load bearing platform moves as a function of applied load.

7. The system of claim 3, wherein the sensor is fixed relative to the first conductive surface.

8. The system of claim 3, wherein each time varying voltage signal of said first set and said second set includes a ramp voltage component.

9. The system of claim 4, wherein said processor comprises means for comparing each of said voltage ramp components of said second set to a reference voltage, a time duration required for each of said voltage ramp components of said second set to attain a level of said reference voltage representing a datum of said load value information.

10. The system of claim 5, wherein said processor comprises an output pulse signal generator, having successive pulse widths, said widths corresponding to a value of the applied load.

11. The system of claim 6, further comprising a power supply and a detector for sensing current variations from the power supply, wherein said processor is coupled to the power supply, said processor being arranged to draw current as function of said series of pulses, whereby the load value information can be obtained from the current variations.

12. The system of claim 6, further comprising a temperature sensor for said varying ambient conditions, said processor varying time intervals between said pulses of said output signal responsive to said temperature sensor.

13. The system of claim 1, further comprising a temperature sensor for generating a signal representing a temperature of said varying ambient conditions, said processor also being responsive to said temperature sensor.

14. The load sensing system of claim 1, wherein the processor includes at least one of the group of:

a display for the load value information;

a device for storing the load value information;

a printer for printing the load value information; and

an alarm for signaling when the load value information meets a predetermined alarm value.

15. The system of claim 1, wherein said first and second conductive surfaces are everywhere substantially equally spaced from one another.

16. The system of claim 1, wherein said sensor comprises a third conductive surface, said third conductive surface being everywhere substantially equally spaced from each of said first and second conductive surfaces.

17. A load sensing system, comprising:

a base plate;

a plurality of posts extending upwardly from said base plate;

a plurality of compression springs, each spring mounted around one of said posts;

a top plate for supporting an object to be weighed, said top plate having a plurality of holes for receiving said posts, said top plate being movably suspended above said base plate by said compression springs;

a circuit board mounted on said base plate, said circuit board providing;

a conductive pad spaced substantially parallel to said top plate;

a voltage generator for supplying a ramp voltage relative to ground to said conductive pad;

a conductive sensor disc spaced between the conductive pad and the top plate and providing a sensor voltage, said sensor voltage being a function of the spacings of the sensor disc from the conductive pad and the top plate and of the ramp voltage;

an electrical pulse generator for producing pulses of variable duration, the duration of each pulse ending when the sensor voltage reaches a predetermined trigger voltage; and

a processor for converting the pulses into weight information.

18. A load sensing system, comprising:

a load sensor for detecting load and producing a first signal representative of said load;

an ambient condition sensor for detecting a parameter of ambient conditions surrounding the load sensor and producing a second signal representative of said parameter; and

a processor for producing a series of pulses responsive to said first and second signals, said series of pulses having pulse widths and frequency corresponding to the values of said first and second signals.

19. The load sensing system of claim 18, wherein the parameter is temperature, said pulse frequency corresponding to temperature and said pulse widths corresponding to load.