Level indicator

• US 4,987,776 A
• Filed: 09/05/1989
• Issued: 01/29/1991
• Est. Priority Date: 03/16/1988
• Status: Expired due to Fees

• Current Assignee: Euromart Corporation
• Original Assignee: Euromart Corporation
• Inventors: Koon, Terry D.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Dowling, William C.
• Application Number:
  US07/403,183
• Time in Patent Office: 511 Days
• Field of Search: 73/304 C, 73/290 R, 340/612, 340/620, 340/618, 361/284, 324/61 P
• US Class Current: 73/304.00C
• CPC Class Codes: G01F 23/265 for discrete levels
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01F 23/268 mounting arrangements of probes

Abstract

A storage installation which is capable of storing a variety of free-flowing materials, both conductive and non-conductive, includes a level sensing device which may be disposed either exteriorly or interiorly thereof. The device has either one or a plurality of level sensor and sensor circuit pairs which are preferably disposed vertically within a non-electrically conducting tube which may be hermetically sealed from contact with the stored material. The level sensors comprise respective sensing capacitors, each having effectively a single plate construction. Grounded electrical contacts, if relatively adjacent, may comprise the other side of the effective sensing capacitor. Electrostatic force lines flow outward from the sensing capacitor(s), and are differentially interfered with by the presence or absence of materials or objects to be sensed. Such interference affects the dielectric constant of the respective sensing capacitor, which can in turn be detected to drive a level indicator display.

Claims

1. A sensing apparatus, comprising:

oscillator sensing means having an oscillator circuit means for outputting an oscillatory signal and a sensing element means associated therewith for radiating an electrostatic field therefrom during operation of said oscillator circuit means, said oscillator sensing means providing a sensing signal output having a voltage level which varies in proportion to changes in such electrostatic field caused by reactions thereof to the proximity of material or object to be sensed; and

output circuit means, responsive to said sensing signal output from said oscillator sensing means, for outputting a voltage level indicative of the proximity of the sensed object or material to said sensing element means;

wherein

said oscillator sensing means further includes a connecting wire interconnecting said oscillator circuit means and said sensing element means, and wherein said connecting wire has a relatively smaller surface area than said sensing element means so as to minimize interference therewith.

2. A sensing apparatus as in claim 1, wherein said voltage level from said output circuit means is a DC voltage, and said output circuit means comprises an operational amplifier with said sensing signal output from said oscillating sensing means connected to the non-inverting input of such operational amplifier.

3. A sensing apparatus as in claim 1, wherein said sensing element means comprises a metallic surface sensor.

4. A sensing apparatus as in claim 3, wherein said metallic surface sensor comprises a section of sensing wire.

5. A sensing apparatus as in claim 3, wherein said metallic surface sensor comprises a metallic plate.

6. A sensing apparatus as in claim 5, wherein said metallic plate is relatively elongated.

7. A sensing apparatus as in claim 1, wherein said sensing apparatus is adapted to be received exteriorly of a container for measuring the level of stored materials therein.

8. A sensing apparatus as in claim 1, wherein said sensing apparatus is adapted to be received interiorly of a container for measuring the level of stored materials therein.

9. A sensing apparatus as in claim 1, further including indicator means, responsive to said voltage level from said output circuit means, for indicating the level of materials within a container with which said sensing apparatus is associated.

10. A sensing apparatus as in claim 9, wherein said indicator means includes at least one voltage comparator means for comparing said voltage level with a predetermined voltage level.

11. A sensing apparatus as in claim 1, wherein said oscillator sensing means includes a plurality of said sensing element means for radiating respective electrostatic fields therefrom for sensing the presence of subject materials or objects at different locations.

12. Detection apparatus, comprising:

oscillator circuit means for outputting an oscillatory signal;

a single-sided capacitive element;

a connecting wire, coupling said capacitive element to the output of said oscillator circuit means, and having a smaller surface area than said capacitive element; and

an operational amplifier, having a non-inverting input thereof connected with said oscillator circuit means output;

wherein said operational amplifier has a DC voltage level output which is proportional to the relative proximity of given materials to said capacitive element, with variations in such relative proximity influencing the electrostatic field emanating from said capacitive element during operation of said oscillator circuit means, whereby such variations in relative proximity are detected.

13. Detection apparatus as in claim 12, wherein said capacitive element comprises a metallic surface element.

14. Detection apparatus as in claim 12, wherein said apparatus is associated with a container for determining the level of materials therein, by which materials the electrostatic field from said capacitive element is differentially influenced, resulting in corresponding changes in said DC voltage level output.

15. Detection apparatus as in claim 14, wherein said apparatus is substantially interiorly associated with a container.

16. Detection apparatus as in claim 14, wherein said apparatus is substantially exteriorly associated with a container.

17. Detection apparatus as in claim 14, further including output indicator means, responsive to said DC voltage level for indicating different levels of materials within the container.

18. Detection apparatus as in claim 14, further including a plurality of such capacitive elements for respectively emanating electrostatic fields from their respective locations.

19. Apparatus for sensing the level of conductive or non-conductive materials stored in a container, without electrical contact with such materials, said apparatus consisting of:

an oscillator circuit connected to single-plate capacitor means and driving same for producing a large, dispersed electrostatic field in the vicinity of a container;

an operational amplifier, with the non-inverting input thereof connected to said oscillator circuit and said capacitor means, and outputting therefrom a DC voltage having a level which varies in proportion to changes to the electrostatic field, which is influenced by the relative amount of stored materials in the container; and

indicator means, responsive to the level of said DC voltage, for indicating the amount of materials stored in the container.

20. A sensing apparatus as in claim 19, wherein said single-plate capacitor means comprises a segment of sensing wire.

21. A sensing apparatus as in claim 19, wherein said single-plate capacitor means comprises a metal surface sensor, the size and construction of which is selected for use with given container applications.

22. A sensing apparatus as in claim 19, wherein said capacitor means is associated with the container exteriorly thereto.

23. A sensing apparatus as in claim 19, wherein said capacitor means is associated with the container interiorly thereof.

24. A sensing apparatus as in claim 19, wherein oscillator circuit includes a junction FET with its gate connected to an inductance coil, its drain connected to a power supply, and its source connected to said capacitor means and to said operational amplifier non-inverting input.