Liquid level measurement system for tanks

• US 5,076,101 A
• Filed: 12/21/1990
• Issued: 12/31/1991
• Est. Priority Date: 12/21/1990
• Status: Expired due to Term

• Current Assignee: Siemens Milltronics Process Instruments, Inc. (Siemens AG)
• Original Assignee: Federal Industries Group Incorporated
• Inventors: Lazure, Gary P.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): GUTIERREZ, DIEGO F
• Application Number:
  US07/631,453
• Time in Patent Office: 375 Days
• Field of Search: 73/290 V, 73/319, 73/305, 73/DIG. 5, 367/908, 367/87, 367/107, 181/123, 181/124, 181/402
• US Class Current: 73/290.00V
• CPC Class Codes: G01F 23/2962 Measuring transit time of reflected waves
• CPC Class Codes: G01F 23/72 using magnetically actuated indicating means
• CPC Class Codes: Y10S 181/402 Liquid
• CPC Class Codes: Y10S 367/908 Material level detection, e.g. liquid level
• CPC Class Codes: Y10S 73/05 Liquid levels with magnetic transmission

Abstract

A system for sensing the level of contents in a container is disclosed. A tubular member is vertically disposed in the container and sealed from the contents of the container. A marker located in the tubular member and generating a peripheral polarized magnetic field, is levitated at the height of float means located around the tubular member buoyed on the contents of the container and generating a polarized magnetic field within the tubular member of like polarity beneath the polarized magnetic field of the marker. A depth transducer located at one end of the tubular member forms part of a pulse-echo ranging system which calculates ranges on the basis of a time lag between emission of an ultrasonic signal by the depth transducer and receipt of at least one return echo signal from the marker in order to determine the depth of the marker in the tubular member, and indirectly, the level of contents in the container.

Claims

1. A system for sensing the level of contents in a container, comprising:

a tubular member having a top and bottom end, vertically disposed in the container and sealed from the contents of the container.

a depth transducer for transmitting and receiving signals located at one end of the tubular member;

a levitating marker located in the tubular member in signal reflecting relationship with the depth transducer, whereby the depth transducer senses the depth of the marker in the tubular member, which corresponds to the level of contents in the container, said levitating marker including means to generate a peripheral polarized magnetic field;

float means surrounding the tubular member and buoyantly supported on the contents in the container, said float means generating, within the tubular member and immediately beneath the field generated by said levitating marker, a peripheral polarized magnetic field of like polarity to and concentric with the magnetic field generated by said marker, thereby levitating said marker; and

means to maintain said marker in a stable equilibrium within the tubular member.

2. A system, according to claim 1, wherein the depth transducer is located at the top end of the tubular member above said maximum upper content level.

3. A system, according to claim 1, wherein the depth transducer is adapted to emit ultrasonic signals into the tubular member and to receive return echo signals, and wherein the marker comprises a target facing said depth transducer, the target having a first reflective surface facing the depth transducer, whereby to echo at least a first portion of the signals back to the depth transducer.

4. A system, according to claim 3, wherein the target has defined therethrough an aperture permitting passage of a second portion of the signals from the depth transducer to an opposite end of the tubular member, said opposite end of the tubular member being adapted to directly echo at least some of said second portion of the signal through the aperture in the target and back to the depth transducer.

5. A system, according to claim 4, wherein the target further comprises a second reflective surface facing the opposite end of the tubular member, whereby some of said second group of signals will echo between said opposite end of the tubular member and the second reflective surface of the target before returning from the opposite and of the tubular member through the aperture in the target and back to the depth transducer.

6. A system, according to claim 3, wherein the marker comprises a hollow piston extending coaxially within the tubular member and having a piston head at its upper end and the target comprises a disc of reflective material on the piston head.

7. A system, according to claim 3, wherein the depth transducer forms part of a pulse-echo ranging system which calculates ranges on the basis of the time lag between emission of a signal by the depth transducer and receipt of at least one return echo signal by the transducer.

8. A system, according to claim 1, wherein the bottom end of the tubular member is secured to a bottom wall of the container.

9. A system, according to claim 1, wherein the bottom end of the tubular member is weighted to counteract buoyant forces applied to it by the contents of the container.

10. A system, according to claim 1, further comprising content egress means located in the container above the bottom of the tubular member.

11. A system, according to claim 1, wherein the float means comprise an annulus of buoyant material surrounding the tubular member, the annulus having at least one magnet affixed to its inner circumference to exert a peripheral polarized magnetic force into the tubular means.

12. A system, according to claim 11, wherein said at least one magnet comprises an array of magnets disposed around the inner circumference of the annulus.

13. A system, according to claim 11, wherein said at least one magnet is an annular magnet.

14. A system, according to claim 11, wherein the annulus is composed of a styrofoam core surrounded by a fluid impermeable coating.

15. A system, according to claim 1, wherein the marker comprises a hollow piston extending coaxially within the tubular member and having a piston head at its upper end.

16. A system, according to claim 15, wherein the piston head is provided with an annular magnet providing the peripheral polarized magnetic field.

17. A system according to claim 15, wherein the piston is provided with an upper annular lip providing loose sliding fit of the piston in the tubular member whereby to substantially centre the piston in the tubular member.

18. A system, according to claim 15, wherein the piston further comprises a depending skirt portion forming the means to maintain stable equilibrium of the marker.