Three-toroid electrodeless conductivity cell

• US 5,157,332 A
• Filed: 10/13/1989
• Issued: 10/20/1992
• Est. Priority Date: 10/13/1989
• Status: Expired due to Term

• Current Assignee: Invensys Systems Incorporated (Invensys PLC)
• Original Assignee: The Foxboro Company (Schneider Electric SE)
• Inventors: Reese, Philip C.
• Primary Examiner(s): Harvey, Jack B.
• Application Number:
  US07/421,484
• Time in Patent Office: 1,103 Days
• Field of Search: 324/204, 324/439, 324/442, 324/445, 324/446, 324/441, 324/448-450, 324/342, 73/861.08, 73/861.11
• US Class Current: 324/445
• CPC Class Codes: G01N 27/023 where the material is placed in the field of a coil
• CPC Class Codes: G01R 27/22 Measuring resistance of fluids

Abstract

An electrodeless conductivity measuring cell having three toroids. In one arrangement, the three toroids are stacked together wherein the center toroid is used for sensing and the two outer toroids are the drive toroids. Alternatively, the center toroid may be used as the drive coil and the outer toroids used as sense coils. Washer-shaped, grounded discs are placed between the outer toroids and the center toroid to provide for improved noise rejection. A method of validating the fluid conductivity measurement of such a measuring cell. The fluid conductivity is measured with a three-cell configuration, and then it is measured with a two-cell configuration. If the conductivity is observed to be the same, the cells are likely functioning normally. If fluid leaks into the cell cavity, the measurement of conductivity will change.

Claims

1. An apparatus for measuring the conductivity of a fluid, comprising:

a housing;

first, second, and third toroids axially spaced along a common central axis in said housing and having an input sinusoidal voltage and current, including means for generating a magnetic field in said fluid, and means for magnetic flux sensing all disposed in said housing within said fluid, said means for magnetic flux sensing having an electrical output,

wherein said first and second toroids are magnetically aligned so that the magnetic field interacts with said third toroid to induce a voltage and current in said third toroid, further including a magnetic shield at least partially surrounding the third toroid, wherein said magnetic shield comprises first and second centrally apertured discs arranged to separate said first, second, and third toroids, wherein said magnetic flux including means comprises two toroids electrically connected together in parallel, wherein said first, second, and third toroids have substantially the same inside and outside diameters and are disposed coaxially within said housing to form a single bore for fluid passage therethorugh, and further including a thermosensor means disposed within said housing for measurement compensation based on fluid temperature.

2. The apparatus of claim 1 wherein said third toroid lies between said first and second toroids in the center thereof.

3. The apparatus of claim 2 further including means for sensing the voltage and current induced by said first and second toroids in said third toroid.

4. The apparatus of claim 1 wherein said magnetic shield is grounded.

5. The apparatus of claim 1 wherein the toroids form a cylinder-shaped bore and said magnetic shield reduces unwanted signal transfer between the toroids.

6. The apparatus of claim 1, wherein said electrical current is alternating current.

7. Apparatus for measuring the electrical conductivity of a fluid, comprising:

a sandwich of first, second, and third toroids, each having a centrally located aperture surrounding an axis, the toroids being stacked together coaxially to form a bore permitting fluid passage therein;

a magnetically transparent housing enclosing said toroids;

a source of electrical current;

mean for inducing a magnetic flux in the fluid passage by application of said electrical current to at least one of said toroids;

means for sensing the magnetic flux coupled to at least one of said toroids; and

switch means for selectively connecting each of said first, second, and third toroids as the magnetic flux including means in the fluid passage, and alternatively as the magnetic flux sensing means.

8. The apparatus of claim 7, wherein said magnetic flux inducing means comprises two toroids electrically connected together in parallel.

9. The apparatus of claim 8, wherein said magnetic flux inducing means comprises two toroids surrounding said magnetic flux sensing means.

10. The apparatus of claim 7, wherein said magnetic flux sensing means comprises two toroids electrically connected together in parallel.

11. The apparatus of claim 10, wherein said magnetic flux sensing means comprises two toroids surrounding said magnetic flux inducing means.

12. The apparatus of claim 7, further including a thermosensor disposed within said housing.

13. The apparatus of claim 7, wherein said electrical current is alternating current.

14. In combination, apparatus for measuring the electrical conductivity of a fluid, comprising:

a sandwich of first, second, and third toroids, each having a centrally located aperture surrounding an axis, the toroids being stacked together coaxially to form a bore permitting fluid passage therein;

a magnetically transparent housing enclosing said toroids;

a source of electrical current;

means for inducing a magnetic flux in the fluid passage by application of said electrical current to at least one of said toroids;

means for sensing the magnetic flux coupled to at least one of said toroids; and

means for measurement validation comprising means for selectively connecting and disconnecting each of said first, second, and third toroids as the magnetic flux inducing means in the fluid passage, and alternatively as to magnetic flux sensing means.

15. The apparatus of claim 14, wherein said magnetic flux inducing means comprises two toroids electrically connected together in parallel.

16. The apparatus of claim 15, wherein said magnetic flux inducing means comprises two toroids surrounding said magnetic flux sensing means.

17. The apparatus of claim 14 wherein said magnetic flux sensing means comprises two toroids electrically connected together in parallel.

18. The apparatus of claim 17, wherein said magnetic flux sensing means comprises two toroids surrounding said magnetic flux inducing means.

19. The apparatus of claim 18, further including a thermosensor disposed within said housing.

20. The apparatus of claim 14, wherein said electrical current is alternating current.

21. In combination, apparatus for measuring the electrical conductivity of a fluid, comprising:

a sandwich of first, second, and third toroids, each having a centrally located aperture surrounding an axis, the toroids being stacked together coaxially to form a bore permitting fluid passage therein;

a magnetically transparent housing enclosing said toroids;

a source of electrical current;

means for inducing a magnetic flux in the fluid passage by application of said electrical current to at least one of said toroids;

means for sensing the magnetic flux coupled to at least one of said toroids; and

means for measurement range selection comprising means for selectively connecting and disconnecting each of said first, second, and third toroids as the magnetic flux inducing means in the fluid passage, and alternatively as the magnetic flux sensing means.

22. The apparatus of claim 21, wherein said magnetic flux inducing means comprises two toroids electrically connected together in parallel.

23. The apparatus of claim 22, wherein said magnetic flux inducing means comprises two toroids surrounding said magnetic flux sensing means.

24. The apparatus of claim 21, wherein said magnetic flux sensing means comprises two toroids electrically connected in parallel.

25. The apparatus of claim 24, wherein said magnetic flux sensing means comprises two toroids surrounding said magnetic flux inducing means.

26. The apparatus of claim 21, further including a thermosensor disposed within said housing.

27. The apparatus of claim 21, wherein said electrical current is alternating current.

28. A method of measurement validation with a fluid conductivity meter including a sandwich of at lest three toroids stacked together coaxially to form a bore permitting fluid passage therein, and a source of electrical current, comprising:

inducing a magnetic flux in the fluid passage by application of said electrical current to a first one of said toroids;

sensing the magnetic flux coupled to a second one of said toroids;

selectively connecting the third toroids as the magnetic flux inducing means in the fluid passage;

an

comparing the sensed magnetic flux before and after connecting the third toroid.

29. A method of measurement validation with a fluid conductivity meter including a sandwich of at least three toroids stacked together coaxially to form a bore permitting fluid passage therein, and a source of electrical current, comprising:

inducing a magnetic flux in the fluid passage by application of said electrical current to a first one of said toroids;

sensing the magnetic flux coupled to a second one of said toroids;

selectively connecting the third toroid as the magnetic flux sensing means; and

comparing the sensed magnetic flux before and after connecting the third toroid.

30. A method of measurement range switching in a fluid conductivity meter including a sandwich of at least three toroids stacked together coaxially to form a bore permitting fluid passage therein, and a source of electrical current, comprising:

inducing a magnetic flux in the fluid passage by application of said electrical current to a first one of said toroids;

sensing the magnetic flux coupled to a second one of said toroids;

selectively connecting the third toroid as the magnetic flux inducing means in the fluid passage; and

measuring the sensed magnetic flux.

31. The method of measurement range switching in a fluid conductivity meter including a sandwich of at least three toroids stacked together coaxially to form a bore permitting fluid passage therein, and a source of electrical current, comprising:

inducing a magnetic flux in the fluid passage by application of said electrical current to a first one of said toroids;

sensing the magnetic flux coupled to a second one of said toroids;

selectively connecting the third toroid as the magnetic flux sensing means; and

measuring the sensed magnetic flux.

32. An apparatus for measuring the conductivity of a fluid, comprising:

a housing;

first, second, and third toroids axially spaced along a common central axis in said housing and having an input sinusoidal voltage and current, including means for generating a magnetic field in said fluid, and means for magnetic flux sensing disposed in said housing within said fluid, said means for sensing having a central axis and an electrical output,

wherein said third toroid is magnetically aligned so that the magnetic field interacts with said first and second toroids to induce a voltage and current in said first and second toroids, further including a magnetic shield at least partially surrounding said first and second toroids, wherein said magnetic flux sensing means comprises two toroids electrically connected together in parallel, wherein said first, second, and third toroids have substantially the same inside and outside diameters and are substantially coaxial within said housing to form a single bore for fluid passage therethrough, wherein said magnetic shield comprises first and second centrally apertured discs, arranged to separate said first, second, and third toroids, and further including a thermosensor means disposed within said housing for measurement compensation based on fluid temperature.

33. The apparatus of claim 32 wherein said third toroid lies between said first and second toroids in the center thereof.

34. The apparatus of claim 33 further including means for sensing the voltage and current induced by said third toroid in said first and second toroids.

35. The apparatus of claim 32 wherein said magnetic shield is grounded.

36. The apparatus of claim 32 wherein the first, second, and third toroids form a cylinder-shaped bore and said magnetic shield reduces unwanted signal transfer between the toroids.

37. The apparatus of claim 32, wherein said electrical current is alternating current.