Non-symmetrical inductive sensors having ferrite coil geometries with different top and base geometries

• US 5,336,997 A
• Filed: 09/21/1992
• Issued: 08/09/1994
• Est. Priority Date: 09/21/1992
• Status: Expired due to Term

• Current Assignee: Virginia Polytechnic Institute and State University
• Original Assignee: Virginia Tech Intellectual Properties, Inc.
• Inventors: Onishi, Shinzo, Anim-Appiah, Kofi D., Riad, Sedki M.
• Primary Examiner(s): Snow, Walter E.
• Application Number:
  US07/947,101
• Time in Patent Office: 687 Days
• Field of Search: 324/219, 324/220, 324/221, 324/226, 324/225, 324/234, 324/236, 324/237, 324/238, 324/239, 324/240, 324/207.12, 324/207.13, 324/207.15, 324/207.16 , 324/207.26, 336/83, 336/221, 336/233
• US Class Current: 324/207.16
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01V 3/10 using induction coils
• CPC Class Codes: H01F 17/04 with magnetic core

Abstract

New core geometries to increase the sensing range of proximity transducers in general, and eddy current killed oscillator mode sensors, in particular. A theoretical analysis yields electromagnetic parameters that facilitate prediction of the sensing capability of any ferrite core geometry. The results of this analysis is applied to a multitude of Finite Element Analysis models to study changes in maximum sensing distance due to ferrite core geometry modifications. This yielded preferred embodiments for shielded and unshielded sensors.

Claims

1. A non-symmetrical ferrite core for use in an inductive sensor that concentrates and focuses a magnetic field produced by a current-carrying winding, said core comprising:

a disk shaped base portion;

a disk shaped top portion; and

an intermediate portion of reduced diameter to define a coil receiving location for receiving the current-carrying winding, said intermediate portion joining said base and top portions in a spaced essentially parallel relationship, said tip portion having a diameter equal to or less than the diameter of said base portion, and said base portion being thicker than said top portion.

2. The ferrite core of claim 1, wherein said thickness of said base portion is greater than twice the thickness of said top portion.

3. The ferrite core of claim 1, further comprising a longitudinal bore extending throughout the entire length of said intermediate portion.

4. A non-symmetrical ferrite core for use in an inductive sensor that concentrates and focuses a magnetic field produced by a current-carrying winding, said core comprising:

a disk shaped base portion having an upper peripheral edge;

a disk shaped top portion;

an intermediate portion of reduced diameter to define a coil receiving location for receiving the current-carrying winding, said intermediate portion joining said base and top portions in a spaced essentially parallel relationship, said top portion having a diameter less than the diameter of said base portion; and

a circumferential ring portion positioned about the peripheral edge of said base portion to provide a side shield about said coil receiving portion.

5. The ferrite core of claim 4, wherein said intermediate portion is sized to provide a space between said top portion and said coil receiving location.

6. The ferrite core of claim 5, wherein, when the dimension of sad space is reduced to zero, the diameter of said top portion is less than the diameter of said base portion by at least the thickness of said ring portion.

7. A non-symmetrical inductive proximity sensor that concentrates and focuses a magnetic field produced by a current-carrying winding, said sensor comprising:

a disk shaped base portion;

a disk shaped top portion;

an intermediate portion of reduced diameter to define a coil receiving location, said intermediate portion joining said base and top portions in a spaced essentially parallel relationship, said top portion having a diameter less than the diameter of said base portion; and

current-carrying winding means operatively positioned within said coil receiving portion.

8. The inductive proximity sensor or claim 7, wherein said base portion is thicker than said top portion.

9. The inductive proximity sensor of claim 7, further comprising a longitudinal bore extending throughout the entire length of said intermediate portion.

10. The inductive proximity sensor of claim 7, wherein said base portion has an upper peripheral edge, and said sensor further comprises:

a circumferential ring portion positioned about the peripheral edge of said base portion to provide a side shield about said coil receiving portion.

11. The inductive proximity sensor of claim 7, wherein said intermediate portion is sized to provide a space between said top portion and said coil receiving location.

12. The inductive proximity sensor of claim 10 wherein, when the dimension of said space is reduced to zero, the diameter of said top portion is less than the diameter of said base portion by at least the thickness of sad ring portion. said top portion