Low saturation pole piece for a magnetic thickness gauge

Claim 2

In a magnetic micrometer of the type wherein a permanent magnet body is employed to contact a surface whose thickness is to be measured, the improvement comprising said magnet body having a first body portion comprising ferromagnetic material having high magnetic saturation greater than 18,000 Gauss and a second polar ferromagnetic portion to be positioned in contact with said surface to be measured having a magnetic saturation of less than 14,000 Gauss, an exterior portion of the surface of said second polar portion being generally convex to provide a substantially point contact with the surface to be measured.

Claim 3

In the invention defined in claim 1, wherein said second portion has a coercivity field strength of less than 3 Oersted.

Claim 4

In the invention defined in claim 1, whrein said second portion has a coercivity field strength of less than 1 Oersted.

Claim 5

In the invention defined in claim 1, wherein the material comprising said second portion possesses a hardness rating on the Rockwell scale of more than 20.

Claim 6

In the invention defined in claim 1, wherein said second portion consists of an alloy of iron, with about 13 to 18 percent aluminum.

Claim 7

In the invention defined in claim 1, wherein said second portion consists of an alloy of iron, with about 16 percent aluminum having a magnetic saturation in the range of between 5, 000 to 10,000 Gauss and a coercivity field strength of less than 1 Oersted.

Claim 8

In the invention defined in claim 1, wherein said second portion consists of an alloy of iron, with up to 8 percent silicon.

Claim 9

In the invention defined in claim 1, wherein said second portion consists of an alloy of iron, with up to 8 percent silicon, having a magnetic saturation in the range of between 5, 000 to 10,000 GausS and a coercivity field strength of less than 1 Oersted.

Claim 10

In the invention defined in claim 1, wherein said second portion consists of a ferrite material.

Claim 11

In the invention defined in claim 1, wherein said second portion consists of a ferrite material having a coercivity field strength of less than 3 Oersted.

Claim 12

In the invention defined in claim 1, wherein said second portion consists of a ferrite material having a coercivity field strength of less than 1 Oersted.

Claim 13

In a magnetic micrometer of the type wherein one pole of an elongated permanent magnetic body is employed to contact a surface whose thick-ness is to be measured, the surface of that portion of the magnetic body which is to contact a surface to be measured being generally convex to provide a substantially point contact, the improvement comprising said magnet body consisting of a ferromagnetic material having a mag-netic saturation of less than 14,000 Gauss.

Claim 14

In a magnetic micrometer of the type wherein one pole of an elongated permanent magnetic body is employed to contact a surface whose thick-ness is to be measured, the surface of that portion of the magnetic body which is to contact a surface to be measured being generally convex to provide a substantially point contact, the improvement comprising said magnet body consisting of a ferromagnetic material having a mag-netic saturation of less than 14,000 Gauss.

Claim 15

In the invention defined in claim 12, wherein said magnetic body has a coercivity field strength of less than 3 Oersted.

Claim 16

In the invention defined in claim 12, wherein said magnetic body has a coercivity field strength of less than 1 Oersted.

Claim 17

In the invention defined in claim 12, wherein the material comprising said magnetic body possesses a hardness rating on the Rockwell scale of more than 20.

Claim 18

In the invention defined in claim 12, wherein said magnetic body consists of an alloy of iron, with about 13 to 18 percent aluminum.

Claim 19

In the invention defined in claim 12, wherein said magnetic body consists of an alloy of iron, with about 16 percent aluminum having a magnetic saturation in the range of between 5,000 to 10, 000 Gauss and a coercivity field strength of less than 1 Oersted.

Claim 20

In the invention defined in claim 12, wherein said magnetic body consists of an alloy of iron, with up to 8 percent silicon.

Claim 21

In the invention defined in claim 12, wherein said magnetic body consists of an alloy of iron, with up to 8 percent silicon, having a magnetic saturation in the range of between 5,000 to 10, 000 Gauss and a coercivity field strength of less than 1 Oersted.

Claim 22

In the invention defined in claim 12, wherein said magnetic body consists of a ferrite material.

Claim 23

In the invention defined in claim 12, wherein said magnetic body consists of a ferrite material having a coercivity field strength of less than 3 Oersted.

Claim 24

In the invention defined in claim 12, wherein said magnetic body consists of a ferrite material having a coercivity field strength of less than 1 Oersted.

Claim 25

In a thickness measuring instrument of the type wherein the indication of the thickness of a layer applied to a ferromagnetic surface is a function of the magnetic flux passing between a soft magnetic pole piece in contact with the exposed surface of said applied layer and said surface, comprising a pole piece provided with a surface for substantially point contact with said layer to be measured, circuit means including a source of alternating current and means to magnetically energize said pole piece, said circuit means also including instrument means to indicate variations in an electrical value of said circuit means cause by variations in said magnetic flux, said pole piece comprising a magnetic material having a magnetic saturation of less than 14, 000 Gauss, a hardness rating on the Rockwell scale of more than 20, and low electrical conductivity.

Claim 26

In a thickness measuring instrument of the type wherein the indication of the thickness of a layer applied to a ferromagnetic surface is a function of the magnetic flux passing between a soft magnetic pole piece in contact with the exposed surface of said applied layer and said surface, comprising a pole piece provided with a surface for substantially point contact with said layer to be measured, circuit means including a source of alternating current and means to magnetically energize said pole piece, said circuit means also including instrument means to indicate variations in an electrical value of said circuit means cause by variations in said magnetic flux, said pole piece comprising a magnetic material having a magnetic saturation of less than 14, 000 Gauss, a hardness rating on the Rockwell scale of more than 20, and low electrical conductivity.

Claim 27

The invention defined in claim 23, wherein said pole piece is elongated, and provided with a convex surface at one end for contact with said exposed surface.

Claim 28

The invention defined in claim 23, wherein said means to indicate variations in an electrical value of said circuit means comprises an electrical bridge circuit, said means to magnetically energize said pole piece being connected in one leg of saiD bridge circuit, said instrument means being connected in another leg of said bridge circuit.

Claim 29

The invention defined in claim 25, wherein said pole piece is elongated, and said circuit means includes an electrical winding surrounding a portion of said pole piece.