Sensor having dual Hall IC, pole piece and magnet

• US 4,935,698 A
• Filed: 03/03/1989
• Issued: 06/19/1990
• Est. Priority Date: 03/03/1989
• Status: Expired due to Term

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Sprague Electric Company
• Inventors: Kawaji, Hideki, Gilbert, Peter J.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US07/318,265
• Time in Patent Office: 473 Days
• Field of Search: 324/207, 324/208, 324/233-236, 324/225, 324/228, 324/251, 324/252, 324/262, 324/117 H, 338/32 R, 338/32 H, 307/309, 328/5, 360/112, 360/113
• US Class Current: 324/207.2
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: H03K 17/9517 using galvanomagnetic devices

Abstract

A Hall elements and magnet assembly for use as a proximity detector includes a magnet, a pole piece mounted to one pole end of the magnet and an integrated circuit having two side-by-side Hall elements, an amplifier, interconnecting wiring providing the difference voltage between the two Hall output voltages at the input of the amplifier, and a Schmitt trigger circuit. The integrated circuit is mounted to the pole piece at the pole end of the magnet. The pole piece is a ferromagnetic member which is thinner in the center than at the periphery for achieving a highly uniform field strength across the surface of the magnet pole end toward reducing the criticality of the position of mounting of the integrated circuit in manufacturing and for extending the range of gap dimensions between a passing ferromagnetic article and the assembly for which proper detection of the passing article can be made to occur. The term "ferromagnetic" as used herein means any material with a relative permeability greater than unity and preferably greater than 100.

Claims

1. In a sensor of the kind including a magnet, a ferromagnetic pole piece mounted to one pole end of said magnet, an integrated circuit die having a pair of Hall elements formed side by side in a face of said die and lying centered about a line in said die face, said die being mounted to said pole piece with said die face about parallel with said pole end, the improvement comprising:

said pole piece having a center portion that, taken in a magnet-axis direction, is thinner going away from said one pole end than is the remaining peripheral portion of said pole piece to divert a portion of the magnetic from the center of said pole end toward the periphery of said pole end and to render the field more uniform along said center line.

2. A dual Hall sensor comprising:

(a) a semiconductor integrated circuit die having two Hall elements formed side by side in a face of said die and lying centered about a line in said die face;

(b) a magnet having one flat pole end lying in one plane;

(c) a ferromagnetic pole piece having a plate portion with one major surface lying in said plane mounted against said one pole end of said magnet and said integrated circuit die being mounted to the opposite major surface of said plate portion with said die face substantially parallel with said one pole-end plane,

said pole piece having a center region that is thinner taken in the direction away from said pole-end plane than are the peripheral regions of said pole piece near said line to divert a portion of the magnetic field from the center of said pole end toward the periphery of said pole end and to render the field more uniform along said center line; and

(d) a differential connection means connected to the outputs of said Hall elements for providing a differential output voltage that is a function of the difference between the strength of the magnetic field at said one and at the other of said Hall elements, respectively, which field is normal to said major die surface.

3. The sensor of claim 2 wherein said center pole-piece region is a plate portion to which said die is mounted and said peripheral region extends away from said magnet in a magnet-axis direction.

4. The sensor of claim 2 wherein said peripheral pole-piece region has the annular shape of a washer and said center region is a hole.

5. The sensor of claim 2 wherein said center region is a plate portion to which said die is bonded and said pheripheral region is a turned up extension of said plate portion extending away from said magnet in a magnet-axis direction.