Magnetic shield for visual display terminals

• US 4,992,624 A
• Filed: 06/12/1989
• Issued: 02/12/1991
• Est. Priority Date: 06/12/1989
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Haynie, Carl R., Benson, Brian L.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): Ledynh, Bot Lee
• Application Number:
  US07/365,075
• Time in Patent Office: 610 Days
• Field of Search: 174/35 MS, 174/35 R, 174/36, 174/102 R, 174/103, 174/104, 174/105 R, 174/106 R, 174/108, 174/109
• US Class Current: 174/391
• CPC Class Codes: H01F 27/36 Electric or magnetic shields or screens movable for varying inductance H01F21/10
• CPC Class Codes: H01F 27/366 made of ferromagnetic material

Abstract

A magnetic shield is designed to be retrofitted over a flyback transformer of a cathode ray tube display terminal. The magnetic shield consists of a layer of metal conductor, for example mu metal, and a layer of insulation, for example polyester film. The layer of insulation is placed upon the layer of metal conductor and the layers are rolled to form a spiral having greater than two windings. Tape may be used to secure the shape of the spiral. Additionally foam rubber pads may be attached to the inside of the spiral to provide a secure mechanical mounting to the flyback transformer and to provide air spacing as additional insulation against corona discharge. Also shrink tubing may be placed over the spiral to provide additional support to the spiral shape and to provide heat and electrical insulation.

Claims

1. A magnetic shield for being placed over a flyback transformer of a cathode ray tube display terminal and for reducing magnetic pulse and field emissions from the flyback transformer, the magnetic shield comprising:

a sheet of metal conductor; and

,

a sheet of insulation, the sheet of insulation being placed upon the sheet of metal conductor and the sheets rolled to form a spiral having greater than two windings the spiral having a ductile springiness;

attachment means for holding the sheet of insulation and the sheet of metal conductor in a rolled spiral shape.

2. A magnetic shield as in claim 1 wherein the sheet of metal conductor comprises mu metal and the sheet of insulation comprises polyester film.

3. A magnetic shield as in claim 1 wherein the attachment means comprises tape.

4. A magnetic shield as in claim 1 wherein the attachment means comprises shrink tubing.

5. A magnetic shield as in claim 1 additionally comprising foam rubber strips attached to the sheet of insulation at the inside of the rolled spiral shape and serving to provide contact with the flyback transformer.

6. A magnetic shield for being retrofitted over a flyback transformer of a cathode ray tube display terminal and for reducing magnetic field and pulse emissions from the flyback transformer comprising:

a sheet of metal conductor;

a sheet of insulation; and

,

attachment means for holding the sheet of insulation and the sheet of metal conductor in a rolled spiral shape;

wherein the sheet of insulation is placed upon the sheet of metal conductor and the sheets are rolled to form a spiral having greater than two windings, the spiral having a ductile springiness.

7. A magnetic shield as in claim 6 wherein the sheet of metal conductor comprises mu metal and the sheet of insulation comprises polyester film.

8. A method for reducing magnetic pulse and fields emissions from a flyback transformer of a cathode ray tube terminal, the method comprising the steps of:

(a) rolling a conductive metal sheet and an insulator sheet together to form a spiral shield with greater than two windings, the spiral shield having a ductile springiness.

(b) Attaching insulating pads to the inside of the spiral shield; and

,

(c) placing the spiral shield over the flyback transformer.

9. A method as in claim 8 wherein step (a) includes taping the rolled conductive metal sheet to prevent the spiral shield from unwinding.

10. A method as in claim 8 wherein before step (c) shrink tubing is placed over the spiral shield.

11. A method as in claim 8 wherein the conductive metal sheet is comprised of mu metal and the insulator sheet is comprised of polyester film.