Method and apparatus for reducing the intensity of magnetic field emissions from video display units

• US 5,561,333 A
• Filed: 09/14/1994
• Issued: 10/01/1996
• Est. Priority Date: 05/10/1993
• Status: Expired due to Fees

• Current Assignee: MTI Incorporated
• Original Assignee: MTI Incorporated
• Inventors: Darius, Ivan H.
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): Elms, Richard T.
• Application Number:
  US08/306,139
• Time in Patent Office: 748 Days
• Field of Search: 307/89, 307/91, 307/326-328, 315/8, 315/85, 361/143, 361/146, 361/149, 361/150, 361/159, 361/267, 174/35 R, 174/35 MS
• US Class Current: 307/91
• CPC Class Codes: H01J 2229/0015 Preventing or cancelling fields leaving the enclosure
• CPC Class Codes: H01J 29/003 Arrangements for eliminating unwanted electromagnetic effects, e.g. demagnetisation arrangements, shielding coils H01J29/06, H01J29/867 take precedence; demagnetisation in general H01F13/00; circuit arrangements therefor H04N9/29; screening of apparatus against electric or magnetic fields H05K9/00
• CPC Class Codes: H04N 9/29 using demagnetisation or compensation of external magnetic fields

Abstract

Method and apparatus for the reduction of the intensity of magnetic field emissions from video display units (VDU) in the vicinity of the user comprising a wire coil shaped to mimic the shape of conventional VDU deflection coils draped over a VDU to produce a cancelling magnetic field synchronous with the magnetic field produced by the unit'"'"'s deflection coil. The cancellation coil is driven by a signature sensor disposed forward of the deflection coil that senses the characteristics of the magnetic field produced by the deflection coil. The gain of the cancellation coil is adjusted to maximize the cancellation coil'"'"'s cancellation effect in the vicinity of the VDU user.

Claims

1. An apparatus for reducing magnetic field intensity at a predetermined location spaced from a video display unit having a screen, said field emanating from said video display unit, comprising:

an electronics housing adjacent said unit;

a generally rectangular frame connected to said housing and extending adjacent said screen, said frame having a channel formed therein;

a cancellation coil extending from said housing comprising;

a first segment extending from said housing into said channel around a first quadrant of said screen to a first vertical midpoint of said frame;

a second segment extending from said first segment around said unit to a second vertical midpoint of said screen;

a third segment extending from said second segment into said channel around a bottom half of said screen to said first vertical midpoint of said screen;

a fourth segment extending from said third segment around said unit to said second vertical midpoint of said screen; and

a fifth segment extending from said fourth segment past said third segment into said channel around a second quadrant of said screen to said housing;

a magnetic field sensor disposed within housing for sensing the signature characteristics of said field; and

electronics disposed within said housing and electrically connected to said first and fifth segments of said cancellation coil for driving said first, third and fifth segments with said signature characteristics at a certain gain to generate a cancelling magnetic field at said predetermined location.

2. The apparatus of claim 1 further comprising:

a magnetic field sensor disposed at said predetermined location for measuring magnetic field strength; and

means for adjusting said gain in response to readings of said magnetic field sensor disposed at said predetermined location to minimize magnetic field strength at said predetermined location.

3. The apparatus of claim 2 wherein said adjustment means are automatic.

4. The apparatus of claim 1 wherein said second and fourth segments of said cancellation coil are helically wound to minimize magnetic field emissions from said second and fourth segments.

5. The apparatus of claim 1 wherein said predetermined location is adjustable during normal operation of said video display unit.