GB2223649A - A screen for an electromagnetic field - Google Patents

A screen for an electromagnetic field Download PDF

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Publication number
GB2223649A
GB2223649A GB8817924A GB8817924A GB2223649A GB 2223649 A GB2223649 A GB 2223649A GB 8817924 A GB8817924 A GB 8817924A GB 8817924 A GB8817924 A GB 8817924A GB 2223649 A GB2223649 A GB 2223649A
Authority
GB
United Kingdom
Prior art keywords
screen
electromagnetic field
coils
field
scanning
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB8817924A
Other versions
GB8817924D0 (en
Inventor
Peter Thompson Wright
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Individual
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Priority to GB8817924A priority Critical patent/GB2223649A/en
Publication of GB8817924D0 publication Critical patent/GB8817924D0/en
Publication of GB2223649A publication Critical patent/GB2223649A/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/86—Vessels; Containers; Vacuum locks
    • H01J29/867—Means associated with the outside of the vessel for shielding, e.g. magnetic shields

Landscapes

  • Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)

Abstract

A "screen" for an electromagnetic field such as can be found emanating from equipment using electromagnetic scanning e.g. a CRT display 1 comprises a number of coils 2 which may be mounted in or on the equipment and provide an equal and opposite screening field. The "screen" is particularly advantageous when applied to each of a number of television monitors when in close proximity to each other. <IMAGE>

Description

A SCREEN FOR AN ELECTROMAGNETIC FIELD The present invention relates to a screen for an electromagnetic field and in particular, but not exclusively to, a screen for an electromagnetic field emanating from equipment using electromagnetic scanning.
Electromagnetic scanning is utilised almost exclusively in television monitors, cameras and similar equipment.
It is frequently necessary to operate more than one item of such equipment in close physical proximity. This generally causes few problems if the scanning systems in each item of equipment are synchronised together, or running at very similar frequencies. In many instances this is impractical, as the signal sources feeding different monitors may require quite different scan frequencies. When this occurs, interference can become apparent on one or more of the monitors due to stray magnetic fields from the scanning coils in any one unit causing slight spurious deflection of the beam in adjoining units. This can appear as a moving or flickering pattern of varying intensity on an affected monitor.
An obvious solution is to fit magnetic screens between units, but this is usually impractical as much of the interfering field can leave or enter a monitor through the monitor screen area, and this, by definition, cannot be obscured by a magnetic screen. The invention here described approaches the problem in a different way.
The electromagnetic field is screened by creating an equal and opposite field from an extra set of coils, which are mounted in or on the equipment generating the electromagnetic field.
According to the present invention there is provided a screen for an electromagnetic field comprising a number of coils providing a screening field for interfering with the electromagnetic field.
Embodiments of the present invention are defined in any one of claims 2 to 5.
By way of example, an embodiment of the present invention will be described with reference to the accompanying drawing, of which: Figure 1 is a schematic diagram of a top view of a monitor; and Figure 2 is a schematic diagram of a side view of the monitor shown in Figure 1.
As television monitors are the most common offenders in this respect, the present invention will be described with reference to monitors 1 as shown in figures 1 and 2. Since monitors situated side by side and very close to each other usually cause the greatest mutual interference, two coils 2 may be mounted in each as shown. The coils 2 are positioned either side of the cathode ray tube (CRT) and scanning coils 3. The coils 2 are fed with scan currents similar in nature to those flowing in the scanning coils 3. The monitor has a vertical scan which is usually responsible for the majority of the interference, so the coils 2 may be wired in series with the vertical scanning coils 3 to ensure the same current flows in each. By choosing the correct number of turns, correct phasing and positioning for the coils 2, the screening field from these can be made to shield the electromagnetic field from the scanning coils 3 either side of the monitor 1.
Alternatively, the coils 2 may be driven by an active circuit (not shown) similar, for example, to a vertical scanning circuit and this is adjusted to screen the electromagnetic field. Extra coils (not shown) could also be placed above and below the CRT and scanning coils 3, to cancel any interfering electromagnetic field component in these directions in a similar manner.

Claims (5)

1. A screen for an electromagnetic field comprising at least one coil providing a screening field for interfering with and thereby diminishing at least part of the electromagnetic field.
2. A screen as claimed in Claim 1, in which the screening field is equal and opposite to the electromagnetic field.
3. A screen as claimed in Claim 1 or Claim 2, in which the coils are coupled to a power source.
4. A screen as claimed in any one of Claim 1 to 3, in which the electromagnetic field emanates from a number of scanning coils.
5. A screen substantially as hereinbefore described with reference to the accompanying drawing.
GB8817924A 1988-07-27 1988-07-27 A screen for an electromagnetic field Withdrawn GB2223649A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8817924A GB2223649A (en) 1988-07-27 1988-07-27 A screen for an electromagnetic field

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB8817924A GB2223649A (en) 1988-07-27 1988-07-27 A screen for an electromagnetic field

Publications (2)

Publication Number Publication Date
GB8817924D0 GB8817924D0 (en) 1988-09-01
GB2223649A true GB2223649A (en) 1990-04-11

Family

ID=10641219

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8817924A Withdrawn GB2223649A (en) 1988-07-27 1988-07-27 A screen for an electromagnetic field

Country Status (1)

Country Link
GB (1) GB2223649A (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0520556A1 (en) * 1991-06-25 1992-12-30 Koninklijke Philips Electronics N.V. Display device comprising compensation coils
EP0523741A1 (en) * 1991-07-18 1993-01-20 Kabushiki Kaisha Toshiba Cathode ray tube apparatus
EP0565120A1 (en) * 1992-04-09 1993-10-13 Kabushiki Kaisha Toshiba Cathode-ray tube apparatus
GB2297423A (en) * 1995-01-24 1996-07-31 Ibm CRT display apparatus with reduced stray magnetic fields
WO2002091389A1 (en) * 2001-05-07 2002-11-14 Iouri Baikov Device for radiation protection (variants)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB729918A (en) * 1951-11-24 1955-05-11 Emi Ltd Improvements in or relating to magnetic deflecting means for cathode ray tubes
EP0220777A1 (en) * 1985-10-25 1987-05-06 Koninklijke Philips Electronics N.V. Picture display device with interference suppression means
EP0235863A1 (en) * 1986-03-07 1987-09-09 Philips Norden AB A method of, and device for, reducing magnetic stray fields of a cathod ray tube
WO1987005437A1 (en) * 1986-03-04 1987-09-11 Autovision S. Blixt Ab A device for the suppression of leakage fields in front of viewing screens and the like
WO1987006054A1 (en) * 1986-03-27 1987-10-08 Telefonaktiebolaget Lm Ericsson Apparatus in cathode ray tubes for reducing the magnetic field strength in the tube environment
WO1988004469A1 (en) * 1986-12-10 1988-06-16 Telub Holding Ab Arrangement for a picture tube
WO1988006346A1 (en) * 1987-02-19 1988-08-25 Hantarex Spa Device for limiting the magnetic emission in cathode ray tube monitors

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB729918A (en) * 1951-11-24 1955-05-11 Emi Ltd Improvements in or relating to magnetic deflecting means for cathode ray tubes
EP0220777A1 (en) * 1985-10-25 1987-05-06 Koninklijke Philips Electronics N.V. Picture display device with interference suppression means
WO1987005437A1 (en) * 1986-03-04 1987-09-11 Autovision S. Blixt Ab A device for the suppression of leakage fields in front of viewing screens and the like
EP0235863A1 (en) * 1986-03-07 1987-09-09 Philips Norden AB A method of, and device for, reducing magnetic stray fields of a cathod ray tube
WO1987006054A1 (en) * 1986-03-27 1987-10-08 Telefonaktiebolaget Lm Ericsson Apparatus in cathode ray tubes for reducing the magnetic field strength in the tube environment
WO1988004469A1 (en) * 1986-12-10 1988-06-16 Telub Holding Ab Arrangement for a picture tube
WO1988006346A1 (en) * 1987-02-19 1988-08-25 Hantarex Spa Device for limiting the magnetic emission in cathode ray tube monitors

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IBM Technical Dsclsr Bltn, Vol 30, N0 12, May 1988, p 9-10 "Cancellation of leaked *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0520556A1 (en) * 1991-06-25 1992-12-30 Koninklijke Philips Electronics N.V. Display device comprising compensation coils
US5399934A (en) * 1991-06-25 1995-03-21 U.S. Philips Corporation Display device comprising compensation coils
EP0523741A1 (en) * 1991-07-18 1993-01-20 Kabushiki Kaisha Toshiba Cathode ray tube apparatus
EP0565120A1 (en) * 1992-04-09 1993-10-13 Kabushiki Kaisha Toshiba Cathode-ray tube apparatus
US5430351A (en) * 1992-04-09 1995-07-04 Kabushiki Kaisha Toshiba Cathode-ray tube apparatus with means for reducing leakage magnetic field
GB2297423A (en) * 1995-01-24 1996-07-31 Ibm CRT display apparatus with reduced stray magnetic fields
WO2002091389A1 (en) * 2001-05-07 2002-11-14 Iouri Baikov Device for radiation protection (variants)

Also Published As

Publication number Publication date
GB8817924D0 (en) 1988-09-01

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Legal Events

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)