GB2217959A - Reducing stray magnetic fields from display devices - Google Patents

Reducing stray magnetic fields from display devices Download PDF

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Publication number
GB2217959A
GB2217959A GB8905779A GB8905779A GB2217959A GB 2217959 A GB2217959 A GB 2217959A GB 8905779 A GB8905779 A GB 8905779A GB 8905779 A GB8905779 A GB 8905779A GB 2217959 A GB2217959 A GB 2217959A
Authority
GB
United Kingdom
Prior art keywords
display device
coil
display
coils
arrangement
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Withdrawn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
GB8905779A
Other versions
GB8905779D0 (en
Inventor
Roger Neil Robinson
Granville John Cooper
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Vistek Electronics Ltd
Original Assignee
Vistek Electronics Ltd
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 Vistek Electronics Ltd filed Critical Vistek Electronics Ltd
Publication of GB8905779D0 publication Critical patent/GB8905779D0/en
Publication of GB2217959A publication Critical patent/GB2217959A/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Withdrawn legal-status Critical Current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
    • H01J29/003—Arrangements for eliminating unwanted electromagnetic effects, e.g. demagnetisation arrangements, shielding coils
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2229/00—Details of cathode ray tubes or electron beam tubes
    • H01J2229/0007—Elimination of unwanted or stray electromagnetic effects
    • H01J2229/0015—Preventing or cancelling fields leaving the enclosure

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)

Abstract

A display device 1 such as a cathode ray tube emits stray magnetic fields in use which can interfere with the operation of adjacent display devices. A number of coils 3 are arranged and driven as to reduce the stray magnetic fields. Preferably the coils are provided with a signal based upon the scanning signal of the display device (see figs 2-5). <IMAGE>

Description

DISPLAY ARRANGEMENT The present invention relates to a display arrangement and in particular to a display arrangement such as a television picture monitor.
The picture on a television picture monitor is produced by means of scanning an electron beam in a cathode ray tube horizontally and vertically to produce a pattern known as a raster. By modulating the electron beam in amplitude a picture composed of a sequential variation in brightness is produced.
The scanning process is conventionally achieved by means of a system of varying magnetic fields produced by means of scan coils on the neck of the cathode ray tube. These varying magnetic fields cannot be completely contained within the scanning assembly and consequently can produce an unwanted deflection in a neighbouring cathode ray tube.
If the scanning rates used in adjacent cathode ray tubes are not the same, then a time varying variation of position of the raster on each cathode ray tube due to interaction with the neighbouring scanning field is observed.
According to one aspect of the invention, there is provided a display arrangement comprising a raster scan display device and at least one coil arranged to receive a signal based on a scanning signal for the display device and arranged so as to reduce stray magnetic field from the display device.
According to another aspect of the invention, there is provided a display arrangement comprising a display device which, in use, emits a signal resulting from operation of the display device, and means for emitting a signal which opposes the signal emitted by the display device.
It is thus possible to provide an arrangement in which the previously described int.eraction between displays is reduced to a level such that the effects are no longer observable.
Embodiments of the invention will be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagram illustrating an embodiment of the invention; and Figures 2 to 5 are circuit diagrams illustrating alternative embodiments.
Figure 1 shows a cathode ray tube 1 provided with a scanning assembly 2. Additional coils 3 are also placed around the tube 1. A current proportional to the scan current fed to the scanning assembly 2 is passed through the coils 3 such that the magnetic field produced by the coils is in opposition to the stray scan field.
The effect of these fields is such as to reduce the magnitude of the stray scanning field in adjacent areas which is especially advantageous when other cathode ray tubes are adjacent The additional coils 3 may be placed either at the sides of the cathode ray tube or above and below it.
The current for the coils 3 may be derived in a number of ways. Figure 2 shows the scan current flowing in the frame scan coils 4 fed directly through the coils 3 in series. In this arrangement the magnitude of the magnetic field produced by the coils 3 is adjusted by altering the number of turns in the coils 3.
Figure 3 shows a modification of this arrangement in which a portion of the current flowing in the scan coils 4 is passed via a variable potentiometer 5 to the coils 3. Adjustment of the potentiometer 5 changes the proportion of the scan current which flows in coils 3 thereby varying the resulting magnetic field.
Figure 4 shows an arrangement for generating the current for the coils 3 by means of an amplifier 8. The amplifier 8 is fed with a voltage from a potentiometer 7 which is in turn fed with a voltage proportional to the frame scan current. Adjustment of potentiometer 7 changes the magnitude of the current in coils 3 and the resulting magnetic field. An additional potentiometer 9 may be used to feed a proportion of the voltage proportional to the line scan current to the amplifier 8 where it is added to the voltage proportional to the frame scan current as shown in Figure 5.
The resulting magnetic field in the coils 3 can be made to cancel the stray fields due to both frame and line scan systems.
The size and position of the coils 3, together with the current passed through them may be varied to take account of constraints imposed by the mechanical arrangements of the monitor or display.

Claims (8)

1. A display arrangement comprising a raster scan display device and at least one coil arranged to receive a signal based on a scanning signal for the display device and arranged so as to reduce stray magnetic field from the display device.
2. A display arrangement as claimed in claim 1, in which the display device and the or each coil are coupled in series.
3. A display arrangement as claimed in claim 1 or claim 2, further comprising a potentiometer coupled to the display device for providing the signal, to be received by the or each coil.
4. A display arrangement as claimed in claim 3, in which the signal comprises current.
5. A display arrangement as claimed in claim 1, further comprising an amplifier coupled to a potentiometer being coupled to the display device for providing a proportion of the scanning signal as a voltage to the amplifier thereby providing the signal to the or each coil.
6. A display arrangement as claimed in any one of the preceding claims in which the display device comprises a cathode ray tube which includes a frame scan coil and a line scan coil.
7. A display arrangement as claimed in claim 6, in which the or each coil is arranged substantially surrounding the frame scan coil and the line scan coil.
8. A display arrangement substantially as hereinafter described with reference to any one of figures 1 to 5.
GB8905779A 1988-03-16 1989-03-14 Reducing stray magnetic fields from display devices Withdrawn GB2217959A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB888806230A GB8806230D0 (en) 1988-03-16 1988-03-16 Display arrangement

Publications (2)

Publication Number Publication Date
GB8905779D0 GB8905779D0 (en) 1989-04-26
GB2217959A true GB2217959A (en) 1989-11-01

Family

ID=10633525

Family Applications (2)

Application Number Title Priority Date Filing Date
GB888806230A Pending GB8806230D0 (en) 1988-03-16 1988-03-16 Display arrangement
GB8905779A Withdrawn GB2217959A (en) 1988-03-16 1989-03-14 Reducing stray magnetic fields from display devices

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB888806230A Pending GB8806230D0 (en) 1988-03-16 1988-03-16 Display arrangement

Country Status (1)

Country Link
GB (2) GB8806230D0 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0500349A1 (en) * 1991-02-20 1992-08-26 Nanao Corporation Apparatus for suppressing field radiation from display device
US5399934A (en) * 1991-06-25 1995-03-21 U.S. Philips Corporation Display device comprising compensation coils
WO1996023315A1 (en) * 1995-01-24 1996-08-01 International Business Machines Corporation Cathode ray tube display apparatus with reduced stray magnetic fields
US6791249B2 (en) * 2002-05-14 2004-09-14 Samsung Sdi Co., Ltd. Cathode ray tube

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
IBM Technical Disclosure Bulletin,Vol 30,No 12,M *
pp 9,10 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0500349A1 (en) * 1991-02-20 1992-08-26 Nanao Corporation Apparatus for suppressing field radiation from display device
US5260626A (en) * 1991-02-20 1993-11-09 Nanao Corporation Apparatus for suppressing field radiation from display device
US5399934A (en) * 1991-06-25 1995-03-21 U.S. Philips Corporation Display device comprising compensation coils
WO1996023315A1 (en) * 1995-01-24 1996-08-01 International Business Machines Corporation Cathode ray tube display apparatus with reduced stray magnetic fields
US5959392A (en) * 1995-01-24 1999-09-28 International Business Machines Corporation Cancellation coil arrangement for reducing stray magnetic field emissions from CRT displays
US6791249B2 (en) * 2002-05-14 2004-09-14 Samsung Sdi Co., Ltd. Cathode ray tube

Also Published As

Publication number Publication date
GB8905779D0 (en) 1989-04-26
GB8806230D0 (en) 1988-04-13

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Legal Events

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