EP0348571A1 - Cathode ray tube display monitor with stray magnetic field compensation - Google Patents

Cathode ray tube display monitor with stray magnetic field compensation Download PDF

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Publication number
EP0348571A1
EP0348571A1 EP88305986A EP88305986A EP0348571A1 EP 0348571 A1 EP0348571 A1 EP 0348571A1 EP 88305986 A EP88305986 A EP 88305986A EP 88305986 A EP88305986 A EP 88305986A EP 0348571 A1 EP0348571 A1 EP 0348571A1
Authority
EP
European Patent Office
Prior art keywords
coils
ray tube
cathode ray
magnetic field
crt
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Withdrawn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
EP88305986A
Other languages
German (de)
English (en)
French (fr)
Inventor
Kenneth George Smith
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.)
International Business Machines Corp
Original Assignee
International Business Machines Corp
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 International Business Machines Corp filed Critical International Business Machines Corp
Priority to EP88305986A priority Critical patent/EP0348571A1/en
Priority to JP8818889A priority patent/JPH0246085A/ja
Priority to EP89303223A priority patent/EP0349098A1/en
Publication of EP0348571A1 publication Critical patent/EP0348571A1/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Withdrawn legal-status Critical Current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
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
    • H01J29/70—Arrangements for deflecting ray or beam
    • H01J29/72—Arrangements for deflecting ray or beam along one straight line or along two perpendicular straight lines
    • H01J29/76—Deflecting by magnetic fields only
    • 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

Definitions

  • This Invention relates to a cathode ray tube monitor having means for reducing stray magnetic field produced in front of the screen.
  • An object of the present invention is to provide a simple but effective solution which will mitigate the effect of the low frequency magnetic field in front of the CRT monitor without requiring more than two coils.
  • a CRT monitor comprises a CRT display together with an electromagnetic yoke assembly for causing an electron beam or beams to scan across the screen of the CRT, and a pair of compensating coils mounted so as to oppose the stray magnetic field in front of the CRT screen caused by the electromagnetic yoke assembly, and is characterised in that the pair of compensating coils is located adjacent the electromagnetic yoke assembly with their axie non-parallel but substantially in the same plane, orientated so that the compensating magnetic field is increased on front of the CRT screen and reduced behind the CRT screen.
  • the two coils are inclined with respect to one another so that their axes intersect at a point behind the CRT screen, preferably on the axis of the CRT and yoke assembly.
  • CRT 1 is provided with an electromagnetic yoke assembly 2 for sweeping the electron beam over the surface of the phosphor layer on the inner surface of the screen 3.
  • an electromagnetic yoke assembly 2 for sweeping the electron beam over the surface of the phosphor layer on the inner surface of the screen 3.
  • a low frequency magnetic field S will often be found in front of screen 3, caused by stray fields from the yoke assembly 2.
  • the stray field S approximates to that which would be produced by a magnetic dipole D positioned with its axis vertical and intersecting the axis 4 of the CRT.
  • a cancellation coil placed in the position of dipole D and energised to produce an equal magnetic dipole of the opposite sense would give effective cancellation of the deflection yoke's stray field S.
  • the glass bulb of the CRT prevents placement of a single cancelling coil.
  • a pair of cancelling coils one above and one below the CRT bulb might be arranged to approximate to a vertically orientated dipole.
  • the conical shape of the CRT bulb prevents placement of the cancelling coils with their axes coincident with one another and with the axis of the equivalent stray field dipole D. Complicated winding arrangements have been suggested to overcome this difficulty.
  • the coils 5 and 6 are inclined so that their axes intersect on the axis 4 of the CRT.
  • stray magnetic fields in the 1 KHZ to 400 KHZ frequency range at a distance 0.3m from the CRT screen can be reduced to less than 20mT/S dB/dt and less than 80 nT ⁇ B.
  • the size of the coil, the number of turns, their angle of inclination, their positions and the amount of current will depend upon the particular CRT and can be found by simple experimentation but by inclining the coils in accordance with the present invention, optimum cancellation of the stray field can be obtained in a simple manner.
  • the invention avoids the additional expense (and increased energy loss) involved if more than two compensation coils are used.
  • the invention is suitable for colour and monochrome CRT display monitors.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
EP88305986A 1988-06-30 1988-06-30 Cathode ray tube display monitor with stray magnetic field compensation Withdrawn EP0348571A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP88305986A EP0348571A1 (en) 1988-06-30 1988-06-30 Cathode ray tube display monitor with stray magnetic field compensation
JP8818889A JPH0246085A (ja) 1988-06-30 1989-04-10 陰極線管デイスプレー装置
EP89303223A EP0349098A1 (en) 1988-06-30 1989-04-18 Cathode ray tube display monitor with stray magnetic field compensation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP88305986A EP0348571A1 (en) 1988-06-30 1988-06-30 Cathode ray tube display monitor with stray magnetic field compensation

Publications (1)

Publication Number Publication Date
EP0348571A1 true EP0348571A1 (en) 1990-01-03

Family

ID=8200124

Family Applications (2)

Application Number Title Priority Date Filing Date
EP88305986A Withdrawn EP0348571A1 (en) 1988-06-30 1988-06-30 Cathode ray tube display monitor with stray magnetic field compensation
EP89303223A Withdrawn EP0349098A1 (en) 1988-06-30 1989-04-18 Cathode ray tube display monitor with stray magnetic field compensation

Family Applications After (1)

Application Number Title Priority Date Filing Date
EP89303223A Withdrawn EP0349098A1 (en) 1988-06-30 1989-04-18 Cathode ray tube display monitor with stray magnetic field compensation

Country Status (2)

Country Link
EP (2) EP0348571A1 (enrdf_load_stackoverflow)
JP (1) JPH0246085A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4138526A1 (de) * 1990-11-29 1992-06-11 Murata Manufacturing Co Ablenkspulenjoch fuer ein fernsehgeraet

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2965769B2 (ja) * 1991-10-17 1999-10-18 三菱電機株式会社 陰極線管ディスプレイ装置
US5499004A (en) * 1993-03-12 1996-03-12 Matsushita Electric Industrial Co., Ltd. Dielectric filter having interstage coupling using adjacent electrodes
GB2293299A (en) * 1994-09-15 1996-03-20 Ibm Electric field emission reduction system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
EP0258891A2 (en) * 1986-09-05 1988-03-09 Murata Manufacturing Co., Ltd. Deflection yoke apparatus with means for reducing unwanted radiation

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3017331A1 (de) * 1980-05-06 1981-11-12 Siemens AG, 1000 Berlin und 8000 München Anordnung zur kompensation von auf farbfernsehroehren einwirkenden magnetischen fremdfeldern

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
EP0258891A2 (en) * 1986-09-05 1988-03-09 Murata Manufacturing Co., Ltd. Deflection yoke apparatus with means for reducing unwanted radiation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IBM TECHNICAL DISCLOSURE BULLETIN, vol. 30, no. 12, May 1988, pages 9-10, New York, US; "Cancellation of leaked magnetic flux" *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4138526A1 (de) * 1990-11-29 1992-06-11 Murata Manufacturing Co Ablenkspulenjoch fuer ein fernsehgeraet

Also Published As

Publication number Publication date
JPH048997B2 (enrdf_load_stackoverflow) 1992-02-18
JPH0246085A (ja) 1990-02-15
EP0349098A1 (en) 1990-01-03

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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