EP0349098A1 - Kathodenstrahlmonitor mit Kompensation für magnetische Streufelder - Google Patents

Kathodenstrahlmonitor mit Kompensation für magnetische Streufelder Download PDF

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Publication number
EP0349098A1
EP0349098A1 EP89303223A EP89303223A EP0349098A1 EP 0349098 A1 EP0349098 A1 EP 0349098A1 EP 89303223 A EP89303223 A EP 89303223A EP 89303223 A EP89303223 A EP 89303223A EP 0349098 A1 EP0349098 A1 EP 0349098A1
Authority
EP
European Patent Office
Prior art keywords
coils
magnetic field
monitor
ray tube
cathode ray
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Withdrawn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
EP89303223A
Other languages
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
Publication of EP0349098A1 publication Critical patent/EP0349098A1/de
Withdrawn legal-status Critical Current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 compensating coils.
  • EP-A-0258891 shows deflection yoke apparatus comprising pairs of horizontal and vertical deflection coils and, in addition, anxiliary coils postioned outside of the vertical deflection coils, which are utilised to reduce the intensity of the leakage magnetic field. No significance is given as to the postioning of the anxiliary coils in relation to one another in order to yield the optimum compensating field.
  • 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 axes 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.
  • saving means for sending the tray magnetic field is employed to provide a feedback signal to control the current in the compensating coils.
  • 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.
  • each sensing coil (8, 9) is positioned such that it links with any stray fields producted, for example by the horizontal deflection coils, and produces a voltage proportional to the differential of the stray field.
  • These "Sensing coil voltages” are amplified accoptified, integrated and subsequently used to provide optimum current for the respective compensating coils (5, 6) (Fig. 3), via voltage controlled current sources.
  • the size of the compensating 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.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
EP89303223A 1988-06-30 1989-04-18 Kathodenstrahlmonitor mit Kompensation für magnetische Streufelder Withdrawn EP0349098A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP88305986 1988-06-30
EP88305986A EP0348571A1 (de) 1988-06-30 1988-06-30 Kathodenstrahl-Monitor mit Kompensation für magnetische Streufelder

Publications (1)

Publication Number Publication Date
EP0349098A1 true EP0349098A1 (de) 1990-01-03

Family

ID=8200124

Family Applications (2)

Application Number Title Priority Date Filing Date
EP88305986A Withdrawn EP0348571A1 (de) 1988-06-30 1988-06-30 Kathodenstrahl-Monitor mit Kompensation für magnetische Streufelder
EP89303223A Withdrawn EP0349098A1 (de) 1988-06-30 1989-04-18 Kathodenstrahlmonitor mit Kompensation für magnetische Streufelder

Family Applications Before (1)

Application Number Title Priority Date Filing Date
EP88305986A Withdrawn EP0348571A1 (de) 1988-06-30 1988-06-30 Kathodenstrahl-Monitor mit Kompensation für magnetische Streufelder

Country Status (2)

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

Cited By (2)

* 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
EP0702389A3 (de) * 1994-09-15 1996-11-27 Ibm System zur Verminderung des Abstrahlung eines elektrischen Feldes

Families Citing this family (2)

* 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

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0039502A1 (de) * 1980-05-06 1981-11-11 Siemens Aktiengesellschaft Anordnung zur Kompensation von auf Farbfernsehröhren einwirkenden magnetischen Fremdfeldern
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 (de) * 1986-09-05 1988-03-09 Murata Manufacturing Co., Ltd. Ablenkeinheit mit Mitteln zur Unterdrückung ungewünschter Abstrahlung

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0039502A1 (de) * 1980-05-06 1981-11-11 Siemens Aktiengesellschaft Anordnung zur Kompensation von auf Farbfernsehröhren einwirkenden magnetischen Fremdfeldern
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 (de) * 1986-09-05 1988-03-09 Murata Manufacturing Co., Ltd. Ablenkeinheit mit Mitteln zur Unterdrückung ungewünschter Abstrahlung

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 (2)

* 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
EP0702389A3 (de) * 1994-09-15 1996-11-27 Ibm System zur Verminderung des Abstrahlung eines elektrischen Feldes

Also Published As

Publication number Publication date
EP0348571A1 (de) 1990-01-03
JPH0246085A (ja) 1990-02-15
JPH048997B2 (de) 1992-02-18

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