EP0401831B1 - Cathode ray tube apparatus intended to reduce magnetic fluxes leaked outside the apparatus - Google Patents

Cathode ray tube apparatus intended to reduce magnetic fluxes leaked outside the apparatus Download PDF

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Publication number
EP0401831B1
EP0401831B1 EP90110822A EP90110822A EP0401831B1 EP 0401831 B1 EP0401831 B1 EP 0401831B1 EP 90110822 A EP90110822 A EP 90110822A EP 90110822 A EP90110822 A EP 90110822A EP 0401831 B1 EP0401831 B1 EP 0401831B1
Authority
EP
European Patent Office
Prior art keywords
cathode ray
ray tube
coil units
magnetic fluxes
tube apparatus
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.)
Expired - Lifetime
Application number
EP90110822A
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0401831A1 (en
Inventor
Masahiro C/O Intellectual Property Div. Yokota
Hideo C/O Intellectual Property Div. Mori
Kiyoshi C/O Intellectual Property Div. Oyama
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.)
Toshiba Corp
Original Assignee
Toshiba Corp
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Filing date
Publication date
Application filed by Toshiba Corp filed Critical Toshiba Corp
Publication of EP0401831A1 publication Critical patent/EP0401831A1/en
Application granted granted Critical
Publication of EP0401831B1 publication Critical patent/EP0401831B1/en
Anticipated expiration legal-status Critical
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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
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • 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

Definitions

  • the present invention relates to a cathode ray tube apparatus and, more particularly, a cathode ray tube apparatus intended to reduce magnetic fluxes leaked outside the apparatus from a horizontal deflection coil unit of the deflection yoke.
  • VDUs visual display units
  • dispute has been focused on what influences are added to the human body by magnetic fields leaked from the VDU. It is not concluded yet whether or not the magnetic fluxes leaked add in fact any influence to the human body and what causes the influence, if any, results from.
  • north Europe moves to issue a notice about and attract attention to the influence of the leakage magnetic fluxes which may be added to the human body.
  • the National Council for Metrology and Testing in Sweden recommends in a guide line (MPR-P 1988) relating to the rule of testing and evaluating the VDUs that the magnetic fields, particularly horizontal deflection magnetic fluxes leaked on a sphere which has a radius of 65 cm (or 50 cm in front of the face plate on the tube axis) around the center of the VDU (or a point separated 15 cm inward from the surface of the face plate along the tube axis) should have a magnetic flux density B equal to and smaller than 50 nT and an induced magnetic flux density dB/dt equal to and smaller than 25 mT/s.
  • MPR-P 1988 guide line relating to the rule of testing and evaluating the VDUs that the magnetic fields, particularly horizontal deflection magnetic fluxes leaked on a sphere which has a radius of 65 cm (or 50 cm in front of the face plate on the tube axis) around the center of the VDU (or a point separated 15 cm inward from the surface of the face plate along the tube
  • the magnetic fluxes is mainly leaked from a horizontal deflection coil of the deflection yoke attached to the cathode ray tube.
  • the deflection yoke is usually provided with a magnetic core and horizontal and vertical deflection coil units, and magnetic fields shown by broken lines in Fig. 1 are generated by the horizontal deflection coil unit 1 wound like a saddle around the tube.
  • These horizontal deflection magnetic fluxes is generally grouped into effective magnetic fluxes Ba and ineffective magnetic fluxes Bb generated by a flange portions 2 of the horizontal deflection coil unit 1.
  • These deflection magnetic fluxes Ba and Bb are generated in those directions which are reverse to each other.
  • deflection magnetic fluxes Ba and Bb are particularly complicated adjacent to the deflection yoke 3 but simple, as shown by arrows 4 in Fig. 2A, on a plane separated about 45 cm from the center of the VDU and perpendicular to the tube axis.
  • the simple leakage magnetic fluxes are distributed, as shown by arrows 5 in Fig. 2B, like a distribution of the magnetic fluxes generated from a coil unit 6 which is so located as to generate magnetic fluxes Bc directed in a direction reverse to that of the effective magnetic fluxes Ba in the center of the VDU.
  • a pair of compensating coil units for eliminating the leakage horizontal deflection magnetic fluxes 8a and 8b are arranged on both sides of the horizontal plane aligned with the tube axis Z and on a plane perpendicular to the horizontal plane and passing through the center O of the leakage magnetic fluxes.
  • Horizontal deflection current is applied to the pair of compensating coil units 8a and 8b to generate magnetic fluxes so as to cancel the magnetic fluxes Bb passing through the coil units 8a and 8b.
  • magnetic fluxes which are directed in same direction as that of the effective magnetic fluxes Ba are generated to reduce the leakage magnetic fluxes.
  • a phase difference ⁇ or time lag is caused, as shown in Figs. 4A and 4B, between a waveform 10 of the magnetic fluxes generated by the paired compensating coil units and a waveform 11 of the leakage magnetic fluxes, because of the inner magnetic shield, shadow mask and dag-coating which are incorporated in the monochromatic or color cathode ray tube and which are located adjacent to the paired compensating coil units 8a and 8b.
  • the impedance of the deflecting circuit is increased and the deflecting power loss is increased accordingly, because horizontal deflection current is applied to the paired compensating coil units.
  • the paired compensating coil units attached to the tube are left unstable and their attaching to the tube is not easy because they must be attached to the tilted outer face of the center portion of the cone of the tube.
  • the present invention provides a cathode ray tube apparatus as specified in claim 1.
  • Figs. 5A and 5B show a color cathode ray tube apparatus according to one embodiment of the present invention.
  • the cathode ray tube apparatus includes a color cathode ray tube 20, a deflection yoke 21 attached to the outer circumference of the tube 20, and a compensating assembly 22 similarly attached to the outer circumference of the tube 20 to generate compensating magnetic fluxes.
  • the color cathode ray tube 20 has an envelope 27 comprising a panel 25 provided with a face plate and a skirt 24 along the outer rim thereof and a funnel 26 integrally connected to the panel 25.
  • a phosphor screen 28 Formed on the inner face of the face plate is a phosphor screen 28 comprising three phosphor layers for emitting blue, green and red light rays when electron beams land on these layers.
  • a shadow mask 29 is arranged adjacent to the phosphor screen 28 and inside the panel 25.
  • the shadow mask 29 is provided with apertures through which the electron beams are allowed to pass, and it includes a mask body 30 opposed to the phosphor screen 25 and a mask frame 31 for supporting the outer rim portion of the mask body 30.
  • These components are made of magnetic material such as low carbon steel.
  • An inner magnetic shield 33 also made of magnetic material is attached to the mask frame 31 of the shadow mask 29 and projected from the mask frame 31 into a conical portion 34 of the funnel 26.
  • An electron gun assembly 36 for generating three electron beams is arranged in a neck 35 of the funnel 26.
  • An inner dag-coating 37 is formed on the inner face of the cone 34 of the funnel 26, spreading near to the inner face of the neck, and an outer dag-coating 38 is formed on the outer face of the cone 34.
  • Reference numeral 39 represents an explosion-proof band for tightening the skirt 24 of the panel 25 and reference numeral 40 denotes a positive electrode terminal located at the cone 34 of the funnel 26.
  • the deflection yoke 21 is attached to the outer surface of the cone 34 and the neck 35.
  • the deflection yoke 21 comprises a horizontal deflection coil unit for deflecting those three electron beams, which are emitted from the electron gun assembly 36, in the horizontal direction, a vertical deflection coil unit for deflecting the electron beams in the vertical direction, and a magnetic core.
  • the deflection yoke 21 of the cathode ray tube apparatus shown in Figs. 5A and 5B includes at least the horizontal deflection coil unit wound like a saddle, and the magnetic core.
  • the compensating assembly 22 for generating compensating magnetic fields comprises a front side pair of compensating coil units 22a, 22b and a rear side pair of compensating coil units 22c, 22d which are located on both sides of a plane 7 perpendicular to the tube axis and passing through center of horizontal deflection leakage magnetic fluxes generated from the horizontal deflection coil unit of the deflection yoke 21.
  • the front side pair of compensating coil units 22a and 22b are symmetrical relative to a horizontal plane which is aligned with the axis Z of the color cathode ray tube 20, and they are fixed by adhesive, for example, to the outer face of the skirt 24 of the panel 25 in which the shadow mask 29 is arranged or to that of the cone 34 of the funnel 26 in which the inner magnetic shield 33 is arranged, in such a way that they are opposed to each other with the horizontal plane interposed between them. Particularly in the case of fixing them onto the skirt 24 of the panel 25, they can be easily fixed there, using the explosion-proof band 39 which tightens the skirt 24.
  • the rear side pair of compensating coil units 22c and 22d are symmetrical relative to the horizontal plane which is on the axis Z of the color cathode ray tube and they are fixed to the magnetic core of the deflection yoke 21 in such a way that they are opposed to each other with the horizontal plane interposed between them.
  • Coil units 22a and 22b are substantially same in size and shape and coil units 22c and 22d are also substantially same in size and shape but it is determined by the distribution of magnetic fields leaked outside the envelope how many turns their coils have and how they are tilted relative to the horizontal plane. They are connected in series or parallel to the horizontal deflection coil unit of the deflection yoke 21 and energized by signal applied from a signal generator 42.
  • the signal generator 42 includes a horizontal signal generator circuit for generating horizontal deflection current, and current which is proportional to the horizontal deflection current is supplied from this signal generator 42 to the compensating coil units 22a, 22b, 22c and 22d. It may be designed that the signal generator 42 is kept independent of the horizontal signal generator circuit. Current proportional in a level to, synchronous with and same in time change as the horizontal deflection current is supplied from the signal generator 42 to the compensating coil units 22a, 22b, 22c and 22d in this case.
  • Table 1 shows more concrete values of the two pairs of compensating coil units 22a, 22b and 22c, 22d which are employed by the color cathode ray tube apparatus according to the present invention, and those of the one pair of compensating coil units 8a and 8b which are employed by the conventional cathode ray tube apparatus.
  • Table 2 shows the comparison of characteristics of the cathode ray tube apparatus, in which the two pairs of compensating coil units 22a, 22b and 22 each having the values shown in Table 1 are included, with those of the cathode ray tube apparatus in which only the one pair of compensating coil units 8a and 8b each having the value shown in Table 1 are included.
  • Induced magnetic flux density dB/dt and magnetic flux density B shown in Table 2 are values at the distance of 30 cm before the panel and the maximum values at the distance of 65 cm on the sphere around the center of the VDU and at an angle of -45° ⁇ 0 ⁇ 45° relative to the horizontal plane.
  • the increased parts of inductance of the horizontal deflection system are denoted by percentages before and after the horizontal deflection coil unit is connected in series to the compensating coil units.
  • the induced magnetic flux densities dB/dt are 13 mT/s at the distance of 30 cm before the panel and 9 mT/s on the sphere having a radius of 65 cm around the center of the VDU and the increased part of inductance is 9.3%, which values are the best achieved by the conventional cathode ray tube apparatus in which the one pair of compensating coil units are included.
  • the two pairs of compensating coil units are used in such a way that the one pair of them are located adjacent to the panel of the funnel and opposed to each other parallel to and in front of the plane perpendicular to the tube axis and passing through the centers of horizontal deflection leakage magnetic fields and that the other pair of them are located on the magnetic core of the deflection yoke and opposed to each other parallel to and at the back of the plane, however, the induced magnetic flux density dB/dt can be reduced to 6 mT/s at the distance of 30 cm before the panel and the increased part of inductance to 7.8%.
  • the compensating assembly for generating compensating magnetic fluxes to reduce horizontal deflection leakage magnetic fluxes includes plural pairs of compensating coil units and at least one pair of them are located on one side of the plane perpendicular to the tube axis and passing through the centers of horizontal deflection leakage magnetic fluxes while at least the other one pair of them on the other side of the plane, as described above, compensating magnetic fluxes generated from the one pair of them on one side of the plane can be made hardly different in phase from horizontal deflection leakage magnetic fields in front of the phosphor screen to effectively compensate the horizontal deflection leakage magnetic fluxes.
  • horizontal deflection leakage magnetic fluxes can be effectively compensated by compensating magnetic fluxes.
  • the present invention can provide a cathode ray tube apparatus capable of fully compensating leakage magnetic fluxes, particularly those leaked in front of the phosphor screen of the VDU.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
EP90110822A 1989-06-09 1990-06-07 Cathode ray tube apparatus intended to reduce magnetic fluxes leaked outside the apparatus Expired - Lifetime EP0401831B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP146979/89 1989-06-09
JP1146979A JPH0752631B2 (ja) 1989-06-09 1989-06-09 陰極線管装置

Publications (2)

Publication Number Publication Date
EP0401831A1 EP0401831A1 (en) 1990-12-12
EP0401831B1 true EP0401831B1 (en) 1996-08-21

Family

ID=15419885

Family Applications (1)

Application Number Title Priority Date Filing Date
EP90110822A Expired - Lifetime EP0401831B1 (en) 1989-06-09 1990-06-07 Cathode ray tube apparatus intended to reduce magnetic fluxes leaked outside the apparatus

Country Status (4)

Country Link
EP (1) EP0401831B1 (ja)
JP (1) JPH0752631B2 (ja)
KR (1) KR920010657B1 (ja)
DE (1) DE69028146T2 (ja)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2297423A (en) * 1995-01-24 1996-07-31 Ibm CRT 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

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR900001503B1 (ko) * 1985-09-13 1990-03-12 미쓰비시전기 주식회사 불요복사 방지장치
SE452077C (sv) * 1986-03-04 1992-12-07 Blixt Autovision Anordning foer att reducera ooenskade laeckfaelt upptraedande framfoer katodstraaleroers bildskaerm
JPS6312148U (ja) * 1986-07-10 1988-01-26
NL8701109A (nl) * 1987-05-11 1988-12-01 Philips Nv Beeldweergeefinrichting met strooiveld-compensatiemiddelen.

Also Published As

Publication number Publication date
JPH0752631B2 (ja) 1995-06-05
KR920010657B1 (ko) 1992-12-12
EP0401831A1 (en) 1990-12-12
DE69028146D1 (de) 1996-09-26
JPH0311531A (ja) 1991-01-18
DE69028146T2 (de) 1997-02-20
KR910001849A (ko) 1991-01-31

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