WO1992019003A1 - Tube a rayons cathodiques - Google Patents

Tube a rayons cathodiques Download PDF

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Publication number
WO1992019003A1
WO1992019003A1 PCT/GB1992/000706 GB9200706W WO9219003A1 WO 1992019003 A1 WO1992019003 A1 WO 1992019003A1 GB 9200706 W GB9200706 W GB 9200706W WO 9219003 A1 WO9219003 A1 WO 9219003A1
Authority
WO
WIPO (PCT)
Prior art keywords
shield
coil
cathode ray
yoke
ray tube
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.)
Ceased
Application number
PCT/GB1992/000706
Other languages
English (en)
Inventor
David George Etherington
Peter Barten
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.)
Rank Brimar Ltd
Original Assignee
Rank Brimar 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 Rank Brimar Ltd filed Critical Rank Brimar Ltd
Publication of WO1992019003A1 publication Critical patent/WO1992019003A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • H01J29/46—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
    • 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
    • H01J29/86—Vessels; Containers; Vacuum locks
    • H01J29/867—Means associated with the outside of the vessel for shielding, e.g. magnetic shields
    • 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
    • H01J2229/003—Preventing or cancelling fields entering the enclosure

Definitions

  • This invention relates to cathode ray tubes and displays incorporating such tubes, and yokes therefor.
  • Cathode ray tubes for example colour cathode ray tubes and also monochrome cathode ray tubes, comprise a tube, an electron gun, and a deflection yoke or coil to which a deflection signal is supplied to scan the beam from the electron gun.
  • the coil is fed with a saw tooth scanning current, to scan the beam linearly across the tube, and commonly a non-linear flyback current pulse in the reverse direction is provided between the linear saw teeth to cause a rapid beam return.
  • the cathode ray tube In displays for many environments (for example, industrial environments) , the cathode ray tube must be screened both to limit the interference in other equipment caused by the electromagnetic radiation from the cathode ray tube and driving circuitry, and likewise to protect the cathode ray tube from any external electromagnetic radiation.
  • Such shields are generally made of a material with a high magnetic permeability so as to provide effective shielding; for example, of nickel iron alloys such as mu-metal. To reduce the volume of shielding material used, and the space occupied by the display, it is common to make the shape of the shields conform closely with the cathode ray tube. However, for different applications the shield may be shaped differently to fit into a different space.
  • an aspect of the present invention provides an additional shield conforming closely around the deflection yoke, or other magnetic components of the CRT tube and circuit, so as to confine the field generated thereby largely or entirely to lie within the additional shield.
  • This has the advantage that the magnetic fields from the deflection yoke do not reach the mu-metal shield assembly or reach it to a lesser extent, so that variations in its shape and size therefore have a reduced effect or no effect on the cathode ray tube performance.
  • the present invention provides a yoke for a cathode ray tube, such as a deflection yoke or a purity and convergence yoke, having magnetic shielding means around the radially outer side of at least one end edge.
  • FIG 1 shows generally a cathode ray tube
  • FIG 2 shows generally a partly cut-away view of a cathode ray tube surrounded by a shield assembly
  • FIG 3 shows schematically the position of the deflection coil in FIGS 1 and 2;
  • FIG 4 shows schematically the magnetic fields set up around a deflection coil
  • FIG 5 shows schematically a cathode ray tube and shields according to a preferred embodiment of the invention
  • FIG 6 shows schematically the fields confined in that embodiment of the invention.
  • FIG 7 shows in more detail a deflection yoke embodying the invention.
  • a colour cathode ray tube 10 (for example, a shadow mask tube) carries a deflection yoke 20 (saddle yoke) feedable with scanning and flyback currents, to generate in response a magnetic field for deflecting the electron beams from each of the electron guns through holes in the shadow mask onto respective colour phosphor dots on the screen, in well known fashion.
  • the cathode ray tube 10 also carries a purity and dynamic convergence yoke 21 and a degaussing yoke 22 in a well known manner.
  • the CRT 10 may carry a contrast enhancement panel 40, with radio frequency interference shielding, on its face plate.
  • the cathode ray tube assembly shown in FIG 1 is inserted into a magnetic shield assembly 30 comprising a box made of a metal or other material with a high magnetic permeability; typically, a mu-metal nickel iron alloy.
  • the assembly 30 confines the electromagnetic - 5 -
  • the shield assembly 30 may, for example, comprise a closely conforming generally hexagonal cross-section tube portion 30a surrounding the CRT 10 and a generally tubular portion 30b surrounding the deflection coil, electron guns and so forth.
  • the portion 30a may be formed in two sections, between which the CRT 10 is inserted, subsequently secured together. It may carry a flange for mounting to an outer cabinet or panel.
  • the shield 30 may be joined to the front panel 40 including some electromagnetic interference/radio frequency interference (EMI/RFI) shielding by a suitable gasket seal 50.
  • EMI/RFI electromagnetic interference/radio frequency interference
  • the deflection yoke 20 is positioned at the neck of the CRT 10. At this point, the cylindrical portion 30b of the shield 30 approaches the deflection coil 20 quite closely; particularly the corner between the portion 30b and the portion 30a.
  • the deflection coil 20 comprises a tubular core 20a made from, for example, ferrite, shown here with generally rectangular cross-section as an example, running round the CRT 10, and a winding 20b running between the core 20a and the CRT 10.
  • the winding or coil 20b is a so-called "saddle winding" .
  • the saddle coil 20b comprises windings wound in, for example, approximately rectangular loops bent so as to conform to the shape of the CRT and/or the core 20a, and consequently having the saddle shape.
  • the loops may run in slots in the inner side of the core 20a.
  • the end edges 20c of the coil are thus proud of the surface of the CRT 10 and the surface contours of the core 20a, and generally rise some way thereabove.
  • a magnetic deflection field 26 within the CRT 10 is set up acting to deflect a beam 27 of electrons passing there through from the electron gun.
  • unwanted magnetic fields 28 are set up and the ferrite core 20a provides only partial external shielding of these fringing fields 28.
  • the deflection field 26 and the fringing fields 28 are shown in broken lines in Figure 4.
  • the shield 30 lies within the periphery of these fields, and effectively shunts the fields altering the magnetic performance of the deflection yoke 20 to an extent depending upon how close the shield 30 is.
  • the electron beams from different colour guns will in general be affected differently.
  • the effect of perturbing the magnetic deflection field is to cause convergence errors (failure of an electron beam to pass through the appropriate holes on the shadow mask for its colour) and purity errors (a portion of the electron beam passes through holes in the shadow mask corresponding to other colours) .
  • convergence errors frure of an electron beam to pass through the appropriate holes on the shadow mask for its colour
  • purity errors a portion of the electron beam passes through holes in the shadow mask corresponding to other colours
  • perturbation of the magnetic fields can cause position errors in the path of the spot on the scan, distorting the display, even in a monochrome cathode ray tube.
  • shield 30 will tend to affect the magnetic fields differently, and consequently have different effects on the performance of the CRT 10.
  • the shape of the shield 30 in the region of the deflection yoke 20 is particularly important in this respect.
  • the additional shield 60a may simply comprise a strip of mu-metal foil, or of any other material with a suitably high magnetic permeability (such as, a ferrite material) stuck around the windings (assuming the windings are insulated) . This is found in practice to be often sufficient to render the deflection yoke 20 insensitive to changes in shape of the mu-metal shield 30 at the region where the portions 30a and 30b intersect.
  • the fringing fields set up at the end edges 20c of the coils 20a are shunted and thus confined by the local shields 60a, 60b and thus are unaffected by the presence of the shield 30 and variations between different shield shapes. Additionally, the local shields 60a, 60b also appear to allow the settling time of the deflected electron beam following flyback to be improved.
  • the cathode ray tube 10 and associated deflection yoke 20 are widely available from a number of manufacturers, for example, a 20 inch colour CRT available from Toshiba has been found suitable for working the invention.
  • the local or inner shield 60 as two discrete shields (60a,60b) in close proximity to the end edges 20c of the deflection yokes, they could in principle extend over the entire outer side of the deflection yoke 20 and possibly other magnetic components of the CRT if so desired; likewise they could be further spaced apart from the deflection coil, although clearly it is preferable to provide the shield 60 relatively close to the deflection coil 20 to provide the maximum amount of freedom in varying the shape of the outer shield 30.
  • FIG. 7 A more detailed drawing of a yoke embodying the present invention is shown in Figure 7.
  • a generally horn shaped or conical ferrite core 20a is provided around the deflection coils 20b.
  • Inner shields 60a and 60b are provided around the end edges 20c of the coils 20b, and overlap the ends of the core 20a slightly in the longitudinal direction of the yoke, at each end of the core 20a.
  • Each of the inner shields 60a, 60b is typically about 0.2mm thick, and may be formed from four turns of mu-metal foil which is 0.05mm thick.
  • the shields 60a, 60b are each supported on respective ring-shaped supports 61, which are provided as epoxy moldings. In Figure 7 each of the supports 61 and local shields 60a, 60b have been partially cut away at the top, to allow the construction to be seen.
  • Each support 61 comprises an axially extending support cylinder 61a, on which the respective shield 60a, 60b rests.
  • the support cylinder 61a extends between radially extending walls 61b.
  • Each wall 61b extends slightly radially outwardly beyond the support cylinder 61a, so as to provide a flange to hold the shield 60a, 60b in place.
  • Electric supply leads 32 for the coils 20b extend through one of the walls 61b of one of the supports 61.
  • the inner shield 60 does not have to be formed of mu-metal in all cases, but may be formed of any suitable high permeability material. In some cases, the inner shield 60 may be ferrite.

Landscapes

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

Abstract

Tube à rayons cathodiques de couleur (10) portant une bobine (20a) faisant partie d'un collier de déviation (20) et enfermé dans un blindage de mumétal (30). Afin de réduire les effets du blindage (30) sur la déviation exercée par la bobine (20a), un blindage localisé (60a, 60b) recouvre au moins les extrémités (20c) de la bobine (20a) et dérive ou limite les champs magnétiques qu'elle crée, de manière que le blindage enveloppant (30) ne perturbe pas lesdits champs magnétiques.
PCT/GB1992/000706 1991-04-18 1992-04-16 Tube a rayons cathodiques Ceased WO1992019003A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9108365.9 1991-04-18
GB919108365A GB9108365D0 (en) 1991-04-18 1991-04-18 Cathode ray tubes

Publications (1)

Publication Number Publication Date
WO1992019003A1 true WO1992019003A1 (fr) 1992-10-29

Family

ID=10693552

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1992/000706 Ceased WO1992019003A1 (fr) 1991-04-18 1992-04-16 Tube a rayons cathodiques

Country Status (3)

Country Link
EP (1) EP0580670A1 (fr)
GB (1) GB9108365D0 (fr)
WO (1) WO1992019003A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996023315A1 (fr) * 1995-01-24 1996-08-01 International Business Machines Corporation Appareil d'affichage a tube cathodique a champs magnetiques parasites reduits

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3887766A (en) * 1973-12-06 1975-06-03 Rockwell International Corp CRT assembly
DE2806844A1 (de) * 1977-05-09 1978-11-23 Hitachi Ltd Bildaufnahmeroehren-aufbau
DE3625770A1 (de) * 1985-07-31 1987-02-12 Rca Corp Ablenkjoch fuer eine kathodenstrahlroehre
AT391380B (de) * 1980-05-14 1990-09-25 Rca Licensing Corp Selbstkonvergierendes ablenkjoch
EP0418126A1 (fr) * 1989-09-12 1991-03-20 Thomson Tubes Electroniques Déviateur de faisceau électronique avec champ magnétique de correction et blindage magnétique auxiliaire incorporé

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3887766A (en) * 1973-12-06 1975-06-03 Rockwell International Corp CRT assembly
DE2806844A1 (de) * 1977-05-09 1978-11-23 Hitachi Ltd Bildaufnahmeroehren-aufbau
AT391380B (de) * 1980-05-14 1990-09-25 Rca Licensing Corp Selbstkonvergierendes ablenkjoch
DE3625770A1 (de) * 1985-07-31 1987-02-12 Rca Corp Ablenkjoch fuer eine kathodenstrahlroehre
EP0418126A1 (fr) * 1989-09-12 1991-03-20 Thomson Tubes Electroniques Déviateur de faisceau électronique avec champ magnétique de correction et blindage magnétique auxiliaire incorporé

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1996023315A1 (fr) * 1995-01-24 1996-08-01 International Business Machines Corporation Appareil d'affichage a tube cathodique a champs magnetiques parasites reduits

Also Published As

Publication number Publication date
GB9108365D0 (en) 1991-06-05
EP0580670A1 (fr) 1994-02-02

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