EP0269498B1 - Earth-magnetic field protection device for cathode ray tubes with a shadow mask - Google Patents

Earth-magnetic field protection device for cathode ray tubes with a shadow mask Download PDF

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Publication number
EP0269498B1
EP0269498B1 EP87402473A EP87402473A EP0269498B1 EP 0269498 B1 EP0269498 B1 EP 0269498B1 EP 87402473 A EP87402473 A EP 87402473A EP 87402473 A EP87402473 A EP 87402473A EP 0269498 B1 EP0269498 B1 EP 0269498B1
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EP
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Prior art keywords
tube
loops
cathode ray
major sides
plane
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EP87402473A
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German (de)
French (fr)
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EP0269498A1 (en
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Guiseppe Giannantonio
Cesare De Paolis
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Videocolor SA
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Videocolor SA
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    • 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
    • H01J2229/003—Preventing or cancelling fields entering the enclosure
    • 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
    • H01J2229/0046—Preventing or cancelling fields within the enclosure
    • H01J2229/0053—Demagnetisation

Definitions

  • the Earth's magnetic field acts on the path of the electron beams emitted by the barrel of a cathode ray tube and can cause what is called in a trichrome tube a "loss of register", that is to say -to say an offset of the impact on the screen of the beams of the three fundamental colors compared to the corresponding phosphors.
  • the amplitude of the parasitic deviation depends on the amplitude of the terrestrial magnetic field, but also on the geometry of the tube (distance gun-mask, parameter called "p”, and distance mask-slab, parameter called "q").
  • This demagnetization makes it possible to locate the magnetization curve on the so-called anhysteresis curve, and thus to obtain a magnetic field of opposition to the more intense terrestrial field, hence better shielding.
  • This demagnetization is conventionally carried out using a coil fixed to the rear of the tube, on the cone.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
  • Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)

Abstract

1. A device for the protection of cathode ray tubes with a mask and with a shielding screen of a material with a low magnetic permeability, with respect to the terrestrial magnetic field, comprising a demagnetizing coil of the type with two loops (10 and 11) of oblong form, whose major sides (12, 13, 16 and 17) are placed substantially horizontally, said two loops being secured to a substantial extent on the cone (3) of the cathode ray tube, symmetrically with respect to a plane passing along the axis of the neck (4) of the tube and connected by a device generating a demagnetizing current, characterized in that the two major sides of these loops furthest removed from each other (16 and 17) are located to the fore of the sintering plane (5) of the tube.

Description

DLa présente invention se rapporte à un dispositif de protection de tubes cathodiques à masque vis-à-vis du champ magnétique terrestre selon le préambule de la revendication 1.DLa present invention relates to a device for protecting cathode ray tubes with mask vis-à-vis the earth's magnetic field according to the preamble of claim 1.

On sait que le champ magnétique terrestre agit sur le trajet des faisceaux d'électrons émis par le canon d'un tube cathodique et peut provoquer ce que l'on appelle dans un tube trichrome une "perte de registre", c'est-à-dire un décalage de l'impact sur l'écran des fais ceaux des trois couleurs fondamentales par rapport aux phosphores correspondants. L'amplitude de la déviation parasite dépend de l'amplitude du champ magnétique terrestre, mais aussi de la géométrie du tube (distance canon-masque, paramètre appelé "p", et distance masque-dalle, paramètre appelé "q").We know that the Earth's magnetic field acts on the path of the electron beams emitted by the barrel of a cathode ray tube and can cause what is called in a trichrome tube a "loss of register", that is to say -to say an offset of the impact on the screen of the beams of the three fundamental colors compared to the corresponding phosphors. The amplitude of the parasitic deviation depends on the amplitude of the terrestrial magnetic field, but also on the geometry of the tube (distance gun-mask, parameter called "p", and distance mask-slab, parameter called "q").

Le champ magnétique terrestre agit par ses trois composantes, à savoir la composante verticale AY, la composante horizontale latérale AX, et la composante horizontale axiale AZ. La composante verticale provoque une déviation parasite vers la gauche dans l'hémisphère Nord, alors que la composante latérale entraîne une déviation parasite du point d'impact vers le bas ou vers le haut selon que le tube cathodique est face à l'est ou face à l'ouest, et la composante axiale une déviation de type rotationnel.The Earth's magnetic field acts through its three components, namely the vertical component A Y, the lateral horizontal component AX, and the axial horizontal component A Z. The vertical component causes a parasitic deviation to the left in the Northern hemisphere, while the lateral component causes a parasitic deviation of the point of impact downwards or upwards depending on whether the cathode ray tube is facing east or facing west, and the axial component a deviation of the rotational type.

Dans les tubes cathodiques' actuels, pour éviter l'action du champ magnétique terrestre, on blinde les tubes sur la majeure partie de la trajectoire des faisceaux. Le blindage est obtenu par l'ensemble cadre-masque et par un écran métallique embouti disposé dans le tube et fixé sur le cadre en épousant sensiblement la forme du cône.In current cathode ray tubes, to avoid the action of the earth's magnetic field, the tubes are shielded over most of the path of the beams. The shielding is obtained by the frame-mask assembly and by a stamped metal screen placed in the tube and fixed to the frame substantially matching the shape of the cone.

Le blindage opère de la façon suivante : le champ magnétique extérieur réaligne dans le matériau constituant l'écran les limites du domaine de WEISS, créant un champ magnétique induit tendant à s'opposer à l'action du champ extérieur qui lui a donné naissance. Si le matériau constituant l'écran présente une haute perméabilité magnétique, par exemple le mumétal, le champ induit s'oppose totalement au champ extérieur. Il n'y a donc alors plus de champ perturbateur à l'intérieur du blindage. Si l'on utilise un matériau à faible perméabilité magnétique (par exemple de l'acier doux), choisi essentiellement pour son faible coût, la compensation n'est plus totale. Pour obtenir une compensation plus efficace, il est nécessaire de désaimanter le matériau de l'écran à l'aide d'un champ magnétique initialement intense et décroissant progressivement. Cette désaimantation permet de situer la courbe d'aimantation sur la courbe dite anhystérésis, et d'obtenir ainsi un champ magnétique d'opposition au champ terrestre plus intense, d'où un meilleur blindage. Cette désaimantation est réalisée classiquement à l'aide d'une bobine fixée à l'arrière du tube, sur le cône.The shielding operates in the following way: the external magnetic field realigns in the material constituting the screen the limits of the WEISS domain, creating an induced magnetic field tending to oppose the action of the external field which gave it birth. If the material constituting the screen has a high magnetic permeability, for example the mumetal, the induced field completely opposes the external field. There is therefore no longer any disturbing field inside the shielding. If a material with low magnetic permeability (for example mild steel) is used, chosen essentially for its low cost, the compensation is no longer total. To obtain more effective compensation, it is necessary to demagnetize the screen material using an initially intense and gradually decreasing magnetic field. This demagnetization makes it possible to locate the magnetization curve on the so-called anhysteresis curve, and thus to obtain a magnetic field of opposition to the more intense terrestrial field, hence better shielding. This demagnetization is conventionally carried out using a coil fixed to the rear of the tube, on the cone.

La Demanderesse a remarqué que l'ensemble cadre-masque a une action de blindage vis-à-vis des composantes horizontales latérale et axiale et de la composante verticale, dont les effets sont diminués respectivement d'environ 90 % au moins, 50 % et 60%. L'introduction d'un écran magnétique en matériau à faible perméabilité permet, après démagnétisation, une meilleure compensation des effets de la composante horizontale axiale et de la composante verticale (diminution des effets d'environ 87 % et 97 % respectivement), mais au détriment de la compensation de la composante horizontale latérale dont les effets ne sont diminués que de 78 % environ. Les variations des effets de ces composantes sont simplement déterminées par mesure des décalages correspondants des registres.The Applicant has noticed that the frame-mask assembly has a shielding action with respect to the lateral and axial horizontal components and to the vertical component, the effects of which are reduced respectively by at least 90% at least, 50% and 60%. The introduction of a magnetic screen made of a material with low permeability allows, after demagnetization, better compensation for the effects of the axial horizontal component and the vertical component (reduction of the effects of approximately 87% and 97% respectively), but at to the detriment of the compensation for the lateral horizontal component, the effects of which are only reduced by approximately 78%. The variations in the effects of these components are simply determined by measuring the corresponding offsets of the registers.

La présente invention a pour objet un dispositif selon la revendication 1 permettant d'améliorer l'effet de blindage d'un écran en matériau à faible perméabilité magnétique coopérant avec un tube cathodique du type à cadre et masque, cette amélioration portant sur la protection vis-à-vis des trois composantes du champ magnétique terrestre à la fois.The subject of the present invention is a device according to claim 1 making it possible to improve the shielding effect of a screen made of a material with low magnetic permeability cooperating with a cathode ray tube of the frame and mask type, this improvement relating to screw protection -to the three components of the Earth's magnetic field at the same time.

Le dispositif conforme à l'invention comporte une bobine de démagnétisation du type à deux boucles de forme oblongue, dont les grands côtés sont disposés sensiblement horizontalement, ces deux boudes étant fixées en grande partie sur le cône du tube cathodique, symétriquement par rapport à un plan passant par l'axe du col du tube, et reliées à un dispositif générateur de courant de démagnétisation, et selon une caractéristique de l'invention les deux grands côtés de ces boucles les plus éloignés l'un de l'autre sont disposés sur la moitié antérieure de la ceinture anti-implosion du tube, avantageusement près de l'axe longitudinal de cette ceinture, juste devant les oreilles de fixation du tube solidaires de cette ceinture.The device according to the invention comprises a demagnetization coil of the type with two oblong loops, the long sides of which are arranged substantially horizontally, these two flanges being fixed largely on the cone of the cathode ray tube, symmetrically with respect to a plane passing through the axis of the neck of the tube, and connected to a demagnetization current generating device, and according to a characteristic of the invention, the two long sides of these loops which are the most distant from each other are arranged on the front half of the anti-implosion belt of the tube, advantageously near the longitudinal axis of this belt, just in front of the tube fixing lugs secured to this belt.

La présente invention sera mieux comprise à la lecture de la description détaillée d'un mode de réalisation pris comme exemple non limitatif et illustré par le dessin annexé, sur lequel:

  • - la figure 1 est une vue arrière d'un tube cathodique muni du dispositif de l'invention,
  • - la figure 2 est une vue de profil du tube de la figure 1,
  • - les figures 3 à 6 sont des vues de profil du tube de la figure 1 pour différentes positions des brins extérieurs des boucles de démagnétisation, les brins intérieurs étant fixes,
  • - les figures 7 à 9 sont des vues de profil du tube de la figure 1 pour différentes positions des brins intérieurs des boucles de démagnétisation, les brins extérieurs étant fixes, et
  • - les figures 10 et 11 sont des diagrammes montrant l'efficacité des corrections obtenues dans les cas des figures 3 à 6 et 7 à 9 respectivement.
The present invention will be better understood on reading the detailed description of an embodiment taken as a nonlimiting example and illustrated by the appended drawing, in which:
  • FIG. 1 is a rear view of a cathode ray tube fitted with the device of the invention,
  • FIG. 2 is a side view of the tube of FIG. 1,
  • FIGS. 3 to 6 are side views of the tube of FIG. 1 for different positions of the outer strands of the demagnetization loops, the inner strands being fixed,
  • FIGS. 7 to 9 are side views of the tube of FIG. 1 for different positions of the inner strands of the demagnetization loops, the outer strands being fixed, and
  • - Figures 10 and 11 are diagrams showing the effectiveness of the corrections obtained in the cases of Figures 3 to 6 and 7 to 9 respectively.

On a représenté sur le dessin un tube cathodique 1 se composant essentiellement, pour sa partie en verre, d'une dalle 2, d'un cône 3 et d'un col 4. On voit sur la figure 2 la trace 5 du plan de "frit", c'est-à-dire du plan de joint entre la dalle et le cône.There is shown in the drawing a cathode ray tube 1 essentially consisting, for its glass part, of a slab 2, a cone 3 and a neck 4. We see in Figure 2 the trace 5 of the plane of "fried", that is to say the joint plane between the slab and the cone.

Une ceinture anti-implosion 6 enserre la jupe de la dalle 2. Cette ceinture 6 est munie, près de ses coins, de quatre oreilles de fixation 7. Ces oreilles 7 sont fixées à peu près au milieu de la largeur de la ceinture 6. Un bloc de déviation 8 est fixé sur le col 4, au ras du cône 3. On n'a pas représenté les autres détails du tube 1, puisqu'ils ne sont pas nécessaires à la compréhension de l'invention. Le tube 1 comporte un écran de blindage (non représenté) à l'intérieur du cône, cet écran étant en matériau à faible perméabilité magnétique, tel que l'acier doux. Cet écran est démagnétisé, chaque fois que nécessaire (en particulier lorsque l'on modifie l'orientation du téléviseur ou moniteur incorporant le tube cathodique) à l'aide d'une bobine de démagnétisation 9.An anti-implosion belt 6 surrounds the skirt of the slab 2. This belt 6 is provided, near its corners, with four fixing ears 7. These ears 7 are fixed approximately in the middle of the width of the belt 6. A deflection block 8 is fixed to the neck 4, flush with the cone 3. The other details of the tube 1 have not been shown, since they are not necessary for understanding the invention. The tube 1 has a shielding screen (not shown) inside the cone, this screen being made of a material with low magnetic permeability, such as mild steel. This screen is demagnetized, whenever necessary (in particular when the orientation of the television or monitor incorporating the cathode ray tube is changed) using a demagnetization coil 9.

La bobine 9 comporte deux boucles identiques oblongues 10, 11 fixées par tout moyen approprié, par exemple par clips de fixation, sur la surface externe du tube 1, et alimentées en parallèle par une source de courant de démagnétisation classique (non représentée) de façon que leurs champs respectifs soient dirigés vers l'avant du tube 1. Les coins de ces boucles relatifs à leurs grands côtés 12, 13 les plus proches du col 4 (brins intérieurs des boucles) sont reliés deux à deux par des fils de maintien 14, 15 qui s'étendent sensiblement verticalement. Les grands côtés 12, 13 ainsi que les deux autres 16, 17 des boucles 10, 11 s'étendent sensiblement horizontalement. La longueur des grands côtés 16, 17 (brins extérieurs des boucles) est sensiblement égale à la longueur des grands côtés de l'écran du tube 9. Ces grands côtés 16, 17 sont fixés sur la ceinture 6, pratiquement au niveau de son axe longitudinal, et passent au niveau des oreilles 7, et dans le cas présent devant (pour un observateur regardant l'écran du tube 9) les oreilles 7, qui sont fixées à peu près au milieu de la largeur de la ceinture 6. Les grands côtés 12, 13 des boucles 10, 11, un peu moins longs (d'environ 1 à 2 cm) que les grands côtés 12, 13, sont fixés, comme c'était le cas pour les bobines de l'art antérieur, sur le côné 3 à faible distance (généralement quelques centimètres) du déviateur 8. Toutefois, on peut ajuster les positions de ces grands côtés 12, 13 ainsi que des côtés 16, 17 en fonction des dimensions des tubes sur lesquels les bobines sont fixées, pour obtenir des résultats optimaux, comme on le verra ci-dessous en référence aux figures 3 à 9.The coil 9 has two identical oblong loops 10, 11 fixed by any suitable means, for example by fixing clips, to the external surface of the tube 1, and supplied in parallel by a conventional demagnetization current source (not shown) so their respective fields are directed towards the front of the tube 1. The corners of these loops relative to their long sides 12, 13 closest to the neck 4 (inner strands of the loops) are linked in pairs by retaining wires 14 , 15 which extend substantially vertically. The long sides 12, 13 as well as the other two 16, 17 of the loops 10, 11 extend substantially horizontally. The length of the long sides 16, 17 (outer strands of the loops) is substantially equal to the length of the long sides of the screen of the tube 9. These long sides 16, 17 are fixed to the belt 6, practically at its axis longitudinal, and pass at the level of the ears 7, and in this case in front (for an observer looking at the screen of the tube 9) the ears 7, which are fixed approximately in the middle of the width of the belt 6. The large sides 12, 13 of loops 10, 11, slightly shorter (about 1 to 2 cm) than the long sides 12, 13, are fixed, as was the case for the coils of the prior art, on the cone 3 at a short distance (generally a few centimeters) from the deflector 8. However, the positions of these long sides 12, 13 as well as the sides 16, 17 can be adjusted as a function of the dimensions of the tubes on which the coils are fixed, to obtain optimal results, as will be seen below in reference e in Figures 3 to 9.

On a représenté en traits interrompus les trajets 18, 19 des boucles des bobines de démagnétisation de l'art antérieur. Les grands côtés extérieurs de ces boucles passent juste derrière le plan de frit 5.The paths 18, 19 of the loops of the demagnetization coils of the prior art are shown in broken lines. The large outer sides of these loops pass just behind the fried plane 5.

Dans le mode de réalisation représenté, on fait passer les grands côtés 16, 17 des boucles 10, 11 selon l'axe longitudinal de la ceinture 6, juste devant les oreilles 7. Toutefois, on pourrait fixer les grands côtés 16, 17 en tout endroit situé en avant (pour un observateur regardant l'écran) du plan de frit, les résultats variant comme représenté en figure 10 et comme expliqué ci-dessous.In the embodiment shown, the long sides 16, 17 of the loops 10, 11 are passed along the longitudinal axis of the belt 6, just in front of the ears 7. However, the long sides 16, 17 could be fixed altogether place located in front (for an observer looking at the screen) of the fried plane, the results varying as shown in Figure 10 and as explained below.

Les résultats obtenus avec les bobines de l'invention, en leur envoyant un courant de démagnétisation de forme et durée habituelles ont été les suivants, en disposant les brins 16, 17 au niveau des oreilles 7, et les brins 12, 13 à mi-chemin entre la face antérieure du déviateur 8 (sa face la plus proche de l'écran du tube) et le bouton d'anode 23 (ou son symétrique 23A), en exprimant en pourcentage le gain au niveau de l'effet du champ, ç'est-à-dire le déplacement résiduel du registre : àX = 42%, AZ= 9% dans les coins et 22 % à 6 heures et 12 heures (c'est-à-dire dans la zone des milieux des grands côtés de l'écran), et AY = 29 %, et ce , pour un tube asphérique de 68 cm de diagonale.The results obtained with the coils of the invention, by sending them a demagnetization current of usual shape and duration were as follows, by placing the strands 16, 17 at the ears 7, and the strands 12, 13 at mid path between the front face of the deflector 8 (its face closest to the screen of the tube) and the anode button 23 (or its symmetrical 23A), by expressing as a percentage the gain at the level of the field effect, that is to say the residual displacement of the register: at X = 42%, A Z = 9% in the corners and 22% at 6 o'clock and 12 o'clock (that is to say in the area of the mediums of large sides of the screen), and A Y = 29%, for an aspherical tube 68 cm diagonal.

Pour déterminer, dans chaque cas, les meilleures positions des brins 16, 17 et 12, 13 par rapport au tube, on a effectué deux séries d'essais : d'abord en gardant les brins 12, 13 au niveau de la face antérieure du déviateur 8 et en positionnement les brins 16, 17 à environ 5 cm en arrière du plan de frit (figure 3), au niveau du plan de frit (figure 4), au niveau des oreilles 7 (figure 5), et à environ 6 cm en avant du plan de frit (figure 6). Les résultats obtenus ont été reportés sur un diagramme (figure 10) donnant l'efficacité E du déplacement du registre en fonction de la position P des brins 16, 17. On a pris arbitrairement comme efficacité égale à 100 % celle obtenue au niveau du plan de frit, ayant une abscisse P nulle. Les différents résultats sont nidiqués, pour la correction EST/OUEST par la courbe interpolée en trait plein, et pour la correction NORD/SUD par la courbe interpolée en trait interrompu. On constate qu'en avant du plan des oreilles de fixation l'efficacité ne varie que très peu pour la correction NORD/SUD et davantage pour la correction EST/OUEST en fonction de la position des brins 16, 17.To determine, in each case, the best positions of the strands 16, 17 and 12, 13 relative to the tube, two series of tests were carried out: first, keeping the strands 12, 13 at the level of the anterior face of the diverter 8 and in positioning the strands 16, 17 at about 5 cm behind the fried plane (Figure 3), at the fried plane (Figure 4), at the ears 7 (Figure 5), and at about 6 cm in front of the fried dish (Figure 6). The results obtained have been plotted on a diagram (FIG. 10) giving the efficiency E of the movement of the register as a function of the position P of the strands 16, 17. The efficiency obtained at 100% was arbitrarily taken as that obtained at the plane fried, with abscissa P zero. The different results are nested, for the EAST / WEST correction by the interpolated curve in solid line, and for the NORTH / SOUTH correction by the interpolated curve in broken line. It can be seen that in front of the plane of the fixing ears the efficiency varies only very little for the NORTH / SOUTH correction and more for the EAST / WEST correction depending on the position of the strands 16, 17.

Dans une deuxième série d'essais, on a fixé les brins 16, 17 au niveau du plan de frit, et on a mesuré les déplacements de registre pour une position des brins 12, 13 au niveau de la face antérieure du déviateur 8 (figure 7), à mi-chemin entre cette position et le bouton d'anode 23 (pour ce qui est du brin 12, et du symétrique 23A du bouton 23 par rapport à l'axe du tube 1 pour ce qui est du brin 13) (figure 8), et au niveau de 23, 23A (figure 9). Les résultats respectifs ont été reportés sur le diagramme de la figure 11 en trait plein pour la correction EST/QUEST et en trait interrompu pour la correction NORD/SUD, les courbes étant tracées en interpolant entre les résultats. Cette figure 11 donne l'efficacité E de la correction en fonction de la position P des brins 12, 13, l'efficacité de 100 % étant prise arbitrairement pour la position moyenne, l'abscisse 0 étant prise au niveau de la face antérieure du déviateur 8.In a second series of tests, the strands 16, 17 were fixed at the level of the fried plane, and the register displacements were measured for a position of the strands 12, 13 at the level of the front face of the deflector 8 (FIG. 7), halfway between this position and the anode button 23 (for the strand 12, and the symmetrical 23A of the button 23 relative to the axis of the tube 1 for the strand 13) (Figure 8), and at 23, 23A (Figure 9). The respective results have been plotted on the diagram of FIG. 11 in solid lines for the EST / QUEST correction and in broken lines for the NORTH / SOUTH correction, the curves being drawn by interpolating between the results. This figure 11 gives the efficiency E of the correction as a function of the position P of the strands 12, 13, the efficiency of 100% being taken arbitrarily for the average position, the abscissa 0 being taken at the level of the anterior face of the diverter 8.

Bien entendu, pour effectuer un réglage correct de la boucle de démagnétisation il faut régler à la fois la position des brins 16, 17 et celle des brins 12, 13, en notant toutefois qu'il est préférable de ne pas trop rapporcher les brins 12, 13 du déviateur pour éviter une action perturbatrice de la boucle sur le fonctionnement du déviateur, à moins de prévoir des moyens ouvrant la boucle lorsqu'elle n'est pas en service.Of course, to carry out a correct adjustment of the demagnetization loop, it is necessary to adjust both the position of the strands 16, 17 and that of the strands 12, 13, noting however that it is preferable not to bring the strands 12 too close together. , 13 of the diverter to avoid a disturbing action of the loop on the operation of the diverter, unless provision is made for means opening the loop when it is not in service.

Claims (4)

1. A device for the protection of cathode ray tubes with a mask and with a shielding screen of a material with a low magnetic permeability, with respect to the terrestrial magnetic field, comprising a demagnetizing coil of the type with two loops (10 and 11) of oblong form, whose major sides (12, 13, 16 and 17) are placed substantially horizontally, said two loops being secured to a substantial extent on the cone (3) of the cathode ray tube, symmetrically with respect to a plane passing along the axis of the neck (4) of the tube and connected by a device generating a demagnetizing current, characterized in that the two major sides of these loops furthest removed from each other (16 and 17) are located to the fore of the sintering plane (5) of the tube.
2. The device as claimed in claim 1, characterized in that the two said two major sides (16 and 17) are placed adjacent to the longitudinal axis of the anti-implosion belt (6) of the tube.
3. The device as claimed in claim 2 for cathode ray tubes with fixing lugs (7) secured to the anti-implosion belt halfway across its width, characterized in that the two said major sides (16 and 17) extend between the plane of attachment of the lugs and the plane of connection of the skirt with the sheet of the screen.
4. The device as claimed in any one of the preceding claims, characterized in that the two major sides nearest to each other of these loops (12 and 13) are placed substantially halfway between the front face of the deflector (8) and the anode button (23) or a structure (23A) symmetrical thereto.
EP87402473A 1986-11-07 1987-11-03 Earth-magnetic field protection device for cathode ray tubes with a shadow mask Expired - Lifetime EP0269498B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8615578 1986-11-07
FR8615578A FR2606574B1 (en) 1986-11-07 1986-11-07 DEVICE FOR PROTECTING CATHODE RAY TUBES WITH A MASK AGAINST THE EARTH MAGNETIC FIELD

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EP0269498A1 EP0269498A1 (en) 1988-06-01
EP0269498B1 true EP0269498B1 (en) 1990-09-05

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EP (1) EP0269498B1 (en)
DE (1) DE3764776D1 (en)
FR (1) FR2606574B1 (en)

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IT1251351B (en) * 1990-06-25 1995-05-08 Videocolor Spa APPARATUS FOR COMPENSATION OF MAGNETIC FIELDS
US5107179A (en) * 1990-10-22 1992-04-21 Sun Microsystems, Inc. Method and apparatus for magnetic field suppression using inductive resonant and non-resonant passive loops
US5229689A (en) * 1991-05-14 1993-07-20 Apple Computer, Inc. Electrostatic shield for nearfield alternating electrical field emission reduction in a CRT display
JPH0541176A (en) * 1991-08-07 1993-02-19 Sony Corp Cathode-ray tube
JP3112317B2 (en) * 1991-10-09 2000-11-27 ソニー株式会社 Degaussing coil for cathode ray tube
US5347367A (en) * 1993-05-03 1994-09-13 Thomson Consumer Electronics, Inc. Cathode-ray tube having implosion protection means with openings
ATE192882T1 (en) * 1994-10-21 2000-05-15 Koninkl Philips Electronics Nv COLOR IMAGE DISPLAY DEVICE WITH COLOR IMAGE TUBE AND DEMAGNETIZING DEVICE
GB2311892B (en) * 1996-04-03 2001-01-24 Samsung Electronics Co Ltd Magnetic field shielding in display
SG93282A1 (en) * 1997-01-29 2002-12-17 Sony Corp Heat shrink band steel sheet and manufacturing method thereof

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NL167289C (en) * 1973-09-13 1981-11-16 Philips Nv COLOR TELEVISION DEVICE EQUIPPED WITH A COLOR TELEVISION IMAGE TUBE AND DEMAGNETIZING DEVICE.

Also Published As

Publication number Publication date
FR2606574B1 (en) 1989-01-13
EP0269498A1 (en) 1988-06-01
FR2606574A1 (en) 1988-05-13
US4940920A (en) 1990-07-10
DE3764776D1 (en) 1990-10-11

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