US3588583A - Magnetic elements mounted on the corners of the screen of color television tubes for compensating for the effect of the terrestrial magnetic field - Google Patents

Magnetic elements mounted on the corners of the screen of color television tubes for compensating for the effect of the terrestrial magnetic field Download PDF

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Publication number
US3588583A
US3588583A US837288A US3588583DA US3588583A US 3588583 A US3588583 A US 3588583A US 837288 A US837288 A US 837288A US 3588583D A US3588583D A US 3588583DA US 3588583 A US3588583 A US 3588583A
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Prior art keywords
screen
magnetic field
effect
tube
corners
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Expired - Lifetime
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US837288A
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English (en)
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Jean Ciecierski
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/16—Picture reproducers using cathode ray tubes
    • H04N9/29—Picture reproducers using cathode ray tubes using demagnetisation or compensation of external magnetic fields
    • 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

Definitions

  • Color television tubes comprise, at one end of the sealed envelope thereof, a flat screen upon which there are deposited in a regularly alternating pattern contiguous vertical rectangular, green, blue and red strips, and at the other end three guns which respectively receive the signals corresponding to these colors.
  • a grid consisting of a flat sheet, parallel to the screen, of mutually parallel wires which are also parallel to the strips of the screen.
  • the electron beams issuing from each gun are accelerated towards the screen which is raised to a high positive potential in relation to the guns (some tens of thousands of volts for example).
  • the impact area of the beam upon the screen is made as small as technologically possible.
  • One of the functions of the grid which is raised to a potential of some thousands of volts positive in relation to the guns, is to concentrate the beams prior to their impact upon the screen, so as to minimize the area of this impact.
  • This effect is particularly marked at the four comers-of the screen.
  • a device for compensating the effect of the terrestrial magnetic field in color television tubes comprising four separate magnetic elements, respectively mounted at the four corners of the screen, for producing a magnetic field parallel to the tube axis and decreasing from the corners towards the screen center.
  • FIG. 1 is a schematic view, in elevation and plan, of one embodiment of a color television tube of the kind to which the invention relates, with a portion of the tube cut away;
  • FIG. 2 diagrammatically shows the trajectory of an electron within the tube
  • FIG. 3 is another illustration of the electron trajectories in a color television tube of a kind to which the invention applies;
  • FIG. 4 is another illustration of FIG. 3 showing the displacements of the points of beam impact on the screen.
  • FIGS. 5 and 6 show the effect of the terrestrial magnetic field upon the trajectories of electrons in a color television tube
  • FIG. 7 is a schematic view of one embodiment of the device according to the invention.
  • FIG. 8 is a perspective view of one of the elements of the device ofFIG. 7;
  • FIG. 9 is a diagram showing how the elements of the device of FIG. 7 are supplied.
  • the tube shown in FIG. 1 comprises a cone C,, a front wall F, carrying a screen E, a grid G formed by wires 3, an anode A and the chromatic purity or correcting electrode P.
  • FIG. 2 shows schematically, in the horizontal central plane of a tube, the trajectory t of an electron coming from a gun situated at O on the axis XX of the tube, the trajectory t making an angle ,8 with this axis;
  • V, B and R are three contiguous phosphor strips, which are respectively green, blue and red.
  • the terrestrial magnetic field can be split into two ponents, one vertical and the other horizontal.
  • the vertical component of the terrestrial magnetic field has a constant intensity, and a constant orientation in relation to the different trajectories followed by the electron beam while the latter is sweeping the screen, and its effect on same, although varying from one trajectory to another, is constant in respect of each of them.
  • the terrestrial magnetic field component located in the horizontal plane is concerned.
  • the latter not only varies with the location as does the vertical component, but has an orientation, in relation to the trajectories of the electron beams, which varies with the orientation of the screen, that is to say the orientation of the television receiver.
  • the disturbing effect of this component upon the electron trajectories varies with the position of the receiver, which position is a matter of random choice for the user and is therefore essentially variable.
  • the disturbing effects due to this component are in opposite directions.
  • This component can in turn be split down into a component parallel to the tube axis and a component perpendicular thereto.
  • FIG. the plane of which is the central horizontal plane of the tube, illustrates in full line the central position 1 of the electron beam and the two extreme positions 2 and 3 of the same beam at the rightand left-hand edges of the screen, in the absence of any terrestrial magnetic field.
  • the vertical component of this field which is directed downwards the plan view of FIG. 1, has the effect of deflecting the beams of electrons which are moving at the velocity v, from the guns towards the screen, towards the left of the screen, as indicated by the trajectories marked in broken lines 1', 2', and 3'.
  • the displacement of the impact area of the beam, due to the vertical component of the terrestrial magnetic field, has been determined by the Applicant, at a certain number of points of the screen, namely at points a and b and at the center C on the horizontal central line Hm, at the points 11,, b, and c, on the horizontal H, at the top of the screen, and at the points a b and c on the horizontal H at the bottom of the screen.
  • the results are indicated in FIG. 5, where E represents the screen comas seen by the viewer and H r the vertical component of the terrestrial magnetic field.
  • the arrows indicate the direction of displacement under the effect of the field H, and its amplitude measured in hundredths of a millimetre, each graduation on the arrows representing three-hundredths of a millimeter.
  • FIG. 4 shows, that the displacements of the points of impact are more marked at the left-hand edge than at the right-hand edge of the screen, since although the radii of the trajectories are the same in both cases, as equation (1) indicates, all the quantities having the same values in both cases, they are differently orientated in relation to the screen.
  • the object of the present invention is to achieve at least an approximative compensation of the effects illustrated in FIGS. 5 and 6.
  • the device in accordance with the invention is formed by four flat coils, independent of one another and located at each comer of the screen, shaped to follow the screen profile. These coils are placed against the screen externally thereof and outside its useful area.
  • the coils B,, B B B have their axes parallel to that of the tube and produce a field parallel thereto.
  • This coil has the particular shape shown: it comprises two horns normal to each other so as to fit into the comer of the screen in which it exerts its action.
  • each electron has a velocity which can be split into three components, one vertical and the other two horizontal, the latter two being respectively directed along the axis and perpendicular to the axis of the tube.
  • the current in the coils B B B B. will have to be adjusted as a function of this orientation.
  • the television set should therefore comprise to this end, where independent coils are used, a control knob for each coil, which the viewer must reset when he changes the position of his receiver.
  • the controls will also have to be reset each time the set is moved from one location to another, where the terrestrial magnetic field has different components.
  • the values indicated in FIGS. 5 and 6 are those found by the Applicant at the spot where he performed the tests.
  • the improvement which, other things being equal, is secured in color television tubes by the device in accordance with the invention, can be evaluated by the acceptable tolerance on the potential of the electrode, responsible for correcting chromatic purity (FIG. I), mention of which has been made earlier.
  • Tubes equipped with the device in accordance with the invention enable a wider tolerance in this respect.
  • 17 enabled a tolerance of better than 50 volts on the potential in question, when equipped with the correcting device of the invention, whilst when not so equipped only 4 of them permitted such a tolerance.
  • I 55 mm current varying from 0 to I00 mA; L mm in one direction or the other.
  • FIG. 9 provides an example of the way in which four independent coils B,, B B B are supplied from a source S (12 volts), through potentiometers p P p P ln the example described hereinbefore, the compensating eflect which it is an object of the invention to achieve is obtained by means of electromagnetic coils with a variable current.
  • these coils can be replaced by permanent magnets fitted with adjustable shunts; by varying the position of the shunts in the magnetic circuit, the compensating field can be varied.
  • a device for compensating the effect of the terrestrial magnetic field in color television tubes comprising a color television tube screen and four separate magnetic elements
  • said coils comprise a central portion and two horns, perpendicular to each other and extending along the two sides of the screen corner in which the coil is located.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US837288A 1968-07-16 1969-06-27 Magnetic elements mounted on the corners of the screen of color television tubes for compensating for the effect of the terrestrial magnetic field Expired - Lifetime US3588583A (en)

Applications Claiming Priority (1)

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FR159318 1968-07-16

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US3588583A true US3588583A (en) 1971-06-28

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US837288A Expired - Lifetime US3588583A (en) 1968-07-16 1969-06-27 Magnetic elements mounted on the corners of the screen of color television tubes for compensating for the effect of the terrestrial magnetic field

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US (1) US3588583A (es)
DE (1) DE1935789A1 (es)
FR (1) FR1600842A (es)
GB (1) GB1257528A (es)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3737716A (en) * 1970-04-10 1973-06-05 Philips Corp Color purity adjustment utilizing a coil attached to the faceplate
JPS4949859U (es) * 1972-08-09 1974-05-01
US3887833A (en) * 1969-06-16 1975-06-03 Hitachi Ltd Color purity adjusting device for a color picture tube
JPS50133857U (es) * 1974-04-19 1975-11-04
US3965386A (en) * 1973-09-13 1976-06-22 U.S. Philips Corporation Degaussing device for a color television display tube
US4243913A (en) * 1979-08-29 1981-01-06 Rca Corporation Color picture tube magnetic shielding and degaussing structure
EP0555094A2 (en) * 1992-02-07 1993-08-11 Matsushita Electric Industrial Co., Ltd. Beam landing correction apparatus for a cathode ray tube
US5583401A (en) * 1992-02-07 1996-12-10 Matsushita Electric Industrial Co., Ltd. Beam landing correction apparatus for a cathode ray tube
US5754007A (en) * 1995-06-14 1998-05-19 Sony Corporation Method of degaussing cathode ray tube

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2196817A (en) * 1986-10-30 1988-05-05 Ibm Degaussing system offsets ambient magnetic fields

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3887833A (en) * 1969-06-16 1975-06-03 Hitachi Ltd Color purity adjusting device for a color picture tube
US3737716A (en) * 1970-04-10 1973-06-05 Philips Corp Color purity adjustment utilizing a coil attached to the faceplate
JPS4949859U (es) * 1972-08-09 1974-05-01
JPS5320993Y2 (es) * 1972-08-09 1978-06-02
US3965386A (en) * 1973-09-13 1976-06-22 U.S. Philips Corporation Degaussing device for a color television display tube
JPS50133857U (es) * 1974-04-19 1975-11-04
JPS5536928Y2 (es) * 1974-04-19 1980-08-30
US4243913A (en) * 1979-08-29 1981-01-06 Rca Corporation Color picture tube magnetic shielding and degaussing structure
EP0555094A2 (en) * 1992-02-07 1993-08-11 Matsushita Electric Industrial Co., Ltd. Beam landing correction apparatus for a cathode ray tube
EP0555094A3 (es) * 1992-02-07 1994-03-16 Matsushita Electric Ind Co Ltd
US5583401A (en) * 1992-02-07 1996-12-10 Matsushita Electric Industrial Co., Ltd. Beam landing correction apparatus for a cathode ray tube
US5754007A (en) * 1995-06-14 1998-05-19 Sony Corporation Method of degaussing cathode ray tube

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Publication number Publication date
DE1935789A1 (de) 1970-03-12
GB1257528A (es) 1971-12-22
FR1600842A (es) 1970-08-03

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