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
  • 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
• • 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

• the present invention relates to an arrangement for a picture tube for reducing the magnetic field strength in the area surrounding the picture tube, at which the picture tube comprises a picture tube neck exhibiting a number of deflection coils which are wound around or are alternatively enclosed by a core, in conjunction with which the arrangement also comprises a number of compensating coils with the ability to generate in the area surrounding the picture tube magnetic fields which act contrary to the magnetic fields of the deflection coils.
• a low—frequency magnetic field occurs around every conductor in which a low—frequency current flows.
• Especially strong magnetic fields occur around coils and transformers.
• the deflection coils for the line and the picture and the line transformer cause relatively strong magnetic fields.
• Other major sources may be other coils, such as the line coil, transformers and currents in wires and in the chassis.
• the magnetic field can be reduced in various ways. 1. Reduce the source
• the magnetic flux density reduces if the current which generates the magnetic field is reduced.
• the magnetic induction the time—related derivative of the flux density, also reduces as the current reduces. Even if the amplitude of the current is unchanged, the induction can be reduced by reducing the time variation of the current.
• the electron beam which draws the image on the screen of a cathode ray tube, moves at a certain speed from one side of the screen to the other, and then returns rapidly to the first side before drawing the next line.
• the magnetic field which controls the beam must be saw—tooth shaped.
• a line is drawn during the period t1, and the beam returns during the period t2.
• the magnetic fields outside the shielding can be reduced significantly by enclosing the sources in a material with good electrical conductivity and/or high permeability. It is difficult to achieve complete shielding in the case of picture tubes, since it is necessary to be able to see the picture screen.
• Magnetic field lines are always closed. Those fields which it is wished to reduce outside the picture screen have field lines which both commence and terminate in a single source, for example the deflection coil. The field lines will pass more easily into a material with high permeability. Iron and ferrite material are substances which exhibit high permeability.
• a magnetic field will be generated by a conductor through which a current is passing.
• a further conductor, through which a current of identical magnitude is passing, but in the opposite direction, will cause a magnetic field of identical
• SUBSTITUTE SHEET magnitude but acting in the opposite direction, to be generated. If these conductors are routed together, so that they lie essentially parallel with and at a negligible distance from one another, the resulting magnetic field will be essentially zero.
• the principle of compensating magnetic fields is thus to create counter—acting magnetic fields exhibiting the same time variation and strength as the field which it is wished to reduce.
• the principal object of the present invention is. thus, in the first instance, to make available an arrangement which solves the problem of reducing the low—frequency magnetic fields which are emitted from those deflection coils of picture tubes which are located at the picture tube neck of the tubes in question. Said object is achieved by means of an arrangement in accordance with the present invention, which is characterized primarily in that the compensating coils and the deflection coils are oriented essentially in a uniform fashion in space, with the compensating coils being so arranged as to extend around the deflection coils and the neck of the picture tube.
• Fig. 1 shows the rear of a picture tube with its associated neck and enclosing coils
• Fig. 2 shows a perspective view of an arrangement of coils
• Fig. 3 illustrates schematically a number of compensating coils
• Fig. 4 shows a first illustrative embodiment of the connection of the coils
• Fig. 5 shows a second illustrative embodiment of a connection diagram for the coils.
• the solution on which the present invention is based involves the arrangement of a number of compensating coils 1, 2, which are so arranged as to compensate for the magnetic field which is created in each of the deflection coils 3, 4 of a picture tube at the neck 5 of the picture tube 6 in question.
• the compensating coils 1, 2 and the deflection coils 3, 4 are so arranged that they are oriented essentially in a uniform fashion in space 7 on the picture tube 6, with the compensating coils 1, 2 being so arranged as to extend around the deflection coils 3, 4 and the neck 5 of the picture tube, so that they give rise to subtraction of the magnetic fields all the way round and not, as in the case of previously disclosed solutions, at those points where compensating coils are arranged at a position other than the positions of the coils whose magnetic field it is wished to compensate for, so that the addition of magnetic fields at certain points occurs.
• the line and picture deflection coils 3, 4 which are so arranged as to extend around the neck 5 of the picture tube.
• the preferable procedure is to make the compensating coils 1, 2 as accurately as possible so that their form resembles that of the deflection coils 3, 4 as closely as possible.
• the compensating coils 1, 2 are also preferably arranged in pairs around corresponding deflection coils 3, 4, substantially directly on top of same, and by positioning one compensating coil 1 above an upper deflection coil 3 and one compensating coil 2 below a lower deflection coil 4, the source for the deflection coils and the compensating coils to all intents and purposes coincide in space.
• the compensating coils 1, 2 are, of course, wound in such a way that they emit a magnetic field which acts contrary to that emitted from the deflection coils, that is to say the deflection coils 3, 4 and the compensating coils 1, 2 are wound in different directions. The above requirement in respect of the positioning of compensating coils 1,
• the compensating field inside the neck 5 of the picture tube is so small that it has a negligible effect on the electron beam, and thus on the picture.
• a cylindrical shield may be placed between the compensating coils 1 and 2 and the deflection coils 3 and 4. The result will be a smaller external field from the deflection coils 3, 4 and a smaller internal field in the neck 5 of the picture tube from the compensating coils 1, 2.
• Said shield which may be either conical or straight, is positioned in such a way that it lies coaxially with the neck 5 of the picture tube between the coils 1—4, with the compensating coils 1, 2 being positioned directly on top of the shield and straight on top of the deflection coil 3, 4 for which it is intended to compensate, in order to achieve an essentially identical spatial pattern of the fields.
• the shield should also be executed from a material which exhibits good electrical conductivity, for example metal.
• the compensating coils 1, 2 can be connected in series from the electrical point of view with the deflection coils
• Fig. 4 can be connected in parallel with the deflection coils 3, 4, and can be connected to a voltage source 8, so that the current is so arranged as to be passed through the compensation coils 1, 2, so that the magnetic field generated in each compensating coil 1, 2 acts contrary to the magnetic field generated in each deflection coil, and so that the fields are essentially of identical magnitude in relation to one another.
• the magnitude of the compensation field can be adapted to the correct strength by selecting the appropriate area and the appropriate number of windings in the compensating coils 1, 2.
• Means should preferably be provided for the fine . adjustment of the strength of the magnetic field in each coil 1, 2 and/or 3,4, which means may consist either of an element 9 ⁇ , which is connected via a wire 9 so as to permit a variable shunt current to be passed in parallel with compensating coils 1, 2 and/or deflection coils 3, 4, which coils 1—4 lie in series with one another, as illustrated in Fig.
• Said elements 9 1 , 10 ⁇ can be so arranged as to permit the current through the coils in question 1, 2 and/or 3, 4 to be controlled, and may, for example, be a variable inductance.
• Use is made in certain cathode ray tubes of deflection coils which produce a field, the strength of which varies considerably around the tube. It is possible in cases such as these to use several compensating coils positioned at different distances ahead of the deflection coils.
• the compensating coils for line deflection can be positioned above and below the deflection coils.
• corresponding compensating coils can be fitted to the left and to the right of the deflection coils.
• the different compensating coils 1, 2 can be connected to the neck 5 of the picture tube and its surrounding components via plastic connector devices 11, 12 of an appropriate kind.

Landscapes

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

Applications Claiming Priority (2)

Publications (1)

Family

ID=20366577

Family Applications (1)

Country Status (3)

Cited By (3)

Families Citing this family (1)

Citations (1)

• 1986
  • 1986-12-10 SE SE8605303A patent/SE456056B/sv not_active IP Right Cessation
• 1987
  • 1987-12-10 AU AU10446/88A patent/AU1044688A/en not_active Abandoned
  • 1987-12-10 WO PCT/SE1987/000589 patent/WO1988004469A1/en unknown

Patent Citations (1)

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