US3456149A - Magnetic deflecting means for cathode-ray tubes - Google Patents

Magnetic deflecting means for cathode-ray tubes Download PDF

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Publication number
US3456149A
US3456149A US431395A US3456149DA US3456149A US 3456149 A US3456149 A US 3456149A US 431395 A US431395 A US 431395A US 3456149D A US3456149D A US 3456149DA US 3456149 A US3456149 A US 3456149A
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United States
Prior art keywords
coil
deflection
current
cathode
resistor
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Expired - Lifetime
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US431395A
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English (en)
Inventor
Johannes Bernardus Gerard Mast
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Thales Nederland BV
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Thales Nederland BV
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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
    • H01J29/46—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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2229/00—Details of cathode ray tubes or electron beam tubes
    • H01J2229/96—Circuit elements other than coils, reactors or the like, associated with the tube
    • H01J2229/964—Circuit elements other than coils, reactors or the like, associated with the tube associated with the deflection system

Definitions

  • Means for reducing the residual magnetism in the ferromagnetic yoke of a CRT deflection system comprises a two-terminal network including, in series circuit, a compensating coil and an adjustable resistor.
  • the network is directly connected in parallel with the deflection coil and has a time constant that is higher than the time constant of the coil whereby a reverse current is caused to flow through the deflection coil during the retrace period of the sawtooth current.
  • the present invention relates to magnetic deflecting means for a cathode-ray tube and, more particularly, to means for eliminating the residual magnetism in a deflection coil system incorporating a ferromagnetic yoke.
  • One object of the invention is to provide improved means for eliminating the residual magnetism in the yoke of a deflection coil system so as to overcome the above mentioned limitations of the known method while retaining the advantages of a ferromagnetic yoke.
  • Another object of the invention is to provide an improved means for eliminating the residual magnetism comprising simple adjusting means that allows for ease in reproducing the desired effect.
  • means are provided for eliminating the residual magnetism of the yoke comprising a plurality of separate two-terminal networks corresponding in number to the number of deflection coils.
  • Each one of the two terminal networks comprises an adjustable resistor and a compensating coil.
  • Each one of said two-terminal networks is directly connected with a diflerent one of said deflection coils so that each two-terminal network is arranged in shunt-relationship with its associated deflection coil exclusively by way of the direct connecting means so as to wholly or partially bridge its associated deflection coil.
  • FIG. 1 represents diagrammatically and partially in block diagram form an embodiment of the deflection coil system according to the invention, in which only one pair of deflection coils is shown; and
  • FIG. 2 shows a set of wave forms indicating various signals which occur in the circuit of FIG. 1 during its operation.
  • FIG. 1 there is shown a magnetic deflection circuit for a cathode-ray tube 1.
  • the cathode-ray tube it is common practice to provide the cathode-ray tube with two pairs of orthogonal deflection coils.
  • the deflection coils are provided with an annular yoke 2 of ferromagnetic material which is schematically represented. These deflection coils are symmetrically energized by the sawtooth current generator 3, and are critically damped by means of the usual damping resistors R resp. R
  • the circuit is further provided with means 4 for eliminating the residual magnetism of the yoke.
  • the latter means comprise a plurality of separate two-terminal networks corresponding in number to the number of deflection coils.
  • Each one comprises an adjustable resistor R resp. R and a compensating coil L resp. L
  • Each one of said twoterminal networks, L R resp. L R' is associated with a different one of said deflection coils L resp. L and each two-terminal network is connected in shunt relationship with its associated deflection coil, exclusively by way of direct connecting means 5, 6, 7 so as to wholly or partially bridge its associated deflection coil.
  • a sawtooth generator 3 provides a current i which splits up into:
  • the current in the deflection coil L and the compensating coil L will at first continue to flow in the same direction as it did during the time-interval t
  • these currents find their return path mainly through the damping resistor R
  • the current through the said damping resistor will reverse its sign.
  • the time constant determined by the deflection coil L and the damping resistor R and the time constant determined by the compensating coil L and the adjustable resistor R are suitably chosen so that the current trough the coil L decreases faster than the current through the coil L.
  • the current in the coil L will then, after some time, find its return path not only through the damping resistor R but also through the deflection coil L It will be evident that the direction of current flow in the coil L will now be opposite to the direction of current flow that occurs during the time interval t In FIG. 2 the instant at which the current through the coil L reverses its direction is represented by T It will also be clear, that by this reversal of direction of the current through the coil L the residual magnetism from the previous excitation cycle will be decreased.
  • the resistor R now can be adjusted so that at the instant T at which the generator 3 starts a new saw-tooth current, the residual magnetism is just completely eliminated.
  • the compensating coil and the deflection coil are not inductively coupled allows the means according to the invention to be located somewhere remote from the cathode-ray tube.
  • This feature is important because it prevents the desired compensating effect from being disturbed by leakage fields and eddy currents in metal parts which often exert influences that are hard to establish.
  • the latter feature and the simplicity of the means for adjustment result in a particularly easy reproducibility of the desired compensating effect.
  • the compensating coil and the adjustable resistor of a two-terminal network are connected in series. It is also possible to connect these components in parallel if such would be better suited, eg in case such a parallel arrangement would yield more appropriate dimensions.
  • each deflection coil is only partially bridged by its associated two-terminal network.
  • Magnetic beam deflecting means for a cathode-ray tube comprising, a deflection coil system including a ferromagnetic yoke, and means for eliminating the residual magnetism in said yoke comprising, separate two-terminal networks corresponding in number to the number of deflection coils, each of said networks comprising a compensating coil and an adjustable resistor for adjusting the time constant of said network as a function of the residual magnetism level in said yoke, means directly connecting each one of said two-terminal networks with a different one of said deflection coils so that each two-ter- 4 minal network is arranged in'shunt relationship with its associated deflection coil exclusively by way of said direct connecting means so as to wholly or partially bridge its associated deflection coil.
  • Magnetic deflecting means as claimed in claim 1 wherein the adjustable resistor and the compensating coil are connected in series in each one of said two-terminal networks.
  • Magnetic deflecting means as claimed in claim 1 wherein the time constant of each one of said two-terminal networks is substantially higher than the time constant of its associated deflection coil.
  • Magnetic deflecting means as claimed in claim 2 wherein the time constant of each one of said two-terminal networks is substantially higher than the time constant of its associated deflection coil.
  • a ferromagnetic core a coil wound on said core, a two-terminal network comprising a compensating coil and a resistor connected together, means directly connecting said two-terminal network in parallel with a portion of said coil, a source of periodic current of a given frequency, means for coupling said current source to said coil and network so that a current flows in said coil in a given direction, said two-terminal network having a time constant that is dependent upon the level of residual magnetism produced in the core by said current flow in the coil, and damping means coupled to said coil so as to provide a current path for dissipating the energy stored in said coil.
  • said current source comprises a sawtooth current generator that supplies a sawtooth current to said coil and to said two-terminal network, the L/R time constants of said twoterminal network and said coil being chosen so that, in the period between the end of one sweep period and the start of the next sweep period of the sawtooth current, said two-terminal network supplies a reverse current to said coil that substantially reduces any residual magnetism in the core produced by the sawtooth current flow in said coil.
  • said resistor is adjustable and the time constant of said twoterminal network is higher than the time constant of said coil
  • said damping means comprises a resistor connected in parallel with said coil and said two-terminal network.
  • a combination as claimed in claim 6 further comprising a second coil wound on a ferromagnetic core and coupled to said current source, a second two-terminal network comprising a second compensating coil and a second resistor connected in series, means directly connecting said second two-terminal network in parallel with a portion of said second coil, and means coupling said second coil to said damping means so as to provide a current path for dissipating the energy stored in said second coil.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
  • Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)
US431395A 1964-02-12 1965-02-09 Magnetic deflecting means for cathode-ray tubes Expired - Lifetime US3456149A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL646401167A NL140650B (nl) 1964-02-12 1964-02-12 Afbuigstelsel voor een kathodestraalbuis, welk stelsel bij elke afbuigspoel voorzien is van een weerstand bevattende middelen voor het opheffen van het remanente magnetisme in de ferromagnetische kern van de normaliter kritisch gedempte afbuigspoelen.

Publications (1)

Publication Number Publication Date
US3456149A true US3456149A (en) 1969-07-15

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US431395A Expired - Lifetime US3456149A (en) 1964-02-12 1965-02-09 Magnetic deflecting means for cathode-ray tubes

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US (1) US3456149A (US20110009641A1-20110113-C00116.png)
BE (1) BE659100A (US20110009641A1-20110113-C00116.png)
CH (1) CH415741A (US20110009641A1-20110113-C00116.png)
DE (1) DE1274744B (US20110009641A1-20110113-C00116.png)
GB (1) GB1048452A (US20110009641A1-20110113-C00116.png)
NL (1) NL140650B (US20110009641A1-20110113-C00116.png)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3851215A (en) * 1971-09-21 1974-11-26 Philips Corp Deflection coil system for colour television
FR2397064A1 (fr) * 1977-07-06 1979-02-02 Philips Nv Procede pour la realisation d'un tube d'images en couleur et tube ainsi realise
US5008600A (en) * 1989-08-30 1991-04-16 Murata Mfg. Co., Ltd. Deflection yoke device

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4095143A (en) * 1976-07-21 1978-06-13 Gte Sylvania Incorporated Electron beam crossover correction circuitry

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2007380A (en) * 1932-11-30 1935-07-09 Rca Corp Cathode ray apparatus
US2114841A (en) * 1936-04-16 1938-04-19 Westinghouse Electric & Mfg Co Regulating system
US2228821A (en) * 1938-10-01 1941-01-14 Gen Electric Magnetic sweep coil circuit
US2279849A (en) * 1940-05-16 1942-04-14 Gen Electric Control of electromagnetic devices
US3153174A (en) * 1961-01-27 1964-10-13 Westinghouse Electric Corp Television width linearity control

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2007380A (en) * 1932-11-30 1935-07-09 Rca Corp Cathode ray apparatus
US2114841A (en) * 1936-04-16 1938-04-19 Westinghouse Electric & Mfg Co Regulating system
US2228821A (en) * 1938-10-01 1941-01-14 Gen Electric Magnetic sweep coil circuit
US2279849A (en) * 1940-05-16 1942-04-14 Gen Electric Control of electromagnetic devices
US3153174A (en) * 1961-01-27 1964-10-13 Westinghouse Electric Corp Television width linearity control

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3851215A (en) * 1971-09-21 1974-11-26 Philips Corp Deflection coil system for colour television
FR2397064A1 (fr) * 1977-07-06 1979-02-02 Philips Nv Procede pour la realisation d'un tube d'images en couleur et tube ainsi realise
US5008600A (en) * 1989-08-30 1991-04-16 Murata Mfg. Co., Ltd. Deflection yoke device

Also Published As

Publication number Publication date
CH415741A (de) 1966-06-30
BE659100A (US20110009641A1-20110113-C00116.png) 1965-05-28
GB1048452A (en) 1966-11-16
NL6401167A (US20110009641A1-20110113-C00116.png) 1965-08-13
NL140650B (nl) 1973-12-17
DE1274744B (de) 1968-08-08

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