US2206125A

US2206125A - Magnetic deflecting system for braun tubes

Info

Publication number: US2206125A
Application number: US80886A
Authority: US
Inventors: Ruska Ernst
Original assignee: FIRM OF FERNSEH AG
Current assignee: FIRM OF FERNSEH AG
Priority date: 1935-05-23
Filing date: 1936-05-20
Publication date: 1940-07-02
Anticipated expiration: 1957-07-02
Also published as: DE724550C; FR806673A; US2186595A; FR47720E; DE901684C; GB475527A; GB475539A

Description

July 2, 1940.

Filed May 20, 1936 Patented July 2, 1940 UNITED STATES PATENT OFFICE MAGNETIC DEFLECTING SYSTEM FOR BRAUN TUBES Application May 20, 1936, Serial No. 80,886 In Germany May 23, 1935 7 Claims.

The present invention relates to all types of cathode ray tubes in which the electron beam is deflected in two directions by means of magnetic fields, and relates more particularly to arrangements in which two magnetic fields disposed perpendicularly with respect to each other are produced at the same or nearly the same point on the axis of the deflected electron beam.

Cathode ray tubes generally possess a source of 10 an electron beam of defined cross-section and a screen against which the electron beam is directed. A deflecting system is associated with such tubes to deflect the beam across the screen and produce a deflection pattern. Such deflecting systems usually consist of a pair of coils for each direction of deflection. The coils are placed around the tube and alternating currents pass therethrough to produce magnetic fields of varying intensity to deflect the electron beam. The

fields produced by the deflecting systems hitherto used are not very homogeneous and therefore cause considerable distortion of the deflection pattern on the screen of the tube.

It is, therefore, an object of the present invention to provide a new and improved deflecting system. It is a further object of the present invention to provide a deflecting system which produces a substantially homogeneous magnetic fleld throughout the entire cross-sectional area through which the electron beam is deflected.

A further object of the present invention is to provide a deflecting system composed of two individual systems in which each system produces linear deflection at a constant sensitivity of deflection independently of the other system. A still'further object of the present invention is to provide a deflecting system in which substantially the entire cross-section of the magnetic field is limited to the cross-sectional area de- 40 scribed by the electron beam when deflected by means of the present system so as to obtain a high degree of sensitivity as well as small inductivity in the system. In accordance with the present invention a system including two long coils is provided, whereby a homogeneous field is produced inside each long coil independently of its cross-sectional shape. According to the invention, the homogeneity of such fields is utilized for deflection purposes by causing the ray to enter and leave the field inside such a coil through the side walls thereof, and in a direction perpendicular to the axis of said coil. The coils may, in such case, be of circular or rectangular cross section, square, or, if desired,

having regard to securing greater sensitivity and at the same time lowest inductivity, they may have a trapezoidal cross section, so that the ray enters at the shorter of the two parallel sides of the trapezoid and emerges at the larger. For thisv purpose, naturally, the ray passage openings must 5 be left free by suitably crimping the coils during winding.

The system according to the invention may be disposed outside, or in a particularly advantageous manner inside an evacuated electron ray tube. 10 The advantage of the system resides in its great sensitivity (low control current consumption) accompanied by the greatest possible freedom from inductivity (reduced control distortion) as well as the great homogeneity of the control field 1 (exact, constant system-sensitivity over the entire deflectional area).

The figures of the drawing illustrate constructional embodiments of the subject matter of the invention. 20

Fig. 1 is an arrangement used hitherto showing two coaxial deflection coils.

Fig. 2 shows the field path in a long deflecting coil having a homogeneous field.

Fig. 3 depicts an embodiment of a deflecting 25 coil system in accordance with the invention.

Figs. 4 and 5 show a cross section and plan View respectively of a further embodiment of a coil system.

From the picture of the magnetic field shown in Fig. 1, it is evident that in the usual arrangements the field in the deflection space between the coils is non-homogeneous. On the other hand the field inside the coil as shown in Fig. 2 is absolutely homogeneous. Such a field, present inside a coil, is used for cathode ray deflection purposes in accordance with the present invenion.

In Fig. 3 two coils I and 2 are provided which intersect each other at right angles. The axes 40 of the coils lie in a plane perpendicular to the axis of the electron beam. The cross section of the coils in this case is chosen as trapezoidal. The cross sectional shapes of both coils are similar to each other and the coils intersect each other 45 in such a manner that their longitudinal axes intersect the axis of the electron beam at the same point. The axial extent of both coils may be greater than the greatest extent of the coil cross section.

In the embodiment of Figs. 4 and 5, the entire double coil system has the shape of a square truncated section of a pyramid wherein each two opposite sides of the pyramid pertain to one coil winding. The size of the hollow space of the Cit ki l

pyramid in that case is somewhat greater than the cross-sectional area which the electron beam traverses during the deflection in order to render harmless the decreased homogeneity which occurs in this embodiment owing to the short length of the individual coil, relative to its crosssection. The coil 3 is disposed on a framework 4 made of heat resisting material, e. g. ceramic material or glass. The frame 4 preferably contains two plates 5, which are square, or else shaped corresponding to the dimensions of the deflection pattern produced by the electron beam. These plates receive and retain the coil windings wherefore their edges are provided with saw-tooth shaped serrations. The plate through which the electron beam enters into the deflecting system is provided with a small hollow cylinder 6, whereas on the plate through which the beam emerges from the deflecting system is provided with a raised retaining frame I which is formed as a continuation of the frame 4 and which surrounds the cross-section from which the beam emerges. The frame I may have a square shape or a shape according to the deflection pattern of the electron beam. The convolutions are coiled sidewise around the raised edges of the members 6 and 1. The edges serve preferably also to attach the deflecting system to a supporting means (not shown). After the coil 3 is wound, rectangular, thin, insulating disks 8 having a correspondingly bored-out, circular or rectangular hole are applied, which serve as a support for the second coil 9 and to insulate it from the first coil 3. Individual wires as well as groups of windings may be laid in the tooth spaces ll] of the saw-toothed plates 5. This permits the adjustment of the specific field strength (ampere turns, per centimeter of length of the individual coil), whereby the field strength along the axis of the coils can be controlled. The entire deflecting system can be incorporated withinv the tube envelope II, only a portion of which is shown in Fig. l of the drawing. Member 6 faces the source of the electron beam, while the member I faces the screen against which the beam is directed.

The coils consist of turns of copper wire, preferably provided with an oxide or carbonate coating for insulation purposes, this coating being adapted to withstand the heating temperature of the tube in case the deflecting system is operated inside the tube in a Vacuum. Such coatings can be produced, for example, by means of a glowing furnace or an open flame and a regulated supply of air or oxygen, or by the admission of carbon dioxide. The wire may however also be insulated by applying to its surface a coating of waterglass mixed with insulating particles, e. g. chalk.

The magnetic lines of force traversing the inside of the coils are also present on the outside of the coils and form complete loops surrounding the coils. The electron beam will also be influenced by the fields on the inside of the coils. This influence should be prevented since these edge fields are non-homogeneous. They cause a deconcentration of the electron beam on the outer portions of the deflection pattern produced by the system. The cross-section of the concentrated electron beam then assumes the aspect of two small wedges standing tip to tip on each other. In order to render the outer fields as harmless as possible in their action, the magnetic flux on the outside of the coils should be guided by means of a ferromagnetic material into the same plane, perpendicular to the axis of the electron beam, as the main flux, i. e. sidewise around the system. The components of the magnetic flux outside the coils intersecting the electron beam in front and back of the deflecting system, should be weakened as much as possible. For this pur pose the embodiment of Fig. 4 uses a closed ferromagnetic hysteresis-free and loss-less jacket (not shown) which likewise has the shape of a truncated pyramid section with or without bored-- out bottom. and top plates and which is disposed over the windings so that the wires of the windings lie close thereto. The use of granulated lowloss materials is also feasible because of the high frequency of the deflection. Such a jacket aids in producing a strongly homogeneous field inside each pyramidic coil and reduces the inductivity to the minimum possible value corresponding to the required beam deflection and beam. intensity and at the same time increases the sensitivity to the maximum value. In case longer individual coils are used, as shown in Fig. 3, the jacket likewise surrounds the entire system.

I claim:

1. In a cathode ray tube, a ray deflecting system comprising two axially intersecting symmetrically cross-sectioned and congruent coils disposed normal each to the other, said coils having a trapezoidal cross-sectional form.

2. In combination with cathode ray deflecting means after claim 1, means for insulating electrically said coils comprising a mixture of heatresistant binding and non-conducting material.

3. In combination with cathode ray deflecting means after claim 1, means for insulating electrically said coils comprising a mixture of chalk and water glass.

4. A cathode ray device comprising an envelope, a ray deflecting system including a coil form in said envelope and having an axial passage therethrough for the ray, and windings wound on said form normal to each other, one of said windings enabling deflection of said ray in one direction, another of said windings enabling deflection of said ray in another direction.

5. A cathode ray device comprising an envelope, a ray deflecting system including a coil form. of truncated shape having a small end and a large end, said coil form being disposed in said envelope with its smaller end facing the source of said ray and having an axial passage therethrough sufliciently large at the larger end of said coil form to permit unobstructed deflection of said ray, windings wound on said form normal to each other, one of said windings enabling deflection of said ray in one direction, another of said windings enabling deflection of said ray in another direction.

6. A ray deflecting system for a cathode ray device comprising a coil form of truncated shape having a small end and a large end and an axial passage therethrough, said passage being larger at the larger end of said form than at the smaller end, and a pair of windings wound on said form normal to each other.

7. A ray deflecting system for a cathode ray device comprising a coil form of truncated shape having a small end and a large end and an axial passage therethrough, said passage being larger at the large end of said form than at the small end, a pair of windings wound on said form normal to each other, said form having a plurality of serrations to receive said windings.

ERNST RUSKA.