US2215199A - Cathode ray tube - Google Patents

Description

w 1940- E. STEUDEL QCATHODE RAY TUBE Filed Dec. 11. 1937 INVENTOR EBERHAPD STEUDEL BY f6? ATTORNEY Patented Sept. 17, 1940 UNITED STATES CATHODE RAY T'UBE Eberhard Steudel, Berlin-Dahlem, Germany, assignor to General Electric Company, a corporation of New York Application December 11, 1937, Serial N 0. 179,232 In Germany December 16, 1936 3 Claims.

The "invention is concerned with an arrangement for a'Braun tube which makes it feasible to operate the tube on lower potentials than heretofore customary, Without losing any of the glow or luminosity intensity, while making brief actions visible for a prolonged period of time. What is used for this purpose is an electrode of the kind known in the art of television. This electrode or screen plate may be made in the following manner:

A metal gauze or network is oxidized with the result that the constituent wires of the reticular structure are covered with an insulating coat or film. Next metal is brought into the interstices or gaps between the Wires of the gauze in some suitable manner so that the entire screen plate eventually becomes a mosaic comprising a multiplicity of metal particles individually insulated from one another, the said metallic particles extending from the anterior face to the posterior face of theelectrode. Thus, if a charged pattern is focused upon the anterior face of the screen plate, the same patternof charges will appear also upon the posterior face thereof.

According to this invention, such a screen plate is used in a Braun or cathode-ray tube, the said screen plate being provided on one face thereof, that is, the posterior face, with a substance which is caused to luminesce when bombarded by electrons. The said luminiscent or fluorescent substance is applied preferably upon such spots of the surface or plate where the insulating grid wires are located so that the so-called electrode or metallic particles will stay bare, that is, will not be coated by the luminescent substance. Now, a Braun tube according to the invention is operated in such a way that upon the anterior face of the electrode, in the usual way, an oscillographic tracing appears, whereas the posterior face thereof is bombarded by an intense and uniform electron pencil being inherently homogeneous.

Now, a Braun tube of this design and type operates in the following fashion: Since the elements upon the anterior face of the screen plate which correspond to the action to be outlined (oscillogram) are negatively charged by the electron pencil of the cathode-ray tube, the uniform cathode-ray pencil which falls upon the posterior face of the electrode will be kept away wholly or partly from these elements, whereas it will excite the luminescent substances of the other elements. In other words, what is obtained is the negative of an otherwise customary tracing.

A Braun or cathode-ray tube as here disclosed offers the advantage that for both cathode-ray beams, that is, for the pencilfalling upon the anterior face of theelectrode, and the auxiliary pencil which would cause homogeneous glow or illumination upon the posterior face of the screen plate or electrode, only comparatively low potentials are required. The delineator or tracing pencil is not in need of a high voltage since it serves solely for the charging of the elements of the screen plate, for it is not called upon to excite the luminescent substance as is usually the case. The auxiliary pencil, on the other hand, which is not subject to control actions and which need not be focused is not required to pass through high voltage. \Vhile it is true that the said auxiliary pencil is required to excite the luminescent substance, it will result in the requisite luminosity or brilliance by higher pencil density. The fact that no high potential is required for thetracing pencil insures at the same time high sensitivity for the tube without it being necessary to provide special steps and means such as space-charge diaphragms or apertures, and supplemental or re-accelerator means' Due to the further circumstance that the luminescent screen may be viewed in plan or directly such losses as are usually caused by light absorption inside the layer are obviated.

Finally, persistence of image or pattern beyond the instant of tracing action is insured because of the fact that the distribution of the charges throughout the pattern is non-instantaneous, and this is an advantageous feature which proves particularly valuable in the tracing of high-speed non-recurrent actions or phenomena as in connection with the use of Braun tubes in television work.

The screen plate itself can be manufactured by extremely simple methods since neither the recording or tracing pencil nor the auxiliary pencil are required to penetrate through the screen plate so that no special precautionary measures are needed to preclude undue thickness of the metallic inserts.

Figure l of the drawings illustrates, by way of example, a screen-plate according to this invention in several stages of its manufacture.

Figure 2 shows a Braun tube fitted with a raster or screen-plate of the kind shown in Figure 1. 5O

Numeral I denotes the metallic network, gauze or grid which is coated with an insulation film 2. In the interstitial spaces or meshes between the grid wires are placed the metal particles indicated by 3. The luminescent substance which posteriorly is applied preferably only upon the insulation portions is designated by 4.

In Figure 2, I0 denotes the screen plate and opposite the anterior face thereof is a source of electrons. The said source consists here of a directly heated cathode iii. For focusing the electron pencil are provided the intermediary partitions or diaphragms l3, intermediate cylinder M, the anode diaphragms or apertures l5, while the intensity of the pencil is regulated or modulated by the potential impressed upon the aperture plate l6. Numerals I1 and I8 denote pencil deflector means. The posterior of the screen-plate ll] which is covered with luminescent substances is bombarded by a homogeneous electron pencil generated by the source of electrons l9 and the condensing device 20, 2! (electric immersion objective).

Viewing may be in the direction of the arrow 22, but if oblique viewing of the screen is to be avoided, then the ray generating means I9, 20, 2] may be so mounted that the homogeneous pencil of electrons will be caused to strike the screen-plate or raster H] obliquely,-say, roughly in the sense of the arrow 22, with the result that the observation of the recording of the luminescent-screen pattern will be at right angles to the screen. Even when the axes of the auxiliary electron source are inclined in reference to the normal to the screen-plate, oblique bombardment with electrons may be avoided by ways and means known in the prior art, that is, by the aid of a magnetic field which is positioned at right angles to the normal to the screen-plate and the axis of the auxiliary electron source.

The leads for current and potential have not been included in the drawing, but it is to be understood that for screen-plate I 0 in a case where the usual current drain by way of the walls of the vessel should prove inadequate, a distinct and separate voltage or current return conductor may be provided to restore the screen-plate to its quiescent or normal potential value after bombardment with electrons has been finished.

thereof comprising a fine mesh screen, a layer of insulation, completely covering said screen, conducting members in the interstices of said screen, and a fluorescent coating deposited only on the insulation and only on the side of the screen toward said flooding source of electrons. 2.. A cathode ray tube comprising an envelope,-

an electrode positioned intermediate the ends of the envelope and normal to the axis thereof, said electrode comprising a fine mesh screen, a layer of insulation completely covering said screen, conducting members in the interstices of said screen, a fluorescent coating deposited only on the exposed insulation and only on one side.

of said screen, means in one end of said envelope adapted to produce a uniform field of flooding electrons and for directing the produced electrons against said one side of the screen, and means at the other end of said envelope adapted to produce a narrow beam of low velocity electrons for systematically scanning the other surface of said screen.

. 3. An electrode member comprising a fine mesh screen grid of conducting elements, a layer of insulation deposited upon each element of said grid, conducting material positioned in the interstices of the screen between each of the grid elements and separated by the insulation on said elements, and a fluorescent coating deposited only on the insulation and only on one side of each of the grid elements to the exclusion of the conducting elements positioned between said elements.

' EBERHARD STEUDEL.

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