US2252744A

US2252744A - Cathode ray tube

Info

Publication number: US2252744A
Application number: US237545A
Authority: US
Inventors: Fleming-Williams Bria Clifford
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-11-03
Filing date: 1938-10-28
Publication date: 1941-08-19
Anticipated expiration: 1958-08-19
Also published as: FR845391A; GB505026A

Description

g- 19, 1941- B. c. FLEMING-WILLIAMS ,744

CATHUDFJ RAY TUBE Filed Oct. 28, 1938 Patented Aug. 19, 1941 CATHODE RAY TUBE Brian Clifford Fleming-Williams, Cranfo'rd,

England Application October 28, 1938, Serial No. 237,545

In Great Britain November 3, 1937 10 Claims.

This invention relates to cathode ray tubes.

A feature of the invention is the provision of a cathode ray tube wherein the beam is divided into two parts which are independently deflectable in one direction.

An arrangement according to the invention may be used, if means are also provided to deflect both parts of the beam together in the perpendicular direction, for the purpose of obtaining 'two traces simultaneously on a fluorescent screen, representing the variations of two different phenomena with respect to a single variable. A simple example is the representation of the variations of a voltage and of a corresponding current with respect to time.

If one part of the beam only is deflected in the direction of independent deflection, then the other part may be employed to trace an axis of abscissae for the curve traced by the first part of the beam.

According to the invention there is provided a hard vacuum cathode ray tube having an electron gun and having a pair of electrostatic deflector plates arranged to provide the first or the only deflection of the electron beam issuing from said gun, characterised in that an additional plate electrode is positioned in the space between said deflector plates with its plane perpendicular to the plane of the deflection produced by said deflector plates and parallel to the axis of the undeflected electron beam, and so that it cuts through the path of the electron beam which will therefore pass partly on one side and partly on the other side of said additional plate, and further characterised in that said additional electrode is arranged to be maintained at the same potential as the final anode of the gun, whereby the electrostatic deflection field produced between said additional electrode and one of said deflector plates by a potential difierence between them will be rendered substantially independent of the potential difference between said additional electrode and the other of said deflector plates.

By the term hard vacuum cathode ray tube in this specification is meant a cathode ray tube in which the electron beam is mainly iocussed by electron lenses.

It will be understood that in the above statement. of the invention the expression the first or the only deflection is not intended to exclude the possibility of a small deflection ap plied in the gun orin the region between the flection may be provided, for example, by magnetic means in order to compensate for inaccuracy of alignment of the additional electrode and the gun, or to obtain a desired distribution of current between the two parts of the beam where widely diiierent writing speeds are to, be employed for the two parts. The expression is, however, intended to exclude any means for providing deflection through angles comparable with the maximum useful angles of deflection obtainable with the deflector plates.

It is desirable that the deflection system should be as near as possible to the gun so that it will operate upon the beam where this is as wide as possible. In this way, loss of current to the additional plate is minimized.

In the accompanying drawing, Figure l is a diagrammatic elevation, shown partly in section, of the electron gun and deflector plates of a high vacuum cathode ray tube according to the invention. Figure 2 is an exploded perspective View of the deflector plates and associated parts of the structure shown in Figure 1.

In Figure 1, the parts I, 2, 3 and 4 indicate diagrammatically an electron gun having the cathode (unseen) within the modulating electrode l, theelectron beam being emitted vertically therefrom through cylindrical first and second anodes Z and 3 (which will also have disc portions which are unseen) and then through the third (final) anode 4 which is shown in section. The disc part 4a of this final anode acts as a mask and collects all electrons from the beam which are not concentrated into the aperture 4b.

The electron beam issues upward from the aperture 4b as a slightly convergent pencil. It then passes between th deflector plates 5 and 8 which are arranged symmetrically and sufficiently far apart to be outside the path of the beam. The additional plate electrode 1 is positioned in th plane which contains the axis of the electron gun (the center line of the beam) and which is perpendicular to the plane of the deflection caused by electrostatic fields due to deflecting potentials on

plates

5 and 6.

The electron beam is of such width at this part of the tube that only a small portion of the electron current is collected by the plate I when this is maintained at the potential of the final anode 4 of the gun. The part of the beam which passes between plates 5 and l is screened by the plate I from the deflecting influence of plate 5.

gun and the deflector plates. Such a small (16- il y, the P Of the be m w ich passes between plates 6 and 1 is screened from plate 5. A deflecting potential applied between plate 1 and either

deflector plate

5 or 6 will produce a deflection only in that part of the beam which passes between that deflector plate and plate 1. It is found that if plate I is not unduly long, as measured along the axis of the tube, then the parts of the beam may be deflected not only in the directions away from plate 1 but also in the directions towards plate 1 without serious loss of current plate I. When no deflecting potentials are applied, the two parts of the beam will focus in a single spot on the screen.

With practicable dimensions of plate I, it is found that the screening of each part of the beam from the opposite deflector plate is not quite adequate for some purposes. fore, preferred that small additional deflector electrodes be provided to compensate for the resulting errors. Such electrodes are shown as wires 8 and 9 which are connected to the deflector plates Band 6 respectively. An alternative method of eliminating these errors is to' provide the necessary degree of coupling between the external circuits connected to

thedeflector plates

5 and 6. Thepreferred method of mounting the plates 5, 5' and 1 will be 'better seen from Figure 2. Annular discs'of mica ill and H have central holes slightly smaller in diameter than the width the slits lea, lilo, the disc H is superposed and the plate l is fitted through the slits Hb lb. The discs lfl and It are secured closely together by eyelets through a number of holes lild, Hd. In this way the flangesFaa, 6a are held in the planes of theadjacent faces of these mica discs, and theinclination of these plates to the axis is thus fixed. The plate I is held in the plane containing the axis by Welding the lugs la to memberl2, which is a metallic plate having a, central aperture slightly smaller than the apertures in discs iii and II and having ears iia which, on assembly, are bent around the edges of, and on to the lower face of, disc It. The member i2 is also provided with lugs i217 which are somewhat springy and are arranged to press against a conductive coating on the envelope of the tube. The connection of plate 1 to the final anode of the gun may conveniently be made by a wire from one of these lugs [21) to the final anode 4 but this connection is shown merely diagrammatically, as also are the connections of wires 8 and 9 to the

deflector plates

5 and 6.

The ears lid and lugs l2b are omitted from Figure 1, in order to render that figure more clear.

The wires 8 and 9 may be supported by welding to longitudinal support wires parallel to the axis passing through holes lild, lid, and through similar holes in micas which support the parts of the gun.

With a diameter of the aperture ib in the final It is, there-.

sions of the deflector plate assembly have been found satisfactory:

Millimeters Length of deflector plates (as seen in Figure 1) 6 Length of plate 7 (as seen in Figure l) 7.5

.Spacing of inner face of each deflector plate from axis:

of each deflector wire (centre) from 5.2 Spacing of each deflector wire (centre) top face of member E2 What I claim is:

l. A cathode ray, tube comprising an electron gun for emitting an electron beam, electrode means for controlling the convergency of said beam, means comprising a plate electrode for dividing said beam into a plurality of parts, means comprising a pair of electrostatic deflector plates co-operating with said second mentioned means for independently deflecting each of said parts and means comprising a pair of additional deflector elements each connected to opposite former mentioned electrostatic deflector plates for controlling the deflection. of said parts.

2. A cathode ray tube comprising an electron gun having an anode for emittingan electron beam, means for controlling the convergency of the electron beam to focus the electrons on a single spot on the screen, a pair of electrostatic deflector plates each of which is independently energized positioned to deflect the electron beam issuing iromsaid gun, a plate electrode connectedto said anode of said electron gun, said plate electrode being positioned between the electrostatic deflector plates in the path of the electron beam whereby the electron beam upon passing the deflector plates and plate electrode is divided into two parts each of which passes onseparate sides of said plate electrode and are independently deflected by the electrostatic deflection fields existing between the plate electrode and each of the electrostatic deflector plates.

3; A, cathode ray tube comprising an electron gun having a plurality of anodes for emitting an electron beam, means for controlling the convergency of theelectron beam to focus the electrons on a single spot on the screen, a pair of independently energized electrostatic deflector plates positioned on each side of the beam, a plate electrode connected to the last anode of the'electron gun, said plate electrode being posi- 1 beam, said plate electrode also being positioned anodeioi' 3 mm, the'following leading dimenso that it. cuts ,the path of. the electron beam which will therefore pass partly on one side and partly on the other side of theplate electrodes whereby each of the parts will be independently deflected by the electrostatic deflection fields existing between the plate electrode and each of the independent electrostatic deflector plates.

4. A cathode ray tube comprising an electron gun having a plurality of anodes, a pair of electrostatic deflector plates positioned one on each side of the beam and arranged to deflect the electron beam issuing from said gun, a plate electrode connected to one of said anodes of the electron gun, said plate electrode being positioned between said electrostatic deflector plates with its plane substantially perpendicular to the plane of the deflection of the electron beam produced by said electrostatic deflector plates and parallel to the axis of the undeflected beam, said plate electrode also being positioned so that it cuts through the path of the electron beam which will therefore pass partly on one side and partly on the other side of the plate electrode, a pair of deflector electrodes arranged one on each side of the beam, means for connecting each deflector plate with a deflector electrode, positioned at the opposite side of the beam, said deflector electrodes being so positioned as substantially to compensatefor any deflection sensitivity of the part of the beam on the same side as the deflector electrode with respect to variations of potential difference between the deflector plate and the oppositely positioned deflector electrode.

5. In a cathode ray tube comprising an electron gun, a pair of deflector plates and a plate electrode positioned between said deflector plates, supporting structure for said plates for positioning them adjacent the axis of the electron gun comprising in combination a disc of insulating material provided with an opening therein, a plurality of slots in aligned position in opposite sides of the opening of said disc, said slots being adapted to receive said elements and hold them inposition transverse of the said central opening.

6. In a cathode ray tube comprising. an electron gun, a pair of deflector plates and a plate electrode positioned between said deflector plates, supporting structure for said plates for position ing them adjacent the axis of the electron gun, comprising in combination a plurality of superimposed annular discs of insulating material containing aligned slots on opposite sides of the central opening for receiving said plates, flanges on said deflector plates positioned between said superimposed discs for maintaining said deflector plates in position, a plurality of lugs on said plate electrode, and means comprising an apertured member secured on said superimposed annular discs co-operating with said lugs for maintaining said plate electrode in place between said deflector plates.

'7. In a cathode ray tube comprising an electron gun, a pair of deflector plates and a plate electrode positioned between said deflector plates, supporting structure for said plates for positioning them in alignment with the electron beam from the electron gun, comprising in combination a disc of insulating material provided with an opening therein containing aligned slots on opposite sides of the opening adapted to receive said deflector plates and plate electrode, a second disc of insulating material provided with an opening therein superimposed on said disc for maintaining said deflector plates in position, aligned slots on opposite sides of the opening of said second annular disc for receiving said plate electrode and means comprising an apertured member superimposed on said second annular disc for securing said p ate electrode in place.

8. A cathode ray tube comprising an electron gun for emitting an electron beam, means for controlling the convergency of said beam to focus the electrons on a single spot on the screen, means comprising a plate electrode located in the path of the beam for dividing the electron beam into a plurality of parts and means comprising a pair of independently energized electrostatic deflector plates each of which is positioned on opposite sides of said plate electrode for producing electrostatic deflection fields for deflecting each of said beam parts, said electrostatic deflection field for each beam part being independent of the energization of the deflection field of the other beam part.

9. In a cathode ray tube comprising an electron gun for emitting an electron beam, means for controlling the convergency of said beam to focus the electrons on a single spot on the screen, a pair of spaced electrostatic deflector plates between which said electron beam passes, a plate electrode symmetrically positioned intermediate said pair of spaced electrostatic deflector plates with its plane parallel to the axis of the electron beam so that the electron beam is divided into two parts by said plate electrode, means for separately energizing each of the said spaced electrostatic deflector plates to produce independent electrostatic deflection fields between the plate electrode and each of the spaced electrostatic deflector plates whereby each of the aforementioned parts of the electron beam are independently deflected in a plane perpendicular to the axis of the plate electrode by the independent electrostatic deflection fields existing between the plate electrode and each of said spaced electrostatic deflection plates.

10. In a cathode ray tube comprising an electron gun for emitting an, electron beam, means for controlling theiconvergency of said beam to focus the electron on a single spot on the screen, a pair of spaced electrostatic deflector plates between which said electron beam passes, an electrode comprising a plate positioned intermediate said pair of spaced electrostatic deflector plates with its plane parallel to the axis of the electron beam, means for producing independent electrostatic deflection fields between said electrode and each of said electrostatic deflector plates whereby said electrode divides the electron beam into two parts and serves to shield each of said beam parts from the influence of the electrostatic deflection field located between the said plate electrode and the electrostatic deflector plate positioned on the opposite side of the plate electrode from each of the bean parts.

BRIAN CLIFFORD FLEMING-WILLIAMS.