US2843799A - Direct-view electrical storage tube and methods of operating same - Google Patents

Description

yDIRECT-VIEW ELLECTRICAL STORAGE TUBE AND METHODS oF OPERATING SAME Filed 'Aug. 14, 1953 'hihi-"15,1958 V H o HK Em. 2,843,799v

- pff/719701Z wr/0 INI/ENTORS United States DIRECT-VIEW ELECTRICAL STORAGE TUBE AND METHODS OF OPERATING SAME Harvey 0. Hook and Max Knoll, Princeton, N. J.,'as signers to Radio Corporation of America, a corporation of Delaware l Application August 14, 1953, Serial No. 374,172 8 Claims. (Cl. 315-12) filed May 29, 1953, by Harvey O. Hook.

A number of presently known signal storage and display systems are used in connection with radar Systems, ground-taair private line communication systems, and

the like. In order to obtainthe features of both signal storage and signal display these storage and display 4systems generally require one or more electrical storage tubes in combination with a separate display tube. Such arrangements are complicated, relatively expensive, and occupy excessive amounts of space which could be used to better advantage, particularly in airborne systems., It is highly desirable in such instances to combine the features of storage and display in a single tube. f

. Such a tube has been developed and is described in detail in patent application Serial No. 295,768, filed June 26, 1952, by Max Knoll. In said application data stored and displayed by the direct View tube is completelyv and almost instantaneously erased by manually adjusting potentials applied to certain electrodes contained therein. Such an erasing technique may be satisfactory for erasing stored transients vand the like. However, the erasure atent ice technique is disclosed wherein a fractional portion of the total stored image pattern is erasedk during either the line or frame deflection flyback interval. Byv

f line of old data may be completely erased just prior to requirements for radar and various other systems arev 'Y more exacting.

In radar systems providing either rectilinear B-scanY or polar coordinate P. P. I. .(plan-p'ositiondndication)' type presentations, it is undesirable to completely erase a storedframe of information before commencing to l write a new frame of data derived in a succeeding search interval. In most of such radar.r systems four to siX seconds is required for completely displaying data derived Iduring a'"360 azimuth search.y If there is instantaneous and complete erasure the four to six second time interval must again transpire before the new frame of information is completely displayed. A further disadvantagey of complete erasure atfthe Vendl of the writing of a given frame is that the eye does not integrate the data last l written and there is an apparent intensity variationor Moreover, information available during shading effect. y the erase period is not stored and therefore is lost.

In a more recently led patent application of Harold Borkan, Serial No. 306,706, filed August 27, 1952, 'an erasing vtechnique is disclosed'for the direct-view tube which 'is ,adaptedl for erasing Bscan or P. P. I. type displays. According to this technique the tube storage electrode assembly includes a plurality of individually insulated charge storage sections. storage section automatically isl controlled for Verasure in 'an vorderly sequence so that old data stored ona given storage section is erased substantially immediately before new data is to be written thereon.

In the application of Harvey Hook, cited above, Serial The potential of each N o. 4358,36l, filed May 29,` 1.953, a further erasingj being replaced with a line of new data. By performing erasing during the frame deection flyback time signal integration may be achieved.

An object of the present invention is to provide improved methods and means for storing and displaying signal intelligence.

Another object of the invention is to provide improved methods and means for utilizing a direct-view storage tube. Y

Another Object of the invention is to provide improved methods and means for either erasing or holding data stored and displayed by the direct-View storage tube.

A further object of the invention is to provide a system of erasure for use with the direct-view tube in which old stored and displayed data is erased just prior to being replaced with new data.

A further object of the invention is to erase data stored in a tube of the above type in a non-synchronous manner so that time-sharing of writing and erasing is not required.

A still further object of the invention is to provide an improved signal storage and display system in which data may be stored for a relatively long periodof time.

, According to the present invention, improved l'methods and means are provided for operating the direct-view storage tube. The technique employed herein does not require the special `target assembly described in application Serial No. 306,706 nor does it require the tin-1esharing arrangement described in application'Serial No. 358,361. y

In the present case pulses are generated non-synchronously with respect to deflections of the tube'writing beam, and are applied to the tube -so that eitherdata erasure or longer signal storage time is provided. With thev amplitude of the non-synchronous pulses adjusted below a predetermined level, each applied pulse causes a fractional portion of the overall stored charged pattern to beerased. By suitably controlling the pulse duration and/or amplitude either signal integration or cyclical erasure of the stored data is attainable. With the amplitude of ythese pulses adjusted to be greater than the above-mentioned predetermined level erasure is not afforded but the storage time of the stored data is increased considerably. l Y

The invention will be described in detail with reference -to the accompanying drawing in which:

Storage tube structure The drawing shows a direct-view type storage tube consisting of an evacuated envelopelltl having two neck sections 12 and 14, respectively. Within the envelope neck 12 is an electron gun 16, hereinafter referred to as the viewing gun. Within neck 14 is asecond or writing electron gun 18 for providing a'modulated beam of electrons which is accelerated into the envelope portion 10.

Mounted at the large end of the envelope portion l0 is anassemly 20 including a glass support sheet 2.?. having a thin Yconductive lm 24 disposed on one surface thereof and facing the electron guns. The film 24 may be formed,

3 V for example, of a metal or metallic compound such as tin oxide. On top of the conductive film 24 is a material 26 such as phosphor which uoresces under electron bombardment.

In the direction towards the electron guns from the surface of the uorescent material 26 is afstorage target assembly 27. The assembly 27 includes ,a 'tine mesh metal screen 28 which is spaced several millimeters from the fluorescent material 26. A storage screen 30 is formed, by evaporation or some other convenient means, on the surface of the conductive screen 28 and lccmprises a dielectricinsulating material such as a film of silica or magnesium fluoride of the order of several microns in thickness. At a distance of the order of several millimeters from the conductive screen 28l in the direction towards the electron guns is a second tine mesh metal screen 32. Screen 32 may be a woven or electroformed mesh of the order of 100 to 500 mesh per inch. The conductive screen 28 and the mesh storage screen 30 also may have a ineness of the order of 100 to S00 mesh per inch.

Assembly 20 is mounted on a ring 36 of insulating material xed within the envelope and adjacent the tube face plate 38. Fixed to the ring 36 is an annular metal support ring 40 which supports intermediate its ends the glass support sheet 22 and across its open end the conductive screen 28. Also mounted on the insulating ring 3 6 is a second annular metal support ring 42 across the ends of which is mounted the woven or electroformed metal mesh screen 32. The conductive tin oxide m 24 is insulated from the support ring 42 by the glass sheet 22 and is connected by a lead 44 to a source of positive potential outside the envelope 10. Mesh screen 32 also is connectedto a source of positive potential via lead 46. The conductive screen 28 during the tube operation, is set either to a predetermined bias potential for writing or at a more 'positive potential for erasure or for holding a stored picture as will be shown hereinafter.

The viewing gun 16comprises a cathode electrode. 48, a control electrode 50, a rst accelerating. electrode 52, and a second accelerating electrode 54 mountedsuccessively along the axis of the. gun 16 toward the face plate 38, During the tube operation these electrodes are maintained at appropriate voltages to form the electron. emission from thefcathode. 48 into a wide beam or sprayl 56 of electrons for flooding a major portion of the surface of the storage screen. Y The inner surface of the envelope 10 has appliedthereto, a conductive coating 58 of colloidal graphitel or tin oxide which coating may be maintained at the same positiveV potential as the second accelerating electrode` 54. A second conductive wall coating 60 extends from a point spaced from. but adjacent coating 58 over the bulb wall enclosing the assemblies and 27. This coatingisata potentialdiferent from that of coating` 58 and thusprovides acollimating electron ,lens to align the electronsofthespray beam 56 in a direction axially, with respect to the target assemblies.

The writing electron gun 18. comprises a cathode electrode 62, a control electrode 64; and, successivelyspaced toward the target, a firstaccelerating electrode 66V and ga second accelerating electrode6S. The wall coating 58 extends into the neck 14 of the writing gun and forms a third accelerating electrodefor. forming. the electrons of gun 18 into a sharplydeined .andlfocused .beam .70;

The voltages applied to the electrodes of the aboveV tube are illustrative of typical suitable operating voltages but should not be considered as. limiting. Forfexample,

the mesh screens 32. may be operatedat between- 200' and 2,000 volts positive with respect to ground.1 The conductive coating 24 may be operated within arangeof from 2,000 to 20,000 volts positive relative toground,

volts relative to. ground.

T ube operation To prepare the storage target for storing a charge pattern on the mesh storage screen 30, it is necessary to establish a uniform potential thereover. With the viewing gun turned on, the electrons of the spray'beam 56 are accelerated with energies of the order of 1,000 volts through the metal mesh screen 32. The conductive screen 28, initially biased by a bias source 71 to a potential such as zero volts, is set to a potential suiciently positive (of the order of 20 volts positive relative to ground) that the electrons of the spray beam 56 strike the surface of the storage screen film 30 at velocities or energies to initiate secondary emission from all portions of the lrn. In the present example the positive potential of 20 volts which is applied, as described hereinafter, to the conductive screen 30 is below the first crossover point on the secondary ratio curve of the silica (or magnesium fluoride) film. The first crossover point for a silica storage film (see Figure 2) is of the order of 75 to 150 volts while the first crossover point for a magnesium fluoride film is approximately 30 to 60 volts. Thus secondary emission is initiated having a ratio less than unity and the storage screen 32 assumes a uniform potential, in this instance viewing gun cathode potential. The entire surface of the storage screen may be brought to a uniform potential as described above in a fraction of a second.

The potential of the conductive screen 2S is then adjusted to approximately zero volts (ground potential). Because of the thinness of the Storage screen 30, screen 30. is closely' coupled capacitively to the screen 28, hence the relative potential dilference therebetween is maintained; i. e., as the potential of screen 28 is changed from a- 20 volts positive relative to ground potential, the potential of screen 30 changes by a corresponding amount from viewing gun cathode potential (ground potential) to approximately minus 20volts relative to ground. The electrons` of the Spray beam 56 are accelerated through the mesh screen 32 and enter a retarding field adjacent the' screen 30, the retarding field turning the electrons back to the metal screen 32 which serves as a collector therefor. The 8,000 volt potential applied to the tin oxide lm 24 creates a field which tends to extend through the interstices of the storage screen 30 to draw electrons through the screen to bombard the uorescent layer 26. The voltage to which the storage screen 30 is set (minus 20 volts), however, just prevents any electrons from passing therethrough.

The Writing gun 18 is then turned on and produces a sharply defined and focused beam which may be deflected to scan over the surface of the storage insulator 30. The `deflection may be accomplished, for example, by supplying vertical and horizontal pairs of deflection plates 72 and 74, respectively,` with suitable deflection signals from deflection signals from deiiection generators 76and 78, respectively. While the writing beam 70 is being deflected in the desired pattern, the beam 70 is modulated by video signals applied to the writing gun control grid 64 from an input circuit 80. The writing beam impinges on the mesh storage screen 30 at a voltage of approximately 3,000 volts which is between the firstandsecond cross-over'points on the secondary emission ratio curve thereof.

In this manner the writing beam initiates secondary emission from the surface of the storage screen such that more electrons leave the surface than impinge thereon. In those areas where the beam 70 strikes, the storage screen surface Iis driven positively from its potential of minus 2,0 volts toward-viewing gun cathode potential or ground, ProvidedV the ratio of the spray beam average current density to. theaverage current density ofthe writing beam-over a giventime intervall is un-ity or greater, no point on the insulator surface will stay positively charged with respect to ground since electrons from the spray beam 56 land continuously at that point and drive it back asserts toA ground potential, or slightly` negativev with respect to ground. In the areas Vwhere the storage screen 3Q. has been driven positively (fromminus 20.volts,)f, the. positive ield of the uorescent layer 26 now penetrates to draw the low energy electrons of the spray beam 56 through the interstices of screens 30- and 2.8 to striloeV the fluorescent screen 26. and cause luminescence. 'I-his luminescence 'appears only on areasvof 'the iluorescent screen 26, corresponding to areas of 4the lstorage linsulator driven positively by secondary emission and hence. corresponding to the image pattern. of the writing beam.

This type of writing provides a. visual display in which stored information `appears as, white 'on a .dark background. Once a signal has been stored and displayed, theoretically it. should remain .stored and displayed indefinitely since thenmodeof tube operation described a'bove is such that the low velocity spray beam 5'6 normally does notv come in contact with the. charged areas of the storage screen 30 and therefore does not disturb theA established charge pattern. Actually, however, the charges established lthereon gradually are. dissipated rby spurious ions produced'within the'tu-be.

Erasingr `A synchronizer 82, a pulse generator, produces pulses at a predetermined pulse repetition rate which simultaneously are coupled to a horizontal deflection wave generator 78 and to a pulse vdividercircuit'84. The, divider circuit produces "an output pulse in response to a prede- 'termined number of input pulses, Assuming that the instant method of erasing is to be utilized in connecion with a typical B-sc-an ra-dar system, and that in the radar system the pulse repetition rate is 1000 pulses per second .and six seconds is required for a 360 azimuth search, the divider circuit 84 produces one output pulse in response to each 6,000 input pulses. Each output pulse derived from the divider 84 is applied to a vertical deflection wave generator 76. The horizontal and vertical dellection generators 78 and 7'6, respectively, produce sawtooth deection signal-s which are applied .to the pairs of deflection y' plates 72 and 74 of the storage tube to deflect the writing beam to rectilinearly scan the storage screen 30.

-During the horizontal deflection intervals video signals are applied to the writing gun control electrode 64 via input circuit 80 Iand modulate the intensity of the writing 'beam 70 to establish a charge pattern on the storage screen 30 and a corresponding visual display on the uorescent layer 26.

Entirely independently of lthe generation of the writing deilection signals, a free-running multivibrator 86 produces pulses at some selectable repetition rate. A multivibrator which is particularly suitable for use inthe present erasing system isa free running positive-bias multivibrator of the type illustrated at page 269 of Reference Data for Radio Engineers (third edition) publish-ed by the Federal Telephone and Radio Corporation. The multivibrator pulses are amplied in a pulse amplifier 88 having a gain control 90. The amplifier output is developed l'across a load impedance 92, each pulse developed thereacross -driving the conductive screen 28 of the storage tube approximately 20 volts positive with respect to ground potential.

The erase process is controlled so that each pulse applied to the screen 28 causes a 'fractional'portion of the overall stored electrical charge pattern to ybe erased. For example, if Ithe multi-vibrator 8-6 -generates 800 pulses per 360 radar search interval, the duration of each pulse is Iadjusted 'by means of a pulse duration or Width control 94 so .that a given pulse 'causes the overall era-sure of an eight-hundredth of the stored charge pattern. If 1000 pulses are 'to be generated during this interval the pulse repetition frequency control `96 and the pulse duration con-trol 94 are adjusted so that the desired number of pulses are produced and only one one-'thousandth of the charge pattern is erased. T-hus either Ior both the pulse repetition rate` and the pulse duration, may-bevaried `for erasure yasi-'clesited by suitably Varying.v circuit constantsin y The circuitry described above may be useds lt-o achieve long Itime storage of electrical dat-a rather thanincremental erasure as heretofore shown. According tov-this mode of operation the ga-in control is set to control the gain yof the pulse 'amplifier 88- so: that lthe pulses` applied to the conductive screen 28- .have amplitudes of the order of 60 volts for a magnesium fluoride insulator andI amplitudes yof the order of volts 'for asilica insulator, in eachcase, just-.abovethei'irstcrossover-point. v Y

' Under su-ch conditions, f or the durationsofthose pulses, portions ofl .the storage-insulator 30 ywhich are carried abovefirst crossover potential are lcharged in a positive direction and` :portions of the insulator 'belowthe rst crossover point' are charged ina negative direction, The portionscarriedabove .the irst crossover potential correspond to yhighlight portions of- !t-he display providedl on the lfluorescent material 26 `while the insulator portions lbelow lfirst crossover correspondto darka-reas ofthe display. A single frame of data stored in the manner described above lmay be retained for a period -of time approximately 103 Itimes longer `than without pulsing.

`In this mode of operation the pulses produced by the multivibrator 86 have durations short enough so that no area Iof the storage insulator 30 remains equal to or greater than the rst ycr-ossover voltage in the intervals between pulses. IIf lthe pul-se duration 'is too great, electrons from .the viewing beam 56 drive these storage areas to lthe potential of the collector screen 32. Thenthe insulator 30 either may break down `or the size of stored charge may increase or ydiminish thereby effectively creeping across the insulator.

What is claimed is:

1. A signal storage system including, an electrical storage tube having an electron permeable charge storage member, means spaced from one side of said charge storage member for providing a stream ofv electrons for ilooding a major portion of the surface of saidmember, a fluorescent viewing screen spaced from the opposite side of said charge storage member, means forv providing a sharply defined and focused beam of electrons, means for deflecting said sharply defined and focused electron` beam across said charge storage member, connection means for a source of signals for modulating said beam during said deflection to write an electrical charge patfor generating time-spaced pulses at a predetermined pulse repetition rate, and means coupling said pulse generating means to said storage tube to pulse said charge storage member with respect to said Hood beam generating means While said focused electron beam is` dellected across said charge storage member.

2. Apparatus as claimed in claim 1 including means for adjusting the pulse duration of said pulses.

3. Apparatus as claimed in claim 1 including means for adjusting the pulse repetition rate of said pulses.

4. Apparatus as claimed in claim l including means for adjusting both the pulse duration and the pulse repetition rate of said pulses.

5. Apparatus as claimed in claim 1 including means for adjusting the amplitude level of said pulses.

6. A signal storage tube system comprising, an electrical storage tube having an electron permeable charge storage member, means spaced from one side of said charge storage member for providing a stream of electrons for ooding a major portion of the surface of said member, a fluorescent viewing screen spaced from the opposite side of said charge storage member, means for providing a sharply defined and focused beam of electrons, means for deecting said sharply defined and focused electron beam across said storage member, connection means for a source of signals for modulating said beam during said deiiection to write an electrical charge pattern on said member, the charge pattern written on said member modulating the iiow of said stream of electrons so that electrons passing through said electron permeable member impinge on said viewing screen and produce a visual display corresponding to said charge pattern, a free-running multivibrator for repetitively generating pulse signals, and an amplifier coupled to the output of said multivibrator and to said charge storage member for pulsing said member with amplied multivibrator signals While said focused electron beam is deflected across said charge storage member.

7. Apparatus as claimed in claim 6 including a gain control circuit for adjusting the gain of said amplifier.

8. A signal storage tube system comprising, an electrical storage tube having an electron permeable charge storage member, means spaced from one side of said CII charge storage member for providing a stream of electrons for flooding a major portion of the surface of said member, a iiuorescent viewing screen spaced from the opposite side of said charge storage member, means for providing a sharply delined and focused beam of electrons, means for deiiecting said sharply defined and focused electron beam across said storage member, connection means for a source of signals for modulating said beam during said deflection to Write an electrical charge pattern on said member, the charge pattern Written on said member modulating the ow of said stream of electrons so that electrons passing through said electron permeable member impinge on said viewing screen and produce a visual display corresponding to said charge pattern, and means coupled to said charge storage member for repetitively generating pulses at 4a predetermined pulse repetition rate for periodically pulsing said storage member while said focused electron beam is deflected across said charge storage member.

References Cited in the le of this patent UNITED STATES PATENTS 2,513,743 Rajchman July 4, 1950 2,532,339 Schlesinger Dec. 5, 1950 2,548,789 Hergenrother Apr. 10, 1951 2,612,634 Mesner Sept. 30, 1952 2,706,246 Klemperer Apr. l2, 1955

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