Illumination and Visibility of Radar and Sonar Displays Proceedings of a Symposium (1958) / Chapter Skim
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Session IV - New Techniques Under Development
Session IV - New Techniques Under Development
Pages 141-196
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S Naval Research Laboratory DIRECT-VIEW STORAGE TUBES George F
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In the Charactron shaped-beam tube, the electron beam imposes a character from a matrix on the phosphor screen. Several important parameters interact with the light output from the tube and the number of characters presented.
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After deflection, the beam is accelerated to a high energy by means of a helical-type accelerator. The shaped electron beam then strikes the phosphor screen where the Here is converted to light.
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The total light output obtainable when using the shaped-beam principle cannot be compared to other types of displays by merely comparing the ratios of beam-current densities employed. A proper evaluation requires a comparison 2This statement holds true only for magnetically deflected displays.
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This relation can be expressed as 1 Fn~a.r ~ X to where Flax is the maximum frame rate in see -1, to is the average time in see necessary to present a character, and N is the total number of characters being considered. This fundamental relation influences many of the parameters involved in the display, such as integrated light output from a given character, flicker, and legibility, as well as the choice of phosphor and ambient illumination.
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LOW SCREEN CURRENT HIGH SCREEN CURRENT ! lava / 1 _...
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. Since it is generally desirable to maximize light output without destroying character legibility, the tube is operated just below the blooming point.
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operating conditions imposed on the tube, a low-level ambient lighting is required. These problems, coupled with others described in a previous paper, have apparently limited the choice to a selective spectrum lighting system, the broad-band blue.
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At high altitudes, the radar indicator of fighter airplanes is subject to intense environmental illumination which tends to wash out the radar information presented on the screen. To attain good detectability, the radar designer should choose the electrical parameters in such a way that the target spots have the best light output possible.
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the difference between spot brightness and background brightness. This is justified since any brightness ~ B produced by the CRT electron beam will add to, or float on top of, and background brightness produced.
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2. Incremental spot intensity required for detection as a function of background brightness.
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3. Spot brightness in ft-l, and peak beam current in pa for one CRT, type 6DP7, as a function of grid voltage at pulse tops.
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4. Spot intensity in millicandes, and spot diameter in mm as ~ function of grid voltage at pulse tops.
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As seen above, detectability of a target on a given background brightness is determined by its intensity impulse. The intensity impulse is given by the area under the curve up to the pulse number chosen.
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This may be seen in Fig. 7, where phosphor efficiency expressed as intensity per unit beam current is plotted as a function of average beam current for three different pulse widths and for dc, and for the two phosphors, P2 and P7.
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7. Efficiency of P2 and P7 phosphors in relation to pulse width, expressed as intensity per unit beam current with prf of 1200.
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In this type of radar application, however, very high instantaneous beam current must be used because of the small duty cycle. Due to its intimate contact with the glass or substrate, the transparent phosphor has high resistance to burning.
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The output can also be fed to an integrator and the integrated light output, or intensity impulse, can be measured for different operating conditions and phosphors.
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WONNELL and WILLIAM E MILLER CAA Technical Development Center Summary Increasing use of radar arid the need for retention of information by air-traffic-control centers have resulted in studies of projection storage tubes, rapid-processing film equipment, and scan conversion.
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1, employs a writing gun mounted at one end of a tube, a reading gun mounted at the opposite end, a thin insulating target between them, and a collector cylinder surrounding the target. The target consists of a sheet of thin insulating material, such as magnesium fluoride, approximately 0.5-,u thick, evaporated onto one side of a thin aluminum foil which is supported on a fine metallic mesh having high electron transmission.
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The evaluation test results of SRD-1 bright-display equipment as a means of producing the desired radar display were negative. Characteristics of the Graphechon scan conversion storage tube as operated in the SOD-!
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The Technical Development Center had practically abandoned the scanconversion approach to the desired air-traffic-control radar display when the ~,, A 1 J French 11-44u scan conversion equipment appeared upon the scene. The Intercontinental Electronics Corporation of Mineola, L
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A number of features available today in radar indicators should be incorporated in the TI-440 scan conversion equipment to tailor the system to the specific needs of CAA air traffic control. These features are mainly concerned with required changes in the writing circuitry to provide for off-centering and timesharing.
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The Spanrad display' or superimposed panoramic radar display, evolved from efforts to utilize the scan-converted picture in a plotting technique with "shrimp-boat" markers under high ambient light levels.
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Operational analysis indicated informational requirements for displays in terms of the phases of a combat mission. A contact analogue was developed to provide orientation information relative to the pilot's need to know his position and motion in space.
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This approach gave a point-of-reference from which to continue the optimum display and control system determinations. Since pilots are generally capable of operating quite effectively under ideal contact conditions, the human engineers had to determine how the visual world provides answers to information requirements: vi%., what factors in the Visual world enable the pilot to operate his aircraft?
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For some cases, the optimum pattern might take various forms, such as randomly located regular shapes, randomly located random shapes, or regularly located random shapes. The real world does not, in general, contain command or director information.
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Those interested should request Army-Navy Instrumentation Program film MC 8833.
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The method, applicable to most common phosphors, yields luminescent screens having the same properties as these phosphors. The many advantages of transparent screens over the conventional powdered screens include high resolution and corz trast.
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transparent screens and (b) powdered screens.
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The electron beam power may consequently be raised by a factor of 2 to 3 without danger of producing screen burn. Formation of transparent luminescent screens :Formation of transparent screens involves essentially two distinct steps.
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The last column of the table lists firing conditions used in forming the luminescent screens. Freshly evaporated films generally exhibit little or no luminescence.
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The luminescent properties of the screens, with the exceptions of a loss of brightness of about 50 per cent, are identical to those of conventional powdered screens. The luminescent emission peaks correspond to those observed in the powdered material.
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There are a number of applications, however, which require the use of transparent screens and which would be impossible with the present opaque powdered screens. Three of these applications, transparent flat tubes, daylight Viewing tubes, and laminated color tubes, are described below.
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The inside of the tube looks black regardless of the lighting conditions. Since cathoderay tubes and pipes do not have the same geometry' one must cause the light to be absorbed by other means such as coating the inside walls of the cathode-ray tube or the back of the transparent screen itself with a light-absorbing medium such as carbon blacl;.
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4. Schematic drawing of a laminated color screen.
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Other bilayer phosphor screens such as: Mg,SiO4 (red ~ /Zn ,SiOi (green) /glass have been examined, as represented by the dotted line in Fig.
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Transparent laminated color screens have the same advantages of contrast and resolution as the single-layer monochrome screens. Transparent luminescent screens are only in their early stage of development.
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The primary function of such a device is to provide a bright and persistent display of nonrecurrent pictorial information. Storage tubes are well suited for the persistent display of such types of information as radar or sonar data, processed alphanumeric information transient waveforms7 and narrow-bard television pictures.
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In areas where the charge pattern is relatively more positive, flood electrons can perpetrate the storage mesh; in areas where the pattern is negative, the flood electrons are repelled and cannot penetrate the mesh. Those electrons which succeed in passing through the storage mesh are then accelerated so that they may strike the phosphor viewing screen at a high energy and produce a light pattern corresponding to the charge pattern on the insulating storage surface.
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From page 181... ...
As long as the collector remains more positive than the dielectric surface, it will attract and collect the secondary electrons so that a net positive charging current will exist. Any tendency of the surface potential to fall below the collector potential is thus compensated for by the positive charging action of the secondary emission.
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per see, with a resolution of 60 white lines per in. The Typotron tube utilizes the same storage assembly, but is equipped with a character-writing gun for writing alphanumeric information directly.
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This means that none of the electrons from the flood gun can strike the storage surface and hence that the charge pattern should be undisturbed during viewing, even without regeneration. Unfortunately, this is not strictly true since positive ions are formed by the flood beam from the residual gas in the tube.
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Thus, any part of the storage surface having a potential on the useful part of the storage characteristic is elevated slightly above the cathode potential. Flood electrons strike the storage surface, and, since they have only a few volts of energy, for which the secondary-emission ratio is less than 184
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Large-screen and multicolor storage tubes More over-all resolution and the convenience of a larger display are desirable in indicator tubes for air-traffic control, ground radar' and processed data 185
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Tonotron tube. Also in the advanced development stage is a multicolor storage tube'89 which incorporates shadow-mask color selection together with halftone storage in a 10-in.
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The writing beam from one gun, say the red gun' can strike the dielectric around only those storage-surface holes that are aligned with red phosphor dots. The flood beam coming through the shadow mask from the extendedsource flood gun illuminates the entire storage surface but penetrates it only where the charge pattern is positive.
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8. Alignment of shadow mask, storage mask, and phosphor dots in the multicolor store ge tube.
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Persistent-emission panels and storage panels are of particular interest. Persistent-emission panels, the construction of which is described, have adequate resolution and are superior in their light output and persistence to the phosphors of conventional cathode-ray tubes.
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1. Pulse radiation can be in the form of either an incident electron beam or light emission from an intermediate phosphor.
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appeared steady. However, at the cessation of the input pulses the light emission fell quite rapidly, and within 1 see was at the.
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It is of interest here that the shape of the plateau, i.e., its height and length, can be significantly changed by varying the frequency. On the other hand, the integrated light output, i.e., the total area under each curve, is approximately constant.
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2~. The various layers are as follows: First, there is a supporting glass substrate, and then a transparent tin oxide conductor continuous over the whole panel.
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Light levels of 100 to 1000 ft-l are achievable with 500 pulses to 50,000 c. A 1-msec envelope of these pulses is sufficient to trigger a corresponding storage cell when the storage panel is adjacent to the trigger panel.
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There are several applications for a display panel with this resolution and writing speed. The combination of trigger panel and storage panel represents a complete display unit.
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