US2416199A - Cathode-ray tube with spot intensity proportional to radial deflection - Google Patents

Description

' Feb. M 1947.

G. W. NAGEL CATHODE RAY TUBE WITH SPOT INTENSITY PROPORTIONAL T0 RADIAL DEFLECTION Filed NOV. 24, 1943 vi & 2

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ATTORN Patented Feb. 18, 1947 CATHODE-RAY TUBE WITH SPOT 1N- TENSITY PROPORTIONAL TO RADIAL DEFLECTION George W. Nagel, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 24, 1943, Serial No. 511m 3 Claims.

My invention relates to cathode ray tubes and, In particular, to such tubes in which the incidence of an electron beam on a screen on the end of the tube produces a luminous spot which is caused to scan, by repeated radial movements, the entire circular end of the tube.

For certain purposes, notably in connection with the present war work, cathode ray tubes are used in which the electron beam by repeated radial movements from the center to the circumference scans the entire circular area forming the luminous screen at the end of the tube The successive radial movements from center to periphery are displaced slightly'in an angular direction from each other, this displacement being such that the adjacent edges of successive radial paths touch each other at the periphery of the screen so that after the entire 360 of circumference has been traversed there are no areas which have not been swept over by the moving spot. However, a moment's consideration will make it evident that successive paths must over lap each other at all radial distances except at the very periphery of the screen under the conditions just outlined. Since the luminous effect itself persists for an interval after the cathode ray has once left a given elementary area on the screen, this repeated traverse by the luminous spot of areas in the central portion of the screen gives such areas a greater specific luminous intensity than is attained by similar areas at the periphery of the screen. In other words, the can tral portions of the screen appear much brighter than the peripheral portions, and this effect may be intensified by the well known phenomenon of persistence of human vision.

One object or my invention is, accordingly, to provide a cathode ray tube in which the luminous screen is scanned by radial movements of the sort above described but in whichthe luminous intensity is made uniform throughout the area of the screen. l

Another object of my invention is to produce a cathode ray tube having a luminous screen subject to radial scansion in which the intensity of electron bombardment of the screen varies inversely with the radial distance from the center of the screen. I

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawing, in which:

Figure 1 is a schematic diagram of the electrical circuits of a cathode ray tube embodying the principles of my invention; and l Figure 2 is a graph illustrating the variation intimeof s erms voltage used in carrying out my invention. l l U A Referring in detail to Fig. 1, item [is a cathode ray tube which comp rises a vacuum-tight tube having a relatively long cylindrical neck portion a which expands at one end to form a circular screen 3, The screen end of the tube is coated on its interior surface with willinanite or other material which isr'endered luminous when loombar ded by electrons. In the other end of the tube is positioned an electron-gun of a type well known in the art comprising an electron emissive surface, and a virtual cathode '4 of small area associated with cylindrical anodes 5 and "Iii through which electrons are projectedin a fine stream along the axis oi the tube I. The cathode 4, nd anodes 5 and Ill, may respectively be en e'rgize'd from a high volta'g'e power supply 6 in which the positive tei'minal is preferably ground ed and the negative terminal connected to the cathode '4. In front of the cathode 4 is located a control electrode 7 through which the abovementioned electron stream is projected. The control electrode 1 maybe connected through a' resistor 8 to a bias battery 1 which makes it somewhat more negative than the cathode. Bee tween the anode l0 and the luminous screen 3 the electron stream passes through the fields of a pair of deflecting magnets 53 of a type Well known in the art which produces a magnetic field trans- Verse to the central axis of the tube I. Such a magnetic field will act upon the electrons travelling along the central axis of the tube l to give them a radial velocity component which lies in a plane passing through the central axis of the tube l normal to the direction of the transverse magnetic field above mentioned. The amountof the radial acceleration producing this velocity will be proportional at any. instant to the strength of the transverse magnetic field. Thus, if the direction of the magnetic field were fixed and invariable, and a constantly increasing current were to provide a uniform increase with time of the transverse magnetic field, the point of incidenc'e on the screen 3 of the electron stream would be iiioved radially outward uniformly from the center totheperiphery of the screen 3. As will be described in more detail below, the tubes ll, [2 and is constitute an electrical generator which causes the transverse magnetic field above mentioned to rise gradually from zero to a maximum at a uniform' rate in each of a series of successive cycles. J} v In order that the" radial movements of the spot of incidence of the electron beam on screen 3 shall gradually traverse the entire area of the screen, the magnetic system above mentioned is arranged to be rotated in a plane perpendicular to the axis of the tube I by an electric motor l4. As a result of this rotation the annular position about said axis in which the electron beam is deflected continually changes at a rate which is small compared to the period of radial movement itself. The relation of the rate of rotation of the motor I4 and the periodicity of the voltage from generator II, I2, I3 is made such that between successive outward sweeps of the electron beam it has moved an angular distance at the periphery at the screen 3 which is substantially equal to the width in a circumferential direction of the luminous spot.

The wave form of the voltage impressed by the generator II, I2, I3 on the windings producing the transverse magnetic field above mentioned is substantially similar to that shown in Fig. 2. At the beginning of each period this voltage rises rapidly to a certain value and thereafter increases uniformly with the time to a maximum value, whereupon it falls rapidly to its original value and so continues until the beginning of a second cycle.

The generator II, I2, I3 comprises an output tube I I of any suitable type embodying an anode, control electrode and a cathode. The cathode is connected through a resistor I5 to the positive terminal of a bias battery I6 of which the negative terminal is connected to ground. The cathode of the tube II is likewise connected through a capacitor H to one terminal of the windings 9 producing the above-mentioned transverse magnetic field, the other terminal of the windings 9 being grounded. The anode of the tube II is connected to a suitable source of positive direct currentpotential of which the negative terminal is connected to ground. The control electrode of the tube II is connected through a resistor I8 and a capacitor I9 to ground. The same control electrode is likewise connected to the anode of the tube I2. The tubes I2 and I3 constitute what is frequently referred to as a multivibrator. The anode of the tube I2 is connected through a resistor to the positive terminal of a suitable voltage source of which the negative terminal is grounded. The cathode of the tube I2 is connected through a resistor 2I to ground. The control electrode of the tube I2 is connected through a capacitor 22 to the anode of the tube I3 and is also connected through a resistor 23 to ground. The anode of the tube I3 is connected through a resistor to the positive terminal of a suitable voltage source of which the negative terminal is grounded. The cathode of the tube I3 is connected directly in parallel with the cathode of the tube I2. The control electrode of the tube I3 is connected to the negative terminal of a suitable biasing voltage sourc 24 of which the positive terminal is connected to ground.

The arrangement so far disclosed would produce the type of luminosity on the screen 3 which is conventional in the prior art; namely, the luminous intensity on the screen would be roughly inversely proportional to the radial deflection.

In practical use of tubes of the type so far described, it is customary to impress varying voltages on the control electrode I of the tube I to produce luminous patterns thereon which are indicative of certain quantities or measurements which it is desired to observe. If, however, the variations of intensity over the screen are to be III 4 truly representative of the variations in intensity of the quantity being observed, it is essential that the luminous intensity of the screen shall be free from variation in accordance with radial distance or any other quantity not related to the quantity being observed. For this reason, a screen in which the luminous intensity is free from variation in accordance with radial distance is a great improvement over the present conventional type of screen.

In accordance with my invention, the quantity which is to undergo observation by producing luminous patterns on the screen 3 is impressed on an input circuit having one terminal 25 connected through a condenser 2'! to the control electrode 28 of an amplifier tube 29, the other terminal 3| of the input circuit being connected to ground. The tube 29 is preferably a remote cut-off type pentode, the gain of which increases as its grid bias is made less negative. The cathode of the tube 29 is connected to ground through a resistor 32 shunted by a capacitor 33 and is likewise connected to a suppressor electrode 34 of the tube 29. A screen electrode 35 of the tube 29 is connected to one terminal of a source of suitable positive voltage of which the negative terminal is grounded. The positive terminal of the above-mentioned source is likewise connected through a resistor 36 to the anode of the tube 29. The anode of the tube 29 is connected through a capacitor 31 to the control electrode 1 of the cathode ray tube I.

In order to so modulate the intensity of the cathode ray beam reaching the screen 3 as to reduced the luminous intensity in the radially inward portion of the screen and to produce uniform luminosity throughout the area of the screen, a portion of the output voltage of the resistor I5 of the tube II which supplies the energy of the magnetic field is connected through a suitable capacitor 38 to the control electrode 28 of the tube 29. The magnitudes of the resistor 32 and of the voltage impressed on the electrode 28 of tube 29, when the voltage impressed across the terminal 25-3l is zero, are adjusted to such a value that the voltage impressed on the control electrode of tube 2 is so low during the troughs of the voltage waves shown in Fig. 2 that no electrons from the cathode I strike the screen 3 with sufficient velocity to form a luminous spot thereon. When the voltage of Fig. 2 rises sufiiciently for current flow to begin through the windings 9 producing the above-mentioned transverse magnetic field, the voltage on control electrode I is made just sufficient to produce a spot of a desired luminous intensity on the screen 3. Since the current though the magnet system 9 is then substantially zero, the luminous spot is the exact center of screen 3. As the voltage curve represented in Fig. 1 rises along the uniformly increasing portion thereof, the abovementioned magnetic field so deflects the electron beam as to move the luminous spot radially outward on the screen 3; at the same time the rising potential of control electrode 28 causes such an increase in the gain of the tube 29 that input signals of a given amplitude impressed across terminals 253I give progressively greater positive potential on the control electrode 1 as to progressively increase the intensity of the luminous spot on screen 3. This increase in intensity in the luminous spot continues throughout its radial deflection and by proper adjustment of the tap point by which the capacitor 38 is connected to a resistor I5, this increase in gain of the tube 29 with the resultant greater intensification for a given input signal may be made substantially proportional to the radial deflection of the luminous spot. The luminous spot arrives at the periphery of the screen 3 at the time the voltage represented in Fig. 1 reaches the maximum point on the curve. This voltage rapidly drops to its initial value and correspondingly the voltage on the contro1 electrode 28 of tube 29 is reduced and the gain of tube 29 is also reduced. This reduces the potential swing of control electrode 1 for the given amplitude of input signal to so small a value that the electrons striking screen 3 do not render the latter luminous. Due to the inherent self inductance of the magnet system 9, the intensity of the deflecting field cannot instantly fall to zero but it rapidly decreases until it reaches the zero value. The electron beam does not, however, produce a visible return path to the center of the screen 3 because, as previously stated, the control electrode 1 has such low-voltage swings impressed upon it by the tube 29 when the voltage of control electrode 28 is impressed with the voltage of the wavetrough in Fig. 2 that it prevents any electrons from reaching the screen 3 with suificient velocityto render the latter luminous.

The above-mentioned events consume one cycle of the wave represented by the curve in Fig. 2.

While I have illustrated the principles of my invention by showing their application in a particular embodiment thereof, it will be evident to those skilled in the art that these principles are of broader application in ways which are evident.

I claim as my invention:

1. In combination, a cathode ray tube comprising a luminous screen, an electron-gun adapted to project an electron stream on a concentrated spot on said screen, a deflector for said electron.

stream adapted to deflect it along a radius of said screen, means for angularly rotating the direction of said radius about a central point of said screen to trace overlapping paths thereon, and means for varying the intensity of said electron stream proportionally with its radial deflection from the center of said screen.

2. In combination, with a cathode ray tube having a luminous screen at one end thereof and an electron-gun for projecting a concentrated beam of electrons into incidence with said screen, a control electrode for varying the energy with which said electron beams strike said screen, means for deflecting said beam along a radius of said screen, means for rotating the direction of said radius about the center of said screen, means for generating a saw-toothed voltage, means for impressing said saw-toothed voltage on said deflecting means, an electrical input circuit, means for connecting said input circuit to said control electrode and means for impressing a voltage derived from said saw-toothed voltage on said control electrode.

3. In combination with a cathode ray tube having a luminous screen at one end thereof and an electron-gun for projecting a concentrated beam of electrons into incidence with said screen, a control electrode for varying the energy with which said electron beams strike said screen, means for deflecting said beam along a radius of said screen, means for rotating the direction of said radius about the center of said screen, means for generating a saw-toothed voltage, means for impressing said saw-toothed voltage on said deflecting means, an electrical input circuit, means for connecting said input circuit to an amplifier tube having an output circuit voltage impressed on said control electrode and means for Varying the current in said output circuit in response to said saw-toothed voltage.

GEORGE W. NAGEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,234,830 Norton Mar. 11, 1941 2,121,359 Luck et al June 21, 1938 2,092,081 McLennan Sept. '7, 1937 2,241,809 De Forest May 13,1941 2,313,966 Pooh Mar. 16, 1943 2,312,761 Hershberger Mar. 2, 1943 2,197,900 Schlesinger Apr. 23, 1940 FOREIGN PATENTS Number Country Date 542,634 British Jan. 21, 1942 107,213 Australian Apr. 17, 1939 Disclaimer 2,416,199.Ge0rge W. Nagel, Baltimore, Md. CATHODE-RAT TUBE Wrm Spo'r INTENSITY PROPORTIONAL '1'0 RADIAL DEFLECTION. Patent dated Feb. 18, 1947. Disclaimer filed May 27, 1949, by the assignee, Westinghouse Electric Corporation. Hereby enters this disclaimer to claim 1 in said patent.

[Oflicial Gazette June 28, 1949.]

Disclaimer 2,416,1995-George W. Nagel, Baltimore, Md. OATHODE-RAY TUBE Wrrn Sm'r INTENSITY PROPORTIONAL T0 RADIAL DEFLECTION. Patent dated Feb. 18, 1947. Disclaimer filed' May 27, 1949, by the assignee, Westinghouse Electric Corporation. Hereb enters this disclaimer to claim 1 in said patent.

Q ficial Gazette June 28, 1.949.]

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