US2416200A - Cathode-ray tube with spot intensity proportional to radial deflection - Google Patents

Description

Feb. 18, 1947. w NAGEL 2,416,200

CATHODE RAY TI JBE WITH SPOT INTENSITY PROPORTIONAL TO RADIAL DEFLECTION 2/ Input 2 7 Tzlme WITNESSES: fly Z INVENTOR Geozye MA/ayeZ.

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ATTORN Patented Feb. 18, 1947 CATHODE-RAY TUBE WITH SPOT INTEN- SITY PROPORTION AL TO RADIAL DEFLEC TION George W. Nagel, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 24, 1943, Serial No. 511,531

2 Claims. (Cl. 315-22) 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 pcriphery 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 moments consideration will make it evident that successive paths must overlap each other at all radial distances except at the very periphery of the screen under the conditions just outlined. Since the luminous efiect 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 central portions of the screen appear much brighter than the peripheral portions, and this efiect may be intensized by the well known phenomenon of persistence of human vision.

One object of 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 which the luminous intensity is made uniform throughout the area of the screen.

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.

Other objects of my invention will become ap parent 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

' I Fig. 2 is a graph illustrating the variation of time of a certain voltage used in carrying out my invention.

Referring in detail to Fig. 1, item I is a cathode ray tube whch comprises a vacuum-tight tube having a relatively long cylindrical neck portion 2 which expands at one end to form a circular screen 3. The screen end of the tube is coated on its interior surface with willmanite or other material which is rendered luminous when bombarded 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 I!) through which electrons are projected in a fine stream along the axis of the tube I. The cathode l, anodes 5 and It, may respectively be energized from taps ona highvoltage power supply 6 in which the positive terminal is preferably grounded and the negative terminal connected to the cathode 4. In front of the cathode l is located a control electrode 7 which is connected through a grid-resistor 53 to the negative terminal of a bias battery '5 of which the positive terminal is connected to the cathode 4. The above-mentioned electron stream is pro jected through the control electrode 1. Between the anode Ill and the luminous screen 3 the electron stream passes through the fields of a pair of deflecting magnets 9 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 I to give them a radial velocity component which lies in a plane passing through the central axis of the tube I normal to the direction of the transverse magnetic field above mentioned. The amount of 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 incidence on the screen 3 of the electron stream would be moved radially outward uniformly from the center to the periphery of the screen 3. As will be described in more detail below, the tubes I I, I 2 and I3 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.

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 14. As a result of this rotation the angular 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 is and the periodicity of the voltage from generator II, l2, l3 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 H, l2, IS 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 H, I2, l3 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 15 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 I? 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 H is connected to a suitable source of positive direct-current potential of which the negative terminal is connected to ground. The control electrode of the tube II is connected through a resistor I B and a capacitor I9 to ground. The same control electrode is likewise connected to the anode of the tube l2. The tubes 12 and t3 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 2| 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 13 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 l2. The control electrode of the tube I3 is connected to the negative terminal of a suitable biasing voltage source 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 defiection.

In practical use of tubes of the type so far described, it is customary to impress varying voltages on the control electrode 1 of the tube l 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 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 illumination.

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 27 to the control electrode E, the other terminal 3| of the input circuit being connected to ground.

In order to so modulate the intensity of the cathode ray beam reaching the screen 3, as to reduce 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 it of the tube 1 I which governs the strength of the magnetic field is connected through a suitable capacitor 28 and a resistor 29 to the control electrode '5. The magnitudes of the portion of the output voltage impressed on the electrode 1, when the voltage impressed across the terminals 25-3l is zero, is adjusted to such a value that the voltage impressed on the control electrode 2 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 suflicient velocity to form a luminous spot thereon. When the voltage of Fig. 2 rises sufficiently for current flow to begin through the windings 9 producing the above-mentioned transverse magnetic field, the voltage on control electrode 1 is made just sufficient to produce a, spot of a desired luminous intensity on the screen 3. current through the magnet system 9 is then substantially zero, the luminous spot is incident upon the exact center of screen 3. As the voltage curve represented in Fig. 1 rises along the uniformly increasing portion thereof, the above-mentioned 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 impressed through capacitor 28 and resistor 29 causes such an increase in positive potential of control electrode 1 as to 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 resistor 29, this increase in intensity 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 impressed on the control electrode through capacitor 28 and resistor 29 reduces the potential of control electrode 1 to so small a value that the electrons striking screens 3 do not render the latter luminous. Due to the inherent self inductance of the magnet systems 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 po- Since the 5 tential impressed on control electrode 1 prevents any electrons from reachin the screen 3 with suificient velocity to render the latter luminous.

The above-mentioned events consume one cycle of the wave represented by the curve in Fig. 1.

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, 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 id screen, means for rotating the direction of radius about the center of said screen, means for generating a saw-toothed voltage, an impedance, means for impressing said saw-toothed voltage on said impedance, means for connecting said deflecting means in a circuit shunting said impedance, an electrical input circuit, means for connecting said input circuit to said control elec trode and means for connecting said control electrode in a circuit shunting part of said impedance.

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, beam-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, a first and a second tube each having a control electrode and having an anode and cathode supplied with current, a first impedance, said cathodes being connected together to one end of said first impedance, a bias battery, the control electrode of said first tube being connected through said bias battery to the other end of said first impedance, a first capacitor, a second impedance, the control electrodes of said second tube being connected through said first capacitor to the anode of said first tube and also being connected to said other end of said first impedance through said second impedance, 9, third impedance, a second capacitor, means for connecting the anode of said second tube to said other end of said first impedance through said third impedance and said second capacitor, a third tube having a control electrode connected to the anode of said second tube and having an anode and cathode traversed by direct current, a fourth impedance connecting the cathode of said third tube to said other end of said first impedance, a third capacitor, means for connecting said fourth impedance in shunt to a circuit comprising said third capacitor and said means for deflecting, a fourth capacitor, and means for connecting a portion of said fourth impedance in shunt to a circuit which includes said fourth capacitor in series with said beam-control electrode and said electrode and said electron-gun.

GEORGE W. NAGEL.

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

UNITED STATES PATENTS Number Name Date 1,535,329 MacGregor- Morris et a1 Apr. 28, 1925 2,241,809 De Forest May 13, 1941 2,312,761 Hershberger Mar. 2, 1943 2,313,966 Pooh Mar. 16, 1943 FOREIGN PATENTS Number Country Date 107,213 Australian Apr. 20, 1939 542,634 British Oct. 16, 1939

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