GB2255700A

GB2255700A - System for measuring cathode ray tube (crt) characteristics

Info

Publication number: GB2255700A
Application number: GB9207614A
Authority: GB
Inventors: Sang-Rok Lee; Woo-Kyung Sim
Original assignee: Samsung Electron Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1991-04-12
Filing date: 1992-04-08
Publication date: 1992-11-11
Anticipated expiration: 2012-04-08
Also published as: CN1030939C; KR920020981A; MX9201634A; GB2255700B; KR940000997B1; CN1065731A; GB9207614D0; RU2117410C1; MY108017A

Abstract

A cathode ray tube characteristic measuring system comprises a plurality of cameras 12, a video processor 30, a monitor 40, a CPU 60, a magnetic field controller 50, a selector 20 and an output portion 70. The system simultaneously calculates beam landing states, with respect to time, at various points of a cathode ray tube under test using the selector under the control of the CPU, and measures the amount of thermal drift, thereby reducing the measurement time and realizing precise measurement. <IMAGE>

Description

SYSTEM FOR MEASURING CATHODE RAY TUBE CHARACTERISTICS The present invention relates to a system for measuring cathode ray tube (CRT) characteristics, and more particularly to a system for measuring the thermal drift of a CRT.

A major factor in evaluating CRT characteristics is the amount thermal drift of a CRT. Thermal drift is the amount of change of an electron beam's landing value due to the thermal expansion of a shadow mask and frame which are metal components in the CRT.

Conventionally, the measurement of the improper landing of an electron beam due to the thermal expansion of the metal components in the CRT, is carried out by a special CRT and manual measurement with a microscope. This method cannot attain accurate thermal drift values due to human error.

Fig. 1 of the accompanying drawings is a block diagram of a conventional CRT characteristic measuring system.

In Fig. 1, a camera 1 which converts the image into an electrical signal receives an image of a test CRT 2 via an image pickup lens la. The electrical signal is output to a video processor 3 to be converted into a digital signal and stored in a built-in memory. A monitor 4 displays the data stored in the memory of video processor 3 as an analog signal.

A CPU 5 analyzes the data stored in the memory of video processor 3 and sends appropriate data based upon the analyzed data to a magnetic field controller 6 so as to forcibly move an electron beam. The data analyzed by CPU 5 is also displayed on another monitor 7 or printed by a printer 8.

Here, the state of the display after movement of the electron beam is re-analyzed by CPU 5, and before-and-after states of the electron beam's movement are compared to calculate its landing value. The degree of thermal drift is measured by repeatedly carrying out the calculation by points and for every period of a predetermined length. However, this CRT thermal drift measurement takes a relatively long time.

Therefore, it is an object of the present invention to provide a thermal drift measuring system for a CRT, which is capable of automatically measuring the amount of thermal drift with elapse of time, simultaneously at many points of the CRT, thereby reducing the measuring time and realizing standardized measurement by quantifying the amount of thermal drift.

Embodiments of the present invention provide a thermal drift measuring system for a CRT which comprises cameras for receiving an image of a measured CRT to convert it into an electrical signal, a video processor for converting an analog signal output from the cameras to store it into a builtin memory, a CPU for analyzing the data stored in the memory of the video processor to output a proper control signal according to the analyzed data, a magnetic field controller for controlling the movement of electron beams by the control signal of the CPU, a selector for selecting analog video signals from the cameras under the control of the CPU and transmitting a magnetic field converting signal from the magnetic field controller to the camera means under the control of the CPU, and an output portion for quantifying the data analyzed by the CPU to display or print the qualified data.

Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a conventional CRT characteristic measuring system; Fig. 2 is a block diagram of a CRT characteristic measuring system of an embodiment of the present invention; Fig. 3 is a block diagram of a camera selecting apparatus of the CRT characteristic measuring system embodying the present invention; Fig. 4 is a detailed circuit diagram of the camera selecting means of Fig.3; Fig. 5 is a block diagram of a magnetic field moving coil selecting apparatus of the CRT characteristic measuring system embodying the present invention; Fig. 6 is a detailed circuit diagram of the magnetic field moving coil selecting means of Fig.5;; Fig. 7 shows a side sectional view of an installation portion where the cameras and CRT of the CRT characteristic measuring system embodying the present invention are installed; Fig. 8 shows a frontal view of the camera installation portion of the CRT characteristic measuring system embodying the present invention; and Figs. 9A and 9B respectively illustrate sectional and side views of the camera holder of the camera installation portion of the CRT characteristic measuring system embodying the present invention.

Referring to Fig. 2, the CRT thermal drift measuring system consists of a camera 10, a selector 20, a video processor 30, a monitor 40, a magnetic field controller 50, a CPU 60, and an output unit 70.

Camera 10 is composed of a plurality of lenses 11 for receiving an image from a test CRT 1, a plurality of CCD cameras 12 in, for example, a 3 X 4 matrix, i.e., twelve, for outputting the image received from respective lenses 11 as an electrical signal, a plurality of magnetic field coils 13 respectively provided on the front of each lens 11 for receiving a magnetic field converting signal from magnetic field controller 50 via selector 20 under the control of CPU 60 so as to move an electron beam, and an XYZ stage 14 for supporting the CCD cameras.

Operation of the CRT thermal drift measuring system of the present invention will be described below in accordance with the above structure.

CPU 60 initializes video processor 30, magnetic field controller 50 and selector 20. Lens 11 receives the image of one point from test CRT 1 and CCD camera 12 converts it into an electrical signal. Video processor 30 converts an analog video signal output from one CCD camera selected by selector 20 under the control of CPU 60 into a digital signal, and stores it in a built-in memory. Here, the stored data is varied according to a continuously varied analog signal and has an X-Y coordinate value and luminance information for one image point displayed on test CRT 1.

Monitor 40 displays the data stored in the memory of video processor 30 as an analog signal. CPU 60 analyzes this data to evaluate the current state of the electron beam characteristics, and transmits the appropriate data to magnetic field controller 50. Magnetic coil 13 forms a magnetic field according to the data transmitted from CPU 60 via selector 20 and moves the electron beam.

Selector 20 is connected to the twelve CCD cameras 12 supported by XYZ stage 14 and coupled to twelve magnetic field coils 13 which are coupled to respective lenses 11, and selects one camera 12 receiving one image point and one magnetic coil 13 mounted thereto.

Meanwhile, CPU 60 receives the state after the electron beam moves and comparatively analyzes it with the state before the electron beam moved, to read out the landing value at the first point. When one point measurement is finished, monitor 70a displays the data value analyzed by CPU 60.

After the completion of the measurement of the first point, according to the above method, initial landing values of the remainder of the twelve points are measured, and after a predetermined time, their landing values are measured again to calculate the amount of thermal drift. Here, the thermal drift value may be quantified and displayed on monitor 70a with a position value for every point, graph, or diagram. The measurement values of the twelve points may be simultaneously output via printer 70b.

In the system of the present invention, the thermal drift values of 12 points can be read into unit ssm, and since it takes less than 5 seconds to read the landing value of one point, twelve thermal drift values can be read every minute.

Referring to Fig.3, the camera selecting apparatus consists of CPU 60, video processor 30, a plurality of cameras CAl-CA12 positioned at respective points in front of CRT 1, and a camera selecting means 100 for selecting one camera among cameras CAl-CA12 to output its video signal.

In camera selecting means 100, control signals from CPU 60, using a control program to control the whole system and select a camera, are input to a latch 110 and an address controller 120. Address controller 120 controls the clock signal for latch 110 in accordance with the control signal of CPU 60.

The output of latch 110 is connected to inputs of camera selector 130 to which individual outputs of cameras CAl CA12 positioned in front of the CRT are connected. The output of camera selector 130 is connected to an output stabilizing circuit 140. Latch 110 generates its output according to the data from CPU 60 and the clock signal from address controller 120.

Referring to Fig.4, latch 110 uses a signal from output D3 among outputs DO to D3 as the enable signal for camera selector 130.

Camera selector 130 comprises two video multiplexers 131 and 132 having eight channels CHl-CH8 and CH9-CH16, respectively. Address inputs A0, Al, and A2 of each video multiplexer 131 and 132 are commonly connected to data outputs DO, Dl and D2 of latch 110. Output D3 of latch 110 is connected directly to the enable port of video multiplexer 132 and to the enable port of video multiplexer 131 via an inverter 133.

Respective channels CH1-CH6 and CH9-CH14 of video multiplexers 131 and 132 are connected to each camera CAl-CA12.

The outputs of video multiplexers 131 and 132 are connected to output stabilizing circuit 140.

Output stabilizing circuit 140 comprises parallel capacitors C1 and C2 for high frequency component compensation and for DC blocking, a resistor R1 for controlling the input level, a non-inverting amplifier OP1, a resistor R2 connected to the non-inverting port of non-inverting amplifier OPl for providing supply voltage Vcc, voltage dividing resistors R3 and R4 and a capacitor C3 which provide a reference voltage by feeding back the output of noninverting amplifier OPl, a capacitor C4 for eliminating the DC component from the output signal of noninverting amplifier OPl, a resistor R5 for controlling the output level, and a resistor R6 for applying the proper DC power from supply voltage Vcc to an output video signal.

Now, operation of the CRT characteristic measuring system embodying the present invention will be described below.

CPU 60 generates a 5-bit control signal according to a predetermined control program. Latch 110 latches the control signal and address controller 120 controls latch 110 under the control of CPU 60. Respective control signals from the outputs DO, Dl and D2 of latch 110 are input to respective inputs A0, Al, and A2 of video multiplexers 131 and 132 of camera selector 130. A control signal from output D3 is input to the enable port of video multiplexer 132 and simultaneously inverted by inverter 133 to be fed to the enable port of video multiplexer 131.

Accordingly, if the logic of output D3 of latch 110 is "l," video multiplexer 131 is disabled and video multiplexer 132 is enabled to select one of channels CH9-CH14 so that the photographed video signal is output via video multiplexer 132.

The video signal output is fed to output stabilizing circuit 140. Since the signal is weak, capacitors Cl and C2 compensate its high frequency component and eliminate the DC component. The video signal is then input to noninverting amplifier OPl via resistor Rl.

The video signal amplified to a sufficient amplitude by noninverting amplifier OPl is input to video processor 30 via resistor R5 with its DC component being removed by capacitor C4. Supply voltage Vcc provides a DC component suitable for the input to video processor 30 via resistor 6 so that the video signal is stabilized.

Meanwhile, if the logic of output D3 of latch 110 is "0," video multiplexer 131 is driven. Thus, one of channels CHl-CH6 is selected in accordance with the control signals of outputs DO, D1, and D2 of latch 110, a corresponding camera is selected, and the video signal is stabilized by output stabilizing circuit 140 to be input to video processor 30.

In other words, by installing output stabilizing circuit 140 for stabilizing a video signal next to camera selector 130, the quality of the video signal is improved and its noise is eliminated.

Referring to Fig. 5, the magnetic field coil selecting apparatus of the selecting means comprises CPU 60 for controlling the whole system and outputting data so as to select a magnetic field moving coil according to a predetermined program, address controller 120 for controlling an address by CPU 60, latch 110 for latching the address signal controlled by address controller 120 and data transmitted from CPU 60, a decoder unit 200 for decoding data according to the output data and enable signal from latch 110, a power separator unit 300 driven according to the output of decoder unit 200 for separately applying a computer's driving power and a magnetic field moving coil's power, a switch unit 400 for selecting one of a plurality of relays according to the driving of power separator 300 to switch the selected relay, magnetic field controller 500 for providing a magnetic field control signal via switch unit 400, and a magnetic field moving coil unit 600 for receiving the control signal from magnetic field controller 500 via switch unit 400 to control the magnetic field moving coil of one point.

Here, decoder unit 200 consists of two 3-to-8 decoders 201 and 202. Since 3-to-8 decoder 201 receives an inverted enable signal of latch 110 via inverter 203 and 3-to-8 decoder 202 receives the non-inverted enable signal, only one of the two 3-to-8 decoders is selected to be driven.

The output of decoder unit 200 is input to power separator unit 300. The corresponding power separator unit 300 comprising a plurality of power separators 301 to 306 and 307 to 312 is driven to provide a supply voltage Vcc to switch unit 400 and the remaining power separators become disabled.

Switch unit 400 only turns on the relay selected by power separator unit 300 and applies the control signal of magnetic field controller 500 to the corresponding magnetic field moving coil 600. Thus, the magnetic field moving coil of a desired point can be selected to perform a characteristic measurement at that point.

In Fig. 6, power separators 301 to 306 and 307 to 312 respectively consist of a light emitting diode (LED) (Dl-D12) receiving respective outputs from decoders 201 and 202 via inverter (11-112), and a photo coupler (PT1-PT12). Here, a first resistor (R1-R24, odd designators) of each power separator 301 to 312 is a current limiting resistor for the LEDs, and a second resistor (R1-R24, even designators) is an emitter resistor for the photo couplers.

The emitter of each photo coupler (PTl-PT12) is also connected to respective driving coils of relays 401-412 of switch unit 400. Two movable contact points of relay 401 are connected to magnetic field controller 500, and its fixed contact points are connected to two input points of magnetic field moving coil 601 of magnetic field moving coil unit 600.

Here, the magnetic field moving coil moves vertically and horizontally in a magnetic field so as to be used for both dotted and striped types.

One sides of the vertical moving coil and horizontal moving coil 601 are connected to the two fixed contact points of relay 401, and their other sides are commonly connected to the output of magnetic field controller 500.

Accordingly, magnetic field controller 500 has four outputs in all. Two outputs are commonly connected to two ports of each magnetic field moving coil 601 to 612 and the other two outputs are commonly connected to the other two ports of magnetic field moving coils 601 to 612 via respective relays 401 to 412. As described above, each of the twelve utilized outputs of decoder unit 200 corresponds to one power separator, one relay and one magnetic field moving coil.

According to the above structure, operation of the magnetic field moving coil selecting apparatus will be described below.

CPU 60 generates a signal for selecting a magnetic field moving coil according to a predetermined control program and address controller 120 transmits clear and clock signals to latch 110.

Latch 110 receives four data signals dO to d3 from CPU 60 and latches them. Latch 110 also generates outputs from outputs Ql to Q4 in accordance with the clock from address controller 120. The signals from three of the four outputs (Ql, Q2 and Q3) are input to three inputs A, B and C of each decoder 201 and 202. Output Q4 is applied to decoder 202 as an enable signal and to decoder 201 via inverter 203 as a disable signal.

Accordingly, if the logic of output Q4 of latch 110 is "1," decoder 202 is selected to be driven. Conversely, if the logic is "0," decoder 201 is selected to be driven.

The output states of decoder unit 200 are as follows. where magnetic field moving coil 601 is provided in front of the test screen so that characteristic measurement is carried out at that point.

As depicted above, a magnetic field moving coil is selected by the signals of outputs dO to d3 of CPU 60, and vertical and horizontal moving coils of the magnetic field moving coil are selected and controlled by the output selection of magnetic field controller 500.

Fig.7 is a side view of a test fixture showing how one column of cameras and the CRT of the characteristic measuring system embodying the present invention are installed.

Referring to Fig.7, test fixture 700 comprises a camera installation portion 702 where cameras 701 are installed, a CRT installation portion 704 where a CRT 703 is installed, and a support 705 for rotatively supporting camera and CRT installation portions 702 and 704.

A CRT holder 706 for fixing CRT 703 is provided in CRT installation portion 704 and installed by a bolt 707 so that the upper and lower parts of the holder 706 are releasably fixed to camera installation portion 702. A support rotator 709 having bearings 708 is provided between support 705 and camera and CRT installation portions 702 and 704.

Meanwhile, as shown in Fig.8, camera installation portion 702 has a disk 716 at its center whose center is fixed to support 711. The upper and lower parts of support 711 are where magnetic field moving coil 601 is provided in front of the test screen so that characteristic measurement is carried out at that point.

Meanwhile, as shown in Fig.8, camera installation portion 702 has a disk 716 at its center whose center is fixed to support 711. The upper and lower parts of support 711 are fixed to the upper and lower parts of camera installation portion 702, respectively, by a bolt 713. A slotted hole (not shown) is formed for bolt 713, allowing support 711 to move back and forth for a predetermined distance.

First and second guide rods 715 and 717 are installed in the diagonal direction and in the horizontal direction of camera installation portion 702, respectively. One side of first guide rod 715 has a slider 721 provided on the periphery of camera installation portion 702 and movable vertically and horizontally as well as a first knuckle 718, so as to be movable. The other side of first guide rod 715 has a second guide rod 717 and a second knuckle 719 to be movable. The other side of second guide rod 717 is connected to disk 716 and a third knuckle 720 to be movable. The rotating directions of first and third knuckles 718 and 720 are the same, and the rotating directions of them and second knuckle 719 are perpendicular.

Meanwhile, one first guide rod 715 has at least two cameras 701, and camera holders 722 for fixing cameras 701 are installed onto first guide rod 715 and movable from left to right and vice versa in the length direction of first guide rod 715.

As shown in Figs.9A and 9B, camera holder 722 consists of a fixing portion 723 for fixing camera 701, a block 724 fixed to first guide rod 715, and a slider 725 for horizontally sliding fixing portion 723. Block 724 is installed onto first guide rod 715 so that camera holder 722 is slid along first guide rod 715, and slider 725 is slid back and forth by a control screw 726 so that the distance of camera 701 can be controlled. A rotating hole 725a is formed in slider 725 so that fixing portion 723 is rotatable along with 725b.

As shown in Fig.7, in the apparatus embodying the present invention, CRT installation portion 704 is fixed in one body by bolt 707 so that when measuring CRTs of the same size, it is not necessary to readjust the distance and vertical relation between the screen of CRT 703 and camera 701, thereby reducing the time required to measure a CRT. If bolt 707 is released considering the separation of CRT 703, CRT installation portion 704 separates from camera installation portion 702.

Support 711 vertically installed on camera installation portion 702 has a slotted hole on its upper and lower parts and is fixed by bolt 713 through the slotted hole so that support 711 is movable back and forth for a distance from camera installation portion 702. Here, disk 716 fixed to support 711 is also movable back and forth by first and third knuckles 718 and 720 so that the distance between camera 701 and CRT 703 is adjustable.

Since sliders 721 connected to one side of first guide rod 715 are movable vertically, if slider 721 is moved in any direction, first guide rod 715 rotates centering second knuckle 719 so as to change the location of camera 701.

Since block 724 of camera holder 722 is fixed to first guide rod 715, camera holder 722 is movable along first guide rod 715 to move the cameras and is rotatable on the axis of first guide rod 715. In Figs.9A and 9B, when control screw 726 is operated, since slider 725 is movable horizontally, camera 701 is movable back and forth. Since fixing portion 723 fixed to camera 701 is connected to slider 725 by fixing screw 727, fixing portion 723 is movable along long hole 725a formed in slider 725, allowing the cameras to move in every direction.

Accordingly, camera 701 may be located in any desired place with respect to CRT 703, and since each camera is movable in any direction, they may be adjusted freely with respect to the screen of CRT 703, thereby precisely measuring the characteristic of the CRTs under test.

Further, camera and CRT installation portions 702 and 704 are freely rotated by support rotator 709 provided on support 705, facilitating measurement in the desired direction.

As described above, in the CRT characteristic measuring apparatus of the present invention, since the camera and CRT installation portions are fixed in one body, the time to prepare for a measuring task is reduced. The CRT installation portion can be separated from the camera installation portion. Further, since the plurality of cameras installed in the camera installation portion are movable along the first guide rod and in any direction, it is easy vertically to adjust the cameras to the CRT's screen and a precise characteristic measurement is achieved.

As a result, the CRT characteristic measuring system of the present invention can simultaneously measure with respect to time the amount of thermal drift at many points of a CRT under the control of a CPU, using a selector means, thereby reducing the measurement time, and obtains a precise and standardized measurement value by quantifying the amount of thermal drift into unit microns.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention.

Claims

1. A cathode ray tube characteristic measuring system comprising: camera means for receiving an image of a cathode ray tube under test to convert it into an electrical signal and moving electron beams; video processor means for converting an analog signal output from said camera means into a digital signal for storage in a built-in memory; a central processing unit for analyzing the data stored in said memory of said video processor means to output a proper control signal according to the analyzed data; magnetic field controller means for controlling the movement of electron beams by means of the control signal of said central processing unit;; selector means for selecting analog video signals from said camera means under the control of said central processing unit and transmitting a magnetic field converting signal from said magnetic field controller means to said camera means under the control of said central processing unit; and output means for quantifying the data analyzed by said central processing unit for display and/or printing out said analyzed data.

2. A system as claimed in claim 1, wherein said camera means comprises: a plurality of lenses for receiving an image of the cathode ray tube under test; a plurality of magnetic field coils provided on the front of said lenses of CCD cameras for receiving a control signal from said magnetic field controller via the plurality of CCD cameras outputting as an electrical signal the image from said lens and said selector means, and moving electron beams; and an XYZ stage for supporting the plurality of CCD cameras.

3. A system as claimed in claim 2, wherein said magnetic field coils of said camera means are located in the necks of said plurality of CCD cameras.

4. A system as claimed in claim 2 or 3, wherein said selector means comprises first means for selecting said plurality of CCD cameras and second means for selecting said magnetic field coils.

5. A system as claimed in claim 4, wherein said first means comprises: a latch for latching the control signal from said central processing unit and generating a camera select signal; an address controller for controlling a clock of said latch according to the control signal of said central processing unit; a camera selector for decoding the output from said latch to select one of the plurality of CCD cameras connected to an input port; and an output stabilizing circuit for stabilizing a video signal output from a camera selected by said camera selector and outputting the signal to said video processor means.

6. A system as claimed in claim 5, wherein said camera selector consists of two video multiplexers each of which has 16 channels and is driven in turn.

7. A system as claimed in claim 5 or 6, wherein said output stabilizing circuit comprises: parallel capacitors for compensating for a high frequency component of a video signal photographed by said cameras and eliminating its DC component; a non-inverting amplifier for amplifying a weak video signal input via said parallel capacitors; feedback voltage dividing resistors and capacitor for providing a reference voltage of said non-inverting amplifier; a resistor for providing a bias of said non-inverting amplifier; a capacitor for blocking the DC component of the video signal output from said non-inverting amplifier; and a resistance circuit for applying the appropriate DC component to said video output signal and outputting the signal.

8. A system as claimed in any of claims 4 to 8, wherein said second means comprises: an address controller for controlling an address according to the selecting instruction of said central processing unit; a latch for latching an address signal of said address controller and data transmitted from said central processing unit; decoder means for decoding data according to the output data and enable signal from said latch; power separator means having a plurality of power separators and being selectively driven according to the output from said decoder means, for separately applying the driving power of said CPU and the power of said magnetic field moving coils; switch means consisting of a plurality of relays for selecting one relay according to the driving of said power separator means to be switched and providing a control signal from said magnetic field controller; and magnetic field moving coil means for receiving the control signal of said magnetic field controller via said switch means to control a magnetic field moving coil at one point.

9. A system as claimed in claim 8, wherein said decoder means comprises: a first decoder for receiving the enable signal of said latch via an Inverter; and a second decoder for directly receiving the enable signal.

10. A system as claimed in claim 9, wherein each power separator of said power separator means consists of a light emitting diode for indicating the active output of said decoders and a photo coupler switched according to the output of said decoder means.

11. A system as claimed in any preceding claim, wherein a test fixture for installing cameras of said camera means and cathode ray tube has a camera installation portion for installing said cameras and a cathode ray tube installation portion for installing said cathode ray tube which are fixed in one body and separable from each other, a support which is movable back and forth located in the front of said camera installation portion to support a disk, and a support rotator located between said camera and cathode ray tube installation portions and a-further support of supporting the portions.

12. A system as claimed in claim 11, wherein said camera installation portion comprises: a plurality of first and second guide rods provided in the diagonal and horizontal directions of said disk; a plurality of first sliders connected to one side of said first guide rods and located in said camera installation portion for moving horizontally and vertically; and a plurality of camera holders located in said first guide rods for rotating said cameras horizontally and vertically.

13. A system as claimed in claim 12, wherein said disk, first and second guide rods and first sliders are connected by first, second and third knuckles.

14. A system as claimed in claim 13, wherein said first and third knuckles and second knuckles move perpendicular to each other.

15. A system as claimed in any of claims 12 to 14, wherein said camera holder comprises a block fixed to said first guide rod, a second slider rotatable by the manipulation of a control screw placed in said block, and a fixing portion fixed to said second slider by a fixing screw and movable along an elongated hold formed in said second slider, for fixing said cameras.

16. A system for measuring cathode ray tube characteristic substantially as hereinbefore described with reference to Figure 2 with or without reference to any of Figures 3 to 9B of the accompanying drawings.