GB2194382A

GB2194382A - Cathode ray tube with heated screen

Info

Publication number: GB2194382A
Application number: GB08620305A
Authority: GB
Inventors: Peter John Dennis Bailey
Original assignee: BAILEY CONCEPTS Ltd
Current assignee: BAILEY CONCEPTS Ltd
Priority date: 1986-08-21
Filing date: 1986-08-21
Publication date: 1988-03-02
Also published as: GB8620305D0

Abstract

A cathode ray tube (10) for use in cold conditions, such as in railway stations, has a faceplate or screen (16) which is provided with means for heating the screen to prevent the formation of ice on it. The heating means, on one or both surfaces, or within a laminated screen, may be thin lines of electric resistance heating elements (18), for a film of electrically conducting material extending over the whole or a part of the viewed area of the screen (16). The current passing through the heating means may be energized synchronously with the frame scan of the tube at the fly back time of the electron beam, so as to avoid distortion of the image by the resulting electric field. Coils may be provided to neutralise the field generated by the heating means. <IMAGE>

Description

SPECIFICATION Cathode ray tubes Field of the Invention This invention relates to cathode ray tubes.

Background to the invention When cathode ray tubes are used in cold conditions (for example for visual display purposes in public places like railway stations) ice tends to form on the screens of the tubes, so impairing clarity of the viewed image and risking mechanical failure of the tubes. The invention aims to overcome this problem.

Summary of the Invention According to the invention, a cathode ray tube has a screen provided with heating means to prevent the formation of ice on the screen.

The heating means are preferably constituted by an electrical resistance heating element which may be in the form of narrow lines of electrically conducting material extending across the viewed area of the screen or may be a transparent film of electrically conducting material (e.g. vacuum metallisedì extending over the whole or a part of the viewed area of the screen. In either case, electrical current passing through the heating element provides resistance heating which warms the screen of the cathode ray tube.

The heating means may be applied to the external surface of the cathode ray tube screen but preferably the heating means are printed or sprayed on to a separate glass faceplate which is positioned closely in front of the screen. The heating means may be deposited on either or both surfaces of the faceplate, or may be laminated between two component glass sheets forming the faceplate.

The electric current passing through the heating means will generate an electric field which may affect deflection of the electron beam of the cathode ray tube, resulting in distortion of the image. To avoid this, the heating means are preferably energized synchronously with the frame scan of the cathode ray tube, the heating means being energized during the frame fly back time but not during line scan, so that any field produced by the heating means does not affect quality of the image displayed. Alternatively, the heating means may be continuously energized and formed so as to constitute coils which substantially neutralize one another in terms of the electromagnetic field produced.As a further alternative, a neutralizing coil or coils separate from the heating means may be provided, theneutralizing coil or coils cancelling the field produced by the current flowing through the heating means.

The heating means are conveniently thermostatically controlled, for example being energized only when the ambient temperature is below a predetermined threshold level at which there is a risk of ice formation on the cathode ray tube screen.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:.

Figure 1 is a diagrammatic side elevation of a cathode ray tube according to the invention, and Figure 2 is a front view of the screen of the cathode ray tube.

Detailed description of the drawings Referring to Figure 1, the cathode ray tube 10 has deflecting coils shown diagrammatically at 12 which control the deflection of an electron beam which impinges on the inner surface of the screen 14 of the tube 10.

In front of the screen 14, there is positioned a glass faceplate 16 on which is printed a pattern of thin lines forming an electrical resistance heating element 18. The faceplate 16 is positioned closely against the screen 14. The lines of the element 18 are thin and do not substantially affect the clarity or definition of the image when the tube 10 is viewed from a normal distance.

Ends of the heating element 18 are brought out and connected in an electrical circuit powered synchronously with the cathode ray tube in such manner that the element is supplied with electrical current only during the frame fly back time. This pulsed energization of the element 18 ensures that any electromagnetic field produced by the current flowing through the electrical resistance heating element 18 does not affect deflection of the electron beam of the tube 10.

The electrical circuit powering the element 18 is thermostatically controlled, so that the heating element 18 is energized if the ambient temperature falls below a predetermined threshold.

The heating element 18 not only prevents the formation of ice on the screen but also lessens the risk of the tube imploding, which can occur when subjected to very low temperatures.

1. A cathode ray tube having a screen, and heating means associated with the screen in order to Prevent the formation of ice on the screen.

2. A cathode ray tube according to claim 1, in which the heating means is constituted by an electrical resistance heating element.

3. A cathode ray tube according to claim 2, in which said heating element is in the form of narrow lines electrically conducting material extending across the viewed area of the screen.

4. A cathode ray tube according to claim 2,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cathode ray tubes Field of the Invention This invention relates to cathode ray tubes. Background to the invention When cathode ray tubes are used in cold conditions (for example for visual display purposes in public places like railway stations) ice tends to form on the screens of the tubes, so impairing clarity of the viewed image and risking mechanical failure of the tubes. The invention aims to overcome this problem. Summary of the Invention According to the invention, a cathode ray tube has a screen provided with heating means to prevent the formation of ice on the screen. The heating means are preferably constituted by an electrical resistance heating element which may be in the form of narrow lines of electrically conducting material extending across the viewed area of the screen or may be a transparent film of electrically conducting material (e.g. vacuum metallisedì extending over the whole or a part of the viewed area of the screen. In either case, electrical current passing through the heating element provides resistance heating which warms the screen of the cathode ray tube. The heating means may be applied to the external surface of the cathode ray tube screen but preferably the heating means are printed or sprayed on to a separate glass faceplate which is positioned closely in front of the screen. The heating means may be deposited on either or both surfaces of the faceplate, or may be laminated between two component glass sheets forming the faceplate. The electric current passing through the heating means will generate an electric field which may affect deflection of the electron beam of the cathode ray tube, resulting in distortion of the image. To avoid this, the heating means are preferably energized synchronously with the frame scan of the cathode ray tube, the heating means being energized during the frame fly back time but not during line scan, so that any field produced by the heating means does not affect quality of the image displayed. Alternatively, the heating means may be continuously energized and formed so as to constitute coils which substantially neutralize one another in terms of the electromagnetic field produced.As a further alternative, a neutralizing coil or coils separate from the heating means may be provided, theneutralizing coil or coils cancelling the field produced by the current flowing through the heating means. The heating means are conveniently thermostatically controlled, for example being energized only when the ambient temperature is below a predetermined threshold level at which there is a risk of ice formation on the cathode ray tube screen. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:. Figure 1 is a diagrammatic side elevation of a cathode ray tube according to the invention, and Figure 2 is a front view of the screen of the cathode ray tube. Detailed description of the drawings Referring to Figure 1, the cathode ray tube 10 has deflecting coils shown diagrammatically at 12 which control the deflection of an electron beam which impinges on the inner surface of the screen 14 of the tube 10. In front of the screen 14, there is positioned a glass faceplate 16 on which is printed a pattern of thin lines forming an electrical resistance heating element 18. The faceplate 16 is positioned closely against the screen 14. The lines of the element 18 are thin and do not substantially affect the clarity or definition of the image when the tube 10 is viewed from a normal distance. Ends of the heating element 18 are brought out and connected in an electrical circuit powered synchronously with the cathode ray tube in such manner that the element is supplied with electrical current only during the frame fly back time. This pulsed energization of the element 18 ensures that any electromagnetic field produced by the current flowing through the electrical resistance heating element 18 does not affect deflection of the electron beam of the tube 10. The electrical circuit powering the element 18 is thermostatically controlled, so that the heating element 18 is energized if the ambient temperature falls below a predetermined threshold. The heating element 18 not only prevents the formation of ice on the screen but also lessens the risk of the tube imploding, which can occur when subjected to very low temperatures. CLAIMS

4. A cathode ray tube according to claim 2, in which the heating element is constituted by a transparent film of electrically conducting material (eg vacuum metallised) extending over at least part of the viewed area of the screen.

5. A cathode ray tube according to any one preceding claim, in which said heating means is applied to the external surface of the cathode ray tube screen.

6. A cathode ray tube according to any one of claims 1 to 4, in which the heating means are printed or sprayed onto a separate glass faceplate which is positioned closely in front of the screen.

7. A cathode ray tube according to claim 6, in which the heating means is deposited on either or both surfaces of the faceplate.

8. A cathode ray tube according to claim 6, in which the. heating means is laminated between two component glass sheets forming the faceplate.

9. A cathode ray tube according to any one preceding claim in which said heating means is energized synchronously with the frame scan of the cathode ray tube, the heating means being energized during the frame fly back time but not during line scan, so that any electromagnetic field produced by the heating means does not affect the quality of the image displayed.

10. A cathode ray tube according to any one of claims 1 to 8 in which the heating means is continuously energized and is formed so as to constitute coils which substantially neutralise one another in terms of the electromagnetic field produced.

11. A cathode ray tube according to any one of claims 1 to 8 further comprising one or more neutralising coils separate from the heating means and effective to cancel the field produced by the current flowing through the heating means.

12. A cathode ray tube according to any one preceding claims, in which the heating means is thermostatidaliy controlled, and is energized only when the ambient temperature is below a predetermined threshold level at which there is a risk pf ice formation on the cathode ray tube screen.

13. A cathode ray tube having a screen, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.