GB1575912A - Display arrangements - Google Patents

Description

(54) DISPLAY ARRANGEMENTS (71) We, ENGLISH ELECTRIC VALVE COMPANY LIMITED, a British Company, of 106, Waterhouse Lane, Chelmsford, Essex CMI 2QU. do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a display arrangement which is capable of presenting relatively large, very bright and readily alterable displays with a moderate power consumption, and is concerned with an improvement in or a modification of the invention which is the subject of Patent Application No. 6455/76 (Serial No. 1 569 973) in the name of the present applicants.

According to claim 1 of this main specification, a display arrangement includes a cathode ray tube having an electron flood gun arranged to produce a solid angle of electrons which irradiates substantially uniformly a segmented mesh electrode which is mounted adjacent to a viewing screen having a layer of fluorescent material on its inner surface, each segment of the segmented mesh electrode being individually addressable to control passage of electrons therethrough; and an apertured metal plate positioned adjacent to the segmented mesh electrode with the apertures aligning with the individual segments of the mesh electrode and the apertured plate serving to prevent unwanted electrons from the flood gun reaching said screen.

It is common to include in a cathode ray tube an electrode which is termed a field grid or collector mesh. This electrode is provided in, for example, storage tubes to improve the collimation of the electron beam, and such an electrode is included in the preferred embodiment of the display arrangement described in the parent patent application. When such an electrode is provided in a cathode ray tube, a potential of the order of +100 volts (relative to cathode potential) or greater has hitherto been applied to it in operation. The present invention stems from the discovery that the use of a much lower voltage gives desirable advantages.

According to the present invention, a method of operating a display arrangement in accordance with claim 1 of the main specification, and having a field grid positioned between the flood gun and said segmented mesh electrodes; in whch said method includes applying to the field grid a potential in the range of zero volts to +15 volts (relative to cathode potential).

Preferably, the potential is between +5 volts and +10 volts, and in some respects a value of +8 volts appears to be optimum.

This contrasts with the potential of about + 100 volts used previously in some kinds of cathode ray tubes, notably storage tubes.

However, it has been found that by applying a much lower voltage, the overall length of the tube can be reduced to about half the value previously required. Typically a length of about 3 inches for a tube in accordance with this invention having a display area of about 3 inches square is possible.

It is believed that this reduction in length is obtainable because the low potential on the field grid allows the cone of electrons from the flood gun to spread outwards to a greater extent, and that a space charge region is formed in the vicinity of the field grid.

The electrons are moving relatively slowly at this point, and it is thought that they are drawn from the space charge region by appropriately energised portions of the segmented mesh electrode and accelerated by the high potential of about lOkV which is present at the flourescent screen.

Whether the foregoing theory and beliefs are correct or not, the use of the lower voltage permits the cathode ray tube to be made in a very compact form. The field grid is sometimes referred to as a collector mesh.

The use of the low voltage inaccordance with this invention has been found to result in a linear relationship between the potential on the accelerator grid of the flood gun, and the brightness of the display as measured by the screen current. This property is useful for setting up and matching tubes.

It has also been found that the display is less susceptible to external magnetic fields; this results in less shielding being necessary and permits economies of construction to be made.

WHAT WE CLAIM IS: 1. A method of operating a display arrangement in accordance with claim 1 of the main specification, and having a field grid position between the flood gun and said segmented mesh electrode; said method including applying to the field grid a potential in the range of zero volts to +15 volts (relative to cathod potential).

2. A method as claimed in claim 1 and wherein the potential is between +5 volts and + 10 volts.

3. A method as claimed in claim 2 wherein the potential has a value of +8 volts.

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. made in a very compact form. The field grid is sometimes referred to as a collector mesh. The use of the low voltage inaccordance with this invention has been found to result in a linear relationship between the potential on the accelerator grid of the flood gun, and the brightness of the display as measured by the screen current. This property is useful for setting up and matching tubes. It has also been found that the display is less susceptible to external magnetic fields; this results in less shielding being necessary and permits economies of construction to be made. WHAT WE CLAIM IS:

1. A method of operating a display arrangement in accordance with claim 1 of the main specification, and having a field grid position between the flood gun and said segmented mesh electrode; said method including applying to the field grid a potential in the range of zero volts to +15 volts (relative to cathod potential).

2. A method as claimed in claim 1 and wherein the potential is between +5 volts and + 10 volts.

3. A method as claimed in claim 2 wherein the potential has a value of +8 volts.