Cathode ray tube display arrangements

Claim 2

A CRT display arrangement comprising a CRT (1) and deflection means (5) for deflecting an electron beam produced by an electron gun of the CRT across the display screen of the CRT and characterised by: electronic storage means (25 to 31 and 33) having a respective storage location for each of a plurality of discrete portions of the display area of the CRT screen; means (13 to 23 and 33 to 41) for storing in each said storage location a value indicative of the temperature in the corresponding portion of said display area due to impact thereon of said electron beam; and means (7) for controlling the electron beam in dependence on the contents of said storage means (25 to 31) so as to prevent excessive heating of a said portion of the display screen.

Claim 3

An arrangement according to Claim 1 wherein said means (17 to 23 and 33 to 41) for storing comprises: means (17 to 23) for producing at intervals an output signal indicative of the particular said portion of said display screen onto which said electron beam is currently directed; means (21, 33) responsive to each said output signal for increasing by an amount dependent on the electron beam current the value stored in the storage location corresponding to the particular said portion to which that output signal relates; and means (21 and 35 to 41) for reducing at intervals the value stored in each said storage location by an amount representative of the heat dissipation from the portion of the display area corresponding to that storage location; and said means for controlling (7) is responsive to the value stored in a location of the storage means (25 to 31 and 33) exceeding a predetermined value.

Claim 4

An arrangement according to Claim 2 wherein said means (17 to 23) for producing an output signal operates in response to signals derived from said deflection means (5) of the arrangement.

Claim 5

An arrangement according to Claim 3 wherein said means (17 to 23) for producing an output signal comprises an adaptive tracking analogue to digital converter means (13, 15) whose tracking step varies in dependence on the deflection rate of the electron beam across said display screen.

Claim 6

An arrangement according to any one of Claims 2 to 4 wherein said means (35 to 41) for reducing comprises means for reducing the value stored in each said storage location by a predetermined fraction.

Claim 7

An arrangement according to Claim 5 wherein said predetermined fraction is half.

Claim 8

An arrangement according to any one of Claims 2 to 6 wherein said electronic storage means (25 to 31 and 33) comprises: a binary digital store (25 to 31) which stores a respective n-bit number in each said storage location; said means (21, 33) for increasing comprises: an n-bit adder (33); means (21) for writing the n-bit number in the storage location corresponding to the particular said portion into said adder (33), increasing the number in said adder (33) by said amount, and then writing the number in said adder (33) back into said storage location; and said means (7) for controlling operates in response to the number in said adder (33) exceeding a predetermined value.

Claim 9

An arrangement according to Claim 7 wherein said digital store (25 to 31 and 33) comprises: a store having n-sections (25, 27, 29 and 31) each of which stores a respective corresponding bit of each said n-bit number; and said means (21 and 35 to 41) for reducing comprises a shift register arrangement (35 to 41) whereby the bits in the store section (31) storing the least significant bits of said n-bit number are discarded, the bits in each other store section (25, 27, 29) are transferred to the store section (27, 29, 31) which stores the next less significant bit of each n-bit number, and the bits in the section (25) storing the most significant bit of each n-bit number are all converted to zeros.

Claim 10

An arrangement according to any one of the preceding claims wherein said means (7) for controlling monitors in turn the value stored in each said storage location and temporarily turns off the electron beam when the contents of a said storage location exceeds a predetermined value.

Claim 11

An arrangement according to Claim 9 wherein said electron beam is turned off until the beam moves to a said portion of the screen where excessive heating would not occur if the beam were on.

Claim 12

An arrangement according to Claim 9 when dependent on Claim 2 wherein said electron beam is turned off until said means for reducing (25 and 35 to 41) is next operative.

Claim 13

An arrangement according to Claim 9 wherein said electron beam is turned off until a predetermined time has passed in which excessive heating would not occur in any of said portions of the display screen if the electron beam were on.