US2242034A

US2242034A - Scanning method for storage tubes

Info

Publication number: US2242034A
Application number: US193987A
Authority: US
Inventors: Knick Ulrich
Original assignee: FIRM FERNSEH AG
Current assignee: FIRM FERNSEH AG
Priority date: 1937-03-06
Filing date: 1938-03-04
Publication date: 1941-05-13
Anticipated expiration: 1958-05-13
Also published as: GB512489A

Description

May 13, 1941;

U. KNICK SCANNING METHOD FOR STORAGE TUBES Filed March 4, 1938 Patented May 13, 1941 UNHTE ST g 5 i i i FFEE SiJ'ANNING METHOD FOR STORAQE. TUBES Application March 4, 1938, Serial No. 193,987 In Germany March 6, 1937 2 Claims.

In known image analyzing tubes possessing a storage member, a certain margin around the scanned picture area is always present which is not scanned by the electron beam, nor illuminated by the light image. Indeed, in production of the storage member, which usually consists of a photomosaic deposited on an insulating coating over a conductive plate as is Well known in the art, it is necessary-or at least preferable-to leave a margin around the mosaic area. Furthermore, a margin which is not scanned has been required because the scanning beam could, otherwise, be deflected over the edge of thestorage member into space, whereby large interfering voltages are generated, as has been experienced.

This margin, however, when not scanned, causes the disadvantage that those peripheral portions of the storage member which are not scanned become increasingly negatively charged by stray electrons. This high negative charge destroys the uniformity of the accelerating field generated in front of the storage member, and as a consequence thereof causes a non-uniform distribution of secondary electrons liberated from the edges of the scanned portion of the storage member by impact of the scanning beam. In practical use this non-uniform field condition causes bright edges in the picture field at the receiver which are also present when the mosaic is not illuminated.

A metallic coating of the margin outside the scanned area, in order that a fixed potential may be applied to it, is out of question because greater capacitance between signal plate and ground would be obtained. Another reason for the inadvisability of doing this is that a great number of secondary electrons can be produced if the scanning beam impacts this metallic coating, when slight disturbances occur in the deflection, and these secondary electrons would destroy the charge distribution on the adjacent portions of the mosaic.

It is the object of the present invention to bring the margins, at least partially, to a defined potential by means of the cathode ray beam. The electron beam is, therefore, deflected over a margin of, for instance, one to two centimeters in width, in addition to the picture area proper. The margin then acquires the same potential throughout, approximately minus 5 volts, with respect to the accelerating electrode, and has the storage condition of no light, because obviously no light image is to be thrown on the margin. The scansion of the margin must, obviously, not subtract from the total time available for scansion of the picture area. Consequently, the scanning beam must pass over the margins at a higher rate of speed than ordinarily and the retrace period must also be shorter than is common in the normal process.

The invention is of particular importance to the vertical margins, which can readily be brought to a defined potential by a corresponding wave shape of the line deflecting fields.

In the attached drawing, the solid curve a shows an example of the line deflecting voltage curve according to the method of the invention, this wave form being readily obtainable by those skilled in the art, while the dotted curve b shows the voltage wave used for normal scansion. Any signal voltages generated during scansion of the margin should be suppressed, or compensated for, by suitable measures. It may also be arranged that they occur at such a time that they coincide with the synchronizing interval. The synchronizing impulses are generated in the usual manner by means of a separate circuit.

I claim:

1. The method ofoperating an image analyzing tube of the type having a storage surface which comprises the steps of scanning substantially the whole area of said storage surface, projecting the image on only the central portion of said storage surface, maintaining the speed of scanning substantially constant over said central portion, and increasing the speed of scanning over the remaining portion of said storage surface.

2. The method of operating an image analyzing tube of the type having a storage surface which comprises the steps of scanning substantially the whole area of said storage surface, projecting the image on only the central portion of said storage surface, maintaining the speed of scanning substantially constant over said central portion, increasing the speed of scanning over the remaining portion of said storage surface, and reducing the retrace time by an amount equal to the time of scanning the remaining portion of said storage surface.

ULRICH KNICK,