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Determining End of Phosphor Life in CRT's

IP.com Disclosure Number: IPCOM000092435D
Original Publication Date: 1966-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 65K

Publishing Venue

IBM

Related People

Gaebelein, GN: AUTHOR [+3]

Abstract

The limit of cathode ray tube phosphor useful life as a scanner can be defined. This is as the point in time at which the gradient of phosphor efficiency has reached some predetermined maximum allowable value as a result of preferential ageing due to particular beam trace patterns. For example, the limit for a given scanning system can be represented by a 30% change in phosphor efficiency over a small distance on the face of the CRT even though the absolute level of phosphor efficiency at any one point is otherwise adequate. A similar difference in phosphor efficiency between two points more widely separated on the face of the CRT can have no effect on system operation if low bandpass gain compensation techniques are used.

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Determining End of Phosphor Life in CRT's

The limit of cathode ray tube phosphor useful life as a scanner can be defined. This is as the point in time at which the gradient of phosphor efficiency has reached some predetermined maximum allowable value as a result of preferential ageing due to particular beam trace patterns. For example, the limit for a given scanning system can be represented by a 30% change in phosphor efficiency over a small distance on the face of the CRT even though the absolute level of phosphor efficiency at any one point is otherwise adequate. A similar difference in phosphor efficiency between two points more widely separated on the face of the CRT can have no effect on system operation if low bandpass gain compensation techniques are used.

The beam of CRT 10 is normally deflected by drivers 12 operated by beam control circuit 13 to scan characters or patterns on document 11. Format control 14 provides signals to beam control circuits 13 and 15. The latter provides signals to deflection drivers 16 which deflect the beam of display CRT 17. The system operates in two modes. One mode is for scanning documents 11 and this is the normal mode. In this mode of operation, photomultiplier tubes 18 receive light reflected from document 11 and provide a signal to video amplifier 19. This includes automatic clipping level circuits. The digitized video data is transmitted to recognition circuits not shown. Also during this mode of operation monitoring photomultiplier tubes 9 provide a signal to amplifier 20. The amplified signal is passed to phosphor noise compensation circuit 21 whose output is fed into amplifier 19 via switch 22, in the normal position.

The other mode is a test mode for making end of phosphor life tests. When in this mode, a plain white highly reflective diffuse surface such as a clean sheet of paper is placed in the scanning position. Switch 22 is placed in the phosph...