Browse Prior Art Database

External Scan Coils for CRT Beam Spot Size Measurement

IP.com Disclosure Number: IPCOM000049833D
Original Publication Date: 1982-Jul-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Burr, P: AUTHOR [+2]

Abstract

An additional pair of specially wound coils are provided externally on the neck of a CRT to cause the CRT beam to scan over a selected region of the tube face in a micro-raster. The light intensity from the microscanning spot is measured as it moves progressively past a light sensitive device and the spot characteristics are derived.

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External Scan Coils for CRT Beam Spot Size Measurement

An additional pair of specially wound coils are provided externally on the neck of a CRT to cause the CRT beam to scan over a selected region of the tube face in a micro-raster. The light intensity from the microscanning spot is measured as it moves progressively past a light sensitive device and the spot characteristics are derived.

The dimensions and light output of the spot produced on the face of a CRT tube is measured by scanning the beam across a predetermined point on the screen in a micro-scan raster of, for example, 2 mm square in steps of 0.1 mm. The light output is measured at each point in the micro-scan raster, and the output plotted as an optical contour map. Such a method and the associated apparatus are described in U.K. Patent Application 2064759. However, it is often necessary in evaluation processes to measure the spot size produced on a complete display monitor where the spot size seen may not be determined solely by the CRT itself, but will also depend on the performance of other parts of the monitor, notably, the video amplifiers. In this case it is undesirable to use the monitor deflection yoke to produce the micro-scan needed for spot characterization, and some other method of moving the displayed image must be found. One method of doing this is to re-time the synch pulses relative to the data pulses, thus providing a displacement of the image. However for monitors which do not have se...