EIA TEP105-9-1987

$22.75

Line Profile Measurements in Shadow Mask and Other Structured Screen Cathode Ray Tubes

Published By	Publication Date	Number of Pages
ECIA	1987	10

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Description

The purpose of this test is to measure the profile of a line on
the face of a shadow mask or other structured screen cathode ray
tube (CRT) in order to estimate the resolution capacity of the CRT.
Since the display on a CRT usually consists of a series of lines or
line segments forming alphanumeric characters or graphics patterns
the line width is an important parameter in the determination of
the resolution. For this reason, the test method discussed below
measures the horizontal and vertical (and possibly diagonal)
profiles of the lines produced by the electron beam or beams. From
these profiles, the line widths can be determined. Only one gun of
a mutiple gun CRT is measured at a time. Such a test for
determining the size of the CRT spot is the first step in any
resolution calculation. Note that line profiles can also be
determined from measurements of the intensity contours of the CRT
spot. This method of determining the line profile is not discussed
in this document.

The line profile of the CRT spot is dependent on a number of
factors in addition to the focused electron beam distribution at
the screen. Some of these factors are:

1. Electron scattering in the screen and support structure

2. Light scattering due to the granular nature of the phosphor
and the aluminum backing of the screen

3. Saturation of the phosphor

4. Internal reflections and absorption of light in the faceplate
and panels mounted onto the faceplate

5. Optical coatings, etches, etc., on the faceplate or panel

6. Static or dynamic convergence of the beams in multiple beam
tubes

External influnces on the resolution of the CRT, including
ambient light, are not discussed in this method. These include the
the transfer characteristics of the viewing system, in particular,
the nonlinear response of a human observer.

Determination of the resolution of a structured screen CRT is a
complex problem which is not completely solved at the present time.
The limiting resolution of the tube can, in some cases, be
estimated by referring to the conclusions reported in recent
papers. For a shadow mask color CRT, the resolution is strongly
dependent on the pitch of the shadow mask. Kojima¹ and
Barten^2,3 suggest that for a dot screen CRT the spot
diameter at 5% of peak brightness should be 2.5-2.6 times the
shadow mask pitch( the center to center distance between nearest
neighbor mask holes ). The same relation seems to hold for line
screen tubes where the pitch is the horizontal distance between the
mask slots. For beams smaller than this, moire patterns are
produced. In addition to the references above, a short bibliography
is attached. The reader is urged to consult these references and
the current literature before making any conclusions about the
resolution of a structured screen display.