Volume 6, Number 3 Fall 2005
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The information presented in this newsletter is a segment of the paper on Display Aging given at the SPIE Symposium in Orlando April 1, 2005 covering CRT Aging
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Substrate Temperature
In 1983 Hitachi presented technical data (ref 11) on Projection Tubes showing how the outside surface and the inside panel glass surface temperature varied with Electron Beam Power. I have used their data to construct a graph for the temperature on the screened surface of a non-cooled PTV panel.
FIGURE 2. Panel Temperature and Electron Power Density
In 2004, Asano San of Hitachi kindly sent me a copy of his 1987 paper on Panel Cooling and aging. (Ref 12). He cooled the outside of the panel with cool air to achieve his panel temperatures. This data (figure 3) from his Japanese article shows that a cooler panel can improve aging. The PTV industry uses liquid cooled panels to control phosphor aging.
Shirai in 1995 in his paper (Ref 13) on PTV tubes reported that “the input power density to the screen is limited under 0.25W/cm^2 to avoid the damage on the phosphor by the heat”. We see from figure 2 that this power density gives rise to a panel temperature of about 72 deg C (345 deg K) and figure 3 does not indicate any drastic aging slope change approaching 72 deg C. Thus the issue of just how serious this damage is needs to be questioned. We can see from the above data that it is not catastrophic burn issue but a gradual aging effect.
FIGURE 3. Phosphor Screen Aging as a function of Panel temperature (from Asano).
Note that the top curve in figure 3 is with a panel temperature of 50 deg C, the next is at 60 Deg C and the last is at 70 Deg C.
Scan velocity. The Scan Velocity is related to the dwell time of the phosphor beam on the sample.
Shirai (ref 13) tells us that under Progressive scan (as in HDTV) at a horizontal Frequency of 31.5KHz the Saturation on the blue phosphor is less and its Luminance is higher for a given cathode current.
It is important to note that, if the dwell time over the phosphor can be reduced then the actual time required to reach a specific (coulomb/cm^2) aging point is increased.