15 Apr
2012
15 Apr
'12
11:23 a.m.
Sander Reiche wrote:
Call me old fashioned, unknowledgable and noob; I am,
in fact, all of
them. But couldn't you just put those things in the sun?
Yes, in perhaps a month. The total necessary UV does for a typical
EPROM is about 15 Watt second/cm^2 at 253.7nm, though wavelengths below
400 nm cause erasure. An EPROM eraser provides about 12 mWs/cm^2. At
sea level, exposure to direct sunlight delivers a maximum of about 0.1
mWs/cm^2, so erasing an EPROM will take 120 times longer, or 40 hours,
but that is 40 hours of peak sunlight, so the actual time is much longer.
The reason you need a UV-opaque label on the window of an EPROM to
prevent erasure by room light or sunlight is that erasure is a
continuous process, so the bits will start to get flaky long before the
part is fully erased.