Appeal No. 1998-2465
Application No. 08/599,192
source for Tregay's probe. Tregay does not disclose what type
of light is used for his probe. Beauvais uses a transparent
prism of polyethersulfone with an infrared light source.
However, Beauvais fails to disclose any reason for using an
infrared type LED as the light source. Beauvais merely states
(column 6, lines 56-57) that in his fluid detector,
"[t]ypically the light source 56 can take the form of a light-
emitting diode, preferably an infrared type."
The examiner maintains (Final Rejection, page 2) that
"[i]t would have been obvious to use the infrared LED in
Beauvais et al as the light source in Tregay to reduce noise
due to the interference of visible light." Appellant argues
(Brief, page 8) that
there is no evidence provided that one skilled in
the art would have had such a notion, or even that
"noise due to interference of visible light" is a
problem in the field. In fact, since the probes in
question are generally used within fluid containers,
such as petroleum tanks, ambient visible light is
not a significant problem.
The examiner, in turn, responds (Answer, page 6) that
[a]mbient or visible light noise to an optical
device is, in fact, a notoriously well known problem
in the art unless an optical device is perfectly
sealed. Even a small crack in the housing in which
an optical device is enclosed would introduce
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