Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1993-11-08
1995-05-09
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250353, 340567, G01V 904
Patent
active
054142555
ABSTRACT:
In an intrusion detector, one or more surveillance zones are imaged using an optical system including a mirror surface and a lens spaced within a small distance of one another and, preferably, in contact. In use, radiation received from said surveillance zone(s) passes through the lens, is reflected from the mirror, re-traverses the lens and falls on a sensing element. In preferred embodiments of the invention the lens is a Fresnel lens and is arranged to create look-down zones for a detector which also monitors forward, side and/or upward surveillance zones.
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Le Que T.
Nelms David C.
Scantronic Limited
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