Radiant energy – Photocells; circuits and apparatus – Housings
Patent
1996-07-19
1998-05-05
Allen, Stephone B.
Radiant energy
Photocells; circuits and apparatus
Housings
250214AL, 250214B, H01J 4014
Patent
active
057477981
ABSTRACT:
A continuously active artificial light source, such as a light-emitting diode (LED), is supported in a housing that also contains a photocell, and is directed at the operating detection surface of the photocell. A light-transmitting diffuser, such as made of translucent plastic, covers the detection surface of the photocell and allows ambient light to pass to the surface, which thereby detect a combination of external ambient light and light from the artificial source. The light source thereby biases the photocell, so that, in normal operation, the photocell produces an output voltage that does not exceed a predetermined value. The predetermined value is set at a level approximating the output voltage measured during total darkness outside the photocell housing. If an open-circuit condition occurs, the voltage of the photocell will exceed that predetermined value, thus permitting the checking circuit to recognize a faulty photocell.
REFERENCES:
patent: 3240943 (1966-03-01), White
patent: 3450939 (1969-06-01), Misencik
patent: 3523739 (1970-08-01), Weisglass
patent: 3630627 (1971-12-01), Low
patent: 4196994 (1980-04-01), de Jesus et al.
patent: 4330706 (1982-05-01), Lawenhaupt
patent: 4644149 (1987-02-01), Tsunekawa et al.
Allen Stephone B.
Hoffman Louis J.
Hughey & Phillips, Inc.
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