Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-12-23
1989-07-11
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250221, G02F 101, H01J 4014
Patent
active
048474886
ABSTRACT:
In a reflection light barrier, improved security against sabotage is achieved through the simultaneous use of radiation with opposite types of polarization, e.g., by means of radiations polarized linearly perpendicular to one another, or radiations polarized circularly with opposite directions of rotation. The two types of polarization are processed separately by the receiver and when there is any disturbance of the equilibrium between the two types of polarization, a disturbance signal is triggered. Placed in front of the transmitter and reflector are polarizing filters with zones of opposite polarization and with different areas which are tuned to one another in such a way that equilibrium is produced at the receiver. In another variant there is provided, in front of the reflector, a quarter-wave plate which rotates the plane of polarization of the transmitted radiation 90.degree., and the receiver separately evaluates the two planes of polarization in order to give alarm and disturbance signals.
REFERENCES:
patent: 4171908 (1979-10-01), Robert et al.
patent: 4224608 (1980-09-01), Lederer
patent: 4339660 (1982-07-01), Buchholz et al.
Muller Kurt
Wuthrich Alfred
Cerberus AG
Nelms David C.
Oen William
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