Passive infrared detector
First Claim
1. A passive infrared detector having an entrance window for infrared radiation, an infrared sensor with an evaluation circuit and having an anti-masking device comprising:
- an optical transmitter;
an optical receiver for detecting at least one of optical changes in front of the detector and changes in the optical properties of the entrance window;
an evaluation circuit having proximity latch (PL) channel and an real time (RT) channel, the PL channel responding to temporally limited phenomena and the RT channel responding to temporally stable phenomena, wherein combined evaluation of the signals in both channels is performed.
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Abstract
The infrared detector contains an entrance window for infrared radiation, an infrared sensor with an evaluation circuit and an anti-masking device having an optical transmitter and an optical receiver for detecting phenomena or optical changes immediately in front of the detector and/or changes in the optical properties of the entrance window. The signals of the anti-masking device are evaluated in two channels, wherein one channel responds to temporally limited phenomena or changes and the other channel responds to temporally stable phenomena or changes. A combined evaluation of the signals in the two channels takes place. In the combined evaluation, the channel processing the signals of the infrared sensor is preferably also included. As a result, the infrared detector acquires an increased immunity to false alarms and a higher sensitivity.
38 Citations
19 Claims
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1. A passive infrared detector having an entrance window for infrared radiation, an infrared sensor with an evaluation circuit and having an anti-masking device comprising:
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an optical transmitter;
an optical receiver for detecting at least one of optical changes in front of the detector and changes in the optical properties of the entrance window;
an evaluation circuit having proximity latch (PL) channel and an real time (RT) channel, the PL channel responding to temporally limited phenomena and the RT channel responding to temporally stable phenomena, wherein combined evaluation of the signals in both channels is performed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A passive infrared detector comprising:
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a housing having a front face and first and second side wall protrusions extending from said front face, said front face having an opening therein located between said side wall protrusions;
an entrance window disposed within said opening in said front face of said housing;
an infrared sensor responsive to infrared radiation incident on said entrance window; and
an anti-masking device comprising;
an optical transmitter;
an optical receiver for detecting at least one of phenomena or optical changes in front of the detector and at least one of changes in the optical properties of the entrance window;
an evaluation circuit having the proximity latch (PL) channel and an real time (RT) channel, the PL channel responding to temporally limited phenomena and the RT channel responding to temporally stable phenomena, wherein combined evaluation of the signals in both channels is performed. - View Dependent Claims (14, 15, 16, 17, 18, 19)
a second optical transmitter which is disposed in the interior of the detector and directs its radiation at the entrance window; and
wherein said first optical transmitter is disposed on the outside of the front of the detector that exposes the space directly in front of the detector to radiation.
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15. The infrared detector according to claim 14, wherein the optical receiver is exposed to that radiation of the first optical transmitter that is reflected from the space immediately in front of the detector and to the radiation of the second optical transmitter that is transmitted by the entrance window.
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16. The infrared detector according to claim 14, wherein the radiation from the second optical transmitter is directed onto the entrance window at a shallow angle of incidence.
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17. The infrared detector according to claim 14, wherein at least one of said side wall protrusions includes a light duct formed therein, said light duct being in optical communication with said second optical transmitter and having an optical passage in communication with said entrance window.
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18. The infrared detector according to claim 17, wherein the optical passage in communication with said entrance window projects the radiation from the second optical transmitter onto the entrance window at a shallow angle of incidence.
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19. The infrared detector according to claim 17, wherein at least a portion of the side wall protrusion opposing said optical passage is provided with an infrared absorbing surface.
Specification