Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1997-11-10
2001-04-10
Swann, Glen (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C250S340000, C250S371000, C250S395000, C356S051000, C356S256000
Reexamination Certificate
active
06215399
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a passive infrared (PIR) motion detector apparatus and method. More specifically, the invention relates to such a motion detector in which pet immunity is provided by the beam design. The invention relates further to a dual PIR sensor motion detector in which the sensors have a simultaneous response with reduced false alarms by requiring a simultaneous response from both sensors to generate an alarm. The invention also relates to a dual PIR sensor motion detector in which the sensors have a simultaneous response with opposite polarity to prevent false alarms due to external interference such as RF noise.
BACKGROUND OF THE INVENTION
Conventional PIR motion detectors have difficulty with “false” alarms resulting from pets moving through detection zones at close range to the detectors. The level of IR radiation emitted by pets is sufficient at such close range to cause an alarm. Usually care is taken to mask such zones or to disable motion detectors where pets are found. Clearly, such total or partial disabling of the motion detection alarm system is not desirable, however, it is considered better to lower the quality of detection to preserve an acceptable low level of false alarms. Alternatively, pet immunity has been provided in the signal processing of the PIR sensor response signal by ignoring low level responses generated by pets and/or requiring more movement before generating an alarm. Such measures risk failing to detect human intruder motion by effectively lowering sensitivity.
Another approach to dealing with pet immunity in motion detectors has been special processing of detector signals, particularly in the case of dual technology detectors, which may be used to distinguish between pets and human intruders, as is disclosed in U.S. Pat. No. 5,473,311 to Hoseit. Such detectors are more complicated and more costly, both at the sensor level and the signal analysis level.
Dual channel PIR motion detectors are known in the art, as for example in U.S. Pat. No. 4,614,938 to Weitman and U.S. Pat. No. 4,963,749 to McMaster. It is known to use a single quad PIR sensor having four IR sensitive elements as well as two PIR sensor devices each having a pair of IR sensitive elements. The advantage of two channels over one is simply greater reliability of sensor output signal. An alarm signal is thus only generated when both channels indicate motion. Preventing false alarms and ensuring detection is of great importance to PIR motion detectors used in the security industry.
In U.S. Pat. No. 4,697,081 to Baker, a quad element sensor is disclosed in which interdigitated IR sensitive elements are provided. By this arrangement, both IR elements respond to infrared radiation collected by the lens, and the risk of false triggering is reduced. In U.S. Pat. No. 5,045,702 to Mulleer, a single channel detector is disclosed in which the sensor element configurations include a diamond pattern with opposed pairs of IR sensitive elements of opposite polarization connected in series. Such motion detectors typically employ a single lens to direct infrared radiation onto the single quad or multi-element sensor.
It is also known in the art to provide dual lens and dual sensor motion detectors. Such systems conventionally have a single housing with two lenses mounted one above the other. Each sensor receives radiation from one corresponding lens. The optical arrangement is such that infrared radiation from a person entering a detection zone will not be simultaneously received by both sensors, but rather sequentially. The response from the sensors is thus separated in time, and has a same polarity since the sensor IR sensitive elements of the two sensors are aligned parallel with like polarity. Such a dual channel motion detector can generate an alarm accurately when the response in both channels is similar and separated in time by the expected amount.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide a PIR motion detector having improved reliability of detection with pet immunity. Accordingly, there is provided a PIR motion detector having a beam design facilitating descrimination of pets from humans. According to one aspect of the invention, there is provided a PIR motion detector having two sensors and two corresponding infrared lenses in which at close range the lenses will not direct infrared radiation simultaneously from small infrared emitting objects onto both sensors, and corresponding detection zones of the lenses at a far range substantially overlap. The detection zones are staggered so that a pet crossing the zones at the same range will generate a signal in each of the sensors alternatingly. The long separation between consecutive motion signals in the same sensor, as well as the generation of motion signals in alternating sensors, allow the easy discrimination of pet-generated motion signals and suppression of false alarms.
The invention also provides a method and apparatus of detecting an intruder in a PIR sensor motion detector having a single sensor and lens in which the zones are staggered in height to prevent alarm signal generation when pets cross only alternate zones at close range.
It is a second object of the invention to provide a dual PIR motion detector in which the sensors and lenses are vertically aligned to have a simultaneous response. When the response from the two detectors is not simultaneous, an alarm signal is not generated, and thus false alarms are avoided. A “simultaneous” response requires accurate alignment of the two sensors and lenses, which can be provided by mounting the lenses and sensors in the same housing. Preferably, the lenses are formed on the same fresnel lens sheet to avoid any minor misalignment between the two lenses.
It is a third object of the invention to provide a dual PIR motion detector having improved immunity to electromagnetic interference, such as RFI. Preferably, two sensors and two corresponding infrared lenses are provided in which the sensors have a simultaneous, opposite polarity response to infrared radiation, while having a same polarity response to RFI. By arranging two PIR sensors with sensor elements vertically parallel and in opposite polarity, the sensors also remain sensitive to far objects moving through part of detection zones, while the reverse polarity of motion signals allow for easy discrimination of interference noise signals.
REFERENCES:
patent: 4523095 (1985-06-01), Keller-Steinbach
patent: 4614938 (1986-09-01), Weitman
patent: 4697081 (1987-09-01), Baker
patent: 4849635 (1989-07-01), Sugimoto
patent: 4963749 (1990-10-01), McMaster
patent: 5045702 (1991-09-01), Mulleer
patent: 5473311 (1995-12-01), Hoseit
patent: 5670943 (1997-09-01), DiPoala et al.
patent: 5923250 (1999-07-01), Pildner et al.
patent: 0624857A1 (1994-11-01), None
Burns Doane , Swecker, Mathis LLP
Shmuel Hershkovitz
Swann Glen
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