Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1998-09-01
2001-11-13
Wu, Daniel J. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S556000, C340S557000, C250S222100, C250S2140LS
Reexamination Certificate
active
06317043
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to systems for monitoring a perimeter of an area and for reliably sounding an alarm in response to ingress or egress across the perimeter.
BACKGROUND OF THE INVENTION
As an introduction to the problems solved by the present invention, consider for example the conventional perimeter alarm system based on laser beam interruption as used to monitor ingress onto a swimming pool apron. Such a system is difficult to initially install and requires considerable maintenance to control the occurrence of false alarms.
Many different physical effects of the installation can independently effect a false alarm. For example, when one infrared laser source is used with several mirrors to create a continuous path around the perimeter to be monitored, the initial alignment of the mirrors is costly. If any one mirror becomes misaligned, through sudden or gradual movement, the beam is interrupted as a false alarm. Correction of misalignment may require use of expensive infrared sensitive equipment. When the several mirrors are aligned sufficiently to remove the false alarm, one or more mirrors may not be positioned to reflect the beam from the center of the mirror. Consequently, the system's tolerance for future misalignment may be lower than expected.
The conventional detector for such a system may raise false alarms in response to light from sources other than from the laser source. Ambient sunlight may impinge upon the detector directly or as reflected by any surrounding surface or mirror. The angle of direct sunlight varies throughout the day and throughout the year to include a very wide range of angles. In addition, sunlight reflects from the surface of water in the swimming pool in an even wider range of angles varying randomly with wind conditions. The amount of background light on which a change is to be detected also varies making false detection more likely. An alignment of mirrors prescribed during installation or maintenance is unlikely to be sufficient for all of the above conditions.
The operator of such a system is exposed to risk of loss unnecessarily. As a result of false alarms, operators of such perimeter monitoring systems may be less likely to respond immediately when an alarm sounds. Failure to timely respond may result in a loss of life or property. When interrupted by a large number of false alarms, the operator may defeat the monitor or the alarm and not reactivate the monitor or the alarm due to operator irresponsibility or forgetfulness.
In view of the problems described above, the need remains in perimeter monitoring systems for higher reliability and lower installation and maintenance costs.
SUMMARY OF THE INVENTION
Accordingly, a perimeter monitoring system in one embodiment of the present invention includes a reflector, and a monitor. The reflector is positioned to receive a beam of light along a segment of a perimeter of an area to be monitored and to provide a returned beam along the segment. The monitor includes an emitter that provides the beam and a detector. The detector has an axis and provides a signal which includes indicia of a lapse in detecting the returned beam received substantially on the axis. In a variation, the detector includes a blocking device that blocks detection of light arriving substantially off the axis.
Initial set up and maintenance of such a system are greatly simplified by the use of visible light, use of a retroreflector, and the combination of visible light and retroreflector. Placement of mirrors in cooperation with the retroreflector is also simplified. The result is a much wider tolerance for misalignment of such mirrors and of the retroreflector, and consequently, a dramatic decrease in installation and maintenance costs.
In another embodiment, a transceiver includes a partition that separates a laser emitter from a detector. In a variation, the partition includes a printed circuit substrate for mounting the emitter and detector. In another variation the detector includes a blocking device that blocks detection of light arriving substantially off the axis.
The use of a blocking device as described above decreases the possibility of false alarm. By blocking the reception of light except in a very small range of angles (e.g., 0.5 to 5 degrees), ambient light, whether sunlight or artificial, and whether direct or scattered, has little or no effect on the detector.
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Bachand William R.
Beamerline, L.L.C.
La Anh
Squire Sanders & Dempsey
Wu Daniel J.
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