Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-01-25
2002-07-02
Dang, Hung Xuan (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S336100, C250S338100
Reexamination Certificate
active
06414314
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a passive-type infrared detector for detecting a trespasser by receiving infrared rays of light emitted from the trespasser entering an alert region.
2. Description of the Prior Art
This type of the passive-type infrared detector includes an optical element for collecting infrared rays of light emitted from a human body and an infrared sensor for receiving the collected infrared rays of light. The angle of coverage of the infrared detector when viewed from top, that is, the detection area on a horizontal plane is generally divided and defined into a plurality of pairs each pair including plus (+) and minus (−) areas. Also, this type of the infrared detector is installed at one extremity of the alert region so that the detection area can traverse from one end of the alert region to be watched towards the other extremity thereof. Electric wiring connection to the infrared detector is carried out by passing electric wires, which extend in a loft or behind the ceiling of a building to a location near the infrared detector, down to behind a wall surface on which the infrared detector is mounted and finally connecting them to the infrared detector.
The infrared detector is available in two types; a wide sensor generally used for detecting a trespasser in a relatively large space such as the interior of a room, and a narrow sensor generally used for detecting a trespasser entering the window or the door facing a narrow pathway. In the case of the wide sensor, considering the purpose for which it is used, the detection area of the detector is provided by a plural number of the pairs (5 to 9 pairs) including the plus and minus areas. The pair is hereinafter referred to as a finger of the detection area. In contrast thereto, in the case of the narrow sensor, the finger of the detection area is defined in a small number, for example, 1 to 2 pairs.
In addition, considering the purpose for which the narrow sensor is used, the distance of detection over which the narrow sensor can monitor is so defined as to be longer than, for example, 1.5 to 2 or more times the distance of detection over which the wide sensor can monitor. As discussed above, in order to expand the detection distance of the narrow sensor to a value longer than that of the wide sensor, the following measures have hitherto been taken.
One of the measures is such as to increase the focal length of a lens element of the narrow sensor to a value sufficient to make the width of an object to be detected and the width of the detection area (or the plus or minus area) equal to each other at the maximum distance (hereinafter referred to as the rated distance) from the position of the detector, where the detector can detect the object to be detected (the trespasser), to the object to be detected.
FIGS. 5A
to
5
F illustrate the detector (narrow sensor)
21
embodying this measure in a plan view, a front elevational view, a left-hand side view, a right-hand side view, a cross-sectional view taken along the line IV—IV in
FIG. 5D
, and a cross-sectional view taken along the line V—V in
FIG. 5B
whereas
FIGS. 6A and 6B
illustrate the detection area of the detector
21
in a top plan view and a front elevational view.
Another one of the measures is such that the focal length of the lens of the narrow sensor remains the same as that in the wide sensor, and that since as compared with the wide sensor the number of the fingers of the detection areas is small in the case of the narrow sensor, the surface area of the lens element (a kind of an optical element) for each of the detection area is correspondingly increased to allow the amount of light received to be increased to thereby increase the rated distance.
FIGS. 7A
to
7
F illustrate the detector (narrow sensor)
31
embodying this measure in a plan view, a front elevational view, a left-hand side view, a right-hand side view, a cross-sectional view taken along the line VI—VI in
FIG. 7D
, and a cross-sectional view taken along the line VII—VII in
FIG. 7B
whereas
FIGS. 8A and 8B
illustrate the detection area of the detector
31
in a top plan view and a front elevational view. It is to be noted that the above described two measures are generally employed in combination.
However, to increase the detection distance of the detector (narrow sensor)
21
according to the measure shown in
FIG. 5
results in increase of the focal length of the lens element
24
, which in turn results in increase of the distance between an infrared sensor
23
and the lens element
24
within a casing
22
of the detector
21
accompanied by an increase of the outer size of the detector
21
. Consequently, when the detector
21
is installed in a building or the like, the detector
21
will be so noticeable that a trespasser will get alerted to the presence of the detector
21
. This brings about reduction not only in an security, but also in aesthetic feature of the building.
Where the detection distance of the detector (narrow sensor)
31
is increased according to the measure shown in
FIG. 7
, the distance between the infrared sensor
31
and the lens element
34
corresponding to the focal length within the casing
32
of the detector
31
can be reduced and the outer size of the detector
31
can also be reduced. However, considering that the width of the detection area is proportional to the ratio between the rated distance and the focal length (as will be discussed in detail later), the width of the detection area increases to a value greater than an optimum value for the object to be detected at the rated distance. Consequently, if the trespasser moves slowly, difficulty will occur in detecting the trespasser. Although it is possible to detect the trespasser moving slowly if the circuit is properly designed, a different problem will occur in such case in that erroneous detection will tend to occur under the influence of external disturbances such as wind and/or change in temperature at a low frequency.
In the case of the narrow sensor, as hereinbefore discussed, it is generally used for the purpose of detecting an entry through a window or door facing a narrow pathway or to watch the perimeter of the building and, therefore, care must be taken at the time of installation that a human body within an area unnecessary to be detected is not detected. In view of this, the width of the detection area is desirably as small as possible and any increase of the width of the detection area which occurs under the previously described measure is undesirable.
In addition, with the prior art narrow sensor, as hereinbefore discussed, the narrow sensor is installed at an extremity of an elongated area such as the inner or outer perimeter of a building which is an alert region and electric wiring connection to the detector is carried out by passing electric wires, which extend in a loft or behind the ceiling of a building to a location near the detector, down to behind a wall surface on which the infrared detector is mounted and finally connecting them to the detector. Accordingly, the electric wiring job is performed in the loft or behind the ceiling of the building. Considering, however, that the roof is generally of a shape downwardly inclined towards a corner, the space available for the electric wiring job is narrow at the corner which may be the extremity of the alert region and, therefore, difficulty tends to be encountered in accomplishing the electric wiring job.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been devised to substantially eliminate the above discussed problems and is intended to provide a compact passive-type infrared detector of a type having an increased detection distance and capable of being easily installed.
To this end, one aspect of the present invention provides a passive-type infrared detector which includes an infrared sensor, a pair of optical elements for defining detection areas opposed substantially 180° to each other for the infrared sensor,
Dang Hung Xuan
Optex Co. Ltd.
Price and Gess
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