EP1089245B1 - Passive infrared detector - Google Patents

Abstract

The passive infra red detector system responds to infra red generated by human bodies,or animals, in a room. In order to cover a wide range the emissions are from a wide area are focussed by a multi section mirror (1) onto a sensor (S). The mirror segments (5-8,13,17,16) are formed to provide overlapping sectors.

Description

The present invention relates to a passive infrared detector with a heat-sensitive sensor and a focusing means for focusing the heat rays falling on the detector from the monitoring room onto the sensor, the focusing means having focusing elements for monitoring areas with different positions in the monitoring room.

Passive infrared detectors of this type have been known and widely used for years. They are used in particular to determine the presence or intrusion of unauthorized persons into the surveillance room by detecting the typical infrared radiation emitted by these persons, which is directed onto the sensor by the focusing means. Either Fresnel lenses that are integrated in the entrance window for infrared radiation located on the front of the detector housing (see, for example, EP-A-0 559 110) or a mirror arranged inside the detector housing, which consists of individual reflectors, are used as focusing means. see, for example, EP-A-0 303 913). Typically several rows of reflectors are provided, each row of a particular surveillance zone, e.g. Far zone, middle zone, near zone and look-down zone.

Both the Fresnel lenses and the mirrors are designed in such a way that each monitoring zone is divided into monitoring areas and thus the space to be monitored is covered in a fan-shaped manner with monitoring areas emanating from the detector. Each reflector thus defines a monitoring area with a defined position in the monitoring room. As soon as an object emitting thermal radiation penetrates into a monitoring area, the sensor detects the thermal radiation emitted by this object, the detection being safest when the object moves across the monitoring area.

Passive infrared detectors of the current generation can reliably detect intruders within the effective range of the detector, but they are usually not able to distinguish people from larger pets, such as dogs, and also give an alarm when an animal is detected , However, these false alarms are tolerated the longer and the security of passive infrared detectors against false alarms, which are referred to as pet immunity and are triggered by pets moving in the surveillance room, has recently become an essential requirement of the market. Passive infrared detectors in the lower price segment are also increasingly required to have pet immunity.

If passive infrared detectors already have pet immunity today, then this is achieved with a few exceptions by reducing the sensitivity of the detector accordingly, which means an undesirable reduction in detection reliability.

In the case of a passive infrared detector with pet immunity, which is described in US Pat. No. 4,849,635, this is achieved in that the focusing means formed by a lens arrangement has a plurality of differently oriented, non-overlapping visual fields or monitoring areas, which fan-shaped in the areas of the lens arrangement Monitoring room run. These monitoring areas are staggered vertically, with gaps of approximately the same size being formed between the individual areas. An intruder with a certain minimum size will always cross at least one surveillance area and thus always generate a sensor signal, and an intruder below this minimum size will alternately cross surveillance areas and only gaps and in the latter case will not generate a sensor signal. In this way, a human being will generate a steady sensor signal with an approximately constant amplitude when moving in the surveillance space, whereas an animal will trigger a pulse-shaped signal of substantially lower maximum amplitude.

Since in this known system the distinction between humans and pets is based on the signal shape, and since the vertical staggering of the surveillance areas is a constant, the risk is relatively high that large pets cannot be distinguished from small people and vice versa.

The invention is now intended to provide a passive infrared detector of the type mentioned at the outset, whose ability to differentiate between humans and animals is significantly improved.

The object is achieved according to the invention in that each focusing element consists of (a number of sub-elements, so that the monitoring areas are split vertically into subzones with slightly different elevations, the elevation of the sub-elements being selected such that in the majority of the monitoring areas at most one there is a slight overlap of the subzones so that the subzones are stacked on top of one another and the layering is selected so that a sequence of dense curtains is created and that the distinction between humans and animals is based on the amplitude of the sensor signal.

The solution according to the invention has the advantage that a pet, however large, as long as its height is smaller than that of a human being, is always distinguished with certainty from a human being. Because an upright person will always cross several subzones of far and middle zones, or middle and near zones, etc. and thereby trigger a sensor signal that is several times larger than an animal of lower height. Because this becomes clear cross fewer subzones and generate a significantly reduced sensor signal. A dog of normal size will cross a sub-zone or at most two, but only partially, and will thereby trigger a signal reduced by half or one third compared to the detector described in EP-A-0 303 913.

A first preferred embodiment of the passive infrared detector according to the invention is characterized in that the number of sub-elements and correspondingly the number of sub-zones increases with decreasing radial distance of the respective monitoring area from the detector.

A second preferred embodiment of the detector according to the invention is characterized in that the sensitivity in the individual subzones is approximately the same. This is achieved by avoiding the overlap of the individual subzones.

A third preferred embodiment of the detector according to the invention is characterized in that the weighting of the individual sub-elements, in particular their optical aperture and area, is selected such that an animal of a selectable size moving across the overlap pattern formed by the monitoring areas has a selectable size for all distances Animal and detector delivers approximately the same small signal. The said animal is preferably formed by a hairy dog 80 cm long and 60 cm high.

A fourth preferred embodiment of the detector according to the invention is characterized in that the focusing means is formed by a mirror arrangement with reflectors forming the focusing elements and each reflector is split into partial areas.

These partial surfaces, which are generally paraboloid partial surfaces, can be combined into groups of connected mirror regions for the production of the injection molding tool for the mirror arrangement, which results in a more cost-effective production and maintenance of the injection molding tool mentioned.

A fifth preferred embodiment is characterized in that the mirror arrangement has a first reflector row for a femzone, a second reflector row for a central zone, a third reflector row for a near zone and a fourth reflector row for a look-down zone, and that the reflectors of the first and the reflectors of the second row are split into three partial areas, the reflectors of the third row into four partial areas and the reflector of the fourth row into five partial areas.

A further preferred embodiment of the detector according to the invention is characterized in that the sensor has four sensor elements combined in pairs, which form two independent channels, and that the respective signal is evaluated in each channel.

Fig. 1

eine schematische Vorderansicht der durch eine Spiegelanordnung gebildeten Fokussiermittel eines erfindungsgemässen Melders,

Fig. 2

einen Schnitt nach der Linie II - II von Fig. 1,

Fig. 3

eine Draufsicht auf das mit der Spiegelanordnung der Fig. 1 und 2 erzeugte Überdekkungsmuster; und

Fig. 4

eine Seitenansicht des Überdeckungsmusters von Fig. 3.

The invention is explained in more detail below on the basis of an exemplary embodiment illustrated in the drawings; it shows:

Fig. 1

2 shows a schematic front view of the focusing means of a detector according to the invention formed by a mirror arrangement,

Fig. 2

2 shows a section along the line II-II of FIG. 1,

Fig. 3

a plan view of the masking pattern generated with the mirror arrangement of Figures 1 and 2; and

Fig. 4

3 shows a side view of the overlap pattern of FIG. 3.

The mirror arrangement 1 shown in FIGS. 1 and 2 is a further development of the mirror described in EP-A-0 303 913, by means of which this mirror is improved so that it is immune to pets in its effective range. As described in the cited EP-A-0 303 913, the disclosure of which is hereby expressly incorporated by reference, the mirror arrangement 1 consists of a number of reflectors which are designed in such a way that the space to be monitored, with monitoring areas originating from the detector, is fan-shaped is covered, with several such "subject areas" or surveillance zones being provided at different distances from the detector. For example, a distinction is made between four surveillance zones, a femzone, a central zone, a near zone and a so-called look-down zone, which are covered by four rows of reflectors offset in the vertical direction.

In the mirror arrangement 1, these rows are the row R ₁ for the far zone, the row R ₂ for the middle zone, the row R ₃ for the near zone and the row R ₄ for the look-down zone, the latter row being only a single reflector having. The fan-shaped coverage is achieved by mutually displacing the reflectors of each row in the horizontal direction, the number of reflectors per row increasing with the distance of the respective monitoring zone from the detector in order to achieve an approximately uniform coverage pattern.

Each reflector "looks" into a certain solid angle of a certain zone, receives the heat radiation incident from this solid angle and focuses it on the heat-sensitive sensor S (FIG. 2), which is formed, for example, by a pyro sensor. The pyro sensor is preferably a so-called standard dual pyro sensor, as is used, for example, in the passive infrared detectors of Siemens Building Technologies AG, Cerberus Division, formerly Cerberus AG (see also EP-A-0 303 913). As soon as an object that emits heat radiation penetrates into a monitoring area, the sensor detects the heat radiation emitted by this object, whereupon the detector emits an alarm signal. This alarm signal indicates that an object, such as an intruder, is in the surveillance room.

As shown, the reflector row R ₁ for the femzone consists of seven paraboloid-shaped, strip-like reflectors 2 to 8, the reflector row R ₂ for the central zone consists of five reflectors 9 to 13, the reflector row R ₃ for the near zone consists of three reflectors 14 to 16 and the reflector row R. ₄ for the near zone from a single reflector 17. This arrangement is the same as that described in EP-A-0 303 913. In contrast to the latter arrangement, however, the individual reflectors do not consist of a single, continuously curved surface, but rather each have a plurality of partial surfaces of different vertical orientation, as a result of which the assigned monitoring areas are correspondingly split into subzones. The transitions between the partial areas are indicated in FIGS. 1 and 2 by dashed horizontal lines or curves.

As can be seen in particular from FIG. 1, the reflectors 2 to 8 for the femzone and the reflectors 9 to 13 for the central zone each consist of three, the reflectors 14 to 16 for the near zone each of four and the reflector 17 for the look zone. down zone of five sub-areas. The individual partial areas are weighted in this way, i.e. their optical aperture and their surface are chosen so that a dog of a certain size (e.g. hairy dog, 80 cm long and 60 cm high) moving across the overlap pattern (Fig. 3) generates a signal that for every distance from the dog to the Detector is about the same size.

3 shows the coverage pattern of the surveillance areas corresponding to the reflectors of the mirror arrangement 1 (FIG. 1) on the floor of the room to be monitored, FIG. 4 shows the course of the heat radiation from the surveillance areas to the detector denoted by reference number 18 along the horizontal diagonal of the square symbolized in FIG. 3 by dash-dotted lines and symbolizing a square surveillance space. The monitoring areas along the diagonal mentioned are analogous to FIG. 1 with 5 ₁ , 5 ₂ , 5 ₃ for the far zone, 11 ₁ , 11 ₂ , 11 ₃ for the central zone, 15 ₁ , 15 ₂ , 15 ₃ , 15 ₄ for the near zone and 17 ₁ , 17 ₂ , 17 ₃ , 17 ₄ and 17 ₅ for the look-down zone. The side reflectors 2-4 and 6-7 of the R ₁ series for the femzone, 9, 10 and 12, 13 of the R ₂ series for the central zone and 14 and 16 of the R ₃ series for the near zone are for reasons of better clarity not designated by reference numerals.

If you compare the coverage pattern shown with that shown in Fig. 3 of EP-A-0 303 913, you can see that the splitting of the reflectors into partial areas leads to a much denser coverage of the monitoring room because there are now significantly more monitoring areas in the monitoring room , If there are sixteen monitoring areas in the detector described in EP-A-0 303 913, there are now 53. These 53 paraboloid partial areas are combined to form 9 contiguous mirror areas which are used in the manufacture of the injection mold for mirror 1 (FIG. 1 ) can be milled as coherent parts, which results in a more cost-effective production and maintenance of the injection molding tool.

The monitoring areas have become significantly longer due to the division into subzones. As can be seen in particular in FIG. 4, the subzones are stacked on top of one another. They touch each other, but overlap at most very little so that no areas of greater sensitivity arise. In the event of overlaps, heat radiation would be focused simultaneously on the sensor in the overlap area from the two respective monitoring areas, and a correspondingly stronger signal would thereby be generated. The mutual non-overlap does not apply to the monitoring areas 5 ₁ , 5 ₂ , 5 _{3 of} the far zone, because an overlap cannot be avoided here due to the flat course of the beams. Due to the geometry of the reflectors 2 to 8, the elevation of the partial areas is selected here such that the monitoring areas overlap in the manner shown in FIG. 4. Since the far zone is at a relatively large distance of around 12 to 15 m in front of the detector, fluctuations in the signal amplitude are not critical here.

In Fig. 4, the detector 18 is 2.25 m above the ground, the two horizontal lines H and M correspond to a height of 0.6 and 1.8 m, respectively, symbolizing the movement of a dog or a person in the surveillance room , As can be seen from the figure, in most cases a dog crosses only one subzone fully or two subzones partially in the effective range of the detector, so that compared to the mirror arrangement according to EP-A-0 303 913, where there are no subzones and therefore a complete monitoring area corresponding to 3 or more subzones is always crossed, the signal from sensor S (FIG. 1) is reduced by approximately 50% to 70%. On the other hand, an upright intruder always crosses several subzones of the far and middle zone or middle and near zone or near and look-down zone and thus generates a signal that is several times larger than that of the dog.

The conditions just described are illustrated in FIG. 4 for three different distances from the detector, E ₁ = 2.5 m, E ₂ = 5 m and E ₃ = 10 m. At a distance E _1, a person (line M) crosses subzones 15 ₂ , 15 ₁ , 11 ₃ , 11 ₂ and 11 ₁ , a dog (line H) only crosses subzones 15 ₂ and 15 ₁ . At a distance E ₂ a person crosses the subzones 11 ₃ , 11 ₂ , 11 ₁ , 5 ₃ , 5 ₂ and 5 ₁ , a dog crosses the subzones 11 ₃ and 11 ₂ . At a distance E _3, a person crosses the sub-zones 11 ₁ , 5 ₃ , 5 ₂ and 5 ₁ , a dog only the sub-zone 11 ₁ .

Practical tests have shown that within an effective range of 12 to 13 m, the sensor signal triggered by a dog of approximately 30 kg body weight is at most 50% of the detection threshold, so that this dog can certainly not trigger a false alarm. Outside the above-mentioned effective range, the dog's signal rises to just below the detection threshold. If the detector's femzones can "see" beyond the effective range through a wall, false alarms from large dogs cannot be excluded.

This problem can be eliminated by using a quadpyro sensor with 4 flakes or sensor elements as sensor S instead of a standard dual pyro sensor (see EP-A-0 303 913). In such a sensor, each pair of sensor elements forms a channel, the two channels effectively corresponding to a vertical splitting of the monitoring areas. Of these two channels, the lower one "looks" into the ground at a distance of about 20 m from the detector, so that the range is limited when a signal is requested in both channels for an alarm. On the other hand, even a large dog will never be able to deliver a signal above the detection threshold in the upper channel, so that even large dogs outside the detector's effective range cannot trigger a false alarm.

A cheaper, but less effective variant compared to the Quadpyrosensor would be to use Longflake-Pyros. With the standard flakes, the image of a medium-sized dog covers significantly more than 50% of the height of the flakes (sensor elements), and the image of an upright person protrudes far beyond the height of the flakes, with the part protruding beyond the flakes contributing nothing to the sensor signal , For example, if you doubled the amount of flakes, the difference between the signals triggered by a dog and a human would be much larger, which would improve the distinguishability. The gain factor (magnification of a human signal) compared to a dual sensor would be about 1.4, for a quad sensor it would be 2.5 to 3.

Claims (8)

1. Passive infrared signalling device comprising a heat-sensitive sensor (S) and a focussing means for concentrating on to the sensor (S) the heat radiation falling on to the signalling device from the surveillance space, the focussing means having focussing elements for surveillance regions having different positions in the surveillance space, characterized in that each focussing element consists of a number of partial elements, so that the surveillance regions are split vertically into sub-zones (5₁-5₃, 11₁-11₃, 15₁-15₄, 17₁-17₅) of slightly different elevations, the elevation of the partial elements being selected such that, in the case of the majority of the surveillance regions, there is produced, at most, a slight overlapping of the sub-zones (5₁-5₃, 11₁-11₃, 15₁-15₄, 17₁-17₅), the sub-zones (5₁-5₃, 11₁-11₃, 15₁-15₄, 17₁-17₅) are stacked in strata on one another, and the stratification is selected such that a sequence of dense curtains is produced, and discrimination between humans and animals is effected on the basis of the amplitude of the sensor signal.
2. Passive infrared signalling device according to Claim 1, characterized in that the number of the partial elements and, correspondingly, the number of the sub-zones (5₁-5₃, 11₁-11₃, 15₁-15₄, 17₁-17₅), increases as the radial distance of the respective surveillance region from the signalling device decreases.
3. Passive infrared signalling device according to either of Claims 1 or 2, characterized in that the sensitivity in the individual sub-zones (5₁-5₃, 11₁-11₃, 15₁-15₄, 17₁-17₅) is approximately equal.
4. Passive infrared signalling device according to Claim 3, characterized in that the weighting of the individual partial elements, particularly their optical aperture and surface area, is selected such that an animal of a certain size moving transversely relative to the coverage pattern formed by the surveillance regions delivers a signal of approximately equally small magnitude for all distances between the animal and the signalling device.
5. Passive infrared signalling device according to any one of Claims 1 to 4, characterized in that the focussing means consists of a mirror arrangement (1) with the reflectors (2-17) forming the focussing elements, and each reflector (2-17) is split into partial surface areas.
6. Passive infrared signalling device according to Claim 5, characterized in that the mirror arrangement (1) has a first reflector row (R₁) for a remote zone, a second reflector row (R₂) for a middle zone, a third reflector row (R₃) for a near zone and a fourth reflector row (R₄) for a look-down zone, and the reflectors (2-8) of the first row and the reflectors (9-13) of the second row are split into three partial surface areas in each case, the reflectors (14-16) of the third row are split into four partial surface areas and the reflector (17) of the fourth row is split into five partial surface areas.
7. Passive infrared signalling device according to Claim 5, characterized in that the sensor (S) has four sensor elements, combined in pairs, which form two independent channels, and an evaluation of the respective signal is effected in each channel.
8. Passive infrared signalling device according to Claim 5, characterized in that the sensor (S) has two sensor elements whose height, compared with the sensor elements of a standard dual pyro sensor, is distinctly elongated.