WO2000038125A1

WO2000038125A1 - Intruder sensor housing and intruder sensor

Info

Publication number: WO2000038125A1
Application number: PCT/GB1999/004239
Authority: WO
Inventors: Juan Sebastian Herrera; Mark Whitehead
Original assignee: Pyronix Limited
Priority date: 1998-12-22
Filing date: 1999-12-22
Publication date: 2000-06-29
Also published as: AU1868400A; GB2345130A; GB9828236D0

Abstract

The present invention relates to housings for intruder sensors and to intruder sensors having such a housing. Many intruder sensors have relatively thick Fresnel lens mounted in a window of the front cover the housing. Such lens produces significant attenuation of any signal passing through it. Furthermore, the lens when mounted in the front cover may be subjected to various impacts. The intruder sensor must be able to withstand impacts of a particular magnitude as are prescribed in various standards. Accordingly, the present invention provides an intruder sensor housing for an intruder sensor comprising a front cover and a lens, the front cover and the lens being unitarily formed. Advantageously, the lens of such a unitary structure relative to a separately formed conventional front cover and Fresnel lens can be made thinner from a given impact resistance requirement. Therefore, the attenuation of any signals passing through the lens is significantly reduced.

Description

INTRUDER SENSOR HOUSING AND INTRUDER SENSOR

The present invention relates to an intruder sensor housing for an intrusion detection device comprising for example, a PIR sensor, a microwave sensor or a combined technology sensor and an intruder detection device.

There are various standards, for example, "Loss Prevention Standard, LBS 1169: issue :2, specification for Passive Infrared Intruder Sensors" which specify the physical requirements or degree of physical protection to which a sensor housing must conform if it is to be certified by the Loss Prevention Certification Board. The physical protection requirements specified in the Loss Prevention Standard indicate that a sensor housing should be constructed to provide class IP 41 protection as defined in British Standard BS 5490. Furthermore, the areas in which the sensing elements, for example, the PIR element, are housed shall be constructed so as to prevent the ingress of insects. Within intruder sensor devices, sealed optics are arranged to prevent the ingress of insects into the device. The ingress of insects could lead to false alarms being generated.

The Loss Prevention Standard additionally specifies the degree of impact resistance which a certified intruder sensor housing shall exhibit for certification. An intruder sensor housing must after having been subjected to three impact blows on each accessible surface of the sensor housing, with an energy at the moment before impact of 0.5 J, in accordance with IEC8I7, shall continue to function correctly and the housing shall continue to meet the requirements of IP 41. It has been found to meet the requirements of physical protection that the Fresnel lens of prior art housings should be approximately 0.7 mm thick. It will be appreciated that as the thickness of the Fresnel lens increases so does the attenuation of any signal passing through Fresnel lens. The attenuation of any signal passing through the Fresnel lens will clearly adversely effect the range of an intrusion sensor or the sensitivity of an intrusion sensor. Accordingly there are conflicting requirements imposed upon the design and structure of an intrusion sensor housing.

Notwithstanding the Loss Prevention Standards physical protection requirements, it is still often the case that a Fresnel lens may be dislodged or disorientated as a result of an impact . Any such dislocation or disorientation would clearly adversely effect the correct functioning of the intrusion sensor.

Still further, it will be appreciated that a conventional intruder sensor housings comprises a significant number of component parts. In particular, the requirement for sealed optics and its solution using a collet and mount together with four screws significantly increases both the number of component parts of a housing and the complexity of manufacture, that is, the complexity of assembling such a housing. Any such increase in the number of component parts or the complexity of manufacture inevitably results in increased cost of an intruder sensor.

It is an object of the present invention to at least mitigate some of the problems associated with the prior art intruder sensor housings.

Accordingly, a first aspect of the present invention provides housing for an intruder sensor comprising a front cover having lens, the front cover and the lens being integrally formed.

Advantageously, an integrally formed front cover and lens significantly increases the impact resistance of the lens .

Accordingly to maintain the same level of physical protection as compared to prior art intruder sensor housings, it is possible to reduce the thickness of the lens. Preferred embodiments have a lens thickness of substantially 0.7 mm. However, the lens thickness can be less than or equal to 0.4 mm, for example.

It can be appreciated that a reduction in the thickness of the lens leads to a corresponding reduction in the attenuation of any signal passing through the lens.

Accordingly, an embodiment provides a housing in which the lens has a thickness of 0.4 mm. Advantageously, the gain of the intruder sensor is increased by approximately 20% relative to a housing having a lens of 0.7 mm. This increase in gain leads to at least one of either an increase in intruder sensor range or intruder sensor sensitivity for a given range.

Conventionally, Fresnel lens are manufactured using flat pieces of suitably moulded plastic. When the lens is incorporated into a PIR housing it is clearly in a stressed state. The stressed state of such a conventional Fresnel lens reduces its impact resistance as compared to the integrally moulded Fresnel lens. Such a lack of stress also contributes to the improved impact resistance of the present invention.

The integrally moulded Fresnel lens may comprise either spherical, aspherical or triangular groove profiles. Alternatively, the lens may comprise a combination of spherical and/or aspherical Fresnel lens profiles as, for example, described in US patent no 4,787,722. Still further, the lens may also comprise either in conjunction with the spherical and/or aspherical Fresnel profile or alone a multiple array lens such as described in, for example, UK patent no GB 2 251 705.

According, to a further aspect of the present invention there is provided an intruder sensor comprising a sensing element that is inclined at a predetermined angle to a given plane of the intruder sensor housing.

Further, the predetermined angle is preferably 70°. The predetermined plane is the plane of the back cover of the intruder sensor.

Prior to a break-in, a potential intruder may block the Fresnel lens using an infrared blocking material thereby rendering the sensor ineffective. However, unlike conventional intruder sensor housings, the embodiments of the present invention do not comprise an externally visible or an externally obvious window. Therefore, in advance of an intrusion, it is difficult or impossible for the intruder to be certain of the location of the Fresnel lens and that the sensor has been effectively obscured.

Preferably, the sensor element is a pyroelectric sensor.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is an exploded view of a conventional PIR intruder sensor housing;

Figures 2a-2c illustrate various elevations of an embodiment of an intruder sensor housing according to an embodiment of the present invention; and

Figure 3 illustrates an internal view of the front cover of an intruder sensor housing according to an embodiment .

Referring to figure 1 there is shown an exploded front and rear views of a prior art intrusion detection device housing 100 for, for example, a PIR sensor. A PIR sensor comprising such a housing is available from Pyronix Limited under the name of, for example, Magnum True Quad™ . The housing comprises a front cover 102 having a first opening 104 for a Fresnel lens 106 and a second opening 108 for transmitting light from a LED (not shown) to the exterior of the housing. The LED provides an indication that the PIR sensor is functioning correctly. Conventionally, to secure the Fresnel lens 106 within the front cover 102 such that it is in registry with the first opening 104, a collet 110 is used. The collet 110 is fixed in place at its corners by four screws (not shown) . The front cover 102 is arranged to co-operate with a back cover 112 to form a complete housing for the PIR sensor and associated electronics which are mounted on a PCB 114. The collet also comprises a peripheral dependant skirt 116 which is arranged to co-operate with a mounting 118 for the passive infrared device (not shown) and the Fresnel lens 106 to define side walls which create, in use, a sealed volume between the inwardly directed rear face of the Fresnel lens 106 and the passive infrared device. The purpose of the sealed volume is to prevent or at least reduce the movement of air within the housing between the Fresnel lens 106 and the passive infrared sensor. Any such movement may lead to false alarms. Such an arrangement is conventionally known within the art as sealed optics. The sealed volume also prevents or at least reduces the possibility of ingress of insects into the chamber containing the PIR sensor, which again leads to a reduction in the occurrence of false alarms.

Referring to figure 2a there is shown a front elevation of the front cover of an intruder sensor device according to the first embodiment of the present invention. Unlike conventional intruder sensor housings, the first embodiment does not comprise an externally visible or an externally obvious window. Therefore, in advance of an intrusion, it is difficult to block the coverage of the sensor by placing an infrared blocking material in front of the lens. The position of the Fresnel lens on the front face of the housing is more difficult to or impossible to ascertain from inspection because the front face is substantially smooth.

It can be seen from figure 2b that the profiling for the Fresnel lens is contained on an inwardly facing rear face of the front cover. Consequently, the position of the Fresnel lens cannot be readily determined by mere visual inspection of the outer face of the front cover since the Fresnel lens is integrally moulded with the front cover.

The Fresnel lens has a thickness of 0.7 mm. However the present invention is not limited thereto. Any thickness convenient thickness can be utilised. Preferably, a chosen thickness should be such that it meets the impact resistance or physical protection requirements set out in the standards described above.

Referring again to figure 2a, the front cover provides an aperture 204 through which light from an internal LED (not shown) can be transmitted to provide an indication that the intruder sensor is functioning correctly. It can be seen from figure 2c that the light from the internal LED is preferably guided from the LED through the aperture via an appropriate wave guide 206.

The passive infrared sensor or other suitable sensing element, 208 is mounted within one of two chambers 210 and 212 of the intruder sensor housing. It can be seen that the sensing element, for example, a passive infrared sensor, is mounted within a first chamber 210 of the intruder sensor housing. A second chamber 212 of the housing is also provided to accommodate electrical connections 214 from the exterior of the intruder sensor to the PCB 216 of the intruder sensor.

The two chambers 210 and 212 are defined by internal webs 218 and 220 that depend from the back cover and front cover respectively of the intruder sensor housing. The webs are arranged to form, in conjunction with the PCB when disposed between the webs, a sealed optics chamber, that is to say, the first chamber 210 is sealed from the second chamber 212 such that there is little or no possibility of air movement within the first chamber 210 as a consequence of any activity associated or within the second chamber 212. This is the case even though holes may be drilled into the intruder sensor housing to reach the electrical connections 214 disposed within the second chamber 212. Furthermore, the sealed first chamber 210 also prevents the ingress of insects into that chamber. Hence, the intruder sensor meets the physical requirements of the various standards described above .

Referring again to figure 2b, although the embodiment illustrated utilises a Fresnel lens, the present invention is not limited thereto. Embodiments can equally well be realised in which the Fresnel lens is replaced or supplemented by some other form of lens such as, for example, a multiple array lens as described in UK patent no. GB 2,251,700.

Preferably, the intruder sensor housing is produced via injection moulding using high density polyethylene. A white pigmentation is used to colour the polyethylene, as is well known within the art.

Since the Fresnel grooves are disposed on the interior of the front cover, the design of the mould tool must be such that the grooved inner surface is able to fall away cleanly from the mould tool. Therefore, any plastic undercuts should preferably be eliminated or compensated for by using a movable mould tool core as is well known within the art.

Often an intruder sensor further comprises means for determining the proximity of a body to the sensor. If a body is determined as being in a very close proximity to the intruder sensor, it is assumed that there has been an attempt to mask the sensor and an appropriate alarm condition is raised. Typically, the means for determining the proximity to the detector comprises an infrared transmitter and receiver. The infrared transmitter and receiver must be placed in front of an infrared transparent material, that is, the material is such that infrared radiation can pass through it and be detected. Conventionally constructed intruder sensors are made of a material which blocks infrared but for the Fresnel lens making it easier for a potential intruder to mask the intruder sensor (since the approximate location of the infrared transmitter and receiver are known) . However, an embodiment of the present invention comprises an intruder sensor housing front cover that is manuf ctured from an infrared transparent material , for example, polyethylene. Manufacturing the front cover using an infrared transparent material allows the infrared transmitter and receiver to be positioned other than only behind the Fresnel lens. The ability to arbitrarily select the location of the infrared transmitter and receiver makes it more difficult for a potential intruder to mask the operation of the intruder sensor.

It can be appreciated from the figures that the surface of the front cover is arcuate or curved. It can be seen that the surface of curvature of the front cover generally and the surface of curvature of that portion of the front cover comprising the Fresnel lens are arranged to form a smooth surface. In effect, the surface of curvature of the front cover and the surface of curvature of that portion of the front cover comprising the lens are co-incident, in the sense of two planes or curvilinear planes being co-planar, or are one and the same .

The Fresnel lens and front cover are formed, that is moulded, into a shape that is not planar. It can be seen that both the Fresnel lens and the front cover both form a curved surface when considered in two non-co-planar or non-parallel planes through the curved surface of the front cover and lens. The Fresnel lens and the front over form part of the same continuous curved surface.

Claims

1. An intruder sensor housing for an intruder sensor comprising a front cover and a lens, the front cover and the lens being integrally formed.

2. A intruder sensor housing comprising front cover and a back and at least one web arranged to divide the interior of the housing into first and second chambers, the first chamber being arranged to accommodate at least one sensing element .

3. A housing as claimed in either of claims 1 or 2 , wherein the first chamber provides a sealed optics environment for the at least one sensing element .

4. A housing as claimed in claim 4, in which the sealed optics environment substantially prevents or reduces air flow within the first chamber and/or substantially prevents ingress of insects into the first chamber.

5. A housing as claimed in any preceding claims, comprising a first inwardly facing web disposed on the front cover that is arranged to co-operate with a corresponding inwardly facing web disposed on a back cover to form the first chamber.

6. A housing as claimed in any of claims 2 to 5, wherein the front cover comprises a lens, the front cover and the lens being integrally formed.

7. An intruder sensor housing as claimed in any preceding claim in which the thickness of the lens is arranged to meet the impact requirements of at least one of IP 41 and IEC817.

8. An intruder sensor comprising a housing as claimed in any preceding claim containing at least one sensing element .

9. An intruder sensor as claimed in claim 8, wherein the line of sight or main beam of the at least one sensing element or Fresnel lens is inclined at a predetermined angle relative to a predetermined plane of the housing.

10. An intruder sensor as claimed in claim 9, wherein the predetermined angle is approximately 70°.

11. An intruder sensor housing as claimed in any of claims 1 to 7 , or an intruder sensor as claimed in claims 8 to 10, wherein at least one of either the front cover and the lens are formed of an infrared transparent material .

12. An intruder sensor housing, intruder sensor or housing as claimed in claim 11, wherein the infrared transparent material in polyethylene.

13. An intruder sensor substantially as described herein with reference to and/or as illustrated by the accompanying drawings .

14. An intruder sensor housing substantially as described herein with reference to and/or as illustrated in the accompanying drawings.

15. An intruder sensor or intruder sensor housing as claimed in any preceding claim, in which the lens and/or the front cover form a curved surface that is curved in at least two non-parallel, preferably orthogonal, planes through the curved surface.