GB2124363A - Intruder detector - Google Patents
Intruder detector Download PDFInfo
- Publication number
- GB2124363A GB2124363A GB08221644A GB8221644A GB2124363A GB 2124363 A GB2124363 A GB 2124363A GB 08221644 A GB08221644 A GB 08221644A GB 8221644 A GB8221644 A GB 8221644A GB 2124363 A GB2124363 A GB 2124363A
- Authority
- GB
- United Kingdom
- Prior art keywords
- window
- segment
- monitored
- intruder
- sensor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000005855 radiation Effects 0.000 claims abstract description 25
- 238000003384 imaging method Methods 0.000 claims abstract description 13
- 230000015572 biosynthetic process Effects 0.000 claims description 16
- 238000005755 formation reaction Methods 0.000 claims description 16
- 239000000463 material Substances 0.000 claims description 10
- 238000010276 construction Methods 0.000 claims description 6
- 239000004065 semiconductor Substances 0.000 claims description 6
- 239000004698 Polyethylene Substances 0.000 claims description 5
- -1 polyethylene Polymers 0.000 claims description 5
- 229920000573 polyethylene Polymers 0.000 claims description 5
- 238000001514 detection method Methods 0.000 claims description 4
- 229920003023 plastic Polymers 0.000 claims description 4
- 239000004033 plastic Substances 0.000 claims description 4
- 238000010586 diagram Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 238000000034 method Methods 0.000 claims description 2
- 230000000116 mitigating effect Effects 0.000 claims description 2
- 238000000465 moulding Methods 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 claims description 2
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
- G08B13/189—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems
- G08B13/19—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using infrared-radiation detection systems
- G08B13/193—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using infrared-radiation detection systems using focusing means
Abstract
In an intruder detector for use in a burglar alarm, infra-red radiation is imaged onto a sensor 16. The imaging system, which serves to divide the area of surveillance into monitored and unmonitored zones and to focus the radiation onto the sensor, consists of a window 12 constructed as a flat one-piece segmented Fresnel lens, each segment 12a, 12b and 12c focusing radiation from a different respective monitored zone onto the sensor 16. The lens is double sided with one side acting as a convex lens and the other as a set of deflecting prisms. <IMAGE>
Description
SPECIFICATION
Intruder detection
The present invention relates to an intrusion detector for use as part of a burglar alarm.
Intrusion detectors are known which operate on the basis of detecting the infra-red radiation emitted by an intruder. The semiconductor devices used in such detectors as sensors are responsive only to changes in the incident radiation and it is therefore necessary to ensure that as an intruder moves about the area under surveillance, the infra-red energy imaged onto the semiconductor device varies.
The usual manner of achieving this aim is to divide the area of surveillance into monitored and unmonitored zones so that as an intruder moves from one such zone to another a significant change occurs in the amount of infra-red radiation falling on the semiconductor device and thereby enables detection.
The known manner for dividing the area of surveillance into monitored and unmonitored zones is to use a multi-faceted mirror but such a construction is both expensive to produce and results in a bulky and obtrusive detector.
With a view to mitigating the above disadvantages, the present invention provides an intruder detector comprising a sensor responsive to changes in the level of incident radiation and an imaging system for focusing energy from only monitored zones of an area of surveillance onto the sensor, the imaging system comprising a window constructed as a flat, integrally formed, segmented Fresnel lens of which each segment is operative to focus radiation from a different respective monitored zone onto the sensor.
Conveniently, the Fresnel lens comprises a sheet of material transparent to infra-red radiation having concentric formations on one surface to define a convex focusing lens common to all the segments and on the opposite surface of the lens each segment comprises parallel formations to act as a deflecting prism, the angle of deflection or the attitude of the prism varying from one segment to another whereby to divide the area of surveillance into monitored and unmonitored zones.
Advantageously, the material from which the window is made is a mouldable plastics material such as polyethylene.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a schematic diagram of an intruder detector,
Fig. 2 is a view of one face of the window of the detector shown in Fig. 1, and
Fig. 3 is a view of the opposite face of the same window.
In Fig. 1 , there is shown an intruder detector in the form a box 10 having a window 12. A printed circuit board 14 is mounted within the box 10 and carries an infra-red sensor 1 6. The circuit and the sensor will not be described in detail as they are conventional and are not directly related to the improvement provided by the invention.
As previously described, it is necessary to divide the area of surveillance into monitored and unmonitored zones. This is achieved by virtue of the fact that the window 12 is constructed as a double sided, flat, segmented Fresnel lens. As seen from Fig. 2, one face of the Fresnel lens consists exclusively of concentric formations 20 so that this surface acts in a known manner as a convex lens to focus the incident radiation onto the sensor 1 6.
On the opposite side, as shown in Fig. 3, there are three sets of parallel formations 22, 24 and 26 each forming part of a respective one of three segments 1 2a, 1 2b and 1 2c of the window. The first segment 1 2a has widely spaced formations 22 each of which is triangular in cross-section with a small apical angle. The second segment 1 2b has less widely spaced formations 24 with a larger apical angle while the third segment 1 2c has still less widely spaced formations with still larger apical angle. As a consequence of this construction each segment acts as a deflecting prism and, as shown diagrammatically in Fig. 1, the window collects radiation from three different monitored zones (shaded) which are separated from one another by unmonitored zones.
It will be noted that the window segment 1 2a for the long range zone has a larger area than segment 1 2b for the medium range zone which, in turn, has a larger area than the segment 1 2c for the short range zone. This variation in the effective aperture of the imaging system is intended to counteract the fact that the energy from an intruder reduces with his distance, following an inverse square law.
The construction of the window in this manner obviates the need for multi-faceted mirrors which require a great deal of space. Furthermore, the window may be made relatively large to achieve the required sensitivity and the energy losses can be reduced as compared with a mirror system.
The main advantage, however, stems from the important reduction in manufacturing costs in that the entire imaging system can be formed integrally using a simple moulding technique from polyethylene which is an inexpensive plastics material. The window can furthermore be assembled with ease and makes for a neater and more compact design.
1. An intruder detector comprising a sensor responsive to changes in the level of incident radiation and an imaging system for focusing energy from only monitored zones of an area of surveillance onto the sensor, the imaging system comprising a window constructed as a flat, integrally formed, segmented Fresnel lens of which each segment is operative to focus radiation from a different respective monitored zone onto the sensor.
2. An intruder detector as claimed in claim 1, wherein the Fresnel lens comprises a sheet of material transparent to infra-red radiation having
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (4)
1. An intruder detector comprising a sensor responsive to changes in the level of incident radiation and an imaging system for focusing energy from only monitored zones of an area of surveillance onto the sensor, the imaging system comprising a window constructed as a flat, integrally formed, segmented Fresnel lens of which each segment is operative to focus radiation from a different respective monitored zone onto the sensor.
2. An intruder detector as claimed in claim 1, wherein the Fresnel lens comprises a sheet of material transparent to infra-red radiation having concentric formations on one surface to define a convex focusing lens common to all the segments and on the opposite surface of the lens each segment comprises parallel formations to act as a deflecting prism, the angle of deflection or the attitude of the prism varying from one segment to another whereby to divide the area of surveillance into monitored and unmonitored zones.
3. An intruder detector as claimed in claim 1 or 2, wherein the window is constructed from polyethylene.
4. An intruder detector constructed substantially as herein described with reference to as illustrated in the accompanying drawings.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08221644A GB2124363B (en) | 1982-07-27 | 1982-07-27 | Intruder detector |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB08221644A GB2124363B (en) | 1982-07-27 | 1982-07-27 | Intruder detector |
Publications (2)
Publication Number | Publication Date |
---|---|
GB2124363A true GB2124363A (en) | 1984-02-15 |
GB2124363B GB2124363B (en) | 1985-12-18 |
Family
ID=10531928
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB08221644A Expired GB2124363B (en) | 1982-07-27 | 1982-07-27 | Intruder detector |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2124363B (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0197583A1 (en) * | 1985-03-29 | 1986-10-15 | Philips Electronics Uk Limited | Arrays of lenses |
US4734585A (en) * | 1985-07-17 | 1988-03-29 | Racal-Guardall (Scotland) Ltd. | Passive infra-red sensor |
GB2205156A (en) * | 1987-05-16 | 1988-11-30 | Graham Wild | Optical detector |
US5668539A (en) * | 1995-08-30 | 1997-09-16 | 1138037 Ontario Ltd. | Thermal emitted radiation detecting device |
US6753766B2 (en) | 2001-01-15 | 2004-06-22 | 1138037 Ontario Ltd. (“Alirt”) | Detecting device and method of using same |
US7634341B2 (en) | 2001-03-07 | 2009-12-15 | 1138037 Ontario Ltd. (“Alirt”) | Detecting device and method of using same |
Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2064108A (en) * | 1979-11-13 | 1981-06-10 | Arrowhead Ets Inc | Passive infrared intrusion detector |
-
1982
- 1982-07-27 GB GB08221644A patent/GB2124363B/en not_active Expired
Patent Citations (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2064108A (en) * | 1979-11-13 | 1981-06-10 | Arrowhead Ets Inc | Passive infrared intrusion detector |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0197583A1 (en) * | 1985-03-29 | 1986-10-15 | Philips Electronics Uk Limited | Arrays of lenses |
US4734585A (en) * | 1985-07-17 | 1988-03-29 | Racal-Guardall (Scotland) Ltd. | Passive infra-red sensor |
GB2205156A (en) * | 1987-05-16 | 1988-11-30 | Graham Wild | Optical detector |
US5668539A (en) * | 1995-08-30 | 1997-09-16 | 1138037 Ontario Ltd. | Thermal emitted radiation detecting device |
US6753766B2 (en) | 2001-01-15 | 2004-06-22 | 1138037 Ontario Ltd. (“Alirt”) | Detecting device and method of using same |
US7634341B2 (en) | 2001-03-07 | 2009-12-15 | 1138037 Ontario Ltd. (“Alirt”) | Detecting device and method of using same |
Also Published As
Publication number | Publication date |
---|---|
GB2124363B (en) | 1985-12-18 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
PCNP | Patent ceased through non-payment of renewal fee |