GB1598052A - Method and apparatus for detecting the entry of an intruder into a secure area - Google Patents

Description

(54) METHOD AND APPARATUS FOR DETECTING THE ENTRY OF AN INTRUDER INTO A SECURE AREA (71) 1, ROBERT CHRISTOPHER BYRNE, a British subject, of 433 London Road, Croydon, Surrey, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of and apparatus for detecting the entry of an intruder into a secure area.

It is known to "fence" a secure area by installing around the perimeter of the area one or more transmitters and receivers, each transmitter being arranged to direct a beam of energy radiation at a receiver. Entry of an intruder into the "fenced" area is detected when a beam is interrupted causing an alarm system to be triggered.

According to one aspect of this invention, a method of detecting the entry of an intruder into a secure area comprises:-- arranging a plurality of perimeter units in spaced relationship along the perimeter of the area; linking adjacent and non-adjacent units by beams of energy radiation by (a) transmitting from a first unit a beam directed at an adjacent second unit and a beam directed diagonally at a third unit immediately beyond an adjacent unit, and (b) receiving at the first unit a beam from an adjacent fourth unit and a beam directed diagonally from a fifth unit immediately beyond an adjacent unit; and in the event of a received beam being interrupted, causing an alarm system to be triggered.

According to another aspect of this invention, apparatus for detecting the entry of an intruder into a secure area comprises -a plurality of perimeter units spaced with respect to each other along the perimeter of the area and having (a) transmitters operable to generate a pattern of beams of energy radiation, (b) receivers to detect the interruption of any of the beams, and (c) means operable to trigger an alarm system in the event of the detection of a beam interruption; the plurality of units including a first unit having one transmitter arranged to transmit a beam directed at a second adjacent unit, another transmitter arranged to transmit a beam directed at a third unit immediately beyond an adjacent unit, one receiver arranged to receive a beam from an adjacent fourth unit and another receiver arranged to receive a beam from a fifth unit immediately beyond an adjacent unit.

In a preferred method the beams linking adjacent units are all directed in one direction around the perimeter and comprise a first chain or beams, and the diagonally directed beams comprise second and third chains of beams, the beams of the second chain being all directed in one direction and linking alternate units, and the beams of the third chain being all directed in one direction and linking alternate units between the units of the second chain.

The method in accordance with the invention thus provides a beam pattern around the perimeter which has a finite depth, so that an intruder crossing the perimeter will pass through at least two beams.

In the preferred embodiment one of the units is a master unit which receives signals from slave units and triggers the alarm system when any of the beams is interrupted. This is carried out by arranging for each slave unit to transmit a modulated beam of infra-red radiation. The modulation signal transmitted by each unit is dependent on the signals received by that unit from other units. If reception of one of the beams is interrupted then the affected receiving unit will transmit a signal to the next unit in the chain which signal contains a code indicative of the location of the interrupted beam. This code signal is passed from one unit to another along the chain containing the interrupted beam until it reaches the master unit which then triggers the alarm and provides information indicating the location of the beam interruption.

The transmitters and receivers may be arranged such that each unit houses two of each and such that the chains of beams are directed around the perimeter in both clockwise and anitclockwise direction. This latter feature, as well as making it more difficult for the intruder to avoid detection, increases the reliability of the system in that when an intruder crosses the perimeter near the beginning of a beam chain, i.e. relatively close to the master unit, he will also interrupt another beamchainnearits end. Therefore, whereas the interruption signal in one chain must travel around most of the units in that chain, the interruption signal in the other chain has a relative short distance to travel to the master unit.

The apparatus of the invention may comprise a number of portable units capable of providing a temporary security system which can be easily removed when no longer required, or it may be in the-form of a permanent installation.

An embodiment of the invention will now be described by way of example with reference to the drawing which is a diagrammatic plan view of apparatus positioned around the perimeter of a secure area.

The apparatus comprises eight perimeters units 1 to 8 spaced around the perimeter of a secure area 9. Each unit contains two transmitters and two receivers, so arranged that three chains of beams encircle the area 9. The first chain links adjacent units, 1, 2, 3 .....

7, 8, 1, each beam being directed in an anticlockwise direction. The second chain links alternate units 8, 6, 4, 2, 8, with clockwise and diagonally directed beams. The third chain links the intevening alternate units 1, 3, 5, 7, 1 with diagonal beams directed anti-clockwise around the perimeter.

It can be seen that an intruder entering the secure area 9 must cross three security "fences"; for example, an intruder entering by the path 10 will interrupt in succession the beams 45, 35 and 64. (Each beam has been given a reference numeral determined by the two units it links).

The units 1 to 8 each comprise a post approximately 1 metre high and constructed of steel. Each post has an opening covered by a tinted perspex or glass screen which is transparent to infra-red radiation but which prevents observation of the position of the transmitters within. The transmitting and receiving devices inside the post are adjustably mounted for rotation about a vertical axis so that each device can be individually aimed at another post when the apparatus is being installed in the field.

The transmitters may include gallium arsenide laser diodes as the actual transmitting devices or alternatively divergent beam transmitters. However, the laser diodes have a greater range for a given power consumption and are also more compact than the divergent beam transmitters. The receivers may each employ any one of a number of devices which are sensitive to radiation in the infra-red range. Silicon photodiodes such as p-i-n diodes meet the requirements and have the advantage of being operable from a low voltage supply. The range obtainable with the above devices may be 300 metres in clear conditions. Rain and snow do not have a significant effect; only fog has a serious attenuating effect on the beams. For operation in foggy conditions a three to one range safety factor is used when determining the positions of the posts in the field.Thus for a 300 metre range in clear conditions the maximum distance between respective transmitters and receivers is 100 metres. Referring to the diagram the spacing between nonadjacent units linked by a diagonal beam (such as units 1 and 3) is 100 metres, with the spacing between adjacent units being a little over 50 metres.

The apparatus may include one or more master units each of which forms the beginning and end of a chain of beams and may contain either an alarm system or means for linking the apparatus with an external alarm system.

Each post is equipped with a rechargeable battery and may thus be constructed either as a portable self-contained unit or as part of a permanent installation. The battery powers two transmitters, two receivers and associated electronic circuitry.

When a beam is interrupted by an intruder the apparatus operates as follows:- (i) The affected receiver in one of the units detects the interruption and causes one of the transmitters in the same unit to signal the interruption to the next unit in the chain. This is done either by modulating the transmitted beam with a signal characterising the affected unit or, more simply, by switching off the transmitter. The interruption signal is propagated in like manner around the beam chain containing the interrupted beam until it reaches a master unit. In the case of a characteristic modulation signal being transmitted the master unit is able to identify the approximate location of the interruption.In the case of the transmitters of a chain being merely switched off there is no indication of where in the chain the interruption has occurred, unless alternative means are provided.

(ii) The master unit then triggers the alarm system which may be housed in the unit itself or may be located elsewhere and triggered via for instance a simple radio link. The radio link may also transmit a signal to a remote security centre indicating the location of the interruption.

The apparatus has fail-safe devices built in to the electronic circuitry which triggers the alarm if a power supply fails or if the intruder tampers with one of the units.

Further refinements which may be added to the apparatus include floodlighting which is arranged to illuminate that part of the peri meter where the interruption occurred, and closed-circuit TV cameras.

WHAT I CLAIM IS: 1. A method of detecting the entry of an intruder into a secure area comprising:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. master unit, he will also interrupt another beamchainnearits end. Therefore, whereas the interruption signal in one chain must travel around most of the units in that chain, the interruption signal in the other chain has a relative short distance to travel to the master unit. The apparatus of the invention may comprise a number of portable units capable of providing a temporary security system which can be easily removed when no longer required, or it may be in the-form of a permanent installation. An embodiment of the invention will now be described by way of example with reference to the drawing which is a diagrammatic plan view of apparatus positioned around the perimeter of a secure area. The apparatus comprises eight perimeters units 1 to 8 spaced around the perimeter of a secure area 9. Each unit contains two transmitters and two receivers, so arranged that three chains of beams encircle the area 9. The first chain links adjacent units, 1, 2, 3 ..... 7, 8, 1, each beam being directed in an anticlockwise direction. The second chain links alternate units 8, 6, 4, 2, 8, with clockwise and diagonally directed beams. The third chain links the intevening alternate units 1, 3, 5, 7, 1 with diagonal beams directed anti-clockwise around the perimeter. It can be seen that an intruder entering the secure area 9 must cross three security "fences"; for example, an intruder entering by the path 10 will interrupt in succession the beams 45, 35 and 64. (Each beam has been given a reference numeral determined by the two units it links). The units 1 to 8 each comprise a post approximately 1 metre high and constructed of steel. Each post has an opening covered by a tinted perspex or glass screen which is transparent to infra-red radiation but which prevents observation of the position of the transmitters within. The transmitting and receiving devices inside the post are adjustably mounted for rotation about a vertical axis so that each device can be individually aimed at another post when the apparatus is being installed in the field. The transmitters may include gallium arsenide laser diodes as the actual transmitting devices or alternatively divergent beam transmitters. However, the laser diodes have a greater range for a given power consumption and are also more compact than the divergent beam transmitters. The receivers may each employ any one of a number of devices which are sensitive to radiation in the infra-red range. Silicon photodiodes such as p-i-n diodes meet the requirements and have the advantage of being operable from a low voltage supply. The range obtainable with the above devices may be 300 metres in clear conditions. Rain and snow do not have a significant effect; only fog has a serious attenuating effect on the beams. For operation in foggy conditions a three to one range safety factor is used when determining the positions of the posts in the field.Thus for a 300 metre range in clear conditions the maximum distance between respective transmitters and receivers is 100 metres. Referring to the diagram the spacing between nonadjacent units linked by a diagonal beam (such as units 1 and 3) is 100 metres, with the spacing between adjacent units being a little over 50 metres. The apparatus may include one or more master units each of which forms the beginning and end of a chain of beams and may contain either an alarm system or means for linking the apparatus with an external alarm system. Each post is equipped with a rechargeable battery and may thus be constructed either as a portable self-contained unit or as part of a permanent installation. The battery powers two transmitters, two receivers and associated electronic circuitry. When a beam is interrupted by an intruder the apparatus operates as follows:- (i) The affected receiver in one of the units detects the interruption and causes one of the transmitters in the same unit to signal the interruption to the next unit in the chain. This is done either by modulating the transmitted beam with a signal characterising the affected unit or, more simply, by switching off the transmitter. The interruption signal is propagated in like manner around the beam chain containing the interrupted beam until it reaches a master unit. In the case of a characteristic modulation signal being transmitted the master unit is able to identify the approximate location of the interruption.In the case of the transmitters of a chain being merely switched off there is no indication of where in the chain the interruption has occurred, unless alternative means are provided. (ii) The master unit then triggers the alarm system which may be housed in the unit itself or may be located elsewhere and triggered via for instance a simple radio link. The radio link may also transmit a signal to a remote security centre indicating the location of the interruption. The apparatus has fail-safe devices built in to the electronic circuitry which triggers the alarm if a power supply fails or if the intruder tampers with one of the units. Further refinements which may be added to the apparatus include floodlighting which is arranged to illuminate that part of the peri meter where the interruption occurred, and closed-circuit TV cameras. WHAT I CLAIM IS:

1. A method of detecting the entry of an intruder into a secure area comprising:

arranging a plurality of perimeter units in spaced relationship along the perimeter of the area; linking adjacent and non-adjacent units by beams of energy radiation by (a) transmitting from a first unit a beam directed at an adjacent second unit and a beam directed diagonally at a third unit immediately beyond an adjacent unit, and (b) receiving at the first unit a beam from an adjacent fourth unit and a beam directed diagonally from a fifth unit immediately beyond an adjacent unit; and in the event of a received beam being interrupted, causing an alarm system to be triggered.

2. A method according to claim 1 wherein the beams linking adjacent unit are all directed in one direction around the perimeter and comprise a first chain of beams, and wherein the diagonally directed beams comprise second and third chains of beams, the beams of the second chain being all directed in one direction and linking alternate units, and the beams of the third chain being all directed in one direction and linking alternate units between the units of the second chain.

3. A method according to claim 2 wherein the beams of the second chain are all directed clockwise and the beams of the third chain are all directed anti-clockwise.

4. A method according to any preceding claim wherein the detection at one unit of a beam interruption causes a change in the characteristics of a beam transmitted by that unit.

5. A method according to claim 2 or claim 3 wherein interruption of a beam causes a change in the characteristics of succeeding beams of the chain containing the interrupted beam so as to pass an interruption signal along the chain.

6. A method according to claim 5 wherein the detection of a beam interruption by the unit at which the interrupted beam is directed results in the succeeding beams of the chain containing the said beam being transmitted with a modulation signal which is characteristic of the said unit or the said beam.

7. A method according to any preceding claim wherein the energy radiation is electromagnetic radiation having a wavelength in the infra-red range.

8. Apparatus for detecting the entry of an intruder into a secure area, comprising a plurality of perimeter units spaced with respect to each other along the perimeter of the area and having (a) transmitters operable to generate a pattern of beams of energy radiation, (b) receivers to detect the interruption of any of the beams, and (c) means operable to trigger an alarm system in the event of the detection of a beam interruption; the plurality of units including a first unit having one transmitter arranged to transmit a beam directed at a second adjacent unit, another transmitter arranged to transmit a beam directed at a third unit immediately beyond an adjacent unit, one receiver arranged to receive a beam from an adjacent fourth unit, and another receiver arranged to receive a beam from a fifth unit immediately beyond an adjacent unit.

9. Apparatus according to claim 8 wherein each unit contains two transmitters and two receivers.

10. Apparatus according to claim 8 or claim 9 wherein each transmitter includes a laser diode which in use emits radiation having a wavelength in the infra-red range.

11. Apparatus according to any of claims 8 to 10 wherein one of the units is a master unit which contains or is connectable to the alarm system, and which serves to trigger the alarm system when an interruption of a beam is detected by one of the other units.

12. Apparatus according to any of claims 8 to 11, wherein the units are portable.

13. Apparatus according to any of claims 8 to 11, wherein the units comprise a permanent installation.

14. Apparatus according to any of claims 8 to 13, wherein each unit is in the form of a post.

15. Apparatus according to any of claims 8 to 13 wherein each unit comprises an upright post or tower, two transmitters each producing in use of the apparatus a beam of energy radiation, two receivers to detect the presence of beams of energy radiation directed at the unit, and a rechargeable battery, the transmitters and receivers being adjustably mounted on the post or tower.

16. A method of detecting the entry of an intruder into a secure area substantially as herein described with reference to the draw- ing.

17. Apparatus for detecting the entry of an intruder into a secure area constructed and arranged substantially as herein described and shown in the accompanying drawing.