WO1997043741A1

WO1997043741A1 - Event detection device

Info

Publication number: WO1997043741A1
Application number: PCT/GB1997/001265
Authority: WO
Inventors: Paul Martin Kenny
Original assignee: Pyronix Limited
Priority date: 1996-05-10
Filing date: 1997-05-09
Publication date: 1997-11-20
Also published as: GB2311158A; GB2311158B; AU2708797A; IL126942A0; GB9609799D0; IL126942A

Abstract

Many intruder detection systems utilise for example, passive infrared sensors to detect the presence of an object within a protected space. However, those sensors cannot distinguish between a small or relatively cool object which is close to the sensor and a large or relatively hot object at a greater distance from the sensor. Accordingly, the present invention provides a combined technology event detection device for detecting the presence of an object within a protected space, said device comprising range finding means for determining the range of the object from said sensor, sensor means for producing an output signal related to at least one physical attribute of the object, and a comparator means for comparing the output signal from the sensing means with a threshold level, said threshold level being determined by said range.

Description

EVENT DETECTION DEVICE

Field of the invention

This invention relates to event detection devices and more particularly to an event detection device having range and movement detection capability.

Background art

Event detection devices, for example, intrusion monitoring devices, are well known in the art. Typically they are used to detect unauthorised entry or intrusion into a protected space.

Commercially available intrusion monitoring devices can be either of the passive or active variety. Passive intrusion monitoring devices can, for example, comprise a sensor which detects infra-red radiation propagated by warm-blooded animals. The amplitude of this radiation is dependent on the body mass and its distance from the device. Typically such passive infra red (PIR) sensor devices comprise a thermal detection device, consisting of one or more thermal detectors adapted to detect infra- red radiation incident thereon, and an optical system for directing incident radiation from a plurality of angular fields of view towards the thermal detection device. Such optical systems may consist of lenses, particularly .

2 Fresnel lenses and/or reflecting surfaces. Normally such devices are activated when a source of infra-red radiation passes from one angular sector to the next. Typical prior art intrusion monitoring devices are illustrated in US patents nos 3703718 and 3958118, and in UK patent no. 1335410. The entire disclosures of all these patents are incorporated herein by reference for all purposes.

The electronic output signal from a PIR sensor is passed through an amplifier. The amplifier output signal comprises two characteristics which contain limited information about an intruder. These characteristics are frequency and amplitude.

The PIR signal frequency represents the angular velocity of an intruder when movement is perpendicular to the detector line of sight.

The PIR signal amplitude varies with the level of infra red energy incident upon the detector. The signal varies according to the difference in received infra red energy between an intruder and the background radiation from the surrounding coverage area.

The overall levels of received energy relate to four basic physical properties of the intruder and the surrounding coverage area: (1) intruder size - the^" larger the intruder the higher the signal amplitude;

(ii) intruder range - the closer the intruder the higher the signal amplitude; (iii) intruder temperature - the greater the intruder temperature the higher the signal amplitude;

(iv) background temperature - the greater the difference between background temperature and intruder temperature the higher the signal amplitude.

Active intrusion monitoring devices are also known which comprise a transmitter and a receiver, the transmitter emitting radiation at a defined frequency and a receiver measuring the Doppler shift in any reflected radiation. Such active devices can, for example, operate at microwave frequencies and use a microwave radiation detection device to detect the reflected radiation.

An electrical circuit is provided to process the electrical output signal of the detection device and to compare that signal with a pre-set threshold signal.

The above technologies can be used alone, or as a combined technology event detection device. Examples of such combined technology devices include specifically the combination of a pyroelectric sensor and a microwave sensor as shown in US patents nos 3725888, 4401976, entitled "Combined surveillance and alarm system", 4710750, entitled "Fault detecting intrusion detection device", 4660024, entitled "Dual technology intruder detection system", and 5216410, entitled "Intrusion alarm sensing unit", in EP-A-0337964, entitled "A combined microwave and IR detector device", EP-A-0259015, entitled "Fault detecting intrusion detection device" and in W095/28692, entitled "Combined technology event detection device". The entire disclosures of all these patents and/or patent applications are incorporated herein by reference for all purposes.

In a typical combined technology event detection device, the outputs of two independent sensing means, responsive to different physical stimuli, are supplied to an AND gate, and if both sensing means register an event within a specified period of time, then an alarm is triggered. In this manner the incidence of false alarms occurring when only a single sensor means is used can be greatly reduced.

Conventional PIR sensors use band limited amplifiers to determine whether an intruder is moving at a velocity appropriate to human movement. Voltage level detection circuits are used to determine whether the intruder is transmitting sufficient energy to be considered a htunan target. Only when the limits imposed on frequency and amplitude are met will an alarm output signal be generated by the detector. A conventional PIR sensor cannot discriminate between the four factors which influence the signal amplitude. For example, a hot object at long range may produce the same amplitude as a cooler object at short range. Similarly a large object at long range may produce the same result as a smaller object at short range.

Combined technology intrusion detection devices attempt to improve upon the basic PIR sensor by including another movement sensor (for example a microwave Doppler shift detector) and only provide an alarm output when both sensors have reacted to sufficient movement of an object. Microwave Doppler shift signals provide information on intruder speed towards or away from the detector, but the direction of movement is not normally established. Thus these types of combined technology intrusion detection devices can discriminate between intruder movement in two dimensions but cannot allow target size and distance to be determined. As a result, they will still not be able to determine whether a moving target is a small object at close range or a large object at long range.

It is an object of the present invention to mitigate some of the problems associated with prior art sensors. Accordingly, the present invention provides a combined technology event detection device for detecting the presence of an object within a protected space, said device comprising range finding means for determining the range of the object from said device, sensor means for producing an output signal related to at least one physical attribute of the object, and a comparator means for comparing the output signal from the sensing means with a threshold level, said threshold level being determined by said range.

The present invention advantageously is based on the appreciation that in order to discriminate correctly between the four factors affecting signal amplitude of a PIR sensor the absolute target range must also be known

The combined technology event detection device is preferably an intrusion detection device, and may incorporate combinations of any known technologies providing the capability of independent range finding and movement detection.

Iή a preferred aspect of the Invention, the range finding sensing means comprises at least one laser oscillator and at least one light receiver for detecting reflected laser light from objects within the protected space. Whilst it may be possible to use one or more lasers transmitting a continuous laser beam, it is preferred to use one or more lasers provided with pulse energisation means for causing the laser or lasers to emit periodically a burst of laser light.

JP 07160956-A, entitled "Intrusion Supervisory Equipment" discloses intrusion supervisory equipment in which an intrusion object is sensed by detecting a reflected wave of a laser beam emitted from a laser oscillator, the detection using a light receiving element. The distance to the intrusion object is determined from the elapsed time between the emission of a laser pulse and its subsequent detection. The ranging device disclosed in JP 07160956-A is suitable for realising an embodiment of the present invention. The entire contents of JP 07160956-A are incorporated herein by reference for all purposes.

A single laser pulse transmitter can be used to estimate the range of an object, for example, by measuring the time lag between transmission and reception of the laser pulse.

The sensor means is preferably a passive infra-red sensor. Such devices respond to body temperature and are capable of detecting movement and/or incident radiation from a body, the amplitude of the signal produced being proportional to body size, range, and relative temperature. Therefore, the physical attribute detected by the sensor means is preferably radiation emanating from the body of the object with the protected space. Alternatively, if a microwave motion detector where utilised as the sensor means, the physical attribute would relate to the actual size of the detected object as the amplitude of the reflected signal would be dependent upon that size. Still further, the physical attribute may relate to the speed of motion of the object.

It can be seen, therefore, that by combining a sensing means or range finding means having range measuring capability with a passive infra-red sensor device it is possible for the event detection device to estimate both the actual size and temperature, or other physical attribute, of an object, which may be moving or stationary, and its distance from the detection device.

In a preferred embodiment of an event detection device according to the invention, there is provided a pulsed laser light sensing means and a passive infra-red sensing means. Larger combinations of three or more sensing means can, of course, be used If desired or appropriate, and sensing means using other suitable technologies, either active or passive, can also be used if desired.

The output signals from the independent range finding and movement measuring means are fed into a comparator means pre-programmed with a pre-set body size threshold level. Information concerning the range and apparent size of the detected moving object within the protected space is then used by the comparator to determine the actual size of the object, which calculated figure is then compared with the pre-set threshold level. If the threshold level is exceeded, the comparator sends an alarm signal to a warning device, which can be, for example, a siren, or a warning lamp in a control centre.

The event detection device of the invention can also comprise a fault monitoring system in accordance with international patent application number W095/28692, entitled "Fault monitoring event detection device", or an anti-masking system in accordance with UK patent application number GB9526004.8, entitled "Antimasking System", the entire disclosures of which are incorporated herein by reference for all purposes.

Description of drawings

An embodiment of an event detection device according to the invention will now be more particularly described, by way of example only, with reference to the accompanying Drawings in which:

Figures 1 and 2 illustrate diagrammatically the operation of a passive infra red sensor; Figure 3 is a plot of the amplifier output signal from the passive infra red sensor of Figures 1 and 2;

Figure 4 illustrates diagrammatically the operation of a combined PIR sensor and pulsed laser transmitter and receiver in accordance with an embodiment of the invention;

Figure 5 shows schematically the variation in the output of the PIR sensor with the range of a detected object;

Figure 6 illustrates schematically the determination of an appropriate threshold detection level for the PIR output using the range of a detected object.

Referring firstly to Figures 1 to 3, the PIR sensor illustrated generally at 1 comprises an infra red lens array or mirror optic system 2, a pyroelectric (thermal) sensor 3 and an amplifier 4.

The lens array divides the protected space 5 into sectors, and as an intruder passes from one sector to the next the electrical output from the pyroelectric sensor 3 passes to the amplifier 4. If either the positive and negative trip thresholds 6 of the amplifier are exceeded, as shown in Figure 3, a signal is passed to the relay 7 which opens to indicate an alarm condition. Referring now to Figure -4, the device 10 comprises a laser range finder 11 comprising, for example, a pulsed laser transmitter and receiver which transmit and receive pulsed laser light and reflected pulses respectively from a moving object in the protected space. Signals from the pulsed laser transmitter and receiver are utilised to determine the range of the object from the device 10. The range of the detected object is output as a signal 12.

The passive infra-red sensor 13, arranged as a movement sensor or otherwise, or a suitable movement detector (such as a microwave Doppler shift detector) detects the presence of a moving object and the output signal 14 of the thermal detector of the passive infra¬ red sensor 13 is fed into an amplifier 15 which amplifies the output signal 14. The amplified output signal is then fed to a comparator means 16.

The output signal 12 of the range finder is used to determine an appropriate threshold level against which the amplified output signal of the passive infra-red device 13 can be compared. Typically, the output signal of the range finder is used to address or select one of a plurality of possible threshold levels. Each threshold level relates to the expected output level of an object to be detected at a corresponding range. Alternatively, the appropriate threshold value may be calculated in a suitable manner.

If the size of the detected object exceeds a preset level corresponding to a moving human target, an alarm signal 17 is output from the comparator 16 indicating that the alarm should be activated. The alarm signal is utilised to produce a suitable alarm output 18, for example, to activate a siren, security lights or to produce an alarm indication on the monitor of a computer.

Referring to figure 5, there is shown schematically an indication of the variation in the amplitude of the output signal 14 from the passive infra-red detector 13 with the range of an object, for example, a human being, from the passive infra-red sensor 13. It will be appreciated a smaller output signal 14 will result from a human being which is remote from the detector 13 as compared to the output signal resulting from a human being being at a closer distance to the detector system.

Figure 6 shows schematically a variation with range of threshold levels which correspond to the anticipated output of the passive infra-red sensor 13 when an object, for example, a human being, of a predetermined size is within the field of view of the passive infra-red sensor 13. Although the above embodiment utilised as a sensor means for producing an output signal related to at least one physical attribute of the object a passive infra-red sensor and the physical attribute detected is heat radiating from the object, the present invention is not limited thereto. Embodiments can be realised in which a microwave detector is used and the threshold level relates to the amplitude of the microwave signal reflected from the object, that amplitude being related to the size of the detected object.

Although the above embodiment utilises a laser based device for determining the distance to an intrusion object, the present invention is not limited thereto and embodiment could equally well be realised in which the distance to an intrusion object utilises a microwave transmitter and detector. The distance to the object would then be determined from either the elapsed time between transmission of a microwave signal and reception thereof or from a comparison of the phase difference between the transmitted and received microwave signals.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLΔIMfi

1. A combined technology event detection device for detecting the presence of an object within a protected space, said device comprising range finding means for determining the range of the object from said device, sensor means for producing an output signal related to at least one physical attribute of the object, and a comparator means for comparing the output signal from the sensing means with a threshold level, said threshold level being determined by said range.

2. A device according to Claim 1, that comprises an intrusion detection device.

3. A device according to Claim 1 or 2, in which the range finding means comprises at least one laser transmitter, and at least one laser receiver for detecting laser light reflected from the object.

4. A device according to Claim 3, wherein said at least one laser transmitter comprises pulse energisation means for causing the transmitter to emit, preferably periodically, pulsed laser light.

5. A device according to any of the preceding Claims, in which the sensor means comprises a passive infra¬ red sensor or a microwave doppler effect device.

6. A device according to any of the preceding Claims, in which output signal and the range are used by the comparator means to calculate a value which is representative of the actual size of the object, said value then being compared with a selectable one of a plurality of pre-set body size threshold levels.

7. A device according to any preceding claim, wherein the sensor means comprises a movement detector.

8. A device as claimed in any preceding claims, wherein said at least one physical attribute is at least one of either size, temperature or motion of said object.

9. A event detection device substantially as hereinbefore described with reference to and/or as illustrated in the accompanying Drawings.

10. An event detection device substantially as hereinbefore described.