EP0499177A1

EP0499177A1 - Anti-intrusion device

Info

Publication number: EP0499177A1
Application number: EP92102193A
Authority: EP
Inventors: Tommaso Pagoto; Carlo Zelferino
Original assignee: Bitron Video SRL
Current assignee: Bitron Video SRL
Priority date: 1991-02-11
Filing date: 1992-02-10
Publication date: 1992-08-19
Also published as: ITTO910082A1; IT1245405B; ITTO910082A0

Abstract

The device comprises a container having a window (106) that allows for the entrance of infrared radiation (108) coming from an eventual intruder, an infrared radiation focusing system on a first infrared detecting element (107), an electronic circuit that receives the signal from the infrared detecting element and processes the value with the aim of detecting an intruder and means for assuring that the device not be put out of use, by means of a masking (110) of the window (106), comprising a source (103) of sample signals situated in the infrared field, but presenting different wave lengths from those typically emitted from the human body, and means that analyse the value of the sample signals with the aims of detecting a variation in their measured value so as to point out any eventual attempts of covering the window.

The principle characteristic of the anti-intrusion device consists in the fact that said means for analysing the sample signals comprise a second infrared detecting element (109), apt of detecting variations of said sample signals (103), due to attempts of tampering with the device by masking said window and that the source of said sample signals and the second detecting element are positioned one inside the other outside of said container and interact through the window.

Description

The present invention relates to an anti-intrusion device comprising a container having a window that allows for the entrance of infrared radiation coming from the surroundings and/or an eventual intruder, an infrared radiation focusing system on a first infrared detecting element, an electronic circuit that receives the signal from the infrared detecting element and processes the value with the aims of establishing whether the infrared radiation received is that naturally produced by the surroundings being supervised or whether it is due to the presence of an intruder and in such a case provides for an intrusion alarm signal to be generated and means for assuring that the device not be put out of use, by means of a masking of the window, comprising a source of sample signals situated in the infrared field, but presenting different wave lengths from those typically emitted from the human body, and means that analyse the value of the sample signals with the aims of detecting a variation in their measured value so as to point out any eventual attempts of covering the window.
Devices of the type mentioned above, are known and frequently utilised for the surveillance of premises such as industrial warehouses, stores, commercial premises, domestic houses etc. These systems however can be put out of use, eventually even by personnel authorised to enter the area under surveillance; this would necessarily take place during the period in which the system has been put on hold, given that in said period, due to the characteristics of the premises, it must be possible for people to enter the controlled area and therefore the system must not initiate the alarm condition even if it detects infrared rays of the type emitted from the human body.
The techniques commonly used for this aim by certain criminals consist in tampering with one or more peripheral devices, masking the infrared radiation entrance by spraying material being opaque for the infrared rays and moreover transparent upon first inspection; spray paints of this type are easily found in commerce, even certain types of hair spray suffice in carrying out such blame worthy function.
In avoiding such inconveniences various solutions are known.
That mentioned in US patent N°4.242.669 provides for the utilisation within each of the peripheral devices of a guard signal generator having a wave length different from that monitored that has the task of surveilling the area under control. Such a generator emits an outward signal through the window provided for in the container and the peripheral device further provides for a second sensor element, placed inside the container and sensitive to said signal, that detects an increase of the signal received and considers this to be a valid indication of an attempt to mask the window.
A second solution, noted in US patent 4.709.153, consists in providing for a signal source having a wave length different from that used for surveilling the area under control, externally mounted with regards the casing containing the infrared sensor and is oriented in such a way so as to irradiate towards the inside of itself, through the window, a control signal, that detected from the self same infrared sensor, reports in the case of a variations with respect the guard value, the attempt of tampering.
All these known solutions however present inconveniences.
The first solution results in not being perfectly functional in all practical conditions, as the window could be made opaque with the use of paint or other radiation absorbing material in such a way that the guard signal would not be reflected and therefore the system would be insensitive to such types of masking; furthermore it results in being difficult to put into operation due to the critical assembly and presenting a low level of reliability in the course of time, due to the very fact of its delicate setting.
The second solution, mentioned above, presents the serious disadvantage of not being able to be utilised with the normal pyrometric capsules that incorporate the infrared sensors (those that generally cover the false alarms), in as much that the signal coming from the external generator would reach with equal intensity on both the sensors and would therefore generate in every case a null signal, even if it receives a varied signal, with respects the guard signal, due to an attempt of tampering.
It is also to be mentioned that due to the common use of remote control devices, for commanding appliances such as televisions, video recorders, sound reproducing systems, and also remote control devices for the opening of doors and similar, this having added to the problems of the constructors of anti-intrusion devices. In fact alarm systems for attempted masking of the intrusion sensor element must not react upon receiving infrared radiation signals from such devices, while they must generate an alarm signal if such elements are used in attempting to blind the anti-intrusion device.
The invention is based on the acknowledgement of these facts. The aims therefore of the present invention is that of obtaining an anti-intrusion device that avoids the above mentioned inconveniences and in particular allows for obtaining an efficient realisation, reliable in all working conditions and being of low costs.
Therefore in allowing such aims the present invention relates to an anti-intrusion device comprising a container having a window that allows for the entrance of infrared radiation coming from the surroundings and/or an eventual intruder, an infrared radiation focusing system on a first infrared detecting element, an electronic circuit that receives the signal from the infrared detecting element and processes the value with the aims of establishing whether the infrared radiation received is that naturally produced by the surroundings being supervised or whether it is due to the presence of an intruder and in such a case provides for an intrusion alarm signal to be generated and means for assuring that the device not be put out of use, by means of a masking of the window, comprising a source of sample signals situated in the infrared field, but having different wave lengths from those typically emitted from the human body, and means that analyse the value of the sample signals with the aims of detecting a variation in their measured value so as to point out any eventual attempts of covering the window.
The principle characteristic of the anti-intrusion device consists in the fact that said means for analysing the sample signals comprise a second infrared detecting element, apt of detecting variations of said sample signals, due to attempts of tampering with the device by masking said window and that the source of said sample signals and the second detecting element are positioned one inside the other outside of said container and interact through the window.
Further aims and advantages of the present invention will become clear from the following detailed description and annexed drawings, supplied as a non-limiting example, wherein:

figure 1 represents a sectioned side view of the container and several elements constituting an anti-intrusion device according to the details of the present invention;
figure 2 represents the block diagram of the electronic circuit, regarding the masking prevention function contained internally of an anti-intrusion device according to the details of the present invention.

Figure 1 only shows the components having important characteristics from the point of view of their being positioned inside the device, while the remaining parts containing the electronic circuit are not evidenced. In figure 1 101 indicates a container, normally a moulded plastic box, that has the task of housing the components of the peripheral surveillance device against intrusions and tampering with the same. The container 101 presents an almost rectangular lateral section with a superior projection 102, taking the form of a console apt of housing an infrared radiation transmitter element 103. The container 101 also has a rectangular cavity section 104, that is closed in line with the anterior wall 105 of the container with a focusing element of the external infrared radiation, constituted by a Fresnel lens; the window and the lens that close it are indicated with the reference number 106. In this way the infrared radiation coming from outside, through the window 106, can reach a infrared radiation sensor 107, positioned on the opposite side of the lens 106 and from the latter be focused on the same sensor 107.
The infrared radiation focusing system is realised according to known techniques in such a way to comprise a visual field as large as possible. The lines 108 indicate in a schematic way the visual field covered by the sensor 107. The latter may be of a pyroelectric type, as those usually used for such applications, for instance those that contain in the same capsule two adjacent sensors.
With the reference number 109 a second infrared radiation sensor is indicated, for example a photo diode, positioned in such a way so as to receive, through the window 106, the infrared signal emitted from the transmitter 103. The form of the window 106 is realised in such a way so as to allow the second sensor 109 to receive the infrared signal emitted from the transmitter 103. Naturally the wave length of the infrared radiation emitted by the transmitter 103 is chosen in such a way as to not interfere with the signals that lie in the infrared field normally emitted from the human body. Reference 111 indicates the course that the infrared radiation normally carries out to directly arrive from the transmitter 103 to the sensor 109, that works as a receiver of the sample signals generated by the transmitter 103.
Reference 112 however indicates the course that the infrared radiation carries out to arrive from the transmitter 103 to the sensor 109, in case of placing a screen 110 between peripheral surveillance device against intrusions 101 and the area that has to be placed under surveillance.
The functioning of the described device is the following.
The sensor 107 is the normal infrared radiation sensor, that through the focusing system constituted by the Fresnel lens 106, detects the human presence within its visual field, starting from the radiation emitted by the human body, being typically that of a wave length of around 10 micron. Naturally downstream from the sensor 107 there is an electronic circuit (not represented in the figure) that works according to the known art and is able to discriminate real states of alarm from false alarms.
The transmitter 103 and the second sensor 109 assure protection against attempts of tampering with the device, followed by the masking in some way of the infrared radiation that reaches the window 106 and from here to the intrusion sensor 107.
In fact the electronic circuit that manages this anti-masking function and that will be explained in more detail in reference to figure 2, provides to monitor the sample signal emitted by the transmitter 103 and to compare it with a reference value. If the value of the sample signal received by the sensor 109, through the window 106 (which is the same through which the radiation coming from outside relating to the presence of eventual intruders passes), removed from a range or band of values granted, be it higher, or be it lower, the electronic circuit provides for the generating of an alarm signal due to attempted tampering.
The fact that the electronic circuit considers that there has been an attempt of tampering when the sample signal exceeds or is below a group of pre-determined values, replies to different methods of possible attempts of blinding the anti-intrusion device. In fact if the tampering has been attempted by placing a screen 110 in front of the device, consequently the reflection of the sample signal (as indicated with the course 112) adds to the direct reception (course indicated with 111) thus causing an increase of the sample signal received; if however the tampering has taken place, spraying the lens 106 with the aims of rendering it opaque to the external radiation, then the sample signal received by the sensor 109 falls below the threshold level permitted and the electronic circuit in this case also signals an alarm condition.
It is also to be noted that the device according to the invention arranged with a pair transmitter elements - autonomous sensors, with respect the sensor used for the anti-intrusion surveillance and dedicated exclusively for anti-masking, and as their mutual positioning does not have bonds with the remaining parts of the device, as demonstrated in figure 1 it is possible to arrange the two elements in the best position for the surveillance of the visual field where attempts of masking could take place, a visual field that never coincides with that of the sensor used for anti-intrusion. In fact the masking takes place in proximity of the surveillance device, while the intrusion usually takes place in a secluded area with respect the device, that is often placed in a high and dominant position.
Figure 2, as previously mentioned regards the electronic part relative to the alarm generating system, in the case of attempts of masking the intrusion sensor element. The remaining electronic part of the circuit contained inside the anti-intrusion device is not shown in figure 2 as it refers to a known circuit operating in a conventional way.
Therefore figure 2, with the reference number 1 indicates an infrared radiation transmitting element (corresponding to 103 in figure 1), typically an infrared LED diode that emits a radiation presenting a wave length of approximately 0,95 m, that transmits pulses, piloted by a circuit generator 2 of synchronising pulses. Such a generator 2, also supplies the signal to a delay circuit 3, which after having introduced a delay to the signal of a pre-determined value, sends it to a timing circuit 4, that acts on the form of the received wave modifying the duty cycle.
At the output B the negative signal is present with respect the signal present at the output A; i.e. a signal presenting a complementary duty-cycle with respect to that presented by the signal available at the output terminal A.
The electronic circuit of figure 2 also comprises a infrared radiation receiving element 6 (for instance a photodiode) apt at receiving the radiation emitted by the transmitter 1. The receiver 6 (corresponding to reference 109 in figure 1) supplies its output signal to two amplification stages containing high-pass filters, indicated with the reference numbers 7 and 8. The signals present at the output of the amplifying circuit 8 together with those present at output A of the timing circuit 4, are fed to the input terminals of a synchronous discriminator circuit 5, that has the task of giving as an output a signal in proportion to the pulse signal periodically emitted by the transmiting element 1 and picked up by the receiving element 6. The analysis of the signal received by the receiver 6 only takes place in those periods of time corresponding to the transmission pulses, timed by the circuit generator of synchronising pulses 2 and it is for this reason that the synchrone discriminator 5 receives the signal coming from the output A of the timing circuit 4. With this in mind it is to be noted that the delay introduced to the signal coming from the circuit generator of synchronising pulses 2, obtained through the delay circuit 3, serves in compensating the propagation delays of the signal transmitted by the element 1, with respect the signal received by the element 6.
The outputting signal from the synchronous discriminator 5, is therefore fed to a compensation circuit 9 of the received signal with respect the slow variations of the infrared radiation of the surroundings picked up by the receiving element 6. The compensation circuit 9 can favourably include a window comparator circuit, i.e. a circuit that works on the principle of commutating the signal present at the output, only when the input signal is not within two pre-determined threshold levels (such comparator can be obtained by a circuit utilising a double differential amplifier).
The outputting signal from the compensation circuit 9 is then sent to a masking comparator circuit 10 of the anti-intrusion device and from this to a masking alarm timing circuit 11 and finally to a relay 12 that produces the alarm signal upon attempts of masking.
The electronic circuit of figure 2 also comprises a spurious radiation detection circuit 13 that receives at its first input C the signal produced by the receiver 6, through the two amplifying circuits 7 and 8, and at its second input D the outputting signal from the terminal B of the timing circuit 4. The outputting signal of the circuit 13 is then finally adopted to a second port of the comparator circuit 10.
The present device functions in the following way.
The impulsive signal generated by the generator circuit 2 is irradiated by the infrared radiation transmitter 1 and picked up by the receiver element 6, in accordance with the spaced disposition of the mentioned elements as has been explained in detail with reference to figure 1.
The infrared radiation detected by the receiver element 6, generates a signal that is amplified by the amplifiers 7 and 8, that present high-pass filters with frequency values appropriately calculated so as to select signals belonging only to the desired bands of frequency.
This signal is adopted by the synchronous discriminator 5 that values it only during the "active" periods, determined by the signal coming from the timing circuit 4. The signal outputting from the discriminator 5 is analysed by the compensation circuit 9 that works in an auto adapting manner, due to the fact that the window comparator varies the value of its threshold in consequence of the medium value of the signal produced by the synchronous discriminator 5. Therefore only if the signal produced by the synchronous discriminator exceeds the range of values granted by the window comparator, due to sudden variations of the signal detected by the receiver element 6, a signal of attempted masking is generated. However this signal is not always adequate, as, before activating the relay 12, it still has to pass the analysis operated by the masking comparator circuit 10.
In fact such circuit does not permit the outputting signal from circuit 9 to pass in the case that the threshold has been exceeded for a brief period of time in which the spurious radiation detector 13 has detected a great increase of external radiation, in relation to the surroundings. This is because the exceeding of the threshold could have been produced for a brief period by a source of infrared radiation that has been accidently picked up by the receiver 6; such sources of short duration infrared radiation could be caused by for example by a television remote control unit or a remote control device functioning by means of emitting signals in the infrared field.
The masking comparator circuit 10 however upon detecting the persistence of a signal that exceeds the pre-determined threshold (high or low), longer than a pre-determined length of time, for instance 2-3 seconds, allows the passing of the alarm signal, as in such a case it means that there is an attempt of obstructing the anti-intrusion device or by means of generating infrared radiation with an autonomous source (the use of an infrared remote control device), or by reflection (by placing a screen in front of the window), or finally because the emission of radiation by the transmitter element has been minimized (spraying of the lens). In each of these cases an alarm signal is generated, through the timer 11, producing the activation of the relay 12 that produces the alarm signal for the complete surveillance system.
From the description the advantages of the anti-intrusion device object of the present invention are clear: also to be mentioned is its reliability, its low cost and efficiency, that allows it to be put to good use in any practical conditions, avoiding the possibility of the anti-intrusion device being put out of use, during the period in which access is allowed of people in the surroundings under surveillance or the generation of false alarms caused by the emission of infrared radiation by domestic appliances.
It is clear that numerous variations are possible, by the man of the art, to the anti-intrusion device described as an example, without however departing from the novelty principles inherent in the present invention.
In particular, among the possibilities, the inversion of the position of the transmitter 103 with that of the second sensor-detector 109 or to operate there positioning in a manner different from that shown in figure 1 could be cited.

Claims

Anti-intrusion device comprising a container having a window that allows for the entrance of infrared radiation coming from the surroundings and/or an eventual intruder, an infrared radiation focusing system on a first infrared detecting element, an electronic circuit that receives the signal from the infrared detecting element and processes the value with the aims of establishing whether the infrared radiation received is that naturally produced by the surroundings being supervised or whether it is due to the presence of an intruder and in such a case provides for an intrusion alarm signal to be generated and means for assuring that the device not be put out of use, by means of a masking of the window, comprising a source of sample signals situated in the infrared field, but presenting different wave lengths from those typically emitted from the human body, and means that analyse the value of the sample signals with the aims of detecting a variation in their measured value so as to point out any eventual attempts of covering the window, characterised by the fact that said analysing means (3-13) of the sample signals comprise a second infrared radiation element (6), apt at detecting variations in said sample signals, due to attempts of tampering with the device (101) by masking of said window (106) and that the transmitter element (103) of said source of sample signals and the second detecting element (109) are positioned one inside the other externally of said container (101) and interact through the window (106).
Anti-intrusion device according to claim 1, characterised by the fact that said second detecting element (109) is positioned inside said container (101), while said transmitter element (103) of said source of sample signals is positioned on the external part of said container (101) in such a way that it can interact with the detecting element (109) through said window (106).
Anti-intrusion device according to claim 1, characterised by the fact that said second detecting element (109) is positioned outside said container (101), while said transmitter element (103) of said source of sample signals is positioned on the internal part of said container (101) in such a way that it can interact with the detecting element (109) through said window (106).
Anti-intrusion device according to claims 2 or 3, characterised by the fact that said container (101) has it superior projection (102) that supports said transmitter element (103) of said source of sample signals or the said second detecting element (109) and is arranged so as to permit an interaction between the transmitter element (103) of said source of sample signals and the second detecting element (109) through said window (106).
Anti-intrusion device according to claim 1, characterised by the fact that said infrared radiation focusing system is constituted by a Fresnel lens situated at the closure of said window (106).
Anti-intrusion device according to claim 4, characterised by the fact that said transmitter element (103) of said source of sample signals and said second detecting element (109) on one side and said first infrared detecting element (107) are arranged in such a way so as to cover two different visual fields.
Anti-intrusion device according to claim 1, characterised by the fact that said means for preventing that the device (101) be put out of use comprises a electronic circuit (1-13).
Anti-intrusion device according to claim 7, characterised by the fact that said electronic circuit (1-13) analyses the value of said sample signal and generates an alarm signal for attempted tampering when the measured value of the signal is superior or inferior to a pre-determined range of values.
Anti-intrusion device according to one or more of tile above claims, characterised by the fact that said transmitter element (103) of said source of sample signals and said second detecting element (109) work in an infrared radiation field different from that in which the infrared radiation typically emitted from the human body lies.
Anti-intrusion device according to claim , characterised by the fact that said electronic circuit (1-13) comprises a circuit generator of sample signals (2) that pilots said transmitter element (103; 1) and a timing circuit (4).
Anti-intrusion device according to claim 10, characterised by the fact that said electronic circuit (1-13) comprises a synchronous discriminator (5) that receives from one side the signal coming from said timing circuit (4) and from the other side the sample signals received by said detecting element (109; 6) and that before being sent to the synchronous discriminator circuit (5) they are manipulated by a high-pass amplifying circuit (7,8).
Anti-intrusion device according to claim 11, characterised by the fact that said electronic circuit (1-13) comprises a compensation circuit (9) of the external surroundings infrared radiation that receives the signal in output of said synchronous discriminator (5).
Anti-intrusion device according to claim 12, characterised by the fact that said compensation circuit (9) is of an auto-adaptive type with respect the slow variations of the external surroundings infrared radiation and comprises in particular a window comparator.
Anti-intrusion device according to claim 10, characterised by the fact that said electronic circuit (1-13) comprises a threshold detecting circuit (9,10,11) that when the value of the sample signal detected by said detecting element (109; 6) and coming from said synchronous discriminator (5) is superior or inferior to a range of pre-determined values generates an alarm signal for attempted tampering.
Anti-intrusion device according to claim 10, characterised by the fact that said said electronic circuit (1-13) comprises a delay circuit (3) that delays the signal coming from said sample signal generator (2) before supplying it to said discriminator circuit (5).
Anti-intrusion device according to claim 10, characterised by the fact that said sample signal generator (2) generates an pulsing signal, that provides for active periods and periods of pause.
Anti-intrusion device according to claim 16, characterised by the fact that said timing circuit (4) manipulates the signal coming from said sample signal generator (2) so as to vary the relationship between the active periods and the periods of pause of said ipulsing signal.
Anti-intrusion device according to claim 16, characterised by the fact that said electronic circuit (1-13) comprises a detecting circuit of external surroundings radiation (13) that analyses the radiation received during the periods of time substantially corresponding to the periods of pause of said generator (2) of pulsing sample signals.
Anti-intrusion device according to claim 18, characterised by the fact that said timing circuit (4) provides for a second output terminal (B) to the ends of which a negative signal is present having active periods and of pause, complementary to those present at its first output terminal (A) and that said negative signal is fed to a synchronising input (D) of said detecting circuit of external surroundings radiation (13), that receives at its signal port (C) the signal coming from said second detecting element (109; 6).
Anti-intrusion device according to claim 10, characterised by the fact that said electronic circuit (1-13) comprises a comparator circuit (10) that receives signals in output from said detecting circuit of external surroundings (13) and consequently based on the value of external surroundings radiation detected in the periods of time in which said sample signal is not transmitted, provides for varying the threshold of said detecting circuit (9, 10, 11).
Anti-intrusion device according to claim 20, characterised by the fact that said comparator circuit (10) in the case of sudden increases of the external surroundings radiation detected and that is protracted for more than a pre-determined period of time, considers such an increase as an attempt of tampering with the anti-intrusion device (101).
Anti-intrusion device according to one or more of the previous claims, characterised by the fact that means (11, 12) are provided for that once a condition of attempted tampering has been detected provide for generating an alarm signal.
Anti-intrusion device comprising a container having a window that allows for the entrance of infrared radiation coming from the surroundings and/or an eventual intruder, an infrared radiation focusing system on a first infrared detecting element, an electronic circuit that receives the signal from the infrared detecting element and processes the value with the aims of establishing whether the infrared radiation received is that naturally produced by the surroundings being supervised or whether it is due to the presence of an intruder and in such a case provides for an intrusion alarm signal to be generated and means for assuring that the device not be put out of use, by means of a masking of the window, comprising a source of sample signals situated in the infrared field, but presenting different wave lengths from those typically emitted from the human body, and means that analyse the value of the sample signals with the aims of detecting a variation in their measured value so as to point out any eventual attempts of covering the window, characterised by the fact that said means (1-13) for preventing that the device (101) be put out of use comprise electric circuits (6,7,8,13,4) that analyse the external surroundings radiation and consequently vary the threshold values to which the a sensor circuit (5,9,10) of attempted tampering of the device (101) reacts and in the case of a sudden increase of the external surroundings radiation detected and that protracts for more than a pre-determined period of time, considers such increase as an act of attempted tampering with the anti-intrusion device (101) and as a consequence generates an alarm signal.