EP0476397A1 - Intrusion detector - Google Patents

Abstract

In a combined infrared/ultrasonic intrusion detector, which simultaneously detects the body radiation and the movement of an intruder in order to raise the alarm, an attempt to render the infrared part of the detector ineffective by mounting a radiation screen in front of the radiation entry window (9) is detected by providing to the side of the window (9) an ultrasonic emitter (10) and an ultrasonic receiver (11), by means of which an ultrasound field is built up in front of the window (9). An interference signal is triggered in the event of a change in sound pressure or sound propagation time. This also makes it possible to recognise screens which are transparent to other radiations, for example light or microwaves, and cannot be detected therewith. In order to prevent the mounting of a screen such as a foil or spray layer directly on the window (9), the window (9) is mounted in a recess (8) on the front side (7) of the housing (1) and covered approximately in the plane of the front side (7) with a cover (14) which has very fine openings and is transparent both to ultrasound and to infrared radiation. An ultrasonic component (10) is located inside the recess (8), while another ultrasonic component (11) is located outside thereof, so that the cover (14) is transirradiated by ultrasound and it is possible to recognise a change in the permeability of the cover (14). <IMAGE>

Description

The invention relates to an intrusion detector according to the preamble of patent claim 1.

Such intrusion detectors are known for example from DE-A-22'16'236. They consist of a combination of a passive infrared detector and an ultrasonic detector, which are connected to one another in an AND circuit. The infrared part reacts to the body radiation of a person in the infrared spectral range and the ultrasound part to the frequency shift of the ultrasound reflected by a moving intruder caused by the Doppler effect. By combining both principles, an unwanted intrusion of a person into a protected area can be detected with greater security and selectivity than by using only a single detection method. In this way, faulty alarm signaling can be avoided with greater certainty.

Passive infrared intrusion detectors are known for example from EP-A1-0'189'536. They are used to detect an object that has entered a monitored area, e.g. to detect an intruder by means of the infrared radiation emitted by the intruder and to trigger an alarm signal via an evaluation circuit. In this case, a corresponding number of spatially distributed sensitivity areas is formed by a number of reflector or mirror segments, via which the incoming radiation is directed to the sensor, and when penetrated by an intruder, a radiation change of the sensor and thus an alarm signal is generated. The sensor can have a single sensor element, or it can be designed as a multiple or dual sensor with two or more separate sensor elements or flakes, whereby the number of sensitivity ranges is at least doubled.

To protect the sensor and the optical reflectors from damage and dust, as well as to camouflage the detector, the housing of the detector is closed in the direction of radiation by a window which is open to the infrared radiation to be detected, e.g. is transparent to the body radiation of a person in the range from about 5 to 15 μm, preferably between 7 to 12 μm, but is largely impermeable to shorter-wave radiation. This window can in turn be optically bundled, e.g. as a Fresnel lens, which generates the desired sensitivity ranges, so that mirror segments can be omitted if necessary.

On the other hand, ultrasonic intrusion detectors, e.g. known from CH-A-556'070 or EP-A1-0'158'022. These have an ultrasound emitter, which emits ultrasound with a frequency of over 20 kHz in the monitored area in front of the detector, and an ultrasound receiver, which records the ultrasound reflected from the room and feeds it to an evaluation circuit. While stationary objects only reflect ultrasound at the transmission frequency, a moving intruder causes a frequency shift according to the Doppler effect. The evaluation circuit triggers an alarm signal if this frequency shift corresponds to values which are typical for a moving person and if at the same time an infrared radiation is received which is characteristic of human intruders.

It is in the nature of things that intruders often try to disable such intrusion detectors. To do this, it would suffice to render only one of the two detection parts ineffective, since these are connected to one another by an AND circuit. To shut down the ultrasonic part, however, the entire detector would have to be covered, which would be immediately visible. Therefore, in order to outsmart the intrusion detector, an attempt is usually made to attach a radiation shield in front of the detector or on the window itself, which keeps the incident radiation away from the sensor. It is relatively easy to make such interventions almost invisible, since most transparent materials in the visible spectral range, such as glass, household foils, hair lacquer spray, transparent protective lacquers, etc., absorb long-wave infrared radiation. For intrusion and intrusion protection systems for objects with high risks, it is therefore desirable to identify and signal such attempts to outsmart the individual detectors.

From EP-A1-0'189'536 or from GB-A-2'141'228 it is known that the transparency of the window for infrared radiation through an infrared radiation source attached to the outside of the housing and through the window onto the Sensor emits to monitor. If this radiation is absent or reduced, a fault is signaled. In this way, however, only a radiation-impermeable layer lying directly on the window can be recognized, but no objects shortly before or at a certain distance from the detector.

This disadvantage, as shown, for example, in US Pat. No. 4,752,768, can be eliminated by using a reflective light barrier with a reflector arranged remotely from the detector, with which the space between the detector and reflector is monitored for the application of radiation shields. The disadvantage here is that the reflector and detector must be precisely adjusted to each other, which makes the system complicated, expensive, difficult to assemble and prone to failure. In addition, only one can be used with an additional reflector Field of view to be monitored. In addition, shorter-wave radiation is used in such known systems for various reasons, so that only objects can be recognized which also absorb radiation in the short-wave infrared at about 0.9 μm.

In another, e.g. infrared intrusion detector known from EP-A2-0'274'889 is an infrared sensor combined with a microwave system in a logic circuit which only triggers an alarm signal if both systems simultaneously emit a signal. In this case, the infrared sensor is arranged between the microwave transmitter and receiver directly adjacent to it behind the entrance window. An attempt to cover the window or to apply a spray layer or to put a shield in front of the window can be detected by the microwave part. However, this can only be used to detect objects that reflect or absorb microwaves, i.e. preferably metallic conductive materials, but just not many foils or lacquers that are opaque to infrared radiation and often used for sabotage attempts.

The invention sets itself the task of eliminating the above-mentioned disadvantages of the prior art and, in particular, to provide a combined intrusion detector of the type specified at the outset which attempts to sabotage or reduce the functionality by means of shielding with greater security and with less effort and can signal.

This object is achieved by the features specified in the characterizing part of patent claim 1. Preferred embodiments of the invention and refinements are defined in the dependent claims.

Such a temporal change in the ultrasound field exists e.g. in a change in the sound pressure or the transit time of the ultrasound reflected by objects in the monitored room. As soon as such a measured variable has changed compared to an earlier point in time or to an average from previous measurements, this is an indication that a change has been made in the room, e.g. a shield has been placed in the room. Such a temporal parameter change of the sound field can easily be processed separately from the Doppler frequency evaluation.

Here, the so far apparently not recognized or considered analogy of far infrared in the frequency range of human body radiation and the ultrasound adjacent to the listening area is exploited with regard to their propagation, in particular the fact that this ultrasound spreads almost freely in air, but from practically all solid surfaces is reflected or absorbed. In this way, ultrasound can also be used to detect shields which absorb radiation in the far infrared, but which are transparent to microwaves or light and to radiation in the neighboring infrared.

Ultrasound emitters and receivers are preferably arranged on different sides of the entrance window, so that the ultrasound field covers the window area. Instead, however, it can be advantageous to arrange the ultrasound emitter and receiver adjacent to the same window side and to guide the ultrasound over the window by means of reflectors which are arranged on one or different sides of the window.

The exit surface of the ultrasound emitter and the entrance surface of the ultrasound receiver are particularly advantageously arranged on both sides of a plane formed by the front wall of the housing at the location of the window, so that at least one acoustically effective area of the ultrasound components, e.g. Emitter, receiver or a reflector lies within the recess. It is of particular advantage here, for example in the plane of the front wall in front of the window, a cover provided with fine openings, which is at least largely transparent to infrared radiation and ultrasound, e.g. a fine-mesh grid or a perforated film to be provided and arranged in such a way that the front surfaces of the ultrasound emitter and receiver lie on different sides of the cover and the cover is thus irradiated by the generated ultrasound. This will result in an attempt at impermeability, e.g. by spraying, monitored.

Since the intrusion detector according to the invention has both an infrared part and an ultrasound part anyway, it can advantageously be supplemented by a temporal ultrasound field evaluation and an infrared window monitoring device which is known in principle, without significantly increased outlay, which optimizes tamper protection and reduces the susceptibility to false alarms.

The invention is explained in more detail using the exemplary embodiments shown in the figures.

• Figur 1 einen erfindungsgmäßen Intrusionsdetektor im Vertikalschnitt entlang der Symmetrieebene S-S (Figur 2),
• Figur 2 einen erfindungsgemäßen Intrusionsdetektor in Frontansicht,
• Figur 3a einen Horizontalschnitt entlang der Ebene A-A,
• Figur 3b einen Diagonalschnitt entlang der Ebene B-B und
• Figur 4 einen weiteren Intrusionsdetektor in Frontansicht.

Show it:

• 1 shows an intrusion detector according to the invention in vertical section along the plane of symmetry SS (FIG. 2),
• FIG. 2 a front view of an intrusion detector according to the invention,
• 3a shows a horizontal section along the plane AA,
• Figure 3b shows a diagonal section along the plane BB and
• Figure 4 shows another intrusion detector in front view.

The infrared intrusion detector shown in Figure 1 has a housing 1, preferably made of plastic. Arranged in the interior of the housing 1 is an infrared radiation in the evaluated spectral range from 5 to 15 μm, in particular from 7 to 12 μm, a highly reflective, preferably metal, mirror or reflector 2, which, for example, as in EP-A1-0'189 '536 or may be configured in a suitable manner as a segment mirror to form a number of spatial sensitivity areas. The part 3 adjoining the mirror segments at the top serves to shield electromagnetic fields from the circuit board 4 arranged in front of it with the components of the evaluation circuit mounted thereon. This is set up in such a way that an irradiation change of the sensor generated by movement of an intruder through a sensitivity range, i.e. upon a predetermined change in the infrared radiation impinging on the sensor, triggers an output signal. The infrared sensor 5 is attached to the lower part of the circuit board 4 and is designed, for example, as a pyroelectric sensor and is sensitive to human body radiation at least in the spectral range. This sensor 5 can have a single radiation-sensitive element or can be designed as a multiple or dual sensor with at least two adjacent sensor elements. In front of the circuit board 4 there is another electromagnetic shield 6, e.g. from a suitable metallic sheet.

On the front wall of the housing 1, an entry window 9 is provided in a recess 8, through which infrared radiation incident on the detector can pass and can reach the sensor 5 via the reflector 2. In order to keep interference radiation of other wavelengths away from the sensor 5, the window 9 is made of a material which is preferably for human body radiation, i.e. is transparent in the wavelength range from 5 to 15 µm, in particular 7 to 12 µm, e.g. made of a suitable plastic such as polyethylene, special glass or silicon. In addition, the window protects the inside of the detector, in particular the optical reflectors 2 and the sensor 5, from damage and dust. The window can also be designed as an optically active element, e.g. as a Fresnel lens, to participate in the beam bundling and the creation of separate sensitivity areas.

In order to prevent the detector from becoming ineffective by attaching a radiation-absorbing shield in front of the detector housing, which shields incoming infrared radiation from the entrance window 9, the detector is equipped with a device for detecting and signaling such a function-reducing shield.

As shown in FIG. 2, this consists of an ultrasound emitter 10 provided on one side of the radiation entry window 9 and an ultrasound receiver 11 located on the opposite side of the window 9. The emitter 10 emits ultrasound in the frequency range somewhat above the hearing range, for example in the frequency range around 25 kHz. Immediately in front of the window 9 and in the entire area in front of the detector, an ultrasound field US1 is formed, which changes when a sound-shielding wall is installed in front of the detector. The receiver 11 is connected to a suitable evaluation circuit which triggers a fault signal when the ultrasound registered by the receiver 11 changes in a predetermined manner, as is characteristic for the application of a shield in front of the detector. In particular, the intensity of the ultrasound received and its time course are compared with the measurement results obtained at an earlier point in time or mean values formed from earlier measurements, and deviations are determined which are typical for changes in the monitored space in front of the detector.

Since an ultrasound field in the frequency range mentioned is influenced by practically all solid interfaces, i.e. all surfaces, but spreads almost unhindered in air, ultrasound is also used to detect and report shielding materials that absorb radiation in the far infrared, but for light and microwaves are practically permeable, which was previously not possible with infrared intrusion detectors with tamper protection devices working on infrared or microwave basis.

Since the intrusion detector contains an ultrasound device anyway, this can be used with surprising advantages and without any special additional effort for function monitoring of the infrared part of the intrusion detector. All that is required is to arrange the ultrasound emitters 10, 12 on the front side 7 of the housing, as shown in FIGS. 2 and 3a, so that the ultrasound emitted into the space in front of the detector forms an ultrasound field in front of the infrared window 9. The evaluation circuit is to be designed in such a way that it triggers an alarm signal when the ultrasound reflected from a moving object shows a predetermined frequency shift in accordance with the speed of movement of the object and at the same time the infrared part emits an output signal and a fault signal when the received ultrasound detects a certain change compared to earlier times. The circuit required for this can be effortlessly and without great effort integrate into the existing evaluation circuit.

Although the device described is capable of determining an infrared shielding in front of the detector over a large distance range with great certainty, a shielding applied directly to the window 9 cannot be detected easily. In order to make such an attempt at sabotage more difficult, the entrance window 9 is installed in a recess 8 in the front wall 7 of the housing, which hinders the application of a suitable shielding film. The window could still be reached with a spray. To protect against such an experiment, it is advantageous to provide a cover 14 provided with fine openings, for example in the plane of the front wall 7 of the housing 1 in front of the window 9, which cover is at least largely transparent to ultrasound and infrared radiation. This can e.g. be a fine-meshed grid, such as that used to protect screens or as an insect screen, or a film with fine holes, e.g. made of polyethylene. The openings should have a size at most in the range of tenths of a millimeter, so that they are closed by spraying and the cover thereby becomes impermeable. If, as shown in FIG. 3b, the sound exit surface of the ultrasound emitter 10 is located inside the recess 8 behind the cover 14, but the surface of the receiver 11 on the front side 7 outside the cover 14, the ultrasound normally penetrates the cover 14 through the openings. However, it is blocked by sprayed paint when the openings are closed, so that an attempt at sabotage is recognized and reported here too.

In order to achieve even greater security, as can be seen in FIG. 2, an infrared radiation source 15 can be provided in the shoulder of the depression 8, said infrared radiation illuminating the sensor 5 through the window 9 via an optical reflector 16. If this radiation is absent or reduced, an interference signal is generated in a manner known per se.

Different variants of the described exemplary embodiments are possible without leaving the scope of the inventive concept. Although two ultrasound emitters and receivers can each be provided, however, as shown in FIG. 4, only a single ultrasound emitter 17 and a receiver 18 can be attached to the same side of the window 9. The ultrasound is here from the emitter 17 via one or more acoustic reflectors 19, e.g. Sheet metal strips, fed through the window 9 to the receiver 9.

It is advantageous to switch the ultrasound receiver 11, 18 in such a way that it detects the occurrence of frequencies shifted according to the Doppler effect alternately in normal operation during certain room monitoring phases, for example of several seconds, in between during the periodic control phases of some However, the test is carried out by means of short ultrasound pulses or modulations of the ultrasound transmitters 10, 12, 17 for a tenth of a second, with striking changes in the sound field compared to previous control phases being regarded as signs of an attempted sabotage.

It is even possible to use only a single ultrasonic emitter / receiver element. The element periodically alternately emits short control pulses and is immediately switched to normal reception mode. On the opposite side of the window, acoustic reflectors ensure that, in the undisturbed case, a well-known echo pulse returns to the receiver, but changes in amplitude and in time with every change due to changed reflections in the space in front of the detector.

Reference numerals

• 1 Reflektor (Spiegel)
• 2 Teil (an Spiegel anschließend)
• 3 Schaltungsplatine
• 4 Infrarotsensor
• 5 (Elektromagnetische) Abschirmung
• 6 Vorderwand
• 7 Vertiefung
• 8 Eintrittsfenster
• 9 Ultraschall-Emitter
• 10 Ultraschall-Empfänger
• 11 Ultraschall-Emitter
• 12 Abdeckung
• 14 Infrarotstrahlungsquelle
• 15 (Optischer) Reflektor
• 16 Ultraschall-Emitter
• 17 Ultraschall-Empfänger
• 18 (Akustischer) Reflektor
• 19

(not part of the description) Housing

• 1 reflector (mirror)
• 2 parts (after mirror)
• 3 circuit board
• 4 infrared sensor
• 5 (electromagnetic) shielding
• 6 front wall
• 7 deepening
• 8 entry windows
• 9 ultrasonic emitters
• 10 ultrasound receivers
• 11 ultrasonic emitters
• 12 cover
• 14 infrared radiation source
• 15 (Optical) reflector
• 16 ultrasonic emitters
• 17 ultrasound receivers
• 18 (acoustic) reflector
• 19th

Claims (10)

1. Intrusion detector with a sensor (5) sensitive to infrared radiation, to which radiation from at least one spatial sensitivity range is incident, with at least one ultrasound emitter (10, 12, 17) and at least one ultrasound receiver (11, 18) and with one Evaluation circuit (4) for alarm signaling with a simultaneous predetermined change in the infrared radiation incident on the sensor (5) and a predetermined change in the ultrasound received by the ultrasound receiver (11, 18), characterized in that the detector has a housing (1) with a Has entry window (9), which is mounted in a recess (8) of the housing (1), that the ultrasound emitter (10, 12, 17) and ultrasound receiver (11, 18) are arranged on the side of the window (9) that an ultrasonic field is formed in front of the window (9) and that the evaluation circuit (4) is designed such that it changes at a predetermined change in time of the ul trasallfelds triggers an interference signal. 2. Intrusion detector according to claim 1, characterized in that the ultrasonic emitter (10) and the ultrasonic receiver (11) are arranged on opposite sides of the window (9). 3. Intrusion detector according to claim 1, characterized in that the ultrasonic emitter (17) and the ultrasonic receiver (18) are arranged on the same side of the window (9) and that at least one acoustic reflector (19) on the other side of the Window (9) is provided to guide the ultrasound from the ultrasound emitter (17) to the ultrasound receiver. 4. Intrusion detector according to claim 3, characterized in that the ultrasonic receiver (18) serves simultaneously as an ultrasonic emitter and is periodically switched alternately as an ultrasonic emitter and as an ultrasonic receiver. 5. Intrusion detector according to one of claims 1 to 3, characterized in that at least one of the emitter (10, 12, 17), receiver (11, 18) and reflector (19) existing ultrasonic components with its acoustically effective area within Indentation (8) lies behind the plane formed by the front wall (7) and at least one other ultrasound component with its acoustically active surface lies outside the indentation (8). 6. Intrusion detector according to claim 5, characterized in that in front of the window (9) approximately in the plane of the front wall (7) is provided with a fine openings at least largely permeable to ultrasound and infrared radiation cover (14). 7. Intrusion detector according to claim 6, characterized in that the size of the openings of the cover (14) is at most in the range of tenths of a millimeter. 8. Intrusion detector according to one of the claims 1 to 7, characterized in that the evaluation circuit (4), with which the ultrasonic emitter (10, 12, 17) and the ultrasonic receiver (11, 17) are connected, at a predetermined change in Sound pressure and / or triggers a fault signal in the event of a predetermined change in the transit time of the ultrasound compared to an earlier point in time. 9. Intrusion detector according to one of claims 1 to 8, characterized in that the evaluation circuit (4) is set up to periodically alternately evaluate a frequency shift of the received reflected ultrasound and a temporal change in the amplitude and / or the time profile of the received reflected ultrasound for signaling. 10. Intrusion detector according to one of claims 1 to 9, characterized in that an infrared radiation source (15) is provided in front of the entrance window (9), which radiates through the window (9) through to the infrared sensor (15).

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