GB2264378A - A frangible sensor for a secure enclosure - Google Patents

Abstract

A sensor for a secure enclosure comprises a substantially nonconductive substrate 17 bearing an elongate electrically continuous conductor 18 distributed over the area of the substrate in such a way that the path of the conductor is not determinable from a detection of a section 21, 22 of the conductor itself. The elongate conductor follows a sinuous path over the area of the substrate with each branch of the sinuous path further incorporating regular or irregular meandering path elements 21, 22. The sensor may be incorporated with the walls of a safe, strongbox or strong room, and is provided as an alarm circuit which responds to an interruption of the continuity of the conductor. The alarm may also respond to hammer attacks using microphones at detectors, Fig 4 (not shown). <IMAGE>

Description

A FRANGIBLE SENSOR FOR A SECURE ENCLOSURE The present invention relates generally to a sensor for a secure enclosure, and particularly to a frangible sensor for detecting attempts at forced entry into a secure enclosure.

The present invention finds application generally, but not exclusively, in connection with security systems for the strong-box, safe or other container housing items requiring protection from theft, and includes application in strongrooms or vaults where appropriate.

The vast majority of security systems for preventing or discouraging unwanted intrusions into a secure environment, particularly for preventing theft or burglary of items of value, largely rely on providing an alarm indication that the security of the container or housing has been breached. Such alarm indications may be audible, visual or remote (that is by communication along a land line or by radio transmission, to a monitoring station).

More recently security systems have been developed in which, in response to attempted forced entry, the security system triggers release of a contaminant which indelibly marks the contents to invalidate them or otherwise render them valueless. Such contaminants, including a contaminating smoke or dye, can also adhere to the skin or clothing of any person coming into contact with the material so that the criminal can be marked for subsequent identification.

In the continuing battle against crime new forms of detector for triggering security systems of all types are constantly being sought in order to keep ahead of the criminal's knowledge of means for disabling or disactivating known sensors.

The present invention is directed at the provision of a new form of sensor which will be extremely difficult to circumvent and which, therefore, may be expected to provide secure environments with a greater degree of protection against forced entry than has hithertofore been possible, and at a cost which is low in relation to the benefits to be obtained.

According to one aspect of the present invention, therefore, a sensor for a secure enclosure comprises a substantially non-conductive substrate bearing an elongate electrically continuous conductor distributed over the area of the substrate in such a way that the path of the conductor is not determinable from a detection of the length of the conductor itself.

Such a sensor, provided with a continuous conductor the integrity of which can be monitored by appropriate electronic detection equipment, can be made in a number of different ways. Its special advantage is that unlike conventional sensors, which are located at a particular point in or within the secure environment or enclosure, the sensor of the present invention may extend over a large area and, in particular, may be formed to enclose the whole of the secure environment.

In one embodiment of the invention the sensor is formed as a laminar panel (not necessarily flat since it may be shaped to follow the contours of the environment or enclosure it is to protect) and a plurality of panels may be joined together electrically and shaped so that their edges are substantially contiguous, so that the panels can be fitted within an enclosure to line the whole of the interior surface thereof.

The elongate conductor preferably follows a sinuous path over the area of the substrate, with each branch of the sinuous path further incorporating regular or irregular meandering path elements. The elongate conductor may, alternatively, follow a spiral path over the area of the substrate, and in this case each turn of the spiral may further include regular or irregular meandering or sinuous path elements. Other basic path forms may be employed. For example the elongate conductor may generally follow an involuted meandering path (often referred to as a greek key pattern) with each curved or rectilinear path element following a further, smaller scale, meandering or sinuous path.

If an attempt is made to penetrate the sensor this will inevitably result in an interruption to the continuity of the electrically continuous conductor and such a break in continuity can be detected by electronic means as will be described in more detail hereinbelow. Because the sinuous, spiral or involuted meandering path of the conductor has further smaller scale path variations juxtaposed on it, even if a criminal is able to expose or otherwise detect an elementary portion of the conductor, it will be impossible from the direction of the conductor to predict either for how long the conductor continues in the same direction, or the direction in which the conductor then turns.

If the sensor is formed as separate panels for attachment, for example, to the interior face of a safe or other secure enclosure, the substrate is preferably an insulating, supporting layer or member, although a substrate having insufficient strength to support the conductor, but which is attachable to a wall of an enclosure to provide such support may be used.

In appropriate circumstances the insulating substrate bearing the conductor may be embedded within a wall or sandwiched between two layers of which a wall is composed. The sensor then becomes incorporated into the structure it is intended to protect and is even more difficult to detect and/or circumvent, especially if the continuity detection apparatus is enclosed within the volume surrounded by the sensor (including a battery or other power supply) since it is impossible for a criminal to interfere with the detection equipment without first passing through the sensor, which will necessarily involve triggering the detector.

In order to be entirely certain that any attempt to pierce the sensor will result in an interruption to the continuity to the conductor, it is preferred that each elementary conductor portion (as hereindefined) is spaced from the nearest adjacent non-contiguous elementary conductor portion by a distance less than the width of the conductor itself.

The present invention also comprehends a detector for a secure enclosure, comprising a sensor as defined hereinabove, and means for detecting an interruption to the continuity of the elongate conductor of the sensor.

As used in this specification, the term "elementary portion" of an elongate electrical conductor, will be understood to refer to a portion of the conductor having a length (that is a dimension in the direction of the length of the conductor) not greater than the width of the conductor itself.

The means for detecting an interruption to the continuity of the elongate conductor may include a pulse generator for applying a recognisable repeating signal to the said elongate conductor.

The said means for detecting an interruption to the continuity of the elongate conductor may also include a latching trigger circuit operable to generate an output control signal. The control signal at the output of the latching trigger may typically be passed to a detector output stage operable, in response to the signal from the latching trigger circuit, to energise an alarm indicator or other alarm system. In particular it is envisaged that the output signal from the output stage will be used to trigger delivery of a contaminating dye or smoke to devalue the contents of the secure enclosure.

The present invention also comprehends a protection device for a secure enclosure comprising a detector as defined hereinabove, together with a device for corrupting or contaminating the contents of the said secure enclosure, such as by the introduction of a contaminant fluid.

The present invention also comprehends a secure enclosure itself, such as a safe, a strong-box or a strongroom, having a sensor as defined hereinabove carried on each interior surface thereof or embedded in each wall thereof, including any closures for the enclosure, the floor, walls, ceiling etc.

Embodiments of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a safe fitted with a sensor formed as an embodiment of the present invention Figure 2 is a schematic plan view of a panel sensor formed as an embodiment of the invention; Figure 3 is a cut away perspective view of a part of a secure enclosure formed as a further embodiment of the present invention; and Figure 4 is a schematic circuit diagram illustrating a detector formed as an embodiment of the present invention.

Referring now to Figure 1, there is shown a safe with its door removed for clarity of illustration. The safe, generally indicated 11, is generally rectangular, having a floor 12, opposite side walls 13, 14 and a ceiling or roof 15. The interior volume of the safe is lined with a plurality of sensor panels each identified with the same reference numeral as that of the wall to which the panel is fitted, with the addition of a subscript a. A back wall panel 16a is fitted to a back wall of the safe which is not visible in Figure 1. Each of the panels 12a, 13a, 14a, 15a, 16a covers substantially the whole of the associated wall and is in both physical and electrical contact with the adjacent panels. The whole assembly of panels is so connected together that the whole of the interior surface of the safe 11 is effectively covered by a single elongate electrically continuous conductor.

A separate panel (not shown) will be fitted to the interior surface of the door and suitable electrical connections made so that electrical continuity of the conductor is preserved when the door is closed, and possibly also when the door is open.

Figure 2 illustrates one form which the panels 13a-16a may take. In Figure 2 there is shown a rectangular substrate 17 of electrically insulating material on which is formed a sinuous track 18 of electrically conductive material. Known techniques, for example those used for the production of printed circuit boards for electronic equipment, may be used to form the conductive track 18 on the insulating substrate 17. The plastics material of which the substrate 17 is formed is sufficiently rigid to be effectively self-supporting in the sizes envisaged, for example, panels up to several feet square. As can be seen from the enlarged inset to Figure 2, the conductive track 18 has a general sinuous path extending from a first terminal 19 in one corner of the substrate 17 to the diagonally opposite corner from which a lead out wire or terminal 20 projects.The generally sinuous path of the conductor 18 is further overlain by a fine detail meandering path as illustrated by the crests 21 and valleys 22 of the encircled enlargement of Figure 2. As can be seen in that drawing the separation between adjacent conductive tracks is somewhat less than the thickness of the conductive track itself. The conductive track may be made to any suitable scale depending on the anticipated nature of an attack on the enclosure it is to protect.For a safe such as that illustrated in Figure 1, which may typically have dimensions of 3 to 6 feet along each side, and the prospective attack which would have to be defended by the sensor may include attempts to drill into the wall with a drill the dimension of which may go down to about 3 mm, it is envisaged that the conductive track may be in the region of 1.5 mm wide with the separation between adjacent tracks in the region of 1 mm wide. The track is so formed that there is effectively no area on the substrate 17 greater than 1 mm in width.

In the alternative embodiment illustrated in Figure 3, which shows a portion of a strongroom or vault 23, the wall 24 and ceiling 25 is made from cast concrete with a sensor panel 26 which may be in all respects similar to that illustrated in Figure 2 (except, perhaps, for the provision of a conductive substrate on both sides of the elongate conductor in order to ensure electrical isolation from the wall of the strongroom).

The sinuous pattern of the conductor 18 illustrated in Figure 2 may be replaced by any other regular or irregular pattern, superimposed with the fine detail sinuous or zigzag track which may be contemplated, including spiral track, key pattern track or an entirely irregular pattern in which the entire surface of the panel is covered with an effectively continuous elongate conductor.

A detector capable of monitoring the integrity of the conductor of a sensor such as that described in relation to Figures 1 to 3 is illustrated in Figure 4. The sinuous conductive track 18 is earthed at one end, identified by terminal 27, and connected at the opposite end via terminal 28, to the junction between a pulse generator, generally indicated 29 and a regenerative latch generally indicated 30.

The conductor 18 is connected in parallel between the output of the pulse generator 29, supplied through a high value resistor 31 and ground via a capacitor 32 the function of which will be described below. The pulse generator 29 applies a periodic voltage to the conductor 18 which, if the conductor 18 maintains its integrity, does not result in a significant voltage rise at the output, for example at terminal 28. The mark-to-space ratio of the pulse generator is held at a low value, typically 1% duty cycle, as a battery saving measure, by the resistor 33. A capacitor 34 is the timing capacitor which determines the frequency at which pulses are generated. As the capacitor 34 is charged, the voltage across it rises until inverters 35, 36 causing discharge of the capacitor 34 through the output resistor 31.

Capacitor 32 is a passive interference protector which effectively presents a short circuit to short, fast pulses or spikes which might otherwise trigger the circuit.

The regenerative latch 30 comprises a diode 37, two antiparallel inverters 38, 39 connected by resistors 40, 41 and an output diode 42. In normal conditions, that is when the conductor 18 is continuous and undamaged, the regenerative latch circuit 30, upon power up, is latched to a state in which the input to the inverter 39 is low and the input to the inverter 38 is, consequently, high.

This is ensured by the capacitor 41 which is connected, via a polarising capacitor 42 to ground.

If an attempt is made to force the safe, either by drilling into the wall, prising the door open, or by heat cutting the walls, this will result in an interruption to the conductive track 18 so that when the next pulse is generated by the pulse generator 29, instead of being conducted to earth via the terminal 27 in the usual way, will result in a rise in voltage at terminal 28 causing the inverter 39 to trigger generating a "low" output signal which is then applied to the input of the inverter 38 which therefore goes "high" latching on the trigger.

The "high" signal is applied via the diode 42 to the gate of a MOSFET output transistor 44 connected in series with the load 45 between a battery 46 and ground. The arrival of a "high" voltage pulse at the MOSFET transistor gate causes this to conduct thereby energising the load and triggering the alarm.

The alarm load 45 may be an audible indicator, visible indicator, remote communicator or a detonator for triggering release of a contaminating dye.

The battery 46 is also connected via a resistor 47 to the positive terminal of the polarising capacitor 42 and, via line 43 to the pulse generator 29. The gate of the MOSFET 44 is held down by connection to ground via a resistor 48.

In addition to the triggering circuit described above, the detector of the present invention also includes means for triggering the load 45 upon detection of attempts to force an entry into the safe by hammering, chiselling or wedging. This comprises one or a plurality of microphones (and only one channel will be described hereinbelow although two are illustrated in Figure 4 and more may be provided in practice). The microphone 49 is connected via a capacitor 50 to a two-stage amplifier generally indicated 51 comprising an inverter 52 centre biased via a capacitor 53 and in parallel with a resistor 54 the output from which is fed to a further inverter 55.

Brief impulses generated for example by hammering, then result in the triggering of the inverters 52, 53 to generate short spike-like pulses which are transmitted via a capacitor 56 to a pump circuit comprising diodes 57, 58 and resistor 59 which effectively supply short positive-going pulses to capacitor 60 which consequently builds a charge over several successive such impacts which, via a variable resistor 61 is supplied to a threshold detector in the form of two series-connected inverters 62, 63 the output from the latter of which is supplied via a diode 64 to the line leading to the gate of the MOSFET 44. The variable resistor 61 acts as a potentiometer to set the relative value of a charge on the capacitor 60 at which the threshold detectors 62, 63 are triggered.

Claims (16)

1. A sensor for a secure enclosure, comprising a substantially non-conductive substrate bearing an elongate electrically continuous conductor distributed over the area of the substrate in such a way that the path of the conductor is not determinable from a detection of a length of the conductor itself.

2. A sensor as claimed in Claim 1, in which the elongate conductor follows a sinuous path over the area of the substrate with each branch of the sinuous path further incorporating regular or irregular meandering path elements.

3. A sensor as claimed in Claim 1, in which the elongate conductor follows a spiral path over the area of the substrate, with each turn of the spiral further including regular or irregular meandering or sinuous path elements

4. A sensor as claimed in Claim 1, in which the elongate conductor generally follows an involuted meandering path with each carved or rectilinear path element following a further smaller scale meandering or sinuous path.

5. A sensor as claimed in any preceding claim, in which the substrate is an insulating non-supporting layer or member.

6. A sensor as claimed in any preceding claim, in which each elementary conductor portion (as herein defined) is spaced from the nearest adjacent non-contiguous elementary conductor portion by a distance less than the width of the conductor itself.

7. A detector for a secure enclosure, comprising a sensor as claimed in any preceding claim and means for detecting an interruption to the continuity of the elongate conductor of the sensor.

8. A detector as claimed in Claim 7, in which the means for detecting an interruption to the continuity of the elongate conductor includes a pulse generator for applying a recognisable repeating signal to the said elongate conductor.

9. A detector as claimed in Claim 8, in which the said means for detecting an interruption to the continuity of the elongate conductor includes a catching trigger circuit operable to generate our output control signal.

10. A detector as claimed in Claim 8, in which the said latching trigger circuit is connected to an output stage operable in response to a signal from the said latching trigger circuit to energise an alarm indicator or other alarm system.

11. A protection device for a secure enclosure comprising a detector as claimed in any of Claims 7 to 10, together with a device for corrupting or contaminating the contents of the said secure enclosure, such as bey introduction of a contaminant fluid.

12. A secure enclose such as a safe, a strong box or a strong room, having a sensor as claimed in any of Claims 1 to 6 carried on each interior surface thereof or embedded in each wall thereof (including closures, floor, ceiling etc).

13. A secure enclosure as claimed in Claim 12, in which the said sensor forms part of a detector as claimed in any of Claims 7 to 10 or part of a protection device as claimed in Claim 11.

14. A sensor substantially as hereinabove described with reference to, and as shown in, the accompanying drawings.

15. A detector substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

16. A safe, strongbox or strong room substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.