FR2510785A1 - Electronically monitored metal wire security fence - has sections linked in pairs for comparison of resistance to check possible break-in using A=D converter, comparator and memorised tables - Google Patents

Abstract

The system uses metal link fencing in which one or a number of conducting wires which are coated in plastic, are woven to form a mesh. The wire forms a part of a conducting loop, along with a length of insulated copper conductor (FF') completing the circuit. This circuit and a similar one from an adjacent section of fencing are connected to electronic detecting equipment responding to differences between the conductivities of the two circuits. Pairs of fence sections all along the perimeter of an enclosure are thus joined together and monitored. The monitoring circuits are then themselves linked together to a guard post. Temp. variations affect adjacent fence sections similarly and do not trigger an alarm. Sections are interconnected by a bus line, to which is joined a resistor for each section. Each resistor is in parallel with a normally closed contact of a relay. A drop in the relay coil voltage causes the contacts to open and thus places the resistor in circuit. An a-d circuit cyclically scans and compares the resistance values with memorised values. The result of the comparison is used to set an alarm system and designate to infringed zone on a display.

Description

 The present invention relates to a burglar-resistant security fence consisting of a plastic wire mesh and intended to ensure detection and signaling at a central monitoring station for any attempt to break in or be crossed by an intruder.

 Burglar-resistant fence networks are already known. They use wire mesh specially designed for this use and incorporating a special conductive wire having the banal external appearance of other wire mesh. This type of trellis has the disadvantage of being very expensive. For these devices, the alarm is triggered by measuring the imbalance caused between two identical panels inserted in a Wheatstone Bridge circuit.

 This connection method allows compensation for variations in resistance due to atmospheric conditions, but it has the disadvantage of being too sensitive and of triggering for causes other than a break-in (fall of a balloon, proximity of parasites, etc.) and create false alerts.

 The object of the invention is to provide a fence providing great trekking protection by using standard plastic-coated wire mesh in use in trade.

 In accordance with the invention, this result is obtained with a security fence for detection and alarm signaling consisting of a plasticized wire mesh stretched between posts, means of detection and signaling of attempted break-in, characterized in that said plasticized wire mesh is of the standard type and and that at least one of the wires which composes it is used directly as an electrical conductor.

 In the fence according to the invention, the meshes of said trellis are therefore electrically insulated, one with respect to the other, and are united at the top and at the bottom, so as to constitute one or more linear electrical zigzag continuities. The conductive line or lines thus formed are closed on a supply circuit and on a detection circuit making it possible to detect any break in the conductive line of the trellis or any variation in electrical resistance due to an attempt at shunting. The present invention furthermore presents any impossibility of returning information or parasites via the earth and thus avoids the risks of false alarms. An essential advantage of this device is its simplicity and its low cost thanks to the use of plasticized mesh, of the trade, its classic use, its absolutely standard aspect therefore apparently banal seen from the outside.

The invention is explained in more detail below using certain of its embodiments, taken by way of illustration but in no way limiting, with reference to the appended drawings in which
- Figures I and 2 show the conductive line or lines obtained in two types of lattice used for the realization of the fence.

 - Figure 3 illustrates by way of example a way to enclose an enclosure according to the invention.

 - Figure 4 is a diagram of the preferred electronic detection circuit.

 - Figure 5 is a block diagram of the circuit of Figure 4.

 - Figure 6 is a block diagram of the transmission circuit and alarm centralization.

 According to FIG. 1, the trellis used is of the plasticized simple metallic twist type, so that the conductors are correctly isolated from each other at the crossover points of the meshes. The process used to achieve the electrical continuity of a single conductive loop consists of pickling the twisted ends of the vertical wires and soldering or brazing them together, then reinsulating them with a plastic coating. The long electric circuit. Thus constituted is brought to one end of a section either by an insulated copper electrical wire FF ′, or by one of the plasticized tensioning wires of the mesh. The large loop thus formed then has a characteristic temperature.

 According to FIG. 2, the trellis used is of the oblique corrugated type in which five electrically independent zigzag loops (or more, or less depending on the height of the mesh used) can be produced, for example the loop 1'1 E E '.

In this preferred type of trellis security is increased because the shunting of several meshes to allow the cutting of a panel is practically impossible due to the independent feeding of the nested loops. In this type of standard trellis, the upper vertices of the zig-zag are already joined by a bent part, it is advisable to join the lower vertices according to the process already used for the simple twist trellis. Obviously this operation becomes useless from the moment we have plasticized wire mesh whose upper and lower vertices of the zig zag are already joined mechanically by a welded part. The protection of a sensitive pqint, a establishment, of a ground, will be thus carried out by a fence made up of meshed elements posed on concrete posts or plasticized metal posts, of a few meters of width. Said elements which can be buried over thirty centimeters to increase security form sections or zones of several tens to several hundred meters if need be protected specifically and autonomously according to the plan of FIG. 3. Each zone made up of a or several loops, similar to the loop 1 '1 E E', and each loop is connected to electronic equipment supplied either by sector, or, preferably by solar sensor supplying a battery via a transistor regulator. This preferred mode of supply has the advantage of saving the laying of electric supply lines, of permanently maintaining the charge of the battery, of having a great autonomy, of being isolated from the ground.

 FIG. 4 shows by way of example, a circuit for interrogating an area comprising 8 loops or 8 electrical circuits and which may be suitable for a fence of maximum 250m in length. In the case of fences of greater length, this device should be provided as many times as necessary. The operating principle of the interrogation circuit is described on the synoptic table figure'5.

It includes a clock (1) controlling the successive excitation of the parts of the eight registers Q1, Q2, Q3, Q4, Q5, Q6,
Q7, Q8 of the set.

 Each output Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8 is connected to one of the eight inputs of the interface assembly (3). This set includes eight electronic circuits each comprising a loop of the fence circuit. Each output of the interface circuit (3) is connected to an input of the eight doors of the comparator assembly (4). There is also a direct connection between each output of the register and the second input of each door of the assembly (4).

 Thus when the output Qi sends the signal the gate 1 receives two identical signals on its two inputs and its output remains at rest. If the interrogated loop is cut or sees its impedance modified by a shunt, the door switches and communicates a voltage to the alarm circuit.

 The closing portions are thus interrogated successively in a time interval of less than one second.

The circuit further comprises a device for resetting the clock to zero when the eight loops have been interrogated so as to recommence interrogation.

 In case a shunt would have been put in place by an intruder, and would connect two loops together, for example loop 1 and loop 8, only one of the two doors 1 or 8 would have these two entries in the same floor since the he clock sends only one signal at a time, the other door then triggers the alarm.

 Figure 5 shows the block diagram of the alarm transmission and centralization circuit. This circuit has the advantage of making the connection between the central station located in the guardhouse and the substations associated with each fencing area using a single wire, saving and ease of installation are not negligible in the case of large fences.

 A constant current, under regulated voltage, flows in said connecting wire also called omnibus line.

 Said bus line comprises as many resistors R as there are zones to be monitored, each resistor R being installed in parallel on a closing contact which, in normal position, is closed. During an alarm, or a power supply fault in the substation, the corresponding relay drops out and its resistance is in circuit.

 The analog digital converter sees its values compared cyclically by the central station to a table of values stored in memory.

 When the value of the converter is equal to a memorized value (in the event of an alarm), the central unit converts said value into a zone number which is then processed by the various signaling circuits indicated in FIG. 6 display, printer, synoptic, audible alarm, alarm report, telephone transmitter ... and can be used either separately, or partially or completely combined.

In addition, the stored table includes an instruction
corresponding to the wire cut in the bus line.

For example, an RCA card fitted with a cosmac microprocessor (Ref. CD P 185604) and a card from the same cons
tructeur (Ref. CD P 183648) are used for the conversion
A / D. The capacity of this conversion, 8 bit multiplexed on 16 lines, allows the system to possibly centralize on the same principle, other alarms such as: monitoring of boiler room burners, temperature of premises, or any other industrial application.

This mode of transmission and centralization has been described without limitation, we can consider using any other mode of transmission (Low frequency or other ...),
Furthermore the electronic device can be com
p lete of a thermistor temperature compensation circuit to take account of variations in ohmic resistance of the wires
trellis according to the outside temperature (-200 to + 500).

Claims (3)

 Safety fence for detection and alarm signaling consisting of a plasticized wire mesh stretched between posts, of means of detection and signaling of attempted break-in, characterized in that said plasticized wire mesh is of standard type and that at least one of the wires composing it is used directly as an electrical conductor. 2. Fence according to claim 1, characterized in that it consists of lattice of the simple twist type in which the plasticized metal wires are joined together so as to form a single conductive line or loop. 3. Fence according to claim 1, characterized in that it consists of an oblique corrugated type lattice in which the plasticized metal wires are joined so as to form several conductive lines or nested zig-zag loops.