Note: Descriptions are shown in the official language in which they were submitted.
The present invention`relates to a thiefproof guard fence
consisting of plastics-coated wire netting and intended
for ensuring detection and signalling to a central watch-
post, of any attempt by an intruder to break ln or get
5 over.
Thiefproof fence networ~s are already known. They
employ wire netting specially desvgned for this purpase and
incorporating a spec~al conductor wire having the ordinary
outer a~pearance of the othex wire~ of the netting. This
f 10 type of netting presents the disadvantage of bein~ very
costly. For these devices the alarm is triggerea by
measurement of the unbalance caused between two identical
panels insei^ted in a Wheatstone bridge circuit.
This method of connection enables compensation of variations
15 in resistance due to atmospheric conditions but it presents
the disadvantage of being too sensitive and being triggered
for other causes than a break-in (the fa~ling of a balloon,
closeness of objects causing interference~..... ~ and of
creating false alarms.
The aim of the invention is to provide a fence which of~ers
ver~ hiyh protection wh:ilst employiny standard wire netting.
In acordance with the invention thi~s result is obtained
with a guard fence for detection and alarm signalling
consisting of a plastics-coated wire netting stretched
between posts and means of detection and signalling of
any attempt to break in, characterized in that the said
wire netting is of standard type having a welded mesh,
over which before coating with plastics, conductive strands
of enamelled or varnishedicopper are woven to form one or
more conductive loops.
~,,~'
The conductive line or lines thus formed are closed across
a supply circuit and across a detection circuit which enables
any breakage or modificat~on o~ ~he conductive lines of
the netting due to an attempt at shunting to be dekected.
The present lnvention in addition offers complete impossibility
of the return o~.information or of interference through
earth and thus avoids the risk of false alarms.
. .
An essential advantage of this device is its low cost
thanks to the employment of standard commercial welded netting
hav1.ng-a rectangular mesh. In addition, after plastics
coating of the whole,the outer appearance of the netting i`s
absolutely ordinary and the presence of the conductor wires
cannot be detected by a possible intruder.
The i.nvention is explained in greater-detail below by means
,' . 15 of certain of its embodiments, taken by way~illustration
but in no way restrictively, whilst referring to the
attached drawings in which: .
-- Figure 1 represents a conductive loop PUt in place on the
supporting netting in accordance with the invention;
~ Figure 2 is a section of the cable composing the netting
after- covering with plastics the whole as Figure 1,
Figure 3 illustrates by way of example a way of fencing
in an enclosure in accordance with the invention;
. .
- Figure 4 is a diagram of the preferred electronic detection
circuit;
- Figure 5 is a synoptic of the circuit as Figure 4;
- Figure 6 is a schematic diagram of the alarm transmission
and centralization circuit;
- Figure 7 is a special barbed wire which ma~ be employed
in combination wlth the invention;
Figure 8 is a diagrammat~c longitudinal section of a
conductor element employed in accordance with a variant
lrnplementation;
Figure 9 illustrates the reali~ation of a conductive
circuit on plast~c-coated netting by a surface treabment;
(: .
Figure 10 illustrates a part~cularly advantageous application
of the fence as in Figure 9.
In accordance with Figure 1 -the wire ~etting serving as
support is of the type having a welded rectangular mesh.
A plurality of strands of enamelled and varnished copper
twisted together i9 put into place so as to form by weaving
along-the horizontal and then vertical stee~ cables a long
continuous loop the two ends A and A' of which meet at one
and the same(;point on the netting. The said strands are
held along the steel cables by stitching by sewing machine
or by stapling or gluing.. The whole is t~en coated with
plastics and aPpears like a normal plastics-coated welded
netking.
Figure 2 represents, seen in section, the cable obtained
after ooating the whole as Figure 1 wi~h plastics. The
steel core l as well as the plurality of strands of cop~er
~ are embedded in the plastics coating 3.
Hence the protection of a sensitive point, of a factory or
a site, will be achieved by a fence consisting of members
of wire netting placed on concrete posts or plastics-coated
metal posts, and several metres wide. The said members
which may be partially or totally sunk in the ground in order
to incxease~ the security, form sections or zones of some
tens to some h~tndreds of metres if necessctry~ protected
~4-
specifically and independently ln accordance with the
plan as Figure 3. Each zone in turn consists of one or
more looPs identical with the loop A-A~ as Figure 1~ In
accordance with the preferred embodiment of -the invention
each loop ~-A' in turn consists o~ a plurallty of conductive
strands of copper, each then,forming a conductive loop. In
accordance wlth one variant embodlmen-k, the conductive strand
(or,strands) forming the loop A-A' may be replaced by a
layer of conductive p'aint or a layer of metallization ' . 10 or any other means o realization oE the conductive loop,
the said layer being de~osited betwe:~n ~wo layers of plastics
coating. Each conductive loop.of each zone is connected
across an electronic equipment fed either from -the local
supply clrcuit or preferably from a solar panel feeding
a battery by way of a transistor regulator. This PreEerred
method of supply has the advantage vf saving the laying
of electric supply lines, of keeping the battery permanently
charged, of being largely independent and of being insulated
from earth.
Fi.~ure 4 represents by way of example a circuit for inter-
rogation of a zone including 8 loops or 8 electrical circuits
and able~suit a :fence of a maximum length oE 250m. In the
case of fences of greater length it is advisablë to provide
this device as many times as is necessary. The princip~e
oE operation of the interrogation circuit is descri~ed .in
the synoptic chart as Figure 5 and in Figure 4.
It comprises a clock (4) controlling the successive excitation
of the portions of the eight registers Ql, Q2, Q3, Q4, Q5,
Q6, Q7, Q8 of the unit (5~.
Ea,ch output Ql, Q2, Q3, Q4, Q~, ~6, Q7, Q8 is connected to
one o:E the eight inputs to the interface unit t5~. This
unit comprises eight elec,tronic circuits each comprising
one loop of the fence circuit. Each output from the interface
circù~t: (63 is connected to one input to the eight
gates of the comparator unit (7)O There exists in addition
a direct connection between each output from the register
and the second input to each gate of the unit (7).
Thus when the output Ql sends the signal the gate 1 receives
two identical signals over its two inputs and its output
remains at rest. If the loop being interrogated is broken
its impedence is seen to be modified by a shunt, the gate
tilts and communicates a voltage to the alarm circuit~
The portions of fence are thus interrogated in succession
during an interval of time less than one second~ Th,e circuit
comprises in addi~ion a device for resetting the clock
to zero when the eight loops have been interrogated so as
-to reco~mence the interrogation.
In the event that a shunt had been put ln place by an
intruder and connected two loops together, for example,
the loop 1 and the loop 8, only one of the two gates ~ or
8 would have both its inputs in the same state since the
clock sends only one signal at a time and the other gate
then triggers the alarm.
The synoptic as Figure 5 represents the detection circuit
described above.
Figure 6 represents the schematic diagram of the alarm
transmission and centralization cîrcuit. This circuit
offers the advantage of effecting the connection between
the central station situated in the guard post and the
assoclated substations at each zone of the fence by means
of a single wire; the economy and the ease of laying are
not negligible in the case of fences of large dimensions.
`
6~
A constant current at a regulated,voltage flows in -the
said connecting wire which is also called the busline.
.
The said busline comprises as much resistance R as there
are zones to be supervised, each resistance R being in-
stalled in paraliel across a closing contact whi~h in thenormal position is closed. At the t~me of an alarm or
of a fault in the supply to the substation the corresponding
relay d~o~s out and its resistallce is in circuit.
( i .
The analogue-digital convertor sees its values compared
cyclically by the central station with a table of values
put in store.
Wnlen the value from the convertor is equal to a stored
value (in the event of alarm) the central unit converts
the said value into a zone number which is then dealt with
by the various signalling circuits indicated in Figure 6:
dlsplay, printer, synoptic, audible alarm, alarm report,
telephone transmitter, ...... and may be employed either
separately or partially or totally combined.
In addition the stored table comprises an instruction
corresponding with cutting the wire o the busline.
By way of example a RC~ card equiPped with a "cosmac"
~icroprocessor (ref. CD P 185604) and a card from the
same manufacturer (refO CD P 183648) are employed ~or the
A/D conversion. The capacity of this conversion, 8 bits
multiplexed over 16 lines, enables the system to centralize
if necessary on the same principler other alanms such as:
supervision of the burners i~ the boiler room~
te,mperature of the buildings, or any other industrial
application.
--7--
.
This method of kransmission and centrallzation has
been described in a non-restrictive way, and one may con-
ceive of employing any other method of transmission (low
~requency or the like..~.).
In addition the electronic device may be comPleted by a
circuit for compensation of temperature by thermis~ance
in order to take into accoun~ variations in the ohmic
resistance of the wires of the netting as a function of
( , the external temperature (-20 to + 50).
In addition, in accordance with a variant upon the invention,.
one may conceive of employing instead of the plastics-
coated netting or in combination with it one or more barbed
wires stretched between the posts. Th:is special harbed
wire is composed of a plastics-coated metal wire (9~
of the same:.structure as the cable described in Figure 2
and twisted with a steel wire car~ying barbs (10).
A variant implementation will now be described by reference
to Figure 8.
A wire treated in accordance with this vari.ant includes.
- a central me-tal core ~11); ,
an insulating layer (12), for example,a layer of plastics;
- a conductive layer (13) applied by surface treatment,
for example, by metallization;
- an outer insulating layer (14).
Hence the conductive element is applied by a surface
treatment directly over the plastics sheath coating the
central core,,the whole being subsequently su~jected to
another coating with plastics or any other suitable
lnsulating material~
--8-
Thus on a plastics~coa~ed wire netting one may achieve a
veritable printed circuit, the application of the surface
treatment being able to be selective and defining conductive
circuits which are then fed and supervis0d in the same
manner as previouslyO
Th~ surface treatment may be, non-restrictively, a metalli~
zation in accordance with techniques which in themselves
are well known and will not be described ln greater detail.
In Figure 9 an embodiment is shown of circuits printed
over a plastics-coated wire netting (15).
The surface treatrnent is applied selectively so as to
define circuits such as (16, 17, 18). Then insulation is
effected eithex hy coating with plastics or by spraying
with any adequate insulating constituent.
Finally in Figure 10 there is shown a supplementary securlty
d~vice which detects any break-in tending to ma]ce the
upper portion of the nettiny tilt.
On the connecting posts (19`20) the d~namometric detection
members are arranged, which consist essentially o~ two
symmetrical bars (21,22) mounted to be able to rotate about
a point on the posts and controlling inside each post a
means of pinching the fence wires, thus triggering the
alarm; the means of pinching are e~uipped with a return
spring which brlngs them back into position when the action
upon them ceases.
Finally barbed wires are stretched across the bars (21,22),
projecting sideways with respect to the plane of the netting
and including a conductive strand produced likewise by
metallization.
Thus a complete protection is obtained:
- detectlon via the netting for breakage and any deterior-
- ation;
- dynamometric detection via the bars on the connecting
posts,
detection for brea]sage and deter~oratio~ of the barbed
~ires.
(
