US3610808A

US3610808A - Area security cable comprising strain and heat-responsive network

Info

Publication number: US3610808A
Application number: US777397A
Authority: US
Inventors: Elwood R Horwinski
Original assignee: Lewis Engineering Co
Current assignee: Lewis Engineering Co
Priority date: 1968-11-20
Filing date: 1968-11-20
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

An area security cable having a network of conductors such as a tamperproof wire screen or a tamperproof cable braid for use with an associated detection circuit. The screen can be part of an enclosure, and can comprise insulated wires connected to form one or more trigger circuits. The cable may comprise a signal carrying core jacketed by one or more braids of insulated wires which are connected with each other to form one or more trigger circuits. Some of the screen or braid wires are resistance wires and at least one is metal of low melting point. The cable also has an unbraided and untwisted wire of high tensile strength, and the screen or cable can have an additional wire not included in the trigger circuit and adapted to constitute the bulb of a resistance thermometer. The trigger circuits can be connected to an energized detector circuit such as an instrument movement and a bridge, whereby any breaking or shorting of one or more of the wires of the cable or screen will result in a response by the instrument movement. The resistance bulb wire can be connected to a temperature bridge so that cable or screen temperature can be read.

Description

Inventor Elwood R. Horwinski OTHER REFERENCES Chesife Colm- Spaghetti Fire Detector in Production" Geo. L. Christian; 968 Aviation Week; May 17, 1954; pp. 60- 67. N 1 5 Primary Examiner-Lewis l-l. Myers 9 t Lewis Engineering Company Assistant Egzmmer-t. Gnmley Naugamck, Conn Altamey- .Cubner e mann ABSTRACT: An area security cable having a network of conductors such as a tamperproof wire screen or a tamperproof AREA SECURITY A E COMPRISING STRAIN cable braid for use with an associated detection circuit. The AND EATRESPONSIVE TWORK screen can be part of an enclosure, and can comprise insulated 6 Claims, 10 Drawing Figs. wires connected to form one or more trigger circuits. The cable may comprise a signal carrying core jacketed by one or U-S. CL...-........-....-....n.nu........................-. more ra o insulated wires are connected h other to form one or more trigger circuits. Some of the sc or braid wires are resistance wires and at least one is met low melting point. The cable also United States Patent [21] AppLNo.

[221 Filed Patented [73] Assignee 174/1 15, 174/110 PM, 174/124 G, 340/227 C Teen 1101b 7/32 a] of 340/227 has an unbraided and untwisted wire of high tensile strength, and the screen or cable can have an additional wire not included in the trigger circuit Field of 276, 285, 280; 337/414, 415; 73/154, 159; 338/26;

d to an energized ded a bridge,

re of the wires by the instruand adapted to constitute the bulb of a resistance thermometer. The trigger circuits can be connecte tector circuit such as an instrument movement an 340/273 whereby any breaking or shorting of one or mo 340/227 C of the cable or screen will result in a response 3140/280 ment movement. The resistance bulb wire can be connected 340/276 to a temperature bridge so that cable or screen temperature 340/276 can be read.

References Cited UNITED STATES PATENTS 8/1876 Lamed 6/1910 Williams. 10/1954 Schmidt 11/1959 lsenberg.......... 12/1964 Rubinstein AREA SECURITY CABLE COMPRISING STRAIN AND IIEAT-RESPONSIVE NETWORK CROSS REFERENCES TO RELATED APPLICATIONS BACKGROUND This invention relates to area security devices such as those which use screens or cables, whereby any tapping of or tampering with the screen or cable, or abnormal conditions of the same will be made known.

Heretofore various systems such as light or infrared beams, electric eyes, high or lethal voltage guards, cable armoring and the like have been utilized to safeguard restricted areas where unauthorized personnel were not desired or to safeguard cable wires. These systems have proved to be satisfactory in a number of instances, but drawbacks still existed. The highvoltage installations constituted a hazard and danger to workers and other authorized personnel in the area. Some prior systems were vulnerable to power failure, others could be defeated too easily by the use of more or less sophisticated equipment in the hands of an unscrupulous person, and most systems were restricted to certain specific conditions whereby other conditions were not covered.

SUMMARY The above disadvantages, drawbacks and limitations of prior devices intended to guard restricted areas, protect cable wires and the like are obviated by the present invention, and ,one object is to provide an improved area or space security network and cable protection means for guarding both cables and restricted areas, which network and means are especially effective and resistant to efforts intended to defeat their purposes, including not only direct actions of unauthorized people but also actions involving fire, excessive. stresses and the like. This is accomplished by the provision of a conductor network which may be in the form of wire braid in a cable, or in theform of a close-woven wire mesh constituted of crossing insulated wires, or in the form of a printed circuit grid, the wires or conductors being connected so as to form at least one continuous trigger circuit or preferably a plurality of such cir cuits, said circuit or circuits being capable of connection to an electrical detection device which will indicate any alteration of the circuit characteristics. The conductors are preferably of appreciable electrical resistance, and include at least one wire or conductor of low melting point, or a conductor of low ductility and high tensile strength, or both. There can also be included an isolated circuit comprising a conductor constituting the bulb of a resistance thermometer. The network comprising wire mesh, grid or braid is arranged to enclose the space being protected or guarded, as by applying it to walls, ceiling and floor surfaces and the like, or incorporating it in wall and other construction panelling, or in a cable as the case may be. For wall purposes, the wire mesh is fabricated to be essentially flat or planar. Other configurations such as the braid in the cable may be utilizedfhowever, to suit particular situations. Excessive heat melts the conductor of low melting point. Excessive stress breaks the conductor of low ductility. Thus these conditions disrupt the trigger circuit, setting off an indication of abnormal conditions. Temperature readings are bad by use of the conductor constituting the resistance bulb.

Other objects and advantages reside in an improved area security apparatus as above which lends itself well to existing cable fabricating processes, and to new constructions of buildings, rooms, vaults, safe boxes and the like; a security apparatus as above which is relatively simple and inexpensive, reliable and foolproof in operation, easily serviced, not subject to malfunctioning because of commercial power failure, wholly safe from the standpoint of fire and explosion hazard,

damage to its environment or danger to personnel; and a highly effective security apparatus which is especially flexible in being adapted to a large variety of conditions and applications.

Other features and advantages will hereinafter appear. In the drawings:

FIG. 1 REVEALS A DIAGRAMMATIC REPRESENTA- TION OF ONE FORM OF SECURITY CABLE AS PRO- VlDED BY THE INVENTION.

FIG. 2 reveals a diagrammatic showing of a cable constituting another form of the invention.

FIG. 3 is a detail of an end portion of a guard-type cable as provided by the invention. I y a I FIG. 4 reveals a diagrammatic showing of a simplified cable circuit as provided by the invention.

FIG. 5 is a diagrammatic representation of another form of cable braid circuit according to the invention.

FIG. 6 is a detail of a low melting point wire according to the invention. 7

FIG. 7 reveals a diagrammatic representation of another embodiment of the invention.

. FIG. 8 is a perspective view of an installation which is guarded by the network of the invention.

FIG. 9 is a fragmentary edge view of a guard-type wallpaper made in accordance with the invention.

FIG. 10 reveals a well-known strain gauge bridge for use with the tamperproof cable of FIG. 3, to measure the strain in the cable. Referring first to the simplified schematic circuit'of FIG. I and to FIG. 3, there is illustrated a representation of a

tamperproof cable

10 or 10a made in accordance with the invention, said cable having a core consisting of four electrical conductors or signal wires labeled respectively A, B, C and'D and which are provided with the usual insulating jackets or sleeving. Surrounding the core wires A, B,'C and D is a woven braid 12 of resistancewires each resistance wire being insulated from the others by sleeving or insulating coatings.

One end of the cable 10 is shown as tenninating at a source of signals, indicated schematically by the broken outline I4. The remaining end of the cable 10 is brought into a sensing or working station designated generally by the broken outline I6, said station including in addition to equipment (not shown) connected to the terminations of the signal wires A, B, C and D an alarm or indicator system described as to its operation and construction in US. Pat. No. 2,76l,052 issued to Knud .l. Knudsen on Aug. 28, I956 and entitled Electric Temperature Control," and in the above identified allowed application of Conrad S. Ham and Elwood R. l-iorwinski.

trigger circuit, said strands having their terminal ends con-.

nected to appropriate equipment (not shown).

It will be understood that, to effect series connections of the,

resistance wires of the braid l2, suitable end connections of the braid wires are made at the signal source 14 as well as at the other cable end comprising the working station.

With the above organization there is hada complete bridge circuit which includes the resistance wires of the braid 12. Such bridge circuit may be balanced by suitable adjustment of the bridge, in conjunction with a proper selection of resistance values for the wires making up the braid 12. Once the bridge is balanced, the galvanometer or responsiveinstrument 36 will indicate a null or zero setting, signifying that there is no breakage of any resistance wire in the cable 10, nor any short circuiting of one resistance wire to another, or short circuiting of resistance wires to the signal wires or to ground. etc. How- 1 ever, if any tampering with the cable 10 occurs. which will cause breakage of one or several of the resistance wires, or shorting of such resistance wires to each other or to the signal wires of the core, the balance of the bridgecircuit would be upset, and the indicating instrument 36 will be deflected or otherwise disturbed to give notice that the cable is no longer intact. The use of the bridge and sets of resistance wires results in an extremely sensitive response to even slight disturbances in such wires.

In accordance with the present invention the cable 10 (or 10a) and preferably the braid and outer portions thereof are constituted in a unique manner whereby it will respond to conditions of elevated temperature by causing an indication to be given, and whereby measurements of the temperature of the cable can also be made. The cable 10 or 100 also has low ductility wires in the outer portion, which constitute a trigger circuit and respond to conditions of elevated stress by breaking, for the purpose of providing indications and has other low ductility wires for the purpose of providing indications of the strain or tensile stress of the cable. In FIG. 1 the cable 10 is shown as having low ductility, high tensile strength strain wires 77 for connection in the bridge circuit, which wires are adapted to break in response to excessive strain. Also, the cable 10 has additional low ductility, high tensile strength wires 79 for connection in a strain gauge bridge circuit 81 for the purpose of indicating or reading the cable strain. Other improvements are more clearly shown in FIGS. 2 and 3 wherein details of a unique tamperproof cable 100 are revealed, together with a somewhat more comprehensive indicating or control bridge circuit described as to its construction and operate in the above-identified allowed application of Conrad S. Ham and Elwood R. Horwinski.

The tamperproof cable 10a has an outermost jacket 56 and an innermost signal-carrying core 58, the latter being constituted of four insulated signal wires A, B, C and D, said core being spiral wrapped with a Mylar or other suitable plastic web 60 over which there is applied a conducting shield constituted of a spiral wrap of bare conducting wires 62. Over the shield 62 there is a second spiral wrap 64 of Mylar, after which there is applied a conductive, trigger network comprising an open weave braid of insulated resistance wires 66, preferably 24 in number. Around the braid 66 of resistance wires there is woven a fiberglass insulating braid 68, which is then enclosed in a flexible metal conduit 70. Surrounding the flexible metal conduit 70 there is a spiral wrap 72 of Mylar strip, and then a second open weave braid 74 of insulated wires. The braid 74 may comprise, for example, insulated resistance wires indicated generally by the letter R, a pair of insulated wires 73 of low melting point, and a second pair of insulated wires 75 of platinum or other suitable metal adapted to constitute the bulb portion of a resistance thermometer. Surrounding the braid 74 is a closely woven fiberglass braid 76, and finally the outer protective solid tubular jacket 56 which is advantageously of polyvinyl chloride.

In FIG. 2, the cable 10a is indicated as extending between two broken lines 80, 82 and the two open weave braids of insulated wire 66, 74, comprising a total of 48 wires, are represented as grouped in four series-connected

sets

84, 86, 88 and 90, each set being indicated as having a nominal resistance of 75 ohms. The set 84 may comprise 10 wires, the set 86 may comprise eight wires, the set 88 may comprise six wires, and the set 90 may comprise eight wires. This gives a total of 32 wires, and the remaining l6 wires are left unconnected and serve no purpose except in physically forming the open basket weave or braid construction.

The set of wires 84 may contain the wires 73 of low melting point. The resistance bulb wires 75 are shown electrically isolated, for connection to the resistance thermometer bridge.

The invention further provides straight or unbraided fine

insulated wires

77a and 79a of low ductility and high tensile strength (for example, piano wire) in the

cables

10 and 10a, having their ends suitably anchored to the cable ends whereby cable strain can be indicated by means of the wires 79a and whereby any undue pulling forces on the cable can rupturejthe wires 77a and resultin an indication being given. In FIG. 2 the wires 77a are shown as included in the set 90, and the wires 79a are brought to terminals for connection to the bridge 81.

Referring to FIG. 2, the spiral wrap shield 62 is shown as connected by a wire 92 to a ground 94. A 100 ohm resistor 98 is connected to the flexible metal conduit 70. The independent sections of

resistance wires

84, 86, 88 and are included in the four legs of a

bridge having junctures

26a, 28a, 30a and 32a.

As shown in FIG. 3, the resistance bulb wires 75 may be incorporated in the braid 74, as well as the wires 73 of low melting point.

FIG. 6 shows one form of low melting point wire, wherein a Teflon (tetrafluorethylene) core 196 is provided with a metallic jacket 198 comprising a tin-lead alloy. The metal jacket 198 is coated with an insulating enamel of any suitable type used for insulating wires. v

The unbraided or

straight conductors

77a and 79a, FIG. 3, may be disposed between the insulating braid 76 and the insulating jacket 56, with the ends folded over and welded to separate, partially circular metal shells 200, 202 provided with connector lugs 204, 206 respectively. The shells 200, 202 (and other similar shells not shown) are insulatedly secured to each other in any suitable manner. At the other cable end, the wires 77a may both be secured to a single metal ring whereby they are electrically connected, and the wires 79a similarly secured independently of the wires 77a.

Another form of the invention is illustrated in FIG. 4. Here,

the core of the cable 10b comprising the conducting wires A,

B, C, and D is surrounded by a woven braid of insulated resistance wires 208 which are so connected that they are all in series. The cable 10 includes insulated low ductility wires 77b and low melting point wires 73b, as well as resistance bulb wires 75b. The

terminations

210, 212 of the wires 208 can be connected to suitable equipment (not shown).

In FIG. 5 another form of the invention is illustrated, wherein the cable signal wires A, B, C and D are enclosed is a resistance and heat-sensitive wire

braid comprising wires

220 and 730 shown as being connected in parallel with each other and with low ductility wires 770. The

terminations

222, 224 of the parallel connected wires can be brought to an indicator device (not shown), such device will be disturbed when any of the wires is broken, melted or else shorted to another wire.

Whereas the foregoing protective wire network has been illustrated as being in the form of a braid in a cable, it could as well have a flat configuration such as wire screening, printed -circuitgrids and the like. In FIG. 7 there is illustrated a flat configuration 226 which may comprise printed circuit conductors 228 on one side of an insulating sheet and printed circuit conductors 230 onthe other side of the insulating sheet. The

conductors

228, 230 preferably are disposed to be perpendicular to each other. The conductors 228 may further include a conductor 232 of low melting point, and the conductors 230 may include a conductor 234 of low melting point.

As shown, all of the conductors are connected in series, with their ends brought out to terminals I and J.

In FIG. 7, there is shown a bridge 236 described as to its construction and operation in the above-identified allowed application of Conrad S. Ham and Elwood R. I-Iorwinski.

The braid 66, 74 of FIG. 3 may be replaced by a planar network configuration like that of FIG. 7, at 226. Such planar configuration could represent part of an enclosure, and such configuration or the network 226 of FIG. 7 may be in the nature of window screening or fly screening or mesh, shown in cross section in FIG. 9. The mesh configuration may be incorporated in wall panels. For example, in FIG. 9a mesh configuration 260 is shown as applied to heavy wallpaper 262 having a backing sheet 264 adapted to be peeled ofi to expose a pres sure sensitive adhesive. The makeup of the mesh and wallpaper shown in FIG. 9 may thus be similar to the configuration 226 in FIG. 7.

A use of the planar mesh or network configuration is illustrated in FIG. 8, which depicts a walk-in vault 266 having all of its sides provided with network configurations 226. The network configurations are connected to constitute trigger circuits which may be connected with the cable a and a detection bridge 8".

The strain gauge bridge 81 shown in a representative manner in FIG. 10.

It will now be seen from the foregoing that l have provided a novel and improved tamperproof area protective construction which is extremely effective and foolproof in preventing undetected and unauthorized tampering with a cable or an enclosure, and in responding to elevated conditions of temperature and strain. Although it might be possible ultimately with the use of sophisticated equipment over a period of time, to tamper with the present improved security system, such possibility is extremely unlikely and not only requires the highest kind of skills but also the use of complicated electronic equipment, employed over an appreciable time.

The improved security apparatus is seen to be relatively simple, of straight-forward design, and to be reliable and foolproof in its operation.

Considering the cable or planar network per se, it will be understood that the severing or melting of any one of the wires making up the trigger circuit, or the shorting of such wires with other wires of the circuit or to ground, will result in the indicator being made operative to either give a signal or else actuate a control for a desired purpose, as for example to shut off power to the wires A, B, C and D. Thus the cable is useful in explosive atmospheres, boiler rooms etc. where the environment is of a nature that could cause cable damage. By quickly disconnecting the power, the likelihood of dangerous sparking is minimized.

Variations and modifications are possible, and portions of the improvement may be used without others.

I claim:

1. A tamperproof cable comprising, in combination:

a. a signal-conducting core,

b. a braid construction constituted of resistance wires surrounding said core, and

c. means insulating the resistance wires of the braid from each other and from the signal-conducting core,

d. said braid construction including at least one wire having a low melting point substantially under that of copper wire. a

2. A tamperproof cable comprising,in combination:

a. signal-conducting core,

b. a wrapping construction constituted of resistance wires surrounding said bore, and I c. means insulating the resistance wires of the braid from each other and from the signal-conducting core,

d. said braid including at least one wire constituting a circuit separate and apart from the remaining wires of the braid.

. A cable as in claim 2, wherein:

. said braid further includes at least one wire having a low melting point substantially below that of copper wire.

4. A tamperproof cable comprising, in combination:

. a signal-conducting core,

b. a wrapping construction constituted of resistance wires surrounding said core, and

c. means insulating the resistance wires of the wrapping construction from each other and from the signalconducting core,

d. said cable comprising one unbraided and untwisted wire of low ductility and high tensile strength, insulated from said braid wires, and

e. means anchoring said high tensile strength wire to end portions of said cable.

5. A cable as in claim 4, wherein:

a. said braid further includes at least one wire having a low melting point appreciably less than that of copper wire.

6. A cable as in claim 4, wherein:

a. the means anchoring the high tensile strength wire comprises bushings carried by the cable,

b. said cable including an outer insulating jacket to which the bushings are secured.

Claims

1. A tamperproof cable comprising, in combination: a. a signal-conducting core, b. a braid construction constituted of resistance wires surrounding said core, and c. means insulating the resistance wires of the braid from each other and from the signal-conducting core, d. said braid construction including at least one wire having a low melting point substantially under that of copper wire.

2. A tamperproof cable comprising, in combination: a. signal-conducting core, b. a wrapping construction constituted of resistance wires surrounding said bore, and c. means insulating the resistance wires of the braid from each other and from the signal-conducting core, d. said braid including at least one wire constituting a circuit separate and apart from the remaining wires of the braid.

3. A cable as in claim 2, wherein: a. said braid further includes at least one wire having a low melting point substantially below that of copper wire.

4. A tamperproof cable comprising, in combination: a. a signal-conducting core, b. a wrapping construction constituted of resistance wires surrounding said core, and c. means insulating the resistance wires of the wrapping construction from each other and from the signal-conducting core, d. said cable comprising one unbraided and untwisted wire of low ductility and high tensile strength, insulated from said braid wires, and e. means anchoring said high tensile strength wire to end portions of said cable.

5. A cable as in claim 4, wherein: a. said braid further includes at least one wire having a low melting point appreciably less than that of copper wire.

6. A cable as in claim 4, wherein: a. the means anchoring the high tensile strength wire comprises bushings carried by the cable, b. said cable including an outer insulating jacket to which the bushings are secured.