US 2518788 A
Description (OCR text may contain errors)
Aug l5, 1950 F. w. JACKSON l-:rAL 2,518,788
HEAT RESPONSIVE ALARM CABLE Filed Aug. 14, 1947 a@ M44 j@ Patented Aug. 15, 1950 HEAT RESPONSIVE ALARM cABL Frank W. Jackson and Harry M. Nacey, Chicago, Ill.
Application `August 14, 1947, Serial No. 768,598
The invention relates generally to electrical cables, and more particularly to a heat responsive cable for actuating iire alarm circuits, sprinkler circuits and the like.
In the past, heat responsive cables have been employed, embodying two conductors insulated from one another under normal conditions, the construction being such that upon the application of a predetermined amount of heat to the cable the insulation is broken down and a connection established between the two conductors, whereby electrical connections are established to operate the alarm or other device. An example of such a type of cable is disclosed in United States Letters Patent to W. G. Holmes, No. 2,185,944, wherein one or both conductors are formed from spring material such as spring or piano wire, the electrical connection between the two conductors upon the application of heat thereto being obtained from the inherent resiliency of the conductor or conductors which are twisted around one another to produce a pinching action therebetween. It will be apparent that the utilization of spring material results in a cable that is stiff and thus relatively difficult to work with as well as being comparatively expensive to manufacture. Likewise, the electrical connection obtained between the conductors is merely one of contact, again resulting from the inherent resiliency of the conductor or conductors.
The present invention has among its objects the production of a heat responsive cable in which ordinary copper or other pliable common types of conductors, may be employed in the manufacture of the cable so that the resulting cable is relatively pliable, and easily spliced and soldered to greatly facilitate installation. Also, if desired other conductors of non-ferrous or non-corrosive metals may be employed.
Another object of the invention is the production of such a cable in which the operation thereof is not dependent upon the resiliency of the conductors, and in which a direct connection may be made between conductors on the application of heat, as distinguished from merely a contact connection.
A further object of the invention is the production of such a cable which may utilize standard electrical materials so that the same is relatively inexpensive to manufacture, and improved operating conditions as to length of lines, voltages and current may be obtained.
Many other objects and advantages of the construction herein shown and described will be obvious to those skilled in the art from the disclosure herein given.
To this end our invention consists in the novel construction, arrangement and combination of parts herein shown and described, and more particularly pointed out in the claim.
In the drawing, wherein like reference characters indicate like or corresponding parts:
Fig. 1 is a diagrammatic view of a simple alarm system utilizing the present invention;
Fig. 2 is a plan view of a cable embodying the present invention with portions of the insulation and other elements broken away to disclose the construction thereof;
Fig. 3 is a sectional view through the cable illustrated in Fig. 2 taken approximately on line 3 3 of Fig. 2;
Fig. 4 is a sectional view similar to Fig. 3 of a modied form of the invention; and
Fig. 5 is a sectional view similar to Fig. 3 oi another modified form of the invention.
The present invention contemplates the use of two ordinary wire conductors of copper or other suitable material which is relatively pliable, the conductors being electrically insulated from one another by suitable insulating material which is responsive to the application of heat, whereby the insulation will break down, in combination with a fusible electrically conducting material such as solder or the like. Thus, upon the application of heat to the cable the insulation will break down and the electrically conducting material will fuse to provide a direct electrical connection between the two conductors at the point of the insulation break down.
Referring to Fig. 1, I indicates generally a section of cable embodying the present invention having two conductors 2 and 3 therein, the conductor 2 in the present instance being connected to one side 4 of an alarm bell 5 or the like, and the conductor 3 operatively connected by a conductor 6 to one side of a battery l, the opposite side of the battery being connected by a con ductor il to the other side S of the alarm bell 5. Thus, as the conductors 2 and 3 are normally insulated from one another the bell circuit may be open, but upon application of heat to the cable and an electrical connection made between the conductors 2 and 3 thereof, the circuit will be closed to actuate the bell 5.
As illustrated in Figs. 2 and 3, the conductors 2 and 3 of the cable l may be twisted together, either one or both being twisted relative to the other, the conductor 2 being provided with a coating of insulation l5. The coating Il may be of any suitable electrically non-conducting material havingthe desired heat characteristics, of which there are numerous types including rubber, cellulose, etc. We have found that cellulose compositions, as for example ethyl cellulose lacquer is suitable for the purpose, which is coated upon the wire in a sufficient thickness to provide the desired insulation. The conductor 3 is loaded or covered with a fusible metal solder I2, the two conductors being covered, if desired, by a suitable woven sheath I3. The coating of insulation Il on the conductor 2 and the fusible metal I2 on the conductor 3 are both so selected that their heat responsive characteristics are approximately the same so that the insulation material will break' down and expose the conductor 2 at substantially the. same temperaturel thatv the conducting material I2 will fuse and ow betweenv the two conductors, thus electrically connecting the same and closing the alarm or other circuit. Thus, by proper selection of these materials cables 5l of various critical heat responsive characteristics may be obtained, whereby the circuits, maybe closed for example, at 160 or 212, etc. It will. be noted that while the electricaly connection be.,- tween the two conductors may be by contact, a direct connection is made by the flowingI` of theV fusible metal between the two conductors, consequently Such. e,0izlneetiferl` is. not. dependent unen inherent resiliency of the, conductors,
While the cable will functionP very satisfactorily without an additionalv Sheath L3, enclosing the two. conductora we prefer toA employ, the:- sheath I3, making the same from av suitable'niaf, terial having greater heat resistance thantheinsulating material II or theV conducting material` I2, whereby the sheath will withstand higher? temperatures than, that required, for breaking down of the insulating materialandfusing-4 of, the, conductingl material, whereby thesheath willr securely hold the conductors in, positionv as, Well. as forming a receptacle4 for the, 'fused conducting material and retain theA same ac'ljacent` thetwo. conductors and maintain the.. el 3ctricalv connec; tion therebetween.
While the construction thus` far described dis.- closes the insulating material and the fusible conducting materialen` differentl conductors, if.` desired, these materials c ouldA be carried by the same conductor, such a con structionbeing illus?, trated in Fig. 4 whereinthe conductor; Ii ispro.- vided with a coating ofv fusible conductingmater, rial 22 over which is a layer of insulating mater.. rial 23, the conductor 24. being.bareand,asheath,v 25 enclosing the two. conductors. This fornilof, cable will function in the samernannen as previously described, for theconstruction,illustrated, in Figs. 2 and 3,A the insulation 2,3V breaking down,v1 upon theY application of the.,required-l amount, of.; heat followed by the fusing of. the condunting` r. terial 22 to establish electrical. connectionubef. tween the' conductors 2-I and 2.4.V
In manufacturing thisconstructiom ifetlie in:V sulating material and fusible ,cpnductingEmateriaL-- are to respond to approximatelythesarne deg/nega of heat, the insulation may beap'pliecl.bysognev other manner thanv dipping, asY for example., by..v helically Winding a sheet stripof-insulationfma e.. rial about the conductor and its coating offnsi; ble conducting material. Y'
In the modified form, ofv theinvention. illustrated in Fig. 5, thetconductor, 3.I is provided with r` a coating of insulation32., this conductorandail insulation coating being lsubst,antialfl7 identical, with the conductor Zand correspondinginsul tion II., while ,the conductor.33is bare. VEx
ing along the twoconductorslis astriptorlrib of. fusible condk cting material-.which.withthe two conductors is enclosedy in'. a'nluter andwhile the crosslsectional isillustrated ascircular,v o of somefotlersuitable shape( The Qperation Of.' this cable likewise wlill'bepsubstantiall asthatdescribed QrQtheothercQns y, insulation y32 breaking'downupo thelap tionoffthe. required amount of. heat/,followed by..
' eetrieelfenr v negentien 1. in heet. respen Ve.; deveesisueh. eating-,may quitebrittleendtnus renderedmnsatisfagtgry,
use as; a conductor dueto possible breakage during installation, etc., breakage vof' theV fusible metal strip 34 would be immaterial insofar as the construction illustrated in Fig. 5 is concerned as the strip 34, does not function as a conductor, consequently breakage thereof would have no egectvA onv the operation of the device and any broken segments would be held in position by the sheath 35 and a supply of material extending throughout the length of the cable at all times. The fusible element could also be formed in some cases as a strip of sheet material and helically Wrapized.21120111111y beth, eendueters.-
It'vill be nete@ that ell, of., the eenstruetiens desetbed include two cendueters operatively in,..-V sulated from one anotherV incombination with a Eligible. conducting Illaterial` onerat'me te ew between andv electrically eenneet the. twe eenduef tofs upon. the blseelfr. down; ef the. nsuletienend. fusing o1. the conducting material.; likewise that. eerlzdueters.. ef. higher. electrical. efleeney, than, av steel, conductor. may: be empleyed.,
It. will. te noted.y from. the aboveY description, that provided. a heat respensive cable which.. be fer-feed. 0f generally' standard. ma-` terials-eni whienisrel vely pliable tefaeiltete.. instellaterl Likewise 1i Willbeneted. thatthe. elieSentecnstluetien prei/ideen, directconneetien between conductors bxasuitable eenduetinemef. terial associated, therewith, independent. ef. en@ Ieslienelt 0f.; beth ef the eeedueters y 113,151 mdeations may, be mede in. the Same. without.. departing from. the. spirit ef. eur invention. hence We de netwish. tube, uudelzsteed; aslimitins. QueSelveStethe .xav/.11; fgml eenstrueiiea. ernaneement. and CombinetiQll if Herts., herein. Shown-l and deSQr-.ileedJ Or uses nflenuonedaheei. reseeueiye eeblathe eembinatien. of; aV pair of relatively soft, pliable conductons,J of eeproiimately. egual. fliemeten et leastv 0f said. eenlueters. beine. twisted argued-f the. einer. ene ef. Seid eenduetersheyinaaeeatina ei annif.. ble..v eleetrieally conducting material, thereon, and, the einer. eeedvete l1 vine a nenne-0i ieerlee tient. tlzvereerlv` Seid. insulation. beine farmed Qi. a materiel which will., bealsdewri respenseta heat, to. servait.v Seid.. @Meeting material?. upon. fusing to flow between the: co d ,and.elec@y tiieelly. eenneet the-Seme; ,and Shealheneleing all. efY thefesneetiveelementsformeel item, terial. requiring greater. emeeretuees forybreeke t ,geistige insulation er` fusible eenfieeina Esneux. JeeKsen..
Ehe. f,ollowirqlg;A references are,r ofv record.yk in. the, ler 0f.: this, patent: