US2470711A - Fire alarm - Google Patents

Description

May 17, 1949.

I. O. MOBERG FIRE ALARM Filed Jan. 3, 1946 2 Sheets-Sheet 1 Patented May 17, 1949 UNITED STATES FATENT OFFICE 2,470,711 F R ALARM Ivar O. Moberg,'Lowell, Mass. Application January 3, 1946,. Serial No. 638,835

This invention relates to automatic fire alarms and fire alarm systems of a type suitable for use in dwellings and other buildings in which elaborate forms of apparatus of this character are too expensive to be afforded. It is an important ob-* ject of this invention, therefore, to devise an exceptionally simple apparatus of this character which can be manufactured and installed economically, but which will be thoroughly practical and reliable.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.

In the drawings,

Fig. 1 is a front elevation of a preferred form of fire alarm embodying this invention;

Fig. 2 is a side elevation of the apparatus shown in Fig. 1;

Fig. 3 is a diagrammatic view of a system embodying features of this invention;

Fig. 4 is a side view of a switch unit designed for use in the system shown in Fig. 3; and

Fig. 5 is a front view of the device shown in Fig. 4 with some parts broken away. 7

Referring first to Figs. 1 and 2, the construction there shown comprises an electric gong ZClaims. (017177-311) the name of Vinyon fiber is preferred.

migh t make it unreliable.

non-absorbent, non-inflammable, except upon 1 of a 'copolymer of vinyl chloride and vinyl acetate. That available commercially under It has the advantage of being exceptionally stable and unaffected by the common agents which For example, it is direct exposure to flame, permanently waterresistant,'mi1dew-proof, and is acid-proof for all practical purposes important in connection with this invention. While the unstretched Vinyon yarn has a very low tensile strength, the stretched varieties are very strong. One form known as ST Vinyon yarn is pre-stretched about 50%, while another, known as HST, is pre-stretched 100%. These both have surprisingly high tensile strength. Also, both have the characteristics,

valuable for the purposes of this invention, of rewith the usual vibrating hammer 4, and the customary, or any other suitable means, for actuating said hammer, said means being enclosed in the casing 5. In the arrangement shown, the panel 2 forms the front of a box or casing 6 in which a dry battery I, or some other convenient source of electric current, such as a bell transformer, is mounted.

For the purposes of this invention, the operating circuit for the bell is controlled by a simple form of switch comprising a wire arm 8, a portion of which is wound around the screw 9 to form a spring l0, Fig. 2, the screw anchoring the spring to the panel. Cooperating with this arm are two stationary contacts a and 12, both formed on, or secured to, a contact plate l2 which is screwed to the panel 2, and the arm carries a contact c positioned between the stationary contacts a and b and adapted to engage either of them. The free end of the spring switch arm 8 terminates in a hook 8" to which a length l3 of thermoplastic thread, string, cord, or other filamentary material, hereinafter referred to generically as thread, is secured, its opposite end being fastened to a binding post l4.

According to this invention the thread I3 is 'maining very stable as to length, as their temperature is raised, up to about 148 F. At this point the thread contracts about 5% in length and contraction continues as the temperature rises until either the melting point of 260 F. is reached or the thread has contracted to its original length. Once contracted, the thread remains stable in length at decreasing temperatures. This characteristic is used in the apparatus shown in Figs. 1 and 2. Assuming that the assembly there shown is in operation, and the temperature of the thread I3 is raised to some point above 148 F., the thread will contract, thus bringing the contact 0 into engagement with the contact I). This completes a circuit from the battery terminal l5 through the conductor l 6, spring switch arm 8, contacts 0 and b, and wire l1, through the bell solenoid and conductor I8, to the other battery terminal 20.

If the fire should reach the thread l3, or it should become broken for any reason, then the switch arm 8 is released, thus bringing the contact 0 into engagement with the contact a and closing the bell circuit again.

Thus the alarm is sounded either upon its rupture or overheating, that is the raising of the temperature of the thermoplastic thread l3 above the critical point in the neighborhood of 148 F.

Because of the nature of fibers made of the copolymer above designated, there is practically no danger of the thread [3 deteriorating sufliciently to render the device inoperative, and a very infrequent inspection of the apparatus is sufficient to determine the operativeness of the electrical elements of the apparatus.

The apparatus may be located in any con- 3 venient spot where it is believed that fire is most likely to occur as, for example, by hanging it on a hook, an aperture 2|, Fig. 1, being provided in the casing 6 for this purpose. When it is desired to use any substantial number of these alarms located at difierent points in the building, a series of independent units, such as that shown in Figs. 1 and 2, may be employed, or a single unit of this nature may be connected up to a number of switch units so that ithezrupture tor cnntmctionof the controlling element I3 at anyone-mt these points will sound the alarm.

A switch unit suitable for this purpose is shown in Figs. 4 and 5 in which the parts corresponding to those shown in Figs. 1 and 2 are designated by the same, but primed, numerals. .lilene the spring arm 8' is arranged as before withits contact 0 operating between'upper and'*lower=cooperating contacts a and b, and the;;plateilflf.

on which the latter aremounted, is provided with 20 ,a terminal bindingscrew 22. The thread L3 ,is

tensioned between the hook of the 'springarm and the binding post [4. .Eor convenience :in installation it is usually preferable totconnect ,the

spring 10' by a conductor 123$.to a-iterminal screw "rise above its critical temperature, or shouldfbu-m .ofisor' become broken, the .alarm will immediately be sounded and .warning givenn'f the .pvefiheatin ,orffailure of one of the thermoplastic "Thus the invention provides ;a .very simple, reliable and inexpensive form. of fire .alarm which can be quickly installedby .any .one {familiar with simple electrical circuits, or even by ".the Ihouseholder himself.

While I have herein shown and described a preferred embodiment of, myinvention it istcontemplated that the invention .may .be embodied in other ,iorms withoutdeparting from the spirit orscope thereof.

Having thus described my invention, what I .desire to claim 7 as anew is:

1. An apparatus of the character described, comprising an electrically operated alarm device, an electric circuit in which said device is operatively connected, 9, switch in said circuit comprisin a movable contact and two stationary contacts, said movable contact being located between said stationary contacts, a means connected with said movable contact and tending to move the latter into engagement with one of said 10 @atationary contacts, and aithread connected with $83! movable contact and holding it normally in its open position, said thread being composed (essentially of a, .copolymer of vinyl chloride and ivinyl acetate and being prestretched, whereby it operates upon overheating to shrink and thereby itmcloseathe circuit through one of said stationary contacts and .upon rupture to close the circuit through "the other of said stationary contacts.

RNA-n apparatus of the character described, comprising an arm carrying a switch contact, stwoiadditionalccontactsbetween which the contactxrmvable .withsaidarm operates, and a prelstretchedathread,composedessentially of a copoldimer of .vinyl ,chloride and vinyl acetate coninettteditmsaid arm .and controlling the engagemerit :01 ithe latter-contact with one of said additionalpontacta-wherebythe,rupture of the thread ,permitssaidiarmtdmove.its contact into engage- ..ment ,Wit h tone .of said :additional contacts and the shrinkage of said thread by overheating ,causesitltozmove,saidarm sufiiciently to make its :cuntact enga e ,the other of said additional rnrrtactssand wielding, 1111531115 connected with said rmvabtetcontact iorlurging thesame toward'one -0: said additional :contacts.

IVAR O. -MOBERG.

.CITED iliize ffiollnmingreferences are of record in the l l file of this patent:

UNIQREE :SZIATES PATENTS Number Name .Date

film-M5 Cantrell Dec. 5 1893 8&73310' Bestul Mar. 19, 1907 1,132,103 -McGlanaha-n Mar. 16,1915

'EQREIGN PATENTS :1hunizer ,Country Date rGreatBritain Aug. 13, 1943

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