Dec' 24, 1946. L. H. VWALBRIDGE 2,413,125 FIRE DETECTOR CABLE Filed Dec. 3l, 1945 // l‘Patentedl Dec. 24, 1946 2,413,125 UNITED STATES PATENT oFFlcE 2,413,125 \ ma DETECTOR CABLE Lyman H. Walbridge, Ashland, Mass., assignor to Fenwai Incorporated, Ashland, Mass., a cor poration of Massachusetts Application December 31, 1943, Serial No. 516,6054 Claims. ( Cl. 201-83) . This invention relates to lire detector cables oi’ the type wherein an undue rise in temperature at any point in the protected area will close a nor mally opened circuit. . the said elements closely iìttlng the tube. Inter posed between the wire I l andthe tube is a quan tity of sodium nitrate or potassium nitrate, or other suitable material, When lire detector cables having a conductor 5 powder, as indicated at in I3. dry form,_ preferably enclosed within a tube and insulated therefrom by closely spaced insulation bodies' are placed In the embodiment of my invention shown in Fig. 2, the wire Il is surrounded by a mass of suit around the walls of a restricted space, such as the cockpit of an airplane, it has been found that able non-combustible porous material which, in the present instance, is shown as a cylinder i3' the sharp bends to which the tubes are subjected l0 of asbestos, or the like, which is impregnated with will cause the insulation bodies to crack and a solution of potassium nitrate, sodium nitrate, otherwise impair the operation of the cable. or any other suitable salt which is non-conduct `The object, therefore, of the present invention ing at low temperature and conducting at abnor ls to provide a ñre detector cable which has suili- mal temperatures. ' cient iiexibility to enable it to be bent on a small l5 An alarm circuit ls indicated diagrammatically radius of curvature without injury. I have disand includes the battery I_I, or other source of covered that certain salts in dry form are elecvoltage, and an alarm or indicating device I5, trically non-conductive at normal temperatures the terminals of said circuit being conducted to and electrically conductive at abnormal temperathe tube I0 and conductor Il. tures, and that such salts may be employedv to 20 In bOth Figs- 1 and 2J the jagged lines 9J? the insulate an electrical conductor from a conductive ends of the tube and the conductor indicate that tube surrounding the same so that an alarm cirthe cables are of indefinite lengths. Each cable, cuit having its terminals connected to the tube throughout its entire length, has Sllñìcient ilexi and conductor will remain open at normal tembility to permit of bending on a small radius of peratures and will be closed at abnormal or lire 26 curvature without injury either to the tubing temperatures, the salt melting or partially melt~ member or the elements enclosed therein, whereby ing to ailîord a conductive path between the tube liability to short circuit is effectively eliminated. and its enclosed conductor, At normal temperatures the circuit of the in The enclosed conductor may be insulated medicator will be' open and at abnormal tempera chanically from the enclosed tube by spaced in- 30 tures, it will be closed through the conducting sulators and the spaces between the latter filled path aiîorded by the material interposed between with the proper salt in dry form, or the enclosed the tube and thecond-uctor enclosed therein. conductor may be insulated with asbestos or other The term “normal temperature” is used in the suitable insulating material impregnated with a speciñcation and claims as deñning a temperature solution of such salt. I have ascertained that po- 35 lower than that which is generally known in this tassium nitrate and sodium nitrate in dry or powart as “llame temperature.” and the term “ab dered form are non-conducting at ordinary temnormal temperature,” as defining “llame tem peratures- and that they melt or partially melt perature” or a temperature higher than the same. and thereby become conducting at higher temHaving thus described illustrative embodiments peratures. These Salts are typical and charac- 40 of my invention without, however, limiting the teristic of those that can be used in the present invention as they are stable and have relatively low melting points. In the accompanying drawing, same thereto, what I claim and desire to secure by Letters patent is; 1. A readily bendable conductor cable of in deilnite continuous length for detection of ab Flgure 1 is a central longitudinal 'section of a 45 normal temperature conditions at any location ñre detector Cable embßdying my invention and Fig. 2 is a similar section of another embodiment adjacently along it, comprising an electrically conductive tubing element adapted for bending thereof. on a relatively small radius of curvature, an un In the drawing selected to more fully disclose insulated electrical conductor extending continu thepl‘inßiple underlying myinventiûn, |015 atube 50 ously through and spaced from said tubing ele Of Suitable metal, Such as Copper. and Il 1S an ment, discontinuous non-conductive means in uninsulated conductor disposti within said tube and Passing through apertures in spaced insulatins elements I2, herein shown as spherical. although they may have any other suitable shape. u tei-engaging said conductor and tubing element and maintaining the spacing thereof subject to bending of the cable, and in the spaces between said conductor, said tubing element and said non antenas conductive means, a substantially ñlling quantity oi non-gaseous material which is electrically non-= conductive normal temperatures electric- ously through and spaced fro lsaid tubing eie ment, discontinuous non-conductive means inter engaging said conductor and tubing element and ally conductive at abnormal tempera i.; maintaining the spacing thereof subject to bend 2. A readily bendable conductor cable ci in-n 5 ing of the cable, and in the spaces between said definite continuous length for detection of abnor- , conductor, said tubing element and said non-con mai temperature conditions at any location adductive means, a substantially filling quantity of jacently along it, comprising an electrically consodium nitrate in dry for-m. ductive tubing element adapted for bending on e. A readily bendable conductor cable of in- .i a relatively small radius of curvature, an unin- l0 definite continuous length for detection ci ab sulated electrical conductor extending continunormal temperature conditions at any location ously through and spaced l¿rom said tubing eleadiacently along it, comprising an electrically ment, discontinuous non-conductive means interconductive tubing element adapted for bending on engaging said conductor and tubing element and a relatively small radius ot curvature, an unin niaintaining the spacing thereof subject to bend- 15 sulated electrical conductor extending continu. ing oi the cable, and in the spaces between said ously through and spaced from said tubing ele conductor, said tubing element and said nonment, :means interengaging said conductor and conductive means, asubstantially filling quantity tubing element and maintaining the spacing of potassium nitrate in dry form. . thereof subject to bending of the cable, said means 3. A readily bendable conducto cable oi’. in- 20 comprising a non-combustible porous non-gase= definite continuous length for detection of abnormal temperature conditions at any location adjacently along it, comprising an electrically conductive tubing element adapted for bending on a relatively small radius of curvature, an un- 25 insulated electrical conductor extending continui-I ous material impregnated with asubstance which is «electrically no -conductive at normal tem peratures and electrically conductive at abnormal temperatures.