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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.
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