Note: Descriptions are shown in the official language in which they were submitted.
A92-451
~ Z~7~L
-- 1
SPECIFICATION
HEAT SENSITIVE CABLE
AND METHOD OF MAKING SAME
Backqround Of The Invention
The present invention relates to heat sensitive
devices and, more particularly, to a heat sensitive cable
and method of making same.
Heat sensitive cables which are characterized by
the use of semiconductive materials having inverse tempera-
ture-resistance characteristics in conjunction with dissimi-
1-~ lar thermoelectric conductors are now well known in the art.
Such cables are particularly suitable where it is desired to
monitor the greatest temperature existing along the length
of the cable, and are exemplified in connection with a sys-
tem for measuring and locating temperature conditions of
interest in U.S. Patent Nos. 3,408,607 and 4,324,138. Ther-
mistor cables which are characterized by a core of semicon-
ductive material surrounded by a mass of temperature-resist-
ant electrically-insulating material covered with a protec-
tive metallic sheath are also well known in the art.
Despite the clear advantages and many applications
for such cables, they have simply not evolved to the point
of providing the desired degree of versatility. It has
remained to develop a heat sensitive cable capable of gener-
ating a measurable and predictable voltage when the entire
length of cable is at ambient, e.g., 72F, wherein the cable
is also adapted to provide a change in the temperature rep-
71
A92-451
- 2 -
resentative measurable voltage with an increase in tempera-
ture above the prevailing ambient at any location along the
cable. If this could be achieved with an electrical insula-
tion having a negative temperature coefficient, the thermo-
electric output of the cable or a section thereof would bealtered in a predictable fashion.
Moreover, if this could be achieved, the cable
location where an increase in temperature takes place could
be located electronically. This could be done, for in-
stance, as fully disclosed and claimed in my earlier U.S.Patent No. 4,324,138, issued April 13, 1982, for a method of
and apparatus and system for determlning temperature candi-
tion~. As set forth therein, the applications are ~irtually
limitless.
While the value of heat sensitive cable has l~ng
been recognized, it has remained to provide such a cable
having the requisite versatility ~or the many applications
to be benefited by use thereof. In fact, despite my many
prior inventions in this field, as exemplified by U.S. Pat-
ent Nos. 3,408,607 and 3,513,432, the missing link to pro-
viding a highly versatile cable has remained. Despite the
advantages that will be recognized by those skilled in the
art, heat sensitive cable which may not only be utilized to
monitor ambient temperature but also may be utilized to
monitor for any localized increase above ambient temperature
has simply not been available.
Accordingly the present invention seeks
to provide a heat sensitive cable having means for generat-
lng a temperature re~resentative measurable voltage.
Further the present invention seeks to
provide a cable of the type described utilizing a pair of
thermoelectric conductors disposed in contacting side-by-
side relation together with means for passively self-gener-
ating a temperature representative measurable voltage be-
71
A92-451
-- 3
tween the conductors when the cable is exposed to ambient
temperature.
Further still the present invention seeks to
provide a cable of the type described utiliæing a flexible
outer jacket formed of an electrically non-conductive mater-
ial to completely surround the conductors.
The present invention also seeks to
provide a cable of the type described which is not only
passive and self-generating to generate a voltage potential
between the thermoelectric conductors indicati~e o the
temperature exis~i~g alo~g ~he entire length o~ the ca~le,
i.e., the ambient temperature, but which also generates a
voltage potential between the ~onductorc indicative of the
hottest point along the length of the cable i~ the tempera-
tures ~re une~ual.
Still further the present in~ention seeks to
provide a cab~e of the type described in which the
passive self-generating characteristic causes a change in
the temperature representative measurable voltage with an
increase or decrease in temperature at every location along
the jacket.
Furthe,,r still the present invention seeks to
provide a cable of the type described in which the
passive self-generating characteristic causes a change in
the temperature representative measurable voltage with an
increase in temperature above the prevailing ambient at any
location along the jacket.
Further still the present'invention seeks to
provide a cable of the type described capable of
precise, non-perishable, reproducible measurement of the
temperature and identification of the location of the hot-
test spot when monitoring with a high input impedance tem-
perature device.
,
...
The present invention still further seeks to provide
a cable of the type described wherein the outer jacket and the
thermoelectric conductors can be formed of various materials
and combinations of materials to yield various mechanical
properties and temperature-voltage response curves.
These and other aspects, advantages and features of
the present invention will be apparent from a consideration of
the accompanying specification, claims and drawings.
Summary Of The Invention
Accordingly the present invention in one aspect
provides a heat sensitive cable operable in a predictable
fashion over a range of temperatures for generating a
measurab~e voltage indicative of the temperature along the
cable to proyide a contin~s tempelature sensor. The cable
includes a pair of thermoelectric conductors disposed in
contacting side-by-side relation with the conductors being
formed of thermoelectrically dissimilar materials and with
means for passively self-generating a continuous temperature
xepresentative measurable voltage between the conductors when
the cable is exposed to ambient temperature without the use of
an external power source. The continuous temperature
representative measurable voltage is adapted for conversion
into ambient temperature measured in degrees, the passive self-
generating means comprising a material having a negative
temperature coefficient associated with the surface of at least
one of the conductors. A flexible outer jacket is formed of an
electrically non-conductive material completely surrounding the
conductors, the jacket holding the conductors firmly together
substantially along their entire length. The passive self-
generating means causes an increase or decrease in thecontinuous temperature representative measurable voltage
responsive to an associated increase or decrease in ambient
temperature at every location along the cable, the change in
the voltage under such condition being measurable and
representative of an increase or decrease in ambient
temperature and adapted for conversion ~nto a new ambient
temperature along the cable measured in degrees. The passive
self-generating means also causes a change in the continuous
temperature representative measurable ~oltage responsi~e to an
associated increase in temperature above the prevailing ambient
at any location along the cable, the change in the voltage
under such condition also being measurable and representative
of an increase in localized ternperature and adapted for
'7~L
conversion into a maximum temperature along the cable measured
in degrees. Thus the hea-t sensitive cable may be utili2ed not
only to monitor ambient temperature but also to monitor for any
localized increase in temperature over the range of
temperatures for the cable in a predictable fashion to provide
a continuous temperature sensor.
In a preferred embodiment, the passive self-
generating means includes an electrical insulation having a
negative temperature coefficient disposed on the surface of at
least one oE the conductors. Preferably, the conductor is
coated with a solution of manganese nitrate or the surface of
the conductor is covered with heat treated manganese dioxide~
By so doing, the resulting electrical insulation which is
formed on the surface of the conductor has a negative
temperature coefficient and will provide the required
temperature representative measurable voltage throughout the
desired range of temperatures.
In addition, the pair of thermoelectric conductors
disposed in contacting side-by-side relation are advantageously
formed of thermoelectrically dissimilar materials. It has been
found suitable, for instance, for one of the conductors to be
formed of a nickel/chromium alloy and the other of the
conductors to be formed of a copper/nickel alloy.
Specifically, the nickel/chromium alloy may comprise
approximately 90 percent nickel and 10 percent chromium and the
copper/nickel alloy may comprise approximately 55 percent
copper and 45 percent nickel.
With regard to the flexible outer jacket, it is
preferably formed of a material -that may be applied to
completely surround the conductors in a fashion applying
pressure to hold the conductors in contacting side-by-side
relation. In this connection, the material may be of a type
adapted to be extruded onto the conductors, or a material of
-the type adapted to be heat shrunk onto the conductors, or a
material of the type adapted to be wrapped onto the conductors.
Once -the material has been applied to the conductors to form
the flexible outer jacket, the heat sensitlve cable may be
stored on spools due to lts 1exibility and later may be
removed and cut to length for use as needed.
~0 The invention also contemplates a method of
manufacturing a heat sensitive cable operable in a predictable
Eashion over a range of temperatures for generating a
measurable voltage indica-tive of the temperature along the
~2~
-- 6
cable to provide a continuous temperature sensor. The method
includes providing a pair of thermoelectric conductors adapted
to be disposed in contacting side-by-side relation, the
conductors being formed of thermoelectrically dissimilar
materials, providing means for passively self-generating a
continuous temperature representative measurable voltage
between the conductors when the cable is exposed to ambient
temperature without the use of an external power source, the
continuous temperature representative measurable voltage being
adapted for conversion into ambient temperature measured in
degrees and the passive self-generating means comprising a
material having a negative temperature coefficient associated
with the surface of at least one of the conductors. The method
~urther includes positioning the pair o~ therm~electric
conductors so as to be disposed in contacting side by-side
relatian and applying a flexible outer jacket to the conductors
formed of an electrically non-conductive material so that the
conductors are com~letely surro~ded by the jac~et and the
jacket is holding the conductors firmly together substantially
along their entire length. The passive self-generating means
is selected so as to cause an increase or decrease in the
continuous temperature representative measurable voltage
responsive to an associated increase or decrease in ambient
temperature at every location along the cable, the change in
the voltage under such condition being measurable and
representative of an increase or decrease in ambient
temperature and adapted for conversion into a new ambient
temperature along the cable measured in degrees. The passive
self-generating means also is selected so as to cause a change
in the continuous temperature representative measurable voltage
responsive to an associated increase in temperature above the
prevailing ambient at any location along the cable, the change
in the voltage under such condition also being measurable and
representative of an increase in localized temperature and
adapted for conversion into a maximum temperature along the
cable measured in degrees. Thus, the manufacturing method
provides a heat sensitive cable which may be utilized not only
to monitor ambient temperature but also to monitor for any
localized increase above ambient temperature over the range of
temperatures for the cable in a predictable fashion to provide
a continuous temperature sensor.
A92-451
- 7 -
Brief Description Of The Drawinqs
In the drawings:
Figure 1 is a perspective view of a section of
heat sensitive cable in accordance with the present inven-
tion
Figure 2 is a cross-sectional view of the ca~le
illustrated in Figure 1:
Figure 3 is an elevational view of a spool con-
taining the cable illustrated in Figure l;
1~ Figure 4 is a 6chematic view of a method of manu-
facturing heat sensitive cable in accordance with the pres-
ent invention:
~igure 5 i6 a top plan view taken along the line
~-~ of Figure 4;
Figure 6 is an elevational view of a section of
heat sensitive ca~le manufactured in accor~ance with the
method of Figure 4;
Figure 7 is a cross-sectional view taken along the
line 7-7 of Figure 6;
Figure 8 is a schematic view of an alternative
method of manufacturing heat sensitive cable in accordance
with the present invention;
Figure 9 is a top plan view taken along the line
9-9 of Figure 8:
Figure 10 is an elevational view of a section of
heat sensitive cable manufactured in accordance with the
method of Figure 8:
Figure 11 is a cross-sectional view taken along
the line 11-11 of Figure 10;
Figure 12 is a schematic view of another alterna-
tive method of manufacturing heat sensitive cable in accord-
ance with the present invention;
~ 7~ A92-451
Figure 13 is an elevational view of a section of
heat sensitive cable manufactured in accordance with the
method of Figure 12;
Figure 14 is a cross sectional view taken along
the line 14-14 of Figure 13; and
Figure 15 is a schematic view of still another
alternative method of manufacturing heat sensitive cable in
accordance with the present invention.
Detailed Descri~tion Of The Preferred Embodlments
Referring to the drawings, and first to Fiqure ~,
the reference numeral lO designates generally a heat sensi-
tiYe ca~le capab~e of generating a temperature representa-
tive measura~le ~ltage. The cable 10 includes a pair of
thermoelectric conductors 12 and 14 disposed in contacting
side-by-side rel~tion t~ether with means ~or ~assively
self-generating a temperature representative measurable
voltage between the conductors 12 and 14 when the cable 10
is exposed to ambient temperature. A flexible outer jacket
18 formed of an electrically non-conductive material is
provided to completely surround the conductors 12 and 14.
The passive self-generating means includes means for causing
a change in the temperature representative mecsurable volt-
age with an increase or decrease in temperature at every
location along the jacket 18. A change in the temperature
representative measurable voltage under such condition is
representative of a change in ambient temperature. The
passive self-generating means also includes means for caus-
ing a change in the temperature representative measurable
voltage with an increase in temperature above the prevailing
ambient at any location along the jacket 18. With this
arran~ement, the heat sensitive cable 10 may be utilized not
only to monitor ambient temperature but also to monitor for
any localized increase in temperature.
A92-451
In a preferred embodiment, the passive self-gener-
ating means includes an electrical insulation 16 having a
negative temperature coefficient disposed on the surface of
at least one of the conductors 12 and 14. Preferably, the
conductor 12, for instance, is coated with a solution of
manganese nitrate or heat treated manganese dioxide on the
order of 2 to 6 mils thick. By so doing, the resulting
electrical insulation 16 which is formed on the surface of
the conductor 12 will provide the required temperature rep-
resentative measurable voltage throughout the desired rangeof temperatures.
With regard to the electrical insulation 16, the
conductor 12 is provided with a treated surface in one em-
bodiment by coating the conductor 12 with a manganese ni-
trate solution. After the conductor 12 has been coated withthe solution, which is preferably approximately 61 percent
manganese nitrate, the conductor is heated to a temperature
of between 300 and 450DF to complete the surface treatment
process whereby the conductor 12 has an electrical insula-
tion 16 with a negative temperature coefficient. Moreover,as shown in Figure 1, the conductor 14 also preferably has
an electrical insulation ~0 having a negative temperature
coefficient provided by a like surface treatment process.
In practice, it has been found advantageous to
provide the solution of manganese nitrate by heating man-
ganese nitrate at a temperature of approximately 100F. The
manganese nitrate is heated at this temperature until melted
and thereafter the melted manganese nitrate is heated at
between approximately 400 to 500F for approximately 3
minutes. With this procedure, the manganese nitrate is
first reduced from a solid to a thin liquid and is then
converted from a thin liquid to a thick, black substance.
Referring to Figure 2, it will be appreciated that
the elements comprising the heat sensitive cable 10 have
3 ~ A92-451
-- 10 --
been exaggerated in size to enhance the illustration. The
electrical insulation 16 on the conductor 12 and the elec-
trical insulation 20 on the conductor 14 both comprise very
thin surface coatings which are sufficient to permit the
conductors 12 and 14 to be disposed in contacting side-by-
side relation, but separated and electrically insulated by
the thin coatings of electrical insulation 16 and 20. By
reason of the intimate electrically insulated contact of the
conductors 12 and 14, the heat sensitive cable 10 may be
utilized to monitor temperature as indicated in a completely
satisfactory manner.
In the embodiment illustrated in Figure 2, the
conductors 12 and 14 disposed in contacting side-by-side
relation are formed of thermoelectrically dissimilar mater-
ials, e.g., one of the conductors 12 is preferably formed ofa nickel/chromium alloy and the other of the conductors 14
is preferably formed of a copper/nickel alloy. It will be
appreciated, however, that all of the embodiments illustrat-
ed in the drawings need only be formed of thermoelectrically
dissimilar materials, e.g., those commonly known as ANSI K,
E, J, or T thermoelectric pairs, or any other conductors
formed of thermoelectrically dissimilar materials. Never-
theless, when nickel/chromium and copper/nickel alloys are
selected, it has been found advantageous for the nickel/
chromium alloy to comprise approximately 90 percent nickel
and 10 percent chromium and the copper/nickel alloy to com-
prise approximately 55 percent copper and 45 percent nickel.
Considering the flexible outer jacket 18, it may
be formed of any of a number of electrically non-conductive
materials with the desired flexibility characteristics. It
is contemplated that the outer jacket 18 may be formed, for
instance, of a material adapted to be extruded onto the
conductors 12 and 14, or of a material adapted to be heat
shrunk onto the conductors 12 and 14, or of a material
~ A92-451
adapted to be wrapped onto the conductors 12 and 14. Re-
gardless of the method of applying the material to the con-
ductors 12 and 14, it is only necessary that the material
hold the conductors 12 and 14 together under some pressure
in contacting side-by-side relation and be sufficiently
flexible to permit the cable to be wound on a spool 22, as
shown in Figure 3.
With respect to the method of manufacturing the
cable, a pair of thermoelectric cGnductors is initially
provided. Next, means are provided for passively self-gen-
erating a temperature representative measurable voltage
between the conductors when the cable is exposed to ambient
temperature. The conductors are then positioned so as to be
disposed in contacting side-by-side relation. Finally, a
flexible outer jacket formed of an electrically non-conduc-
tive material is applied to the conductors so that the con-
ductors are completely surrounded by the jacket. The pass-
ive self-generating means is selected so as to include means
for causing a change in the temperature representative meas-
urable voltage with an increase or decrease in temperatureat every location along the jacket. A change in the temper-
ature representative measurable voltage under such condition
is representative of a change in the ambient temperature.
The passive self-generating means is also selected so as to
include means for causing a change in the temperature repre-
sentative measurable voltage with an increase in temperature
above the prevailing ambient at any location along the jack-
et. With the manufacturing method of the invention, a heat
sensitive cable is provided which may be utilized not only
to monitor ambient temperature but also to monitor for any
localized increase above ambient temperature.
As previously mentioned, the surface of the con-
ductor is treated by coating the conductor with a manganese
nitrate solution. It is preferable for the solution to
~2~71 A92-451
- 12 -
comprise app~oximately 61 percent manganese nitrate. After
the conductor has been coated, it is heated to a temperature
of between 3000 and 450F to provide an electrical insula-
tion having ~ negative temperature coefficient.
While the invention is not to be construed as
limited to any specific components, one practical embodiment
utilizes either extruded or heat shrinkable rubber for the
flexible outer jacket 18. In this embodiment, one of the
two conductors 12 is 14 gauge Chromel brand wire of Hoskins
Manufacturing Co., Detroit, Michigan, and the other of the
conductors 14 is 24 gauge Constantan brand wire available
from the same co~pany, where both of the wires have been
subjected to a surface treatment process in which they have
first been abrasively cleaned and then coated with a chemi-
cal, such as a manganese nitrate solution, which when heated
and applied under controlled conditions results in a perma-
nent change in the electrical resistivity of the outside
surface of the wires. Specifically, the two wires are
treated by dipping or otherwise coating them in a solution
of 61 percent manganese nitrate and then subjecting them to
temperatures of 300 to 400F for a short period of time in
the range of approximately 3 to 5 minutes.
Referring now to Figures 4 through 7, an alterna-
tive embodiment of the present invention is illustrated.
The heat sensitive cable 24 is preferably identical to the
heat sensitive cable 10 with a single exception, i.e., the
electrical insulation 26 provided on the surface of at least
one of the conductors 28 and 30. As shown, the electrical
insulation 26 is comprised of a powder embedded in a bonding
material.
As illustrated, the surface of the conductor 28 is
provided by coating the conductor 29 with a bonding material
as at 32. Heat is applied to the conductor 28 as at 34
tand/or prior to application of the bonding material) and
* Trade Marks
~2~7~
A92-451
- 13 -
the powdered clectrical insulation is applied as at 36 and
38. As will be seen, the powdered electrical insulation as
at 36 and 38 is embedded in the bonding material 32 by means
of rollers at 40 and 42, respectively. Heat is then applied
as at 44 after the powdered electrical insulation has been
embedded in the bonding material. Finally, the conductors
28 and 30 are inserted into a flexible outer jacket 46,
which is preferably made of heat shrinkable material, after
which heat is applied as at 48 to shrink the flexible outer
jacket 46 thereby forcing the conductors 28 and 30 into
intimate contact with one another.
As for the bonding material, any material capable
of use within the desired temperature limits can be util-
ized. For instance, clear silicone rubber caulk manufac-
tured by General Electric Company is suitable as the bondingmaterial for many applications because it is unaffected by
temperatures ranging from -65DF to 500~F, and it is also
possible to use a conducti~e adhesive such as Amicon CT--
5047-2, C-840, or C-950 sold by the Polymer Products Divi-
sion of Amicon Corporation. When a conductive adhesive isused, it is possible to provide a heavier coating on the
conductors than silicone will normally permit.
With regard to the powdered electrical insulation,
it is preferably heat treated manganese dioxide following
the teachings in myu.s. patent No. 4,491,82~, issued
January 1, 1985 and divisionals thereof including my patents
No. 4,614,024 granted September 30, 1986 and No. 4,540,972
granted September 10, 1985. With this material, the
insulation has an insulation resistance of between
approximately 3,000 and 6,000 ohms at approximately 72F which
has been found sufficient to produce a negative temperature
coefficient insulator operable over a wide temperature range.
* Trade Mark
~ ~s~7~ A92-451
- 14 -
Referring now to Figures 8 through 11, another
alternative embodiment of the present invention is illus-
trated. The heat sensitive cable 50 is comprised of thermo-
electrically dissimilar conductors 52 and 54, and electrical
insulation as at 56 applied on the surface of at least one
of the conductors 54, and a flexible outer jacket 58. As
shown, the electrical insulation as at 56 is applied in a
unique fashion.
In particular, the surface of the conductor 54 ls
provided with an electrical insulation by utilizing a flex-
ible wrap material 60. The flexible wrap material 60, which
can be any flexible material but preferably one that is
absorbent, is covered with a bonding material as at 62 and
the bonding material is embedded with a powdered electrical
insulation as at 64 and 66. Thereafter, the conductor 54 is
wrapped with the flexi~le wr~p material 60.
Once again, the bonding material as at 62 is pref-
erably a temperature resistant adhesive and the powdered
electrical insulation as at 64 and 66 is preferably heat
treated manganese dioxide. The flexible wrap material 60
may be heated before and/or after application of the bonding
material as at 67, it is then rolled as at 68 and 70 immedi-
ately after application of the powdered electrical insula-
tion as at 64 and 66, respectively, and heat is applied
subsequent to rolling as at 71. After the flexible wrap
material 60 has been prepared, it is then wrapped about the
conductor 54, the conductors 52 and 54 are inserted in a
flexible outer jacket 58 of heat shrinkable material, and
heat is applied as at 72.
As shown in Figure 10, the electrical insulation
56 need not totally cover the outer surface of the conductor
54. It is only necessary that the treated flexible wrap
material 60 comprising the electrical insulation 56 be
wrapped sufficiently close together to maintain the surfaces
~ 7~ A92-451
- 15 -
of the conductors 52 and 54 out of contact with one another.
As long as this condition is met, the cable 50 will function
in the intended fashion.
Referring now to Figures 12 through 14, still
another alternative embodiment of the present invention is
illustrated. This embodiment is similar to the embodiment
discussed in connection with Figures 8 through 11, but dif-
fers in that the flexible wrap material which is treated
with bonding material and heat treated manganese dioxide in
Figure 8 has been replaced by a wire 74 formed of heat
treated manganese dioxide as at 76. In other respects, the
cable 78 is essentially the same as the cable 50 in Figures
8 through 11.
In particular, the cable 78 is comprised of a pair
of thermoelectrically dissimilar conductors 80 and 82. The
wire 74, which may be manufactured in accordance with any
desired techni~ue, e.g., the continuous casting method dis-
closed in U.S. Patent No. 3,881,541, is then wrapped about
the conductor 82, the conductors 80 and 82 are inserted into
a flexible outer jacket 84 of heat shrinkable material, and
heat is applied as at 86 to complete the manufacturing pro-
cess. When this has been done, the cable 78 will function
in like fashion to the cable 50 in Figures 8 through 11.
Finally, Figure 15 illustrates one method of manu-
facturing the heat sensitive cable 10 discussed in connec-
tion with Figures 1 through 3. It will be seen that the
cable 10 can be formed by applying the manganese nitrate
solution (prepared as previously discussed) to at least one
of the conductors 14 of the pair of thermoelectrically dis-
similar conductors 14 and 16, and this can be done by spong-
ing on the manganese nitrate solution as at 88, then apply-
ing heat as at 90, and again sponging on manganese nitrate
solution as at 92, and then applying heat as at 94, and
these steps, i.e., sponging on manganese nitrate solution
~ 7~ A92-451
- 16 -
and thereafter heating, can be used once, twice, or as many
times as desired to build up a coating of the desired thick-
ness in assembly line fashion. When the coating has been
applied to the conductor 14, the conductors 14 and 16 are
inserted into the flexible outer jacke~ ~8 ~ he~t shrink-
able material and heat is applied as at g6 to force the
conductors 14 and 16 into intimate contact.
Still referring to Figure 15, it will be observed
that the positive conductor 14 is larger in diameter than
the negative conductor 16. This is done to facilitate wir-
ing the cable to suitable monitoring equipment by assuring
that even untrained personnel will be able to visually iden-
tify the positive conductor and thereafter attach it to the
positive terminal of the equipment and in like fashion iden-
tify the negative conductor and attach it to the negativeterminal, particularly when it is considered that the posi-
tive and negative conductors will usually be the same color.
When it is considered that the size of the conductors can be
as small as approximately 0.012 inches, the advantage of
providing a visibly larger diameter positive conductor will
be apparent.
With regard to coating the surface of one or both
conductors with an electrical insulation, the sole criteria
is to apply a coating that remains ductile. In other words,
the coating is provided with a thickness wherein the cable
is capable of being bent around a small diameter, e.g.,
one-half to one inch in diameter without cracking or other-
wise impairing the surface coating of electrical insulation.
Depending on the diameter of the conductors, the coating
will be thicker or thinner to achieve this result.
With the present invention, a heat sensitive cable
has been provided which is capable of generating a measur-
able voltage when exposed to a temperature of, e.g., 72F.
The voltage measured is representative of that temperature
~ A92-451
- 17 -
(ambient) and the thermoelectric output of the cable or a
section thereof when exposed to a higher temperature will
generate a voltage representative of the higher temperature.
Noreover, the heat sensitive cable is capable of generating
a measurable and predictable voltage as the ambient to which
the entire length is exposed is raised above or reduced
below 72F., e.g., a temperature between around -20F and
500F or higher depending upon the limitations of the mater-
ials being used. The voltage measured is representative of
that temperature (a new ambient) and the thermoelectric
output of the cable or a section thereof when exposed to a
higher temperature would again generate a voltage represent-
ative of the higher temperature. Therefore, the heat sensi-
tive cable may be utilized not only to monitor ambient tem-
perature but also to monitor for any localized increaseabove ambient temperature, and the exact location along the
cable where any localized increase occurs can be located
electronically.
As previously mentioned, the conductors include
chemically treated surfaces, preferably treated with a solu-
tion of manganese nitrate, to provide a permanent insulation
having a high negative temperature coefficient. The thermo-
electric conductors when placed in contacting side-by-side
relation along their entire axial length and held firmly
together by means of the flexible outer jacket over their
entire axial length, as required for a specific application
or measurement, will generate a voltage representative of
the highest temperature along the length of the cable.
Additionally, the cable may be provided with a continuous
metallic sheath for certain applications in accordance with
the teachings of U.S. Patent No. 3,737,997.
As will be appreciated, the heat sensitive cable
of the present invention will constantly generate a measur-
able voltage. This voltage is usable with conventional,
A92-451
- 18 -
inexpensive pyrometers, analog meters, digital readout indi-
cators, strip chart recorders, temperature controllers and
transmitters, state of the art microprocessor based data
loggers, calculating data loggers, programmable controllers,
etc. Further, with the use of conventional time domain
reflectometers and electronic circuitry, the exact-location
along the cable where the maximum temperature exists may be
located.
While all of the embodiments illustrated in the
drawings utili~e a pair of conductors, it will be appreciat-
ed that one or more additional conductors may also be pro-
vided. Such an additional conductor, whether insulated or
non-insulated, may be useful, for instance, where a bridge
network type of location device will be u~ed. Accordingly,
the present invention is to be construed as requiring a
minimum of two thermoelectric conductors.
With the present invention, an inexpensive product
has been provided which may be easily installed by inexper-
ienced persons utilizing the same conventional means as used
in modern home construction and wiring. The cable is also
reusable (within the limits of the cable materials) and
effectively provides a continuous temperature sensor. More-
over, the present invention results in the formation of a
permanent, flexible, exterior surface insulation condition
with a high negative temperature coefficient.
Finally, it is possible to provide an essentially
continuous heat sensitive cable, i.e., the cable can be
produced in lengths of thousands of feet, at a fraction of
the cost of making conventional types of constructions of
heat sensitive devices or cables.
With the present invention, the heat sensitive
cable provides a thermocouple temperature monitoring device
which consists of a pair of conductors having surfaces
treated with an electrical insulation having a negative
~ ~ A92-451
-- 19 --
temperature coefficient within a flexible outer jacket. The
cable is passive and self-generating to generate a voltage
potential between the thermoelectric conductors which is
indicative of the temperature existing along its entire
length, or if the temperatures are unequal, at the hottest
point along the cable length when subjected to external
temperatures. When monitored by a high input impedance
temperature device, the heat sensitive cable is capable of
(1) precise, nonperishable, reproducible measurement of the
temperature and (2) identification of the location of the
hottest spot, and is capable of utilizing varying combina-
tions of materials to yield various mechanical properties
and temperature-voltage response curves.
Various changes coming within the spirit of the
present invention may suggest themselves to those s~illed in
the art. Hence, it will be understood that the invention is
not to be limited to the specific embodiments shown and
described or the uses mentioned. On the contrary, the spe-
cific embodiments and uses are intended to be merely exem-
plary with the present invention being limited only by thetrue spirit of the scope of the appended claims.
