WO2003010779A1

WO2003010779A1 - Heat sensitive cable and method of making same

Info

Publication number: WO2003010779A1
Application number: PCT/US2001/023043
Authority: WO
Inventors: Bayard C. Davis
Original assignee: Xco International Incorporated
Priority date: 2001-07-23
Filing date: 2001-07-23
Publication date: 2003-02-06

Abstract

A heat sensitive cable (10) capable of generating a temperature representative measurable voltage includes a pair of thermoelectric conductors (12 & 14) formed of thermoelectrically dissimilar materials, wherein at least one of the conductors (12 & 14) is coated with a negative temperature coefficient material. A fiberglass insulation material (16) is associated with the surface of at least one of the conductors (12 & 14), wherein the fiberglass insulation material (16) is treated with a moisture impervious solution to provide protection against the ingress of moisture. The conductors (12 & 14) are formed into and maintained as a contacting pair to permit the generation of a measurable temperature indicative voltage wherein the conductors (12 & 14) are held in contact by a surrounding fiberglass material (20) which is also treated with a moisture impervious solution. A shielding material (24) having a non-conductive material (24a) and a conductive outer layer (24b) is applied so as to completely surround and enclose the pair of conductors (12 & 14) in order to maximize the shielding effectiveness thereof. A outer layer of insulation (28) surrounds the overall fiberglass layer (20). Additionally, a flexible jacket (22) formed of electrically non-conductive material is applied to completely surround and enclose the shielding material (24) in order to hold the conductors (12 & 14), the surrounding fiberglass insulation (20), the overall insulation layer (20) and the shielding material (24) firmly in a desired position.

Description

HEAT SENSITIVE CABLE AND METHOD OF MAKING SAME

FIELD OF THE INVENTION The present invention generally relates to heat sensitive devices and, more particularly, to a heat sensitive cable and method of making same.

BACKGROUND OF THE INVENTION

For years, heat sensitive cables characterized by the use of semiconductive materials having inverse temperature-resistance characteristics in conjunction with dissimilar thermoelectric conductors have been known in the art. There are many applications where it is desired to have the capability of monitoring the greatest temperature existing along the length of the cable, and heat sensitive cables of the type described are particularly suitable for such applications. Additionally, thermistor cables characterized by a core of semiconductive material surrounded by a mass of temperature-resistant electrically-insulating material covered with a protective metallic sheath are also well known in the art.

Unfortunately, such cables have simply not evolved to the point of fully providing the desired degree of versatility despite the clear advantages and many applications for them. However, the art of heat sensitive cables was advanced considerably by the teachings in my earlier U.S. Patent No. 4,647,710 which provided for a cable contained within a flexible outer jacket formed of an electrically non- conductive material and which had the unique capability of not only monitoring a prevailing ambient temperature but also monitoring for any localized increase in temperature relative thereto at any location along the cable. By achieving this with an electrical insulation having a negative temperature coefficient, it was possible to ensure that the thermoelectric output of the cable would be altered in a predictable fashion.

While the value of heat sensitive cable has long been recognized, the goal of providing such a cable with the requisite versatility for many applications was achieved by U.S. Patent No. 4,647,710. However, while the cable there disclosed represented a significant step forward, it has remained to provide such a cable with resistance to moisture and elimination or significant reduction in the four types of noise which bother process instrumentation, i.e., static, magnetic, crosstalk, and common mode. Accordingly, the present invention is directed to improving heat sensitive cables by accomplishing such objectives to thereby further advance the art in at least the foregoing important respects.

SUMMARY OF THE INVENTION In view of the foregoing, the present invention is directed to a heat sensitive cable having a construction that provides for significantly enhanced moisture imperviousness and/or shielding effectiveness. The cable comprises a pair of thermoelectric conductors which are formed of thermoelectrically dissimilar materials wherein at least one of the conductors has a negative temperature coefficient material which is associated with the surface thereof. With this arrangement, the cable also includes a flexible outer jacket formed of electrically non-conductive material to hold the pair of conductors in contact by completely surrounding and enclosing them. In a first embodiment, the heat sensitive cable includes a fiberglass insulation material covering the surface of at least one of the conductors. The fiberglass insulation material is advantageously treated with a moisture impervious solution to provide protection against the ingress of moisture. The conductors are advantageously formed into, and maintained as, a contacting pair to permit generation of a measurable temperature indicative voltage. For this purpose, the pair of conductors are also surrounded by and covered with a fiberglass insulation material that has been treated with the moisture impervious solution.

With the foregoing construction, the flexible outer jacket preferably surrounds and completely encloses the fiberglass insulation material surrounding and covering the pair of conductors.

In a highly preferred embodiment of the invention, fiberglass insulation material which has been treated with a moisture impervious solution covers the surface of both of the conductors. The pair of fiberglass insulation covered conductors are then, in turn, further surrounded by and covered with the same type of moisture impervious fiberglass insulation material which, in each instance, preferably takes the form of individual continuous wraps of braided fiberglass thread. Advantageously, the pair of conductors is formed into a twisted pair and the moisture impervious solution used to treat the fiberglass insulation material is a silicone-based waterproofing compound.

In another important respect, the heat sensitive cable preferably includes a shielding material having a non-conductive inner layer as well as a conductive outer layer which completely surrounds and encloses the pair of conductors to maximize shielding effectiveness. The shielding material is preferably disposed outwardly of the fiberglass insulation that surrounds and covers the insulation covered conductor pair. With this arrangement, the flexible outer jacket then completely surrounds and encloses the shielding material in such a manner as to cause the pair of conductors to be held in a contacting position so as to be able to generate a measurable temperature indicative voltage.

Advantageously, the shielding material is a tape helically wound so as to be in overlying relation to completely surround and enclose the conductors. In a further respect, it can also be advantageous to utilize an insulation layer tightly positioned about the helically wound tape to ensure a continuous tubular outer conductive layer for maximum shielding. In a still further respect, a drain wire can be provided between the conductive outer layer of the shielding material and the electrically non-conductive flexible outer j acket. In addition to the heat sensitive cable, the present invention is also directed to a method of manufacturing a heat sensitive cable which comprises the step of providing a pair of conductors formed of thermoelectrically dissimilar materials which are adapted to be disposed in contact. The method also includes the step of applying a fiberglass insulation material to the surface of at least one of the pair of conductors and treating the fiberglass insulation material associated with the surface of the at least one conductor with a negative temperature coefficient material. The method further includes forming the conductors after applying the fiberglass insulation material to the surface of at least one of them into a twisted pair to thereby provide for magnetic noise reduction and then applying a fiberglass insulation material to the twisted pair of conductors to maintain conductor contact. The method still further includes treating the fiberglass insulated twisted pair of conductors with moisture impervious solution to protect against moisture ingress and then applying a shielding material having a non-conductive inner layer and a conductive outer layer to enclose the conductors. Finally, the method includes applying a flexible outer jacket formed of an electrically non-conductive material to surround and enclose the shielding material and hold the components in a desired operative assembled position and relationship where the heat sensitive cable can function to provide a temperature representative measurable voltage.

With the foregoing, the method preferably includes utilizing a continuous wrap of braided fiberglass thread for the fiberglass insulation material applied to the surface of at least one of the pair of conductors. However, it is advantageous for there to be a separate continuous wrap of braided fiberglass thread applied to each one of the pair of conductors. Still further, a continuous wrap of braided fiberglass thread is preferably applied about the insulation covered pair of conductors as the fiberglass insulation material for maintaining conductor contact. In accordance with the method, the moisture impeivious solution used to treat the continuous wraps of braided fiberglass thread preferably comprise a silicone-based waterproofing compound. Further, the shielding material is advantageously applied by helically winding a tape having a non-conductive inner layer and a conductive outer layer to completely enclose the conductors and an insulation layer is advantageously applied tightly about the helically wound tape to ensure a continuous tubular outer conductive layer for maximum shielding. With this understanding of the method, a drain wire is preferably applied between the conductive outer layer of the shielding material and the electrically non-conductive flexible outer jacket. Other objects, advantages and features of the present invention will become apparent from a consideration of the following specification taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an elevational view of a section of heat sensitive cable in accordance with the present invention; Fig. 2 is a cross-sectional view of the heat sensitive cable illustrated in Fig. 1 taken generally along the line 2-2;

Fig. 3 is an elevational view of a spool which has been wrapped with the heat sensitive cable illustrated in Fig. 1 ; Fig. 4a is a schematic view of a one portion of a method of manufacturing heat sensitive cable in accordance with the present invention; and

Fig. 4b is a schematic view of another portion of a method of manufacturing heat sensitive cable in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first to Fig. 1, the reference numeral 10 designates generally a heat sensitive cable capable of generating a temperature representative measurable voltage which includes a pair of thermoelectric conductors 12 and 14 formed of thermoelectrically dissimilar materials in accordance with the present invention. The conductors 12 and 14 are such that at least one of them has a negative temperature coefficient material associated with the surface thereof. The heat sensitive cable 10 also includes a fiberglass insulation material 16 associated with the surface of at least one, and preferably both, of the conductors 12 and 14. The fiberglass insulation material 16 is treated with a moisture impervious solution to provide protection against the ingress of moisture. The heat sensitive cable 10 is also such that the conductors 12 and 14 are formed into, and maintained as, a contacting pair generally designated 18 to permit the generation of a measurable temperature indicative voltage. The contacting pair 18 is formed and maintained as such by a surrounding fiberglass insulation material 20 treated with a moisture impervious solution. With this arrangement, a flexible outer jacket 22 formed of an electrically non-conductive material completely surrounds and encloses the surrounding fiberglass insulation material 20 to hold the contacting pair 18 of conductors 12 and 14 and the surrounding fiberglass insulation material 20 firmly in the desired position.

In a preferred embodiment, the fiberglass insulation material 16 is associated with the surface of both of the conductors 12 and 14. A continuous wrap of braided high temperature fiberglass thread may be used as the fiberglass insulation material 16 applied to the conductor surfaces. Further, the moisture impervious solution used to treat the fiberglass insulation material 16 may be a silicone-based waterproofing compound.

In the preferred embodiment, the contacting pair 18 of conductors 12 and 14 are a twisted pair held in position by the flexible outer jacket 22. The fiberglass insulation material 20 which surrounds the fiberglass insulated conductors 12 and 14 may also comprise a continuous wrap of braided high temperature fiberglass thread treated with a moisture impervious solution. Thus, the moisture impervious solution used to treat the fiberglass insulation material 20 may also be a silicone-based wate roofing compound.

Referring now to Figs. 1 and 2, the heat sensitive cable 10 may include a shielding material 24 having a non-conductive inner layer 24a and a conductive outer layer 24b. The shielding material 24 may completely surround and enclose the fiberglass insulated conductors 12 and 14 to maximize the shielding effectiveness thereof. As shown, the flexible outer jacket 22 entirely surrounds and encloses the shielding material 24 to hold the conductors 12 and 14 so as to generate a measurable temperature indicative voltage.

As will be appreciated, the shielding material 24 may comprise a tape helically wound so as to be in overlying relation to completely surround and enclose the conductors 12 and 14. This tape 24 is approximately 0.0015 inch thick laminated aluminum/Mylar foil shield of the type produced and sold by DuPont. Still additionally, the heat sensitive cable 10 may include a drain wire 26 disposed between the conductive outer layer 24b of the shielding material 24 and the electrically non- conductive flexible outer jacket 22. As previously mentioned, the conductors 12 and 14 may be formed into a twisted pair which assists in providing magnetic noise reduction, and the shielding material 24 may completely enclose the conductors 12 and 14 and the surrounding fiberglass insulation material 20. This maximizes the shielding effectiveness. With this arrangement, the flexible outer jacket 22 completely surrounds and encloses the shielding material 24 to hold the twisted, contacting pair 18 of conductors 12 and 14, the surrounding fiberglass insulation material 20 and the shielding material 24 firmly in the desired position.

As previously suggested, the fiberglass insulation material 16 associated with the surface of one or both of the conductors 12 and 14 is a continuous wrap of braided fiberglass thread. It will be appreciated in this connection that the fiberglass insulation material 16 will comprise a separate continuous wrap of braided fiberglass thread associated with each one of the conductors 12 and 14. As also previously suggested, the fiberglass insulation material 20 surrounding and holding the conductors 12 and 14 in a twisted, contacting pair 18 is a continuous wrap of braided fiberglass thread.

Additionally, the moisture impervious solution used to treat each of the continuous wraps of braided fiberglass thread is preferably a silicone-based waterproofing compound. The shielding material 24 may comprise a tape helically wound so as to be in overlying relation to completely surround and enclose the conductors 12 and 14 and, further, an insulation layer 28 may be tightly positioned about the helically wound tape 24 to ensure a continuous tubular outer conductive layer 24b for maximum shielding. Still further, the drain wire 26 may be provided between the conductive outer layer 24b of the shielding material 24 and the insulation layer 28 under the flexible outer j acket 22. In addition to the foregoing, the present invention is directed to a method of manufacturing a heat sensitive cable 10 which includes the step of providing a pair of conductors 12 and 14 formed of thermoelectrically dissimilar materials which are adapted to be disposed in contact (see Fig. 1). The method also includes the step of applying a fiberglass insulation material 16 to the surface of at least one of the pair of conductors 12 and 14 (see Fig. 1) and treating the fiberglass insulation material 16 associated with the surface of the at least one conductor with a negative temperature coefficient material (see Fig. 4a). The method further includes forming the conductors 12 and 14 after applying the fiberglass insulation material 16 to the surface of at least one of them into a twisted pair 18, e.g., on a 1 inch lay, to thereby provide for magnetic noise reduction and then applying a fiberglass insulation material 20 to the twisted pair 18 of conductors 12 and 14 to maintain conductor contact (see Fig. 1). The method still further includes treating the fiberglass insulated twisted pair 18 of conductors 12 and 14 with moisture impervious solution to protect against moisture ingress (see Fig. 4b) and then applying a shielding material 24 having a non-conductive inner layer 24a and a conductive outer layer 24b to enclose the conductors 12 and 14 (see Fig. 1). Finally, the method includes applying a flexible outer jacket 22 formed of an electrically non-conductive material to surround and enclose the shielding material 24 and hold the components in a desired operative assembled position and relationship where the heat sensitive cable 10 can function to provide a temperature representative measurable voltage (see Fig. 1). In a preferred manner, the method incorporates utilizing a continuous wrap of braided fiberglass thread as the fiberglass insulation materials 16 and 20 applied to the surface of at least one of the pair of conductors 12 and 14 and applied about the pair of conductors 12 and 14 to maintain conductor contact, respectively.

As for other features, the fiberglass insulation material 16 is preferably applied as a separate continuous wrap of 0.015 inch braided fiberglass thread to each one of the conductors 12 and 14. The fiberglass insulation material 20 which is provided to maintain conductor contact may also be applied as a continuous wrap of 0.012 inch braided fiberglass thread about the pair of conductors 12 and 14, and the moisture impervious solution used to treat the continuous wraps of braided fiberglass thread 16 and 20 may comprise a silicone-based waterproofing compound, e.g., a mixture of the types sold under the trademarks or trade designations TPR 178 and TPR 179 by General Electric at a 9:1 ratio (TPR 178 to TPR 179) in a 0.40% solution of zinc octoate, mineral spirits and glycol ether . Also, the shielding material 24 may be applied by helically winding a tape having a non-conductive inner layer 24a and a conductive outer layer 24b so as to have overlapping edges to completely enclose the conductors 12 and 14.

In a highly preferred manner, the method includes the step of applying an insulation layer 28 tightly about the helically wound tape 24 to ensure a continuous tubular outer conductive layer 24b for maximum shielding capabilities. The insulation layer 28 may comprise a high temperature, high dielectric strength fiber tape of the type sold under the trademark "Nomex" by DuPont applied so as to have overlapping edges. Still additionally, the method comprises the step of applying a drain wire between the conductive outer layer 24b of the shielding material 24 and the insulation layer 28 under the electrically non-conductive flexible outer jacket 22.

As will be appreciated from the foregoing, the heat sensitive cable 10 formed in the manner described is capable of generating a temperature representative measurable voltage. This is preferably achieved by utilizing means for passively self- generating a temperature representative measurable voltage between the conductors 12 and 14 when the cable 10 is exposed to ambient temperature. In this connection, the passive self-generating means may include means for causing a change in the voltage with increased or decreased temperature at every location along the cable 10.

When there is such a change in temperature at every location along the cable 10, the temperature representative measurable voltage is indicative of a change in ambient temperature. The passive self-generating means also includes means for causing a change in the voltage with an increase in temperature above the prevailing ambient at any particular location along the cable 10. With this arrangement, the heat sensitive cable 10 may be utilized not only to monitor ambient temperature but also to monitor for any localized increase in temperature above the ambient.

In a preferred manner, the passive self-generating means includes a negative temperature coefficient material which is applied by dipping the conductors 12 and 14 after applying the fiberglass insulation material 16, twisting the conductors

12 and 14, and applying the fiberglass insulation material 20 for 30 minutes as a coil 30 in a tank 32 containing a solution of manganese nitrate 34 which is circulated by an impeller 36 driven by a motor 38 (see Fig. 4a). By saturating the braided fiberglass thread 16 and 20 in a 61% manganese nitrate solution 34, allowing the dipped assembly to drip dry and then baking the assembly at approximately 120° C for 72 hours in an oven 40, it is possible to generate the requisite temperature representative measurable voltage for the heat sensitive cable 10 throughout the desired range of temperature (see, again, Fig. 4a).

As indicated above, the conductors 12 and 14 disposed in contacting twisted-pair relation 18 are formed of thermoelectrically dissimilar materials, e.g., one of the conductors 12 is preferably formed of a nickel/chromium/alloy and the other of the conductors 14 is preferably formed of a copper/nickel alloy. It will be appreciated, however, that the heat sensitive cable 10 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. Nevertheless, when nickel/chromium alloy and copper/nickel alloy are selected, it has been found advantageous for the nickel/chrome alloy to comprise approximately 90% nickel and 10% chromium and the copper/nickel alloy to comprise approximately 55% copper and 45% nickel.

Considering the flexible outer jacket 22, it may be formed of any of a number of electrically non-conductive materials which have the desired flexibility and environmental characteristics required for satisfactory use in a given application for the heat sensitive cable 10. It is contemplated that the outer jacket 22 may be formed, for instance, of a material that can be extruded onto the conductors 12 and 14, or of a material adapted to be heat shrunk onto the conductors 12 and 14, or a material adapted to be wrapped onto the conductors 12 and 14. Regardless of the method of applying the material to the conductors 12 and 14, it is only necessary that the material hold the conductors 12 and 14 together in contacting relation and be sufficiently flexible to permit the cable 10 to be wound on a spool 42 as shown in Fig. 3.

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 22. In this embodiment, one of the two conductors, such as 12, is 24-gauge Chromel brand wire of Hoskins Manufacturing Co., Detroit, Michigan, and the other of the conductors, such as 14, is 24-gauge Constantan brand wire available from the same company. The wires comprising the fiberglass wrapped conductors 12 and 14 are subjected to a surface treatment where they are cleaned and coated after the wrapping of the fiberglass insulation materials 16 and 20 by dipping them as a coil 30 into the tank 32 having a chemical such as a 61% manganese nitrate solution. After the dipping step, the twisted-pair 18 of conductors 12 and 14 are baked in an oven 40 which results in a permanent change in electrical resistivity of the surface of the wires (see Fig. 4a). After the baking step, the fiberglass wrapped conductors 12 and 14 are saturated by dipping then in the previously described silicone-based waterproofing solution generally designated 42 as a coil 44 in a tank 46 which is circulated by an impeller 48 driven by a motor 50 (see Fig. 4b). After the dipped assembly has been saturated with the silicone-based waterproofing compound, it is allowed to drip dry and then baked in an oven 52 at approximately 120° C for 24 hours in order to dry the assembly for application of the tape 24, drain wire 26, insulation material 28 and flexible outer jacket 22 (see Fig. 4b).

As an alternative, the steps of applying the negative temperature coefficient material and the waterproofing compound can be combined into a single step. When this is done, it is only necessary to have a single tank 32 and a single oven 40 such as those illustrated in Fig. 4a and the negative temperature coefficient material can again be a 61% manganese nitrate solution although it has been found advantageous to use a waterproofing compound such as that sold by General Electric under the trade designation SF99 or a similar or comparable compound. When using a single step and such materials, it is has been found advantageous to drive the impeller at 6500 RPM until the solution is warmed to a temperature of approximately 32° C.

After the solution of negative temperature coefficient material and waterproofing compound have been applied, either before or after the conductors have been formed into a contacting, preferably twisted, pair, the assembly is baked in the oven 40 in the manner previously described.

With the present invention, a heat sensitive cable has been provided which is capable of generating a measurable voltage when exposed to an ambient temperature of, e.g., approximately 22° C. The voltage measured is representative of that temperature 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. Moreover, 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 approximately 22° C, e.g., any temperature between around -40^° C and 260° C or higher depending upon the limitations of the materials which are being utilized. 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 representative of the higher temperature. Therefore, the heat sensitive cable may be utilized not only to monitor ambient temperature but also to monitor for any localized increase above ambient temperature, and the exact location of any localized increase can be located electronically.

With the present invention, an inexpensive product has been provided which may be installed by any experienced person 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. Moreover, it is possible to provide an essentially continuous heat sensitive cable that can be produced in lengths of thousands of feet at a fraction of the cost of making conventional types or 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 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, non-perishable, reproducible measurement of the temperature and (2) identification of the location of the hottest spot, while utilizing various materials to yield various mechanical properties and temperature-voltage responsive curves.

While the invention has been described in conjunction with preferred embodiments, various changes coming within the spirit of the present invention may suggest themselves to those skilled 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 specific embodiments and uses are intended to be merely exemplary with the present invention being limited only by the true spirit and scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A heat sensitive cable, comprising: a pair of thermoelectric conductors formed of thermoelectrically dissimilar materials, at least one of the conductors having a negative temperature coefficient material associated with the surface thereof; a fiberglass insulation material associated with the surface of at least one of the conductors, the fiberglass insulation material being treated with a moisture impervious solution to provide protection against the ingress of moisture; the conductors being formed into, and maintained as, a contacting pair to permit the generation of a measurable temperature indicative voltage, by a surrounding fiberglass insulation material treated with a moisture impervious solution; and a flexible outer jacket formed of an electrically non-conductive material completely surrounding and enclosing the surrounding fiberglass insulation material to hold the contacting pair of conductors and the surrounding fiberglass material in position.

2. The heat sensitive cable of claim 1 wherein the fiberglass insulation material is a continuous wrap of braided fiberglass thread.

3. The heat sensitive cable of claim 1 wherein the fiberglass insulation material is associated with the surface of both of the conductors.

4. The heat sensitive cable of claim 1 wherein the contacting pair of conductors are a twisted pair held in position by the flexible outer jacket.

5. The heat sensitive cable of claim 1 wherein the moisture impervious solution is a silicone-based waterproofing compound.

6. A heat sensitive cable, comprising: a pair of thermoelectric conductors fonned of thennoelectrically dissimilar materials, at least one of the conductors having a negative temperature coefficient material associated with the surface thereof; a shielding material having a non-conductive inner layer and a conductive outer layer, the shielding material completely surrounding and enclosing the conductors to maximize the shielding effectiveness thereof; and a flexible outer jacket formed of electrically non-conductive material completely surrounding and enclosing the shielding material to hold the conductors in position to generate a measurable temperature indicative voltage.

7. The heat sensitive cable of claim 6 including a fiberglass insulation material treated with a moisture impervious solution associated with the surface of at least one of the conductors.

8. The heat sensitive cable of claim 7 including a fiberglass insulation material treated with a moisture impervious solution entirely surrounding and maintaining the conductors in contact.

9. The heat sensitive cable of claim 6 wherein the shielding material is a tape helically wound so as to be in overlying relation to completely surround and enclose the conductors.

10. The heat sensitive cable of claim 9 including a drain wire between the conductive outer layer of the shielding material and the electrically non- conductive flexible outer jacket.

11. A heat sensitive cable, comprising: a pair of thermoelectric conductors formed of thermoelectrically dissimilar materials, at least one of the conductors having a negative temperature coefficient material associated with the surface thereof; a fiberglass insulation material associated with the surface of each of the conductors, the fiberglass insulation material being treated with a moisture impervious solution to ensure against the ingress of moisture; the conductors being formed into a twisted pair to provide magnetic noise reduction, the conductors being held in twisted position by a surrounding fiberglass insulation material treated with a moisture impervious solution; a shielding material having a non-conductive inner layer and a conductive outer layer, the shielding material completely enclosing the conductors and suπounding fiberglass insulation material to maximize shielding effectiveness; and a flexible outer jacket formed of an electrically non-conductive material surrounding and enclosing the shielding material to hold the twisted pair, the suπounding fiberglass insulation material and the shielding material in position.

12. The heat sensitive cable of claim 11 wherein the fiberglass insulation material associated with the surface of at least one conductor is a continuous wrap of braided fiberglass thread.

13. The heat sensitive cable of claim 11 wherein the fiberglass insulation material is a separate continuous wrap of braided fiberglass thread associated with each one of the conductors.

14. The heat sensitive cable of claim 13 wherein the fiberglass insulation material surrounding and holding the conductors in a twisted pair is a continuous wrap of braided fiberglass thread.

15. The heat sensitive cable of claim 14 wherein the moisture impervious solution used to treat the continuous wraps of braided fiberglass thread is a silicone-based waterproofing compound.

16. The heat sensitive cable of claim 11 wherein the shielding material is a tape helically wound so as to be in overlying relation to completely surround and enclose the conductors.

17. The heat sensitive cable of claim 16 including an insulation layer tightly positioned about the helically wound tape to ensure a continuous tubular outer conductive layer for maximum shielding.

18. The heat sensitive cable of claim 11 including a drain wire between the conductive outer layer of the shielding material and the electrically non- conductive flexible outer j acket.

19. A method of manufacturing a heat sensitive cable comprising the steps of: providing a pair of conductors formed of thermoelectrically dissimilar materials which are adapted to be disposed in contact; applying a fiberglass insulation material to the surface of at least one of the pair of conductors; treating the fiberglass insulation material associated with the surface of at least one of the conductors with a negative temperature coefficient material; forming the conductors into a contacting twisted pair to thereby provide for magnetic noise reduction; applying a fiberglass insulation material to the twisted pair of conductors to maintain conductor contact; treating the fiberglass insulated twisted pair of conductors with moisture impervious solution to protect against moisture ingress; applying a shielding material having a non-conductive inner layer and a conductive outer layer to enclose the conductors; and applying a flexible outer jacket formed of an electrically non- conductive material to surround and enclose the shielding material and hold the components in position.

20. The method of claim 19 wherein the fiberglass insulation material applied to the surface of at least one of the pair of conductors is a continuous wrap of braided fiberglass thread.

21. The method of claim 20 wherein the fiberglass insulation material is applied as a separate continuous wrap of braided fiberglass thread to each one of the pair of conductors.

22. The method of claim 21 wherein the fiberglass insulation material for maintaining conductor contact is applied as a continuous wrap of braided fiberglass thread about the pair of conductors.

23. The method of claim 22 wherein the moisture impervious solution used to treat the continuous wraps of braided fiberglass thread is a silicone- based waterproofing compound.

24. The method of claim 19 wherein the shielding material is applied by helically winding a tape having a non-conductive inner layer and a conductive outer layer to completely enclose the conductors.

25. The method of claim 24 including applying an insulation layer tightly about the helically wound tape to ensure a continuous tubular outer conductive layer for maximum shielding.

26. The method of claim 19 including applying a drain wire between the conductive outer layer of the shielding material and the electrically non- conductive flexible outer jacket.

27. The method of claim 19 wherein the steps of treating the with the negative temperature coefficient material and treating with moisture impervious solution are performed as a single step.

28. The method of claim 27 wherein the single step is performed before the conductors have been formed into a contacting twisted pair.

29. The method of claim 27 wherein the single step is performed after the conductors have been formed into a contacting twisted pair.