Flexible Electrical Resistance Heating Element

Abstract

An electricl resistance element having a conductor provided with a pair of lead attaching ends, each lead attaching end having a plurality of spaced and predetermined lead attaching parts therealong. A pair of leads are respectively electrically attached to one preselected lead attaching part of each end of the conductor so that the desired electrical resistance is provided through the conductor between the attached parts of the leads. An encasing structure completely covers the conductor and part of the leads whereby the remainder of the leads extend from the encasing structure, the encasing structure being provided by a pair of flexible tape-like strips superimposed on each other and securing part of the leads and the conductor therebetween.

Description

This invention relates to an improved electrical resistance element and to a method of making the same.

It is well known from the U.S. patent to Snoberger et al., No. 3,537,053, that a flexible temperature sensor can be provided for motor protection purposes and be formed by a conductor that is secured between two flexible stip-like members superimposed upon each other with a pair of leads being attached to the respective ends of the conductor so that the conductor will provide a certain electrical resistance between the leads at certain temperatures whereby such flexible temperature sensor can be utilized for motor protection purposes by being inserted in the coil means of an electrical motor to detect the temperature changes therein by having the changes in the electrical resistance of the encased conductor sensed by an appropriate sensor.

However, it has been found according to the teachings of this invention that the precision or accuracy of the above described temperature sensor depends upon the length of the wire between the soldered connections of the leads thereto as well as the uniformity of the conductor throughout its length and that measurement of the actual resistance of such conductor during assembly of the sensor is not feasible.

Accordingly, it is a feature of this invention to provide an improved electrical resistance element of the above the like wherein a desired electrical resistance of the conductor can be readily ascertained during the making of such electrical resistance element or the like.

In particular, one embodiment of the electrical resistance element of this invention comprises a conductor having a pair of lead attaching ends each having a plurality of spaced and predetermined lead attaching parts therealong. A pair of leads are respectively electrically attached to one preselected lead attaching part of each end of the conductor so that the desired electrical resistance is provided through the conductor between the attached leads because a testing of the electrical resistance of the conductor between various lead attaching parts thereof can be readily determined before the leads are attached thereto. After the leads have been attached to the preselected lead attaching parts of the lead attaching ends of the conductor, an encasing structure completely covers the conductor and the attaching parts of the leads whereby the remainder of the leads can extend from the encasing structure for control device attaching purposes or the like, the encasing structure comprising a pair of flexible tape-like strips superimposed on each other and securing the conductor and the attaching parts of the leads therebetween.

Accordingly, it is an object of this invention to provide an improved electrical resistance element having one or more of the novel features set forth above or hereinafter shown or described.

Another object of this invention is to provide an improved method of making such an electrical resistance element or the like, the method of this invention having one or more of the novel features set forth above or hereinafter shown or described.

Other objects, uses and advantages of this invention are apparent from a reading of this description, which proceeds with reference to the accompanying drawings forming a part thereof and wherein:

FIG. 1 is a perspective view illustrating one embodiment of the improved electrical resistance element of this invention.

FIG. 2 is a schematic broken away, cross-sectional view of an electrical motor utilizing the electrical resistance element of FIG. 1 for motor protection purposes.

FIG. 3 is an exploded perspective view illustrating the various parts of the electrical resistance element of FIG. 1.

FIG. 4 is a perspective view illustrating the method of making the electrical resistance element of FIG. 1.

FIG. 5 is a top view of part of another electrical resistance element of this invention.

While the various features of this invention are hereinafter described and illustrated as being particularly adapted to provide a temperature sensor for motor protection purposes or the like, it is to be understood that the various features of this invention may be utilized singly or in any combination thereof to provide an electrical resistance element for other purposes as desired, such as for making an electrical heating element or the like.

Therefore, this invention is not to be limited to only the embodiments illustrated in the drawings, because the drawings are merely utilized to illustrate one of the wide variety of uses of this invention.

Referring now to FIGS. 1 and 3, the improved electrical resistance element of this invention is generally indicated by the reference numeral 10 and comprises a pair of flexible tape-like strips 11 and 12 formed of insulating material hereinafter set forth and being superimposed upon each other to be heat sealed together by an apparatus that is generally indicated by the reference numeral 14 in FIG. 4 and hereinafter described, the tape-like strip 12 having printed, etched or otherwise disposed thereon a conductor 15 formed in a predetermined tortuous path between two lead attaching ends thereof that are generally indicated by the reference numerals 16 and 17 in FIG. 3.

The lead attaching ends 16 and 17 of the conductor 15 are each provided with a plurality of flat rectangular lead attaching parts 18, 19 and 20, spaced from each other along the respective lead attaching ends 16 and 17 so that the conductor 15 between each pair of adjacent lead attaching parts 18 and 19 or 19 and 20 has a length thereof also disposed in a tortuous path therebetween so that resistance can be added or subtracted to the remainder of the conductor 15 depending upon where leads are attached to the lead attaching ends 16 and 17 thereof as will be apparent hereinafter.

For example, it may be desired to make the electrical resistance element 10 so that the same has a resistance of approximately 75 ohms between the desired lead attaching location thereof when the element 10 is at approximately 75.degree.F.

Thus, before a pair of leads 21 and 22 are attached thereto, the strip 10 with the conductor 15 thereon is maintained at 75.degree.F. and the resistance of the conductor 15 is appropriately measured between the lead attaching parts 18 of the lead attaching ends 16 and 17, the resistance of the conductor 15 is measured between the lead attaching parts 19 of the lead attaching ends 16 and 17 and the resistance of the conductor 15 is measured between the lead attaching parts 20 of the lead attaching ends 16 and 17 to find out which combination of lead attaching parts 18, 19 or 20 will provide a resistance closest to the desired 75 ohms. In fact, such testing or measuring could be between the lead attaching parts 18 and 19 of the respective lead attaching ends 16 and 17, etc., as desired.

Such testing of the resistance of the conductor 15 on the strip 12 can be made at a location remote from the apparatus 14 and the resistance between the various lead attaching parts of the lead attaching ends 16 and 17 could be appropriately marked on the tape-like strip 12 so that subsequently a person can attach the leads 21 and 22 thereto at whichever resistance producing arrangement is desired.

In any event, it can be seen that the conductors 21 and 22 are adapted to have the insulation 23 thereof removed adjacent the ends 24 and 25 thereof with the ends 24 and 25 respectively having outwardly turned parts 26 so that the lead ends 24 and 25 can be disposed between the spaced and parallel lead attaching ends 16 and 17 while the outwardly turned parts 26 thereof will respectively contact the lead attaching parts 18, 19 or 20 as illustrated to be readily soldered or otherwise suitably electrically attached thereto, the lead attaching parts 18, 19 and 20 being substantially large rectangularly shaped conductor sections printed, etched or otherwise disposed on the tape-like member 12 as illustrated to facilitate lead attachment thereto.

After the lead ends 24 and 25 have been attached to the desired lead attaching parts 18, 19 or 20, or any desired combination of the parts 18, 19 and 20, of the conductor 15, which in the embodiment illustrated in the drawings are the lead attaching parts 19 of the lead attaching ends 16 and 17 in the manner illustrated in FIG. 3, the strip 11 can be superimposed thereon and be heat sealed thereto by the apparatus 14 whereby the conductor 15 and the end parts 24 and 25 of the leads 21 and 22 are completely covered or encased in the flexible strips 11 and 12 in the manner illustrated in FIG. 1 to complete the electrical resistance element of this invention. Thus, it can be seen that the actual resistance of the conductor 15 between the lead attaching parts 26 of the leads 21 and 22 has been accurately provided as the resistance between the lead attaching parts 19 of the lead attaching ends 16 and 17 of the conductor 15 was readily predetermined in the manner previously described so that the electrical resistance element 10 will be most accurate for its intended purpose.

For example, the completed electrical resistance element 10 is adapted to be readily disposed between various coils 27 and 28 of the coil means 29 of an electrical motor means 30 as illustrated in FIG. 2 and be interconnected by the leads 21 and 22 thereof to a control device 31 which will sense the change in the resistance of the conductor 15 as the motor 30 heats up so that should the temperature of the motor 30 exceed a certain limit, the sensor 31 can turn off the motor 30 to avoid an adverse situation whereby it can be seen that the element 10 of this invention can be utilized for motor protection purposes.

For further details of the use of the element 10 for motor protection purposes and the various advantages thereof over other known types of motor protection temperature sensing means, see the aforementioned U.S. patent to Snoberger et al, No. 3,537,053, which is incorporated in this application by reference.

As previously stated, the tape-like strips 11 and 12 are formed from non-conductive material and can each comprise a polyimide resulting from the polycondensation reaction between pyromellitic dianhydride and an aromatic diamine sold by the E. I. DuPont de Nemours & Company, Inc., of Wilmington, Del., under the trade name of "Kapton." The heat sealing facing surfaces of the strips 12 and 11 can be coated with a copolymer of tetrafluoroethylene and a hexafluoropropylene sold under the trademark of "Fep-Teflon" by E. I. duPont de Nemours & Company, Inc., of Wilmington, Del.

In this manner, when the teflon coated sides of the strips 11 and 12 are brought together in the manner illustrated in FIG. 4 and heated by heat sealing elements 32 and 33, the facing sides of the strips 11 and 12 are completely heat sealed together in the manner fully set forth in the aforementioned patent to Snoberger et al., No. 3,537,053.

While one particular tortuous pattent of the conductor 15 of the element 10 of this invention is provided in FIGS. 1 and 3, it is to be understood that various other patterns of the conductor 15 can be utilized and another such arrangement is illustrated in FIG. 5 wherein a flexible strip 34 has a conductor 35 printed, etched or otherwise disposed thereon in a tortuous pattern and having lead attaching ends 36 and 37 respectively provided with spaced lead attaching parts 38, 39 and 40 therealong for subsequently having leads attached thereto and be covered by a superimposed strip in the same manner as the strip 12 previously described.

However, it can readily be seen in FIG. 5 that the particular tortuous pattern of the conductor 35 between adjacent lead attaching parts 38 and 39 or 39 and 40 of the respective lead attaching ends 36 and 37 places a greater amount of the trim resistors in what would be considered the sensing area of the strip 34 than might be the case with the areas disposed between the attaching parts of the conductor 15 previously described.

Therefore, it can be seen that this invention not only provides an improved electrical resistance element, but also this invention provides an improved method of making such an electrical resistance element or the like.

While the form and method of this invention now preferred have been illustrated and described as required by the Patent Statute, it is to be understood that other forms and methods can be utilized and still come within the scope of the appended claims.

Claims

What is claimed is:

1. An electrical element comprising a conductor having a pair of lead attaching ends, each lead attaching end having a plurality of spaced and predetermined lead attaching parts therealong, a pair of leads respectively electrically attached to one preselected lead attaching part of each end of said conductor so that a desired electrical resistence is provided through said conductor between said leads, and an electrically non-conductive and flexible encasing structure having opposed ends completely covering said conductor and having part of one of said opposed ends covering part of said leads whereby the remainder of said leads extend from said one opposed end of said encasing structure.

2. An electrical element as set forth in claim 1 wherein said conductor is disposed initially generally in one plane in said encasing structure.

3. An electrical element as set forth in claim 2 wherein said conductor is disposed in a tortuous pattern between the lead attaching parts that provide the shortest electrical circuit through said conductor between said lead attaching ends thereof.

4. An electrical element as set forth in claim 3 wherein each lead attaching end is disposed in a tortuous pattern between adjacent lead attaching parts thereof.

5. An electrical element as set forth in claim 4 wherein the lead attaching parts of each lead end are disposed in aligned relation with each other.

6. An electrical element as set forth in claim 5 wherein the lead attaching parts of said lead ends are disposed in two rows disposed parallel and spaced from each other. disposed;

7. An electrical element as set forth in claim 6 wherein said leads are disposed between said rows and have ends outwardly turned to engage the desired lead attaching parts and be secured thereto.

8. An electrical element as set forth in claim 1 wherein said encasing structure comprises a pair of flexible tape-like strips superimposed on each other and securing said part of said leads and said conductor therebetween.

9. An electrical element as set forth in claim 1 wherein said element comprises a temperature sensor.

10. An electrical element as set forth in claim 1 wherein said element comprises an electrical heating element.