US1985691A

US1985691A - Resistor

Info

Publication number: US1985691A
Application number: US494281A
Authority: US
Inventors: Jr Alexander L Pugh
Original assignee: International Resistance Co
Current assignee: International Resistance Co
Priority date: 1930-11-08
Filing date: 1930-11-08
Publication date: 1934-12-25
Anticipated expiration: 1951-12-25

Description

Dec. 25, 1934. A. L. PUGH. JR

masrswon Filed Nov. 8, 1930 Til/75L A TION DEV/CE- INVENT OR ATTORNEY:

. Patented Dec. 25, 1934 UNITED STATES PATENT OFFICE RESISTOR Application November 8, 1930, Serial No. 494,281

8 Claims.

This invention relates to resistance devices, particularly to wire-wound resistance devices.

An object of the invention is to provide a resistance device of high precision. Another object of the invention is to provide a resistance device of relatively low ohmic resistance and high precision. Another object of the invention is to provide a resistance device in which the effects of thermal electromotive forces are minimized so as to be negligible or are neutralized. Another object of the invention is to provide a resistance device having a low temperature coefficient of resistance. Another object of the invention is to provide a resistance device having a relatively low temperature coefllcient and adapted to generate a counter thermal electro-motive force to neutralize an undesired electro-motive force. Another object of the invention consists in providing a resistance device which, when connected to the terminals of a particular type of circuit, reduces the thermal electromotive force set up in the circuit to a negligible quantity. Another object of the invention is to provide a sectionalized resistance device in which current variations or microphonic characteristics at the junction of the windings are largely eliminated in order, for example, to make the device noiseless in an audio circuit.

Another object of the invention is to provide a method of making resistance devices, having one or more of the above characteristics, which may be readily carried out in practice. Another object of the invention isto provide a method of making resistance devices, having one or more of the above characteristics, whereby the articles may be produced at minimum cost. Another object of the invention is to provide a method of producing resistance devices of relatively low resistance and high precision, which shall be mechanically and electrically sound. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements,

' arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing, in which is shown one of various possible embodiments of the mechanical features of this invention,

Figure 1 is an axial sectional view of the resistance device,

Figure 2 is a view'showing the resistance device and connecting terminals in elevation, and a circuit in which the resistance device is connected in diagram,

Figure 3 is an elevation of the form and windings, before the terminals are integrally connected, and

Figure 4 is an elevation of a binding post terminal.

Similar reference characters refer to similar parts throughout the several views of the drawmg.

The resistance wire of the resistance device is preferably wound upon a ceramic form 10, Fig ures 1 and 3, which has grooves 11 and 12 for the resistance wire, separated by

central flanges

13, 13 integrally formed on the form 10, and bounded by

end flanges

14, 14 which are also integrally formed on the form of ceramic material. By this construction, two entirely separate grooves for resistance wire are provided, these grooves being bounded by insulating flanges, and the wire being adapted to be wound upon cylindrical portions of insulating material, preferably ceramic material.

I first coat the cylindrical portions and the flanges of the grooves 11 and 12 with bakelite varnish, in order to make the winding easier,

and in order to prevent the ceramic material, which, in its natural state, is somewhat of an abrasive, from injuring the insulation of the wire being wound during the winding process.

Extending longitudinally through the form 10 is a central axial bore 15, and thus the form may be mounted upon an arbor for rotation of said form. At both ends of the form 10 are

cylindrical portions

16, 16, one of which may be gripped by a chuck or the like of any suitable winding apparatus adapted to rotate the form 10, in order that resistance wire may be wound into one of the grooves, for example the groove 11. Preferably by means of such a winding apparatus, I wind a desired amount of relatively high resistance wire 17 into the groove 11. Preferably this wire has high resistance, and also a low temperature coefficient. Preferably the greater amount (for example from 93% to 99%) of the total resistance of the device represented by the winding 1'7.

In order to wind the high resistance wire 17 into the groove 11, I preferably secure one end thereof to a chuck and cause the form 10 to be rotated, thus winding the wire into the groove 11. In the commercial production of resistance devices of this general character, it is desirable to have a standard form upon which to'wind the wire. It is highly desirable, therefore, to have definite places where the wire emerges from the winding and leads to binding post terminals, or other devices, whereby the entire unit is placed in circuit with other electrical apparatus. It rarely happens, however, that the exact resistance length of wire desired has a lineal length exactly fitting the form and adapted to fit in the place provided for it without leaving the wire loose. In the attempt to make a device of the right resistance length, and at the same time free from objectionable loose coils, much time has heretofore been wasted. I therefore wind as much of the resistance wire 17, which is preferably nickel alloy wire, into the groove 11 as will make a total resistance slightly less than the resistance desired for the entire device, so that the resistance may be completed to within precision limits by a relatively very small number of turns of low resistance wire. Stating the matter in another way, it is diflicult, if not impossible, in the commercial production of resistance devices of this character to bring the total resistance to the desired amount with high resistance wire, because as the desired resistance is approached, one more turn may make the resistance too high, or one less turn may make the resistance too low. I therefore carefully check the resistance of the nickel alloy wire being wound and stop winding it and cut the end thereof when the resistance length is just below the entire resistance desired. This leaves the form with turns of wire 17 in the groove 11 and two loose ends of wire projecting from it. As an example of what I mean by a nickel alloy wire, a copper nickel wire of 60% copper and 40% nickel may be used.

Some of the advantages of the invention would be secured by completing the resistance device with a winding, in the groove 12, of nickel alloy wire of large diameter, and therefore of low resistance. The desired resistance value of the entire device could thus be reached within high precision limits. But to attain other objects of the invention, I prefer to wind wire 18 into the groove 12 of a metal other than nickel alloy, and preferably I use copper wire. I use copper wire in order to prevent the generation of an undesired net thermal electro-motive force which would otherwise (that is, with the use of a winding 18 of nickel alloy wire) be generated, for the following reasons:

Resistance devices of this general type are adapted to be used-in many kinds of electrical circuits, butv in most electrical apparatus where they might be used connecting terminals or electrodes are made of copper. Copper, of course, is widely used because of its high conductivity, its relative cheapness when used in small quantities, ahd its malleability and ductility, which permit it to be forced into any shape desired. As all metals have a definite place in the thermal electric series, and as nickel alloy wire is separated by a substantial distance from copper in this series. and as in fact most metals of low conductivity are spaced apart in this series from copper, whatever heat the entire resistance device generates produces, by reason of the thermo couple including the end 17a of the winding 1'7 and the outside copper terminal, a thermal electro-motive force of some magnitude. Assuming the winding 18 to be of nickel alloy wire, a thermo couple opposite in potential to the aforesaid thermo couple would exist at the opposite end of the device, including motive force of substantially the same magnitude and opposite in direction. I therefore wind the groove 12 with a winding 18, preferably of copper wire, and as the connecting ends 17b and 18b of the

windings

17 and 18 are located adjacent the winding 17, the thermo couple constituted thereby is subject to as much heating as the thermo couple formed by the end 17a of the winding 17 and the outside copper terminal, and consequently the first thermal electro-motive force is balanced by an equal thermal electro-motive force acting in the opposite direction, and the entire device will generate practically no net thermal electro-motive force.

The winding of the wire 17 having been stopped, preferably at that complete turn which leaves the resistance of the wound wire just below the desired resistance, I wind just enough copper wire 18 into the groove 12 to bring the total resistance of the entire device to the desired amount within very close limits. Owing to the fact that the wire 18 is of relatively low resistance, the difference of resistance in the entire device produced by any single turn thereof is small as compared with the total resistance, and hence it is possible to obtain results of high precision. The exact number of turns of wire 18 may be readily calculated from its known resistance and the known resistance of the entire winding 17.

I now remove the insulation from the four ends of the two windings l7 and 18 and pass the ends 171) and 182) through

slots

20, 20 into a central groove 21 which is bounded by the

walls

13, 13 of the ceramic form 10. As is clearly shown in Figure 3, the

end walls

14, 14 of the ceramic form 10 have

transverse holes

22, 22 therethrough, penetrating to the interior axial bore 15. I now pass the outer ends 17a and 18a of the

windings

17 and 18 through the

opposite holes

22, 22 respectively, and out of the opposite ends oi the bore 15, leaving the uninsulated ends of the wire projecting a slight distance from each end of the

cylindrical end portions

16, 16. The device is now in the condition shown in Figure 3. Desirably I twist together the ends 1% and 18b.

Referring now to Figure 4, the device preferably includes metal binding posts 23, illustrated in that figure. These binding posts include a shank portion 24, a threaded portion 25, and a central enlarged portion 26. I now insert the shanks 24 of the binding posts 23 into the opposite ends of the central axial bore 15, the shank 24 passing alongside the ends of the two separate windings. Enough wire is provided to project from the ends of the bore by such a distance that, when the binding posts 23 are in position, the scraped ends, or the ends from which the insulation has been removed, will project slightly beyond the enlarged portions 26.

I now relate the entire device to a suitable mold, and mold metal upon both

cylindrical end portions

16, 16 of the ceramic form 10, and in the central groove 21. The metal employed is desirably type metal which may be readily molded, but

,of the binding posts 23.

. equal extent.

couples that the addition of a third metal at the any other metal which forms a good electrical union and which has other desirable characteristics, such as the ability to adhere tightly to the ceramic form l0, may be employed. I thus form integral metal' end portions 27a, 27b integrally embedding the binding posts 23 and firmly connecting them to the ceramic form 10, and also integrally embedding the ends 17a and 18a of the

windings

17 and 18 respectively in these metal end portions. The metal flows into the bore 15, but is quickly cooled by the wide area of theceramic material which it contacts and also by the shank 24, and so does not go beyond the shank 24 union between the winding 17 and one metal end piece 26 on the one hand, and the winding 18 and the other metal end piece 26 on the other hand, is thus secured, and in fact the metal end pieces are integral with the windings. Microphonic effects or current variations are entirely avoided.

The metal 28 in the central groove 21 serves to integrally unite and embed the ends 171) and 18b of the

windings

17 and 18, thus entirely eliminating microphonic effects or current variations at this junction. The metal 28 serves as the junction between the two

windings

17 and 18, and its position relative to the winding 17 is the same as the position of the cast metal end piece 27a. Consequently the rise in temperature, due to the heating of the winding 17, of the cast metal junction 28 is substantially the same as the rise in temperature of the cast metal end 'piece 27a. Preferably the mass of the cast metal portions 28 and 27a is about the same. This rise in temperature is effective in generating, at the thermo couple constituted by the ends 17b and 181), a thermal electro-motive force of sufficient magnitude to balance the thermal electro-motive force generated at the cast metal end piece 27a. The winding 17, which generates by far the greater amount of heat generated by the entire device, is thus included between the two metal pieces 27a and 28 which are raised to substantially the same temperature. Thus the entire device is in perfect thermal electric balance despite the provision of a winding of different metal on the same ceramic form 10. It may here be noted that the fact that the cast metal end piece 27a and the binding post 23 are interposed between the end 17a of the winding 17 and an outside terminal 29, either in series or in parallel, does not change the magnitude of the thermal electro-motive force generated at this end of the device to any substantial extent, because all these parts are heated to an It is the general law of thermo same temperature at a heated union between two metals does not change the net thermal electromotive force.

I next coat the entire device with another coating of bakelite and bake the same, so as to reinsulate any exposed portions from which the insulation was removed during the manufacture of the device. As shown in Figure 2, I desirably provide nuts 31, 31 fitting the threads on the threaded

portions

25, 25 of the binding posts 23. In this way the resistance unit may be placed in circuit in any desired apparatus, being shown in Figure 2 as securely clamped between

copper terminals

29 and 30.

The completed device is adapted to be used in any circuit where a known amount of resistance is desired, and such a circuit is indicated diagrammatically in Figure 2. In the circuit of Figure 2, which is merely illustrative of any electrical cir- A perfect electrical cuit in which the device might be used, there is no net thermal electro-motive force generated although there are two thermo couples which generate equal and opposite electro-motive forces. In this circuit the winding 18 generates, under normal conditions, a negligible amount of heat; hence it can have no eilect upon the temperature of the metal 28 serving as the junction of the two

windings

17 and 18. Atall events, the thermal electric balance of the circuit cannot be disturbed because there is no thermo couple between the terminal 30 and the winding 18, as both are made of copper. i

It will thus be seen that there has been provided by this invention a method and apparatus in which the various objects hereinabove set forth, together with many thoroughly practical advantages, are successfully achieved.

As various possible embodiments might be made of the mechanical features of the above invention, and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter herein set forth, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A resistance device comprising a form having a pair of grooves, a winding of high resistance wire in one groove, a winding of low resistance wire in the other groove, molded metal end pieces in which the opposite ends of the windings are integrally embedded, and a central molded metal piece in which the adjacent ends of the windings are integrally embedded. v

2. A resistance device comprising a winding the end of which is embedded in cast metal, a second winding having a different position in the thermal electric series from the first winding, and cast metal in which the ends of the two windings are integrally embedded.

3. A resistance device comprising a ceramic form, end walls provided by said ceramicform, a pair of walls provided in the central portion of said ceramic form, resistance wire wound between one end wall and one of the central walls, resistance wire of low resistance wound between the other end wall and the other central wall, binding posts, integral cast metal end pieces holding said binding posts to said ceramic form, the ends of said wire being embedded in said east end pieces and cast metal between the central walls in which the ends of the two windings are embedded.

4. A resistance device comprising a form, a relatively long winding of high resistance wire upon said form, a relatively short precision winding of low resistance wire wound upon said form, a molded metal piece embedding the adjacent ends of said windings, there being passages for passing the other ends of said windings through said form, said passages being existent in said form prior to the winding thereof and having predetermined circumferential locations, the entire unit having a predetermined resistance value within plus or minus a relatively small resistance value.

5. A resistance device comprising a form, a

relatively long winding of high resistance wire wound upon said form, a relatively short precision winding of low resistance wire wound upon said form, a molded piece of metal in which the adjacent ends of said windings are embedded, and molded metal end pieces embedding the remaining ends of said windings, said remaining ends passing into said molded metal end pieces at predetermined places on said form, the entire unit having a predetermined resistance value within plus or minus a relatively small resistance value.

6. A resistance device comprising a form, a winding of relatively high resistance, a precision length of wire, the aforesaid winding being composed of wire of a different metal, and a piece of relatively high specific heat capacity connecting the precision length and. the winding to induce, when the piece is heated, a thermal electromotive force counter to the normal electromotive force generated at or adjacent the opposite ends of the resistance.

, 7. A resistance device comprising a form having a pair of grooves, a nickel alloy winding in one groove, 2. copper winding in the other groove, means connecting said windings forming a thermocouple, means forming with the nickel alloy winding at the other end thereof and an outside copper conductor an equal and opposite thermo couple, and heat absorption means on either side of the nickel alloy winding positioned to receive substantially the same amount of heat from said windings.

8. A resistance device comprising a spindlelike form having a pair of grooves, a winding of resistance wire of high resistance wound in one groove around the spindlelike form, a winding of resistance wire of low resistance connected to the winding 01' high resistance and wound in the other groove around the spindlelike form, the two windings having different places in the thermal electric series, and molded metal in which .the ends of the wires are embedded.

ALEXANDER L. PUGH, JR.