US2487839A - Nonlinear resistance element - Google Patents

Description

Patented Nov. 15 1949 NONLINEAR RESISTANCE ELEMENT De Witt '1. Van Alen, Delavan, Wis., assignor to The George W. Borg Corporation, Chieagu, 111., a corporation of Delaware Applieation November 7, 1945, Serial No. 627,244

The present invention relates to non-linear resistance elements, for use in rheostats and Dotentiometers and in other devices, and made preferably by winding resistance wire on an insulating strip or support. The object of the invention is the production of a new and improved resistance element of this character.

The invention may be considered as being an improvement on or further development of the invention disclosed in my Patent No. 2468,144 granted April 26, 1949.

In the pending application referred to, a nonlinear resistance element is disclosed comprising a resistance wire of uniform diameter wound on a strip of uniform width and thickness, and having a non-linear resistance curve which is obtained by a varying or changing spacing of the turns of the winding. The spacing is referred to as a quantity Q, defined as the ratio of the space between turns to the diameter of the wire, and it is pointed out that permissible values of Q range from a minimum of about .25 to a maximum of about 4. This limited range of Q limits the utility of the invention to cases where the desired resistance curves do not depart very much from straight lines.

The present invention, on the other hand, is free from the above limitation and may be used in the manufacture of a resistanee element hav ing any resistance curve that may be required, so far as known. At any rate, the useful field that may be covered through the medium of a varying turn spacing is Very greatly extended. This result is accomplished, in a typical case, by employing a continuous resistance wire comprising two sections of diierent diameters joined by a tapered section and by winding the wire on the strip with a spacing which varies in each section in the proper manner to give the resistance element the required resistance curve.

The invention will be described more in detail hereinafter, reference being had to the accompanying drawings, in which Fig. 1 is a plan view of a resistance element embodying the invention;

Fig. 2 is a graph showing the resistance curve of the resistane element of Fig. 1; and

Fig. 3 is a diagrammatic representation of the wire with which the resistance element is wound.

Referring now to Fig. 1, the strip is made of Bakelite or other suitable insulating material and is of uniform width and thickness. Terminals I I and I2 may be made of thin sheet copper and. are located naar opposite ends of the strip, respectively, where they are secured in place by 16 Claims. (Cl. 201-63) rivets as shown. The strip also has perforated end extensions 13 and l4 by means of which it is held in the winding machine during the winding operation.

In the specific resistance element which is shown and described herein, the dimensiens of the strip as to width and thickness are such that the length of each turn is 915 inch. The distance between terminals, or the length of the winding spaee, is 3% inches.

The winding is made of a suitable resistance wire which may have a resistance of 600 ohms per circular mil foot, for exampie. The other values given herein are based on the for going value fox the specific resistance of the wire.

A resistanee wire ready for winding is shown in Fig. 3 and comprises a section 11 of wire which is 5.6 mils in diameter and 114.1 inches long, a tapered section 18 which is 83 inches long, and a section I9 which is 3.377 mils in diameter and 113.7 inches long. These secti0ns preferably form a continuous wire 310.8 inches in length which is Wound on the strip l0 between the terminals [1 and I2. The wire aotually is langer than this since surplus wire must be allowed at each end for wrapping around terminals ll and 12 and an additional amount at the end of section 19 for operation of the winding machine.

The wire may be made by means of a wire tapering apparatus such as is disclosed in the pending application of Thomas B. Gibbs et al. Serial No. 525,764, filed March 9, 1944. According to the disclosure in this application, an electrolytic cell system is provided eomprising a large number of serially related electrolytic cells in which the wire or wires to be tapered function as the anode and are redueed in diameter by anodic reduetion. In usng this apparatus to make wires such as shown in Fig. 3, a pluralty of wires having a diameter of 5.6 mils are placed in the eleetrolytic ce11 system and are pulled through at the proper speed to reduce them to a diameter of 3.377 mils. This operation is continued until somewhat more than 113.7 inches of each wire has been pulled entirely through the electrolytic cell system, thereby forming a cylindrical seetion such as l9 at the end of each wire. The current is then shut ofi, but the pulling operation is continued until the sections which were in the bath at the time the current was shut 0 (tapered from 5.6 mils to 3.377 mils) and enough more to make the cylindrical sections such as I'! have been pulied th1ough. The wires are, pulled through the electrolytic cell system by winding them on spools and. are cut oi next to the electrolytic cell system When the operation is completed. The tapered sections are equal in length to the length of the electrolytic cell system, which in the case of the apparatus available for making the wires described happened to be 83 inches. Shorter tapered sections may be made by cutting out one or more cells, and longer tapered sections can be made by the method. described in the Gibbs et al. application referred to.

The wire is wound on the strip I 11 by means of a winding machine such as described in the pending application of Gilman et al., Serial No. 563,522, filed Nov. 15, 1944, now Patent No. 2466,227, issued April 5, 1949. The winding isstarted at the left hand end of the strip and includes a few turns which are wrapped around the projecting end of terminal II. operating the machine by hand and are so adjusted as regards number and spacing that the beginning of section I'| of the wire, which is preferably marked When the wire is made, is in the first turn beyond the strip. The machine winds on the rest of the wire automatically and is so set up that the end of section 19 is reached in the last turn which does not overlap terminal l2. After about half a dozen or so turns have been wrapped around terminal I2 the machine stops automatically.

When the winding is completed the ends are secured to the strip by small pieces of tape or in any other suitable manner and the wound strip is removed from the machine. The wire is then preferably soldered to terminals II and I2 and the surplus is cut 01.

The completed resistance element may be utilized in the manufacture of a potentiometer of knownmechanical construction, including a cylindrical casing made of insulating material. For this purpose the strip Il is cut off at both ends along the dotted lines 55 and 16 and is bent into a circular formation so that it can be inserted in the casing, where it is held in place in any suitable manner. The potentiometer may also include a shaft rotatably mounted on the casing and carrying a wiper which is adapted to successively engage the turns of the resistance element as the shait is rotated. The shaft may also have a calibrated dial and suitable stops may be arranged so that When the dial is in zero position the wiper will engage the last turn which is soldered to terminal I whereas When the dial is fully rotated the wiper will engage the first.

turn which is soldered to terminal I2.

It will be understood that the resistance element described is so designed that the resistance curve of the potentiometer in which it is used will conform to a particular required resistance curve. This curve is shown in Fig. 2 and is constructed by plotting resistance in ohms against percentage of wiper rotation ranging from rotation to 10 percent rotation. The curve is defined by the equation in which Y is equal to the resistance in ohms and X is equal to the percentage of rotation of the potentiometer wiper. The resistance is measured between terminal 11 and the wiper terminal.

The curve, Fig. 2, may be considered as being composed of three sections, Rl, R2 and R3. Section RI, as measured along the X axis, extends from 0 percent rotation to 45 percent rotation, section R2 extends from 45 percent rotation to 70 These turns are put on by 4 percent rotation, while section R3 covers the range from 70 percent rotation to percent rotation. Fig. 1 is so aligned with Fig. 2 that distance along the winding can readily be translated into percentage of rotation, or vice versa, whereby it can be seen that sections RI R2 and R3 of the curve correspond, respectively, to the sections |8 and I9 of the winding.

The resistance for any percent of rotation or for any distance along the strip can be read by projecting the corresponding point on the curve to the Y axis. Thus When the potentiometer dial is set at zero, the wiper being then in engagement with the last turn which is soldered to terminal II, the resistance is zero. As the dial and wiper are rotated the resistance increases in the manner shown by the curve until at 45 percent of rotation the resistance has a value of about ohms. The calculated value at this point is 181.9 ohms. This is the resistance of section I'l of the winding. The value for '70 percent of rotation, which marks the end of section l8 of the winding, is 401.3 ohms. The total resistance is 900 ohms, attained upon 100 percent rotation, When the wiper of the potentiometer will be in engagement.

with a turn of the winding which is soldered to terminal 12.

The spacing of the turns on the strip may now be explained. As indicated in Fig. 1, section I9 is wound on the strip with a decreasing spacing,.

section !8 with an ncreasing spacing, while in section 1! the spacing again decreases, from left to right.

The winding ofsection I! is started with a wide spacing which if continued would cause the resistance curve to take a straight line form such as indicated by the line 25. By means of a progressively decreasing spacing, however, a progressively increasing number of turns per unit distance along the strip is obtained, whereby the resistance curve is made to conform to section RI of the required curve.

The length of section I! in percent of rotation (45 percent) is so selected that the resistance curve Rl can be obtained, without exceeding the permissible value for Q at either end of the section; in fact the values of Q are well wthin the range that can be employed. The average value of Q as calculated for the first sub-section of section 11 extending from 0 rotation to 5 percent rotation is 2.5? and for the 9th sub-section extending from 40 percent rotation to 45 percent rotation is 43.

The tapered section 18 of the wire has a greaterjslope than is required to obtain the resistance curve R2 with a uniform spacing of the turns. In other words, if the section were to be wound with the same spacing as used in the 9th subsection of section I! the resistance would increase too fast and the resistance curve would take the general direction of line 26. Section I! is therefore wound with an increasing spacing, or value of Q, which for the 14th sub-section extendi ng cent rotation to 75 percent rotation the average value of Q is 2.27. The value decreases to 1,91

A decreasing spacin the 16th sub-section and continues to decrease in the remaining sub-sections until in the 20th sub-sectionit reaches It will be seen that the inveniion may be ernployed in the manufacture ofresistance elements having a widevariety of resistance curves, in- ;cluding curves that cannot be obtained merely by a varying s pacing of a uniform diameter wire on a strip of uniform width. Such curves could beobtained with a tapered wire, but only at a considerably greater oost, for the wire shown in Fig. 3, having only a short tapered section equal in length to the length of the electrolytic cell system in which it is made is much less exponslve than a wire which is tapered throughout its length. In general, a resistance wire made in accordance with the invention should be designed with a section such as I! which is as long as can be used, in order to obtain the maximum economy. This principle was not adherecl to fully in the design of the resistance element shown herein, as will be evident from the fact that the maximum value of Q in section l'l is less than 3 while the minimum value is considerably greater than 25.

In some cases it will be possible to omit the last section such as 19, using a resistance wire having only two sections one of which is of uniform diameter and the other of which is tapered to a smaller diameter. Or the required resistance curve may be such as to require or make it more ponvenient to use a wire comprising a tapered section and a section of uniform diameter which is the same as the smaller diameter of the tapered section.

It will be understood that the values given herein apply only to the specific resistance element shown. The invention could have been explained in general terms but it is believed that the description of a specific embodiment of the invention with the actual values of resistance, turn length, spacing, etc. will promote a clearer understanding of the invention and gve a better idea of its practical application.

The values for other specific resistance elements and the data required for setting up the winding machine can readly be calculated by following the procedure explained in the application Serial No. 602,813, prevously referred to.

The invention having been described, that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

I claim:

1. A resistance element having a non-linear resistance curve comprising a continuous resistance wire wound on a strip of insulating material of uniform cross-section, said wire comprising a section of uniform diameter and a tapered section, and the said resistance curve being obtained in part by the taper in said tapered section and in part by a varying turn spacing in both sections.

2. A resistance element having a non-linear resistance curve, comprising a continuous resistance wire wound on a strip of insulating material of uniform cross-section, said wire comprising two sections of different diameter joined by a tapered section, and the said resistance curve being obtained in part by the taper in said tapered section and in part by a varying turn spacing in all three sections.

3. A resistance element comprisng a winding of resistance wire on a suitable support, said wire having two sections of different diameter joined by a tapered section, said two sections being 6 wound witha varyingspacing whiehincre'nsw in the same direction and said tapered section being wound with a varying spacing which increases in the opposte direction,

4. A resistance element having a logarithmc resistance curve, comprising a winding of resistance wire wound on a suitable support, said wire comprising a section of uniform diameter which is wound on said support with a decreasine turn spacing, a tapered section which is wound on said support with an increasing turn spacing, and a section of uniform diameter less than the diameter of the first section which is wound on said support with -a decreasing turn spacing.

5, A nonlinear resistance element, comprising a. winding of resistance wire on a strip of insulating material of uniform crosssection, said wire having a section in which the wire is of uniform diameter and is wound on said strip with a. decreasing turn spacing and an adjoining section in which the wire is tapered and is wound on said strip with an increasing turn spacing.

6. A non-linear resistance element, comprising a continuous winding of resistance wire on an insulating strip of uniform cross-section, said winding having two adjacent sections in one of which the resistance wire is of uniform diameter and in the other of which the resistance wire is tapered to a smaller diameter, the said section in which the wire is of uniform diameter having a varying turn spacing which decreases in the direction of the section in which the wire is tapered.

7. A non-linear resistance element, comprising a continuous winding of resistance wire on an insulating strip of uniform cross-section, said winding having two adjacent sections in one of which the resistance wire is of uniform diameter and in the other of which the resistance wire is tapered to a different diameter, the said section in which the wire is of uniform diameter having a varying turn spacing which increases er decreases in the direction of the section in which the wire is tapered depending on whether the wire in the latter section is tapered to a larger or smaller diameter.

8. A resistance element having a non-linear resistance curve, said element comprising a continuous winding of resistance wire on an insulating strip of uniform cross-section, said winding having a section in which the resistance wire is of uniform diameter and is wound on the strip with a turn spacing which gives the corresponding section of said resistance curve the required direction, said winding also having an adjacent section in which the resistance wire is tapered more than is neoessary to give the correspond ing section of said resistance curve the required direction and is wound on the strip with a turn spacing which compensates for the excessive taper.

9. A resistance element having a non-lnear resistance curve, said element comprising a continuous winding of resistance wire on an insulating strip of uniform cross-section, said winding having a section in which the wire is of uniform diameter and is wound on the strip with a turn spacing which gives the corresponding section of said resistance curve the required direction, said winding also having an adjacent section in which the resistance wire is tapered and is wound on the strip with a varying turn spaoing such that the combined effects of the taper and turn spacing give the corresponding section of the said resistance curve the required direction,

:F 105 resistarce element having ia, ron-lnear resistance curve, said element comprising a windng of resistance wre having equal length turns,

sad winding havng first and thrd setionsn which the wre is of luniform.dameter the wre in. the third section beng smaller in.diameter than t is in the first section, and a. second secton n.which the wire is tapered, the sad first and. third sections having a decreasing turn spacing to give the correspondng sectons of sad resistance curve .the requred directon, and the taper en the wire in the second section being enough greater than is required to give the correspondng secto n;of the resistance curve the'required direc tonso that the turn spacng in the second secton can be increased without abrupt cha;nge from the narrow spacng at theend. of the first section to.the:wder spacing at the begnnng ofthe thrdsection.

REFERENCES CITE The following references are of record in the file of this patent:

UIITED STATES PA'I'ENTS Number Name Date 1755,314 Carter Apr. 22, 1930 1,987,118 Lodge Jan. 8, 1935 2,058,525 Takanashi Oct. 27, 1936 FORE'IGN PATENIS Number Country Date 163,072 Great Brtain May 2, 1921

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