US3648216A

US3648216A - Resistance elements

Info

Publication number: US3648216A
Application number: US26332A
Authority: US
Inventors: Jacob Rector
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-04-07
Filing date: 1970-04-07
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07

Abstract

Linear and nonlinear electrical resistance elements having base members integrally formed with ridges having plane top surfaces, the resistance material being applied to the ridges on one or more of the surfaces, the configuration of the ridges being formed to attain a predetermined resistance value and taper and the resistance material being applied to provide one resistance track or two or more parallel resistance tracks. In an alternate form of the invention, the ridge is formed with one or more peaks with the resistance material applied to a predetermined height on the upward extending sides, to form two or more parallel resistance tracks.

Description

1 United States Patent Rector Mar. 7, 1972 [54] RESISTANCE ELEMENTS [21] App1.No.: 26,332

[52] US. Cl ..338/l42, 338/195, 338/217,

[56] References Cited UNITED STATES PATENTS Re25,479 l1/1963 Coleret al. ..338/333X 2,962,393 11/1960 Ruckelshaus 338/308X 3,277,418 10/1966 Norman et a1. ..338/308 X Primary Examiner-Lewis H. Myers 7 Assistant Examiner-D. A. Tone AttorneyG1oria K; Koenig [57] ABSTRACT Linear and nonlinear electrical resistance elements having base members integrally formed with ridges having plane top surfaces, the resistanc'e' material being applied to the ridges on one or more of the surfaces the configuration of the ridges being formed to attain a predetermined resistancevalue and taper and the resistance material being applied to provide one resistance track or two or more parallel resistance tracks. In an alternate form of theinvention, the ridge is formed with one or more peaks with the resistance material applied to a predetermined height on the upward extending sides, to form two or more parallel resistance tracks.

10 Claims, 13 Drawing Figures v PAIENTEDHAR H972 3,648,216

sum 1 BF 2 1 14 1 10 j 11 ii 14a 1 %8 14 WNW Jacob R321 BY 94% X5 44 A 'I' TORNEY RESISTANCE ELEMENTS BACKGROUND OF THE INVENTION This invention relates to the structure of resistance elements with base members integrally formed with ridges having plane or flat top surfaces with resistance material applied to one or more of the surfaces and which may be used as fixed resistors or in variableresistance devices such as potentiometers and rheostats and the like.

Conventional potentiometers and fixed resistances are produced by screening, painting or depositing resistor materials onto insulator bases. lnthe case of small conventional-type potentiometers, there is often a large variation in performance because of the imprecision of the resistance track. In the case of small annular potentiometers the processesin use have inherent limitations as to the attainable resistance track in regardto the width, length and thickness of the track. These annular potentiometers are generally made by printing resistance material onto flat planes so that the resolution is limited by the accuracy of the printing 'method. Very precise and expensive screening machines are required to adjust the track, but it has been difficult to achieve good accuracy and reproducibility. I

Another problem encountered in the use of small potentiometers is the attainment of smooth wiper or slidable contact registration over the whole of the resistance track. In conventional potentiometers, ball or single point contacts of solid metals or electrographitic materials and digitated, metallic brushes or brooms" are used. in most cases much manipulation is required to obtain usable wiper registration over the whole of the resistance track. When considering resistance element diameters of a few millimeters with wiper radial widths of small fractions of a millimeter; the great difficulties in obtaining suitable wiper registration and wiper contact resolution are obvious.

Previous small potentiometers of the crowned type in which the track projects upwardly from the base generally operate with point contact wiper elements which do ,not produce good sliding contact and result in high local pressure which is destructive to the resistance track surface. Such point contact by the wiper. element also distorts the natural and desirable lines of current flow through the resistance element and can result in failure of a potentiometer because of localized current concentrations and collateral local heat generation.

As the resistance elements, potentiometers and rheostats become smaller as required by modern electronics technology, there is great difficulty in obtaining a predictable product. Small potentiometers have been produced but they usually require preproduction and postproduction reworking or trimming" to attain a required resistance value as well as a required resistance taper, i.e., specific resistance value per unit length. In miniature sizes these trimming operations become time consuming because of the elaborate equipment required and the limited working areas presented by the small resistance element.

it is an object of this invention to provide a resistance element having an insulating base integrally formed with a ridge having a flat or plane top surface coated with resistance material, the dimensions of the top surface of the ridge precisely defining the desired resistance value and taper.

it is another object of this invention to provide a resistance element having an insulating base integrally formed with a ridge having a flat or plane top surface and having two surfaces extending upward from the base coated with resistance material, to provide two parallel resistance elements whose values are adjustable by the height of the surfaces of the ridge extending upward from the base.

Another object of this invention is to provide a resistance element having an insulating base integrally formed with a ridge in the form of a peak, the two surfaces extending upward from the base being coated with resistance material to a predetermined height, the top of the peak being left uncoated, to provide two parallel resistance tracks.

Another object of this invention is to provide a resistance element having a plurality of ridges on one base, three or more surfaces of the ridges extending upward from the base being.

coated with resistance material to a predetermined height, to provide three or more parallel resistance tracks.

Another object of this invention is to provide a resistance element having an insulating base integrally formed with a ridgehaving a flat or plane top surface, having the top and sides of the ridge coated with resistance material, to provide a resistanceelement whose value can be adjusted by trimming the sides without disturbing the flat top surface.

Still another object of this invention is to provide a miniature resistance element in which the resistance track is precisely located and which is extremely economical to produce. In addition, this invention opens areas for new wiper contact designs, because of the precision and uniformity with which the resistance track can be produced.

SUMMARY OF THE INVENTION This invention contemplates a resistance element comprising an insulating base having a ridge integrally formed with said base, the ridge having a flat or plane upper surface to provide a small flat surface over which a potentiometer wiper may move. The configuration of the ridge is determined by the type of resistance element desired andmay be formed in an annular, rectilinear or irregular configuration to provide a linear or nonlinear resistance element. Using a known composition of resistance material having known electrical resistance properties, the shape of the resistance track necessary to attain a resistance with a given value and taper can be mathematically calculated. The insulating base with the precisely formed raised shape positioned thereon may be manufactured'by various means. The top flat surface of the preformed configuration is then coated with resistance material. No trimming or other adjustment of the resistance element is necessary as the resistance value and taper are determined by the configuration of raisedshape formed on the basefand the resistivity constant of the resistance material. 3

In another form of my invention, the ridge on the base is made in the form of a peak with a triangular cross section, the sides extending upward from the base beingcoated with resistance material, the top of the peak being left uncoated, resulting in a device having two parallel resistance tracks whose values are adjustable by grinding down the apex or by conventional means of adjustment. A modification of this form of my invention may be made by forming two or more ridges on the base and coating three or more surfaces extending upward from the base to a predetermined height, leaving the top of the ridges uncoated to form three or more parallel resistance tracks. As explained in regard to the form of my invention in which the resistance coating is on the top surface, no trimming of the thickness or depth of the resistance coating is necessary, the value of the resistance being detennined by shape of the ridge or ridges.

in another form of my invention, the resistance element comprises an insulating base having an annular ridge integrally formed with said base, the ridge having a flat or plane upper surface, all sides of which are coated with resistance material. This form of my invention provides a resistance element whose value can be adjusted by trimming of the side surfaces or by adding resistance material to the side surfaces of the ridge without disturbing or injuring the top surface over which a wiper moves.

The resistance elements described provide linear or nonlinear resistance elements, easily shaped by methods well known in the prior art. The preciseness of the location of the resistance track eliminates the undesirable radial sawing motion of a wiper contact, of either the point or line type, against the resistance track. When used in a variable resistance device, such as a potentiometer, the resistance elements of my invention provide the option of using a line contact for the wiper over the entire discrete shape of the resistance track or using a conventional point or ball contact. A line contact maintains an isometric current flow and eliminates high localized contact pressures on the resistance element.

These and various other objects and advantages of this invention will be more fully apparent from a detailed consideration of the following description, the appended claims and accompanying drawings showing preferred forms of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing one form of resistance element in accordance with the present invention.

FIG. 2 is a perspective view of another form of resistance element in accordance with the present invention.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1.

FIG. 4 is a sectional view of a modified form of the resistance element before coating with resistance material in a view similar to FIG. 3.

FIG. 5 is a sectional view of the modified form of the resistance element shown in FIG. 4 after coating with resistance material and after grinding, in a view similar to FIG. 3.

FIG. 6 is a sectional view of another modified form of the resistance element in a view similar to FIG. 3.

FIG. 7 is a sectional view of another modified form of the resistance element in'a view similar to FIG. 3.

FIG. 8 is a sectional view of another modified form of the resistance element in a view similar to FIG. 3.

FIG. 9 is a diagrammatic plan view of a typical potentiometer fabricated in accordance with the present invention.

FIG. 10 is a diagrammatic plan view of a potentiometer having parallel resistance elements fabricated in accordance with the present invention.

.FIG. 11 is an enlarged perspective view of a portion of a resistance track on a linear resistance element.

FIG. 12 is an enlarged perspective view of a portion of a resistance track of a nonlinear resistance element.

FIG. 13 is a graph illustrating one computational method of determining the values of a specific configuration of a resistance element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now specifically to the drawings, FIGS. 1 and 2 show two embodiments of the present invention. A nonconductive or insulating substrate 10 comprises a base 11 integrally formed with a ridge 12 which has a flat or plane top surface 13. The substrate 10 may be formed by stamping with a die, molding, machining or electroforming and may be composed of ceramic, glass compositions, synthetic resins or like materials by methods well known in the art. The base 11 may be rectangular, round, or in any convenient shape. The ridge 12 may be annular, rectilinear or irregular in configuration. When the resistance element is to be used in a variable resistance device, such as a potentiometer or rheostat, the base is formed with an aperture 18 for mounting a wiper element, the aperture being positioned at a predetermined position with respect to the ridge 12.

In the preferred form of my invention the top flat surface 13 of the ridge 12 is coated with resistance material 14, applied, for example, by a roller. The final thickness of the coating of resistance material 14 is determined by the composition of the resistor ink, and such factors as the viscosity of the ink, rate of application, temperature and humidity.

Using a composition of resistance material with known resistivity, the dimensions of the top surface of the ridge 12 are predetermined by mathematical calculation to, attaina desired resistance per unit length function. When either a linear or nonlinear function is required, the ridge 12 is easily and precisely shaped by known methods to mechanically represent the required electrical taper. It is a basic feature of this invention that the thickness or depth of the resistance material is immaterial to attaining a required taper. The coating of the resistance material 14 on the flat top surface 13 of the raised shape may be considered to be a two-dimensional plane, the length and width being precisely that of the raised shape of the ridge 12. No trimming or other adjustment of the resistance element is needed as the resistance value and/or taper are determined by the raised shape formed on the basefThe resistance element shown in FIG. 1, shows one configuration of a linear function; the resistance element shown in FIG. 2 shows one configuration of a nonlinear function.

- The method of predetermining the dimensions of a resistance element are illustrated by reference to FIGS. ll, 12 and 13. FIG. 11 shows a portion of a linear resistance track. The width of the track is indicated by the letter a, the length is indicated by the letter b and the depth or thickness of the coating of resistance material 14 applied to the inert substrate is indicated by the letter 0. The calculations depend upon the following postulates: (l) the dimension c is constant; (2) the active face 14 on the plane top surface of the resistance element is the surface bounded by the numerals l, 2, 3 and 4 in FIGS. 11 and 12; (3) the bulk resistivity of the resistance material 14 is expressed by the constant p; (4) the ohms per square of the resistance material is expressed by the constant p; and (5) the resistance, as a function of the length of the resistance track b, is measured for example from

line

5, 6 and referred to

edge

1, 2 or 3, 4. I

The terminal value of the resistor R shown in FIG. 11 may be expressed by the relationship:

R=p'X(b/a) from which it follows that the dimension a is defined by the relationship,

a=('n"/R) b For linear incremental motion of

line

5, 6, along the active surface of the resistance track, dimension a remains constant for a linear resistance potentiometer.

For predetermination of dimension a for a desired nonlinear resistance change per unit length along dimension b, reference is made to FIG. 11. Dimension a varies along dimension b in a relationship expressive of the desired nonlinearity. By calculation similar in nature to that of the linear resistance track, and well known' to those skilled in mathematics, the desired nonlinearity along dimension b may be reduced to variations of dimension a, as for example, between a and a FIG. 13 represents a graphic method of making the determination of values of the width a for a specific potentiometric configuration. Points P and P represent positions along dimension b where the absolute value in ohms has been specified. The increments R, S and S, T of FIG. 13 are equal and of a convenient length along dimension b. I

In the preferred form of my invention only the top surface 13 of the ridge is coated with resistance material 14, to form a resistance track which is precisely located in all respects by the original die construction. The resulting resistance element is shown in FIG. 3 in cross-sectional view. When used in a device such as a potentiometer, the resistance element is uniformly and predictably located with reference to the wiper contact mounted in the aperture 18. Because of the precision with which the resistance element can be made, a line contact wiper or crossbar can be used without any undesirable sawing action which is destructive of the resistance track surface. With such a wiper, lower unit pressures are applied to the resistance element with more reliable, reproducible and resettable performance by the potentiometer.

In another embodiment of my invention, the substrate 10 is formed with a ridge l2 shaped as a peak 15 having a triangular cross section as shown in FIG. 4. The ridge 12 is coated with resistance material 14 on its inner and outer faces by rolling or dipping. The ridge is then truncated, as by grinding down, to a desired predetermined height, forming a device shown in cross section in FIG. 5, having an uncoated top flat surface 13 and having two

parallel resistance elements

14, 14a extending upward from the base, whose values are adjustable according to the depth to which the apex is ground. When the triangular cross section of the ridge is in the form of an isosceles triangle, the inner and outer faces have equal dimensions and the resulting device has two substantially identical parallel resistance elements, whose values are adjustable according to the depth to which the apex is ground.

The device shown in FIG. 5 may also be made by masking the apex of the peak 15 with an inert coating, such as paraffin, coating the lower exposed portion of the peak, melting off the wax and grinding off the apex of the peak 15 to attain a predetermined height extending upward from the base. Another modification of this form of resistance element, having two substantially parallel resistance tracks, may be formed by masking the apex of the peak 15 with an inert coating, such as paraffin, to a predetermined level, coating the lower exposed portion of the ridge 12 with resistance material and melting off the wax. The resulting element which is shown in cross section in FIG. 6, has two substantially parallel resistance tracks 14, 14a extending upward from the base and may be used without grinding of the apex of the peak 15.

In another modification of the forms of my invention, as shown in FIGS. 4, 5 and 6, the substrate is formed with a plurality of ridges shaped as peaks with triangular cross sections on a single base 11. A cross-sectional view of this form of my invention with two peaks is shown in FIG. 7. Three or more faces of the ridges extending upward from the base may be coated with resistance material to form three or more parallel resistance elements, depending on the number of ridges formed on the base 11. It is not necessary that both sides or faces of a ridge be coated with resistance material, although both sides may be coated to obtain either an odd or even number of parallel resistance elements as required. As

shown in FIG. 7, two

ridges having peaks

15, 15a are coated I on three sides extending upward from the base to a predetermined height, the top portion of each ridge being uncoated to form a device having three

parallel resistance elements

14, 14a, 14b. The device shown in FIG. 7 may also be coated on the fourth upward extending side to form a device having four parallel resistance elements. As described for the forms of my invention shown in FIGS. 5 and 6, the plurality of ridges may be coated with resistance material and then truncated, as by grinding down to a desired predetermined height, to form a device having two or more ridges with uncoated top flat surfaces 13 and three or more parallel resistance elements extending upward from the base. Alternately, the plurality of peaks may be masked with an inert coating to a predetermined level, the lower portions of the ridges coated with resistance material, and the inert material coating the apex of the peaks removed, to form a plurality of substantially parallel resistance tracks, extending upward from a base and which may be used without grinding of the apex ofthe peaks 15, 15a.

Like the resistance element having resistance material 14 only on the top flat surface 13 of the ridge 12 described above, the configuration of the ridge of the resistance elements having parallel resistance tracks may be precisely and accurately formed on the base 11 by stamping, molding or other methods well known in the art and the ridge 12 may be annular, rectilinear or irregular in configuration. The resistance values and tapers are determined by the composition of the resistance material and the preformed dimensions of the resistance track. However, the resistance values may also be varied by conventional means of adjustment of the composition and dimensions of the resistance tracks.

In another embodiment of my invention, the ridge 12 is formed with a plane top surface and is coated on all sides with resistance material 14. This form of the invention is shown in cross section in FIG. 8. The resistance value of this form of resistance element can be adjusted by adding to or reinoving resistance material from the upwardly extending sides of the ridge 12 without disturbing or injuring the flat top surface.

FIG. 9 shows a plan view in diagrammatic form of a potentiometer fabricated with a resistance element formed in accordance with the present invention, having the resistance track 14 on the top flat surface 13 of the ridge 12 as shown in FIGS. 3 and 8. The ends of the resistance track 14 are connected to appropriate

electrical terminals

16 and 17 for applying a potential across the resistance track. An aperture 18 is formed in the base 10 for movably mounting a wiper element 19 having a contact element 20 with a terminal connected to an external circuit. As noted above, the precision with which the entire resistance element 10 including the resistance track 14 and the aperture 18 for mounting the wiper element can be formed eliminates the undesirable radial sawing motion of the wiper contact, of either the point or line type, against the resistance track.

FIG. 10 shows a plan view in diagrammatic form of a potentiometer fabricated with a resistance element formed in accordance with the present invention, having two substantially parallel resistance tracks '14, 14a extending upward from the base 11 as shown in FIGS. 5 and 6. The ends of the resistance tracks 14, 14a are connected to appropriate electrical terminals l6 and 17 and the ends of the parallel resistance track are connected to appropriate

electrical terminals

16a and 17a, for applying a potential across the resistance tracks. An aperture 18 is formed in the base 10 for movably mounting two

wiper elements

19 and 19a each having a

contact element

20 and 20a, respectively. Each of the wiper elements 19,190 has its own electrical terminal connected to an external circuit. A similar arrangement may be used for a resistance element having a plurality of resistance tracks.

While the diagrammatic form in FIGS. 8 and 9 indicates an annular configuration of the resistance elements, it is to be understood that the resistance element may be of any configuration required.

It can thus be seen that I have provided new and improved forms of resistor elements applicable to miniature resistance elements as well as to resistance elements of any shape and size. Modifications may, of course, be made in the illustrated and described embodiments of my invention without departing from the invention as set forth in the accompanying claims.

I claim:

1. A potentiometer comprising:

a. a base member integrally formed with a ridge having a plane top surface and with an aperture in the base in a predetermined position with respect to the ridge, the base and ridge being formed of insulating material, the dimensions of the plane top surface of the ridge varying in accordance with a predetermined function; I

b. a thin coating of resistance material having known electrical resistance properties affixed to and completely covering the plane top surface of the ridge to provide a resistance track whose dimensions are defined by the dimensions of the plane top surface of the ridge;

c. a pair of terminals in electrical contact at spaced points on the resistance track for applying a potential across the resistance track;

a wiper element having a wiper contact member movably mounted in the aperture of the base to traverse the plane top surface of the resistance track; and

e. means to connect the wiper element to an external circuit.

. A potentiometer comprising:

a. an insulating base member integrally formed with a ridge and with an aperture in the base in a predetermined position' with respect to the ridge, the ridge having a top portion, an inner face and an outer face, said inner and outer faces extending upward from the base, the base and ridge being formed of insulating material, the dimensions of the ridge varying in accordance with a predetermined function;

. a thin coating of resistance material having known electrical resistance properties affixed to and covering the faces of the ridge to a predetermined height, leaving the top portion of the ridge uncoated to provide two resistance tracks;

a pair of terminals in electrical contact at spaced points on each of the two resistance tracks for applying a potential across each resistance track;

d. two wiper elements, each having a wiper contact member, movably mounted in the aperture of the base to traverse each of the two resistance tracks; and

e. means to connect each of the two wiper elements to an external circuit.

3. A potentiometer as set forth in claim 2 wherein the ridge is shaped as a peak with a cross section in the form of a triangle.

4. A potentiometer as set forth in claim 2 wherein the ridge is shaped as a peak with a cross section in the form of an isosceles triangle, the two faces extending upward from the base having equal dimensions and the resistance material is affixed to and covers the faces of the ridge to a predetermined height, leaving the top portion of ridge uncoated to provide two substantially equal, parallel resistance tracks.

5. A potentiometer as set forth in claim 2 wherein the ridge is formed with a plane top surface, the height of the faces extending upward from the base varying in accordance with a predetermined function and the thin coating of resistance material is afiixed to and entirely covers the faces of the ridge extending upward from the base.

6. A resistance element comprising: a. an insulating base member; 7 b. a ridge of insulating material integrally formed on the base member, the ridge having sides extending upward from the base and having a plane top surface, the dimensions of the plane top surface varying in accordance with a predetermined function; and

c. a thin coating of resistance material having known electrical resistance properties affixed to and covering the plane top surface and the sides of the ridge to provide a resistance element whose value can be adjusted by adding to or removing resistance material from the sides extending upward from the base without disturbing the flat top surface.

7. A resistance element as set forth in claim 6 wherein the base member is formed with an aperture in a predetermined position with respect to the ridge.

8. A method of making a resistance element comprising the steps of a. forming a base member integrally with a ridge, the base and ridge being formed of insulating material, the ridge having a plane top surface and sides extending upward from the base;

b. shaping the ridge in accordance with a predetennined function; and

c. coating the plane top surface and the sides extending upward from the base with a thin layer of resistance material having known electrical resistance properties to provide a resistance element whose value can be adjusted by adding to or removing resistance material from the sides extending upward from the base without disturbing the flat top surface.

9. A method of making a resistance element as set forth in claim 8 wherein the base member is formed with an aperture in a predetermined position with respect to the ridge.

10. A potentiometer comprising:

a. a base member integrally formed with a ridge and an aperture in the base in a predetermined position with respect to the ridge, the base and ridge being formed of insulating material, the ridge having sides extending upward from the base and a plane top surface, the dimensions of the top plane surface of the ridge varying in accordance with a predetermined function.

b. a thin coating of resistance material having known electrical resistance properties affixed to and covering the plane top surface and the sides extending upward from the base of the ridge to provide a resistance element whose value can be adjusted by adding to or removing resistance material from the sides extending upward from the base without disturbing the flat top surface.

c. a pair of terminals in electrical contact at spaced points on the resistance track for applying a potential across the resistance track; d. a wiper element having a wiper contact member movably mounted in the aperture of the base to traverse the plane top surface of the resistance track; and e. means to connect the wiper element to an external circuit.

' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated March 7, 1972 Patent No. 3 648 216 Inventor(s) I h Rani-n1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 30 formula:

am) x' b Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Commissioner of Patents Attesting Officer USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE: 1-969 O366-334 ORM PO-1050 (10-69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 648 216 Dated March 7 1972 Inventor(s) Iacab It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line: 30 formula:

I a" (P /R) xb Signed and sealed this 25th day of July 1972.

(SEAL) Attest:

EDWARD M.FLETCHBR,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 603764 69 U.S. GOVERNMENT PRINTING OFFICE: I969 D-3G6-334 ORM PO-105O (10-69)

Claims

1. A potentiometer comprising: a. a base member integrally formed with a ridge having a plane top surface and with an aperture in the base in a predetermined position with respect to the ridge, the base and ridge being formed of insulating material, the dimensions of the plane top surface of the ridge varying in accordance with a predetermined function; b. a thin coating of resistance material having known electrical resistance properties affixed to and completely covering the plane top surface of the ridge to provide a resistance track whose dimensions are defined by the dimensions of the plane top surface of the ridge; c. a pair of terminals in electrical contact at spaced points on the resistance track for applying a potential across the resistance track; d. a wiper element having a wiper contact member movably mounted in the aperture of the base to traverse the plane top surface of the resistance track; and e. means to connect the wiper element to an external circuit.

2. A potentiometer comprising: a. an insulating base member integrally formed with a ridge and with an aperture in the base in a predetermined position with respect to the ridge, the ridge having a top portion, an inner face and an outer face, said inner and outer faces extending upward from the base, the base and ridge being formed of insulating material, the dimensions of the ridge varying in accordance with a predetermined function; b. a thin coating of resistance material having known electrical resistance properties affixed to and covering the faces of the ridge to a predetermined height, leaving the top portion of the ridge uncoated to provide two resistance tracks; c. a pair of terminals in electrical contact at spaced points on each of the two resistance tracks for applying a potential across each resistance track; d. two wiper elements, each having a wiper contact member, movably mounted in the aperture of the base to traverse each of the two resistance tracks; and e. means to connect each of the two wiper elements to an external circuit.

5. A potentiometer as set forth in claim 2 wherein the ridge is formed with a plane top surface, the height of the faces extending upward from the base varying in accordance with a predetermined function and the thin coating of resistance material is affixed to and entirely covers the faces of the ridge extending upward from the base.

6. A resistance element comprising: a. an insulating base member; b. a ridge of insulating material integrally formed on the base member, the ridge having sides extending upward from the base and having a plane top surface, the dimensions of the plane top surface varying in accordance with a predetermined function; and c. a thin coating of resistance material having known electrical resistance properties affixed to and covering the plane top surface and the sides of the ridge to provide a resistance element whose value can be adjusted by adding to or removing resistance material from the sides extending upward from the base without disturbing the flat top surface.

8. A method of making a resistance element comprising the steps of a. forming a base member integrally with a ridge, the base and ridge being formed of insulating material, the ridge having a plane top surface and sides extending upward from the base; b. shaping the ridge in accordance with a predetermined function; and c. coating the plane top surface and the sides extending upward from the base with a thin layer of resistance material having known electrical resistance properties to provide a resistance element whose value can be adjusted by adding to or removing resistance material from the sides extending upward from the base without disturbing the flat top surface.

10. A potentiometer comprising: a. a base member integrally formed with a ridge and an aperture in the base in a predetermined position with respect to the ridge, the base and ridge being formed of insulating material, the ridge having sides extending upward from the base and a plane top surface, the dimensions of the top plane surface of the ridge varying in accordance with a predetermined function. b. a thin coating of resistance material having known electrical resistance properties affixed to and covering the plane top surface and the sides extending upward from the base of the ridge to provide a resistance element whose value can be adjusted by adding to or removing resistance material from the sides extending upward from the base without disturbing the flat top surface. c. a pair of terminals in electrical contact at spaced points on the resistance track for applying a potential across the resistance track; d. a wiper element having a wiper contact member movably mounted in the aperture of the base to traverse the plane top surface of the resistance track; and e. means to connect the wiper element to an external circuit.