US2909751A

US2909751A - Variable resistor

Info

Publication number: US2909751A
Application number: US599419A
Authority: US
Inventors: Schwartz Harry
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1956-07-23
Filing date: 1956-07-23
Publication date: 1959-10-20
Anticipated expiration: 1976-10-20

Description

oct 20, 1959 H. SCHWARTZ 2,909,751

-VARIABLE: REsIs'roR Filed July 23, 1956 2 Sheets-Sheet 2 i?. 7 F495. 5 @y United States Patent() VARIABLE RESISTOR Harry Schwartz, Detroit, Mich., assignor to General Electric Company, a corporation of New York Application July 23, 1956, Serial No. 599,419

6 Claims. (Cl. 3158-190) This invention relates to variable resistors and more particularly to variable resistors of non-linear resistance material which provide a multiplicity of possible resistance values at any given voltage.

Non-linear resistors have found important applications in the electrical power, communications and electronic industries. Heretofore, when a plurality of resistance values were necessary, a corresponding number of individual resistors were generally employed. The peculiarities of design and operation of non-linear resistor devices has rendered it difficult to develop a variable nonlinear resistor in the manner ordinarily used with linear resistors.

It is therefore an object of this invention to provide a variable resistor of non-linear resistance materials having a vast number of possible resistance values or levels. It is also an object of this invention to accomplish this result with a device which is relatively simple in function and which is economical to manufacture.

Briefly stated, my invention comprises a body of nonlinear resistance material having a plurality of isolated conductive areas on both sides and contact means for engaging at least two of the isolated conductive areas of said resistance material.

My inventionfurther comprises a variable non-linear resistor having a plurality of isolated conductive areas on both sides, each of the conductive areas onL one side of said resistance material having a path which, when projected through the resistance material, is coincident with at least a portion of the path of at least one -of the conductive areas on the other side of said resistance material. n

My invention will be better understood by considering the following description taken in connection with the accompanying drawings, in which Figure 1 is a plan view of one embodiment of my invention showing a non-linear resistance material having longitudinally extending isolated conductive strips thereon.

Figure 2 is a plan view of the reverse side of the resistance element shown in Figure l.

Figure 3 is a perspective view, partly broken away, of the embodiment shown in Figures l and 2 in combination with contact means for engaging the conductive strips.

Figures 4 and 5 are fragmentary plan views of a modiiication of the embodiment shown in Figures 1 and 2.

Figure 6 is a perspective View, partly in phantomoutline, of another embodiment of my invention.

Figures 7, 8, and9 are cross-sectional views of modiied forms of resistance plates which can be used in th practice of this invention.

Referring to the `drawing and more particularly to Figures l, 2, and 3, a non-linear resistance material 10 is coated with a plurality of isolated and longitudinally extending conductive strips 11 on one side. The other side is likewise coated with a plurality of strips 12. These isolated strips may be any conductive material such as brass, copper, stainless steel or aluminum. The conductive material may be applied to the surface by depositing metal particles on the surface of the resistance material by spraying with metallic paint, by electrop'lating, by silk screen or llame plating or by like methods. The strips 12, in the embodiment shown, are substantially perpendicularly disposed with respect to the strips L11 on the opposite surface of the resistor.

Instead of strips of perpendicularly disposed conductive areas on both sides of the resistance material, various configurations and various numbers of isolatedV conductive areas obviously may be employed in the practice of this invention. For example, the paths may be disposed at angles with respect to each other which are greater or less than the ninety degrees illustrated. Figures 4 and 5 illustrate a fragmentary portion of a re'- sistance material in which the

strips

13 and 14 on both sides of resistance material 10 are at an oblique angle with respect to the perimeters of the resistance material,

yrather than parallel or perpendicular as in Figures l and 2.

Each of the

strips

11 and 12 in Figures 1 and 2 and

strips

13 and 14 in Figures 4 and 5 are spaced from each other by a portion of the

resistance material

10 and 10 respectively. lt has been found that the current flowing across the resistor surface, transversely from one conductive area to the adjacent conductive area on the same side of the resistance material, is negligible in relation to the currrent which will flow perpendicular to the surface through the resistance material. Accordingly, the conductive strips -11 and`1'2 (and 13 and 14) are eilectively isolated from each other.

One contacting assembly for use with the resistor shown in Figures l and 2 is shown in Figure 3. In this gure the

strips

11 and 12 are energized through contacts 15 and cams 16 and `17. The contacts are insulated'f'rorh each other and from the cams 16 and 17 by insulators 18 and 19. Insulator 18 is contiguous to one surface of the resistance material, while insulator 19 is contiguous to the other surface. Embedded in insulators 18 and y1.9 are a series of contacts 15. These contacts, which may be of any conductive material, are spaced so that each contact is positioned in abutting relation with each one of the conductive strips `11 and 12. It will be noticed that each of the contacts `15 are slightly longer than the width of the insulators 18 and 19. The purpose of this is to ensure contact between the strips of

conductive material

11 and 12 and the cams 16 and 17. Cams 16 and 1 7 are positioned -directly above and below the 4in sulators 18 and 19 respectively. Cams 16 and 17 function to bring into circuit relation as many or as few ofthe

respective strips

11 and 12 as may be desired. The entire assembly may be secured in the above described relationship by, for example, four screws 20, to the other end of which a nut (not shown) is attached.

Knobs

21 and 22 are provided for rotation of cams 16 and 17 respectively.

In operation, when `any one of the conductive areas on one side of the resistancematerial 10 is broughtinto circuit relation with any onev of the conductive areas .on they other side, current will pass through the resistor at Vthe point at which the projected paths of the resistance material coincide. Thus if the single strip 11 which is uppermost in Figure 1 and the single strip 12 which is at the far left in Figure 2 are brought into circuit relation, the resistance path through the non-linear resistor will be at the single point A. If, however, more than one of the conductive areas on either or both sides are brought into circuit relation, the current will flow through a plurality of points, either in parallel or in seriesparallel, depending on the number and relation of the contacts, made. In effect, the single resistance material becomes a multitude of-isolated resistances at the points of coincidence of the projected paths of the conductive areas. It can thus be seen that a vast number of possible resistance values may be achieved for any given voltage by simply selecting the number and relation of the resistance areas which it is desired to bring into play.

In place of the contiguously placed electrical contact ployed. One such means is by attaching leads to each of the conductive areas and forming electrical contact with the leads at some position external to the resistor itself. Figure 6 illustrates one embodiment of this type of contacting means with a resistance plate in which the isolated conductive areas on one side of the resistance plate are substantially axially `aligned with the conductive areas on the other side. In this embodiment, the conductive areas take the form of a plurality of isolated spots '|23 on one side of resistance plate 25 and a plurality of axially aligned isolated spots 24 on the opposite side. Leads 26 are attached to each of the isolated spots on one face of the resistance plate 25 and leads 27 to the opposite side. These leads are attached at their opposite end to contact 28 embedded in insulator 29. Cam 30 contacts as many or as few of the contacts 28 as is desired. Knob 31 is used to control the action of cam 30. The leads 27 on the opposite side of plate 25 lead to an identical insulator plate and cam assembly on the opposite side.

The operation of the embodiment shown in Figure 6 will be substantially the same as that of Figures 1, 2 and 3. Thatis, when a conductive spot 23 is brought into circuit relation with a conductive spot 24 on the op-,

posite side, the resistance path through the resistance material will be at the single location between the aligned spots. By bringing a plurality of spots on both sides into the circuit a plurality of isolated resistance paths vwill be set up in parallel. By bringing into contact the proper conductive spots, the isolated resistance paths may also be connected in series relationship or in seriesparallel using the plates shown in Figure 6.

By a non-linear resistance material, I mean a material which will present a low resistance when subjected to a high voltage and a high resistance when subjected to ka comparatively low voltage. Such a resistance material is well knownin the prior art and one form thereof and method of making the same is shown and described in United States Patent 1,822,742, issued September 8, 1931,

of Figure 3, other suitable contacting means may be emto K. B. McEachron and assigned to the same assignee 'Y i' as the present invention. A preferred form of nonlinear resistance material is that sold under the trademark Thyrite by the assignee of the present invention. This material is made by pressing silicon carbide with a suitable ceramic binder at high prmsure followed by N a firing operation at a high temperature (approximately 1200 C.).

Additional variations in the resistance may be achieved by varying the dimensions of the conductive paths on one or Yboth sides of the resistance material. By varying the thickness of the resistance material, ythe resistance levels may be correspondingly varied. Some of the varied forms of resistance materials which may be used in the practice of this invention are illustrated in Figures 7, l8 and 9,. If these varying forms are combined with n suitable conductive areas, a broad range of resistance values may be obtained. 'I'he cross sections of Figures 7, 8 and 9 correspond to the substantially uniform cross section of the resistance material 10 of Figures 1, 2 and 3.

In addition to making possible the use of a single nonlinear resistor in applications where a plurality of individual resistors were heretofore necessary, the resistors of this invention possess a large number of potential applications. They may be utilized for example in circuits having aging or drift characteristics which necessitate resistance adjustments.

What I claim as new and desire vto secure by Letters Patent of the United States is:

1. A variable resistor comprising a plate of non-linear resistance material whose resistance varies inversely with the voltage, said plate having a plurality of conductive areas on the opposite surfaces thereof, each of said conductive areas being isolated from the remaining conductive areas on the same surface, and cumulative contact means on the opposite surfaces of said plate engaging in single circuit relation at least two of the isolated conductive areas on each surface so as to pass current transversely through the plate.

2. A variable resistor comprising a plate of non-linear resistance material whose resistance varies inversely with the voltage, said plate having a plurality of conductive areas on opposite surfaces thereof, each of said conductive areas being isolated from the remaining conductive areas on the same surface, each of the conductive areas on one surface of said resistance material having a path which, when projected through the resistance material, is coincident with at least a portion of the path 'of at least one of the conductive areas on the other surface of said resistance material, and cumulative contact means on the opposite surfaces of said plate engaging in single circuit relation at least two of the isolated conductive areas on each surface so as yto pass current transversely'through the plate.

3. A variable resistor comprising a plate of non-linear resistance material whose resistance varies inversely with the Voltage, said plate having a plurality of areas on the opposite surfaces thereof having a conductive coating applied thereto, each of said conductive areas being isolated from the remaining conductive areas on the same surface, and cumulative contact means on the opposite surfaces of said plate engaging in single circuit relation at least two of the isolated conductive areas on each surface so as to pass current transversely through the plate. 4. A variable resistor comprising a plate of non-linear resistance material whose resistance varies inversely with -the voltage, said plate having a plurality of conductive strips on the opposite surfacesV thereof, each of said strips being isolated from the remaining strips on the same surface, the strips on one surface being angularly disposed with respect to the strips on the other surface, and cumulative Contact means on opposite surfaces of said plate engaging in single circuit relation at least two of the isolated conductive areas on each surface so as to pass Current transversely through the plate.

5. A variable resistor comprising a plate of non-linear resistance material whose resistance varies inversely with the voltage, said plate having a plurality of conductive strips on the opposite surfaces thereof, each of said conductive strips being isolated from the remaining conductive strips on the same surface, the conductive strips on one side being substantially perpendicularly disposed with respect to the strips on the other surface, and cumulative contact means on opposite surfaces of said resistance material engaging in single icircuit relation at least two of the isolated conductive strips on each surface so as to pass current transversely through the plate.

6. A variable resistor comprising a plate of non-linear resistance material whose-resistance varies inversely with the voltage,`said plate having a plurality of conductive areas on the opposite'V surfaces thereof, each of said conductive areas lbeing isolated from the remaining conductive area$ QI 1 the Same surface, said conductive areas on 5 one surface being substantially axially aligned with the conductive areas on the other surface, and cumulative contact means on opposite surfaces of said plate engaging in single circuit relation at least two of the isolated conductive areas on each surface so as to pass current transversely through the plate.

References Cited in the tile of this patent UNITED STATES PATENTS 252,395 Odell Jan. 17, 1882 6 Jones Dec. 25, 1900 McEachron Sept. 8, 1931 Siegel Feb. 27, 1934 Saville .Tune 25, 1940 Clancy Apr. 14, 1942 Christensen Sept. 10, 1946 Schwartz July 24, 1956