US2663003A - Adjustable potentiometer - Google Patents

Description

Dec i5, 1953 F G, LANDls 2,663,003

ADJUSTABLE POTENTIOMETER Filed April 16, 1949 Patented Dec. 15, 1953 UNITED STATES PATENT OFFICE ADJUSTABLE POTENTIOMETER Massachusetts Application April 16, 1949, Serial No. 87,896

14 Claims. l

The present invention relates to adjustable potentiometers and, particularly, to those of a type adapted to serve as a voltage divider foralternating potentials.

Adjustable potentiometers heretofore have been constructed with an elongated element exhibiting substantial electrical resistance between its end terminals and an electrically conductive contact which electrically engages the resistive element and is adjustably positioned along the latter by which to derive from the resistive element a proportionate part of the voltage applied across its terminals. The resistive element is conventionally formed either by a multiplicity of turns of resistive Wire or by a graphite coating placed upon a dielectric base material.

There are many instances, as in a conventional volume control of a radio receiver, where the potential applied across the terminals of the resistive element of a potentiometer includes both a unidirectional component and 4alternating components of which it is desired that only the latter be translated to an electrical circuit connected between one terminal of the resistive element and the slider of the potentiometer. In these instances, it has heretofore been necessary to couple the slider of the potentiometer through a series condenser to the electrical circuit in order that only the alternating components of the impressed voltage may be translated.

There are also many instances, of which the detector circuit of a conventional radio receiver furnishes an illustrative example, where it is desirable to include a low-pass resistor-condenser filter network between the voltage source and a potentiometer across which the voltage is impressed in order that only lower-frequency a1- ternating components ci voltages may be applied to the potentiometer. It vrhas heretofore been necessary in .these instances to construct such filter Ynetworks of electrical components separate and apart from the potentiometer,

In many situations of the type last mentioned, the use of circuit components separate and apart from the potentiometer effects an undesirable increase of the cost oi the apparatus with which the potentiometer is associated. This is Vdue not only to the additional cost of the circuit components employed but also -to the element of labor required to perform the necessary wiring steps.

Additionally, many oi the potentiometer constructions heretofore proposed often are subject to electrical failure after repeated operations due to the fact that the slider of the potentiometer.

directly engages and slides over its resistive element. There is also the serious disadvantage heretofore experienced Where potentiometers are necessarly associated With a number of associated components that the potentiometer and associated components necessarily occupy a volume of space much larger than desirable in many applications. This is particularly true in the eld of small socalled personal radios of the portable type and in hearing aids where it is most desirable that the apparatus be enclosed Within the most compact carrying case possible.

It is an object of the present invention, therefore, to provide a new and improved adjustable potentiometer which avoids one or more of the limitations and disadvantages of those heretofore proposed.

It is an additional object or" the invention to provide an adjustable potentiometer wherein resistive and capacitive circuit components which are desirably associated with the potentiometer are included as a .part of its construction. It is an additional object oi the invention to provide a novel adjustable potentiometer having integrally formed in the potentiometer structure a plurality of resistive and capacitive circuit components, and yet one which is oi simple, inexpensive and compact construction.

It is yet another cbj ect of the invention to provide a new and improved adjustable potentiometer having an operating life which may be almost unlimited.

In accordance with the invention, an adjustable potentiometer comprises a planar resistive element exhibiting substantial electrical resistance between its ends, an electrically conductive member supported in insulated relation to all or at least the major portion of the resistive element and including a portion movable along the element, and a planar member of dielectric material continuously positioned between and effecting physical separation of the element and the aforementioned portion of the member to provide capacitive coupling between the member and that area of the element which at any time lies in opposing relation to the aforementioned portion of the conductive member. in many applications of the invention, the dielectric material may be a titanium-dioxide ceramic material which provides a very substantial capacitive coupling between the movable member and the resistive element. One or more conductive elements may be xedly positioned in spaced relation along the resistive element but separated therefrom by a dielectric material, such as a titanium-dioxide 3. cerarrlc, to provide one or more condensers of fixed capacitance coupled to the resistive element.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring now to the drawing, Figures 1 and 1A illustrate respectively in plan view and in cross-sectional elevational View an adjustable potentiometer embodying the present invention in a particular form: Figure 2 is a'circuit diagram representing the electrical circuit arrangement of the Figs 1 and 1A potentiometer as employed in a portion of a circuit of a radio receiver; Figure 3 is a fragmentary view illustrating a modified form of potentiometer embodying the invention; Figure 4 is a fragmentary view in cross section illustrating an additionally modified form or" the invention; and Figure 5 is an elevational view in cross section illustrating yet another form of the invention.

Referring now more particularly to Figs. 1 and 1A of the drawing, there is illustrated an adjustable potentiometer having a strip of material or resistive element iii exhibiting substantial electrical resistance between its ends. The element IG, which is of open-ring-shaped configuration, may comprise a conventional body of graphite or a conventional resistive element formed by coating a dielectric material with graphite. The element i c is supported on one surface of a member Ii of dielectric material, which preferably is one having a large dielectric constant such as a titanium-dioxide ceramic, a titanium-dioxide magnesium titanate, a titanium-zirconium dioxide ceramic, or the like. The ends oi the element i@ are connected electrically to a pair of terminals i2, I3 as by rivets i4 which extend through apertures in the member i I The member l l with its resistive element Iii are secured together with a collar E5 of dielectric material on a hollow shouldered bushing i5 in conventional manner as by spinning over the end of the bushing against a shoulder of the collar l5. One end of the bushing le externally threaded to receive a nut I 'i which, with a washer i8, maintains the potentiometer in position in an aperture of a panel I9 of an apparatus of which the potentiometer forms a component.

The potentiometer also includes an electrically conductive member or slider 2li supported in insulated relation to at least the maior length of the resistive element or strip It and including a portion 2i movable along the element it. In particular, the member 2i! is secured by a machine screw 22 and washer 23 to one end of a shaft 2li, of insulating material, which is journaled in the bushing i6 and is maintained in position in the latter by a loci: ring 25 which engages a groove 26 of the shaft 24. The member 2i! is of disc shaped configuration but has an extending resilient arm 21 which terminates in the portion 2i of the slider member. A corrugated washer 28 of spring material is assembled between the member 20 and the collar l5 and is restrained against angular motion relative to the latter by pins 2c, it being the purpose of the washer 28 to complete an electrical connection between the member 2E) and a terminal 3! of the potentiometer. The member 26 and shaft 2d are locked together for unitary movement by amT suitable means, as by the provision of a milled dat Si on the end of the shaft 24 which c0- operates with an aperture of similar coniiguration provided in the member 2t.

In the potentiometer construction thus far described, the portion 2i of the slider member 2c is constrained to move along the resistive element i9 but is continuously spaced from the latter during such movement by the dielectric member i E, the latter thus serving to provide substantial capacitive coupling between the conductive mem" ber Eil and that area of the resistive element ifi which at any time lies in opposing relation to the portion 2i of the conductive slider member ZB. l

The potentiometer also includes a plurality of conductive tabs 33 and @il which are xedly positioned at individual spaced points along the length of the resistive element It! but are sepas rated from the latter by dielectric material to provide capacitive coupling between each such tab and a corresponding point on the resistive element Iii. in particular, the conductive tabs 32 and 33 are cemented or otherwise suitably secured to the dielectric member il on the side thereof opposite the resistive element le, while the tab 3d is secured to a layer oi dielectric material 35 which in turn is secured directly upon the surface of the resistive element iii, the assembly of elements 3d and Se upon the element iii being conveniently accomplished by a suitable cement or the like.

Figure 2 is a circuit diagram representing a typical application of a potentiometer embodying the Figs. l and 1A construction in which the potentiometer is used for conventional volume control in a radio receiver. In this arrangement, the circuit elements shown are identied by reference numerals which serve to identify the correspondn ing structural elements oi the potentiometer. The radio receiver is assumed to be ci the superheterodyne type having an output intermediater frequency transformer 3S the windings or" which are tuned by oondensers 39 and iii to the inter= mediate frequency. The secondary winding of the transformer is coupled to the anode of a diode rectifier ii and to the terminal l2 of the potenti* ometer, the cathode of the rectifier being coupled to the terminal i3 of the potentiometer. The conductive tabs 32 and 33 of the potentiometer are connected to the terminal i2, which is connected to ground as indicated, while the tab 3d o the potentiometer is coupled to ground through a resistor 132 which constitutes with the condenser 34 a conventional tapped-volumecontrol arrangement. The terminal of the potentiometer is connected to the control electrode of an audio amplifier tube having an input-circuit resistor dli. The portion of the resistive element it of the potentiometer lying between the conductive tabs 32 and 33 is indicated in Fig. 2 by the resistor ita, while the portions of the resistive element between the tabs 33 and and between the tab 3v", and the terminal i2 are represented by respective resistors i tb i te. The capacitive coupling between the portion 2i of the slider member E@ of the potentiometer and the resistive element Iii is indicated in Fig. 2 by a condenser Z! which, since the slider portion 2i of the potentiometer may be positioned` at any point along the resistive element it) between the terminal i2 and the tab 33, is indicated as adjustably coupled to the portions Ilb and IE@ of the resistive element by a slidable tap.

It will be apparent from this circuit arrangement that the tabs 32 and 33 in conjunction with that portion of the resistive element iii lying betrol. The confinotiveA slider member .2B Vis only.

capacitively coupled to tn portions les and la@ of the resistive .elementi il, and consequently `oni-y the .'audioffreguency components of the applied potential are applied from .the .output terminal 39 ci the potentiometer -to the audio-frequency in piier 1tube is. I-t'willbeapnar fro. thisen uit arrangement that a potentiometer' embed invention inherently tides in its const. most of the numerous circuit components which are employed in a conv ntional network used to couple a modulation-signal detector to an audio..- frequency amplifier stage. While the resistors 42 and 44 are indicated as circuit components separate and apa-rt from the potentiometer, it Will be apparent that the resistor '32 may coinpiise one formed by printing or painting the re sistor in conventional manner on the lower surface of the dielectric member l i between the conductive tab si; and the terminal l2 and the resistor i4 may be similarly formed on the upper surface of the membei` Il. Thus all of the resistive and capacitive circuit components shown in the arrangement of Fig. 2 may readily and easily be incorporated in the potentiometer it self.

Figure 3 illustrates a portion of a potentiometer embodying the invention in a-mpdied form, elements oi Eig. 3 correspond-ing tc similar elements of Figs. 1 and 1A being designated by `similar reference numerals. ,this rnodication the resistive element lil is extended beyond the ter.- minai is and the terminait@ is bent down and electrically vconnegoed totheend he resistive element by ,a rivet v4S which extends hi'oush the dielectric member i l. W ith this construction, the portion or vthe resistive element i3 between the terminals l2 and Sil :may -iorm the iixed resistor 4t shown in the arrangement of Fig. 2. It will be evident, of course, that the portion of the resistive element i9 which lies between the terminals l2. and 35i might alternatively be on the upper surface of the element il, rather than on its lower surface, where this construc tion more conveniently enables the attainment of diierent velues of resistance for the element ld and the extended portion thereof.

Figs. l and 1A oi the drawing indicate that the dielectric member which provides the capacitive coupling between the slider 2li and the resistive element has substa al. thickness- This, however, is done only for purpese-s of clarity oi illustration and it will ,be un derstood that practice the thickness oi the member il is .normally the minimum value that can be tolerated While still providing adequate mechanical strength Afor the element.

In those applications where it is desired thaA even larger values of capacitive couplingbe provided between the elements in and 2B, the diodi. iisd formv oi theinvention illustrated in e may be employed. In this arrangement, the electric member I l merely serves as a supporI for the resistive element I0, yand the arm 2: of the conductive slider member '2B terminates in o. .contact structure 55. The latter is cornprised by a plurality of condenser Iplates ml.

Gil

sandwiched a plurality of layers 52 of dielectric material with alternate ones of the plates electrically Connected to the arm 2? of thelconductive slider member and the intervenH ing plates electrically connected to a conductive contact memberwhich effects electrical engagement with the ysur-face of the resistive element l t. The condenser plates 5j may conveniently be formed as U-shaped members as indicated, and the condenser elements 5| and 52 may be assembled as a, unitary structure by cementing or otherwise securing the .elementstogethen Figure 5 illustrates an adjustable potentiometer Y einbodyins an addition 1y modiied form of the invention. .elements of Figure 5 correspondinsto .Similar elementsv 0i Fis-.S` 1 and 1A beine indicated by similar reference numerals and analogous elemer 1t. s y .by similar reference numerals primed- ,For simplicity, only the maior constructional fea-tures are shown. A dual potentiometer arrangement is illustrated wherein olle potentiometer is comprised by the resistive element I0, the conductive slider member and the shaft 24'. A ring 54 of dielectric material, having a large dielectric constant is positioned on the-element lil to provide the desired capacitive coupling between the latter and the conductive slider member 2G. T -he second potentiometer comprises a similar ring-shaped resistive element 55, which is positioned on the opposite side of the dielectric supporting member i l', and a com ductive slider member 56 mechanically connected to a hollow shaft .5l which surrounds the shaft 24 of the first potentiometer. A ring 5S of dielectric material is likewise used in the second potentiometer to provide the capacitive coupling desired between the resistive element .5 3 the slider member 53. The potentiometer structure is maintained in assembled relation by the provision 4of a col-lar 5S on the shaft 5l, a housing ed having an annuler seat 55| at its open end to receive lthe dielectric member il', a set screw 62 Which engages a groove 53 in the shaft 2d', and a locking ring 64 which is seated in a groeve E5 of theishaft'l.

It will be apparent from the several modified forms of the invention disclosed that an adjustable potentiometer .embodying the invention is adaptable to numerous types oi construction, and that it lhas utility in a wide range of applications. potentiometer embodying the invention has the advantages of great compactness, simplicity of construction, and relatively low manuiacturing cost. The present invention makes it possible to eliminate many of the circuit components ordinarily employed in an electrical circuit in association with a potentiometer, and this without adding materially to the cost of the potentiometer.

While there have been described `what are at present rconsi,dared to be the preferred embodiments of this invention, it will be obvious to those skilled inthe .art that various changes and modiiications vmay be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scopeof the invention.

I claim:

1, An adjustable potentiometer comprising, a strip of material exhibiting substantial electrical resistance between its ends, and an electrically conductive member supported in insulated relation to at least the major length of said strip and including a vcontact structure electrically engaging said strip and .movable therealong, .said coni? tact structure comprising a plurality of condenser plates sandwiched between a plurality of layers of dielectric material with alternate ones of said plates electrically connected to said conductive member and the intervening plates electrically connected to a conductive contact member which effects said electrical engagement with said strip, whereby said first-mentioned conductive member is capacitively coupled to that area of said strip which at any time is engaged by said contact structure.

2. An adjustable potentiometer comprising, a resistive element exhibiting substantial electrical resistance between its ends, and an electrically conductive member movably supported in insulated relation to at least the major length of said element and including a contact structure mechanically and electrically engaging said element and movable therealong, said contact structure comprising a condenser having one terminal mechanically and electrically connected to said member and a second terminal effecting said mechanical and electrical engagement with said element, whereby said member is capacitively coupled to that area of said element which at any time is engaged by said contact structure.

3. An adjustable potentiometer comprising, a strip of material exhibiting substantial electrical resistance between its ends, an electrically conductive member supported in insulated relation to atleast the major length of said strip and including a portion movable along said strip and electrically coupled to that area of said strip which at any time lies in opposing relation to said movable portion, and a conductive tab xedly positioned at a selected point along the length of said strip but separated therefrom by dielectric material to provide capacitive coupling between said tab and said selected point of said strip.

An adjustable potentiometer comprising, a strip of material exhibiting substantial electrical resistance between its ends, an electrically conductive member supported in insulated relation to at least the major length of said strip and including a portion movable along said strip and electrically coupled to and that area of said strip which at any time lies in opposingT relation to said movable portion, and a plurality of conductive tabs fixedly positioned at individual spaced points along the length of said strip but separated from said strip by dielectric material to provide with a portion of said strip a filter network comprised by capacitive and resistive elements.

5. An adjustable potentiometer comprising, a planar member of relatively rigid thin titaniumcompound dielectric sheet material, a resistive material of open-ring-shaped conguration supported by and in engagement with one surface of said member and exhibiting substantial electrical resistance between its ends, and a pivoted electrically conductive member supported in insulated relation to at least the major length of said resistive material and including a portion engaging the opposite surface of said dielectric member and movable in an arc along said resistive material in opposing relation thereto,.said dielectric member providing substantial capacitive coupling between said conductive member and that area of said resistive material which at any time lies in opposing relation to said portion of said conductive member.

6, An adjustable potentiometer comprising, a planar open-ring-shaped member of relatively rigid thin titanium-compound dielectric sheet material, a resistive material of open-ring-shaped configuration integrally formed with said member on one surface thereof and exhibiting substantial electrical resistance between its ends, and a pivoted electrically conductive member supported in insulated relation to at least the major length of said resistive material and including a portion engaging the opposite surface of said dielectric member and movable in an arc along said resistive material in opposing relation thereto, said dielectric member providing substantial capacitive coupling between said conductive member and that area of said resistive material which at any time lies in opposing relation to said portion of said conductive member.

7. An adjustable potentiometer comprising, an electrically continuous resistive element exhibiting substantial electrical resistance between its ends, an electrical terminal at each end of said element, a conductive tab affixed with intervening dielectric material in opposing relation to an intermediate fixed point on said element spaced from one terminal thereof, and an electrically conductive member supported in insulated relation to at least the major length of said element and including a portion movable along said element between said one terminal thereof and said intermediate fixed point and capacitively coupled to said element.

8. An adjustable potentiometer comprising, an electrically continuous resistive element exhibiting substantial electrical resistance between its ends, an electrical terminal at each end oi said element, a conductive tab aiiixed to said element at a fixed point intermediate the ends thereof but spaced from said element by dielectric material and electrically connected to one of said terminals, and an electrically conductive member supported in insulated relation'to at least the major length of said element and including a portion movable along said element between said one terminal thereof and said intermediate fixed point and capacitively coupled to said element.

9. An adjustable potentiometer comprising, an electrically continuous resistive element exhibiting substantial electrical resistance between its ends, an electrical terminal at each end of said element, a plurality of conductive tabs afiixed to said element at individual fixed spaced points intermediate the ends thereof but with each tab spaced from said element by dielectric material and electrically connected to one of said terminals, and an electrically conductive member supported in insulated relation to at least the major length of said element and including a portion movable along said element between said one terminal thereof and one of said intermediate fixed points and capacitively coupled to said element4 l10. An adjustable potentiometer comprising, an open-ring-s'naped electrically continuous resistive element exhibiting substantial electrical resistance between its ends, an electrical terminal at each end of said element, an electrical terminal intermediate said last mentioned terminals, resistive material between one of said iirst mentioned terminals and said intermediate terminal, and a pivoted electrically conductive member electrically connected to said intermediate terminal and including a portion movable in an arc Valong said resistive element in capacitively coupled relation thereto.

ll. An adjustable potentiometer comprising, an electrically continuous resistive element exhibiting substantial electrical resistance between its ends and including an end portion which has a different value of resistance per unit length than does the remainder of said element, electrical terminals at each end of said element and at each end of said portion thereof, and an electrically conductive member electrically connected to the remote terminal of said end portion and including a portion movable along said element and capacitively coupled thereto.

12. An adjustable potentiometer comprising, an electrically continuous resistive element exhibiting substantial electrical resistance between its ends, electrical terminals at each end of said element, a terminal intermediate said last mentioned terminals, resistive material between one of said first mentioned terminals and said intermediate terminal, a conductive tab aiilxed to said element at a fixed point intermediate the ends thereof but spaced from said element by dielectric material, and an electrically conductive member electrically connected to said intermediate terminal and including a portion movable along said element between said one terminal thereof and said intermediate fixed point and capacitively coupled to said element.

13. An adjustable potentiometer comprising, an electrically continuous resistive element exhibiting substantial electrical resistance between its ends, electrical terminals at each end of said element, a terminal intermediate said last mentioned terminals, resistive material between one of said rst mentioned terminals and said intermediate terminal, a plurality of conductive tabs anixed to said element at individual fixed spaced points intermediate the ends thereof but each spaced from said element by dielectric material and electrically connected to said one terminal, and an electrically conductive member electri cally connected to said intermediate terminal and including a portion movable along said element and capacitively coupled thereto.

14. An adjustable potentiometer comprising, a planar member of relative rigid thin sheet dielectric material having a large dielectric constant, resistive material of open-ring shaped configuration supported in engagement with one planar surface of said member and exhibitingl substantial electrical resistance between its ends, and a pivoted electrically conductive member supported in insulated relation to at least the major length of said resistive material and including a portion engaging the opposite planar surface of said dielectric member and movable in an arc along said resistive material in opposing relation thereto, said dielectric member providing substantial capacitive coupling between said conductive member and that area of said resistive material which at any time lies in opposing relation to said portion of said conductive member.

FRANKLIN G. LANDIS,

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,838,987 Cooper Dec. 29, 1931 1,980,146 Vingerhoets Nov. 6, 1934 2,481,456 Tyzzer Sept. 6, 1949 OTHER REFERENCES

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