US3601743A

US3601743A - Miniaturized single turn potentiometer with hermetically sealed rotor and substrate

Info

Publication number: US3601743A
Application number: US862888A
Authority: US
Inventors: Victor G Mathison; Robert M Hayflick; Bo Gustaf Fahlstrom; Charles W Yungblut
Original assignee: Electra Midland Corp
Current assignee: Electra Midland Corp
Priority date: 1969-10-01
Filing date: 1969-10-01
Publication date: 1971-08-24
Anticipated expiration: 1988-08-24
Also published as: DE2047568B2; JPS4916144B1; BE756846A; DE2047568C3; GB1307129A; DE7035855U; FR2068245A5; DE2047568A1; NL7014312A

Abstract

A miniaturized single turn potentiometer having a rotor and substrate and in which the rotor is of recessed configuration having peripheral contact with the substrate and hermetically sealed with respect to the latter, with a contact spring seated in the recess for wiping the resistance element. Means are included for ensuring optimum contact pressure and to facilitate assembly so that proper phasing of the wiper with respect to the lead mounting is assured. Provision is made for substitution of bases for different mounting styles with minimum change in the basic structure.

Description

United- States Patent [72] Inventors Victor C. Mathison Solana Beach;

Robert M. l-layflick, La Jolla; Bo Gustaf Fahlstrom, San Diego; Charles W. Yungblut, San Diego, all of, Calif. 862,888

Oct. 1, 1969 Aug. 24, 1971 Electra/Midland Corporation Kansas City, Kans.

Appl. No; Filed Patented Assignee MINIATURIZED SINGLE TURN POTENTIOMETER WITH HERMETICALLY SEALED ROTOR AND SUBSTRATE 10 Claims, 14 Drawing Figs.

U.S. Cl 338/ 164, 338/174, 338/202 lnLCl l-l0lc 9/02 Field ofSearch 200/168 G,

[56] References Cited UNlTED STATES PATENTS 3,222,467 12/1965 Meyer ZOO/168 X 3,237,140 2/1966 Barden 338/164 3,309,471 3/1967 Korrell 200/11 3,350,673 10/1967 Spaude 338/174 3,512,113 5/1970 Kirkendall 338/163 Primary ExaminerLewis H. Myers Assistant Examiner--Gerald P. Tolin Attorney-Wolfe, Hubbard, Leydig, Voit & Osann ABSTRACT: A miniaturized single turn potentiometer having a rotor and substrate and in which the rotor is of recessed configuration having peripheral contact .with the substrate and hermetically sealed with respect to the latter, with a contact spring seated in the recess for wiping the resistance element. Means are included for ensuring optimum contact pressure and to facilitate assembly so that proper phasing of the wiper with respect to the lead mounting is assured. Provision is made for substitution of basesfor different mounting styles with minimum change in the basic structure.

PATENTEDAUGZMQYI 3601.743

SHEET 1 [1F 3 lwvsmons Vac-ran G. MATHISON ROBERT M. HAYFLIQK Bo GUSTAF' FAHLSTROM CHARLES W. Yuu'e SLUT PATENTEU AUG24|97I 3601; 743

sum 2 [IF 3 Mi 4Z Ill INVENTGRS VIcTOR G. MATHISON ROBERT M. HAYFLICK Bo Gusmr FAHLSTROM CHARLES W. YUNGBLUT PATENIEMusamn 360L743 SHEET 3 UF 3 INVENTORS VICTOR G. MATHISON ROBERT M. HAYFLICK Bo GUSTAF FAHLSTROM CHARLES W. Yu-sswr y: 116%,MJJMMMATTYS MINIATURIZED SINGLE TURN POTENTIOMETER WITH HERMETICALLY SEALED ROTOR AND SUBSTRATE It is an object of the present invention to provide a single turn miniaturized potentiometer which, in spite of its extremely small physical size, on the order of one-fourth inch in diameter, is reliable and long lived and hence particularly well suited for commercial applications, as well as military and space hardware, where reliability is of prime consideration. More specifically, it is an object to provide a potentiometer of the above type in which contact forces may be controlled within a narrow range. It is a related object to provide a single turn miniaturized potentiometer which, in spite of the special techniques of miniaturized design and construction, may be manufactured at low cost in a quantity production line.

It is another object of the invention to provide a single turn potentiometer of the hermetically sealed type but which avoids the problems usually associated with sealing especially where epoxy or other cementing substances are used requiring a curing step. It is, on the contrary, an object to provide a miniaturized potentiometer in which the rotor and stator are sealed, not only by engagement at mating surfaces but with an O-ring engaging both rotor and substrate and in which the degree of compression is fixed with a high degree of precision to provide uniformity of sealing integrity from unit to unit. In one of its aspects, it is an object of the present invention to provide a rotor assembly made up of a small molded plastic rotor element and a spring contact element which is not only mounted on and enclosed by the rotor, but which is effectively and irrevocably locked to the rotor in a precise phase position to avoid any possible looseness or play during either assembly or subsequent'usage.

It is still another object of the present invention to provide a miniaturized single turn potentiometer'which, though tiny, is strong and durable, which is made up of a minimum number of parts, each of the parts being simply and inexpensively formed for easy assembly to produce a final construction in which the parts are. intimately keyed together for reliable operation under the most challenging environmental conditions.

It is yet another object of the present invention to provide a miniaturized potentiometer which may be readily produced in a number of different mounting configurations without requiring any change in the operative parts and with only inconsequential change in mode of assembly. Thus it is an object to provide a potentiometer which may be usedalmost universally wherever variability of resistance with an appropriate rating of heat dissipation is required. Indeed, the construction is such that heavy overloads may be tolerated without running the risk of catastrophic failure.

Other objects and advantages of the invention will become apparent upon reading theattached detailed description and upon reference to the drawings:

FIG. 1 is a perspective view, greatly enlarged, of a potentiometer constructed in accordance with the present inventron;

FIG. 2 is a vertical section taken along the line 2-2 in FIG. 3;

FIG. 3 is a horizontal section looking along the line 33 in FIG. 2;

FIG. 4 is a bottom view of the potentiometer of FIG. 2;

FIG. 5 is an exploded view showing the parts which are as sembled to form the construction of the preceding figures;

FIG. 6 is a profile view of the contact spring;

FIG. 7 is a vertical section taken through the rotor assembly looking along the line 77 in FIG. 8;-

FIG. 8 is a bottom view of the rotor assembly shown in FIG. 7;

FIG. 9 is a vertical section taken along the line 9-9 in FIG.

FIG. 10 is a section taken through the base and substrate along the line 10-10 in FIG. 4;

FIG. 11 is a fragmentary section through the base and substrate taken through the line 11 -11 in FIG. 4; and

FIGS. 12, 13 and 14 are top, sectional, and bottom views respectively of a modified form of the invention.

While the invention has been described in connection with certain preferred embodiments, it will be understood that we do not intend to be limited to the particular embodiments shown but intend, on the contrary, to cover the various alternative and equivalent constructions included within the spirit and scope of the invention.

Turning now to the drawings there is shown in FIGS. 1 to 4 a miniaturized single turn potentiometer 20 having terminal leads 21, 22, a central or wiper lead 23. The potentiometer is adjusted by inserting a tool in a screwdriver slot 24 with the range of turning being limited by

stops

25, 26.

In accordance with the invention a rotor 30 is provided which is of shallow cup shape having an axially extending flange 31 adjacent the periphery which encloses a central recess 32 and which further defines a peripheral shoulder 33. Positioned below the rotor is a wafer of substrate of disc shape and approximately the same diameter as the rotor 30. The ends of the lead wires, indicated at 21a, 22a, penetrate the substrate for making contact with the ends of the resistance element. The central lead 23 projects through the substrate to present an upraised tip 23a for engagement by the contact spring to be described.

Secured within the recess 32 on the underside of the rotor is a contact spring (see FIGS. 6-9 inclusive) having a generally flat body with an integral resilient wiper 51 formed of three parallel fingers which extend crosswise at one end. The fingers are rounded at the tips and sprung outwardly away from the plane of the body. Also formed integrally with the contact spring is a resilient leaf or tab '52 which is sprung outwardly for axial engagement of the tip 52a with the tip 23a of the central lead.

For registered and secure seating of the contact spring in the rotor, the spring body is formed with a nonsymmetrical profile and the recess in which it is received is of corresponding profile providing an interference fit. Thus in the present embodiment the spring contact is made straight sided, having

edges

53, 54 and the recess 32 is formed with

internal walls

55, 56, respectively, which are straight sided and which are nonsymmetrically arranged with respect to the axis of the rotor (see FIGS. 8 and 9). As a result, the contact spring can only be inserted into the rotor in one way to avoid bility of a reversal of position during assembly.

To facilitate assembly and ensure positive retention the contact is formed with points on at least one of its ends which dig into the rotor material, specifically, into the internal surface of the flange 31. As shown in FIGS. 6 and 8, the points, lying in the plane of the body, are indicated at 57, 58. The opposite end of the spring contact member is preferably rounded to conform to the inner contour of the flange as shown at 59. Thus, in assembly, the

points

57, 58 are first inserted, with seating pressure being applied at the opposite end of the member until the rounded edge 59 clears the flange for firm seating in the bottom of the recess. The contact spring and rotor, from that point on, form a subassembly which can be separately handled without risk that it will come apart; nor is there any possibility of play between the parts.

As shown in FIG. 9, the wiper S1 is presprung outwardly from the plane of the member to project axially beyond the flange 31 by a distance l-ll. Since the flange seats on the substrate, and since the cermet resistance element is of constant thickness, maintaining a constant degree of projection H1 under production conditions ensures a wiper pressure falling within closely specified limits. Similarly, the central resilient leaf 52 is downwardly sprung so that it engages the central contact 23a which is raised above the surface of the substrate to achieve a high per unit pressure thereby reducing the casual resistance in the circuit to substantially zero.

In accordance with one of the features of the invention, an

any possi- 'O-ring 60 is provided adjacent the axial flange 31 and which bears against the shoulder surface 33 as well as against the land surface 46 on the substrate, the O-ring having a normal axial dimension which exceeds the length of the flange 31 by a predetermined amount indicated at H2 in FIG. 7, so that the O-ring is subjected to a predetermined amount of axial compression when the parts are assembled together. Thus with the lead wires 21-23 cemented in place in the substrate with a suitable, permanent and impervious cement, such as epoxy, the inner space 32 within the cup-shaped rotor is hermetically sealed against the entry of water vapor or air borne impurities. The structure is to be distinguished from prior constructions in which epoxy or similar cement is utilized in a final sealing step and where the expansion of air within the confined space in- .cident to a high-temperature curing step may result in blow holes and other imperfections in the seal.

In accordance with one of the aspects of the present invention, a base member is provided under the substrate, and the assembly consisting of the rotor, substrate and base, are all enclosed in a cup-shaped shell-type enclosure which may, for example, consist of thin metal, and which has an opening at its end to provide access to the rotor slot 24 for adjusting the rotor position limited by engagement of

stops

25, 26. Thus surrounding the assembly is an enclosure 70 of cup shape having bendable tabs along its lower edge indicated at 71-73 and having a central opening 74 for the purpose of clearing an embossment 65 which is integrally molded in the rotor and which contains the screwdriver slot 24. The base, indicated at 80, which is dimensioned to correspond to the substrate, includes recesses 81-83 on its underside for receiving the tabs 71-73. In order to ensure that the path of movement of the wiper is properly phased with respect to the resistance element 45, the wafer of substrate 40 and the enclosure 70 are both uniquely keyed to the base 80. The enclosure is keyed to the base by making the tabs 71-73 on the enclosure nonsymmetrical both in width and position and by forming the recesses 81-83 in the base of corresponding width and position to receive the inwardly bent tabs in a unique position. As will be noted in FIG. 4, the tab 71, received in recess 81, is substantially wider than the

tabs

72, 73, ensuring that the enclosure and base can only be assembled in one way. For the purpose of keying the substrate 40 to the base 80, the substrate is formed with a pair of integral protuberances 85 which, when the parts are fitted together (see FIG. 11), are registered in correspondingly spaced recesses 86 in the base.

To additionally anchor the leads 21-23 against the possibility of pulling out the substrate and to ensure a desired location of the exiting leads, the base 80 is channeled out to define L- shaped paths, such as that indicated at 87 in FIG. 2, requiring each lead to adopt a zigzag configuration. Accordingly, each lead has a radially extending portion, indicated at 21b, 22b, 23b, respectively, at right angles to the line of pull. Preferably, after the resistance element 45 has been fired in place on the substrate, preformed lead wires are inserted in the base 80, epoxy is applied, following which the substrate is seated on the base with the lead wires projecting through, and cemented to, the substrate as shown and with the protuberances 85 seated in alignment with recesses 86. An electrical connection is then established between the

tips

21a, 22a of the lead wires and the ends of the resistance element by application of a suitable conductive paste which is reduced to metal by application of heat. This provides a base subassembly, upon which the rotor subassembly is placed, with the O-ring 60 in encircling position. The shell enclosure is then telescoped over the assembly with the tab 71 in alignment with the recess 81 in the base, following which the tabs are bent into final position to complete the assembly.

The keying together of the various elements with one way assembly between all of the parts ensures that the range of movement of the wiper will correspond precisely to the path of the resistance element on the substrate. Moreover, the prespringing of the wiper 51 and resilient leaf and the thickness of the O-ring 60 (see 111 and H2 in FIGS. 9 and 7 respectively) ensure that the wiper and O-ring will exert precisely the right amount of force against the surfaces which they engage notwithstanding the normally encountered tolerances in the molding of the rotor and notwithstanding the fact that the net-prespringing beyond the surface of the rotor flange 31, may be measured in terms of thousandths of an inch. If desired, the rotor assemblies may be checked in a jig prior to final assembly to ensure the proper amount of projection of the resilient elements and O-ring with respect to the 1 presented face of the flange 31 used as reference.

side of the structure and with corresponding parts being indicated throughout by corresponding reference numerals with the addition of subscript b. The base b has a circular pedestal portion which directly underlies the substrate, just as in the preceding embodiment, but such pedestal is downwardly extended and provided with an integral side bracket which is separated from the pedestal by an arcuate groove 91 to accommodate the shell housing and which has through-

openings

92, 93 for reception of the

tabs

72b, 73b, which are bent over as shown (FIG. 14) to complete the assembly. The construction of rotor, substrate and spring contact, as well as the construction of the housing, remain unchanged in this embodiment.

We claim as our invention:

1. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having an axial flange spaced inwardly from the periphery to define a central recess and an annular axially facing shoulder, a wafer of substrate of substantially the same diameter arranged below the rotor and contacting the lower surface of said axial flange, an interrupted circular resistance element on the substrate centered about a central contact, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, said resilient leaf extending from the plane thereof so that when the contact spring is seated in the recess the wiper extends slightly beyond the axial flange thereby to ensure engagement with the resistance element and central contact respectively when the-axial flange is ridingly seated on the substrate, a resilient O-ring encircling the axial flange and resiliently sandwiched between the shoulder on the rotor and the surface of the substrate for providing an hermetic seal between the rotor and substrate in all rotational positions of the rotor, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, and means enclosing the rotor, substrate and base member while providing access to the rotor for rotational adjustment, said enclosing means pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide said hermetic seal between said rotor and substrate.

2. In a miniaturized potentiometer the combination comprising a rotor of shallow cup shape having an axially extending flange extending about its periphery defining a central recess, an O-ring mounted adjacent the flange having a normal diameter greater than the height of the flange, a wafer of substrate arranged below the rotor having an interrupted circular resistance element surrounded by a land engaging the lower surface of said axial flange and said O-ring, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, said resilient leaf extending from the plane thereof so that when the contact spring is seated in the recess the wiper extends slightly beyond the axial flange thereby to ensure application of predetermined pressure against the resistance element when the flange is in riding engagement with the substrate, a central lead penetrating the substrate for making pivoting contact with the resilient leaf, terminal leads penetrating the substrate for making contact with the ends of the resistance element, a base member immediately underlying the substrate and supportingly engaging the lower surface of said substrate, said base member being channeled for reception of the leads, the rotor, substrate and base having substantially the same diameter, a cup-shaped enclosure surrounding the rotor, substrate and base, said enclosure pressing against the upper surface of said rotor and the lower surface of said base to hold the rotor, substrate and base together while slightly compressing said O- ring to provide a hermetic seal between said rotor and substrate, stop members interposed between the rotor and enclosure for determining the limits of movement of the rotor, means for keying together the substrate and base, and means for keying together the enclosure and base for automatic positional phasing of the wiper with respect to the resistance element,

3. The combination as claimed in claim 2 in which the keyed connection between the enclosure and base is in the form of nonsymmetrical inwardly bent tabs on the enclosure registering with corresponding nonsymmetrical recesses in the base.

4. The combination as claimed in claim 2 in which the leads are sealed to the substrate and in which the base is formed with channels for accommodating the lead wires of L-shaped configuration so that the leads are bent sharply within the base for mechanical anchoring thereof.

5. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having an axial flange spaced inwardly from the periphery to define a central recess and an annular axially facing shoulder, a wafer of substrate of substantially the same diameter arranged below the rotor and contacting the lower surface of said axial flange, an interrupted circular resistance element on the substrate centered about a central contact, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, an O-ring surrounding the flange and sandwiched between the substrate and shoulder thereby to provide a moisture and dustproof seal for the resistance element and contact member, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, an enclosing shell surrounding the rotor, substrate and base member while permitting access to the rotor for angular adjustment of the latter, said enclosing shell pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide a hermetic seal between said rotor and substrate said shell and said rotor having cooperating stops to define the range of angular movement of the rotor, the shell being keyed to the substrate and the contact spring being keyed to the rotor thereby to ensure that the path of the wiper on the contact spring is phased with the resistance element.

6. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having an axial flange spaced inwardly from the periphery enclosing a central recess, a wafer of substrate of substantially the same diameter arranged below the rotor and contacting the lower surface of said axial flange, an interrupted circular resistance element on the substrate centered about a central contact, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, an O-ring ad- 5 jacent the flange for contacting the substrate, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, an enclosing shell surrounding the rotor, substrate and base member and having a central opening for permitting access to the rotor for angular adjustment of the latter, said enclosing shell pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide a hermetic seal between said rotor and substrate, said shell and said rotor having cooperating stops to define the range of angular movement of the rotor, the shell being keyed to the substrate and the contact spring being keyed to the rotor thereby to ensure that the path of the wiper on the contact spring is phased with the resistance element.

7. The combination as claimed in claim 6 in which keying between the rotor and contact spring is brought about by forming the recess to match the profile of the contact spring with an interfering fit for permanent retention of the spring after it has been pressed into place.

8. The combination as claimed in claim 6 in which the contact spring is straight sided and in which the recess in the rotor is correspondingly formed for permanent keyed reception of the contact spring.

9. The combination as claimed in claim 6 in which the wiper is at one end of the contact spring, the recess being conformed to mate with the profile of the contact spring for nested reception of the spring, and the recess being nonsymmetrical with respect to the axis of the rotor to ensure unique orientation of the wiper with respect to the stop on the rotor.

10. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having a peripheral flange enclosing a central recess, and O-ring arranged adjacent the flange, a substrate having an interrupted circular resistance element surrounded by a land engaging the lower surface of said flange and said O-ring, a contact spring secured to said rotor in said central recess and having a flat body integrally ineluding a resilient wiper and a central resilient leaf extending from the plane thereof and engaging said resistance element, leads penetrating the substrate for making connection to the ends of the resistance element, a central lead penetrating the substrate and projecting beyond the surface thereof for making contact with the resilient leaf on the contact spring, said leads being sealed to the substrate, the rotor having an adjusting slot formed in its upper surface, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, means including a shell for enclosing and clamping together the rotor, substrate and base member and including a central aperture for access to the adjusting slot, said shell pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide said hermetic seal between said rotor and substrate.

Claims

1. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having an axial flange spaced inwardly from the periphery to define a central recess and an annular axially facing shoulder, a wafer of substrate of substantially the same diameter arranged below the rotor and contacting the lower surface Of said axial flange, an interrupted circular resistance element on the substrate centered about a central contact, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, said resilient leaf extending from the plane thereof so that when the contact spring is seated in the recess the wiper extends slightly beyond the axial flange thereby to ensure engagement with the resistance element and central contact respectively when the axial flange is ridingly seated on the substrate, a resilient O-ring encircling the axial flange and resiliently sandwiched between the shoulder on the rotor and the surface of the substrate for providing an hermetic seal between the rotor and substrate in all rotational positions of the rotor, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, and means enclosing the rotor, substrate and base member while providing access to the rotor for rotational adjustment, said enclosing means pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide said hermetic seal between said rotor and substrate.

2. In a miniaturized potentiometer the combination comprising a rotor of shallow cup shape having an axially extending flange extending about its periphery defining a central recess, an O-ring mounted adjacent the flange having a normal diameter greater than the height of the flange, a wafer of substrate arranged below the rotor having an interrupted circular resistance element surrounded by a land engaging the lower surface of said axial flange and said O-ring, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, said resilient leaf extending from the plane thereof so that when the contact spring is seated in the recess the wiper extends slightly beyond the axial flange thereby to ensure application of predetermined pressure against the resistance element when the flange is in riding engagement with the substrate, a central lead penetrating the substrate for making pivoting contact with the resilient leaf, terminal leads penetrating the substrate for making contact with the ends of the resistance element, a base member immediately underlying the substrate and supportingly engaging the lower surface of said substrate, said base member being channeled for reception of the leads, the rotor, substrate and base having substantially the same diameter, a cup-shaped enclosure surrounding the rotor, substrate and base, said enclosure pressing against the upper surface of said rotor and the lower surface of said base to hold the rotor, substrate and base together while slightly compressing said O-ring to provide a hermetic seal between said rotor and substrate, stop members interposed between the rotor and enclosure for determining the limits of movement of the rotor, means for keying together the substrate and base, and means for keying together the enclosure and base for automatic positional phasing of the wiper with respect to the resistance element,

6. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having an axial flange spaced inwardly from the periphery enclosing a central recess, a wafer of substrate of substantially the same diameter arranged below the rotor and contacting the lower surface of said axial flange, an interrupted circular resistance element on the substrate centered about a central contact, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf engaging said resistance element, an O-ring adjacent the flange for contacting the substrate, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, an enclosing shell surrounding the rotor, substrate and base member and having a central opening for permitting access to the rotor for angular adjustment of the latter, said enclosing shell pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide a hermetic seal between said rotor and substrate, said shell and said rotor having cooperating stops to define the range of angular movement of the rotor, the shell being keyed to the substrate and the contact spring being keyed to the rotor thereby to ensure that the path of the wiper on the contact spring is phased with the resistance element.

10. In a miniaturized potentiometer, the combination comprising a rotor of shallow cup shape having a peripheral flange enclosing a central recess, and O-ring arranged adjacent the flange, a substrate having an interRupted circular resistance element surrounded by a land engaging the lower surface of said flange and said O-ring, a contact spring secured to said rotor in said central recess and having a flat body integrally including a resilient wiper and a central resilient leaf extending from the plane thereof and engaging said resistance element, leads penetrating the substrate for making connection to the ends of the resistance element, a central lead penetrating the substrate and projecting beyond the surface thereof for making contact with the resilient leaf on the contact spring, said leads being sealed to the substrate, the rotor having an adjusting slot formed in its upper surface, a base member underlying said substrate and supportingly engaging the lower surface of said substrate, means including a shell for enclosing and clamping together the rotor, substrate and base member and including a central aperture for access to the adjusting slot, said shell pressing against the upper surface of said rotor and the lower surface of said base member to hold the rotor, substrate and base member together while slightly compressing said O-ring to provide said hermetic seal between said rotor and substrate.