US2023382A - Interposed disk rheostat - Google Patents

Description

Dec. 3, 1935. N. c. SCHELLENGER INTERPOSED DISK RHEOSTAT Original Filed May 1, 1933 3 Sheets-Sheet l 3 maentor 2 /ZW2 @wia/Zwgar Dem 1935- N. c. SCHELLENGER 2,023,332

INTERPOSED DISK RHEOSTAT Original Filed May 1, 1933 3 Sheets-Sheet 2 l'mventor.

Gttornegs Dec 3, 1935. N. c. SCHELLENGER 2,023,382

INTERPOSED DISK RHEOSTAT Original Filed May 1, 1953 3 Sheets-Sheet 5 Enneutor Patented Dec. 3, 1935 warren srArss PATENT OFFICE Chicago Telephone Supply- 00.,

diana a corporation of In Eikhart, lnd.,

Original application May 1, 1933, Serial No.

15 Claims.

My invention relates to con rol devices for electrical circuits, and more particularly, to variable resistance devices of the general type set forth in my prior Patent No. 1,851,933, granted March 29, 1932.

The present application is directed toward improving variable resistance devices of the intermediate contact disk type, and especially those that are exceedingly small and compact. This application is a division of my application Serial No. 668,757, filed May 1, 1933.

Heretofore, in the types of devices characterized above, it has been impossible to obtain a clear, sharp, well defined line of contact between the contacting disk and the resistance element. This has been particularly true in devices of this type wherein the diameter or width of such devices is quite small; i. e., not in excess of three inches.

This condition has been due to the fastening means employed between the contact disks or rims and their central hubs. These fastenings usually were straight, radial spokes, which were necessarily short to conform with the requirements of the small mountings and casings within which they were assembled.

In the radial spoke type of intermediate disk, when the rim is depressed intermediate any two of the spokes, the spokes bend at portions along their length. These increments of bent portions lie within, or parallel to, chords of a circle lying within the rim, and to which chords, the longitudinal axis of the depressor arm is always substantially normal. This action causes the entire segment of rim subtended by the major chord to be depressed downwardly toward the resistance element, and a considerable amount of the entire depressed segment actually engages the resistance element. Thus, if a substantially planar resistance element is employed, a fine, well defined line of contact cannot be effected, and a sensitive variation in resistance values is rendered impossible.

Another difliculty in the prior art has been encountered in the connecting of flat, carbonaceous resistance elements to terminals by means of rivets, screws, etc. It is necessary that some such fastenings be utilized to effect contact between the resistance element and the terminals at the high and low resistance ends of the element. This has been done heretofore by appropriating the extreme end portions of the resistance element to fasten, by means of large headed rivets that project above the contact surface, the resistance element and to Divided and this 30, 1935, Serial No. 38,494

application August the base. This type of assembly necessitates the forfeiture of that portion of the rwlstance element underlying the fastenings, as well as portions lying beyond the fastenings, which, of course, means a sacrifice of eifective resistance. 6

Other ways, equally as troublesome, have been tried without success. One of these contemplated countersinking a cylindrically-headed rivet in a complementary aperture in the base, to permit the passage of the contactor member thereover. 10 It was found, however, to be impossible to obtain a smooth connection surface between the rivet and the resistance, since either the rivet head would project and engage the contactor prematurely to short-circuit some eifectlve resistance, or else it would fail to touch at all, (Ming countersunk too great a depth), whereby a high minimum resistance value resulted at the low resistance terminal.

In combination variable resistance and power switch units, wherein both devices are controlled by a single actuating shaft, there has heretofore been a further sacrifice of effective resistance. The switch mechanism was caused to be actuated over a portion of resistance element adjacent the low resistance end, which means that the switch was caused to open the circuit before maximum low resistance position could be reached by the contactor; and, conversely, when the contactor was moved from the extreme low resistance position, a substantial amount of the resistance element was traversed before the switch was actuated to close the circuit. Thus, a considerable amount of otherwise effective resistance was rendered totally unuseable.

Covers or housings for devices of the character described, and particularly those covers adapted to carry power switches, have been the source of much consternation and worry in the trade.

First, it was necessary to provide proper spacing means between the cover and the variable resistance device, to insure that parts of the switch and resistance device were in proper cooperative relation. Secondly, there had to be provided means to retain the cover in positive engagement with the variable resistance device to insure against any relative movement there between. Thlrdly, to position the cover, provision had to be made for terminals and other projections extending from the variable resistance device. These necessitated the provision of apertures, which permitted dust, dirt and other for- @151; matter to find its way into the casing to the u detriment of the sensitive parts therein contained.

Therefore, it is an object of my invention to provide a variable resistance device of the interposed contacting disk type wherein contact of the disk with the resistance element approaches a linear tangency as a limit.

It is another object of my invention to provide a contacting disk for variable resistance devices of the interposed contacting disk type, that is highly flexible and which is capable of having peripheral portions distorted out of their normal plane without disturbing the position of its other portions.

It is still another object of my invention to provide a durable, inexpensive cover for a variable resistance device, which has novel means for engaging the base of such device for retention thereon.

It is a further object of my invention to provide novel means for spacing portions of a cover from portions of a variable resistance device in predetermined relation, and to render said cover dustproof.

It is still a further object of my invention to provide for fastening a flat carbonaceous resistance element to a base member by means lying within the path of the contactor of a variable resistance device without affecting the predetermined resistance gradient of the element.

It is still a further object of my invention to provide a combined variable resistance and power switch unit wherein the switch is actuated when the contactor arm is not in contact with any portion of the effective resistance.

With the above and related objects in view, my invention consists in the following details of construction and combination of parts, as will be more fully understood from the following specification, when read in conjunction with the accompanying drawings, in which:

Figure 1 is a perspective view of a variable resistance device constructed in accordance with my invention, illustrated with the cover removed;

Figure 2 is a top plan view of Figure 1;

Figure 3 is a mid-sectional view of the variable resistance device and cover having a switch mounted thereon, the switch not being shown in section;

Figure 4 is an exploded perspective view of the variable resistance device and cover illustrating the relation of parts and order of assembly;

Figure 5 is a top plan view of a modified form of a pressure arm;

Figure 6 is a sectional view taken on line 66 of Figure 5;

Figure 7 is a plan view of the pad holding blank;

Figure 8 is a side view of the modified pad holder;

Figure 9 is a fragmentary exploded sectional view of a holding structure at each end of the resistance element;

Figure 10 is a fragmentary assembled view of the elements shown in Figure 11;

Figure 11 is a bottom plan view of the assembly shown in Figure 10, more clearly showing the peened over holding bolt;

Figure 12 is a modified form of pad holding blank;

Figure 13 is a side elevational view of the modified pad holder made from the blank shown in Figure 12; and

Figure 14 is a bottom plan view of the modified pad holder shown in Figure 13.

Referring in detail to the drawings: An insulating base A, generally circular in formation, has mounted upon one face it), near its periphery,

a circularly disposed resistance element 13 of the carbonaceous type, although a wire wound resistance element arcuately disposed may readily 5 be employed.

A sleeve or journal bushing C extends through an opening il in the base. The bushing C may serve as a mounting device for the unit, by being threaded at one end H for the reception of 10 a nut by which the assembly is clamped upon a suitable bracket.

The bushing G contains an enlarged head I 6 disposed against the surface of the baseupon which the resistance element is located, and if 15 desired this head l6 may be serrated or knurled as shown at 18, see Fig. 3, so that it will bite into the base to prevent any relative rotary movement between the base and bushing.

A shoulder of the bushing protrudes through 20 the base opening and also through a holding clamp H and the free end of the shoulder is exd panded to grip one face of the clamp for the prevention of longitudinal motion and to grip a plurality of spaced niches 22 cf the clamp for the 25 prevention of rotary motion. An annular shoulder 24 disposed interiorly from the enlarged head l6 constrains an insulating washer D upon which an interposed low resistance fiat contact disk E rests.

The fiat disk E is preferably comprised of a rim 26 and hub portion 28 which are connected by a plurality of flexible serpentine spokes 30. The spokes are substantially of uniform width from the center hub to the rim but take a circuitous path from the hub to the rim in substantially an S-shape- The spokes are positioned so that deflection of the disk under a given pressure will be substantially the same at any point along the circumference. An electrical conductor tab 49 32 is formed upon the hub by cutting away the surrounding area. A plurality of positioning cars 34 are also formed on the hub by a punch press operation, and the ears tightly grasp notches 35 in a positioning insulating washer F to prevent radial movement of the disk.

The spokes are highly flexible and yieldable, and due to their serpentine configuration, are almost twice as long as they would be were they disposed along radii of the disk throughout their r entire length. The increased length of serpen tine spokes over radial spokes increases the effective flexibility of the spokes.' The rim supported by them, being held by such highly flexible media, is permitted far greater freedom of movement than has heretofore ever been possible.

The advantages of this increased flexibility may better be seen by comparing these types of devices with those of the prior art. A rheostat of small diameter, having an interposed contactor disk of the radial spoke type, will upon actuation of the contactor arm, short circuit a considerable amount of the effective resistance. The short, stiif spokes tend to hold the rim rigidly between them, whereupon, when the rim is depressed in one portion, a substantial segment of the rim is caused to follow the depressed portion to engage the resistance element for a considerable distance adjacent the contactor arm. Thus, a sharp or delicate line of contact is made impossible, and a considerable amount of the efiective resistance is short-circuited.

The serpentine spokes, however, permit the rim to be rather abruptly distorted out of its normal plane at the point of contact without disturbing 75 to any material extent the planar disposition of its remaining portion. In this manner, a fairly sharp line of contact is obtained, and the shortcircuiting of effective resistance is minimized.

The disk E'and the washer F are secured in place by turning over or peening the end 35 of the bushing against the washer F. If desired, a metal washer may be placed over the washer F to prevent breakage of the washer F provided it ismade of fragile material.

A pressure or wiper arm 6, of the general type shown in my application filed January 31, 1930, Serial No. 424,775, which is now Patent No. 1,913,- 686, dated June 13, 1933, may conveniently consist of a central portion 38 secured to the end of a shaft 38 as by heading over the splined endiof the shaft. A crescent-shaped arm 40 has its ends connected to the central portion by the bight portion 42. A tongue ll, carrying a pressure pad 48 and projecting from the crescent arm 40, is adapted to strike radially projecting ears 46 of the cupshaped housing or covering J, in order to limit the rotation of the arm.

The pressure pad may be secured to the under side of the arm and may, however, takea variety of forms. In the form shown in Fig. 4, the pad is formed of a cylindrical block of material, such as oil impregnated leather, and is held in an inverted cup in any desired manner.

In Figure 5, another modification of the pressure arm and the pad holder is shown. An aligned opening 50 and a notch 52 are cut into the crescent-shaped arm 40, and a metal strip 56 is formed to have one end 58 of Ushaped formation, in order to grasp a suitably shaped pressure pad ill and to fit into the notch 52. The other end is offset at GI and suitably passes through the opening 50. The ton ues 62 and 64, protruding radially from the periphery of the crescentshaped arm 5|, push the pad around the rim 26.

Wings 86 and 68, see Figs. 7 and 8, are formed transversely of one end of the strip 56 to firmly grasp the pressure pad 60.

The housing J has an insulated strip line K disposed upon the inner peripheral surface to provide a substantially dust-proof housing, to

guard any live parts from coming into contact with the housing or shell, and to cover the gap or space between the housing and the terminals. A plurality of slots 10' in the liner K have the stop members 46 of the housing completely pass therethrough and occupy the space defined therein.

The housing J, within which the rheostat is housed, is provided with a plurality of projecting tongues 12 of sufficient length to be bent over to attach the housing to the plate A. An elongated notch I4 is cut in the free end of the cylindrical wall of the housing. Thebase A has an arcuate peripheral extension I6 through which suitable terminals pass and the peripheral extension is constructed to interilt with the notch H of the housing. The registration of the extension of the base and the notch 14 in the housing with the plate A accurately aligns the cover with respect to, the plate both in a rotary direction about the axis of the shaft and in a direction along the shaft.

The elongated notch ll of the housing J provides some clearance over the terminals to prevent any short circuit and the clearance is filled by the insulated strip liner K.

The liner K, is of such breadth that it will extend from the end wall portion of the housing J down the inner face of the side walls thereof to a peripheral line near their open' end. This peripheral line is spaced from the free edge of the cylindrical side walls a distance substantially equivalent to the thickness of the base member A. Since the housing is of such size and configuration 5 as to snugly telescope upon the base member A, the liner K, being disposed around the inner side walls of the housing, diminishes the inside diameter thereof to such a degree that it is less than the mean diameter of the base A; hence the hous- 10 ing is unable to telescope over the base beyond the strip's edge.

Thus, it will be seen that the lower edge of the liner forms a bearing shoulder which abuts the base member adjacent the edge of its inner face, 15 and since its upper edge abuts the inner face of the end wall of the housing, it serves as a spacer to maintain the housing, base and associated parts in predetermined spaced relation.

When the cover is placed on the base so that 20 notch I4 registers with the terminal mounting extension of the base, the insulating liner strip K, being of the same breadth throughout, closely en-v gages the base member around its periphery, and closes the notch 14 which overlies the terminals. 25

The liner, being of flexible material, closely adheres to all portions of the base, and adjusts itself to all irregularities thereof to render the casing dust-proof.

The ears I! are then crimped over to engage the 30 base whereby a compact, rigid and dust-proof unit is provided.

The advantage of the ears I is manifest in assembling the unit when a liner strip is emplayed. The press that crimps the ears into en- 35 gagement with the base first forces the base into firm engagement with the edge of liner K, and then crimps the ears over to maintain the parts in this firm engagement. Since this is all done by one operation, a material saving of time and 40 material is eifected over the old types of. fastening means, and a far superior product results therefrom.

Although the resistance element base is annular in formation, the effective conducting sur- 45 face of the resistance element is arcuate in formation, leaving but a small are ineffective. This small ineffective arcuate distance is utilized for the transient movement of the pressure arm during the closing of the switch. 50

Heretofore, combined switches and variable resistance devices have been so constructed that the switch was actuated over an effective portion of the resistance. Thus when the contactor arm was moved from its point of lowest resistance, 55 the switch moved to closed position, but not before the contactor arm had traversed a substantial amount of the effective resistance. Likewise, when it was desired to move the contactor arm to its extreme low resistance position, the switch 60 would be'actuated into open position to break the circuit before this could be effected. Consequently, a substantial amount of the effective resistance was rendered useless. In my present structure, this fault is entirely overcome. 65 It is essential that the entire upper surface of the resistance element base lie substantially in the same plane, otherwise the rim of the low resistance interposed disk will be bent and a kink permanently established therein. 70 The base portion is provided with apertures 18 and which are of such size as to receive rivets 82 and 84. The edges of the apertures adjacent the inner face of the base are beveled to form tapering countersunk portions. The re- 78 sistanceelement having rivet apertures of the same size overlying the base apertures 18 and 80, is drawn down into the tapered countersink by the tapered portion of the rivet head. The resistance element in this position forms a lining for the countersink and coacts with the rivet head to effect a perfectly tight, smooth fit. The rivet head being fiush with the resistance elements contact surface permits the contactor member to pass beyond the eflective resistance area during the actuation of the switch mechanism.

The openings 86 and 88 through the conducting ends of the resistance element, seeFigs. 4, 9, and 10, are of the same diameter as the openings. I8 and 80 through the base, and as the rivets are of electrical conducting materials, the electrical circuit from the ends of the resistance element to the outside terminals 90 and 92 will be completed.

In order to prevent any damage to the resistance element great care must be exercised in fastening the rivets 82 and 84 to the ends of the resistance element. The most suitable manner is to expand the tip 94 of the bolt at a plurality of points 96, 98, I00, and I02 as shown in Figs. 9, 10, and. 11.

A rivet I04 of conducting material, see Fig. 3, attached to the tab 32 of the flexible disk-E and an intermediate electrical/terminal I 06 provides the electrical take-off for the variable contact on the resistance element.

Switch Operation My rheostat may, also, be used in conjunction with the operation of a snap switch S,- whereby a rotary or oscillatory movement of the-pressure arm over a short peripheral length of the circumference actuates operably connected mechanism to open or close the snap switch. However, the relationship of the switch to the rheostat is such that none of the effective conducting surface of the resistance element between the zero resistance terminal and the maximum resistance terminal is contacted by the interposed member upon movementof the pressure arm, during the operation of the switch.

In order to provide for the operation of the switch or circuit controller, the pressure or wiper armG may be provided with a normally projecting, insulated, eccentrically mounted pin I08, see Figs. 1 and 3. This pin I08 projects normal to the plane of the pressure arm G and into such position that it may transiently engage an operating ear IIII of the switch mechanism S. A transient movement of the pressure arm G will therefore operate the switch mechanism. The switch S, shown by way of example, may

be any preferred type of switch suitable for this purpose, such as for example the switch shown in my copending application Serial No. 602,006, filed March 30, 1932, to which application reference is here made for the details of construction of the switch and the manner of mechanical arrangement.

Terminals As will be best seen in Figures 1, 2, 3, and 4, the temiinal member I06, and the same details of construction apply to the terminals 90 and 92, of a single strip of conducting material of uniform thickness, has a foot I I2 connected, by means of the bolt, rivet or eyelet I04 which pierces the base, to the tab of the interposed disk which forms the intermediate variable contacting conductor. The foot 2 of the terminal is disposed aoaasaa upon the outer face of the baseA and has a neck 4 therefrom bent normal to the plane of the base. The neck fits within a suitable slot 6 in the mounting plate to prevent the terminal member from being turned with respect to this plate. Shoulders H8 and I20 extend from the neck 4 of sufilcient width to rest and engage the opposite face of the mounting base A so. that movement of the terminal in any direction is prevented. The shoulders then taper or 10 merge into a lug portion until the notch or eye I22 is reached,- thus when the various lead wires are being attached to the terminals there can be no inadvertent bending of any of the terminals so that the terminal rivets may be disturbed which might result in an increased minimum resistance, particularly at the low resistance end of the resistance film.

Furthermore, the terminal arrangement hereinbefore described prevents the inadvertent pressing of the terminal against the metal panel for the radio set to complete the short-circuit which short-circuit may do considerable damage during the testing or inspection of the radio set.

My preferred form of rheostat construction lends itself quite readily to the tandem or double type of rheostat in which-a second or duplicate rheostat structure is placed over the first rheostat in place of the cover J.

In Figure 12 is shown another modification of the pad-holder blank. A tall 200 merging into a body portion 202 has material for wings 204 and 206 at each end adjacent a head portion 208. Upon forming the blank, as shown in Figures 13 and 14, the tall 200 is offset from the body 202 and the head 208 is bent in a U-shaped formation which together with the wings 204 and 206 forms a basket or receptacle for the .pad, which pad preferably may have irregular sides.

Although this invention has been described in 0 considerable detail, such description is intended as illustrative rather than limiting, as the invention may be variously embodied, and the scope of the invention is to be determined as claimed.

I claim:

1. A planar disk for a rheostat comprising a flexible rim, a hub, and a plurality of flexible serpentine connecting spokes between the rim and hub.

2. In a rheostat, a fiat supporting base, a resistance element mounted upon said fiat base,'a planar contacting member adapted to be flexed into contact with the resistance element, said contacting member comprising a rim portion and a hub portion, and a plurality of flexible s-shaped spoke members extending between said rim portion and said hub portion.

3. In a rheostat, a resistance element lying in a plane, a flat circular low resistance member comprising a hub portion and a circular peripheral portion connected to said hub portion by flexible S shaped connections, all portions of said low resistance member normally lying in a plane parallel to the resistance element, said conducting member being adapted to be flexed along its peripheral portion into contacting engagement with the resistance element, means for progressively pressing successive portions of the low resistance member against the resistance element, and means for holding the hub portion of the con tacting member rigidly against circular movement.

4. A variable resistance device comprising a flat substantially annular resistance element, a

normally planar contactor having an annular aosassa rim portion, a hub portion and a plurality of flexible serpentine spokes connecting said hub portion to said rim portion, means mounting said contactor in alignment with said resistance element and spaced therefrom, and means including a member movable over the surface of said contactor for successively flexing adjoining portions of the rim portion into contact with the surface of said resistance element.

5. A variable resistance device comprising a flat substantially annular resistance element, a contactor having a closed rim, a hub and integral flexible serpentine spokes lying in the plane of said rim and connecting said rim to said hub, means mounting said contactor overlying said resistances and in spaced parallel relation thereto, and means including a presser element for successively flexing portions of said contactor into engagement with successive portions of said resistance element.

6. A variable resistance device comprising a base, a flat resistance element disposed on said base, a normally planar contactor having a rim portion, a hub portion, and a plurality of flexible serpentine spokes extending between said hub portion and said rim portion, means mounting said contactor in spaced alignment with said resistance element, means for successively flexing said contactor into contact with successive portions of said resistance element, said means including a shaft journaled in said base, an insulating presser element contacting the rim of said contactor and a spring arm on said shaft and carrying said presser element for movement along the rim of said contactor.

7. A combined variable resistance device and switch comprislng'a housing, a resistance element in said housing, end terminals for said resistance element, a contactor, means including a movable element for bringing said contactor into contact with successive portions of said resistance element, a switch mounted on said housing and means carried by said movable element for operating said switch during a portion of the travel of said movable element wherein it is ineffective to produce contact between said contactor and the portion of said resistance element connected between said end terminals.

8. A variable resistance device comprising a base, a contactor having arr annular portion spaced from said base, means for flexing successive portions of said contactor into contact with successive portions of said base, a resistance path on a portion only of the area of said base contactable by said contactor, end terminals connected to spaced points on said resistance portion of said base, a switch and means actuated by the movement of said flexing means for operating said switch during the flexing of said contactor into engagement with a portion of said base other than the resistance included in circuit with said end terminals.

9. A variable resistance device and switch unit comprising a base, a conducting path disposed thereon, end terminals connected to spaced points on said path, a contactor spaced from and overlying said base, means including a movable pressure arm for flexing adjoining portions of said contactor into contact with said base to make electrical contact successively with adjoining portions of said conducting path, a switch and means including said pressure arm for operating said switch when said contactor engages a portion of said base other than the portion of the conducting path connected between said end ter minals.

10. m a combined variable resistance and switch surface thereof, a base member mounting said resistance element having a perforation underlying said aperture, atapering countersink adjacent one end of said perforation, a rivet lying in said aperture and perforation having a head 10 portion substantially coniplemental to said countersink, said rivet head drawing a portion of said resistance around said aperture into said countersink to form a lining therefor, said portions of the resistance forming a countersunk seat for 15 the rivet head to cause a tight cooperation of surfaces therebetween, whereby a flat, smooth contact surface is secured.

11. A combined variable resistance device and switch comprising a housing, an arcuate resistance element in the housing, end terminals connected to said resistance element at spaced points.

a contactor, means including a movable element for bringing said contactor into contact with successive portions of said resistance element, a switch mounted on said housing, and means actuated by 'said movable element for operating said switch during a portion of the travel of said movable element wherein it is effective to produce contact between the contactor and said re- 80 sistance element beyond one of said end terminals.

12. A combined variable resistance device and switch comprising a housing, an arcuate resistance element in the housing, end terminals connected to said resistance element at spaced points, said terminals being formed flush with the surface of said resistance element, a contactor, means including a movable element for bringing said contactor into contact with successive portions 40 of said resistance element and with said terminals, a switch mounted on said housing, and means actuated by said movable element for operating said switch during a portion of the travel of said movable element wherein it is effective to produce contact between the contactor and said resistance element beyond one of said end terminals.

13. A combined variable resistance device and switch comprising a base, a flat arcuate resistance element disposed on said base, terminals for said resistance element adjacent the ends thereof, rotatable means for causing contact with the resistance element, a housing for the resist ance element and contact means having an opening therein, a switch housing closing said opening, a switch in said switch housing and having an operating portion extending into the resistance housing, and means carried by the rotatable means for transient engagement with the switch 60 operating portion to operate said switch during a portion of the travel of said rotatable means wherein it is ineffective to produce contact with the portion of the resistance element connected between the terminals.

14. A combined variable resistance device and switch comprising a base, a flat arcuate resistance element disposed on said base, terminals for said resistance element adjacent the ends thereof, rotatable means for causing contact with the resistance element, a housing for the resistance element and contact means having an eccentric opening therein, a switch housing closing said opening, a switch in said switch housing and having an operating portion extending into the re- 15 sistance housing, and insulating means carried by the rotatable means for transient engagement with the'switch operating portion to operate said switch during a portion 01 the travel of said totatable means wherein it is ineffective to produce contact with the portion of the resistance element connected between the terminals.

15. A combined variable resistance device and switch comprising a cup-shaped housing, a flat, arcuate carbonaceous resistance element in the housing, end terminals connected to said resistance element at spaced points, a contactor, rotatable means for causing the contactor to engage progressively the resistance element in an arcuate path, the path being unobstructed by said terminals, a switch mounted on the base of the housing and having an operating'portion projecting into the housing,'and means actuated by the rotatable means for engaging the switch operating portion for operating said switch during a portion of the rotation of the rotatable element wherein it is eifective to produce contact between contactor and the resistance element be- 10 yond one of said terminals.

NEWTON C. SCHELLENGER.

CERTIFICATE OF CORRECTION.

Patent No. 2,023,382.. December 3, 1935.

NEWTON c. scHELLENcER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line 5,, claim 10, for "constant" read contact; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of January, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.

CERTIFICATE or CORRECTION.

Patent No. 2,023,382. December :5, 19:55.

NEwToN C. SCHELLENCEE.

It is hereby certified that error appears in the printed specification of 1 above numbered patent requiring correction as follows: Page 5, second columr line 5,. claim 10, for "constant" read contact; and that the said Letters Pate should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of January, A. D. 1936.

Leslie Frazer (Seal) Acting Commissioner of Patents.

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