US2477711A - Rheostat - Google Patents

Description

Aug. 2, 1949. J. YouHoUsE RHEOSTAT Original Filed Jan. 28, 1942 INVENTOR dife/9k Voy ozzse ATTORNEYS Patented Aug. 2, 1949 RHEOSTAT."

Joseph Youhouse, Fairfield, Conn.,y assigjnon toV Casco: Products Corporation, Bridgeport, Conn.. acorporation of Connecticut Original application January 28, 1942, SerialA No. 428,454; Divided and this application January;

14, 1947, Serial No. 721,979

(Cl. B01-67) 1.1 Claims.

This: invemnon relates to electrical rheostats, especially rheostats for` controllingl heatingv pads and' the like' wherein: av plirazlity: of: heat adjustments desired. This application. a division of. my application, Serial No.. 428,454, filed Januar-y-` 28,. 1942;. now" Patent No. 2,415,858, entitled Switch device and issued. February 1'8, 1947.

Rheostat control devices havefbeen provided in the past. and are known for controlling or setting an electricy heating pad'. toy provide. for various degrees of heat.v Generallyy these rheostats or control devices.` have had included in theirst'ructmfca caslngand a manually operable mem-ber located exterlbrly of the casing for manipulation by a user' to the setting of the rhe'ostat. The arrangement. of the casing and manually' operable member was such that theV user had to employ two hands' in order to. adjust the rheostat toi-tssettlngwith any degree of convenience and certainty.

An object of' the presentv invention is to overcome this disadvantage in prior rheostat type controls by the provision of a structure including a casing' and manually operable member which are so shaped and arranged thatbuta single hand is required to conveniently adjust the rheostat.

In accomplishing this there is provided, in the specic embodiment of the invention illustrated herein as exemplary thereof, an elongate casing having a shape which may be comfortably received and heldin the palm of the hand, the said casing' carrying an adjustment wheel which with its periphery is so arranged that it may be quickly and conveniently manipulated by the thumb of the hand which holds the casing or by one of the other lingers of said hand. The remainder of the periphery of the wheel .is enclosed and therefore shielded sothat it cannot be opposed in its movements by contact with other fingers or another portion of the hand, or with adjacent articles. Also, the periphery of the adjustment wheel is provided with an anti-slip configuration which further facilitates its being turned by a nger of the hand which holds the casing. By this organization the adjustment of the heating pad for example is considerably simplified and made more convenient, and this is an important consideration since very often a person who is using the pad finds it dimcult to grasp the control rheostat with both hands.

Another object of the invention is to provide a compact .control rheostat as above which is of simple construction, requiring a minimum number of parts for performing several circuit control operations in a simple and effective manner, and

2 which has parts readily produced. for instance by stamping or molding operations andV capable of assembly with maximum. economy.`

Still another .object of the invention is, to provide a control rheostat of the above type which is positive and reliable inits operation at all times.

A feature of the invention is the provision. in a control rheostat, of areslstanceooil of especially simple and efficient construction. capable ofV economical manufacture in masse production.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Fig. 1 is a plan view of a rheostat control made in accordance with the invention..

Fig. 2 is a view of the control but with the cover removed.

Fig. 3 is an axial section of the. control taken .on the line 3 3 of Fig. 1.

Fig. 4 is a detail of the manually operable Wheel of the control..

Fig. 5 is a side view of the resistance element of the control. Y

Fig. 6 is an end view of the resistance element.

Fig. '7 is a heating pad wiring diagram including the rheostat control.

Fig. 8 is a perspective view of the contactor of the control device, and

Fig. 9 is a fragmentary view of the control showing a modified arrangement of the. resistance element.

The rheostat control device of the present invention as shown includes a. casing 2l) which may be conveniently manufactured of molded plastic. The casing 20 when assembled is of elongate shape having tapered ends and a. substantially oblong central transverse cross-section. It is separable into two parts 20a and 20h along a substantially axial plane parallel to its broader lateral surface. The two parts are held together by means of screws 2l adjacent opposite ends of the casing, and at each end the edges of the casing parts are recessed tov provide apertures 22 and 23 (when the two halves are assembled) to receive conductors extending into the interior of the control device.

Approximately at the center of the two casing halves 26a and 2Gb, their opposite lateral edges are recessed to form a pair of longitudinal slots 24 when the casing is assembled, through which an adjustment disk 25 carried within the casing may extend. The casing portion 20h is also providedwith a sight opening or aperture 2S for observing a visual indicator or dial 21a. The sight opening 26 preferablyhas a central arrow tip y26a at one side thereof for cooperation with the dial 2id to provide a reference point therefor.

A pair of conductors 28 entering the casing 25 Y through the aperture 22 thereof is adapted to cona pair of terminal screws 30 and 3l carried by a web 32 formed in the casing half 20a. A web 35 is also formed in the central wall of the casing half 25a and comprises a semi-circular portion 33a adjacent the web 32 and oblong portion 33h extending toward the opposite end of the casing. The breadth of the oblong portionsof the web 33 is such as to allow for a pair of clearance grooves 35 and 35 which extend between the said portions and the lateral casing walls to receive connectors ley-passing the said web.

A central recess 35 substantially at thecenter of the casing half 29a is formed in the web 33 with an annular bearing surface 3'! surrounding a .central spindle-receiving cavity or bearing 33 at its base. The opposite half 2Gb of the casing is provided with' a similar bearing cavity 35 disposed directly oppositepavity 38, said cavities receivingthe ends of a spindle (il)v serving as the shaft for the indicator dial 21a` and'the adjustment disk 25. The translucent dial 21a is attached toa collar 4| on the upper end of the spindle 4 adjacent the bearing 35,l and a portion of itssurface extends under the' sight opening 25 whichjisoifset from the axis of the spindle. f e

The adjustment dislr'25 may be formed for instance of molded plastic'material and isof generally l circular shape. It comprises ahub 42 molded on spindle on the opposite side of the disk collar di, its lower surface forming an abutment to engage the bearing surface 3l. The peripheral edges of the disk 25 extend through the lateral slots "24, so that the protruding arcuate portions of the said disk are available for its manipulation. By virtue of this arrangement, the casing 2 may be lield conveniently in one hand, and the disk 25 rotatedat will by a thumb or finger or" the -sar'ne' hand.V The peripheral edge of the disk 25 is knurled as indicated at 43 and is pr-ovirded'at intervals with buttons 44 arranged in predetermined relationship so as to provide means for adjusting the position of the disk by tactual sensation alone.

The portion 33D of web-33 has a' transverse slot therein, adjacent-the circular recess 36, for receiving connector or'resistor means, and bey-ond theslot twoscrews 46 and 48 are threaded into the web. IAnY elevated portion of the web 53 beyond slot i5 forms an additional web dgp'which carries a pair o f terminal screws 55 and 5l adjacent end aperture 23. As indicated in Fig. 2, the three conductors 52a, V5212 and 52o are connected vto terminal'screws 5U, 5i and 48 respectively. Theseconductors are adapted to connect the control device to a devicesuch as a heating pad to be controlled.

Terminal 3 is connected directly to terminal 5iv by means of an insulated conductor 53 which hes inlateral groove 35 of the casing part 20a. Terminal 3i kcarries a resilient conductor strip or Aspring Contacty 54;which extends through lateral groove 34 of casing'part 23a to a point op- Aiosite the spindle 40 o r its bearing 38. An angular tip 55 on the spring contact 5 4 extends inwardinto the 'circular recess 36 through a radial groove or slot 55 in the side of the web 33, termi- 4 nating just short of the hub 42. The spring contact 54 is mounted so that its resilience normally urges its tip 55 toward the top of the slot 55 in. web 33.

A metal contactor 5l, Fig. 8, comprises a circular cup-shaped portion 57a having a central aperm ture in its'base adapted to -re-ceive the hub t@ of spindle 4Q, and comprises a pair of diametricallyA opposite radial wings 57h, each having a pair.I The ex-A posed surface of each of the wings 5% is cylin The arms 51C are adapted toy engage the edges of a pair of correspondingly dis-` posed apertures 5S in the adjusting disk 25 so that the disk 25 and contacter 5i, when assembled asillustrated in Figs. 3 and li, are coupled for mutual of folded lateral anges or arms 5in.

drically convex.

rotation.

A coiled compression spring 55 surrounds hub d?. and is supported at one end against the face of the disk 25. The opposite end of the spring 5S bears upon the base of the cupushaped portion 57a, of contacter 5l; Thus when. the Vcontrol device is assembled, spring 59 urges the contactor 5l toward the wall of the casing half 25a, and presses wings 51h toward the upper surface of web 33, Fig. 3, while therarms 57o thereof engage the apertures 58 in the disk 25 so that the contactor is rotatable thereby.;

The tip 55 of resilients'pring contact 5d is positioned beneath the lower surface of the cupshaped portion 57a of the contacter and by virtue of its resilience, yieldably engages said contactor forming a continuous electric contact therewith in angular positions ofthe contactor.

The upper surface of web 33 is provided with a pair of integral raised portions 55 on opposite sides of the recess 35, having concave upper surfaces forming projections adapted to serve as insulating detents for yieldably holding the wings 57h of contaotor 57 positioned transversely of the casing 23. One of these raised detents is split, as shown by the slot 55 through which the tip 55 of spring Contact 54 extends.V

The resistor element of the control device is in the form of a resistance coil which comprises resistance wire wound around an insulating core 8B, the element being press-tted in the slot 55 of the casing half 20a.

The terminals 55 and 48 carry a pair of metal conductive clips or retainers 8l and 38 which extend toward the recess 35 and have narrowed contact surfaces as shown in Fig. 2 for engagement with the wings 51h of the contacter 57. The clips 81 and 83 overlie and' are clamped against the opposite ends of the resistance coil 55 and form electric contact therewith. The narrowed contact surfaces of the clips 5l and sa are preferably flat so that they do not act as detents when engaging the wings 51h of the contacter 5l.

A flat metal segment or sector contact 8a is providedto extend arcuately around the side of the recess 36 opposite the slot 55, the said contactor being anchored by a terminal screw 5i and overlying the arcuate portion of the web 35 and terminating adjacent the raised insulating detents 65 of said web.

The dial Zla has the words Ofi Low, Medium, and Highj each repeated once, as shown in Fig. 4 and also has a pair of graduated scales extending over arcs which correspond with the energizing adjustment ranges, said scales having numerical indicia which increase' from low to high. All of the indicia on the dial 27a are consecutively visible in the sight opening 25u/hen the wheel 25 is turned.

Terminal screw 61 is connected by a conductor or bus bar to terminal screw 5D, and hence to conductor 52a.

A U-shaped bracket 1l secured to the web 33 by a screw 12 carries between its arms a miniature luminous gaseous discharge tube 13, illled with some suitable gas, `such as neon, at reduced pressure. The arms of bracket 1l extend .between disk 25 and the translucent dial 21a so that the lamp is below said dial and aligned with the sight opening 26. Accordingly, when the. lamp is illuminated, the indicia of the dial 21a are clearly visible in the sight opening. By using a gaseous discharge tube which generates substantially no heat, the control device may be safely operated for a relatively long period of time without danger of fire or damage by overheating. Since such lamps are not subject, as are incandescent lamps, to burning out they will in general remain operative indefinitely.

One terminal of the lamp 13 is connected by a wire 99 to a clip 9i carried by the terminal screw 51 threaded into the web 33. The opposite lamp terminal is connected by a wire 15 to one end of a resistor 16 which adapts the lamp for use at the line voltage. The resistor 16 is carried in pocket 11 in the wall of the casing half 20a. The opposite end of the resistor 16 is connected by a wire 18 to the input terminal 30.

As a result of this construction, contactor 51, when rotated by disk out of its transverse, insulated detent-engaging position in the casing is. forms a bridge between sector contact 89 and various points on the resistance coil 85, or its terminal clips 81 and 8B, and is accordingly adapted to connect these elements with terminal 3l through the spring contact '5A-55.

The wiring diagram of the control device of Figs. 1 through 6 and a heating pad to be controlled thereby is shown in Fig. 7. The heating pad here comprises a main heating coil 92 with a pair of safety devices 93, such as fuses or thermostats (preferably the latter) included in its circuit. One end of the main heating coil 92 is connected to terminal 5l by conductor 52h, and thence through conductor 53 to input terminal 3l! and conductor 2s. The opposite end of the coil S2 is connected in series with a normally closed bimetal switch 94. The latter is connected through a pair of parallel circuits to the other input terminal 3l and its associated conductor 28.

One of these circuits traverses conductor 52o to terminal 58 and its associated clip 88 at one end of the resistance coil 85, then through the turns of the latter coil included between clip 88 and contactor 51, and finally through the latter and spring contact 54-55 to input terminal 3|.

The other parallel circuit from the bimetal switch 94 to terminal 3| includes an auxiliary heating coil 95 in the heating pad, which is connected by conductor '52a to terminal 50. From the latter, it traverses bus bar 10, sector contact 89 and contactor 51, rejoining the rst-described circuit at spring contact v54m-55, carried by input terminal 3l.

The auxiliary heating coil 95 is adapted, either alone, or in conjunction with the main heating coil 32 to control the temperature, and hence the operation, of the bimetallic switch 94. When the temperature of the bimetallic switch 94 is sufciently raised by the heat generated in coil 95, possibly supplemented by that generated in coil 52, switch 94 opens, interrupting the circuit through coil 92 as well as the aforesaid parallel circuits.

On cooling suillciently, the bimetallic switch automatically recloses and reestablishes the circuits.

It will be observed that contacter 51 upon clockwise rotation from the position in which it engages insulated detent 60 initially engages clip 81 at one end of the resistor coil 85, and simultaneously, sector contact 89. Referring to the wiring diagram of Fig. '7, it will be seen that the maximum number of turns of resistance coil 85 is thereby included in parallel with auxiliary coil 55. Upon continued clockwise movement, contactor 51, while remaining in engagement with sector contact 99, moves across the coil 85 including progressively fewer and fewer turns of the resistance in parallel with the auxiliary heating coil 95. Finally, it reaches clip 88 at the opposite end of said resistance coil. At this point, the resistance 85 no longer remains in the circuit, while auxiliary coil 95 is shunted. and the full line voltageis impressed across the terminals of the heating coil 92.

Since the auxiliary heating coil 95 is connected in parallel with that portion of the resistance 85 which is included between contactor 51 and clip 88, the current flowing through the main heating coil 92 is equal to the sum of the currents in auxiliary heating coil 95 and resistance 85.

In order to avoid undue generation of heat in the control device, the resistance of auxiliary coil 95 is made very much smaller than that of the main heating coil 92, so that the maximum power converted into heat in resistance 85 is never more than a very small proportion of the total power supplied to the heating pad.

When the entire resistance coil 85 is included in the circuit, that is, when contactor 51 engages clip 81, auxiliary heating coil 95 carries the maximum proportion of the current flowing through the main heating coil 92, and accordingly, heats the bimetallic switch 94 with maximum rapidity causing it to open in the shortest possible time interval after closure of the circuit. As the resistance of that portion of resistor 85 included in the circuit is decreased by clockwise rotation of contacter 51, coil 85 carries more and more of the current, and auxiliary heater 95 less and less, so that the interval between each closure of the circuit and the succeeding interruption thereof by the bimetal switch 94 becomes correspondingly longer. Finally, when coil 85 is cut out of the circuit entirely by movement of contactor 51 into engagement with clip 88 at its opposite end, coil 55 carries substantially no current, and the closed-circuit interval of switch 94 becomes maximum. In fact, with this adjustment, the switch 94 is responsive only to the heat generated by coil 92, or if the latter is not arranged to operate the bimetal switch, it remains closed, leaving the control of the circuit to the auxiliary devices 93 which in this case are thermostats.

Since the rate of cooling of the switch 94, which determines the time interval required for its reclosing the circuits is substantially the same under any given condition of use, being a function of radiation and conduction of heat by the surrounding media, the longer the circuit-closing period of switch 94 becomes as a result of the aforesaid adjustment of contact 51, the greater is the cumulative or average electrical energy converted by heater coil 92 in a unit period of time, and the greater becomes the amount of heat generated in the pad.

Thus, upon moving the contact 51 clockwise by corresponding rotation of disk 25, through the arc denned by its engagement with coil 85, the

average-power supplied to the pad may-be progressively increased from a predetermined'minimum to a maximum value-"Clockwise vrotation of the disk 25 beyond the point Where contactor l' engages clip 88, -returns the Vcontacter to its traverse position in which it engages insulated detents EB, and interrupts the circuit, not only to the resistance coil 85 and its associated circuits, but also to the sector contact 89.r

Asindicated in Fig. '7, lamp i3 is connected in series with its resistor l5, between terminal te and sector contact 89. Accordingly, in this case, the lamp is energized to illuminate dial 21a in sight opening 26 only while switch contactor 5l is turned to an energizing or circuit-closing position. However, energization of the lamp remains independent ofthe thermostatic switches B4 or 93 controlling the heating pad circuit. Lamp 'F3 could be connected to the terminals Sii and 3i if it is desired to illuminate the dial 21a while Ythe control device is turned offf As shown in Fig. 4, the indicia on the dial 27o,

and the buttons 44 on disk 25 are so arranged with'referen'ce to disk aperture 5S, that when contactor 51- is positioned transversely7 of the casing 2B so that the heating coils in the pad are deenergized, the word Off on dial 27a appears below the sightiopening 26, and only the knurled periphery 43 of disk 25 without any of the buttons 44, extends through the slots 2li in the side walls of the casing 2li. Whenfthedisk 25 is rotated clockwise so as to energize the resistor 8'5 the word Low on dial 21a appears in the sight opening 25, While arcuate portions of disk 25, each bearing a single button 134 at their approximate midpoint protrude through slots 24.

Further clockwise rotation of disk 25 to cut out one-half ofthe resistor 35 brings a pair of buttons e4 to the center of each of the protruding arcuate portions ofthe disk 25, and the letters Med (standing for"medlum) on dial Zio appear below the sight opening 26.

Further clockwise rotation ofthe disk 25 aligns the word High with the sight opening 26, While each protruding portion of the disk 25 now carries three buttons 44. Meanwhile, contactor 5l engages clipBfi and cuts out the resistor S5 entirely.

`The next clockwise manipulation of the disk 25 again positions contactor 51 transversely of the casing corresponding to the circuit-interrupting, starting position and the word Off again appears in the sight opening 26, the indicia on the dial' Zlabeing repeated on each half thereof. 1-Thus, as a result of provision of the illuminated dial, and of the buttons t4 on the periphery of the disk 25, the control device can be adjusted to any desired'setting in' the dark by tactual sensation alone,or by visual observation of the dial in the sight opening.

The portion of the numerical scale on the dial Zio which is visible at the center of sight opening 25 gives an empirical indication of the power setting, while-*the accompanying words Low, Med and-High which are similarly Visible, characterise the general state of adjustment. When the lamp is extinguished the control device is oi The 'buttons 44 provide a tactual means for determining the setting of the control device.

in a modification of the control device of Figs. 1 to 6, shown in Fig. 9, clips 8l and 88 may be replaced by clips Bla and 62o, which are similar in shape to clips 6I and 62 and a clip 63a carried byfa terminal screw 41a, may be employed in conjunction with the resistance coil 5 of Figs. 1 to 6. Clips @la and 62a, like clips 8l and 83 engage opposite ends of the resistance coil E5, while clip 63a engages the approximate midpoint of the said coil. rlhe contact surfaces of the three clips-are concave, so as to form detents cooperating with the movable contactor 5?.

Operation of this modication is similar to that of the device of Figs. 1 to 6 except that the portion of the resistance coil included in the circuit' is not universally variable. Only three closed-circuit adjustments are possible, namely, low, medium or high, corresponding to inclusion of all, haii or none of the turns of coil i in the circuit by engagement of contacter 5l with clip Gla, @3a or 62o respectively.

The construction of the resistance coil $5 as shown in Figs. 5 and 6 lends itself to convenient and economical manufacture by mass production methods. Instead of employing a unitary core, the core 86 consists of two separate rectangular halves. Resistance wire 95, having'an insulating coating, is Wound around the juxtaposed halves of the core 86, inserting the opposite ends Si of the said ends of the coil. By this means, unwinding of the wire is eiectively prevented and no 'special fastening means is required therefor.

To complete the coil, the insulation is removed from the outer surface of the wire S5 on that face of the coil l5 which is to be exposed at the top of the slot l5 so that the turns of the coil are adapted to form electrical contact with contactor 51, and with clips 8'! and 38, or Bia, 52d and 53a.

Variations and modications may be made within the scope of this invention and portions .or the improvements may be used without others.

I claim:

l. In a rheostat, a resistance coil comprising a core of insulating material, said core having two separable portions; and a coil of resistance wire wound about said core, an end 'portion of said wire being held between the two portions of the core.

.2. In a rheostat, a resistance coil comprising an elongate core having a substantially rectangular cross-section, said core being formed of insulating material and consisting of two elongate, laterally separable portions of rectangular crosssection; and a coil of resistance wire Wound about said core, the ends of said wire being held be" tween the two portions of the core adjacent the ends thereof.

3. A rheostat comprising a body of insulating material; a manually operable member rotatable on the body and having a pair of Contact arms extending from it in opposite directions and yieldable thereon, said body having pairs of integral, spaced projections on opposite sides of the rotatable member, said projections being traversable by the Contact arms and providing detents for said arms; a metal contact segment extending along,r one side of the rotatablel member and between the pairs of projections of the body, said segment being engageable by one or the other of the contact arms; an elongateV generally straight resistance element extending along the other side of the rotatable member between the pairs of projections ofthe body, said element be ing engageable by one or the other of the ccntact arms; and a pair of metal retainer fingers for the resistance element, located respectively adjacent corresponding projections of Vthe said pairsysaid retainer fingers overlying and contact- ..9 ing the ends of the resistor elementand being engageable by said Contact arms.

4. A'rheostat comprising a body of insulating material;V a manually operable member rotatable on the body and having a pairof contact arms extendingirom it in oppositeV directions and yieldable thereon, said body having pairs of integral, spaced projections on opposite sides of the rotatable member, said Vprojections being traversable by the yContact arms vand providing detents for said arms; -a metal contact segment extending along one side ofthe rotatable membfrand between the pairs of projections of the body, said segment `being engageable by one or the other of the Contact arms; an elongate generally straight resistance element extending along the other side of the rotatable member between the pairs of projections of the body, said element being engageable by one or the other of the contact arms; and a pair of metal retainer iingers for the resistance element, one end of each finger being located respectively adjacent corresponding projections lof the said pairs, the other ends of the iingers being remote from the said projections and being anchored to the casing, and the lingers being engageable by the said contact arms and intermediate their ends overlying the ends of the resistor element.

5. A rheostat comprising a body of insulating material; a manually operable member rotatable in the body and having a pair of contact arms extending from it in opposite directions and yieldable thereon, said body having a portion adjacent said arms and completely surrounding said member, and having on said portion pairs of integral oppositely-disposed spaced projections traversable by the contact arms, said projection-s providing detents for said arms; a metal contact strip extending along said portion of the body at one side of the rotatable member and between the pairs oi projections of the body, said strip being engageable by one or the other of the contact arms; a resistance element extending along said portion of the .body at the other side of the rotatable member and between the pairs oi projections of the body, said element being engageable by one or the other of the contact arms; and a pair of metal retainer fingers for the resistance element, located respectively adjacent corresponding projections of the said pairs, said iingers overlying the ends of the resistor element and being engageable by the said contact arms and at least one of said ngers contacting said element.

6. A rheostat comprising a body of insulating material, a manually operable member rotatable in the body and having a pair of rigidly joined contact arms extending from it in opposite directions and yieldable thereon, said body having a circular portion adjacent said arms and completely surrounding said member, and having on said portion pairs of integral oppositely disposed spaced projections traversable by the contact arms, said projections providing detents for said arms; a metal contact strip extending along said portion of the body at one side of the rotatable member and between the pairs of projections of the body, said strip being engageable by one or the other of the contact arms; an elongate generally straight resistance element extending along a tangent to said portion of the body at the other side of the rotatable member and between the pairs of projections of the body, said element being engageable by one or the other of the contact arms; and a pair of metal retainer nn'gers for the resistance element, located respectively adjacent corresponding projections of the said pairs, said fingers overlying and contacting the ends of the resistor element and extending laterally therefrom in a direction toward the rotatable member so as to .be engageable by the said contact arms.

7. A rheostat comprising a body oi insulating material; a manually operable member rotatable on the body and having a pair of Contact arms extending from it in opposite directions and yieldable thereon, said body kheaving pairs of integral spaced projections onopposite'sides of the rotatable member, said projection-s being traversable by the contact arms and providing detents for said arms; a metal contact segment extending between the pairs of projections of the body, said segment being engageable by one or the other of the contact arms; a resistance element extending along the other side of the rotatable member between the pairs of projection-s of the body, said element being engageable by one or the other of the contact arms; and three metal retainer fingers for the resistance element, two of said fingers being located respectively adjacent corresponding projections of the said pairs and the third finger being located between said two iingers, all of said fingers overlying the resistor element and being engageable by the said contact arms, and at least two of said ngers contacting said element at different locations thereon.

8. A rheostat for controlling an electric appliance, comprising a hollow casing shaped to receive electrical conductors for connection to a source of current and to the appliance to be controlled, said casing being separable into two parts the edges of which are cut away to form a slot in a side wall of the casing; variable resistor means 'a mounted within the casing; and a wheel within the casing connected with said resistor means to vary the same, said wheel having a peripheral portion protruding through the slot in the casing wall for manual engagement.

9. A rheostat for controlling an electric appliance, comprising a hollow casing shaped to receive electrical conductors for connection to a source of current and to the appliance to be controlled, said casing having a pair of oppositely located slots in opposite walls thereof; variable resistor means mounted Within the casing; and a wheel within the casing connected with said resistor means to Vary the same, said wheel having peripheral portions protruding through the slots in the casing wall for manual engagement.

10. A rheostat for controlling an electric appliance, comprising a hollow casing shaped to ren ceive electrical conductors for connection to a source of current and to the appliance to be controlled, said casing being separable into two parts the edges of which are cut away to form a slot in a side wall of the casing; variable resistor means mounted within the casing; aligned bearing means formed in the respective casing parts; and a Wheel within the casing, carried by said bearing means and connected with said resistor means to ivary the same, said wheel having a peripheral portion protruding through the slot in the casing wall for manual engagement.

l1. A rheostat for controlling an electric appli ance, comprising a hollow casing shaped to receive electrical conductors for connection to a source of current and to the appliance to be controlled, said casing having a slot in its wall and having a sight aperture; variable resistor means 11 mounted within the casing; a wheel within the easing,V connected with said resistor means to vary the same, said wheel having aperipheral portion protruding through the slot in the casing Y Wall for manual engagement; and indicator means in the casingymova-ble with said Wheel and disposed adjacent the sight opening to be Visible therethrough.

Y JOSEPH YOUHOUSE.

REFERENCES CITED The following references are of record in the le of this patent:

Number 12 UNITED STATES PATENTS Name Date Phelps Nov.A 13, 1923 Peterson v July 21, 1931 Megow Dec. 5, 1933 Frank et al. Nov. 3, 1936 Krieger Mar. 21, 1939 Axtel Sept. 12, 1939 Schellenger Oct. 24, 1939 FOREIGN PA'I'ENTS Country Date Number Germany .Y Jan.Y 26, 1939

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