USRE19607E - Rheostat potentiometer and method - Google Patents

Description

TRUCTING THE SAME June 1l, 1935. D. T. SIL-:GEL

RHEOSTAT POTENTIOMETER AND METHOD OF CONS Original Filed March 4. 1932 iii Ressued June l11, 1935 UNITED STATES RHEOSTAT POTENTIOMETER AND METHOD F CONSTRUCTING THE Sm David T. Siegel, Chicago, Ill.

Original No. 1,942,495,

Serial No. 596,787, March 4, for reissue November '1, 1934, Serial No.

Claims.

'Ihis invention relates to improved resistance devices, particularly potentiometers or rheostats, comprising a dielectric structure in which the base and wound core are fused into an integral unit.

The main object of my improved device is to provide a unit structure in which the base becomes an integral part of the core, increasing the effective radiating surface for ,the dissipation of the heat generated; and further to provide a structure in which the resistance element stays in fixed position independent of its expansion; to provide a core which can be wound in equal or progressive sizes of wire and later fused into a unit ceramic structure with a base; to provide a heat treatment in forming the unit structure which stabilizes the resistance; to provide a structure which is rigid and forms a protection for the resistance element; to provide contacting surfaces on a resistance element embedded in a ceramic structure; to provide an improved contact maker capable of maintaining a clean smooth surf ace on the resistance wire; to provide in the ceramic structure limits to the swing of the sweeper arm; to provide a self-adjusting non-arcing brush or contactor; and to provide improved means for maintaining efficient electrical connection. between the resistance wire and the contacter arm.

An illustrative embodiment of my invention is shown in the accompanying drawing in which;

Figure l is a plan View of a porcelain base forming part of the resistance device.

Fig. 2 is a plan view of a porcelain core with metal terminals attached and windings shown in part.

Fig. 3 is a plan view of a porcelain base with the core seated in place.

Fig. 4 is a section taken on the line 4-4 of Fig. 3, showing the core in dotted lines.

Fig. 5 is a section on the line 5--5 of Fig. 2.

Fig. 6 is a plan view of a complete assembly of a potentiometer rheostat.

Fig. 'l is a cross section on the line 1-1 of Fig. 6.

In the form of my improved rheostat shown, the unit ceramic part is constructed by assembling a circular porcelain base I and a split porcelain ring 2 having flattened sides. A seat for the split or cutout ring 2 is formed in the base I by a ledge 3, a cone-shaped raised center 4, and a radial raised arm.

The cut-out ring 2 is uniformly wound with resistance wire 6. Copper terminals 1 surround the ends of the core 2, and the ends are brazed to the resistance wire Ii. Fusible ceramic material Il, shown in Fig. 7, fills the seat and covers the entire cutout ring 2, including the wire 6. and termidated January 9, 1934, 1932. Application '151.917

nal 1. By the term fusible ceramic material I refer to the substance commonly used for coating ceramic products and known in the trade as a vitreous enamel slip or flux; and the term as used in the claims should be so understood. The cutout ring 2 is then placed in its seat, with the contacting surfaces 9 uppermost. When seated, a part of the resistance 6 contacts with the base I.

The commutation or contacting surfaces 9 and the punched ends Ill of the terminal 1 are then wiped clean and the combination is placed in a ceramic furnace, where the ceramic material 8 is fused. After the ceramic unit with embedded wires is formed, the contacting surfaces 9 are polished smooth, and the terminals Ill are ground and solder-dipped.

Through the center of the cone 4 is a central aperture I I, in which is fitted a metal bushing I2, externally threaded to receive a lock-nut I3, and

provided at the opposite end with a thrust bearing I4. The thrust bearing I4 co-acts with a metal connecting strip I5, which extends from the center of the cone 4 over the raised arm 5, forming an electrical terminal I6.

The movable parts of the rheostat comprise a shaft I1, which is seated in the metal bushing I2. One end of the shaft I1 is shouldered and squared to receive a slotted sweep arm I8, which is riveted to the shaft I1. Threaded on the shaft l1 is a spring washer I9 arranged to maintain fixed tension between the sweep arm I8 and the fixed metal bushing I2 and a circular groove 20 is cut in the shaft I1 to receive a thrust washer 2| which co-acts with the threaded end of the metal bushing I2.

A control knob 22 is fastened to the projecting end of the shaft I1 by a set screw 23, which contacts with a plane surface 24 on the shaft Il. The outer end of the sweep arm I8 is bent to form a mechanical guard 25 for an independent carbon graphite button 26, which rides on the contacting surface 9.

The mechanical guard 25 is punched to form an aperture at the bend. The carbon graphite button 26 is seated in a crown top metal casing 21 and soldered to the metal casing 21 is a flexible cable 28, which is electrically connected to the sweep arm I8 by a rivet 29. The rivet 25 also fastens a double bend steel spring 30 to the sweep arm I8. The free end of the spring 3U has two apertures, through which the cable 2B is threaded in such manner that the crowned casing 2l of the graphite button is normally held under spring tension on the contacting surface through what is substantially a ball and socket joint. The spring 30 passes through the aperture 32, punched in the sweeper arm I8, and the punching 33 forms a stop for the arm through contact with the radial rib 5.

In operation the carbon graphite button rides on the polished contacting surfaces oi' the turns of the resistance wire and the tension between the button and the resistance wire is maintained substantially constant at all positions.

With my construction the control knob gives positive control of the location of the graphite button on the resistance wire, and the ball and socket-like mounting of the button assures positive contact with the resistance wire even though the wire and button both become worn. Experience has proved that a carbon graphite button with free seating, as here provided, and under tension, does not tend to abrade the resistance wires, and since the button bridges several wires, there is no destructive arcing at the contacting surface.

In my improved construction, the cable 28 carries substantially all the current passing through the device, thus preventing heating of the spring and deterioration of the spring temper, and one of the advantages of my construction is the formation of. a compact unit, in which the heat generated is dissipated by the entire surface of the structure forming the mounting, thus maintaining under load, a comparatively low temperature.

Another important advantage of my improved construction lies in the fact that each turn of the resistance wire wound upon the supporting core is solidly backed throughout the entire length of its convolution and in the baking process each individual turn of the resistance element is solidly and entirely fused onto the supporting core which backs it up. On the under side of the core the resistance wire is also fused both to the core and to the base upon which the core is mounted. Thus each turn of the resistance element is securely fastened to the core and can in no way be displaced laterally under the sliding action of the contactor element. Regardless of the expansion of the resistance wire, that is usually resultant as the element is heated in operation, the possibility of the individual turns of wire being moved so as to vary the setting of the control knob for any certain resistance is entirely eliminated.

Although but one specific embodiment of this invention has been herein shown and described, it will be understood that certain details of the construction shown may be altered or omitted without departing from the spirit of this invention as dened in the following claims.

I claim:

l. The process of making a resistance device in forming a ceramic core, tightthroughout said limited portion to provide an extended area oi bare wire, locating the wound core in its position on the base, and baking the assembly to fuse the said material and to permanently Join the core to the base and the resistance Wire to the core.

2. The process of making a resistance device which consists in forming a ceramic core, tightly winding a resistance wire upon said core, securing a terminal to said core and brazing the to said resistance wire,

of the base with a fusible ceramic material, removing the said material from a limited portion of the wound core whereby to expose the top surfaces of the wire throughout said limited portion to provide an extended area of bare wire, locating the wound core in its position on the base, and baking the assembly to fuse the said material and to permanently join the core to the base and the resistance wire to the core.

3. The process of making a resistance device which consists in tightly winding a resistance wire upon a suitable ceramic core, providing a ceramic base grooved to receive the wound core, coating the Wound core and the groove of the gether and the resistance wire is entirely and immovably fused to the core.

4. A resistance device, comprising, in combif:

nation, a core of arcuate outline, said core beengagement with said 5. A resistance device comprising, in combination, a generally circular, ceramic core, a resistance Wire on said core, a the core and permanently joined to an end of said Wire, a ceramic base on which said core is mounted, and a baked, fusible ceramic material covering said core, terminal mounting and the surface of said base on which said core is mount- DAVID T. SIEGEL.

terminal secured on

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