US597002A - Graphite rheostat - Google Patents

Description

(No Model.)

E. W. JEWELL. GRAPHITE RHEOSTAT.

Patented Janfll lll lllllllllllll UNITED STATES PATENT EEicE.

EDIVARD W. JEVELL, OF CHICAGO, ILLINOIS.

GRAPHITE. RHEOST'I.

SPECIFICATION forming part of Letters Patent No. 597,002, dated January 11, 1898.

Application led May 8,1897. Serial No. 635,658. (No model.)

To @ZZ whom t may concern:

Be it known that I, EDWARD XV. J EwELL, a citizen of the United States, residing at Ohicago, in the county of Oook and State of Illinois, have invented a certain new and useful Improvement in Graphite Rheostats, (Oase No. 1,) of Which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to rheostats; and I have found it to be 0f special value in electro therapeutic operations, where a very gentle and gradual variation of current in the working circuit is essential.

The resistance material which I employ is graphite evenly distributed upon an insulating-base, preferably of stone or slate. This resistance, of uniform cross-sectional area at all points, is introduced in shunt to the operating-circuit, one of whose terminals consists of a suitable contact-arm arranged to make a iirin electrical connection with any part of the graphite resistance, the other terminal being at one end of the resistance.

In accordance with the law of divided circuits the Voltage in the operating-circuit will vary directly with the increase or decrease of resistance in the shunt as the contact-arm is moved along the graphite, thus producing what may be termed a 4uniformly-graded7 resistance.

By this construction I am enabled to secure insensible variations in Voltage, it being possible te change from the full strength of eurrent down to zero in a perfectly uniform ratio with no sudden jerks which are unpleasant and injuriousin medical treatment, and which have been almost impossible to avoid heretofore.

It has been impossible heretofore to construct a rheostat for electroinedical work in which the variations in voltage could be made so gradual as to be insensible to the patient, especially in connection with dental surgery. It has been proposed to introduce a resistance of gradually-increasing cross-section in series with the operating-circuit. This, however,

has been found inefficient, because it is extremely difficult to start or regulate the current by means of such a rhecstat without causing a perceptible jerk in the current, and consequently intense pain to the patient.

By the use of my invention these harmful effects are avoided, and in starting a current, especially the increase from absolute Zero to any required strength, is made in a perfectly uniform gradation, as a movement of the contact-arm through a given distance along any portion of the surface of the graphite will always change the Voltage in the exact ratio in which such distance is proportioned to the total length of the graphite path.

My invention has been especially successful in operations of electrolysis and electric diffusion as performed in dental surgery, where the utmost care is necessary to prevent sudden changes in the strength of the current.

A further feature of my invention consists 7 in an improved binding-post which will permit the connection of a second conductor without in anyway disturbing a connection already made. I find this especially useful, for instance, in connecting a voltmeter across 7 the circ uit without disturbing the connections or operation of apparatus which may be included between the same two binding-posts.

My invention further contemplates an improved and novel method of maintaining a 8 good electrical connection between the graphite and the conductor, attached thereto.

rIhe accompanying drawings will assist in explaining the operation of my invention.

Figure l is a plan View, the electrical con- 8 nections being indicatedl in dotted lines. Fig. 2 is a sectional view taken along the line 2 2 of Fig. l. Fig. 3 is a detail view of the improved binding-post of my invention. Fig.

4: illustrates a screw provided with a conical 9 washer of soft metal, which I employ in electrically connecting a conductor with the graphite resistance.

Like letters are used to designate like parts in all figures. 9

The graphite resistance c is applied uniformly to a raised portion h' of the slate base h. In the center of the base is pivoted an arm c, provided with metallic contact-springs c c', which are maintained in firm sliding engagement with the surface of the graphite. rIhe handle c2 may be grasped to rotate the con IOO tact-arm. The binding-posts P and N are for connection with the positive and negative terminals of the battery or other source of current. Conductor d serves to connect the post P with one end of the graphite resistance at the point af, while conductor e similarly connects post N with the other end of the resistance at the point y. Binding-posts P P and N N are respectively the positive and negative terminals of the working or patients circuit, a conductor f connecting post P l) with the contact-arm o and conductor g eX- tending from the post N N to the point where conductor e is united with the end of the graphite resistance. Current entering at l will flow from the point agthrou gh the graphite a, to the point 1y, going ont by the post N. ln this distinct circuit ior the current it will meet with a uniformly graded resistance, preferably of several thousand ohms. lletween the points .t and 1/ there will be a difference of potential corresponding to the electromotive force of the current, with a uniform drop in that potential all along the line. Thus if the rheostat is used on a twenty-volt circuit the difference of potential between the middle point of the rheostat and the point jz/ will be ten volts, while at the points S and S2 it will be live volts and fifteen volts, respectively. lf the contact-arm be placed at the point 'y and rotated in a clockwise direction, the difference of potential between the posts P P and N N will rise very gently and gradually from zero to the full twenty volts when it reaches the point a'. The voltage in the patients circuit thus depends upon the relative position of the contact-arm upon the graphite surface.

lVith the use of my invention current may safely and advantageouslyT be taken from an ordinary one-huiidred-and-ten-volt in candescent-lighting circuit even for the most delicate electrotherapeutic operations.

The screws t' 'L' t" t, which are used to make connection between the graphite resistance and the plates L 7e', to which conductors are soldered, are preferably provi-ded with conical washers of soft metal, such as block-tin. The graphite is firmly packed about the sides of the countersunk holes, in which the screwheads rest. The conical block-tin washers Z are interposed between the screw-heads and the graphite, so that when a nut is tightened upon the shank of a screw the washer is slightly expanded and forced into very lirm rengagement with the graphite. More graphite is then tamped into the countersunk hole to cover the head of the screw, and the union is complete. 'Conductors which it is desired to electrically connect with the graphite are preferably soldered to one of the plates 7.: 7d, according to which end of the graphite is to be connected.

The binding-post illustrated in Fig. 3 of the J drawings l lind to be a very valuable accessory. lt has two points of advantage over the ordinary variety in that the binding-nut 7L may not be wholly removed and lost from the threaded stem L/ of the post, the outer end ol said stem being enlarged to retain the nut. The threaded stem or shank is also hollow to aiford an auxiliary socket or seat for an auxiliary switch pin or plug, which may be inserted therein. l find it desirable to make permanent connections7 so to speak, by means ol' the plug-and-socket device,when other connections may readily be made in the usual manner by the threaded bin ding-nut 7L without in any wise disturbing the lirst circuit. This mode of connection is most desirable, for it is essential in medical treatment, as l have before stated, to avoid suddenly making or breaking a circuit and also to avoid sudden changes of resistance in the working circuit due to loose or imperfect connections. Binding-posts such l have described readily permit changes of connection without suddenly breaking or altering the condition of the circuit.

It is evident, of course, that the use of my invention is not restricted to electromedical work. ln fact, l have found it very desirable as a iield-rheostat for dynamo-electric machines.

Having described my invention, what l claim as new, and desire to secure by Letters Patent, is-

l. In a rheostat, the combination with an insulating-base, of a uniformly-gradcd graphite resistance mounted thereon, a contact-arm adapted to travel over and make lirm electrical connection with said graphite resist-- ance, binding-posts P N in electrical connection with each end of said gra `phite resistance, binding-posts P P and N N in electrical connection with the said contact-arm and one end of said graphite resistance respectively, and auxiliary sockets in said binding posts adapted to receive independent s vitch plugs or connectors, substantially and for the purpose described.

2. ln a rheostat, the combina-tion with a uniformly-graded graphite resistance in shunt with the workin g circuit, a contact-arm adapted to travel over said graphite resistance and forming one terminal of said working circuit, binding-posts for making suitable connce tions, and auxiliary sockets in said bindingposts adapted to receive switch plugs er pins, independent of such connections, substantially as described.

3. The combination with the base h, of a screw having an enlarged conical head, a countersunk portion in said base adapted to receive said screw-head, graphite applied to the sides of said countersnnk portion, and a conical soft-metal washer interposed between the screw-head and graphite, substantially as and for the purpose specified.

Ll. ln a binding-post, the combination with the threaded shank, of a threaded nut therefor, and an enlargement upon the end of said shank to prevent the total removal of said n ut, substantially as described,

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5. In a binding-post, the combination with the threaded shank, of a threaded bindingnut therefor, and a socket or seat in said shank adapted to receive a switch pin or plug, substantially as an d for the purpose specied.

G. In an electrotherapeutic apparatus, the combination with a working or patients circuit forming one distinct path for the electric current, of a thin layer of graphite evenly distributed upon an insulating-base forming a second path of high resistance for the cur rent, a contact-arm arranged to travel along said graphite layer and make electrical contact therewith, the cross-sectional area of said graphite path being substantially equal at all points of adjustment of said arm, an elec-

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