Variable Adjustable Resistance for Electric Currents.
Year: 1888

page_text: Date of Application, 11th Oct., 1888
Complete Specification Left, 11th July, 1889-Accepted, 17th Aug., 1889
PROVISIONAL SPECIFICATION.
Variable Adjustable Resistance for Electric Currents.
ERNEST GEORGE CRAVEN Electrical Engineer 22 Great George Street West-
minster London S.W. do hereby declare the nature of this invention to be as
follows:-
My invention relates to an improved method of short-circuiting or cutting out of
circuit at will the coils of a Resistance composed preferably of German silver or other
high resistance wire, and of re-introducing in circuit such coils as have been short-
circuited and my method differs from that commonly employed in the following
respects.
The ordinary wire Resistance is composed of a number of spiral coils each of a
certain electrical resistance the ends of which coils are so connected with the points of
a multiple-way switch as to be cut out or reintroduced in circuit according as the said
switch is moved from point to point. It follows, to effect a fine adjustment with such
a resistance that the coils must be very numerous and the points of the switch
equally so.
My method consists in winding the wire selected for the resistance, in, one continuous
coil and longitudinally upon a suitable frame composed preferably of slate or other
non-inflammable and non-conducting material, a sufficient space being left between
each convolution of said wire, and each end of said wire being attached to a suitable
terminal or binding-screw, mounted at convenient points on said frame. The short-
circuiting or re-introducing in circuit of any desired quantity of the said continuous
resistance wire is effected in the following manner; a suitable roller of non-conducting
material is prepared of sufficient length that when laid at right angles to the said
longitudinally wound resistance wire it will extend entirely across from side to side of
the frame on which the said wire is wound. The said roller has a certain portion of
its surface covered with a plate of sheet copper or other metal of high conductivity,
the shape of said plate of metal being such, and its position upon the roller being so
arranged that on rotating the said roller upon the surface of the wires against which it
is held by suitable supports and bearings, a larger or smaller surface of the conducting
face or plate of the said roller is brought in contact with the resistance wire, according
to the direction in which tho said roller is rotated thus short-circuiting or reintro-
ducing in circuit such proportion of the coiled resistance wire as may be from time to
time in contact with the metal face of the roller or released from its contact there-
with.
ليم
1
1000
FREDK. WALKER & HYDE,
4, Moorfields, E.C., Agents for Applicant.
COMPLETE SPECIFICATION.
Variable Adjustable Resistance for Electric Currents.
I, ERNEST GEORGE CRAVEN of 22 Great George Street, Westminster, London,
S.W. Electrical Engineer do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement :-
My invention relates to an improved method of "short-circuiting" or cutting out
of an electrical circuit at will, the coils of a resistance composed preferably of German
silver, or other wire of high electrical resistance, and also of re-introducing into the
circuit such coils as have been short circuited, and my improved method differs from
those hitherto employed in the following respects, that is to say,-
The ordinary wire resistance is composed of a number of coils, each of a
certain

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graded electrical resistance, and the ends thereof connected to the terminals of a
multiple-way switch so as to be cut out of, or introduced into, the circuit, as the
lever, or moveable contact of said switch is moved from point to point. It is neces-
sary, therefore, in carrying out this method of adjustment or regulation, to provide a
number of resistance coils, and an equal number of contact points upon the switch, the
number in either case being greater than is required for the limits of resistance that is
to be included in, or cut out of, the electrical circuit.
In order that my invention may be the better understood, I have appended the
accompanying sheet of drawings, in which Figure 1 represents a plan view of a set of
resistance coils in which the electrical contacts are not made with the wire forming
the coils, but with separate tongue pieces, to be hereinafter described. Figure 2 is a
side elevation of the same, and Figure 3 is a plan view of an alternative device, in
which the requisite contact is made with the actual resistance wire. Figure 4 is a
view of the helical contact, shewn detached, and in perspective.
In carrying my invention into effect I may arrange a series of coils of wire to form
the requisite electrical resistance shewn by a Figure 1. mounted upon a suitable
framo A, and connected in series so that the terminals T T allow the whole of the
series to be included in the circuit, or any part thereof. The base terminal of each
coil of the series is connected to a tongue piece t, projecting beyond said coil over a
roller R, which is suitably mounted upon the frame. Said roller R is preferably
formed of any substance that is a good insulator, and is, at the same time otherwise
suitable for the purpose.
A strip of metal M, with one edge formed, or cut so as to
describe a semi helical curve, is attached to the roller R. This arrangement is shewn
detached, and drawn to a larger scale, in Figure 4, and similar letters of reference
indicate corresponding parts in these, and the other views upon the sheet of drawings.
One edge therefore, of the metallic strip M is exactly, or approximately, parallel to
the axis of the roller R, and the other edge thereof describes a half turn around the
circumference, and within the length of said roller, or in other words, a semi-helix, as
above described. A worm wheel w is keyed, or otherwise attached to the end of the
spindles, supported in bearings upon the frame A, a worm c engaging
therewith, to the spindle or axis of which is fixed a handle 4, or other equivalent
.device.
By means of said handle 1, and the worm and wheel above mentioned, the roller R
may be rotated in either direction at will. In the case of its being rotated toward the
terminals TT, it is evident, by referring to the plan view Figure 1, that each tongue
piece t, starting from the right hand side, must be successively placed in electrical
contact by means of the strip M, until the edge that is parallel to the axis or spindle
places each tongue in contact, including that indicated by n, when the whole of the
resistance is "short-circuited," or cut out of the electrical circuit, since n is directly
coupled to the terminal T, and the extreme right hand tongue piece to the terminal T,
and the strip M places these in direct metallic connection, with a negligible electrical
resistance. By reversing the direction of rotation of the roller R, one coil after
another may be included in the circuit, and the actual resistance thus interposed may
be varied within the limits of the several degrees corresponding to the number and
calibre of the coils a, at will. In order to render the manipulation of the apparatus
perfect, I may, if necessary, mark the several degrees of resistance upon the outer face
of the worm wheel w as shewn by the side elevation Figure 2, where a fixed pointer p
enables the exact resistance to be read off at a glance. I may employ any other form
of index or scale for this purpose, the motion thereof corresponding to that of the
roller R, and the relative positions of the tongue pieces t and the metallic strip M. I
may also, if desirable, impart rotary motion to said roller R by means of a handle or
equivalent device attached to the spindle s without the intervention of worm or other
gearing.
As an alternative device according to my invention, I may use a continuous length
of wire a Figure 3, wound over two stretchers S S¹, attached to the frame A. said
• "stretchers, as well as the frame being made of slate, or other noncombustible and
insulating substance. The two ends of the continuous wire a are coupled to

page_text: terminals T T, and being composed of German silver, platinoid, or other bad conductor
of electricity, practically forms the resistance, which is graded or divided according to
the number of convolutions passing over the stretchers S S¹. In this case the roller R,
with the metallic strip M attached thereto as before, is arranged so as to rotate
between the convolutions of wire a, and is operated by the worm-wheel w, worm c, and
handle 1, in exactly the same manner as that of the first example, shewn by Figures 1
and 2, and hereinbefore described. Each convolution of the single wire resistance
may thus be placed in circuit in succession, or similarly cut out or "short-circuited."
I may, however, dispense with the worm wheel 20 and worm c and substitute.other
gearing therefor, or I may operate the roller R by attaching a handle or other device'
directly to the spindle s.
Having now particularly described and. ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is,
First. In au electrical resistance, the employment of a metallic strip M, Figures 1,
3 and 4, with a semi-helical edge for making or breaking contact with the several
sections of said resistance substantially as herein described, with reference to the
accompanying drawings.
Second. In an electrical resistance, the employment of a series of coils a and
tongue pieces t Figure 1, in connection with a metallic strip M, substantially as and
for the purposes herein set forth, and shewn by the drawings.
Third. In an electrical resistance, the employment of a continuous wire a mounted
upon stretchers S S¹, in connection with the metallic strip M, Figure 3, substan-
tially as herein described and shewn by the accompanying drawings.
Fourth. In an electrical resistance, as referred to in the preceding claims, the
employment of an index p and scale, Figures 1 and 2 substantially as and for the
purposes herein described, with reference to the drawings.
Dated this 10th dov of lule 1880
FREDK. WALKER & HYDE,
4, Little Moorfields, London, E.C., Agents for the Applicant.
FREDK. WALKER & HYDE,
4, Little Moorfields, London, E.C., Agents for the Applicant.