Improvements in Electrical Resistances.
Year: 1896

page_text: Date of Application, 27th Feb., 1896
Complete Specification Left, 27th Nov., 1896-Accepted, 2nd Jan., 1897
Improvements in Electrical Resistances.
I WILLIAM JAMES DAVY, Engineer, of Rostrevor, Boundaries Road, Balham,
in the County of Surrey, do hereby declare the nature of this invention to be as
follows:-
This invention relates to electrical resistances or rheostats and has for its object
to provide a simple and effective device for readily altering or interposing any
given resistance in an electric circuit and which shall be so constructed as to be nou-
inductive, the magnetic flux induced by the different currents traversing the
apparatus being neutralised.
In one arrangement of rheostat constructed according to this invention two discs
of insulating material arranged, preferably, horizontally and at a suitable distance
apart are perforated for the reception of conducting wires of suitable resistance
which are threaded alternately through the upper and lower discs and joined
together in series, the ends being connected to terminals on the said discs. The
lower disc, which may slide on a vertical spindle, is of sufficient weight to stretch
the wires taut. Slidable contact plates connect the different pairs of adjacent
wires by means of which the current may be short circuited and the resistance
thereby adjusted as will be readily understood. It will be obvious that by threading
the wires as herein before described, the current is caused to traverse any two
adjacent wires in opposite directions, neutralising the magnetic flux, and thereby
preventing self induction.
The apparatus is preferably arranged with the wires vertical as described, but
the discs inay obviously be mounted on a horizontal axis and adjusted, for the
purpose of stretching the wires, by a suitable screw or other device.
Dated this 27th day of February 1896.
WHEATLEY & MACKENZIE,
Agents.
COMPLETE SPECIFICATION.
Improvements in Electrical Resistances.
1, WILLIAM JAMES DAVY, Engineer, of 27 Drayton Park, in the County of
London, late of Rostrevor, Boundaries Road, Balham, in the County of Surrey,
do hereby declare the nature of this invention and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
This invention relates to electrical resistances or rheostats and has for its object
to provide a simple and effective device for readily altering or interposing any given
resistance in an electric circuit and which can be so constructed as to be non-
inductive, the magnetic flux induced by the different currents traversing the apparatus
being neutralised.

page_text: In the accompanying sheet of drawings,
Fig. 1 is a side elevation of an electrical resistance constructed according to this
invention. Fig. 2 is a plan and Figs. 3 and 4 are elovations of the two ends of
the same.
Fig. 5 shows a side elevation of a modified arrangement of noninductive electrical
resistance and Figs. 6 and 7 end elevations of the same.
Referring to Figs. 1 to 4 inclusive: Two dises a of insulating material mounted
on brackets, secured to a base c of channel section, and placed nt a suitable
distance apart as shown, are perforated by holes through which helically wound
conducting wires of suitable resistance are threaded alternately and joined
together in series, the ends being connected to terminals. The discs a nre secured
to the brackets & by bolts and nuts h, by menus of which the wires may be
stretched tant. Slidable contact plates i connect different pairs of adjacent wires
by means of which the current may be short circuited and the resistance thereby
adjusted as will be readily understood.
The wires e are enclosed by a cover 2 in order to prevent tampering or injury.
Referring to Figs. 5 to 7 inclusive, straight wires in are threaded through the
holes d in the insulating dises a a pin n being passed through the loop formed at
one end to prevent the wires being redrawn through the holes d, and also to keep
them at a suitable distance apart. When the resistance is in operation the current
passes along each pair of wires in opposite directions, the inductive effect being
thereby neutralised.
It will be obvious that hy threading the wires as hereinbefore described, the
current is caused to traverso any two adjacent wires in opposite directions,
neutralizing the magnetic flux, and thereby preventing self induction.
Having now particularly described and ascertained the nature of my said inven-
Lion and in what manner the same is to be performed, I declare that what I
claim is :
1. An electrical resistance comprising a number of helically wound conducting
wires secured by insulating discs and connected in series and provided with slidable
contact plates, substantially as described and for the purpose set forth.
2. An insulated electrical resistance arranged and constructed substantially as
described with reference to Figs. 1 to 4 of the drawings.
3. An insulated electrical resistance arranged and constructed substantially as
described with reference to Figs. 5 6 and 7 of the drawings.
Dated this 27th day of November 1896.
WHEATLEY & MACKENZIE,
40 Chancery Lane, London, W.C., Agents.