Improvements in the Construction of Electrical Resistance Coils.
Year: 1894

page_text: Date of Appl cation, 14th Mar, 1894
Complete Specification Left, 27th Nov., 1894-Accepted, 29th Dec., 1894
PROVISIONAL SPECIFICATION.
Improvements in the Construction of Electrical Resistance Coils.
I JOHN AMBROSE FLEMING of University College Gower Street London W.C.
in the County of Middlesex, Doctor of Science do hereby declare the nature of this
invention to be as follows:-
My invention relates to methods of making and winding coils of metallic wires
on frames or supports so constructed that when an electric current is sent through
the wire or wires thereby heating it or them, the wire is always preserved in the
same state of tension and the expansion of the wire due to heat is compensated by
an automatic adjustment of the dimensions of the frame or frames on which the
wire is wound. In carrving this invention into effect I place at one end of a metal
or non metallic rod a fixed head piece which may be square, hexagonal or any
other convenient shape, and which is perforated by the rod and fixed to it. This
fixed headpiece may be made of wood, ebonite, porcelain or other non-conducting
material or it may consist of wood or metal and have porcelain, ebonite, bone,
ivory or glass insulating studs or insulators affixed to it. This head piece is fixed
transversely to the central rod. In some cases I use more than one rod passing
through and attached to a fixed headpiece. The other end of the rod or rods
This moveable
traverses a moveable headpiece of like nature with the fixed one.
headpiece slides easily on the rod or rods and is kept apart from the fixed head-
piece by a spiral spring. In preparing the resistance coil the moveable headpiece
is first forced towards the fixed headpiece so as to put the spring or springs into
compression and the moveable headpiece is then held in this condition of compression
by a pin or pins placed through a hole in the rod or rods. A single or multiple
strand of wire which may be of platinoid, manganese steel or other suitable material
for forming an electrical resistance is then wound over the insulators fixed on the
headpieces in the following fashion. Beginning at one point on the fixed head-
piece, the wire or wires are wound longitudinally parallel to the fixed rod, passing
round one of the insulators or studs or projections on the one headpiece and then
round one on the other. In this way the wire is wound zig-zag fashion and finishes
off at a point on the same headpiece at which the winding began namely on the
fixed headpiece. After the wire is so wound the pin put in temporarily to restrain
the noveable headpiece is withdrawn. The spring or springs then keeps the wire
or wires tight. If an electric current is sent through this wire and so heats it, the
wire expands. The moveable headpiece is then thrust forward by the spring or
springs and the wire or wires kept in the same state of tension or tightness. As
the wire cools it draws back the headpiece. Instead of affixing insulators to the
head pieces these last may have slits or slots cut in them through which the wire is
wound. A series of one or more of such resistances may be fixed in a frame and
connected electrically in any convenient way.
This invention is specially applicable in the construction of resistances intended
to be approximately non-inductive, and also in the construction of resistances
intended to absorb or dissipate electrical power. Bare or uncovered wire may be
used and as in consequence of the construction the wire is wholly exposed to the
A set of
air a high current density can be employed in using such resistances.

page_text: such resistances may be arranged to be put in parallel or in series by a suitable
switch.
Dthin th
Monch 1001
Improvements in the Construction of Electrical Resistance Coils.
I JOHN AMBROSE FLEMING of University College Gower Street London W.C.
in the County of Middlesex, Doctor of Science, 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:—
My invention relates to methods of making and winding coils of metallic wires
on frames or supports so constructed that when an electric current is sent through
the wire or wires, thereby heating it or them, the wire is always preserved in the
same state of tension, and the expansion of the wire due to heating is compensated
by an automatic adjustment of the dimensions of the frame or frames on which the
wire is wound, such resistances being so constructed as to have a very small
co-efficient of self-induction and also capable of dissipating with great rapidity the
heat generated in them.
In carrying this invention into effect, I place at one end of a metal tube or
metallic rod a fixed head piece, which may be round, square, hexagonal, or any
other convenient shape, and which is perforated by the rod or tube, and fixed
to it.
This fixed head piece may be of wood, ebonite, porcelain, or other non-conducting
material, or it may consist of wood or metal, having ebonite, porcelain or other
insulating studs fixed to it. I prefer however, to construct this head piece
entirely of porcelain or glass, and to make it as follows:-
A disc of porcelain or glass (see Fig. 1.) is perforated by a hole in the centre,
and by four other small holes. A plan, elevation and perspective view of this head
piece are shown in Figs. 1, 2 and 3. The central aperture or hole marked A. in
Figs. 1 and 2 is intended to be traversed by the rod or tube above mentioned.
The four smaller openings or holes perforated through the porcelain and
marked b. c. d. e. in Fig. 1. are intended for the passage of conducting wires.
This porcelain or glass head piece is formed or fashioned with a number of round
pins or projections standing up upon it, as shown in Figs. 1, 2 and 3. A convenient
size for this head piece is about 2 or 3 inches in diameter, each pin or projection
being about half an inch in diameter and half an inch high. The whole head piece
is easily constructed or moulded out of glass or out of porcelain pressed in a mould,
this last subsequently being fired and glazed.
Two of these head pieces are slipped upon a metallic rod, preferably a brass
tube about or inch. in diameter. One of the head pieces H (see Fig. 4) is
fixed to the rod or tube and kept in position by a metal pin x (see Fig. 4.) passed
through a hole in the metallic rod. This head piece will be referred to as the fixed
bead piece.
The second head piece H' (see Fig. 4) is slipped on to the rod with its pins or
projections placed in an opposite direction to those of the fixed head piece and a
spiral metallic spring S, preferably of steel, is slipped on to the rod before putting
on the second head piece. This spiral spring marked S. in Fig. 4. is kept from
slipping on the rod by a pin w passed through a hole in the rod. This spiral spring
is conveniently made of steel wire, about feth. of an inch in diameter, and may have
any convenient length. The spiral spring should be so made that it fits loosely
upon the central metallic rod, and be capable of being compressed so as to diminish
its effective length by at least one inch. This spiral spring should be so tempered

page_text: that when it is slipped upon the central rod and the pin w, put into position, the
length of the spring should preferably be about 4 inches, and it should be so wound
as to be capable of being compressed into a length of 3 inches or less.
The central opening in the moveable head piece should be of such size that the
central rod passes easily through it without any friction, but is yet a good fit.
In preparing the resistance coil, the fixed head piece is first placed into position
on the central rod and fastened by means of the pin . The pin w. is then put into
position, the spiral spring S. is slipped upon the rod, and the second or moveable
head piece is placed in the right position upon the rod. The moveable head piece
is then forced backwards so as to compress the spiral spring S. by about an inch,
and it is kept in this position by a pin v, which is temporarily placed through a
hole in the central rod to keep it in this position, but which is afterwards with-
drawn. Two copper wires, which may be bare or covered wires, and which are
preferably of the size known as "No. 16, standard wire gauge," are then passed
through the holes b. c. d. e. in the fixed head piece H. (see Fig. 2), being threaded
through in such manner that one wire, marked L. passes down through the hole b.
in the fixed head piece, is then bent up through the hole c., and then finally turned
down so as to form a small hook l. The other wire marked M. (Fig. 4) is then
used in the same manner with respect to the holes d. and e. in the head piece,
passing down through the hole e. up through the hole d. and being bent over to
form a small hook m. (Fig. 4). The lengths of wires L. and M. may conveniently
be about a foot or 18 inches, and may be preferably insulated with cotton or india-
rubber on those parts which are not threaded through the fixed head piece. These
wires L. and M. form the leading-in wires and may be of high conductivity copper
and of such section that they are not sensibly heated by the current which the
resistance is intended to carry.
A resistance coil is then constructed on this frame in the following manner :-
A single or multiple strand of platinoid, manganese-steel, platinumn-silver, or
wire of other suitable material is taken and wound on the above described
resistance coil in the following manner :-The end of the single or multiple strand
of wire is first of all soldered to one of the terminal hooks l'or man.l the wire is
then wound round the pins on the fixed and moveable head piece as follows: the
wire is carried parallel to the central rod-wound round one pin on the moveable
head piece, then carried back and turned round a corresponding pin on the fixed
head piece, and so on, being wound parallel to the central rod and kept in position
by being turned over the pins or projections on the insulating head pieces as shown
in Fig. 5.
The other end of the wire is finally soldered to the other hook, l. or m. which
are the terminations of the wires L and M and it is wound in a zigzag fashion over
the pins or projections on the two.head pieces.
When this winding is complete the pin on the underneath side of the moveable
head piece H' is drawn out and the spiral spring S. now exerting its expansive
power, forces the moveable head piece outwards, and strains the resistance wire
wound over the head pieces quite tightly. The spring must be strong enough to
strain the wire quite tight.
If this resistance wire is heated, and so expands, the spiral spring pushing
outwards against the moveable headpiece always keeps the resistance wire in
tension, and when the wire cools and contracts, the wire draws the moveable head
piece back again against the expansive force of the spring.
The resistance wire is preferably formed of many strands of fine wire to give a
large surface for radiation. Such resistance coil when complete, can be mounted
up in a frame as shown in Fig. 6. which consists of two metallic terminal pieces
shaped like a cross (see P. and Q. Fig. 6) connected together by 4 rods, such rods
being kept in position by circular rings K and G through holes in which the rods
pass. Such a resistance I call a resistance cage or inductionless ventilated
resistance. A series of one or more such resistances can be fixed in a frame made
of wood or metal, or can be supported against the wall by brackets.

page_text: .
I proceed then to describe more particularly the dimensions of such a resistance
coil which is suitable for carrying one ampere of current, and for being placed
across two electric mains, between which there is a difference of pressure of
100 volts. The porcelain head piece may conveniently have a diameter of about
3 inches and have 8 studs, pins or projections upon it half an inch in diameter and
half an inch high. The central rod may be a brass tube a quarter of an inch in
diameter, and 3 ft. 6 ins. in length. The porcelain head pieces should be fixed on
this rod about 3 feet apart, and the spiral spring may have about 30 turns, and be
4 inches in length. The resistance wire may be of platinoid, of a size known as
"No. 36, standard wire gauge" which is very nearly 008 of an inch in diameter.
Such a wire has a resistance of about 4 ohms to the foot, and will carry without
overheating a current of half an ampere when bare or uncovered and exposed to
the air. Two strands of this wire, each of them 50 feet in length, are then wound
in parallel round the fixed and moveable head pieces as above described, and cut
such exact lengths that they terminate on the hooks l. and m. There will therefore
be 16 parallel strands, each strand consisting of two platinoid wires. These two
parallel wires will then have a resistance of about 100 ohms, and will carry without
heating a current of one ampere, and can therefore be placed across electric mains
between which there is a pressure of 100 volts. Such a resistance I call a one
ampere cage. By using four wires in parallel of the same size, and maintaining
the other dimensions of the frame the same I make a two-ampere cage, and by
using 10 such No. 36 platinoid wires in parallel I make a five-ampere cage.
If it is required to construct resistances for less pressure than 100 volts it can be
done by proportionately shortening the length of the wire; thus a 1-ampere
resistance intended to be put across a 50-volt circuit might be constructed by
employing 2 strands in parallel each of 25 feet of platinoid wire 008 inches
in diameter, wound on a resistance frame of appropriate length made as above
described.
This invention is specially applicable in the construction of resistances intended
to be approximately non-inductive, and also in the construction of resistances
intended to absorb or dissipate electrical power, since the active resistance wire
may be a bare wire and is very well ventilated or exposed to the air and a high
current density can be employed in using such a resistance. The 1-ampere,
100-volt resistance made as above described, dissipates when placed across a
100 volt circuit, 100 watts, and resistance cages can be easily constructed in this
manner to dissipate 1 H.P. when put across 100-volt circuit.
"
In order that the mode of carrying into effect my invention and constructing by
this method a definite resistance may be well understood, I proceed to explain that
by the term platinoid wire is meant a wire of the alloy commercially called
platinoid" which is analogous in composition to German-silver and is a well
known alloy. The term manganese-steel is intended to define an alloy of steel
with 12 or 13 per cent. of manganese in it, and the alloy of platinum-silver is an
alloy of platinum and silver in the proportion of two parts of platinum to one of
silver.
These alloys are well known as materials which have a high specific electrical
resistance. The dimensions which any desired resistance coil should have, are
determined as follows: Let it be desired to make a resistance coil which shall
be capable of carrying one ampere when placed across electric mains between
which a difference of pressure of 100 volts exists. The first step is to select a wire
which will carry, without heating to a higher temperature than 100° C., a current
of one ampere.
A length of this wire equal in resistance to one hundred ohms is
then taken and a frame prepared as above described on which to wind it. If the
head-pieces have, say, 16 teeth or pins, then it is clear that the distance between
the head-pieces must be one-sixteenth part of the length of the above selected wire.
Whether one wire or a strand of wires is used, the process of determining the size
of frame for a given resistance coil is the same. Such resistance coils when made
for various ampere capacities can obviously be combined in a frame containing one

page_text: or more coils and having an appropriate switch or switches for joining in parallel
or series two or more of the resistance coils as desired.
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 :
1. In the construction of electrical resistance coils, the arrangement of fixed and
movable head-pieces, pressed or pulled apart by a spring or springs substantially
constructed as described with reference to Figs. 2, 4 and 5.
2. In the construction of electrical resistance coils, the combination of fixed and
movable head-pieces, pressed or pulled apart by a spring or springs and the mode
of winding a resistance wire longitudinally over projections or teeth formed on or in
the said head-pieces substantially as described with reference to the Figures 4, 5
and 6.
Dated this Twenty-seventh day of November 1894.
JOHN AMBROSE FLEMING.