Improvements in Rheostats for Electric Circuits.
Year: 1898

page_text: PROVIDIONAL DE MOTOR
Improvements in Rheostats for Electric Circuits.
I, CHARLES WIRT, of 1028, Filbert Street, Philadelphia, State of Pennsylvania,
United States of America, Electrical Engineer, do hereby declare the nature of this,
nvention to be as follows:
My invention relates to rheostats or variable resistance devices for use in electric
circuits or in connection with electric translating devices, having for its object an
apparatus which will remain stable in its mechanical and electrical properties for
a longer period than is common and will be simple and cheap of construction.
The chief feature of the invention is a method of forming the resistance devices.
which are cut into circuit in steps by the operation of the device, so that the
entire series which constitute the rheostat will be of a single length or piece of
ribbon or wire, thereby avoiding joints in which resistance and heat would be
developed. Another feature is involved in providing a considerable area of
contact-surface between the rheostat-coils or sections and the contact-blocks or
conductors by which the resistance is graduated; thereby promoting radiation of
heat, and dispensing with soldered connections liable to work loose under the
influence of heat. I preferably use as a resistance material a metallic ribbon of
comparatively poor conductivity which I wind upon a suitable mandrel to such a
number of turns as will suffice for one section of the rheostat. The unwound
portion of the ribbon then being shifted axially and a second coil then wound in
the same manner as the first, and so on until the desired number of coils to
constitute a rheostat of the number of steps desired. I then remove the coils
from the mandrel and flatten them by squeezing the sides together after which
they are laid in series on a range of contact-blocks to which they are firmly
clamped by pressure. The ribbon of which the coils are formed may be given
a preliminary treatment by being carried through a bath of insulating cement or
superficially oxidised or otherwise coated to ensure protection against short-circuit-
ing between contiguous layers. After the coils and contact-blocks have been
assembled, a revolving brush or circuit-closer is mounted in operative relation to
the blocks so as to cut the coils into or out of circuit progressively. Instead of
winding the coils on a mandrel the ribbon may be folded or otherwise compactly
arranged, the essential idea being that the entire group of coils which constitute
the variable resistance may be formed by a single integral length of conductor. I
preferably arrange the coils and contact-blocks in circular order in a strong iron
frame from which I insulate them by layers of fire-proof insulating material, such
for example, as mica or asbestos, and the containing frame may be ribbed or
corrugated to assist dissipation of heat. The revolving brush is insulated from
the casing by mica or asbestos washers and is electrically connected with a binding
post on the outside of the casing. The terminal coils of the rheostat are preferably
arranged so as to bear upon adjacent contact blocks, one of which connects with a
movable brush and the other with the final resistance coil. The coils are placed
one on each contact-block and after being covered with an annular strip of fire-
proof insulating material are firmly clamped down to the casing. After the parts

page_text: have been assembled I sometimes embed the contact-blocks in cement to prevent
displacement in service.
Dated this 5th day of May 1900
BOULT & WADE,
Agents for the Applicant.
.1%
Pin neostats for Electric Circuits.
I, CHARLES WIRT, of 1028, Filbert Street, Philadelphia, Pennsylvania, United
States of America, 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 ascertained in and by the following statement:-
This invention relates to rheostats or variable resistance devices for use in electric
circuits or in connection with electric translating devices. The object of the
invention is to provide a device of this character which will admit of cheap
construction and will remain stable both in its mechanical and its electrical
properties for a longer period of service than such devices as commonly constructed.
The chief feature of the invention is to form the entire series of resistances
which constitute the rheostat of a single length or piece of ribbon or wire conductor,
and to provide a considerable area of contact surface between the several sections
of the rheostat and the contact-blocks or conductors connected with them, such
increased area of contact surface insuring better working conditions by promoting
radiation of heat and dispensing with the necessity of soldered or other connections
which are liable to work loose under the influence of heat. In carrying out my
invention I preferably use as a resistance material a metallic ribbon of German
silver or iron, which I wind upon a mandrel cylindrical or elliptical in cross-section,
building each coil up to a sufficient number of layers to constitute an ohmic
resistance as large as is required for each section of the variable rheostat.
insulating heat-refractory medium may be interposed between the several spirals,
or the ribbon may be carried through a bath of insulating cement, or it may be
provided with a superficial coating of high resistance by oxidation, or in any other
suitable way.
After a sufficient length of the ribbon has been wound to constitute
one section of the rheostat, the other end of the ribbon is shifted axially of the
amandrel and a second coil is wound in the same manner as the first, after which the
free end of the conductor is again shifted axially of the mandrel and a third, fourth
and fifth coil, or as many as may be needed, wound in the same manner.
coils are then removed from the mandrel and flattened by squeezing the sides
together, after which they are laid in series on a range of contact-blocks and firmly
clamped or otherwise secured thereto. Thus each contact-block bears upon a
considerable superficial area of the resistance medium, and a good electrical and
heat conductive joint is established. A brush is mounted in suitable relation to the
contact-blocks and the terminal coils of the rheostat are provided with connectors
for including the rheostat in an electric circuit.
An
The
The metallic ribbon I prefer to use may be of iron, German silver or other alloy
having a high resistance; it may be in the neighborhood of .005 of an inch in
thickness and narrow in width, say an eighth of an inch or thereabout and the coil
which constitutes a section being when flattened, about three inches in length.
These proportions may be varied quite widely and are noted simply by way of
example. The essential features of my invention comprise a rheostat in which the
resistance sections are formed of a single integral piece of electric conductor
coiled, folded or otherwise compactly arranged into a plurality of sections placed
1

page_text: side by side and mounted in co-operative relation to metal meat radiating
placed on the long side of the respective coils and a switch to cut the steps of the
rheostat successively into circuit; the effect of the construction being that the coils
or sections are very long, thin and narrow, and thorough radiation and uniformity
of heat are promoted.
In the accompanying drawings which illustrate the invention;
Figure 1 is a top plan view, part broken away, of a rheostat embodying my
improvements;
Figure 2 is a side elevation partly in section, of the organization shown in
Figure 1;
Figure 3 is a perspective view of a ribbon-conductor folded in a way to embody
my improvements; and
Figure 4 is a similar view of a conductor wound according to my invention.
Referring first to Figure 4, a narrow metallic ribbon is wound in a lathe,
preferably on an elliptical or oblong mandrel, so as to form a plurality of coils a, b,
side by side, of a single length of ribbon; the coils are removed from the mandrel
and flattened, as indicated in the figure. If desired, the ribbon may be folded
in lieu of being wound; such an organization is shown in Figure 3. I prefer
however to form it in coils as the operation is much more rapid and therefore
cheaper to conduct. Any suitable mode of insulating the successive spirals or folds
from one another may be employed. I preferably apply an insulating cement to
the ribbon as it is wound and permit it to dry and harden while the coils are
held under compression, after which they may be removed from the mandrel and
placed in the rheostat-casing, each coil lying on a contact-plate c, d giving an
area of contact equal to its entire length. A series of plates c, c (see Figure 1), are
placed in a suitable casing or frame, in co-operative relation to a travelling
contact. As shown, the contact-blocks are arranged in circular order in an
iron frame d, d, being insulated therefrom by layers of mica or
asbestos e, f. The coils are placed one on each contact-block, covered
with an annulus of mica or asbestos f, and firmly clamped in place by a
co-operative member of the casing by screws, as shown. Ribs or corrugations
may be provided, as indicated in the drawing, to assist dissipation of the heat
generated by the rheostat in service. A brush g, mounted upon a stem projecting
into the casing, to which is connected a handle 7, permits the spiral contact-blocks
to be brought successively into circuit. The brush is insulated from the casing
and from the handle by mica or asbestos washers, see Figure 2, and is connected
with a metallic strip i, leading to a binding-post j, on the outside of the casing.
The strip may serve as one of the contact-blocks, as shown in Figure 1, a co-
operative binding-post j¹ may be mounted upon the adjacent contact-block.
As thus organized, the terminal coils of the resistance bear upon adjacent contact-
blocks, one of which connects with the brush, so that by turning one brush more
or less of the coils may be cut into a circuit in which the device may be included.
An annular spring m may be interposed between the bottom of the casing and the
annulus n of slate which supports the inner ends of the contact-blocks c, c¹.
If desired, the casing of the rheostat may be formed of slate or similar non-
conducting and fireproof material, but I prefer iron in most cases to permit more
rapid radiation of heat. The contact-blocks may be held in place while the
apparatus is being assembled by a weight, or clamp, or they may be cemented to the
mica insulation. After the parts have been assembled, the coils and contact-blocks
may be embedded in cement to prevent displacement in service.
Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. A rheostat comprising a continuous length of conductor metallically integral
throughout its length, wound or folded in a plurality of independent sections,
each of which is brought into contact with an independent heat radiating device
to promote the dissipation of heat.

page_text: 2. A rheostat formed of a continuous length of metallic ribbon integral through-
out its length, wound or folded into a plurality of independent resistance sections,
each in contact with an independent heat radiating body and contacts for a switch
leading from the several sections.
3. A rheostat comprising a plurality of resistance sections, all formed from a
continuous integral length of metallic ribbon, each section having a length much
greater than its thickness and in contact over its long side with a heat radiating
body.
4. A rheostat provided with a resistance coil formed of metallic ribbon coiled or
folded upon itself a number of times into a long, flat coil or bundle, and bearing on
its flat side upon a heat radiating contact-block.
5. A rheostat comprising as plurality of resistance sections made of metallic
ribbon, each wound or folded into a long, flattened coil or bundle, and in contact on
its broad face with a metallic contact-block, and a switch for successively engaging
contacts electrically connected with the contact-blocks.
6. A rheostat comprising a plurality of resistance sections clamped into an
enclosing case and held in place by pressure, and a switch for successively
connecting with the several sections."
7. The complete rheostat substantially as described or illustrated in the
accompanying drawing.
Dated this 6th day of February 1899.
BOULT & WADE,
Agents for the Applicant.