Improvements in Resistance Panels or Grids.
Year: 1899

page_text: Date of Application, 7th Feb., 1899-Accepted, 11th Mar., 1899
[Communicated from abroad by ALVA OYLMER DINKEY, of Munhall, in the County.
of Allegheny, State of Pennsylvania, one of the United States of America,
Electrical Engineer.]
Improvements in Resistance Panels or Grids.
I, WILLIAM BURGELAND JOHNSON, of 4, Clayton Square, Liverpool, in the County
of Lancaster, 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, reference being had to the accompanying
drawings, forming part of this specification, in which:-
Fig. 1 is a front elevation of a resistance grid constructed in accordance with
my invention. Fig. 2 is a partial rear elevation of a rheostat provided with
my improved resistance, with the rear plate removed; and Figs. 3 and 4 are
detail views showing the hook shaped terminals for the resistance strips, and the
loose connection for the grid support.
My invention relates to the resistance employed in connection with rheostats
and other electrical instruments and is designed to provide a holder for the resis-
tance strip which will automatically adjust itself in length during the expansion
and contraction of the strip, to provide an adjustable connection or stretcher
by which the strip may be drawn taut after winding, and to provide a simple
and cheap resistance grid which shall give a high resistance in a small space.
In the drawings, 2,2 represent a pair of side members preferably formed of
hollow tubing and having at one end a transverse shaft upon which are placed
a series of china insulating spools 4. Into the opposite ends of the side tubes
project the screw threaded stems 5 of two holders or bearings 6, 6 for a transverse
shaft 7 which is also provided with a series of insulating spools 8. The stems 5
project through nuts 9 which bear upon the ends of the side tubes, so that by
rotating the nuts the shaft 7 may be moved endwise of the grid. Intermediate
of the end shafts are provided the cross shafts 10 each having a long insulating
spool thereon, and which serve to keep apart the several strands of the resistance
strip or ribbon.
The resistance ribbon or strip 11 is wound in the form of an elongated coil over
the spools upon the end shafts as shown in Fig. 1, and its ends are secured to
the hook shaped terminals 12 which take over the end spools upon the shafts 7,
and are provided with suitable binding screws 13 for attachment of the electrical
connections. After the ribbon has thus been wound as tightly as possible, each
coil being tightened successively the wound ribbon is drawn taut by rotating
the nuts 9 and thus increasing the distance between the end shafts and stretching
the coil.
In using these grids, I preferably provide upon one face of each grid a series
of spacing spools 14, of insulating material secured by wires 15 extending through
holes in the side tubes and secured therein. These spools upon each grid prevent
the ribbon contacting with the ribbon of the next grid, if any buckling occurs,
and thus insure the correct action of each grid.
In using the panels or grids, the rhoestat or resistance box is provided with

page_text: an upper rectangular frame 16 having a series of opposite registering grooves
which are engaged by the projecting ends of the shafts 7 of the several grids.
These grids hang side by side as shown in Fig. 2 and the ends of their side tubes
may project through holes in the floor of the chamber as shown. The width of the
resistance ribbon in the various grids is changed to vary the amount of resistance
and the insulating spools upon which the ribbon is wound are correspondingly
changed, several widths of these spools being used. No surrounding box is used
for each separate grid and a thorough, ventilation of the ribbon is afforded.
The advantages of my invention will be apparent to 'those skilled in the art.
A device for stretching the ribbon after winding is important as in practice it
is found impossible to wind the ribbon sufficiently taut and it must be pulled taut
after winding. The loose connection at one end of the frame allows the grid to
drop down during expansion of the ribbon consequent upon its heating by the
current and thus given an automatic adjustment. The stretching device is simple
and effective, the grids are easily and 'cheaply built and wound and the construc-
tion lends itself readily to changes in the width and length of the resistance ribbon.
Many changes may be made in the stretcher for pulling the winding-taut, ás
well as in the loose connection to allow lengthening of the frame during expansion
and in the construction and arrangement of the other parts without departing
from my invention.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:—
1. An expansible frame for resistance material, the frame having a loose con-
nection to allow a change in its length during the expansion or contraction of
the resistance winding; substantially as described.
2. A resistance frame having a movable support over which the winding
extends, and means for adjusting this support to pull the winding taut; sub-
stantially as described.
3. A resistance frame having supports over which the winding passes, these
supports being adjustable to and from each other, said frame being hung upon one
of the supports, so that the frame will elongate automatically upon expansion
of the winding substantially as described.
4. A resistance grid, having at its ends rods provided with removable separate
spools over which the ribbon is wound, and intermediate separating bars or spools
to keep the coils separate; substantially as described.
5. A resistance grid having at one end a support carried in screw threaded
holders engaging the main frame; substantially as described.
6. A resistance grid having tubular side rods and end supports carried by
holders having screw threaded stems entering the side rods and engaging nuts at
their ends, and a resistance ribbon passing over the support, substantially as
described.
7. A resistance box having separate frames therein, each provided with resis-
tance ribbon wound thereon, and spacing bars of insulating material between
the nanels and contacting with the ribbons, substantially as described.
8. A resistance grid, having end shafts, one movable toward and from the other.
a resistance ribbon wound upon insulating spools on these shafts, and hook shaped
terminals secured to the ends of the ribbon and taking over one' of the shafts;
substantially as described.
9. A resistance grid, having at one end a shaft upon which the frame is hung,
a loose connection between the frame and the shaft, and a coil of ribbon wound
around the shaft and the frame; substantially as described.
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