A New Non-inductive Adjustable Carbon Resistance.
Year: 1896

page_text: Date of Application, 5th Feb., 1896
Complete Specification Left, 14th Sept., 1896-Accepted, 14th Nov., 1896
PROVISIONAL SPECIFICATION.
A New Non-inductive Adjustable Carbon Resistance.
I, SIDNEY PRATT BLACKMORE of Georg Goch Mine, Witwatersrand (P.O.
Box 540 Johannesburg), South African Republic, Electrical Engineer, do hereby
declare the nature of this invention to be as follows:-
My invention relates to a simple and compact adjustable carbon resistance
which, being connected to an electric circuit, allows the passage of undue static
or high potential currents such as lightning to earth while resisting the passage of
the ordinary current. For this purpose, I fill a tube of non-conducting material
with powdered wood charcoal between metal or carbon plugs which close the ends
of the tube, and serve as connections to the circuit and to earth respectively. By
pushing either or both these plugs more or less in and so more or less compressing
the carbon powder, the resistance can be adjusted as required, being lessened the
more the powder is compressed.
Dated this 5th day of February 1896.
ABEL & IMRAY,
Agents for the Applicant.
A New Non-inductive Adjusta Die
1, SIDNEY PRATT BLACKMORE, of George Goch Mine, Witwatersrandt (P.O.
Box 540 Johannesburg) South African Republic, Electrical Engineer, do hereby
declare the nature of my invention and the manner in which the same is to be
performed to be particularly described and ascertained, in and by the following
description and by the accompanying drawings:-
My invention relates to the class of devices and instruments employed to control
the flow of electricity and is especially applicable to lightning arresters for use
with electric light and transmission of power conductors in which it can be used
with manifold advantages.
Hitherto it has been the object of electricians and others interested in electrical
science to construct a device which will permit of the passage of any undue static or
bigh potential induced atmospheric charge, to earth, without permitting the passage of
auy generated current from a dynamo or transformer, through the passage traversed
by such undue static or high potential induced atmospheric charge. Various
methods have hitherto been proposed and employed for accomplishing this end, as
for example: the interposition, in the earth, of a water resistance; such method
has many disadvantages, the chief of which is loss of power by partial short
circuit, it is not self contained and requires a very considerable amount of personal
attention added to other troubles.
The object of my invention is to dispense with such troubles, which I have done
by the construction of a device, which is absolutely self contained, is small and
compact and of large conductive capacity, and is capable of being adjusted so as
to offer the least resistance to the passage of undue static charges to earth, without

page_text: permitting of any passage whatsoever of the generated current through the passage
traversed by such undue static charge, and after once being adjusted to suit the
pressure of the circuit upon which it is used, needs no further attention whatso-
ever. To accomplish this end, I use (preferably); a tube of insulating material
which is partly filled with powdered wood carbon, (made preferably from ordinary
pine wood) the ends of such tube being closed with loose fitting hard carbon or
metal blocks which are made to project, and also to serve as terminals forming
electrical connection with the powdered wood carbon; if the wood carbon be com-
pressed as the result of external pressure upon the projecting ends of the hard
carbon or metal blocks, the resistance of the wood carbon will vary with the
pressure brought to bear upon it, the resistance becoming lower as the pressure
increases. A tube of 5 inches internal diameter and three inches long containing
two linear inches of powdered wood carbon and subjected to a pressure of
one pound, was found to have a resistance of two thousand ohms; at a pressure of
25 pounds the resistance was found to be one hundred ohms and was found to
become lower with greater pressures, and to increase and decrease in a corresponding
ratio with the amount of pressure employed.
The application of my invention is shown on the accompanying drawing. The
figure generally shows the arrangement of apparatus in multiple for the purpose
of presenting a low resistance path to earth for any undue static charge, which
at the same time will present an infinitesimal resistance to the passage of the
generated current from a dynamo or transformer.
Referring to the drawing; apparatus (B) is drawn in section for the purpose
of showing its general construction, being precisely similar to the apparatus (C. D)
which are shown in plan for the purpose of facilitating description.
(a) is a tube or cylinder of insulating material the outer ends of which are
screwed externally at (b. b), (c) indicates the powdered wood carbon contained
within the tube or cylinder (a), (d. d) are blocks of hard carbon which are made
to fit easily within the cylinder (a), which not only serve as buffers for compressing
the wood carbon (c), but serve also as electrodes for electrically connecting with
the powdered wood carbon (c); (e. e) are brass caps which are made to screw on
to the outer screwed ends (b. 6) of the tube or cylinder (a); it will be
observed that the cap (e) is deeper than the cap (e) which is shallower, and is
screwed on and fixed so as not to be removable; the cap (e) being made adjust-
able is made deeper than the cap (e) for the purpose of affording a greater range
of adjustment for regulating the pressure upon the hard carbon block (d) and
thereby varying the resistance of the powdered wood carbon (c); the metal
. caps (e. e) being in electrical contact with the hard carbon blocks (d. d') also serve
as terminals for connecting therewith; (f.f) are screws for securing electrical
connection with the device; (h) is a "tap wire' (from any ordinary lightning
arrester); with branches (i.) which are connected with the "air gaps" (g.g'g')
which are of any ordinary construction and which are connected to the
apparatus (B. C. D) by means of wires (h¹ h³ ³) the apparatus (B. C. D) being
connected to earth by means of the common earth wire (j. 1) and earth
plate (P).
It will be observed that the drawing shews the apparatus (B. C. D) connected
respectively in series with air gaps (9. g' g) which are of ordinary construction
and may be considered as a portion of any known lightning arrester with the
exception that I use three air gaps in the place of one; so that any static charge
that may be thrust from the lightning arrester will pass through wire (h) distributing
itself through branch wires (i. i), through air gap
apparatus (B. C. D), to earth by means of wires (and thence, through
earth plate (P), so
that by distributing static discharges through a multiple path in the manner
described, it will be readily understood that each of the apparatus (B. C. D) may
be of such high resistance, as to render it impossible for a sufficient quantity of
the comparatively low potential generated current, to pass as would maintain an
arc across the air gaps, while the combined arrangement of apparatus in multiple

page_text: will present a sufficiently low resistance to admit of an uninterrupted passage of
static discharges to earth.
It will of course be understood that the arrangement shown in the figure is
especially designed for use with lightning arresters, but other applications of my
invention will readily occur to electricians wherein it can be used with advantage;
I wish it to be understood that my invention is not limited to use with lightning
arresters only, but has manifold uses in the electrical industry.
I am quite aware of the fact that it is common knowledge that the resistance
of a great majority of substances may be varied with the application of pressure;
I do not claim to have discovered any new property pertaining to carbon in general,
or to wood carbon; but I claim to have invented a novel application and construction
of adjustable carbon resistance.
Having now particularly described and ascertained the nature of my inven-
tion and in what manner the same may be performed, I declare that what I
claim is :-
1. A carbon resistance, embodying the combination of a tube of non-conducting
material, containing powdered wood carbon upon which rest at both ends,
hard carbon or metal blocks which fit loosely in the tube, and over which
are caps which screw down upon the latter for the purpose of exerting
pressure upon the wood carbon contained therein, such pressure being variable at
will to regulate the flow of electricity, substantially as described in the foregoing
specification and illustrated on the accompanying drawing.
2. In combination with lightning arresters, the arrangement of a non-conducting
tube or tubes containing wood carbon, with hard carbon or metal blocks, and fitted
with screw caps; connected in series with an air gap, and also connected to each
"tap wire" as would form one of any lightning arrester, substantially as described
in the foregoing specification and illustrated on the accompanying drawing.
3. In combination with lightning arrester the arrangement of compressed wood
carbon resistance devices in multiple, connected in series with air gaps, and
connected to each "tap wire" as would form one of any lightning arrester, substan-
tially as described in the foregoing specification and illustrated on the accompanying
drawing.
Dated this 14th day of September 1896.
ABEL & IMRAY,
Agents for the Applicant.