Improvements in Apparatus for Varying the Strength and Direction of Electric Currents.
Year: 1892

page_text: Date of Application, 26th July, 1892
Complete Specification Left, 8th Apr., 1893-Accepted, 13th May, 1893
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Varying the Strength and Direction
of Electric Currents.
We, JAMES ALFRED EWING, Professor of Mechanism and Applied Mechanics
in the University of Cambridge, and CHARLES GEORGE LAMB, Demonstrator of
Engineering, Engineering Laboratory, Cambridge, do hereby declare the nature of
this invention to be as follows:-
In certain applications of electric currents it is desired to make the current vary
from a positive to an equal negative value, and back again, in a continuous gradual
manner, instead of suddenly, as when an ordinary reversing commutator is used.
The object of our invention is to provide a convenient means of doing this when
the source of current is a battery or continuous current dynamo or other non-
alternating source. For this purpose we employ a non-conducting vessel, generally
cylindrical, containing a conducting liquid, with a pair of conducting plates
immersed in the liquid & fixed, preferably to the sides of the vessel at opposite
ends of a diameter. Another pair of conducting plates is also immersed in the
liquid and is supported on opposite sides of a revolving boss within the vessel, or
otherwise in such a manner that they are free to turn, with the effect that when
they are turned one of them passes close to one of the fixed plates at the same
time that the other passes close to the other fixed plate. The two revolving plates
may conveniently be carried on a solid cylinder or boss which nearly fills the vessel,
leaving an annulus in which there is conducting liquid. The liquid in this annulus
acts as conductor between the fixed & the revolving plates. The revolving plates
are electrically connected by collecting rings & brushes to a pair of terminals.
One pair of plates is electrically connected to the source of electricity; the other
pair supplies the variable current when the revolving plates are turned. Thus,
calling the fixed plates A & A', let A be connected to the positive side of the
source & A to the negative side. Calling the revolving plates B & B', B will
positive when it is near A, & B' will then be near A¹ & will be negative. Then,
as the plates turn, their difference of potential diminishes, passes through zero, and
becomes reversed when B is near A & B is near A. As the revolution continues
the difference of potential will again pass through zero and return to its original
value. The plates may conveniently be of amalgamated zinc and the conducting
liquid a solution of sulphate of zine. By giving various forms to the plates various
modes of variation of the current may be arranged. The waste of current which
occurs through direct conduction from one plate to the opposite plate, in the pair
connected to the source, is made comparatively small by using a narrow annulus of
conducting liquid, which may be formed either between the wall of the containing
vessel & the surface of a revolving boss, or between an outer & an inner fixed wall,
the revolving plates being then carried by an independent support.
Dah dan of L. 1809
J. A. EWING.
C. G. LAMB.

page_text: COME LEIE DE MULLICATION.
Improvements in Apparatus for Varying the Strength and Direction
of Electric Currents.
We, JAMES ALFRED EWING, of Langdale Lodge, Cambridge, Professor of
Mechanism and Applied Mechanics, Cambridge University, and CHARLES
GEORGE LAMB, Engineering Laboratory, Cambridge, Demonstrator in Mechanism
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:—
In certain applications of electric currents it is desired to make the current vary
from a positive to an equal negative value, and back again, in a continuous gradual
manner, instead of suddenly as when an ordinary reversing commutator is used.
The object of our invention is to provide a convenient means of doing this when
the source of current is a battery or continuous-current dynamo or other non-
alternating source. For this purpose we employ a non-conducting vessel, generally
cylindrical, containing a conducting liquid with a pair of conducting plates
immersed in the liquid and fixed, preferably to the sides of the vessel at opposite
ends of a diameter. Another pair of conducting plates is also immersed in the
liquid and is supported on opposite sides of a revolving boss within the vessel, or
otherwise in such a manner that they are free to turn, with the effect that when
they are turned one of them passes close to one of the fixed plates at the same
time that the other passes close to the other fixed plate. The two revolving
plates may conveniently be carried on a revolving solid cylinder or boss of non-
conducting material, which nearly fills the interior of the vessel, leaving an annulus
in which there is conducting liquid. The liquid in the annulus acts as conductor
between the fixed and the revolving plates. The revolving plates are electrically
connected by collecting rings and brushes to a pair of terminals. One pair of
plates is electrically connected to the source of electricity; the other pair supplies
the variable current when the revolving plates are made to turn. Thus, calling the
fixed plates A and A', let A be connected to the positive side of the source and A¹
to the negative side. Calling the revolving plates B and B', B will be positive
when it is near A, and B¹ will then be near A and will be negative. Then, as the
plates turn, their difference of potential diminishes, passes through zero, and
becomes reversed when B is near A¹ and B' is near A. As the revolution
continues the difference of potential will again pass through zero and return to its
original value. The plates may conveniently be of amalgamated zinc and the
conducting liquid a solution of sulphate of zinc. By giving various forms to the
plates various modes of variation of the current may be arranged. The waste of
current which occurs through direct conduction from one plate to the opposite
plate, in the pair connected to the source, is made comparatively small by using a
narrow annulus of conducting liquid, which may be formed between the wall of the
containing vessel and the surface of the revolving boss, or between an outer and
an inner fixed wall, the revolving plates being then carried by an independent.
support.
Figs. 1 and 2 show one form of this apparatus in sectional elevation and plan.
The plates B B' are in this case carried by a revolving boss of slate which is free
to turn within the stoneware vessel C. This vessel also contains the stationary
plates A A'. The plates are of zinc and the space between is filled with a weak
solution of sulphate of zinc. The plates A. A' are wider at the middle than at the
top and bottom in order to make the current increase and diminish less suddenly
than it would do if they were of uniform width. Contact is made with the
revolving plates by means of the brushes D which rub on rings carried by the
spindle of the revolving boss.

page_text: Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. Continuous commutators for electric currents in which gradual variation and
reversal of the currents is effected by means of a pair of fixed conductors together
with a pair of revolving conductors, both pairs being immersed in a conducting
fluid.
2. The continuous commutator consisting of a revolving boss carrying two
conductors and immersed in a conducting fluid along with a pair of fixed conductors,
substantially as described.
J. A. EWING.
C. G. LAMB.