Improvements in Electrodynamometers.
Year: 1895

page_text: Date of Application, 2nd Feb., 1895
PROVISIONAL SPECIFICATION.
Improvements in Electrodynamometers.
We, SIEMENS BROTHERS & Co. LIMITED, and EDWARD FRIEDRICH
HEINRICH HERMANN LAUCKERT, of 12 Queen Anne's Gate, Westminster, in
the County of Middlesex Electrical Engineers, do hereby declare the nature of
this invention to be as follows:-
This invention relates to the well known Siemens electrodynamometer, in which
a swinging coil is combined with a stationary coil in such manner that on passing
the current to be measured through both coils in series, the swinging coil tends to
assume an angular position relatively to the fixed one which is proportionate to the
square of the strength of the current. The tendency to assume an angular
position is counteracted by the torsion of a helical spring; and since the torsion is
thus proportional to the square of the current strength, the range of any single
instrument is somewhat limited. With these electrodynamometers, when the
current to be measured is considerable the cost of the apparatus is disproportionately
great, as compared with that of apparatus for currents of small strength, on account
of the necessity of making the swinging coil and the mercury cups very large for
carrying the full current.
The present invention has for its object to reduce the cost of such dynamo-
meters for large currents, and at the same time to obtain instruments with very
wide range, and consists in constructing them of two separate stationary coils and
swinging coils arranged as follows.
The two stationary coils which we will term A and B are connected together at
the terminal to which the conductor of the current to be measured is connected, so
that a portion of the entering current flows through each coil. The current from
the one stationary coil, say, B, flows on directly to the place of consumption, while
that passing through the coil A flows first through the swinging coil of A, thence
through a series of adjustable resistances to the swinging coil of B, and thence it
joins the current passing away from B.
From this it will be seen that, firstly, owing to the said resistances only a very
small proportion of the total current will be made to pass through the coil A and
the two swinging coils, so that these parts and the mercury cups can be kept very
small proportionately to the total current passing through the combined apparatus,
and secondly, a very considerable range of indications can be obtained by the
combined apparatus according to the extent of the resistances included in the
branch circuit of A. Thus if, for example, A be constructed to measure
from 1 ampere to 20 amperes and the resistance in A. be made 50 times that of B,
then it follows that the current in B can vary from 50 to 1,000 ampères.
If on the other hand the resistance included in A be made equal to 500 times
that of B, then the current in B can vary from 500 to 10,000 ampères. Thus by
varying the amount of resistance included in the circuit of A (the exact value of
which resistance need not be known) the range of this instrument can be varied
within very wide limits..
:
For central stations where a number of instruments are required in the same
room, only a single auxiliary instrument A may be combined with any number of

page_text: main current instruments, a regulator being preferably provided for keeping the
current in all the swinging coils constant.
Dated this 2nd day of February 1805
ABEL & IMRAY,
Agents for the Applicants.
Improvements in Electrodynamometers.
We, SIEMENS BROTHERS & Co. LIMITED, and EDWARD FRIEDRICH
HEINRICH HERMANN LAUCKERT, of 12 Queen Anne's Gate, Westminster, in
the County of Middlesex, Electrical Engineers, 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 the well known Siemens' electrodynamometer in which
a swinging coil is combined with a stationary coil in such manner that on passing
the current to be measured through both coils in series the swinging coils tends to
assume an angular position relatively to the fixed one which is proportionate to
the square of the strength of the current. The tendency to assume an augular
position is counteracted by the torsion of a helical spring, and since the torsion
is thus proportional to the square of the current strength, the range of any single
instrument is somewhat limited. With these electrodynamometers when the
current to be measured is considerable the cost of the apparatus is dispro-
portionately great, as compared with that of apparatus, for currents of small
strength, on account of the necessity of making the swinging coil and the mercury
cups very large for carrying the full current.
The present invention has for its object to reduce the cost of such dynamometers
for large currents, and at the same time to obtain instruments with very wide
range, and consists in constructing them of two separate stationary coils and
swinging coils arranged as follows:-
The two stationary coils which we have designated by A and B on the
accompanying diagram are connected together at the terminal 1 to which the
conductor of the current to be measured is connected so that a portion of
the entering current flows through each coil. The current from the stationary
coil, say B flows on directly to the place of consumption through terminal 2
while that passing through the coil A flows first through the suspended swinging
coil a controlled by a torsion spring 7 thence through a series of adjustable
resistances R to the suspended swinging coil controlled by a torsion spring 8,
and thence it joins the current passing away from coil B.
'
The resulting angular deflection of the two coils a and b may be utilised in
various ways for indicating the strength of the current, in the arrangement
shewn by way of example on the accompanying diagram, the axes of the
swinging coils a and b are provided with pointers 5 and 6 which, for convenience
in manipulation, we arrange with their ends close together, and we adjust the
torsion springs 7 and 8 through sets of bevel wheels 9 and 10 by the two hand
wheels 11 and 12. To these bevel wheels are attached pointers 13 and 14 which
indicate on a divided dial the angle of torsion required on springs 7 and 8..to
bring the pointers 5 and 6 to zero. Handwheel 11 works pointers 5 and 13. and
handwheel 12 works pointers 6 and 14; to prevent mistakes in reading, one
handwheel with its respective pointers may be painted one colour, and the other
set another colour.
"
The mode of working the instrument is as follows:-When the current to be
measured passes through the instrument both pointers 5 and 6 will be deflected ;
the handwheels 11 and 12 are turned until the pointers 5 and 6 are brought back

page_text: to the zero position, when the angles of torsion are read off by the positions which
the pointers 13 and 14 indicate on the dial. Should the current to be measured be
so large that the torsion which can be put on either spring 7 or 8 is not sufficient
to bring the pointers 5 or 6 to zero, it will be necessary to increase the resistance R
until the current flowing through A. a. R. and b is sufficiently reduced to be able
to take readings on pointers 13 and 14. The total current measured will then
✓ angle of torsion on A × constant A + angle of torsion on B x constant B
divided by angle of torsion on A x constant A. Constant A is determined in
the same way as that of an ordinary electrodynamometer. The constant B can be
calculated from the above formula when the total current which has been measured
is known.
be =
For central stations where a number of instruments are required in the same
room, only a single auxiliary instrument A a R may be combined with any number
of main current instruments, a regulator being preferably provided for keeping the
current in all the swinging coils constant.
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. An electrodynamometer, consisting of the combination of two stationary coils
and two suspended swinging coils controlled by torsion springs, these several parts
being so arranged that one portion of the current to be measured is made to pass
directly through the one stationary coil to the supply conductor, while another
portion after passing through the second stationary coil, both swinging coils, and
through a resistance also passes to the supply conductor, the extent of the resulting
angular deflections of both swinging coils being made by suitable means to indicate
the strength of the current, substantially as described.
2. An electrodynamometer with two stationary and two swinging coils combined
and operating substantially as herein described with reference to the accompanying
drawing.
Dated this 25th day of October 1895.
ABEL & IMRAY,
Agents for Applicants.