Year: 1887

page_text: Date of Application, 2nd Feb., 1887.
Complete Left, 7th July, 1887.
Complete Accepted, 9th Aug., 1887.
WALTER THOMAS GOOLDEN of 2 Victoria Mansions, Westminster in the county of
Middlesex, electrical engineer, and SYDNEY EVERSHED of Kenley in the county of
Surrey, electrician, do hereby declare the nature of this invention to be as follows:-
In several electro-magnetic measuring instruments heretofore made, a small mass
of iron attached to an arbor is attracted by the current to be measured flowing in a
coil, against the attraction of gravity or a spring. The maximum rotation and range
of readings are usually small in such instruments, while the scale is often irregular.
The forces acting on the movable iron being small compared with the mass of the
movable system, small periodic variations of current in the coil produce large
oscillations in such instruments.
The objects of our invention are (1) to increase the maximum rotation of the movable
system to 90° or more, (2) to facilitate the construction of electro-magnetic
instruments with more regular scales and having any desired range of readings, and
(3) to check the oscillations of such instruments. Thus, according to our invention a
small mass of inagnetic material within a coil may be attached to an arbor lying along or
parallel to the axis of the coil, and the magnetic induction within the coil may be
directed and distributed by means of blocks of magnetic material fixed within the coil
of such shape and in such positions as shall give the instrument the range of readings
and rotation required. Thus a block of magnetic material within the coil having a
plane face next the movable magnetic material inclined to the plane of rotation of the
inovable system, will give a shorter or longer range of readings according as the
inclination is less or greater. The maximum rotation of the arbor will depend on the
angle between a line normal to the arbor passing through the movable magnetic

page_text: material, and a line in the plane of rotation parallel to the face of the fixed block of
magnetic material. Thus when these two lines are parallel the maximum rotation
will be 90°. The magnetic induction may be concentrated on the movable magnetic
material by means of the fixed blocks of the same so as to increase the magnetic force
and therefore require an increased opposing force; the forces being thus increased
without increasing the mass of the movable system to the same extent; the
oscillations due to small periodic variations of the current in the coil can thus be
checked.
Dated this Thinter first day of Januar 1007
COMPLETE SPECIFICATION.
Electric Measuring Instruments.
We, WALTER THOMAS GOOLDEN of 2 Victoria Mansions, Westminster in the county
of Middlesex, electrical engineer, and SYDNEY EVERSHED, of Kenley, in the county of
Surrey, electrician, 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 several electro magnetic measuring instruments heretofore made, a small mass
of iron attached to an arbor is attracted by the current to be measured, flowing in
a coil, against the attraction of gravity or a spring. The maximum rotation and
range of readings are usually small in such instruments, and the mass of the movable
system being large compared with the forces acting on the movable iron, small
variations of the current in the coil produce large oscillations of the movable system.
The objects of our invention are (1st) to increase the maximum rotation to 90° or
more (2nd) to facilitate the construction of electro magnetic instruments with any
desired range of readings, within certain limits; and (3rd) to check the oscillations
in such instruments.
According to our invention, a small mass of magnetic material, within a coil, is
attached to an arbor lying along or parallel to the axis of the coil, and the magnetic

page_text: field within the coil is directed and distributed by means of pieces of magnetic
material fixed within the coil for the purpose of giving the instrument the range of
readings and the rotation required; and also for the purpose of increasing the forces
acting on the movable system, so as to both check oscillation and overcome the
mechanical friction of the movable system.
One of the ways of carrying out our invention is shown in Figs. I, II and III of
the drawings attached; showing a plan, elevation, and cross section respectively, of
the working parts of an instrument in which gravity is used as the controlling force.
Within a coil T, T, (shown in section in Fig. 1) we fix a brass plug-piece B, which
serves to support a brass arbor A, pivoted in jewel holes at J, J; the arbor has a
light brass arm G, attached to it at the centre of the coil, which arm carries a small
rod of soft iron B; this rod lies in a direction parallel to the arbor and to the axis
of the coil; an index H, is fixed on the arbor outside the coil in a position and of such
weight as to balance the rod and arm. Outside the coil another arm carries a
weight W, to give the controlling force. When no current flows in the coil the
weight W, brings the movable system to rest in the position shown in Fig. III. that
is to say with the arm G and the index H at about 45° to the vertical. The index H
ranges over a suitable scale on a dial in the usual manner.
The brass plug D is cut away throughout a large portion of its length to a nearly
semicircular section, on the flat surface of which are fixed two blocks of soft
iron P, P one on each side of the rod B, leaving sufficient space between them to
allow of the free rotation of the arbor and rod. The adjacent faces of the blocks
are not parallel, but shaped as shown in Fig. I; so that as the arbor rotates the
ends of the rod B approach the faces of the blocks. The range of readings is
determined by the angle, indicated in Fig. I by the dotted lines E, between the plane
of one face of a block and a plane at right angles to the axis of the coil, and we
prefer to make this angle about 6° which we find gives as long a range as is consistent
with an open scale, since the total rotation cannot exceed 90° in an instrument
controlled by gravity. One of the corners of each block, namely that nearest to the
zero position of the rod B, is rounded off as shown, in order to make the scale of the
instrument more uniform.
-
The working of the instrument described above, is as follows:-The current to be
measured flowing in the coil creates a magnetic field which would be nearly uniform
within the coil, but for the effect of the blocks P, P; the latter not only greatly
increase the strength of the field in the space between them but in consequence of
their inclined faces produce a field which is not uniform, being strongest where the
faces are nearest; the rod is therefore attracted in the direction of the arrow towards
the stronger portion of the field, and rotates the arbor until the magnetic attraction
is balanced by the force due to the weight W.
Although for most purposes we prefer to use gravity as the controlling force, we
do not claim the employment of gravity as part of our invention; and it is obvious
that the instrument described may be controlled by a spring, instead of the weight W,
acting on the arbor. Thus for use on board ship we modify the construction of
the instrument in order that a spring may be used to the best advantage. The iron
blocks in such an instrument take the form of thick iron tubes concentric with the
axis of the coil and with the axis of the movable system; the adjacent ends of the
tubes, between which the iron rod moves, are not parallel to each other but are
shaped so that the distance between them continuously diminishes in one direction;
thus the magnetic field continuously increases in that direction and the rod is
attracted towards the stronger portion of the field, and rotates the arbor until the
magnetic attraction is balanced by the force of a metal spring acting on the arbor.
A wide longitudinal slit is made in each tube between the zero position of the rod
and the position of maximum deflection in order to ensure the rod being always
attracted in one direction. The angular width of the slit should be not less than 90°.
The movable system in this form of instrument must be very carefully balanced so
that its centre of gravity lies exactly in its axis of rotation. A range
of 180° or
more may be used in this instrument.

page_text: Instruments constructed according to our invention may have their coils wound
either as voltmeters or as ampère-meters, and we prefer to use from 200 to 600
ampère-turns on the coil.
Having now particularly described and ascertained the nature of our said Invention,
and in what manner the same is to be performed, we declare that what we claim is :-
(1) In an electric measuring instrument, the employment of fixed pieces of
magnetic material to distribute the magnetic field within a coil, as, and for the
purposes, set forth.
(2) In an electric measuring instrument, the employment of fixed pieces of
magnetic material to increase the force operating the movable system, as, and for the
purposes, set forth.
(3) In an electric measuring instrument, the combination, within a coil, of fixed
pieces of magnetic material operating a movable rod of magnetic material,
substantially as described.