Improvements in Electric Measuring Instruments.
Year: 1896

page_text: Date of Application, 13th Jan., 1896
Complete Specification Left, 12th Sept., 1896-Accepted, 7th Nov. 1896
PROVISIONAL SPECIFICATION.
Improvements in Electric Measuring Instruments.
We EVERSHED & VIGNOLES LTD., of 1, Woodfield Road, Harrow Road,
London W. Electrical Engineers, and SYDNEY EVERSHED of the same address,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to that class of electric measuring instruments in which
the whole or a portion of the current to be measured traverses a coil capable of
rotation in a fixed magnetic field, and its object is to facilitate the construction and
repair of such instruments by mounting the movable coil (herein called "the coil")
together with its axle, controlling springs and index in a framework so designed as to
enable the coil and framework to be removed from the remainder of the instrument
without separating the several parts of the magnetic system which is used to produce
the fixed magnetic field.
According to our invention the magnetic system may comprise a permanent
magnet bent into a ring or other convenient shape, with its two poles formed like the
pole pieces of an ordinary two-pole dynamo. Between the two poles and concentric
with their circular bore a hollow soft iron core of cylindrical shape may be fixed
so as to close the magnetic circuit with the exception of a narrow annular space or
air gap.
The coil will be like a single coil of a two-pole continuous current dynamo with
the exception that instead of both ends being straight and at right angles with the
sides forming a rectangular coil, only one end is to be straight and at right angles
with the sides. The other end when wound should be semicircular of a diameter
equal to the radial breadth of the coil, and after the winding is completed, one
half of the wires in the semicircular end are bent until they are in a plane at
right angles to the plane of the rectangular portion of the coil. The other half
of the wires are bent similarly but in the opposite sense until the two semi-
circular halves form a ring in one plane at right angles to the plane of the
rectangular portion of the coil. The complete coil so formed is to be fixed to
a rigid frame which is itself fixed to an axle so that the coil may be free to rotate
on an axis lying in the plane of the rectangular portion of the coil and passing
through the centre of the circular ring end of the coil. When the instrument is
to be a periodic or "dead beat" in its movements the frame to which the coil is
attached may conveniently be made of some metal of high conductivity.
The axle is to be pivotted in a framework designed to allow free rotation of the
ccil through about ninety degrees, and it should also carry the supports to which
the fixed ends of the controlling springs are attached. If it is desired to provide
a zero adjustment for the springs their fixed ends may be attached to a ring sprung
into a circular recess in the framework and co-axial with the axis of rotation of
the coil.
When the framework is put into its place in the instrument the ring end of
the coil passes easily through the annular air gap of the magnetic circuit and
when in its proper position the straight end of the coil just clears one end of
the framework which itself just clears the flat end of the soft iron core. The two
straight sides of the coil lie in the air gap at right angles to the magnetic
induction, while the ring end of the coil is in a space purposely left in the pole

page_text: pieces and core at the end where the latter is fixed to the frame or base plate which
serves to carry the several parts of the magnetic system.
The current may be led into the coil through the controlling springs or separate
flexible connecting wires may be employed in which case only one controlling spring
will be necessary. A light index attached to the axle and ranging over a
dial serves to indicate in the usual manner the strength of the current flowing in
the coil.
An instrument constructed in accordance with this invention may be used as a
voltmeter by placing a large fixed resistance in series with the coil, or as an ammeter
by connecting the coil as a shunt on a low resistance traversed by the current to be
measured. This invention is also applicable to the movable coils of wattmeters
and in general to any electrical instrument in which a movable coil is required to
operate in a magnetic field.
Dated this 2nd day of January 1896.
EVERSHED & VIGNOLES, LIMITED,
HORACE M. GREGORY, Directors.
ERNEST B. VIGNOLES, S
We, EVERSHED & VIGNOLES, LTD., of 1 Woodfield Road, Harrow Road,
London W. Electrical Engineers, and SYDNEY EVERSHED, of the same address,
Electrical Engineer, 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 that class of electric measuring instruments in which the
whole or a portion of the current to be measured traverses a coil capable of rotation
in a fixed magnetic field, and its object is to facilitate the construction and repair
of such instruments by mounting the movable coil (herein called "the coil")
together with its axle, springs or other controlling force in a framework so designed
as to enable the coil and framework to be removed from the remainder of the
instrument without separating the several parts of the magnetic system which is
used to produce the fixed magnetic field.
According to our invention the magnetic system may comprise a permanent
magnet bent into a ring or other convenient shape, with its two poles formed like
the pole pieces of an ordinary two-pole dynamo. Between the two poles and
concentric with their circular bore a hollow soft iron core of cylindrical shape
is fixed so as to close the magnetic circuit with the exception of a narrow annular
space or air gap.
The coil is like one coil on the drum armature of a two-pole continuous current
dynamo with the exception that instead of both ends being straight and at right
angles with the sides forming a rectangular coil, only one end is straight and at right
angles with the sides. The other end when wound should be semicircular of a
diameter equal to the radial breadth of the coil; and after the winding is completed,
half of the wires in the semi-circular end are bent until they are in a plane at
right angles to the plane of the rectangular portion of the coil, and the remainder
of the wires are bent similarly but in the opposite sense until the two semi-circular
halves form a ring in one plane at right angles to the plane of the rectangular
portion of the coil. The complete coil so formed is fixed to a rigid frame which
is itself fixed to an axle so that the coil may be free to rotate on an axis lying in
the plane of the rectangular portion of the coil and passing through the centre of

page_text: the circular ring end of the coil. When the instrument is to be a periodic or
"dead beat" in its movements the frame to which the coil is attached may
conveniently be made of some metal of high conductivity.
The axle is pivotted in a framework designed to allow free rotation of the coil
through about ninety degrees, and it should also carry the supports to which the
fixed ends of the controlling springs are attached. If it is desired to provide a zero-
adjustment for the springs their fixed ends may be attached to a ring sprung
into a circular recess in the framework and co-axial with the axis of rotation of
the coil.
When the framework is put into its place in the instrument the ring end of the
coil passes easily through the annular air gap of the magnetic circuit and when
in its proper position the straight end of the coil just clears one end of the frame-
work which itself just clears the flat end of the soft iron core. The two straight
sides of the coil lie in the air gap at right angles to the magnetic induction, while
the ring end of the coil is in a space purposely left in or beyoud the pole pieces and
core at the end where the latter is fixed to the base plate which serves to carry the-
several parts of the magnetic system.
The current may be led into the coil through the controlling springs, or separate
flexible connecting wires may be employed in which case either one controlling
spring or a gravity control can be employed. A light index attached to the axle
and ranging over a dial serves to indicate in the usual manner the strength of the
current flowing in the cuil.
The accompanying drawings show the essential features of a measuring instrument.
constructed in accordance with our invention.
Fig. 1 is a front elevation with a portion of the dial removed.
Fig. 2 is a section on the vertical centre line of Fig. 1, and
Fig. 3 is a section across the pole pieces.
In Figs. 2 & 3 the coil and othe" moving parts are shown in elevation.
In all three figures like letters refer to the same parts.
M is the rectangular coil attached at one end E to the axle A and having the-
circular portion R at the opposite end. The axle is pivotted at J J in a brass
frame FF which is fixed to the dial D by means of screws not shown. The
coil is free to rotate in the annular air gaps between the pole pieces PP and
hollow cylindrical core C. The magnetic induction is derived from a permanent
magnet N S whose poles are in close magnetic contact with PP. The pole pieces.
and core are fixed to suitable projections on the brass base plate B, to which the
dial is also attached by means of pillars.
An index I is attached to the axle and ranges over a scale on the dial. When,.
as in the instrument shown, a spring control is used the scale will be one of nearly
equal parts. With a gravity control the scale will be one in which the distances.
between successive divisions corresponding to equal increments of current will
gradually increase from zero upwards. With a spring control as shown it is
convenient to lead the current from an insulated terminal at T to one end of
the coil by means of a flexible wire L. The other end of the coil being soldered
to the axle, the current is able to return by means of the working spring W to a
second terminal at T. The jewelled centres at J J serve to insulate the coil from.
the body of the instrument. The terminals T to which the spring W and wire L
are attached, are fixed to a split ring Z which is snapped into a recess turned in.
the flange of the frame F, and the index can be adjusted to zero by rotating the
split ring.
In Figs. 1 & 2 the coil is shown in the position it occupies when the index is at.
zero, while the position of the coil in Fig. 3 corresponds to a deflection half way
between zero and the maximum reading of the scale.
An instrument constructed in accordance with this invention may be used as a
voltmeter by placing a high resistance in series with the coil, or as an ammeter by
connecting the coil as a shunt on a low resistance traversed by the current to be
measured. This invention is also applicable to the movable coils of wattmeters,.

page_text: and in general to any electrical instrument in which a movable coil is required to
operate in a fixed magnetic field.
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) In an electric measuring instrument of the class specified, a movable coil
system adapted to be inserted into and withdrawn from the fixed magnetic system
without displacing or disturbing the component parts of either system; substantially
as described.
(2) In an electric measuring instrument of the class specified, a movable coil
having three rectangular sides in an axial plane and one circular end at right angles
thereto, for the purpose set forth and substantially as described with reference to
the accompanying drawings.
(3) An electric measuring instrument substantially as described with reference
to the accompanying drawings.
Dated this 12th day of September 1896
EVERSHED & VIGNOLES, LIMITED,
E. B. VIGNOLES,
Managing Director.