Improvements in Ammeters and Voltmeters.
Year: 1893

page_text: Date of Application, 27th July, 1893
Comp ete Specification Left, 25th Apr., 1894-Accepted, 30th June, 1894
PROVISIONAL SPECIFICATION.
Improvements in Ammeters and Voltmeters.
1, ERNEST FRANCIS MOY, of 20 Loraine Road, Holloway, in the County of
London, Electrical Engineer, do hereby declare the nature of this invention to be
as follows:-
This invention relates to the class of electrical instruments known as ammeters
and voltmeters used in measuring the quantity and electro motive force of electric
currents, the object being to construct such instruments in a manner allowing of
comparatively rough handling without liability to get out of order, while they are
sensitive and reliable in action.
In the case of ammeters, I mount within a case a coil of thick copper, having a
few turns, and which is intended to magnetize the core of an electro magnet,
pivoted within the coil. I preferably form the coil by cutting a coarse thread
upon and through a copper tube, and I make circuit connections therewith at the
top and bottom of the coil at right angles to the axis of the coil: The iron core
of the electro magnet is sometimes made hollow, but in any case it is provided at
the ends with pivots supported in jewelled or other suitable bearings. The lower
end of the core is formed with or carries an elongated pole piece having two
ends; and a double yoke springs from the upper part of the core, bends
downward, and is brought with its two extremities in close proximity to the
central pole piece aforesaid. The exciting coil is thus placed surrounding the
core, but is itself enclosed at two opposite points by the double yoke, and its
thickness-together with the usual working clearance-forms the width of the
gap between the central pole piece and the extremities of the double yoke.
Consequently, the two ends of the central pole piece forms à pole of the same
name, while the two ends of the double yoke form an outer pole of the opposite
name, with a part of the exciting coil between the poles. This latter named, part
of the coil is elongated and cut through at the working range of the poles, to form
an oblong hole on each of the opposite sides, so that the current passes at the two
ends of each hole on its way to or from the exciting coil.
In the case of a voltmeter, a high resistance solenoid takes the place of the
aforesaid coil, and two flattened coils of many turns of fine wire are oppositely
placed in such a position at the gap as to act simultaneously upon the respective
arms of the double yoke. The fine wire coils are wound upon thin wood bobbins,
and that part of each bobbin traversed by its corresponding arm of the double
yoke is cut away so as to bring the polar surfaces in close proximity to the coils.
In some cases I employ a single yoke electro magnet instead of the two arm or
double yoke above described. The core is, in general respects, constructed and
arranged as before, but a thin strip of soft iron is magnetically connected to each
end of the core, extending therefrom at right angles to fully clear the exciting
coil, and then bending them towards each other to form poles; a gap being left
between the ends of the strips. For ammeters, the exciting coil which surrounds
the core is connected at one end with a wide and thin copper conductor from one
of the terminals, and in any convenient manner to the other. But the wide
conductor is so arranged and adapted in position that it lays in the centre of the
aforesaid gap between the strips. Consequently, the magnetic lines of force-in

page_text: "
their circuit-have to pass the gap and copper conductor; the width of the gap,
and clearance between the poles and the wide conductor being made as small as
practicable. The width of the wide conductor, and the polar strips, together with
their relative position are such that the poles are always over some portion of the
conductor within the range of movement allowed. With the needle at zero, the
poles enclose a portion of the conductor at or near one edge thereof, while with
the needle at the other extremity of the scale, the poles correspondingly enclose a
portion of the conductor at or near its opposite edge; its width being therefore
proportioned to the length of arc traversed by the poles. By making the latter
named edge of the conductor thicker than the zero edge, there is a greater flow of
current along the edge of largest area with a corresponding action upon the upper
range of the indicating needle; and this enables us to mark proportionately wider
divisions than is usual at the upper end of the scale. Other parts of the scale are
modified by corresponding means.
For voltmeters constructed with the single yoke electro magnet, a solenoid
..wound with fine wire takes the place of the coiled conductor used in the ammeter,
and a flattened coil of many turns of fine wire replaces the wide conductor last
described. The flattened coil can be varied in its sectional area in any required
part by suitable winding, substantially in the same manner and for the same purpose
as described for ammeters with the wide conductor, and its bobbin is cut away, as
before stated, where traversed by the magnet poles.
A suitable counterweight is used for the single yoke magnet, and the indicating
needle is suitably mounted in any known manner.
Dated this 26th day of July 1893.
FAIRFAX & WETTER,
433, Strand, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Ammeters and Voltmeters.
I, ERNEST FRANCIS MOY, of 20 Loraine Road, Holloway, in the County of
London, Electrical Engineer, do bereby 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 class of electrical instruments known as ammeters
and voltmeters, used in measuring the quantity and potential energy of electric
currents. The object of the invention is to so construct the said instruments as to
allow of comparatively rough handling without liability to get out of order, while
making them sensitive and reliable in action.
Reference is made to the accompanying drawings, in which
Fig. 1 is a plan of an ammeter in its case, with the top bearing plate and scale
omitted;
Fig. 2 is an elevation of the principal parts of Fig. 1 showing the top bearing
plate, but omitting the case;
Fig. 3 is a section through Fig. 2, and
Fig. 4 is a sectional plan of Fig. 1.
Fig. 5 is a face view or plan of a voltmeter as it appears when ready for
indicating the potential energy in an electric circuit, Fig. 6 is a sectional elevation
through the same;
Fig. 7 is a face view or plan of Fig. 5 but with the scale and top bearing plate
omitted,
Fig. 8 is a plan, and Fig. 9 an elevation of a flattened coil of many turns of fine
wire;

page_text: Fig. 10 is a section through an ammeter coil somewhat ŝimilar to Fig. 3 but with
a single magnetic yoke instead of a double one; and
Fig. 11 is a transverse section through the wedge-shaped conductor shown in
Fig. 10.
For ammeters (Figs. 1 to 4) I mount within the case a, a coil & of thick copper
having a few turns, which is intended to magnetize the core c of an electro magnet
provided within the coil. I preferably form the coil 6 of a piece of copper tube,
of suitable thickness and length, upon which a coarse thread is cut along part of its
length and entirely through its thickness, thus forming a spiral ending in a short
tube; and make circuit connections therewith at right angles to its axis. The
iron core c of the electro-magnet, is sometimes made hollow, but in any case it is
provided at the ends with pivots d, supported in jewelled or other suitable bearings.
The lower end of the core c is formed with or carries an elongated pole piece c
having two oppositely placed radial arms, the ends of which closely approach the
interior of the coil b. A double yoke c² of iron springs from the upper part of the
core c, bends downward, and is brought with its two extremities in close proximity
(on the outside of the coil ) to the central pole piece el aforesaid. The exciting
coil b is thus placed surrounding the core c but is itself enclosed at two opposite
points, c, and the thickness of the copper tube-together with the usual working
clearance forms the width of the gap between the central pole piece c¹ and the
extremities of the double yoke c². Consequently the two ends of the central pole
piece e form poles of the same name, while the two ends of the double yoke c2 form
outer poles of the opposite name, with the tubular part of the exciting coil b
between opposite poles. This latter uamed part of the coil is cut through at a
point outside the working range of the poles in the form of an oblong hole & on
each of the opposite sides, as shown in Figs. 2 and 3; so that the current passes
along that part of the copper tube which lies between the poles, on its way to or
from the exciting coil, in accordance with the direction of current through the
instrument.
The magnetic lines of force pass through the conductor at right angles to the
direction of the current. The length of the oblong holes, referred to above, is
such that the polar strips are always separated by (together with the usual working
clearance) some portion of the tubular part of the coil or conductor within the
predetermined range of movement, and these said parts of the conductor are made
of varying or tapered cross section (as shown in Figs. 4, and 11) so as to cause
more current to flow along the thickened part as, and for the purpose, more fully
described hereinafter.
In the case of a voltmeter, (shown by Figs. 5 to 9) a high resistance solenoid e
takes the place of the aforesaid coil b, and two flattened coils el of many turns of
fine wire are oppositely placed (as shown in Figs. 6 and 7) at the gap between the
poles e¹ and as to act simultaneously upon the respective arms of the double yoke.
The fine wire coils el are wound upon thin wood or ebonite bobbins, and that part
of the bobbin traversed by the poles c' and c³ is cut away (as shown at e², Figs. 7, 8
and 9) to admit of bringing the polar surfaces in close proximity to the coils.
These coils (e) can also be varied in sectional area by suitably winding the con-
ductor to act as, and for the purpose of the tapered solid conductor referred to in
the case of ammeters.
In some cases I employ a single yoke electro magnet, instead of the two arm or
double yoke above described. The core is, in general respects, constructed and
arranged as before, but a thin strip of soft iron c is magnetically connected to each
end of the core c extending therefrom at right angles to fully clear the exciting coil,
and then each is bent towards the other to form poles; a gap being left between
the ends of the strips, as shown in Fig. 10.
For ammeters, the exciting coil which surrounds the core is connected at one end
with a wide and thin copper conductor from one of the terminals, and in any
convenient manner to the other. But the wide conductor is so arranged and

page_text: adapted in position that it lays in the centre of the aforesaid gap between the
strips. Consequently, the magnetic lines of force-in their circuit-have to pass
the gap and copper conductor; the width of the gap, and clearance between the
poles and the wide conductor, being made as small as practicable. The width of
the wide conductor, and the polar strips, together with their relative position are
such that the poles are always over some portion of the conductor within the range
of movement allowed. With the needle at zero, the poles enclose a portion of the
conductor at one or near one edge thereof, while with the needle at the other
extremity of the scale, the poles correspondingly enclose a portion of the conductor
at or near its opposite edge; its width being therefore proportioned to the length
of arc traversed by the poles. By making the latter named edge of the conductor
thicker than the zero edge, as shown at Fig. 11, there is a greater flow of current
along the edge of largest area with a corresponding action upon the upper range of
the indicating needle; and this admits of marking proportionately wider divisions
than is usual at the upper end of the scale. Other required parts of the scale are
similarly enlarged or reduced by increasing or reducing the thickness at the
corresponding part of the conductor. The thickness of the coil is similarly
varied at the required parts, in connection with the double yoke arrangement in
Fig. 4.
-
For voltmeters constructed with the single yoke electro magnet, a solenoid
wound with fine wire takes the place of the coiled conductor used in the ammeter,
and a flattened coil of many turns of fine wire replaces the wide conductor last
described. The Hattened coil can be varied in its sectional area in any required
part by suitable winding, substantially in the same manner and for the same
purpose as described for ammeters with the wide conductor, and its bobbin is cut
away, as before stated, where traversed by the magnet poles.
It is found that the double yoke magnetic circuit arrangement is practically
astatic, but in order to ensure this more perfectly in practice, it is found better to
avoid using iron strips (which may vary somewhat in sectional area) for the arms c²
of the double yoke, and use iron wire instead, on account of its sectional area being
more uniform.
It is to be, understood that the magnetic gaps, in the case of the double yoke
electro magnet, and the magnetic gap in the case of the single yoke arrangement,
may be so adapted in combination with either of the instruments that movements
take place in either a vertical or a horizontal plane. A suitable counterweight f
Fig. 10, is used to bring the pointer to zero when no current is passing; and the
indicating needle is suitably mounted in any known manner.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
1 claim is :-
1. In an ammeter, the combination of an exciting coil having circuit con-
nections and with a magnet core e pivoted within the said coil and carrying
arms c and c³, substantially as and for the purpose herein shown and described.
2. In a voltmeter, the combination of an exciting coil e, with one or two flattened
coils e, and a pivoted magnet core c carrying arms e¹ and c³, substantially as and
for the purpose herein shown and described.
3. A coil formed by cutting a coarse thread upon and through a copper tube,
and provided with holes at opposite points thereof, substantially as and for the
purpose herein shown and described with reference to Figs. 2 and 3.
4. The combination of two flattened coils of fine wire e', having the shell cut
away at e to expose the conductor, combined with a double yoke electro magnet
having poles c¹ and 2 adapted to work over the coils at the said points es, sub-
stantially as and for the purpose herein shown and described with reference to
Figs. 6, 7, 8, and 9.
5. In an ammeter, or voltmeter, the combination of the polar extremities of a

page_text: magnetic circuit arranged and adapted to traverse a solid or wound conductor, the
transverse sectional area of the said conductor being variable along the path.
traversed by the said polar extremities, substantially as and for the purpose herein.
shown and described.
Dated this 18th day of April 1894
FAIRFAX & WETTER,
433, Straud, London, Agents for the Applicant.