Improvements in or relating to Electric Meters.
Year: 1898

page_text: COMPLETE SPECIFICATION.
Improvements in or relating to Electric Meters.
A communication from LUIGI ENRICO GIUSEPPE CAURO, of 250, Via Roma, Naples,
in the Kingdom of Italy, Electrical Engineer.
I, ALFRED JULIUS BOULT, of 111, Hatton Garden, in the County of Middlesex,
Chartered Patent Agent, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
"
This invention relates to electrical meters provided with a constant electric field
hich, together with that formed by the principal coils, causes an armature to
rotate which then registers in the well known manner the consumption of electric
current or energy.
The object of having a constant field is, as will be easily understood, to create
a rotary, couple acting on the armature and capable of overcoming the passive
resistance of the meter.
The field in question may be supplied by a magnet or electro-magnet or simply
by a wire-winding; it may be placed between the main coils of the meter, side
by side with the armature.
A meter constructed on the above lines is naturally very sensitive, and what is
more important its indications will be exactly in proportion to the quantity of
energy passing through it.
The main idea on which the construction of this meter is based, is illustrated in
the accompanying drawing in which A (Fig. 1) is a closed coil conducting the
electric current, shaped to represent a flat and regular figure, having a number
of sides greater than two and connected, as shown in the diagrammatic drawing,
to the segments of a commutator C. The coil and the commutator are secured
together and to the small spindle o passing through the centre of the coil and
rotating about its own axis.
After
Let us assume that there is a second coil also flat and conductor of electricity
and made of a shape similar to the coil B indicated in the drawing; so that from
the point which is the point where the axis xx¹¹ meets the coil B, the latter
symmetrically moves away from said axis until the points are passed which
represent the points of intersection of B with the normal to the axis of symmetry
through, with the coil A through the centre of which the axis passes.
having passed said points all the coil B is constituted by a curve parallel to A.
When an electric current is sent into the coil A and another into the coil B,
by means of the two brushes S suitably arranged on the commutator, the coil A
will have a tendency to turn until one of its segments comes to lie in such position
that its own axis is situated in the axis of symmetry of B. If the brushes occupy
on the commutator such a position that before attaining said end-position the
direction of the current is reversed on that segment of A which was just about to
attain said end position said segment which at first had a tendency to approach
CD 077

page_text: the coil B will now have a tendency to move away from it, the direction of rota-
tion remaining the same owing to the action of the other segments. The force of
the rotary couple of the coil A is in proportion to the product of the strength
of the current passing through A and that of the current passing through B. If
the coil B has passing through it, in series, the current of a given electric circuit,
and if the current of A is a shunt current of the same circuit the strength of current
in this latter coil will be in proportion to the difference of potential at its terminals,
that is to say to that of the current; from which it follows that the couple
energising the coil A is in proportion to the product I E of the current I circulating
in the current owing to its difference of potential E, that is to say to the electric
energy transmitted by the circuit.
Let us suppose now that the work produced by the coil A in its rotation is
absorbed by means of an electric brake constituted by a copper-disc rotating
between the poles of a permanent or electro magnet, or by paddles striking the air,
and rotated by a small spindle secured to the coil A, and let us imagine that the
small spindle itself actuates a revolution counter which indicates the number of
revolutions by hands moving on graduated dials.
A
In this way the number of revolutions of the small spindle under the influence
of the current will be determined and thus, in the way stated the electric energy
transmitted by the circuit into which the apparatus is switched is indicated.
preliminary operation, made with all the conditions known, will give the value
of the constant factor of the apparatus, or the relation between the energy passing
through the circuit in a given time and the number of revolutions made in the
same time.
Example of a practical application of the theory enunciated above.
In a practical application the coil A is constituted by a long and fine wire wound
on one of the segments of a regular polygon, for instance an octagon (Fig. 3) in
such manner as to have the same quantity wound round each segment. The
segments are preferably made of light and insulated material. When the polygon
chosen is an octagon, each segment has a shape similar to that of the parts a, b, c,
d, e, f, g, h, i, l, m, n. On the part c, d, i, l, the wire is wound normally to the
axis of symmetry of the figure, as will be seen by the two full segments in which
the direction of the wire is indicated.
Figure 4 which in the drawing ought to have been shown arranged in the same
direction as Figs. 5 and 6 shows, a section of the armature A, made by a plane
passing through the small spindle and shows the manner in which the two faces
of each segment are covered with wire. The windings of different segments are
connected in series. The points where different windings are joined together are
each connected to a segment of the commutator, there being as many segments
in the commutator as in the coil the number being, however, of no importance.
The coil B on the contrary is constituted by a short conductor, the section of
which depends on the strength of the current which has to pass through it.
A similar conductor is wound several times about itself so as to form a coil of
which Figs. 2 and 4 shows a plan and a longitudinal section through the axis of
symmetry. The armature being covered with wire on both its faces, it is advisable
to place two coils as B, one in front of each face of the armature and as near to
it as possible so as to obtain the greatest possible useful effect.
The apparatus presents, in practice, a number of passive resistances which,
remaining nearly constant at different speeds, would interfere with the pro-
portionality of the speed of rotation of the armature and the energy passing
through the circuit.
On this account there is placed in series with the coil constituting the armature
a second coil, of course separated from the first, and arranged so as to produce a
field capable of nearly moving the armature when the coil B has no current passing
through it. Said field counter-balances the passive resistance of the apparatus
whenever the difference of potential of the circuit remains constant. This coil
may have in plan the same shape as B and be superposed on the latter, or have

page_text: a rectangular shape and be placed between the coils B, but always so as to have
the current passing through it normal to the axis of symmetry of B.
When the potential at the terminals of the shunt formed by the armature and
for the said coil increases it might happen that the armature would start rotating
even when no current was passing through the coil B. To prevent this, a brake
is used, Figures 5 and 6 showing two different constructions of a suitable device.
In order to render it clearer, the two figures also show diagrammatically the
electrical connections of the circuits of the meter.
First arrangement. M is a permanent or electro magnet (Fig. 5) arranged at
the end of a balance beam g¹ there being a balance-weight and an extension
the other end.
at
If the magnet M be an electro magnet the wire wound round it is in series with
the winding of the armature A, and extended partly into a solenoid B¹, the latter
being wound in series with the winding B, i.e., the main current to be measured
passes through both. The windings are arranged so that when there is current
in the winding B it exercises a repelling action on M, when M is magnetised.
The beam is balanced so that when there is no current in B the extension p rests
against the disc g acting as a brake.
When on the contrary there is a current in B and consequently in B¹ the latter
repels the magnet M and the extension p moves away from 9 and so releases the
meter.
Second arrangement. If the end of g¹ terminates in a platinum extension p¹
(Fig. 6) adapted to rest on a spring contact gl also of platinum the parts B', M
and g remaining the same, the solenoid B and the magnet M are wound so that
they attract each other when the current passes through B¹ and the arm g¹ is
electrically connected to one of the ends of the winding of the armature A, the
contact is connected to the terminal of the coil balancing the passive resistances
when there is no current in B₁ and p and q are in contact the result being that the
armature A and said coil are short circuited together, so that the rotary couple
which they develop is sufficiently weak not to allow the movable portion to turn.
It follows from the above that the balancing of active resistances can be carried
to its extreme limit, the meter being rendered very exact and sensitive. These
devices will be called a brake.
Figures 4 and 2 are a longitudinal section and a plan of the motor apparatus
clearly showing the arrangement of the whole device. The armature A is secured
to the small vertical spindle o terminating in two tempered points one end of
which rests on a small hard stone or bearing slightly concave the other end being
free to rotate in a metallic bearing which guides it and serves to keep the spindle
in position. These two bearings are supported by two metallic brackets r, one of
which supports by means of a screw a revolution counter S which receives its
motion from a worm on the spindle o. The two coils B are each supported by a
metallic bracket . Finally the brackets r and u are bolted to a metal plate on a
plate of refractory insulating material, on which is mounted the motor, brake and
binding screws for connecting the apparatus with the circuit. The whole is then
enclosed in a light and non-magnetic metal box provided with a small window
through which the dials of the revolution counter can be seen.
The arrangement of electric circuits in the interior of the meter and its con-
nections to the outer circuits will be understood from diagrammatic arrange-
ment shown in Figs. 5 and 6.
It must be pointed out that in Fig. 4 the disc q and the magnet z constitute a
Foucault brake, the object of which is to absorb the mechanical work produced
by the motor.
In Figs. 5 and 6 is the coil producing a magnetic field adapted to overcome
the passive resistances, we is the balance-weight for balancing the magnet M. L is
the apparatus (lamp, motor etc.) the consumption of energy by which is to be
registered by the meter.
When the meter is to be used for a two-wire circuit the two coils are placed in

page_text: series with one of the conductors of the circuit the current passing through them
in opposite directions. In case of a 3-wire circuit, each coil is placed in series
with one of the outer wires. For a 5-wire circuit it is sufficient to wind each coil
with two wires insulated from each other, and the 4 windings are suitably con-
nected to the 4 wires of the net.
The armature may be in all these cases, shunted on the outer wires or on any
two wires of the net when the differences of potential between wire and wire are
constant, and its resistance will be in all cases in proportion to the difference of
potential determined at the ends. The meter can it will be evident be used both
for continuous and alternating currents.
Having now particularly described and ascertained the nature of this inven-
tion as communicated to me by my foreign correspondent and in what manner the
same is to be performed I declare that what I claim is:-
1. Apparatus for measuring electrical energy in which the motor is formed by
an armature and the field coils are wound in the manner described.
2. In a meter of the character described means for preventing the armature
from moving when there is no current in the circuit the consumption of energy
of which is to be measured and consequently no current in the coils forming the
principal field of the meter, said means either acting as a mechanical brake on the
movable part of the meter or short-circuiting armature and coil employed to
balance the passive resistances of the motor substantially as described.
3. The combination and arrangement of parts constituting the complete appara-
tus for use in measuring electrical energy substantially as described and illustrated
in the accompanying drawings.