Improvements in Electricity Meters.
Year: 1898

page_text: Improvements in Electricity Meters.
I, GEORGE HOOкHAM, of 7 and 8, New Bartholomew Street, Birmingham,
Manufacturer, do hereby declare the nature of this invention to be as follows:-
My improvements relate to that class of meters which consist fundamentally of
a meter having a torque proportional to the energy to be metered, controlled by
a brake whose resistance is proportional to the velocity.
My objects are (1) to reduce the consumption of energy usual in this class (2) to
greatly reduce or altogether dispense with the large permanent torque or start-
ing force hitherto found necessary (3) to render negligible the friction of the com-
mutator at the same time increasing its reliability, (4) to reduce the wear on the
pivots, or to allow of finer pivots being used, (5) where permanent magnets are
used for the brake, to vary their force within the limits of their elasticity so as
to correct slight errors of the meter at high loads, or to correct fluid friction error
and so increase the range of the meter (6) to construct the armature in such a
way that a large number of turns, say from ten to twenty thousand or more, may
be wound upon it with little cost.
The first object I attain mainly by the use of iron in the armature. I find
that if this is properly proportioned it does not interfere with the straight line
curve of the meter even over a large range, and, since its polarity is continually
being reversed, no error from hysteresis is experienced, at the same time for a
given number of ampere turns in field and armature the use of iron very greatly
increases the torque. Hence a given torque is procured with much less expendi-
ture of energy.
The second object that of avoiding the use of a large starting force--hitherto
a most objectionable feature in these meters I attain mainly by placing a float
under the armature which very nearly lifts the rotating part of the meter off its
bearings. By this means also my fourth object that of relieving the pivots is
secured. My improvements in the commutator, constituting my third object
consist of increasing the pressure of the brushes by means of the current as it
increases, this enabling me to start with a very light pressure. I prefer to turn
the end of the vertical commutator to a very flat cone and allow the brushes to
rest on this cone. The brushes may rotate and in this case are formed of two
crown wheels (without teeth) the lower edges of the crowns resting on the cone
of the commutator. If the cone is very flat it is thus the equivalent of a circle
of very great radius.
To attain object No. 5 I prefer to use a choked magnet of the type well known
from use in my meters, but in this case I use a double choke one above and one
below the brake-disc; one or both of these poles has a part between the choke
and the brake disc long enough to take a few turns of the conductor carrying the

page_text: main current. In this position the current turns may either weaken or strengthen
the field between the poles from 5 to 10 per cent., without appreciably affecting
the induction in the body of the magnet. I may of course produce the same
effect by a separate electro-magnet acting on the brake.
My sixth object is attained by making the armature as a gramme ring split
in two in a radial plane so that small bobbins, easily wound in the lathe may be
slipped on, the halves of the ring being afterwards pinned together.
My general construction consists in placing the armature above, and the brake
dise below the lower bearing of the spindle on which both are fixed. Thus the
neutral or nearly neutral parts of the permanent magnet alone need approach
the armature, but even from these if desired, a slight initial force may be
obtained; but I may altogether screen the armature by a thin disc or cup of
sheet iron rotating with the armature but forming part of the magnetic circuit
of the field coils. This also will then be free from hysteresis.
MARKS & CLERK,
18, Southampton Buildings, London, W.C., and
13, Temple Street, Birmingham, Agents.
Improvements in Diectricity meters.
I, GEORGE HOOKHAM, of 7 and 8, New Bartholomew Street, in the City of
Birmingham, Manufacturer, 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:-
My invention relates to that class of meters which consist fundamentally of
a meter having a torque proportional to the energy to be metered, controlled by
a brake whose resistance is proportional to the velocity.
My objects are (1) to reduce the consumption of energy usual in this class (2) to
greatly reduce or altogether dispense with the large permanent torque or start-
ing force hitherto found necessary (3) to render negligible the friction of the com-
mutator, and at the same time increasing its reliability: (4) where permanent
magnets are used for the brake, to vary their force within the limits of their
magnetic elasticity, so as to correct slight errors of the meter at high loads, or to
correct fluid friction error and so increase the range of the meter: (5) to construct
the armature in such a way that a large number of turns, say from ten to twenty
thousand or more, may be wound upon it with little cost.
The first object I attain mainly by the use of iron in the armature. I find
that if this is properly proportioned it does not interfere with the straight line
curve of the meter even over a large range, and since its polarity is continually
being reversed, no error from hysteresis is experienced, at the same time for a
given number of ampere turns in field and arniature the use of iron very greatly
increases the torque. Hence a given torque is procured with much less expendi-
ture of energy.
My improvements in the commutator constituting my second object, consist of
increasing the pressure of the brushes by means of the current as it increases,
thus enabling me to start with a very light pressure. I prefer to turn the end
of the vertical commutator to a very flat cone and allow the brushes to rest on this
cone. The brushes may rotate and in this case are formed of two crown wheels
(without teeth) the lower edges of the crowns resting on the cone of the com-

page_text: mutator. If the cone is very flat it is thus the equivalent of a circle of very
great radius.
3
To attain my fourth object I prefer to use a choked magnet of the type well-
known from use in my meters, but in this case I use a double choke, one above
and one below the brake disc: one or both of these poles has a part between
the choke and the brake disc long enough to take a few turns of the conductor
carrying the main current. In this position the current turns may either weaken
or strengthen the field between the poles from 5 to 10 per cent., without appreci-
ably affecting the induction in the body of the magnet. I may of course produce
the same effect by a separate electro magnet acting on the brake.
My fifth object is attained by making the armature as a gramme ring split
in two in a radial plane so that small bobbins, easily wound in the lathe, may be
slipped on, the halves of the ring being afterwards pinned together.
My general construction consists in placing the armature above, and the brake
disc below on the spindle to which both are fixed. Thus the
neutral or nearly neutral parts of the permanent magnet alone need approach
the armature, but even from these if desired a slight initial force may be
obtained but I may altogether screen the armature by a thin disc or cup of
sheet iron rotating with the armature but forming part of the magnetic circuit
of the field coils. This also will then be free from hysteresis.
Referring to the accompanying sheet of drawings illustrating one modification
of my invention as applied to a continuous current three-wire energy meter.
Figure 1 is an elevation of the meter with the front of the case removed.
Figure 2 is a perspective view, showing the working parts swung out of the
case.
Figure 3 is a plan of the brush contact arrangement.
Figure 4 is a side elevation of the same.
Figure 5 is a detail view showing one of the brake magnets.
A is the core of the motor armature by the rotation of which the current is
measured. This armature is mounted on a vertical spindle C carrying the
pinion D (Figure 2) which gears with indicating mechanism E of any ordinary
construction. H is the brake-disc mounted on the spindle C so as to revolve
between the poles of the permanent magnets I, I, attached to the back of the
meter case. The spindle C is provided with conical or pointed pivot-ends and is
supported at K and K' on the meter framework. The main windings G of the
motor, the indicating mechanism E, and the meter connections N, are supported
on the framework in the positions shown, the framework being fixed to a vertical
bar which is free to turn in the fixed bearings and F. The framework may
thus be swung round and out of the case as shown in Figure 2, and the working
parts are therefore readily accessible for examination and adjustment. The
screw N secures the framework in its position when it is inside the case.
The armature of the motor is of the gramme type and consists of a laminated
soft iron ring core A upon which are mounted the bobbins B wound with fine
wire and connected to the commutator S. The armature ring is split radially
into two parts so as to allow the bobbins B to be slipped into their proper positions
the halves of the ring being afterwards pinned together. The armature is thus
easily constructed as the bobbins B can be readily wound separately in a lathe.
It is also possible in this way to wind a large number of turns of wire upon the
armature at a very small cost. I find that if the amount of iron in the core A is
properly proportioned it does not interfere with the straight line curve of the
meter over a long range and that it is advantageous as it increases the induction
in the armature; consequently, for a given number of turns in the armature and
field windings, a given torque is procured with much less expenditure of energy.
There is no hysteresis error produced as the polarity is continually reversed.
In the meter shown, which is adapted for a 200 or 400-volt circuit, a fixed
resistance L (Figure 2) attached to the back of the case is connected in series with
the armature coils B so that it and the armature may be connected directly across

page_text: the mains. The coil L is provided with an iron core M and its winding is so
proportioned as to reduce the tendency, common to this class of meters, to run
on the shunt, when the E.M.F. rises abnormally high.
The tendency to run on the shunt is due to the stray field from the permanent
magnets acting as motor field to the armature, and the coil L is so wound as to
neutralize the stray field by producing an opposing polarity on its core.
The disc A is of aluminium and it is attached to the bottom of the armature
to serve as a mechanical support.
.
i
The brake-magnets I, I, of the type well-known in connection with my meters
are provided with two "choke" pole-pieces J, J, (Figures 1 and 2) one above,
and the other below the brake disc H. One or both of the pole-pieces has a
part between the neck or choke," and the brake-disc of suitable length to carry
a few turns of the main conductor, through which the current to be metered
passes. By suitably winding the conductor round one or more of the pole-pieces
(as shown in Figure 5) the field between the poles J, J, may be strengthened or
weakened 5 or 10 per cent. without effecting the permanent induction of the body
of the magnet.
It is thus possible to correct slight errors at high loads con-
sequently increasing the range of the meter. In a meter using a mercury motor
such as is described in my Patent No. 14239 of 1892, the error due to fluid friction
at high loads may be corrected by this arrangement of double "choke" pole-pieces
provided with a few turns of the conductor carrying the current.
In place of the arrangement I have just described, however, a separate electro-
magnet might be employed.
In Figures 3 and 4 which illustrate in detail the arrangements for controlling
the pressure of brush contact so as to render negligible at light loads as well as
high, the friction of the brushes upon the commutator, the brushes P P rest upon
the upper end of the commutator S. This end is turned to the shape of a flat cone.
The brushes P P consist of two pieces of platinum wire or other suitable metal
attached to springy metal pieces R, R, attached to ebonite blocks R1, R2. The
shunt connections for the armature are made at the screws R3, one of which
only is shown at Figure 4. The blocks R' and R2 are pivoted side by side in a
frame U fixed to the main frame of the meter. T, T, are two pieces of iron wire
attached at one end to the blocks R and R2, and cranked or bent at the other
end to form cores or plungers for the two solenoids G1, G2, which are connected
in series with the main motor windings G, G. When no current is passing
through the meter, the brushes rest very lightly upon the commutator being
simply pressed thereon by the weight of the cores, T, T; but as the current
increases the attraction of the solenoids G1, G2 for the cores T T, and therefore
the pressure of the brushes upon the commutator, increases.
In consequence
of the varying pressure of the brushes with different loads a slight angular move-
ment is obtained, due to the coned end of the commutator, which serves to keep
the contacts clean.
It is obvious that I may control the pressure of the brushes by arranging the
solenoids to act directly upon cores attached to the brushes without the use of
intermediate core levers.
By the above described arrangements I obtain a meter which registers accurately
at low loads as well as high loads and in which the consumption of energy is very
small.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1. In an electricity meter, a motor armature comprising an iron core carrying
the windings, constructed substantially as, and for the purposes hereinbefore
described.
↓
2. In an electricity meter, providing the necked pole-pieces of the brake-

page_text: magnets with a winding of the main conductor substantially as and for the pur-
poses hereinbefore described.
3. In an electricity meter controlling the pressure between the brushes and
motor commutator, substantially as and for the purposes hereinbefore described.
4. In an electricity meter, a solenoid and core or solenoids and cores connected
in series with the main windings in combination with contacts operated from
said solenoid or solenoids, substantially as described.
5. The general arrangement and construction of an electricity meter, substanti-
ally as described with reference to the accompanying drawings.
Ռ
1000
MARKS & CLERK,
18, Southampton Buildings, London, W.C.,
13, Temple Street, Birmingham, and
25, Cross Street, Manchester, Agents.
MARKS & CLERK,
18, Southampton Buildings, London, W.C.,
13, Temple Street, Birmingham, and
25, Cross Street, Manchester, Agents.