Year: 1894

page_text: Date of Application, 24th Dec, 1894
Complete Specification Left, 24'h Oct., 1895-Accepted, 30th Nov., 1895
1, GEORGE HOOKHAM, of Nos. 7 and 8 New Bartholomew Street, in the City
of Birmingham, Manufacturer, do hereby declare the nature of this invention to be
as follows
My invention relates to alternating or interrupted current electricity meters of
the kind in which eddy currents are generated in a disc by a shunt magnet whose
poles are fixed one on each side of the disc, the driving force being supplied by the
interaction of the said eddy currents, and currents passing through flat coils
carrying the current to be metered
In meters hitherto constructed of this type difficulties have been found in
producing revolutions of the disc accurately proportional to the current and the
object of my present invention is to provide a simple meter m which these
difficulties have been overcome.
My invention consists of a new combination of parts comprising a shunt
electro-magnet suitably arranged, with a rotating disc or other rotating surface;
coils placed close to the disc or equivalent surface carrying the current to be
metered; a permanent magnet arranged neur the disc to act as a brake in
combination with an auxiliniy biake such as a fan; and other new combinations of
parts to produce current and energy meters.
In one method of carrying my invention into effect, I construct a disc preferably
of aluminium, and arranged to rotate in a horizontal plane, at one part of the
cl cumfe once place an electro-magnet built up of thm iron plates or lamina and
excited by a shunt current, the poles of this shunt magnet are suitably disposed
above and below the disc so as to generate eddy currents in the disc. To one side
of this muguet I place flat spiral coils in series above and below the disc which
coils carry the current to be metered. These coils pass between the poics of the
shunt magnet and the disc and the said poles are removed far enough from the
disc to allow of this. The two helds uz that produced by the shunt maguet and
that produced by the main current overlap so as to produce a driving effect in a
manner well understood. The rotation of the disc so driven 18 controlled by a
permanent magnet It is obvious that in order to secure proportionality in the
meter the driving force should be exactly proportioned to the current. I have
found, however, that in practice this is not always the case; since in this
arrangement the series coils may produce a driving effect even when unassisted by
the shunt coils Consequently when full current is passed through the meter, the disc
tende to run fastor in one direction than the other and so introduces an error of
excess or defect of registration according to the direction of rotation.
I prefer to run the meter in the direction in which it overruns with full load
and I prevent the error which would otherwise be produced by supplementing the
action of the permanent magnet brake (of which the biaking action varies directly
as the speed) by means of an additional brake of any kind which may vary as the
square of the speed. I preferably use for this purpose a paddle moving in a fluid
preferably a fan moving in air. Au electro-magnetic device may also be used for
this purpose which may consist of a flat coil carrying the main current partially
screened by a plate of copper acting on the disc.
Such an electro-magnetic device may also act to accelerate the disc.

page_text: When a fan is used I may get the blades on springs or actuate them by weights
to diminish the resistance at high speeds.
By these devices I obtain great accuracy of measurement through a long range
of load variation.
In the arrangements hereinbefore described the driving force depends on the
shunt and main currents being in different phase and in order to correctly measure
electrical energy delivered to a machine (such as an electric motor or an are
lamp) in which considerable self induction exists, it is necessary that the self
Induction of the shunt magnet should be as high and the "ohnic" resistance as
low as possible To obtain this effect I curve the sun fares of the poles, making
them nearly touch the disc along a radius of the disc bisecting the pole and
gradually civing or slanting away from the disc on each side of this radius.
I may ma corresponding manner shape the coil carrying the main current by
entting or filing away part of the said coil, so that it has a slanting sun face on one
side. I can thus slide it under one side of the pole This formation also reduces
the retarding eddy curients produced by the shunt magnet to a minimum these
being in some cases objectionable
It is to be understood that it is not always necessary to cause the series coils to
lie in part under the poles.
In order to secure constancy in the permanent magnet I neck it in, providing
a byc pass for the greater part of the lines of force through a strip of iron
bridging the poles and lying against the bar of the magnet, but not touching it,
ou each side, for the space of about one much or an inch and a half. By this
means saturate the reduced necks even more effectually than by previous
methods.
To enable the meter to start readily a small copper screen is permanently fixed
between one side of a pole of the shunt magnet and the disc.
In a modified form of current meter lantange a copper or other screen and
preferably suspend it by a wire in torsion in such manner as to be capable of
being swung between one of the poles of the shunt magnet and the disc and I so
connect it to a solenont, of which the core is formed of on wies and the coil is
in series with the main current, that when the desired minimum of measurable
current is passed the screen enters far enough to start the disc and enters still
further as curieut mureases till the maximum effect is produced. By this
arrangement a curient meter is produced, but by winding the solenoid core with
a suitable winding may so modify the action as to produce an energy meter
capable of accurately registering the supply to machines in which self induction
takes place.
If the currents in the solenoid and those in the coils on the core are in the same
phase then airange the shunt magnet so as to have as high "olimic" and as low
inductive resistance as possible The coils round the solenoid core and those
round the shunt magnet are preferably in series
My screen is preferably mounted on a torsion wire although other suspending
and resisting devices may be used and suitable precautions are taken against
temperature erro in order to maintain a constant strain on the torsion wire.
When a toision wire is used the highest and lowest points of the scale may be
determined by varying the stains on the wire; and the intermediate points by
shaping the screen or by shaping a second soreen introduced between the first
screen and the pole piece.
I do not confine myself to a copper disc and electric currents for use in this
meter but may use magnetic ai raugements.
I may apply the ariaugements here before described to an irou disc or ring
and obtain by means of such a disc.h motor whose torque varies as the current;
checking its motion by a second disc of copper or aluminium in which eddy
currents are generated by a permanent magnet such as described above
supplemented if necessary in the manner described.
1
Th either of the arrangements described the permanent brake magnet may be

page_text: replaced by a suitably proportioned shunt magnet and in the screen arrangement
the shunt magnet may be devised to act as both motor and brake magnet.
Dated this 22nd day of December 1894.
MARKS & CLERK,
18 Southampton Buildings, London, W.C, and
13 Temple Street, Birmingham, Agents for the Applicant.
Improvements in Electricity Meters.
1, GEORGE HOOкшAM, of Nos. 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
ascertained in and by the following statement.-
My invention relates to alternating or interrupted cunicat electricity meters of
the kind in which eddy currents are generated in a dise by a shunt magnet whose
poles are fixed one on each side of the disc, the diving force being supplied by the
interaction of the said eddy currents, and currents passing through flat coils caLiying
the current to be metered.
In meters hitherto constructed of this type, difficulties have been found in
producing revolutious of the disc accurately proportional to the current, and the
object of my present invention is to provide a simple meter in which these difficulties
have been overcome.
My invention consists of a new combination of parts comprising a shunt electro-
magnet stably arranged, with a rotating disc or other rotating surface, coils
placed close to the disc or equivalent surface carrying the current to be metered;
a perinanent magnet arranged near the disc to act as a brake in combination with an
auxiliary brake such as a fuu, and other new combinations of parts to produce
current and energy meters,
Refering to the accompanying sheet of drawings⚫
Figure 1 is an elevation of my improved electricity meter
Figure 2 is a plan showing the essential parts
Figure 3 is another plan showing the starting screen.
Figure 4 is an enlarged view of a modihcation of the construction of the permanent
brake magnet.
In one method of carrying my invention into effect, I construct a disc A prefer-
ably of alummum, and a range it to rotate in a horizontal plane, at one part of the
circunference I place an electro-magnet B built up of thu non plates or lamina,
and excited by a shunt curent, the poles B' B2 of this shunt magnet are suitably
disposed above and below the disc A so as to generate eddy curients in the disc.
To one side of this electro-magnet A I place fint spiral coils CC in series above
and below the disc, which coils carry the current to be metered. These coils puss
between the poles of the shunt inaguet and the disc and the said poles are removerl
far enough from the disc to allow of this The two fields, viz. that produced by
the shunt magnet and that produced by the main current overlap so as to produce
a driving effect in a manner well understood The rotation of the disc A so driven
18 controlled by a permanent magnet D of which the poles are disposed close to the
two sui faces of the disc, and which, by producing Foucault currents, act as a brake.
It is obvious that in order to secure proportionality in the meter the driving force
should be exactly proportioned to the current. I have found, however, that in
practice this is not always the case, since, in this arrangement, the series coils C C'
may produce a diving effect even when unassisted by the shunt coils. Conse-
quently, when full current is passed through the meter, the disc tends to run faster

page_text: in one direction than the other, and so introduces an error of excess or defect of
registration according to the direction of rotation.
I prefer to run the meter in the direction in which it overruns with full load, and
1 correct the crior which would otherwise be produced by supplementing the action
of the permanent magnet brake D (of which the baking action vanes duectly as
the speed) by means of an additional brake of any kind which may vary in a higher
ratio, as, for instance, as the square of the speed. I preferably use for this purpose
a paddle moving in a fluid, preferably a fan moving in air. Such a fan I have shown
at E as attached to the spinille A' of the disc A. The fan Eis so proportioned
that it compensates for the increase of diving force which is not met by the permanent
magnet bake. By this device of an auxiliary air or fluid brake I obtain greatly
increased accuracy of measurement of the current and a long range of load yaun-
tion, and am enabled to change the law of the total brake resistance to suit the
conditions of the meter by properly proportioning the share of the brake action
between the permanent magnet biake and the fan or paddle brake.
This is especially necessary in connection with an iron cover, which, in practice,
is almost an essential for all ineters.
When a fan is used I may set the blades on springs or actuate them by weights
to diminish the resistance at high speeds.
By these devices I obtain great accuracy of measurement through a long rauge
of load variation.
In the arrangements hereinbefore described, the diving force depends on the
shunt and main curients being in different phase, and in order to comectly measure
electrical energy delivered to a machine (such as an electric motor or an arc lamp)
in which considerable self induction exists, it is necessary that the self induction
of the shunt magnet should be as high and the "ohmic" resistance as low as
possible.
"
It is to be understood that it is not always necessary to cause the series cuils to
le in part under the poles, nor is it necessary to have coils on one side only of the
magnet poles. The coils may be arranged on both sides.
In order to secure constancy in the permanent magnet I neck it in as shown at D¹
Figure 4, D, D' being the poles and A the disc, providing a bye pass for part
of the lives of force through a strip of iron F bridging the poles and lying
against the bar of the magnet upon stups G G of non-magnetic metal. By
this means I effectually saturate the reduced neck D and so secure the constant
brake action of the magnet.
To enable the meter to start readily a small copper screen F Figure 3 15
permanently fixed between one side of a pole of the shunt magnet and the disc.
The main curient is carried to and from the coils CCF by the wires G H
Figure 2.
I do not confine myself to a copper disc and electric currents for use in this
meter but may use magnetic arrangements
I may apply the arrangements hereinbofore descubed to an iron disc or ring
and obtam by means of such a disc a motor whose torque vaties as the current;
checking its motion by a second dise of copper or aluminium in which eddy cutients
are generated by a permanent magnet such as described above, supplemented, if
necessary, in the manner described.
The permanent brake magnet may be replaced by a suitably proportioned shunt
magnet.
It is to be distinctly understood that alternating curient mieters have been
proposed, operated by shunt magnet, series coils, rotating disc and bake inagnet,
but in such meters it was impossible to secure accurate registration and propor-
tionality at different loads without a very powerful shunt magnet. This involved
a gient consumption of energy to excite the electio-maguet, and so such meters
have been found to be impracticable.
The meter her embefore described permits the use of a very weak shunt magnet
and consequently involves only a very small consumption of electrical energy, while

page_text: the error of some seven per cent which would be introduced without the auxiliary
governor 18 compensated for within one per cent. by the use of the air fan or fluid
paddle.
The auxiliary brake permits the law of the resistance of the biake to be varied
to keep pace with the law of the increase of driving force; hence, I succeed in
producing an accurate meter.
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 18:
1. An electricity meter for alternating currents comprising in combination—a
rotating aluminum or other metal disc, a shunt excited electro-magnet having its
poles arranged to produce eddy currents in the disc, a driving coil or driving coils
carrying the main current and disposed close to the disc and near the electro-
magnet, a permanent magnet with its poles near the disc so as to act as a brake and
a fan in air or paddle in fluid arranged to co-operate with the magnet brake to
increase the braking action, the whole combination being so proportioned as to
permit the use of a weak shunt electro-maguet and a small consumption of electrical
energy in the said magnet, while the error in registration so introduced is corrected
by the auxiliary fluid brake as herein described.
2 An electricity meter for alternating currents comprising in combination. a
rotating aluminium or other metal disc; a shunt excited electro-magnet having its
poles arranged to produce eddy currents in the disc, a driving coil or driving coils
carrying the main current and disposed close to the disc, and near the electro
magnet; a permanent inagnet with its poles near the disc so as to act as a brake;
together with a copper or like screen placed between part of one of the poles
of the shunt magnet and the disc to ensure the starting of the disc with small
current.
3. In electricity meters of the kind claimed in Claims 1 and 2, securing the
constant action of the permanent magnet by necking down a pole or poles, and
bridging the two poles by a strip of iron arranged outside the rotating disc and
preferably separated from the said poles by non-magnetic metal or other device, as
herein set forth
CHIO
MARKS & CLERK,
18, Southampton Buildings, Loudon, W.C., and
13, Temple Street, Birmingham, Agents.