Improvements in Electricity Meters.
Year: 1892

page_text: Date of Application, 6th Aug., 1892
Complete Specification Left, 6th June, 1993-Accepted, 6th Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in Electricity Meters.
I, 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 further improvements in the type of meter with immersed
armature described in Letters Patent granted to me and numbered 40 of 1891 and
4064 of 1891 respectively.
In my present meter the armature and brake disc are separate, the brake disc
being mounted on the same spindle as the armature and above it. The form of the
magnets is generally similar to that shown in Figure 1 of the earlier of the before
mentioned Specifications, and I prefer to use permanent magnets. The armature
field is a uniform circle, but the outer part of the field of the brake is an
interrupted circle in order to induce strong Foucault currents in the brake disc.
The lines of force (except as regards a portion, as hereinafter described) pass
through the armature and brake, the space between the two being nearly filled
with a thickness of iron, which decreases the magnetic resistance, and also forms
the cover or lid of the closed vessel containing the mercury, in which the armature
is immersed. There is a small central hole in this iron cover through which the
spindle of the armature passes, the mercury rising about half way up this hole, and
the spindle cutting the mercury at this point. If the volume of the armature is
not sufficient to just float the brake disc and spindle when at rest, I increase the
volume by adding a layer of vulcanised fibre or other light material. As soon as
the armature attains a certain speed the centrifugal force of the rotating mercury
draws down the armature on to its lower bearing which may consequently be made
less delicate than the upper one. To the iron lid of the armature cup (which also
forms on its upper surface the lower part of the field of the brake with its
interrupted circle above referred to) is affixed a flat iron bar which extends laterally
from the lid and turns down by the side of the armature field and reaches a little
below it. This bar is wound with a certain number of turns of the conductor
which carries the current to be measured, or "series turns." It will be obvious
that when no current is passing in these "series turns" the curved iron bar attracts
to itself the waste field of the armature, and also to some extent robs the armature
field; so that under these conditions more lines of force pass through the "brake
disc" than through the armature. But when current is passed round the series
coils this ratio begins to change. For a certain value of the current the iron bar
(which at first is strongly magnetic) becomes neutral, and at this point the lines of
force passing through the armature and brake are practically equal.
For higher values of the current an opposite magnetism is induced in the bar
and more lines of force pass through the armature than the brake, the excess being
carried by the central uniform portion of the brake field. The total result is that,
as the current increases, the strength of the armature field increases relatively to
the brake field, and I thus obtain a correction for the error introduced by fluid
friction; the proper number of series turns being found by trial. I have found
that the effect of a heavy current through the series turns is to relatively strengthen
the armature field more or less permanently, and thus alter the calibration of the
meter. I obviate this by winding a certain number of series turns (also found by
trial) round the upper part of the permanent magnet or its polar extension, as close
as possible to the brake field, in such a sense as to strengthen the said magnet.
The projections of iron forming the interrupted circle on the iron lid of the
armature cup I neck down at their attachment to the lid to about one third of

page_text: their thickness. This neck is therefore partially saturated, and the result is that
the strength of the brake field is changed very little even for considerable changes
in the total induction; with the amount of necking indicated I can so arrange
matters that even for an appreciable falling off in the strength of the permanent
magnets, the rate of the meter is practically unchanged. The temperature error
may be rendered negligible by using instead of copper for the brake disc an alloy
of copper with a small percentage of manganese or of manganese bronze. The entire
instrument is enclosed in an iron cover which can be sealed by the inspector, but
which after it has been so sealed can be raised to a fixed height such as will allow
the supply company to connect their leads, but not such as to allow them to alter
the rate of the meter. It is then lowered and separately sealed by the supply
company.
In one arrangement of electricity meter constructed in accordance with my
invention, I provide a vertical brass case to contain a number of permanent bar
magnets and I build up my meter from the said brass case or pillar by means of
pole pieces preferably of soft cast iron attached to the case. The pole pieces
extend horizontally above and below and are connected by a magnetically
discontinuous pillar or bar, arranged however in such manuer
as to be
mechanically continuous. The upper and the lower parts of this bar are of soft
iron in magnetic continuity with the upper and lower pole pieces and the
intermediate gap piece is of brass or other suitable non-magnetic metal or
material. The upper and lower parts of the bar thus form polar extensions of
the upper and lower pole pieces. To these upper and lower parts I attach
preferably by sliding sockets and set screws flat plates or pieces with flat surfaces
also of soft iron preferably cast, likewise in magnetic continuity, which thus form
upper and lower pole pieces arranged in opposition to each other. On the smooth
surface of this lower pole piece I mount a copper piece or ring, having a
circular aperture and external projections to receive conducting wires. This ring
is bolted to the lower pole piece by a suitable cover hereinafter described, and is
insulated from it and made mercury tight by a leather or other suitable jointing
and non-conducting ring. In the centre of the circle formed by this copper ring
on the lower flat pole piece I provide an aperture and insert a copper plug passing
under the pole piece arranged to couple up to a conductor. Through the centre of
the copper plug I pass a steel pivot pin adjustable by external screw.
The leather packing ring is laid upon a disc of paper which may be varnished,
and the paper is cut out at the centre to expose the copper plug and pivot.
On the steel pivot I mount a metallic spindle preferably by a socket terminating
with a jewel and I carry on this spindle a disc armature of copper, nickel plated on
the flat surfaces, but having a serrated edge which I amalgamate with mercury;
I likewise amalgamate a ring near the centre of the lower disc surface of the
armature, cutting through the plating if necessary. To the upper surface of the
armature attach a disc of vulcanized fibre sufficient in volume to enable
the armature with its load to float in mercury as hereinbefore indicated. The
cover of the copper ring I also construct of soft iron and arrange it as a disc with
lugs to take the screws for bolting it down and securing the copper ring to its
leather washer. I also secure the said cover by washer above the copper ring and
so form a cylindrical chamber capable of containing mercury. The armature
spindle I pass through a hole in this cover and upon it above the cover I mount a
disc of copper which serves as a brake upon the motor part of the apparatus. The
brake disc rotates close to the upper pole piece which is preferably formed with
projecting pieces or serrations projecting from its surface. The cover of the
mercury vessel also carries serrations or projections which form a circle and stand
near the disc but I prefer to undercut these projections so that a magnetic choking
effect is produced.
A central ring serves to carry a variable portion of the field to the lower side
operating the armature, but does not interfere with the brake action. The said
iron cover is also extended downwards within the mercury vessel so as to present
a

page_text: surface close to the armature, and the armature disc thus rotates with its upper
surface near the iron cover, and its lower surface near the flat surface of the lower
pole piece. The iron cover thus forins an intermediate piece between the brake
and the armature and acts as a magnet, the upper part acting on the brake disc and
the lower part in the motor armature.
The spindle carrying both brake disc and armature disc connects to suitable
registering clockwork in any well known manner.
When in action, the current passes into the copper ring by a conducting wire;
from the copper ring through the mercury to the serrated edge of the armature
and through the armature metal to the amalgamated circle at the centre whence it
passes to the copper plug below through the mercury.
The disc thus rotates as hereinbefore described due to well understood forces.
The current passes from the copper plug through a coil or a soft iron bar
attached to the intermediate piece or cover, thence to a coil wound round the
upper part of the pillar pole piece and then back to the other terminal.
The coil on the soft bar attached to the intermediate piece is so arranged that
the motor magnetic field is strengthened by the current and the coil on the pillar
pole piece is proportioned to prevent or neutralize any action by the first coil on
the brake or main magnets.
The intermediate piece or cover and the lower pole piece are connected by a soft
iron bar clear of magnetic contact which may be however approached nearer to or
further from both surfaces. The interior portion of the intermediate piece or
cover is recessed to prevent spilling the mercury.
Dated this 5th day of August 1892.
GEORGE HOOKHAM,
7 & 8, New Bartholomew Street, Birmingham.
COMPLETE SPECIFICATION.
Improvements in Electricity Meters.
I, GEORGE HOOKHAM, 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 further improvements in the type of meter with immersed
armature described in Letters Patent granted to me and numbered 40 of 1891
and 4064 of 1891 respectively.
In my present meter the armature and brake disc are separate, the brake disc
being mounted on the same spindle as the armature and above it. The form of
the magnets is generally similar to that shown in Figure 1 of the earlier of the
before mentioned Specifications, and I prefer to use permanent magnets. The
armature field is a uniform circle, but the outer part of the field of the brake is an
interrupted circle in order to induce strong Foucault currents in the brake disc.
The lines of force (except as regards a portion, as hereinafter described) pass
through the armature and brake, the space between the two being nearly filled
with a thickness of iron, which decreases the magnetic resistance, and also forms.
the cover or lid of the closed vessel containing the mercury, in which the
armature is immersed. There is a small central hole in this iron cover
through which the spindle of the armature passes, the mercury rising about
half way up this hole, and the spindle cutting the mercury at this point.
If the volume of the armature is not sufficient to just float the brake disc and
spindle when at rest, I increase the volume by adding a layer of vulcanized fibre or
other light material. As soon as the armature attains a certain speed the centri-
fugal force of the rotating mercury draws down the armature on to its lower
bearing which may consequently be made less delicate than the upper one.
iron lid of the armature cup (which also forms on its upper surface the lower part
To the

page_text: ove referred to is unxed
.
flat iron bar which extends laterally from the lid and turns down by the side of
the armature field and reaches a little below it. This bar is wound with a certain
number of turns of the conductor which carries the current to be measured, o
"series turns." It will be obvious that when no current is passing in these "series
turns "the curved iron bar attracts to itself the waste field of the armature, and
also to some extent robs the armature field; so that under these conditions more
lines of force pass through the "brake disc" than through the armature. But
when current is passed round the series coils this ratio begins to change. For a
certain value of the current the iron bar (which at first is strongly magnetic)
becomes neutral, and at this point the lines of force passing through the armature
and brake are practically equal. For higher values of the current an opposite
magnetism is induced in the bar and more lines of force pass through the armature
than the brake, the excess being carried by the central uniform portion of the
brake field. The total result is that, as the current increases, the strength of
the armature field increases relatively to the brake field, and I thus obtain a
correction for the error introduced by fluid friction; the proper number of series
turns being found by trial. I have found that the effect of a heavy current
through the series turns is to relatively strengthen the armature field more or less
permanently, and thus alter the calibration of the meter. I obviate this by winding
a certain number of series turns (also found by trial) round the upper part of the
permanent magnet or its polar extension, as close as possible to the brake field, in
such a sense as to strengthen the said magnet. The projections of iron forming the
interrupted circle on the iron lid of the armature cup I neck down at their attach-
ment to the lid to about one third of their thickness. This neck is therefore
partially saturated, and the result is that the strength of the brake field is changed
very little even for considerable changes in the total induction; with the amount
of necking indicated I can so arrange matters that even for an appreciable falling
off in the strength of the permanent magnets, the rate of the meter is practically
unchanged. The temperature error may be rendered negligible by using instead of
copper for the brake disc an alloy of copper with a small percentage of manganese
or of manganese bronze.
Referring to the three sheets of drawings accompanying :-
Figure 1 is an external elevation of my meter with the cover removed.
Figure 2 is a section corresponding to Figure 1.
Figure 3 shows the meter with the cover down.
0
Figure 4 shows the meter with the cover up to allow the leads to be connected.
Figure 5 is an outline front view to show more particularly the position of the
bar V relative to the magnets.
Figure 6 is a plan showing the outline configuration of the pole pieces and
connections.
In one arrangement of electricity meter constructed in accordance with my
invention, I provide a vertical brass case A to contain a number of permanent bar
magnets B and I build up my meter from the said brass case or pillar by means of
pole pieces C D preferably of soft cast iron attached to the case.
The pole
pieces CD extend horizontally above and below the case A and are connected by
a magnetically discontinuous pillar or bar E F G, arranged however in such
manner as to be mechanically continuous. The upper and the lower parts of this
bar respectively E G are of soft iron in magnetic continuity with the upper and
lower pole pieces and the intermediate gap piece F is of brass or other suitable
non-magnetic metal or material. The upper and lower parts E and G of the bar
thus form polar extensions of the upper and lower pole pieces C and D). To these
upper and lower parts E and G 1 attach preferably by sliding sockets and set
screws horizontal plates H and I or pieces with flat surfaces also of soft iron
preferably cast, likewise in magnetic continuity, which thus form upper and lower
pole pieces arranged in opposition to each other.
On the smooth surface of this lower pole piece, I, I mount a copper piece or

page_text: ring K having a circular aperture and external projections to receive conducting
wires. This ring K is bolted to the lower pole piece I, by a suitable cover herein-
after described, and is insulated from it and made mercury tight by a leather or
other suitable jointing and non-conducting ring. In the centre of the circle formed
by this copper ring on the lower flat pole piece I provide an aperture and insert a
copper plug L passing under the pole piece arranged to couple up to a conductor
by a terminal screw M. Through the centre of the copper plug I pass a steel
pivot pin P adjustable by external screw.
The leather packing ring is laid upon a disc of paper which may be varnished,
and the paper is cut out at the centre to expose the copper plug L and pivot P.
On the steel pivot P I mount a metallic spindle Q preferably by a socket
terminating with a jewel, and I carry on this spindle Q a disc armature R of copper,
nickel plated on the flat surfaces, but having an edge R' which I amalgamate with
mercury; likewise amalgamate a ring R* near the centre of the lower disc
surface of the armature, cutting through the plating if necessary. To the upper
surface of the armature disc Ŕ I attach a disc of vulcanized fibre sufficient in
volume to enable the armature with its load to float in mercury as herein before
indicated. By this device at low currents the spindle Q bears upon the upper
jewelled bearing T, which bearing may be made very delicate, and so the minimum
of friction is obtained at low currents, when it is very necessary to ensure accurate
operation. At higher currents and speed the centrifugal force of the rotating
mercury causes a downward pressure on the disc R, which brings into action the
stronger bearing at the bottom and thus obviates wear at the heavier loads. The
cover N of the copper ring K I also construct of soft iron and arrange it as a disc
with lugs to take the screws for bolting it down and securing the copper ring to its
leather washers. I also secure the said cover by washer above the copper ring and
so form a cylindrical chamber K' capable of containing mercury. The armature
spindle Qpass through a hole O in this cover N and upon it above the cover I
mount a disc S of copper which serves as a brake upon the motor part of the
apparatus. The brake disc S rotates close to the upper pole piece H which is
preferably formed with projecting pieces or serrations H¹ projecting from its
surface. The cover N of the mercury vessel also carries serrations or pro-
jections N which form a circle and stand near the disc S, but I prefer to undercut
the said projections N' so that a magnetic choking effect is produced. The central
ring left after undercutting serves to carry a variable portion of the field to the
lower side operating the armature or motor dise R, but does not interfere with
the brake action. The said iron cover N is also extended downwards within the
mercury vessel by the conical projection N¹, so as to present a surface close to
the armature disc R, and the armature disc thus rotates with its upper surface near
the iron cover, and its lower surface near the flat surface of the lower pole piece.
The iron cover N thus forms an intermediate piece between the brake and the
armature and acts as a magnet, the upper part acting on the brake disc and the
lower part on the motor armature.
The spindle Q carrying both brake disc and armature disc connects to suitable
registering clockwork in any well known manner as shown in the drawings.
When in action, the current passes into the copper ring vessel K by a conducting
wire b; from the copper ring K through the mercury U to the amalgamated
edge R' of the armature R and through the armature metal to the amalgamated
circle K at the centre whence it passes to the copper plug L below, through the
mercury.
The disc thus rotates as hereinbefore described due to well understood forces.
The current passes from the copper plug through a coil d on a soft iron bar V
attached to the intermediate piece or cover, thence to a coil e wound round the
upper part of the pillar pole piece and then back to the other terminal.
The coils d and are thus in series.
The coil on the soft bar attached to the intermediate piece is so arranged that
the armature magnetic field is strengthened by the action of the current and the

page_text: coil on the pillar pole piece is proportioned to prevent or neutralize any action by
the first coil on the brake or on the main magnets. The intermediate piece or cover
and the lower pole piece are connected by a soft iron bar clear of magnetic contact
which may be, however, approached nearer to or further from both surfaces.
The interior portion of the intermediate piece or cover is recessed to prevent
spilling the mercury.
An error is introduced if the temperature of the instrument be increased or
diminished by reason of the increased or diminished resistance of the brake disc,
and I obviate or reduce this by constructing the brake disc of an alloy having
the property of nearly uniform resistance with considerable change of temperature.
A copper and manganese alloy I find very suitable for these purposes as not-
withstanding this property of nearly constant resistance the conductivity is high.
The entire instrument is enclosed in an iron cover X (Figures 3 and 4) which
can be sealed by the inspector, but which after it has been so sealed can be
raised to a fixed height such as will allow the supply company to connect their
leads, but not so as to allow them to alter the rate of the meter. After connecting
the leads the cover is lowered and separately sealed by the supply company.
first seal is shown at X' and it allows the cover to be raised on the rods X*X*
sufficiently to connect the leads. The second seal-X is put on after the cover has
been put fully down on the rods and so prevents the consumer from tampering with
the leads.
The
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. An electricity meter comprising in combination :-a motor disc and a brake
disc mounted on a spindle, the motor disc being wholly immersed in mercury and
rotating near the flat surfaces of polar extensions of a permanent magnet; a
mercury vessel having one of the said polar extensions arranged at its bottom, and
the other as its cover, the side walls being formed of a copper or like ring insulated
from the pole pieces and jointed or clipped between the two said polar extensions
so as to form a mercury tight vessel; an iron bar or extension attached to the
cover pole of the mercury vessel wound with coils in series with the current to be
measured and so proportioned as to increase the intensity (relative to the brake
disc field) of the motor disc field, as the current increases; and a series coil wound
round an iron piece connecting the permanent magnets with the polar extension
acting on the brake disc field and so arranged as to neutralize any effect the first
mentioned coil might otherwise have on the brake magnetic field or on the
permanent nagnets, substantially as hereinbefore described.
2. In an electricity meter where separate motor and brake magnetic fields are
used to actuate and control the rotations of a metallic disc or discs or other
rotating surface of revolution; a coil in series with the current to be measured
wound round an iron projection in magnetic connection with a pole piece of the
motor field in such manner as to strengthen the motor field as current increases
without affecting the brake field whether the said coil is used alone or in combina-
tion with a second series coil wound round a pole piece of the brake field
substantially as and for the purposes hereinbefore described and illustrated.
3. The arrangement and construction of electricity meter herein before described
consisting of permanent magnets as A B; pole pieces as C, D, with compound
pillars as F E G: motor and brake discs as R S on rotating spindle as Q;
mercury vessel as K; and series coils as d e, all substantially as hereinbefore
described and illustrated at Figures 1 and 2, 5 and 6 of the accompanying
drawings.
4. In an electricity meter where a motor disc or other figure of revolution is
employed wholly immersed in mercury; floating the said disc or its equivalent by
means of suitable attached material in such manner that at low currents the friction
of one pivot is avoided while at higher currents or more rapid revolutions the

page_text: centrifugal force of the rotating mercury causes the said disc or its equivalent to
be borne down on a stronger or less delicate pivot as and for the purposes herein-
before described.
0
5. In an electricity meter having a brake disc or its equivalent, the use of an
alloy such as that of copper and manganese, of constant or nearly constant
resistance for moderate changes of temperature for the purpose of correcting for
temperature error substantially as hereinbefore described.
6. In an electricity meter-a metallic case as X arranged to slide on pillars
having two seals one of which permits the connection of the leads without allowing
access to the mechanism of the meter and the other seal closes up the whole meter
and prevents access to the leads, substantially as hereinbefore described with
reference to Figure 3 and Figure 4 of the drawings.
Dated this 5th day of June 1893.
MARKS & CLERK,
13, Temple Street, Birmingham, Agents for the Applicant.