Improvements in or relating to Electric Recording Watt Meters."
Year: 1897

page_text: Date of Application, 28th Sept., 1897-Accepted, 11th Dec.,
1897
COMPLETE SPECIFICATION.
"Improvements in or relating to Electric Recording Watt Meters."
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street, in
the city of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to them from abroad by William H.
Pratt, of Lynn, in the County of Essex, State of Massachusetts, United States of
America), and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The present invention relates to electric meters employed in measuring the electric
energy which is consumed by translating devices; and has for its object to provide
a recording meter which is astatic so that the readings obtained therefrom are
unmodified by magnetic fields external to the meter, for example fields induced
by magnets or by currents traversing electric conductor in proximity to the
meter.
In
Our correspondent has found that in employing standard types of watt meters
for recording the electric output of a large generator or of a station, the magnetic
field induced by heavy currents passing to and from the meters, or in proximity
thereto, is sufficient to affect the meter and render its registration inaccurate.
some instances the magnetic field induced by the conductors is in a direction to
accelerate the speed of the meter armature, and in other instances to retard it. It
may also act upon the rotating disc and serve as an additional damping device, or it
may weaken the damping magnets and permit the speed of the meter arinature to
increase. Such increases are especially liable to occur in central station meters where
bus-bars and other conductors carrying heavy currents are arranged on the switch
boards in proximity to the meter.
To overcome this objection, both motor and damping mechanism are divided into
two or more parts, which are so arranged that stray magnetic lines which tend
to strengthen one part of the motor or damping mechanisin will decrease the strength
of the remaining part or parts, so that the effect of the stray field on the meter is
neutralised and can be disregarded. While it is proposed to use a meter in which
both the motor and damping mechanism are rendered astatic by being divided into
two parts arranged as described, as the most perfect form of the invention, yet the
invention is not limited to such a construction, but covers also a meter in which the
motor mechanism alone is so treated, or even the damping mechanism alone.
In the accompanying drawing, attached to and made a part of this specification,
Fig. 1 is a perspective view of a meter embodying the invention; Figs. 2 and 3 are
modified forms of the field-magnet construction, and Fig. 4 is a modification of the
damping device.
The invention is shown as applied to a station watt meter of the Thomson type,
which is designed to measure very heavy currents. At A and A¹ Fig. 1are
indicated terminals which extend through the back of the meter casing B (shown
in dotted lines), and are connected in series with the circuit to be measured. The
field-magnet consists of a flat-strip copper conductor C provided with enlarged ends C¹
which surround the terminals A, A1 and are electrically connected thereto. The
magnetic field is set up by the conducting system comprising the parts C C¹ and A¹,

page_text: these being equivalent to a single turn, but as it is intended for very heavy currents
the magnetism is sufficient to cause the armature of the meter to rotate when
current flows therein. The invention, however, is not limited to recording meters
only for circuits carrying heavy currents, for it is applicable to meters for all kinds
of service.
Mounted upon the shaft D is an armature divided into two parts E and E¹; these
are located respectively above and below the field-magnet conductor C. The armature
is connected in shunt to the mains which supply current to the translating devices.
The two armature sections, as shown in Fig. 1, are connected in a circuit leading
from a single commutator T. Instead of a single armature divided into two parts
and arranged as described, two separate armatures having individual commutators
may be employed, though the former construction is preferred. In either case the
windings are so arranged that they both tend to propel the armature shaft in the
same direction. The magnetic flux due to the conductor C affects both parts of
the armature winding equally, but in opposite directions, since one section is situated
above and the other below the said conductor C. The direction of winding in the
two sections is such that both act cumulatively. It will be seen that any stray
magnetic field tending to increase or retard the speed of the upper part E of the
armature will have an opposite effect upon the lower part E¹; since the stray field
and normal motor field will act cumulatively upon one armature section, but
differentially upon the other. The armature sections being located so close together,
the effect of a stray field is approximately equal on both, and any effect upon one is
counteracted by the other.
Bolted to the upper side of the enlarged ends C₁ of conductor C and insulated
there from, is a U-shaped frame J which carries the dial K and also supports the
bearing (not shown) for the upper end of the armature shaft. Extending
rearwardly from the frame J is a bracket L which supports the commutator
brushes.
To produce a starting or initial torque to overcome friction, auxiliary shunt field
coils M are employed, which surround the upper part E of the armature on
two sides; these are in series with the armature and in shunt to the supply
mains.
Bolted to the under sides of the enlarged ends of conductor C and insulated
therefrom, are downwardly extending frame pieces U, U¹, which support the main
and auxiliary bases F and F¹.
The armature shaft D is mounted at its lower end in a jewel bearing G which is
carried by the main base F. Two copper damping discs H and H' are rigidly secured
to the armature shaft and rotate between the field poles of permanent magnets I.
The magnets acting upon their respective discs are arranged in pairs, with their like
poles adjacent, as indicated by N, S, S, N. Half of the magnets are carried by the
main base F, the remainder by the auxiliary base F¹. The magnets are mounted in
adjustable clamps T' which are so arranged that they may be moved toward or away
from the armature shaft to adjust the damping effect of the magnets. Any stray
magnetism will, on account of the nearness of the pairs of magnets, affect both of
them equally, but in such manner that where it strengthens one of a pair it weakens
its mate, so that the total effect of the damping is nor changed.
.
The surrounding case B may be made of iron and act as a magnetic shield.
In Fig. 2 is shown a modification of the field coil, consisting of right and left
hand copper castings and 0¹, each casting forming a single turn.
The upper
and side portions of the castings are insulated from each other by an air space P³,
but the lower horizontal portions are somewhat thicker and are in electrical contact.
When assembled an opening P is formed in which one element of the armature
rotates; the other element or armature may be above or below, as desired. Extending
rearwardly from each casting are lugs 02 forming terminals for the meter.
arrows show the direction of current flowing in the coil.
The
Fig. 3 is a modification of the field coil differing from the one shown in Fig. 2, in
that the field conductor is arranged to surround both armatures. The coil consists of

page_text: counterpart castings 0 and 01 rectangular in form, and provided with central
pieces 0s; these pieces are connected to the casting at one end, and are free at the
other. The castings are separated from each other by an air space P³, with the
exception of the pieces 0³, which are in contact and form the electrical connection
between the castings. In this case the parts of an armature or armatures are
mounted in the openings P and P¹. The arrows indicate the direction of current
flowing through the coil.
In Fig. 4 is shown a modification of the damping device, in which discs H and H¹
of conducting material are rigidly mounted upon the armature shaft D and revolve
within the field of magnets I. The magnets have three extensions, one between the
discs, the other two outside. The polarity of the middle extension is so arranged that
it is opposite to that of the outside ones.
The armature is divided into two parts E and E¹, and is provided with a single
commutator T. One part of the armature revolves within field coils C and the other
part is located above the coils and is to a certain degree affected by them.
Since the armatures are affected by the field coil or coils to produce rotation in one
direction, while external or stray magnetism retards one armature but assists the
other, it follows that one armature may revolve in a stronger field than the other
without detriment to the compensation, provided that the armature windings are so
adjusted that the stray field will tend to speed one armature and retard the second by
corresponding amounts. It is however preferable to have both armatures revolving
in fields which are substantially equal in strength.
In all the arrangements herein set forth the different armatures or armature
sections cut the magnetic lines of the field-magnet in opposite directions, but co-act
to produce torque on the meter shaft in the same direction. Hence of course any
external field, which may act upon both armature sections in the same direction will
tend to create additional torques upon the armature shafts in opposite directions, and
such torques will be self compensating in so far as their influence upon the speed of
the meter is concerned. Hence the meter will be astatic as against the influence of
all stray fields which act upon the different parts of the motor mechanism in the
same direction, and this will be found sufficient for practical purposes.
Furthermore while the induction influence of stray fields may not be precisely the
same upon both armature sections, yet the different sections will usually be quite
close together, and the inductive distance from the source of stray fields sufficiently
the same to answer all practical purposes.
Having now particularly described and ascertained the nature of the said invention
(as communicated to us from abroad) and in what manner the same is to be performed,
we declare that what we claim is :-
1. In a recording meter, the combination of an astatic motor mechanism, comprising
more than a single armature winding, or section of winding which respectively act
under the influence of magnetism in opposite directions to rotate the shaft in the
same direction, and a damping mechanism.
2. In a recording meter, a motor mechanism having more than a single winding,
or section of winding, arranged so that the influence of any external magnetism
acting upon said armature sections in the same direction will tend to create a torque
in opposite directions, thereby rendering the meter astatic, as described.
3. In a recording electric meter, the combination of a motor mechanism, a recording
mechanism, and an astatic magnetic damping mechanism having parts which are
acted upon differentially by stray or external fields, so as to preserve a constant
magnetic drag substantially uninfluenced by stray fields, as described.
4. In an electric recording meter, the combination of an astatic motor mechanism
affording a torque proportional to the energy metered uninfluenced by stray fields,
and an astatic magnetic damping mechanism affording a drag constantly proportional
to the velocity, as set forth.
5. In an electric recording watt meter, the combination of a double-U-shaped field
exciting conductor, and an armature wound with two sections located respectively in

page_text: or near the bends of the field conductor, said armature sections having a single
commutator, as set forth.
6. In a recording watt meter, the combination of a field-magnet circuit, an
armature divided into two parts and forming an astatic motor mechanism for driving the
meter, and an astatic damping device consisting of a pair of discs made of conducting
material, each disc moving in a separate magnetic field.
7. In a recording watt meter, the combination of a field-magnet circuit, with an
armature divided into two parts, the parts being so arranged that both are acted
upon by the field magnetism to produce rotation in one direction, but are acted upon
differentially by an external magnetism.
8. In a recording watt ineter, the combination of a field-magnet conductor, an
armature divided into two parts, one part being located above the conductor, the
other below, the coils on both parts being so arranged that they are influenced by the
field to produce rotation in the same direction, and a recording mechanism.
9. In a recording watt meter, the combination of a field coil, an armature
divided into two parts, each part being acted upon by a magnetic flux
differing in its direction, each part of the armature being so arranged that both tend
to rotate in the same direction under the inductive action of the field coil, but are
acted upon differentially by any external magnetism.
10. In a recording watt meter, the combination of a field coil, a rotating armature
divided into two parts and so arranged that both parts tend to revolve in the same
direction under the influence of the field-magnet, but act differentially under the
influence of external or stray magnetism, and a damping device comprising two discs
of conducting material revolving in a magnetic field, the arrangement of discs and
magnets being such that they act differentially under the influence of external
magnetism.
11. In a recording watt meter, the combination of a field coil, an armature, and a
damping device consisting of two discs of conducting material moving within a
magnetic field, the arrangement of discs and magnets being such that external
magnetism will weaken one of the magnets and consequently the effect upon its
disc, and strengthen another of the magnets and increase the effect upon its disc,
thus balancing the total damping effect.
12. In a recording watt meter, the combination of a field conductor, an armature
divided into two parts and situated respectively above and below the conductor and
partially surrounded by it, a single commutator for the armature, a base supported
by depending pieces from the field conductor, an auxiliary base, a set of magnets
supported by each base, and copper discs secured to the armature shaft and revolving
in the magnetic fields.
13. In a recording watt meter, the combination of a field coil, a main and auxiliary
base, magnets supported by the bases, and arranged with their like poles adjacent,
clamps in which the magnets are adjustable, and copper discs revolving in the
magnetic fields.
0011
1
1005
J. C. CHAPMAN,
Chartered Patent Agent, 70, Chancery Lane, London, W.C.