Improvements in Electric Meters.
Year: 1897

page_text: Date of Application, 26th Jan., 1897-Accepted, 6th Mar., 1897
Improvements in Electric 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 us from abroad.
by Walter C. Fish 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 :-
This invention relates to electric meters of the "Thomson type "; and has for
its object to prevent the creeping of electric meters of this type, in which an initial
starting torque, intended to compensate for the friction of the moving parts, is
produced by continuing the fine wire shunt circuit through a field coil coincident.
in position with the main field coil, after leaving the armature of the meter; the
fine wire circuit comprising also and in larger part, a non-inductive resistance, the
inductive resistance and armature being located in the shunt circuit, and the field.
coil being connected in series with the mains of the circuit in which the meter is
connected.
.
The invention consists in an apparatus for periodically during the movement of
the meter, removing the influence of the initial energy coil, or at least in weakening
it, to the end that the meter shall be stopped except in case current flows through
the coarse wire coils of the meter, as when lights are turned on; this effect is
accomplished by shunting a fine wire field coil at intervals by means of contacts
closed and opened during the revolution of the meter mechanism.
In the accompanying drawing, Fig. 1 is a diagrammatic illustration of the
manner of carrying out the invention; Fig. 2 is a modification thereof.
A is the armature of the meter, B, B' its brushes; m, n the mains of the circuit
in which the meter is connected, and L, L lamps or other translating devices in
said circuit, the current of which is to be measured by the meter. M, M are the
main field coils, and S, S¹ fine wire shunt field coils coincident in position with the.
main field coils M, M, and forming a continuation of the fine wire shunt circuit c„er.
said circuits c, e comprising in larger part a non-inductive resistance R, and said
non-inductive resistance, armature A and the field coils being connected in shunt.
between the mains of the circuit in which the meter is connected. The circuit a, d
is a shunt.circuit between the brush B' and the main m; that is, a shunt circuit.
around the fine wire shunt field coils S, S.
Included in the circuit a, d are brushes b, b' bearing upon contacts f of a
commutator C mounted on a worm-wheel W forming one of a train of gear.
wheels C of the meter registry mechanism and shown in dotted lines. The worm-
wheel W meshes with a worm w on the shaft X of the meter A. During the
revolution of the wheel W the contacts alternately close and open a circuit between
the brushes b, b', which shunts at intervals the fine wire field coils S, S¹, and thereby
periodically during the movement of the meter removes the influence of the initial
energy coils, or at least weakens them so that the meter will be stopped except
when current flows through the coarse wire coils of the meter, as when lights are
turned on.
"
With this arrangement the meter will ". creep as usual until the circuit is
:

page_text: completed between the brushes b, b¹, and it then stops. The time during which
circuit is established in this manner may of course be anything desired by selecting
the number or breadth of the segments of the commutator borne upon the wheel W.
If the ratio of gearing between the shaft X and the wheel W be as one to one
bundred, then connection between the brushes b, b' will be established once in every
twenty-five revolutions of the meter, or rather more than this, allowing for the
breadth of the segments as indicated in the drawings. It might be supposed that
withdrawing the effect of the fine wire field coils would impair the accuracy of the
registry of the meter, and such would be the case were it not for the fact that a
ready means of compensation is found by adjusting the number of turns of the fine
wire field coil. Thus, assuming that these fine wire field coils are shunted one-
third of the time and in circuit two-thirds of the time, and that the meter readings
are five per-cent. too low, it is simply necessary to increase the number of turns of
the fine wire coil to compensate for this loss by an equal accelerating action during
the time that the fine wire field coil is energized; and evidently this adjustment for
accuracy of registration may be used with any number of closures between band b
or for various durations of closure. It has been found by experiment that closure
of said circuit for one-third of the time will give accurate results. It is of course
evident that the circuit through S, S¹ need not be entirely short circuited, but may
be so weakened as to produce the same results as, for instance, are produced by a
resistance in the branch a, d.
Whilst this invention has been described as employed in an apparatus to measure
a direct current, it may be adapted to one for measuring an alternating current, as
illustrated in Fig. 2, where the inductive resistance is omitted and instead a
transformer T is located in the mains and a step-down transformer T2 is in circuit
with the mains and the armature A of the meter, with the same effect of weakening
the field as in the case set forth in connection with Fig. 1. In Fig. 2 the brushes b. bl
are shown in position between the contact of the commutator C of worm-wheel W,
in which position the shunt field is in circuit; whilst in the position of the
brushes b, 6 shown in Fig. 1, the shunt field is cut out.
The commercial use of electric meters of certain types has developed the fact
that when the meter is installed in a position where it is subject to vibration, and
also when the potential between the mains rises to a value higher than the normal
potential, the meter is apt to "creep," as it is termed ; that is, under such conditions
it slowly moves and registers a consumption of energy when none should have been
recorded. The object of the present improvement is to prevent this effect.
Having now particularly described and ascertained the nature of this inven-
tion (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 an electric meter, the combination of an armature, a field coil therefor,
recording mechanism actuated by the armature, and means for weakening the field
periodically or at intervals, substantially as set forth.
2. In an electric meter, an armature in shunt to the mains, an initial energy coil,
and means for periodically or intermittently weakening the initial energy coil
during the movement of the meter, substantially as set forth.
3. In an electric meter, an armature in shunt to the mains, a non-inductive
resistance in the shunt circuit, an initial energy coil, and means for periodically or,
intermittently weakening the initial energy coil, substantially as set forth.
4. In an electric meter,. an armature in shunt to the mains, a non-inductive
resistance in the armature circuit, a field coil, and means for periodically or
intermittently weakening the field, substantially as set forth.
5. In an electric meter, au armature in shunt to the mains, a field coil, and,
means for periodically or intermittently weakening the field during the movement
of the meter, substantially as set forth.
6. In an electric meter, au armature arranged in shunt to the mains, field coils in

page_text: the main circuit, supplemental field coils in shunt to the mains, a non-inductive-
resistance in the armature circuit, and means for periodically or intermittently.
weakening the field, substantially as set forth.
DL
2
1007
Dated this
20th day of January
1007
For the Applicants,
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.