Improvements in Electric Meters.
Year: 1898

page_text: Date of Application, 20th Sept., 1898-Accepted, 12th Nov., 1898
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 Caryl D. Haskins.
of Newton Centre, in the County of Middlesex, State of Massachusetts, United
States of America, Electrical Engineer,) 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, and has for its object to correct an error
that sometimes occurs in operating such devices in places where there is considerable
vibration such as the switchboards of large power stations, in factories or other
places where machinery is running. In such cases where the meters are provided
with starting coils, consisting of a few turns of fine wire in series with the armature
and in shunt to the load, so designed as to give just sufficient torque to counter-
balance the friction of the armature, but not to start it at no load, the meters will
run correctly when first calibrated, and will not run when the field in series with
the work is cut out. Under vibration, however, the armature is apt to creep, and
thus there is a steady source of error, almost imperceptible from observation, but
in the course of time noticeable in the registration. It is the object of the present
invention to correct this by adjusting the starting coil to local conditions after the
meter has been installed. The method of accomplishing this result is to change the
ampere turns of the coil itself by changing its resistance or the resistance in
series with it, without changing the resistance of the armature circuit as a whole
This adjustment is effected after the meter is in place, and may be made just such
as is necessary to prevent vibration or any extraneous influence to which the motor
may be exposed from affecting the registration.
To effect the results pointed out there is placed in series with the starting coil
an auxiliary resistance, which is also in series with the usual current reducing
resistance of the armature circuit, and in shunt to the starting coil but in series
with the armature and its main resistance is a second auxiliary resistance. By the
inverse regulation of these auxiliary resistances, the effect of the coil may be
adjusted so that just the amount of field necessary to give the desired torque will
be developed, without varying the resistance of the armature circuit as a whole,
and thus without varying the current passing in the armature.
A
The accompanying drawing is a diagram which illustrates the application of
the invention to the well-known Thomson recording watt-meter. In this draw-
ing, a, b are the mains, or branches from the mains between which are included
the lamps 1, forming the load. The armature A is, as is well known, in shunt
across the mains, and is of high resistance so as to take but small current.
main resistance R, of large amount, is also included in the circuit of the armature,
so that the current flow is still further reduced. C is the starting coil, which is
in shunt to the mains and in series with the armature. Between the coils C and
the resistance R are the auxiliary resistances D, D¹. These may be of any material

page_text: desired, though small carbon rods are a good form. A slider E provided with
contact pieces d, d, acts to cut in or out suitable portions of the resist-
ances D, D¹, in inverse relation. It will be observed that the entire change of
resistance in the circuit of the starting coil is between the points a¹, a³, but the
resistances D, D¹, are so proportioned that however the resistance of the two
circuits between these points may be shifted, the total resistance between them is
always the same; thus the current flow in the armature will always be the same,
and the speed will be maintained in exact conformity with the factory calibration.
If the slider E be moved to the right, for instance, a part of the resistance D will
be cut out and the current flow in the starting coil C will be proportionately
diminished, but the total current flow between the points a¹, a³, will be preserved
constant, because the same movement of the slider causes part of the resistance D'
to be cut into circuit in series with the resistance D and the starting coil C.
The method of operation is thus seen to be the preservation of a constant current
flow in the circuit of the starting coil, so as to afford exactly the proper amount
of torque.
Having now particularly described and ascertained the nature of our said 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 in shunt to the mains
and field coils in series with the load, with a starting coil also in series with the
armature and in shunt to the mains, and means for changing the current flow in
the starting coil without affecting that in the armature circuits.
2. In an electric meter, the combination of a field coil in series with the work,
an armature in which a sensibly constant current is to be maintained, connected
across the mains, a starting coil in series with the armature and with an auxiliary
high resistance, two resistances, one in series with the coil, the other in shunt
thereto, and means for inversely regulating the two resistances.
3. The method of calibrating an electric meter, which consists in changing the
current flow in the starting coil to compensate for local errors without changing
the current flow in the armature circuit.
Noted this 20th day of Contember 1808
THE BRITISH THOMSON-HOUSTON CO., LTD,
A. R. MONKS,
Director,
ALFRED CLEMENTS,
Assistant Secretary.