Improvements in Electric Meters,
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 3rd Feb,, 1900
Improvements in Electric Meters,
We, THE BRITISHI 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 Elihu Thomson,
residing at Swampscott, in the County of Essex, 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:
The present invention relates to a method of and apparatus for measuring
electric energy, and in the specific embodiment herein described it comprises a
motor the speed of which is varied by intermittently applying energy thereto
at such intervals as to maintain its speed proportioned to the current flowing
in the work circuit. A counter registers the number of revolutions of the motor,
and thus furnishes a measure of the energy consumed.
The breadth of the invention will be more clearly set forth and its details more
particularly pointed out in the appended claims.
In the drawings, A represents the armature of a motor generator, the shaft of
which is mechanically geared to and drives the revolution counter C. The supply
terminals t, of the motor generator are connected in shunt across the mains 1, 2,
If found necessary or desirable, a suitable resistance R may be included in this
circuit to limit the flow of current.
The magnetic field in which the armature A revolves is intended to remain
constant and this result is preferably obtained by the employment of a permanent
magnet M, as shown in the drawing. Any other suitable means for accomplishing
the same purpose may, however, be used."
It is evident that with a constant magnetic field and with a practically con-
stant electromotive force impressed upon the motor terminals, the speed of the
armature A would ordinarily remain constant. In order to vary the speed, how-
ever, a switch S, is interposed in the motor supply circuit and this switch is
arranged to remain open at intervals so timed as to reduce the speed of the motor
to practical proportionality to the current in the work circuit.
The switch controlling device is like a differentially wound ammeter and con-
sists of a fixed and a movable member.
As we prefer to construct it, the fixed member is composed of two coils K K¹.
The coil K is in series with the work circuit, which in this case is shown as
feeding lamps L. The coil K is in series with the secondary winding on the
armature A of the motor-generator, and is connected therewith through the ter-
minals, . It is obvious that this secondary winding might be replaced in
function by a separate generator whose electromotive force is proportional to the
speed of the armature A, or indeed by any other source of electromotive force
having the same proportionality. The movable coil P is shunted across the
supply mains 1, 2, and if desired a resistance R' may be interposed to prevent
too great a flow of current. As shown in the drawing, the movable coil is
.

page_text: mounted on a rotatable shaft T, and connections are made with the terminals
of the coil in any suitable manner, as for instance through oppositely wound
spiral springs 3, 4.
Carried by the shaft T is a switch arm 5 which makes contact with the switch
plate 6. Current is conveyed to the arm 5 by means of the brush bearing on
the shaft T. Any other suitable circuit closing device may be employed, the one
illustrated being shown merely as an example of one of the many possible con-
structions. A spring 8 maintains the switch S normally open.
The coil P is arranged to be dynamically acted upon by current in the coils K,
K. The coils K, K are, however, so connected that the currents therein act
in opposition to each other. It is evident, therefore, that when the torque exerted
by the current in coil K is insufficient to neutralize the torque due to current
in K, the switch S'will be closed, and that when a condition of equality is
reached the spring 8 will cause the switch S to open. The mode of operation is
as follows:-
When current passes through the series coil K¹ to the lamps L, or other trans-
lating devices, a torque is exerted between that coil and the movable coil P, and
the switch S is closed. As soon as the switch S is closed, current passes to the
armature of the motor generator, which, thereupon, commences to revolve.
The voltage at the generator terminals 1, rises directly with the speed, until
the current passing in the coil K is sufficient to balance the torque produced by
current in the series coil K¹.
The switch S then opens and the motor-generator slows down, thus lessening
the current in the coil K. The current in the series coil K¹ then overpowers
that in the coil K and the switch S closes. The motor-generator then speeds
up until a condition of balance is reached, and the switch again opens.
This
operation is repeated indefinitely, and with a rapidity dependent upon the pro-
portioning of parts and the delicacy of adjustment. For every different current
passing in the series coil K. it is evident that a proportionate amount of current
in the coil K will be required to neutralize its effect. Since the speed of the
motor generator is proportional to the current flowing in the coil K, it follows
that the number of revolutions registered by the counter C in a given time is
proportional to the amount of current flowing in the work circuit in the same
time. The counter, therefore, reads in ampere hours or the equivalent, when the
potential difference between the mains is constant or varying.
Having now particularly described and ascertained the nature of our 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-The method of measuring electrical energy which consists in generating
an electric current proportional to the current to be measured by mechanically
rotation a conductor in a magnetic field, transmitting the current so generated,
controlling thereby the rate of rotation of said conductor in accordance with the
current to be measured, and recording the revolutions of said conductor.
2 The method of measuring electrical energy, which consists in producing
two opposing torques, one of which is proportional to the energy to be measured,
the other proportional to the speed of a dynamo electric machine, maintaining
said torques at an approximate balance and registering the revolutions of said
dynamo-electric machine.
3-The method of measuring electrical energy, which consists in supplying
current to a dynamo electric machine, generating thereby a current proportional
to the speed of said dynamo electric machine, maintaining the current so gene
rated proportional to the energy to be measured, and registering the revolutions of
said dynamo electric machine.
4-The method of measuring electrical energy, which consists in producing
a torque proportional to the energy to be measured, supplying from a dynamo
electric machine a current exerting an opposing torque, maintaining the flow of

page_text: said current so that the resultant torque approximates zero, and registering the
revolutions of said dynamo electric machine.
5 In an electric meter, the combination of a motor-generator, and means,
controlled by the current generated thereby, for opening the supply circuit of the
motor-generator when its armature reaches a rate of rotation corresponding to
the energy to be measured.
GA motor generator having a permanent magnetic field, a circuit of constant
resistance connected to its generator terminals, and means for intermittently
supplying current to the motor element of the motor generator.
In a measuring instrument, the combination of a circuit closing device
having separate coils in fixed relation to each other and a third coil movable
relatively thereto, with means for sending currents through all the coils.
8 The combination of a motor-generator, a switch for closing the supply circuit.
of the motor generator, a switch actuating device having three coils, one of which
is relatively movable with respect to the other two, and means for supplying
current generated by the motor-generator to one of said coils.
9-The combination of two coils in fixed relation to each other, a third coil
movable relatively thereto, and a switch controlled by relative movement between
said coils.
10 In an electric meter, the combination of a motor-generator a switch in the
supply circuit of said motor generator, and a switch closing device having two
relatively movable members.
11 In an electric meter, the combination of a motor generator, a switch in the
supply circuit of said motor generator, and a switch closing device having two
relatively movable members the torque between which is the resultant of the
differential action of two currents in one member upon a current in the other
member.
12 In an electric meter, the combination of a motor generator, a switch in the
supply circuit of said motor generator, a switch-closing device having two rela-
tively movable members, one of which consists of two coils, one in series with
the work circuit, the other supplied with current from the motor generator, and
a coil comprising the other member of the switch-closing device and fed with an
approximately constant current.
13 In an electric meter, the combination of a motor generator, a switch for
closing the supply circuit of the motor generator, and a switch controlling device,
consisting of two relatively movable members, one of which is adapted to be
acted upon dynamically by two mutually opposing currents in the other member,
one of which currents is proportional to the energy to be measured, the other to
the speed of said motor generator.