Improvements in or relating to Electric Meters.
Year: 1899

page_text: Date of Application, 1st Aug., 1899
Cunnifination Inte 40th An
4000
Locontest
10th May
1600
Date of Application, 1st Aug., 1899
Complete Specification Left, 10th Apr., 1000 Accepted, 12th May, 1000
PROVISIONAL SPECIFICATION.
Improvements in or relating to Electric Meters.
We, JOHN HENRY BARKER, Engineer, of 26, Park Parade, Cambridge, in the
County of Cambridge, and JAMES ALFRED EWING, Professor of Applied
Mechanics, of Langdale Lodge, Cambridge, in the County of Cambridge, do
hereby declare the nature of this invention to be as follows:-
:-
Our invention relates to improvements in electric meters and has special refer-
ence to apparatus which is incorporated in such meters for the purpose of indicat-
ing the maximum rate of supply of electric current or electric energy.
In certain well known types of electric meters the rotation of a disc or other
revolving conductor is opposed by the electro-magnetic drag between it and a
magnetic brake consisting of a fixed magnet or magnets, in consequence of the
eddy currents which are generated in the conductor by such relative rotation.
In carrying out our invention we suspend or pivot the magnetic brake in such
a way that it is allowed to move through a small distance against a spring or
other suitable controlling force and thereby to actuate an indicator which multi-
plies the small motion of the brake and indicates the amount of the greatest
drag between it and the disc.
The spring or other controlling force is made comparatively strong in order
that the motion of the magnet poles may be so small as not to affect the rate of
the meter and also in order that the period of oscillation of the suspended
system may be short. When a sudden increase takes place in the rate of supply
the magnetic brake would tend to swing beyond the position proper to the new
rate of supply if their period of oscillation were not short in relation to the time
taken by the revolving parts of the meter to acquire their new velocity. This
tendency is obviated by making the period of the magnets sufficiently short in
relation to the time during which the disc is undergoing acceleration when a
current is suddenly applied or suddenly increased. Further advantages of the
strong controlling force and consequently small movement of the magnets, are
that the brake may be pivoted eccentrically to the disc and also that there is no
necessity for the use of dash-pots or similar arrangements to check the oscilla-
tions although such means may be used if desired. Again, the small movement
of the magnets assists in preventing disturbance of the indications through
the direct effect of the motor coils in cases where continuous currents are used.
In one construction of meter according to this invention we mount the magnets
upon a bridge-piece or frame which is pivotted or suspended about an axis
parallel to the axis of the disc and at a convenient distance from it.
imagnets are attached to the bridge-piece by means of clamps or stirrup pieces
and slots are provided so that the distance between the magnet poles may be
adjusted. The magnetic brake is carried upon an axle which is supported in
suitable bearings attached to the frame of the instrument, and a spring is pro-
The

page_text: Improvements in or relating to Electric Meters.
We, JOHN HENRY BARKER, Engineer, of 26, Park Parade, Cambridge, in the
County of Cambridge, and JAMES ALFRED EWING, Professor of Applied
Mechanics, of Langdale Lodge, Cambridge, in the County of Cambridge, 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 follow-
ing statement:-
Our invention relates to improvements in electric meters and has special refer-
ence to apparatus which is incorporated in such meters for the purpose of in-
dicating the rate of supply of electric current or electric energy, and of recording
the maximum rate of such supply. Such a device may be called a demand
indicator.
In certain well-known types of electric meters the rotation of a disc or other
revolving conductor is opposed by the electro-magnetic drag between it and a
magnetic brake consisting of a fixed magnet or magnets, in consequence of the
eddy currents which are generated in the conductor by such relative rotation.
In carrying out our invention we suspend or pivot the magnetic brake in such
a way that it is allowed to move through a small distance against a spring or
other suitable controlling force and thereby to actuate an indicator which multi-
plies the small motion of the brake and indicates the amount of the drag between
it and the disc.
The spring or other controlling force is made comparatively strong in order
that the motion of the magnet poles may be so small as not to affect the rate of
the meter and also in order that the period of oscillation of the suspended
system may be short. When a sudden increase takes place in the demand for
current and consequently in the rate of supply the magnetic brake would tend
to swing beyond the position proper to the new rate of supply if its period of
oscillation were not short in relation to the time taken by the revolving parts
of the meter to acquire their new velocity. This tendency is obviated by making
the period of oscillation of the brake sufficiently short in relation to the time
during which the disc is undergoing acceleration when the current is suddenly
applied or suddenly increased. Further advantages of the strong controlling
force and consequently small movement of the brake, are that the brake may be
pivotted eccentrically to the disc without causing its motion to affect the rate of
the meter, and also that there is no necessity for the use of a dash-pot or similar
arrangement to check the oscillations, although such means may be used if
desired. Again, the small motion of the brake assists in preventing disturbance
of the indications through the direct effect of the motor coils in cases where
continuous currents are used and the field of the motor is produced by current
in coils.
In the accompanying drawings:
Figure 1 is a side elevation partly in section showing a portion of one con-
struction of meter according to this invention,
Figure 2 is a front elevation,
Figure 3 is a plan with parts removed for the sake of clearness, and
Figure 4 is an elevation of a portion of the device looking in the direction
of the arrow in Figure 3.
Like letters indicate like parts throughout the drawings.
A is a disc of conducting material supported on an axle A' and revolving

page_text: In order that the oscillating system may be securely held and prevented from
being damaged during transport, screwed holes C7 are formed in the ends of the
bridge-piece C. Before transport, screws 08 are passed through clearing holes
in brackets C, attached to part of the frame G, into the screwed holes C' so that
the magnetic brake is lifted from its bearing at E and is held fixed.
Although it is preferred to apply the pivotted pawl M and its rack M¹ to the
whole oscillating system as described, we may, if desired, apply such an arrange-
ment to the pointer only, so that the brake is free to return when the drag
diminishes, leaving the pointer in its position of maximum deflection. In such
a case two pointers may be provided, one with a retaining device and the other
free to follow the movements of the brake. Further the retaining device may
be entirely dispensed with if the indicator is required only to indicate the
amount of the reaction between the revolving disc and the brake without record-
ing the greatest amount of that reaction..
To reduce the influence of friction on the pivotted brake we may use the
device of making the drag between the revolving disc and the brake suffer small
periodic variations in amount as for example by having one or more holes cut
in the disc with the effect that when a hole passes the poles of a brake magnet
the drag of the brake is momentarily lessened and the brake consequently
receives a slight motion of oscillation which assists in overcoming any frictional
sticking to which it may be subject.
In meters for measuring supply by continuous currents care must be taken to.
arrange the magnetic brake so that the electric currents in the meter do not
directly tend to displace it. For this purpose we prefer to invert one of the two
magnets forming the brake so that the pair shall constitute an astatic or nearly
astatic system. When this is done it may in some cases occur that the stray field
from the magnets constituting the brake affects the field of the motor and con-
sequently disturbs the rate of the meter. We may compensate for this by
several devices, such as introducing a separate compensating magnet to balance,
on the motor armature, the field produced by the magnets of the brake, or using
a shunt field-coil in the motor for the same purpose.
It is to be understood that the details of this device may be varied without
departing from the spirit of the invention which may be applied to other types
of electric meters, such for instance as those in which the motion depends upon
an oscillating movement instead of a revolving movement or to meters in which
the magnetic drag is produced by causing the magnets to move while the con-
ductor is held from following.
The invention may also be applied to other types of brake beside magnetic
brakes, and the magnetic brake indicating mechanism may be applied to meters
having other forms of brake,-air brakes for example.
In meters in which the main braking action is other than electromagnetic we
may use in the revolving portion of the meter a conductor or magnet acting
electro-magnetically on a pivotted or suspended magnet or conductor in the
manner described and for the purpose of obtaining a record of the greatest rate
of supply. The device thus added will increase any braking action to which
the revolving piece may be otherwise subject, and a corresponding reduction may
be made in the other part of the braking action.
Although it is convenient to use for the magnetic brake two magnets coupled
by a bridge-piece as herein described, yet a single magnet or more than two
magnets, may, if desired, be used. Further although it is preferred to pivot_the
revolving disc and the magnet about parallel axes, it is possible to pivot them
so that their axes are coincident.
We are aware of Wilson's Patent No. 8068/96 of which we are proprietors,
and we make no claim to anything therein described and claimed.
We are also aware that, among other means, a device consisting of a pawl and
rack has previously been patented for retaining the pointer of an electric