Improvements in Watt-hour Meters and in the Means for Damping in same.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improvements in Watt-hour Meters and in the Means for Damping
in same.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, and FRANK HOLDEN,
all of 83, Cannon Street, in the City of London, Electrical Engineers, do hereby
declare the nature of this invention to be as follows:-
-
This invention relates to Watt-hour meters for measuring and recording the
energy expended by electric currents and also to a novel means for damping in
same and has for its object the provision of a thoroughly reliable meter.
lute mean.
The improved instrument takes an observation of the load to be measured at
certain fixed periods such as may be found desirable, and sums up the successive
readings, the mean being for commercial purposes practically equal to the abso-
In a meter constructed in accordance with our improvements we
employ a current coil or coils forming a magnetic field and an oscillating coil
which carries the electric current in shunt; the current coils are preferably
wound open so as to surround said shunt coil which may conveniently be made
rectangular and preferably astatic by forming it of two coils wound in opposite
directions so as to be independent of the earth's or other fields. The shunt coil
is mounted upon a vertical shaft freely and accurately pivotted in the frame,
and it is capable of an angular motion limited by certain determined stops.
The current is admitted through two conducting springs of suitable kind or
equivalent conductor may be used, for the purpose of bringing the said shunt
coil back to the starting position.
Below the shunt coil shaft and with its axis in the same line with it, is another
shaft, properly pivotted for revolving freely and carrying a disc, wheel, or equiva-
lent device with its plane at right angles to the shaft axis and having radial corru-
gations or horizontal ratchet teeth on its upper surface. Over these corrugations
or equivalents is arranged a light pawl of such kind as to be certain of engaging
same in one direction; it is carried by an arm projecting from the shunt coil
or its spindle described above, so that when the said coil moves, the lower shaft
is compelled to move with it in one direction. The disc or equivalent above
referred to is made large enough to have a sufficiently great moment of inertia
to ensure the most efficient and desirable speed. Our novel means for producing
the required damping or retarding force for obtaining constant torque is as follows.
Upon the lower or disc-shaft is fixed a mass of iron having a suitable hysteresis
loss, and such mass is arranged to nearly fill the space and revolve between the
poles of a permanent magnet, and this causes a constant retarding couple to be
exerted against the rotation of the disc or equivalent and its shaft. This arrange-
ment is an important feature of our invention inasmuch as by it the interpolar
space being almost completely filled with magnetic material the magnet is ren-
dered far more permanent than is the case with usual arrangements for damping

page_text: in which the interpolar space is entirely filled with copper or other non-magnetic
material, and, as is well known, the magnet is thus more liable to demagnetization.
In a meter, in connection with this last described part a recording counter such
as is ordinarily used in meters, is employed.
In all Watt-hour meters the couple acting on the shaft coil is proportional to
the product of the values of the currents in the shunt and current coils. This
action serves to cause the shunt.coil to rotate and, by the pawl above described,
its rotation is transmitted by means of the ratchet to the lower shaft and counting
mechanism.
A clock is provided, preferably a self-winding electrical clock adapted to make
the contact periodically and so constructed as to keep the shunt circuit closed
during the time the shunt coil is rotating through its entire range, but the
circuit may be opened directly after this is effected.
The shunt coil being at rest because of having come against the limiting stops
above mentioned, the lower or disc-shaft will continue to rotate till brought to
rest by the hysteretic torque. For each closing of the shunt circuit the disc or
equivalent will move through an angle proportional to the Watts being expended
at that time, and consequently the record of the counting gear will indicate in
the usual way the total energy consumed. When the number of rotations of the
lower shaft is to be proportional to the Watt-hours measured by the instrument
at all loads, the mean couple exerted by the shunt coil spring should be equal
to the moment of the couple exerted by the magnetic drag multiplied by the
moment of inertia of the shunt coil and divided by the moment of inertia of the
disc and the several connections.
The force exerted by the shunt coil spring device opposes the forward rotation
of the shunt coil and may be used to return it to its initial position and some
convenient kind of cushion is provided for bringing it to rest with no rebound.
In our improved arrangement the total weight of the rotating parts is con-
siderably less than of Watt-hour meters as usually hitherto constructed and the
pivot friction and liability to deterioration is greatly reduced.
Also there are no brushes and commutators such as are usually employed and
therefore the friction due to such appliances is avoided, and also the uncertainty
of contact from this it follows that our improved Watt-meter will work in so
far as errors from friction are concerned with smaller forces than have hitherto
been generally possible. Iron can be readily obtained with a very closely con-
stant hysteresis loss for long periods of time, and with great ranges of tempera-
ture; as a consequence the only temperature error would be that due to the
change of resistance of the shunt circuit, and as this would be chiefly made of
German silver, this would be practically negligible.
The only causes of change would be those of a purely mechanical character.
Dated the 15th day of November 1897.
COMPLETE SPECIFICATION.
Improvements in Watt-hour Meters and in the Means for Damping 45
in same.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, and FRANK HOLDEN,
all of 83, Cannon Street, in the City of London, Electrical Engineers, do hereby
declare the nature of this invention, and in what manner the same is to be

page_text: performed, to be particularly described and ascertained in and by the following
statement:-
This invention relates to Watt-hour meters for registering the energy expended
by electric currents and also to a novel means for damping in same, and has for its
object the provision of a thoroughly reliable, accurate and cheap, meter of this
class.
Heretofore it has been proposed to construct meters having a periodic relative
motion of the two coils of a Watt-dynamo-meter, but the general tendency has
been to obtain a movement of the coils which would be proportional to Watts.
Although such an arrangement may give accurate readings for high loads it would
only be possible to obtain accurate readings for low loads by the greatest refine-
ment in the construction of the instrument, so that the instrument is either lacking
in accuracy or is too expensive for practical purposes.
An important feature of our new meter is that the moving coil is deflected
through a constant angle at all loads within the range of the meter, and so even
at the lowest loads nearly the same accuracy is obtained as at the highest loads
without any complicated or difficult construction being necessary. The improved
instrument is so arranged as to take observations of the load to be measured at
certain fixed periods such as may be found desirable, for example, an observation
every one or two minutes, and these successive observations are summarized by a
counter.
The meter is controlled as is hereinafter explained by a clock which may be
either electrically self-winding or an ordinary clock but preferably one capable
of running for a long period without requiring winding up. Also several nieters
may be operated by one clock which may be enclosed in the meter case or form
a separate part thereof.
In order that the invention may be clearly understood and readily carried into
practice we will now fully describe the same with reference to the accompanying
drawings, in which Fig. 1 is a front elevation partly in section; Fig. 2 is a side
elevation, some of the parts being broken away; and Fig. 3 is a sectional plan
of our improved Watt-hour meter; in these figures the outer casing has been
omitted for clearness' sake. Fig. 4 is a diagrammatic view showing the method
of connecting. A is the main frame made preferably of non-magnetic material
and having arms or brackets a a' and a³, between which are mounted on pivots
so as to move with very little friction two vertical spindles B and B¹. These two
spindles are lineable with each other and are supported in adjustable jewelled
screw-bearings such as are shown. From the sides of the frame A extend two
arms A¹ A² having firmly secured to them two coils C C formed with a central
opening and arranged to allow of the passage of the current of the load which
is to be registered. These coils are insulated from the frame and astatically
connected together. On the spindle B is rigidly mounted a potential coil D
consisting of two parts astatically connected with one another and projecting with
their outer portions into the openings of the coils CC which may thus form a
magnetic field for the coil D and cause this latter together with its spindle B
to make a limited angular movement within the said openings. The potential
coil 1 is made preferably of wire drawn from German silver or other high
resistance metal, and it is advantageously of the form shown in the drawings.
Near the upper end of the spindle B and firmly secured thereto is a short
cylindrical block E of ebonite carrying the two terminals bb1 of the shunt coil D.
To each of these terminals is joined a thin metallic strip or band 63 and 4 which
is about 001 of an inch thick, and is wound around a portion of the periphery
of the cylindrical block E as best seen in Fig. 3. Each strip 63 64 is connected
to one end of a spring wire F, which in turn is secured to an adjustable metal
spring G. These springs G form the terminals of the shunt circuit and are fixed
to an ebonite block H attached to the arm of the main frame, and they are
provided with adjusting screws 9 by means of which the couple tending to

page_text: rotate the coil D may be altered and adjusted to the proper degree. In connection
with the springs G additional resistance may be employed where necessary, but
such will not be required under ordinary circumstances, that is to say for
example in cases of lighting circuits of 230 volts or thereabouts, providing the
coil D is made of German silver as before mentioned or of other high resistance
metal.
is
On the spindle B near its lower end is also fitted an arm 65 carrying at its free
end a very light pivotted pawl I, adapted to engage ratchet teeth or corrugations j
formed on the upper face of a horizontal disc J mounted rigidly on the spindle B₁,
the arrangement being such as to be capable of transmitting the angular motion
of the coil 1) in one direction only to the said disc, without causing the latter
to be influenced by the return motion of the coil. Another light pawl
pivotted to the bracket a¹ of the main frame in such a manner as to oppose the
return motion of the disc J. This disc which is made preferably of non-magnetic
material is designed to have a large moment of inertia with comparatively little
weight. The movement of the coil D is limited by stops such as d arranged to
strike against the sides forming the opening in the coils C, or any other convenient
arrangement of stops may be employed.
Below the disc J and rigidly mounted on the same spindle B¹ is another disc K
made of iron, steel or other magnetic material and revolving between the poles
of a small permanent horse-shoe steel magnet L.
The poles of this magnet are displaced so that while each presents a large
surface close to the magnetic disc yet the poles are not opposite one another.
By this means the density of the magnetic flux in the iron is made a maximum,
and the density in the air space a minimum.
The magnet L is mounted on a support which permits of an adjustment of the
poles towards or away from the centre of the disc K for the purpose of calibrating.
By this arrangement when once adjusted a constant force is produced opposing
any motion of the disc.
A worm M provided near the lower end of the spindle B serves for operating
& counter or recording mechanism which is not shewn in the drawing, but is or
may be of the kind ordinarily used in recording meters.
The clock above referred to is for connecting the potential or shunt circuit to
the line circuit a record of which is to be made, and for keeping the circuit closed
for a sufficiently long period (of say two or three seconds) to enable the coil to
move through its entire range of motion. This involves no construction not already
well understood in the art.
.
In the diagram Fig. 4 the main or line conductors feeding the lamps 02 are
represented at 0 0' and the coils C C are connected to the line wire O by wires c cl
and one with the other by a wire 2. The coil D arranged between the coils CC
is connected by a wire d with the wire c and by a wire with the clock move-
ment N. The clock is provided with a contact which is moved by the clock
against a contact connected with the wire leading to the line wire O¹.
On the circuit being open the action of the springs F F causes the coil I) to
rotate until one of its stops d comes against the inner side of one of the coils C,
but on the shunt circuit being closed while there is a load on the meter, i.e. while
a current is passing through the coils C C, the mutual effect of the currents
produces a turning moment in the spindle B proportional to the Watts. The
consequent movement of spindle B is transmitted to the disc J by the pawl I,
causing them both to revolve with the same velocity until the motion of the coil D
is arrested by one of the stops d above referred to. Shortly thereafter the clock
movement interrupts the potential circuit and allows the coil ID to return to its
initial position while the disc J continues its rotary movement until brought to
rest by the action of the drag consequent upon the hysteretic loss in the disc K.
By properly adjusting the tension of the springs F F the angle of deflection
of the disc J may be rendered proportional to the Watts being expended at the

page_text: time of observation. The required tension for the springs is found by trial in
calibrating the meter.
We desire it to be understood that our invention is not to be limited to the
particular form of spring construction above described, as other arrangements
may be used, for instance, two spiral springs such as are commonly employed in
electrical instruments could be readily substituted.
The constant of the meter may be increased by augmenting the resistance of
the potential or shunt circuit, or by decreasing the angle of deflection of the
coil D, or by strengthening the magnet L or moving its poles towards the peri-
phery of the disc K. At high load the tension of the springs F F has but little
effect on the readings, so that a correct calibration is obtained after getting the
high load reading nearly right by one or more of the above means, preferably
by moving the magnet and then adjusting the said springs F F by turning the
screws g until the low load reading is nearly correct.
Then another adjustment of the magnet is made at high load so as to correct
for the variations made in the tension of the springs and a final adjustment at
low load renders the meter practically correct for all loads within the range of
the meter.
As the damping force due to the hysteretic loss in the disc K is constant and
does not decrease with the load, as is the case with magnetic damping devices
provided with copper discs as usually hitherto employed, the instrument gives
very accurate readings even down to the lowest load which it is capable, of regis-
tering, as the variable frictional forces always remain relatively very small.
Furthermore, the coefficiencies for German silver and the hysteretic loss in
the iron being low, the instrument will have a low temperature coefficient.
the shunt connection is made for only about three seconds at most and then open
for the remainder of a minute the resistance of the potential circuit may be as
low as 500 ohms with an average loss of one Watt in the potential circuit when
on a 100 volt circuit. Such loss may be reduced by taking observations at longer
intervals.
A.s
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that what
we claim is:-
1. A Watt-hour meter for registering the energy expended in electrical cir-
cuits, having a Watt-dynamo-meter arrangement of which one member is pivoted
and capable of a limited angular motion, combined with a revoluble part to which
it transmits its motion, the latter part being provided with a damping device and
counter for registering the revolutions, substantially as herein described.
2. In a Watt-hour meter the means for producing a damping effect consisting
of a body of magnetic material revolving in proximity to the poles of a constant
magnet, substantially as herein described.
3. In Watt-hour meters for periodically registering the energy expended in
electric circuits, the use of an electro-dynamometer, one member of which is
caused to move through a constant angle in the magnetic field formed by the
other member, substantially as herein described.
4. A Watt-hour meter constructed arranged or adapted to operate substantially
in the manner herein set forth in reference to the accompanying drawings.
Dated thin wist h 3
For the Applicants,
J. C. CHAPMAN,
Chartered Patent Agent, 70, Chancery Lane, London, W.C.