Improved Apparatus for Measuring and Rocording Electric Currents.
Year: 1891

page_text: Date of Application, 27th Oct., 1891
Complete Specification Left, 27th July, 1892-Accepted, 22nd Oct., 1892
PROVISIONAL SPECIFICATION.
Improved Apparatus for Measuring and Rocording Electric Currents.
I, WILLIAM THOMSON, Baron Kelvin of Largs, Professor of Natural Philosophy
in the University of Glasgow, North Britain, do hereby declare the nature of this
invention to be as follows:-
For measuring electric currents I use a steel magnet straight or of horseshoe
shape with one end or both ends attracted by a fixed solenoid or two fixed solenoids
in the manner described in my Specification No. 4617 A.D. 1883. Or instead of
the steel magnet I use an electro-magnet consisting of a thin bar of soft iron with a
solenoid of fine insulated wire wound upon it. The two ends of this wire are
connected with fixed conductors by two fine elastic wires which may be in the shape
of spiral springs and may be used for bearing the weight of the electro-magnet.
The current to be measured passes through a fixed solenoid or two fixed solenoids
attracting inwards one end or both ends of the moveable electro-magnet. I find
that the force of this attraction is very nearly the same, for the same strength of
current through the fixed solenoid or solenoids, and very nearly in simple porportion
to the strength of this current, through a wide range of motion of the moveable
electro-magnet, having its end or ends within the hollows of the fixed solenoids,
provided that the magnetising force of the current in the electro-magnet is sufficiently
strong to magnetise the soft iron nearly to saturation. Thus the strength of the
current through the fixed solenoid or solenoids may be very approximately read
off on a straight scale of equal divisions indicating the distance through which the
moveable electro-magnet is pulled against the force of its bearing springs, when it
is hung by spiral springs as described above. When it is desired to magnify the motion
to be read by eye, this may be done by a thread or fine wire attached to the
moveable electro-magnet, and wound upon a finely pivoted pulley carrying a long
index-arm moving over large divisions on a circular scale. The indications of the
instrument may be recorded on a curve by means of a pen slipping on paper moved
uniformly by clockwork. When it is desired to eliminate error due to friction of
the pen on the paper this may be done by the method described in my Patent
No. 15769, A.D. 1889. Two or more wires may be wound on the fixed solenoid or
solenoids in any case in which compound winding is wanted, as for instance in the
supply of electric energy for electric lighting or other purposes, when the instrument
is to serve for measuring the pressure at the distant end of a pair of feeding
conductors or the mean of the pressures at the ends of several pairs of feeding
conductors. The fixed conductor or conductors may be of other than solenoidal
configuration when sufficiently approximate uniformity of field through a sufficient
space can be otherwise more conveniently obtained. For example, when the
currents to be measured are very large, a vertical plate, conducting the current
horizontally may be used for the fixed conductor, and a horse-shoe magnet with its
poles on the two sides of the plate may be used to indicate by upward and down-
ward motions, the strength of the currents.
To measure the total quantity of electricity supplied in electric lighting, I use a
counter like that described in the same Patent (No. 16769 A.D. 1889), but having
a broad flat rim for its roller instead of a fine edge. At periodic intervals of time
this roller is, by a revolving cam or otherwise, caused to press against a light bar
of metal or wood or vulcanite or other suitable material, carried by the electro-
magnet, and so cause this bar to press against a roller kept revolving uniformly by
clockwork or otherwise. In virtue of this pressure and motion the bar is lifted, and
causes the roller of the counter to turn through a corresponding space. A fixed
stop prevents the bar from being lifted above the position that it occupies when

page_text: borne by the electro-magnet, and when the electro-magnet is in its zero position,
that is to say, the position in which it rests when no current passes through the fixed
solenoid. The bar may be firmly attached to the electro-magnet, in which case the
electro-magnet is caused to move with the bar by the action of the rollers. Or it
may rest on the bottom of a guiding tube firmly attached to the electro-inagnet;
and thus the electro-magnet may not be compelled to follow the bar through the
whole space of its motion to the zero stop.
Instead of causing the bar to move to its zero position by pressing it against a
drum always revolving in one direction, it may be lifted and let down, or pressed
down and allowed to rise again by a platform, or a pin, or fork, which is kept
moving up and down regularly by clockwork or otherwise; the roller of the counter-
train being caused by a cam to press on the bar and to cease pressing so as to bring
it into proper position for being thus acted on, and to leave it free again.
Dated this 26th day of October 1891.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.
.
COMPLETE SPECIFICATION.
Improved Apparatus for Measuring and Recording Electric Currents.
I, WILLIAM THOMSON, Baron Kelvin of Large Professor of Natural Philosophy
in the University of Glasgow, North Britain, 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 following statement :-
For measuring electric currents I use a steel magnet straight or of horse-shoe
-shape with one end or both ends attracted by a fixed solenoid or two fixed solenoids
in the manner described in my Specification No. 4617, A.D. 1883. Or instead of
the steel magnet I use an electro-magnet consisting of a thin bar of soft iron with a
solenoid of fine insulated wire wound upon it. The two ends of this wire are
connected with fixed conductors by two fine elastic wires which may be in the shape
of spiral springs and may be used for bearing the weight of the electro-magnet.
The current to be measured passes through a fixed solenoid or two fixed solenoids
attracting inwards one end or both ends of the movable electro-magnet. I find that
the force of this attraction is very nearly the same for the same strength of current
through the fixed solenoid or solenoids, and very nearly in simple proportion to the
strength of this current, through a wide range of motion of the movable electro-
magnet, having its end or ends within the hollows of the fixed solenoids, provided
that the magnetising force of the current in the electro-magnet is sufficiently strong
to magnetise the soft iron nearly to saturation. Thus the strength of the current
through the fixed solenoid or solenoids may be very approximately read off on a straight
scale of equal divisions indicating the distance through which the movable 'electro-
magnet is pulled against the force of its bearing springs when it is hung by spiral
springs as described above. When it is desired to magnify the motion to be read
by eye, this may be done by a thread or fine wire attached to the movable electro-
magnet and wound upon a finely pivoted pulley carrying a long index arm moving
over large divisions on a circular scale; or by a rack and pinion. The indications
of the instrument may be recorded on a curve by means of a pen-slipping on paper
moved uniformly by clockwork. When it is desired to eliminate error due to friction
of the pen on the paper, this may be done by the method described in my Patent
No. 15,769, A.D. 1889. Two or more wires may be wound on the fixed solenoid
or solenoids in any case in which compound winding is wanted, as for instance in
the supply of electric energy for electric lighting or other purposes, when the
instrument is to serve for measuring the pressure at the distant end of a pair of
feeding conductors, or the mean of the pressures at the ends of several pairs of
feeding conductors. The fixed conductor or conductors may be of other than

page_text: solenoidal configuration when sufficiently approximate uniformity of field through a
sufficient space can be otherwise more conveniently obtained. For example when
the currents to be measured are very large, a vertical plate conducting the current
horizontally may be used for the fixed conductor, and a horse-shoe magnet with its
poles on the two sides of the plate may be used to indicate by upward and down-
ward motions the strength of the currents.
To measure the total quantity of electricity supplied in electric lighting I use a
counter like that described in the same Patent (No. 15769, A.D. 1889) but having a
broad flat rim for its roller instead of a fiue edge. At periodic intervals of time
this roller is, by a revolving cam or otherwise caused to press against a light bar of
metal or wood, or vulcanite or other suitable material, carried by the electro-magnet,
and so cause this bar to press against a roller kept revolving uniformly by clockwork
or otherwise. In virtue of this pressure and motion the bar is lifted and causes the
roller of the counter to turn through a corresponding space. A fixed stop prevents
the bar from being lifted above the position that it occupies when borne by the
electro-magnet, and when the electro-magnet is in its zero position, that is to say,
the position in which it rests when no current passes through the fixed solenoid.
The bar may be firmly attached to the electro-magnet, in which case the electro-
magnet is caused to move with the bar by the action of the rollers. Or it may
rest on the bottom of a guiding tube firmly attached to the electro-magnet, and thus
the electro-magnet may not be compelled to follow the bar through the whole space
of its motion to the zero stop.
Instead of causing the bar to move to its zero position by pressing it against a
drum always revolving in one direction, it may be lifted and let down, or pressed
down and allowed to rise again by a platform or a pin or fork, which is kept moving
up and down regularly by clockwork or otherwise; the roller of the counter-train
being caused by a cam to press on the bar, and to cease pressing so as to bring it
into proper position for being thus acted ou, and to leave it free again.
In order that my invention may be properly understood and readily carried into
effect I have hereunto appended three explanatory sheets of drawings in the several
figures of which corresponding parts are marked with the same letters of reference.
On Sheet 1 the instrument is shown in its simplest form for measuring electric
currents.
On Sheets 2 and 3 the instrument is illustrated as arranged for recording the
total quantity of electricity supplied.
Figure 1 is an elevation.
Figure 2 is a vertical section.
Figure 3 is a vertical section of the upper part taken at right angles to that
shown by Figure 2.
Figure 4 is an elevation of the recording instrument.
Figure 5 is a section of the fixed solenoid.
Figure 6 is an end view of the recording instrument.
In carrying out my invention I use a movable electro-maguet consisting of a thin
bar of soft iron a with a solenoid of fine insulated wire wound upon it. The two
ends of this wire are connected with fixed binding screws b, b by two fine elastic
wires which may be in the shape of spiral springs as shown at cc, and may be used
for bearing the weight of the electro-magnet. The current to be measured passes
through a fixed solenoid d attracting inwards one end of the movable electro-magnet.
From one of the binding screws b, ha connection is made to the terminal u.
From
the other of the binding screws bb a connection is made to one end of an anti-
inductive resistance of fine wire vv, the other end of this resistance being joined to
one of the terminals of the fixed coil w w. The anti-inductive resistance is of an
amount sufficient to ensure that the current passing through the electro-magnet will
magnetise the iron nearly to saturation. Two fixed stops xx are placed so as to
regulate the range of the electro-magnet and ensure that it cannot be thrown out of
the fixed coil d and that it cannot be drawn down by the attraction of the fixed
solenoid so far as to cause damage. I find that the force of this attraction is very

page_text: nearly the same for the same strength of current through the fixed solenoid and
very nearly in simple proportion to the strength of this current through a wide range
of motion of the movable electro-magnet having its end within the hollow of the
fixed solenoid, provided the magnetising force of the current in the electro-magnet
is sufficiently strong to magnetise the soft iron nearly to saturation. Thus the
strength of the current through the fixed solenoid may be very approximately read
off on a straight scale e of equal divisions by means of a pointer indicating the
distance through which the movable electro-magnet is pulled against the force of its
bearing springs when it is hung by spiral springs as shown on the drawings. The
springs used to suspend the movable electro-magnet are made one right-handed and
the other left-handed, so that when the electro-magnet is pulled down, the tendencies
of the springs to uncoil being approximately equal and opposite, the parallelism of
the line of motion of the pointer to the scale e is preserved and friction avoided.
The binding screws b, b are carried by a piece of vulcanite or other insulating
material, which can be raised or lowered a little by means of the screw h in order
to adjust the pointer to the zero of the scale. When the instrument is used to
measure currents such as those supplied by a dynamo machine or electric battery,
the fixed solenoid is inserted in the circuit of the current to be measured by means
of the binding screws to, w, and a connection is taken from the binding screw u to the
main from the other pole of the battery or dynamo.
The instrument adapted for use as a meter for measuring the total quantity of
electricity supplied is shown on Sheets 2 and 3 of the accompanying drawings.
The electrical measuring part of this instrument is similar in every respect to that
already described, but I attach a guiding tube i at the bottom end of the electro-
magnet a, and a loose light bar i resting on a projecting ring in the bottom of the
guiding tube. I use a counter k similar to that described in my previous Patent
No. 15,769, A.D. 1889, but the roller k¹ has a broad flat rim instead of a fine edge.
The loose bar hangs between the roller k¹ and another roller. The range of the
electro-magnet a is fixed by stops, and the end of the bar is guided by the cheekst,
so that it cannot be thrown out from between the rollers and 1. At periodic
intervals of time the roller is, by a revolving cam m, caused to press the bar j
against the roller k', and at the same time, and actuated by the same cam wheel m,
a platform n is lifted till it touches the lower surface of the cheeks t, and lifts up
the bar j, and causes the roller k¹ of the counter to turn through a space proportional
to the amount of current passing through the fixed coil d.
The zero position of the electro-magnet a is adjusted so that the extreme end of
the bar j just touches the platform n when the latter is drawn up against the lower
surface of the guiding cheeks (.
:.
"
*-
The cam wheel mis kept revolving uniformly by clockwork, and has attached to
it a stud m', Figure 6, which carries the platform n by a fine connecting wire o
having a small spiral spring o'. As the cam wheel revolves, the platform n is lifted
till it presses against the lower surface of the guiding cheeks t, and lowered till it is
below the lowest possible position of the rod j, by the rising and falling of the
stud m. The roller is pivoted to a rod attached to a cross-piece which is
pivoted to the framework of the instrument. Attached to the cross-pièce q there is
another springy rod which carries a roller & which is kept in contact with the cam
wheel. The cam wheel is shown detached at Figure 44, and it will be seen that
part of the circumference is of larger radius than the other part. While the
portion of the can wheel m which is of larger radius is passing the roller & the
roller is pressed towards k', and the loose piece ; is nipped between the rollers!
and A'. At this time the platform n is at the bottom of its range.
If a current is passing through the fixed coil d, the electro-magnet a, and
consequently the bar j, is pulled down by a corresponding amount, and the platform'n
in its upward motion carries the barj back to its zero position, at the same time
turning the rolling wheel kl. When the platform n first touches the lower surface
of the guiding cheeks t the stud is not quite at its highest position, and while it
rises to it the spring o' is elongated. When the stud m² begins to fall the spring

page_text: contracts, and at the same time the bar j is unclamped from between the rollers k¹
and I, so that by the time the platform n begins to fall, the bar j is hanging quite
free.
When no current is passing the bar j is clamped at its zero position, and the
platform n on being lifted touches the end of the bar ; and the lower surface of the
j
cheeks t at the same time, and no record is made on the roller k¹.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The instrument for measuring electric currents substantially as described with
reference to Figures 1, 2, and 3.
2. The instrument for measuring and recording electric currents substantially as
described with reference to Figures 4, 5, and 6.
3. The suspended electro-magnet with either or both its poles actuated by electric
current or currents through a fixed conductor or conductors for the purpose of
measuring this current or these currents in the manner described.
4. The use of two spiral springs, right-handed and left-handed, for the purpose
of preventing the suspended electro-magnet from turning under the influence of the
forces concerned.
5. The mode of recording the total amount of the measured current substantially
as described.
Dated thin wath of T... 1000
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.