Apparatus for Measuring and Recording Electric Currents.
Year: 1889

page_text: Date of Application, 8th Oct., 1889
Complete Specification Left, 7th July, 1890-Accepted, 16th Aug., 1890
PROVISIONAL SPECIFICATION.
Apparatus for Measuring and Recording Electric Currents.
I, Sir WILIAM THOMSON, Knight, of Glasgow College; Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, North Britain do hereby declare the nature of this invention
to be as follows:-
This apparatus consists of a moveable body, which, for brevity I shall call the
indicator, carrying a pointer and recorder; wheel-work to actuate the recorder; an
electric motor or clock-work to keep the wheel-work in motion; and electric con-
ductors for the currents actuating the indicator.
in
The indicator is a body caused to take different positions according to the different
strengths of the currents to, be measured. It may be soft iron, or a steel magnet
actuated as in known forms of instruments for measuring alternate or direct
currents. For measuring either alternate or direct currents I prefer for indicator
a coil of insulated wire, supported on knife-edges and adjusted by a weight clamped
proper position on a slide, allowing it to be moved up or down along a line which
is vertical when the indicator is in its zero position. To approximately enough
equalize the motions of the indicator for equal differences of current in different
parts of its scale, I use one or more pendulums hanging vertically down from a fixed
point, or points, and touched by a bar or bars projecting from the indicator when
it comes to positions beyond which its motions, unresisted by the pendulums, would
be too large. The indicator carries a pointer by which its position is read off on a
fixed, scale graduated to equal divisions, or to divisions corresponding to amperes
or decimals of an ampere by comparison with one of my standard balances, or other
apparatus for absolute measurement of electric currents. To equalize its deflec-
tions at different temperatures with the same difference of potentials between its
terminals, I attach to it an appliance analogous to the temperature compensation of
a clock pendulum, arranged to raise or lower the centre of gravity when the tempera-
ture is raised or lowered.
The recorder consists of a marker carried by the indicator on a sliding or jointed
mounting, allowing it relative motion perpendicular to the line of motion of the.
indicator. A cam, having its axis as nearly as may be parallel to the line of motion
of the indicator touches the marker periodically (once every three minutes for
example) and presses it against a very slowly moving drum, on which it leaves a
mark. These marks. shew the strengths of the current which was passing at the
times corresponding to the positions of the drum when they were made. The total
quantity of electricity which has passed may be found by addition of the numbers
expressing the current strengths. To obviate the labour of this computation I
attach to the marker a light train of wheels counting the turns of a very small roller,
against which the cam presses to give the periodic motion to the marker. The act-
ing surface of the cam in different planes perpendicular to its axis extends through
a greater or a less portion of the circumference in proportion to the strength of the
current required to bring the indicator to the corresponding positions. Thus the
roller is kept in action for a longer or shorter time of every period, and is turned to
an extent proportional to the strength of the current at the instant when the cam
commences its action.
The moveable coil of the indicator is acted on by one or by two fixed coils through
which the current to be measured flows. The moveable coil may also carry the
current to be measured, but when the apparatus is employed as a meter for electric
light I prefer to give it a current from the mains through a highly resisting fixed
conductor. To render the apparatus applicable to alternate currents as well as to

page_text: direct currents this conductor ought to have resistance several times greater than
that of the moveable coil, and to have an anti-inductive configuration; and whether
for direct or alternate currents its resistance ought to have but small temperature
variation, and it ought to expose as large a surface as may be to the air to get quit
of the heat generated in it. I therefore make it of fine platinoid wire wound in
parallel lines on two sides of a square or oblong of thin insulating material, such as
glass, or wood, or mica, or an endless cloth (like a miniature roller towel) stretched
between two thin parallel bars such as ivory knitting needles. When this arrange-
ment of cloth is used I fix the two parallel portions together by paste or glue, so as
to bring the parts of the wire in which the current goes in opposite directions as
close together as may be and to prevent the wire from shifting I fix it by an outer
coating of cloth, pasted or glued upon it, and the inner cloth in the spaces between
it and for farther security I sometimes wind on a thread of insulating material
over the spaces between the successive lines of the wire before gluing on the cover-
ing cloth.
The motor is provided with a governor to properly regulate the speed.
mcent Street, Glasgow, Appucants Agents.
COMPLETE SPECIFICATION.
Apparatus for Measuring and Recording Electric Currents.
Ì, Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of Laws and
Professor of Natural Philosophy in the University and College of Glasgow, in the
County of Lanark, 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:-
This apparatus consists of a moveable body, which for brevity I shall call the
indicator, carrying a pointer and recorder; wheel-work to actuate the recorder; an
electric motor or clock-work to keep the wheel-work in motion; and electric con-
ductors for the currents actuating the indicator.
The indicator is a body caused to take different positions according to the different
strengths of the currents to be measured. It may be soft iron, or a steel magnet
actuated as in known forms of instruments for measuring alternate or direct
currents. For measuring either alternate or direct currents I prefer for indicator
a coil of insulated wire supported on knife edges and adjusted by a weight clamped
in proper position on a slide, allowing it to be moved up or down along a line which
is vertical when the indicator is in its zero position. To approximately enough
equalize the motions of the indicator for equal differences of current in different
parts of its scale I use one or more pendulums hanging vertically down from a fixed
point or points, and touched by a bar or bars projecting from the indicator when
it comes to positions, beyond which its motions, unresisted by the pendulums, would
be too large. The indicator carries a pointer by which its position is read off on a
fixed scale graduated to equal divisions, or to divisions corresponding to amperes
or decimals of an ampere by comparison with one of my standard balances, or other
apparatus for absolute measurement of electric currents. To equalize its deflec-
tions at different temperatures with the same difference of potentials between its
terminals I attach to it an appliance analogous to the temperature compensation of
a clock pendulum arranged to raise or lower the centre of gravity when the tempera-
ture is raised or lowered.
The recorder consists of a marker carried by the indicator on a sliding or jointed
mounting, allowing it relative motion perpendicular to the line of motion of the
indicator. A cam, having its axis as nearly as may be parallel to the line of motion
of the indicator, touches the marker periodically (once every three minutes for
example) and presses it against a very slowly moving drum, on which it leaves a
mark. These marks show the strengths of the current which was passing at the

page_text: times corresponding to the positions of the drum when they were made: The total
quantity of electricity which has passed may be found by addition of the numbers
expressing the current strengths. To obviate the labour of this computation I
attach to the marker a light train of wheels counting the turns of a very small roller,
against which the cam presses to give the periodic motion to the marker. The act-
ing surface of the cam in different planes perpendicular to its axis extends through
a greater or a less portion of the circumference in proportion to the strength of the
current required to bring the, indicator to the corresponding positions. Thus the
roller is kept in action for a longer or shorter time of every period, and is turned to
an extent proportional to the strength of the current at the instant when the cam
commences its action.
The moveable coil of the indicator is acted on by one or by two fixed coils through
which the current to be measured flows. The moveable coil may also carry the
current to be measured, but when the apparatus is employed as a meter for electric
light I prefer to give it a current from the mains through a highly resisting fixed
conductor. To render the apparatus applicable to alternate currents as well as to
direct currents this conductor ought to have resistance several times greater than
that of the moveable coil, and to have an anti-inductive configuration; and whether
for direct or alternate currents its resistance ought to have but small temperature
variation, and it ought to expose as large a surface as may be to the air to get quit
of the heat generated in it. I therefore make it of fine platinoid wire wound in
parallel lines on two sides of a square or oblong, of thin insulating material, such as
glass, or wood, or mica, or an endless cloth (like a miniature roller towel) stretched
between two thin parallel bars such as ivory, knitting needles. When this arrange-
ment of cloth is used I fix the two parallel portions together by paste or glue, so as
to bring the parts of the wire in which the current goes in opposite directions as
close together as may be; and to prevent the wire from shifting I fix it by an outer
coating of cloth, pasted or glued upon it and the inner cloth in the spaces between
it; and for farther security 1 sometimes wind on a thread of insulating material
over the spaces between the successive lines of the wire before gluing on the cover-
ing cloth.
The motor is provided with a governor to properly regulate the speed.
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.
Figure 1. is a front elevation,
Figure 2. is an end elevation.
Figure 3. is an elevation and plan of the recorder.
Figure 4. is a plan of the wheel-work.
The indicator is shown at b, b, DD, yr, (Figures 1 and 2). It carries the coil of
fine insulated wire bat its top. Two straight bars A, B, (Figures 1 and 2) are
attached to the indicator in directions at right angles to one another, and preferably
so placed that B is vertical or nearly so when, as is shown in Figure 2, the indicator
is in its zero position. These bars carry weights cand d, each of which is adjustable
by screw or slide to different positions along its bar. The bar A has at its outer end
the knife-edge f fixed, on which a weight can be hung to test the sensibility of the
system. Thus the user can at any time accurately re-adjust the instrument if by
accident or otherwise it has got out of adjustment. On the knife-edge f, hangs by
a hook and fine thread, a horizontal dise, submerged in a vessel H of oil or other
viscous liquid, the arrangement constituting a dash-pot to check the vibrations of
the indicator. The graduated scale and pointer by which the position of the
indicator can be read off are shown at g, h, (Figure 2).
The recorder is shown at E E, in Figure 1. It is shown in elevation and plan in
Figure 3. It is pivoted on to the lower end of the indicator by the axle i,
(Figures 1, 2, 3) supported by the bracket y. The part of the recorder to one
side of the axle is occupied by the train of small counting wheels q, while that

page_text: to the other side consists of the marking arm to trace the record on the drum.
This arm is made up of two pieces of metal, one rr, thin and springy, the
other ss, thick and quite stiff. The strip is sprung so as always to press against
the bar, except when, the point is pressed against the drum to make the mark.
A screw prevents the recorder from falling too low when it leaves contact with
the cam I I.
The wheel-work for actuating the recorder is shown below the indicator and
recorder in Figures 1 and 2, and is shown separately in plan in Figure 4. The
weight F, acting by a cord on the drum j, keeps the system in motion, which is
maintained uniform by the centrifugal governor G.
The cam, from whose surface the rolling wheel of the recorder is driven, is shown
at II, in Figures 1, 2, 3.
The drum which receives the cylinder of paper upon which the recorder traces
the historical curve is shown at JJ, (Figures 1, 2, 4).
The whole current to be measured passes through the thick copper coil a,
(Figures 1 and 2),. into which it is conducted by heavy copper conductors m, n,
(Figure 2). The coil is supported from the base of the instrument by the
upright C. The circuit of the fine coil bb is completed through electrodes fixed on
the indicator and springs P, P, of which the lower ends are joined to fixed elec-
trodes. The current through it may be produced either by the supply conductors
of the electric lighting system, or by an independent source.
In some cases I use a pendulum or spring supported on one of the brackets Z to
control the motions of the indicator by being touched for part of the range by a
pin attached to the indicator.
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 and recording electric currents, substantially
as described and shown on the drawings.
2. In an instrument for measuring and recording electric currents by different
positions of an indicator, the use of two bars attached to the indicator at right
angles to one another, carrying adjustable weights for varying and adjusting the
sensibility and zero of the instrument.
3. In an instrument for measuring and recording electric currents, the combina-
tion of an indicator and recorder with a cam caused to turn at a uniform speed the
recorder coming in contact with the came once in each revolution, and remaining
in contact for a longer or shorter time according to the strength of current, and
recording the amount of current while in contact with the cam either by a trace
on a revolving drum or by a train of counting wheel-work, or by both simul-
taneously, substantially as described.
4. In an instrument for measuring and recording electric currents, the use of a
pendulum or spring for controlling the motions of the indicator by touching it
through part of its range.
Dated this 5th day of July 1890
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.