Improvements in Instruments for Measuring Electric Currents.
Year: 1896

page_text: Date of Application, 25th Feb., 1896
Completo Sonnifination Loft 25th Nov 1008 Accented
Oth lon 1807
PROVISIONAL SPECIFICATION.
Improvements in Instruments for Measuring Electric Currents.
1, WILLIAM THOMSON, BARON KELVIN OF LARGS, Professor of Natural
Philosophy in the University of Glasgow, do hereby declare the nature of this
invention to be as follows:-
The improvement relates to that class of instruments in which a soft iron rod or
wire, which I shall call plunger for brevity, is drawn by electromagnetic force into
the vacant core of a bobbin wound round with a conductor carrying the current,
or into the magnetic field of an equivalent arrangement for producing an intense.
electromagnetic force in approximately parallel lines.
Instead of modes of suspension hitherto used, I hang the plunger by a flexible
cord, or chain, or wire, from a circular arc fixed to one end of the beam of a balance
in such a manner that the cord passes tangentially downwards from this arc. Thus,
when the beam of the balance turns through any angle great or small, the plunger
moves, as nearly as may be, exactly in the straight line of its own length.
I may use a small length of spiral spring or of indiarubber between the plunger
and the bearing cord, to prevent the cord from slacking in the event of a sudden
starting or stopping of the electric current.
may also use an air damper or oil dash-pot to check the vibrations of the
balance.
I prefer to make the bearing cord of non-conducting material, especially when
the instrument is to be used on high tension circuits. This allows the balance to
be kept connected with the earth whatever may be the electric pressure in any part
of the solenoid or of its supports.
By means of attached weights and springs applied so as to pull or push upon
moving parts of the balance through the whole or through parts of its range,
I adjust the sensibility of the instrument so as to give a scale with convenient
divisions through the whole range of the currents to be measured.
Dated this 21st day of February 1896.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.
Improvements in instruments for easuring
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 and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
The improvement relates to that class of instruments in which a soft iron rod or
wire, which I shall call plunger for brevity, is drawn by electromagnetic force into
the vacant core of a bobbin wound round with a conductor carrying the current
or into the maguetic field of an equivalent arrangement for producing an intense
electromagnetic force in approximately parallel lines.
Instead of modes of suspension hitherto used, I hang the plunger by a flexible

page_text: cord, or chain, or wire, from a circular arc fixed to one end of the beam of a balance
in such a manner that the cord passes tangentially downwards from this arc. Thus,
when the beam of the balance turns through an angle great or small, the plunger
moves, as nearly as may be, exactly in the straight line of its own length.
I may use a sinall length of spiral spring or of india-rubber between the plunger
and the bearing cord, to prevent the cord from slacking in the event of a sudden
starting or stopping of the electric current.
I may also use an air damper or oil dash-pot to check the vibrations of the
balance.
I prefer to make the bearing cord of non-conducting material, especially when
the instrument is to be used on high tension circuits. This allows the balance to
be kept connected with the earth whatever may be the electric pressure in any part
of the solenoid or of its supports.
By means of attached weights or springs applied so as to pull or push upon
moving parts of the balance through the whole or through parts of its range,
I adjust the sensibility of the instrument so as to give a scale with convenient
divisions through the whole range of the currents to be measured.
Figure 1 is a front elevation and
Figure 2 is a cross section of an ampere gauge.
A is the solenoid into the core of which the soft iron rod or wire B is drawn by
electro-magnetic force when the current is passing through the conductor of the
solenoid. The iron rod or wire is hung by a flexible cord or chain or wire C from
a circular arc D. The cord is fixed at d and passes round the arc D. The arc D
is fixed to a beam E which is supported in a similar manner to that described in
the Specification of my Patent No. 2198 of 1893 by two knife edges resting in V's
formeu in the hooks F, F. A pointer G is also attached to the beam E and a scale
is provided for reading off the current passing. H is a weight which can be moved
along the screwed rod I for adjustment.
The arrangement described in the drawings gives the scale in a position found
convenient for many purposes especially in respect to compactness of the instrument.
In some cases I attach the pointer in other positions, as for instance in the line
from the middle point of the arc D perpendicular to the axis. This allows the
movable part of the balance to be made lighter and, allows a heavier soft iron
plunger, giving greater moving power, to be used.
In the drawings two forms of dash-pots are shown either of which may be used.
In one form an arm K is attached to the beam E and carries at its other end a
disc L, which moves approximately horizontally in a vessel containing oil or other
fluid.
In the other form a rod M of non-magnetisable material is attached to the
plunger B. This rod M carries a disc N, which moves up and down with the plunger
in a pot containing oil or other liquid. The latter form of dash-pot with disc
attached to the plunger is dynamically preferable when there is space convenient
for it in the instrument.
The vessel containing oil or other liquid may be placed in the core of the solenoid
and the disc may be attached direct to the end of the plunger.
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 1
claim is :-
In instruments for measuring electric currents the improved method of suspending
the soft iron rod or plunger by means of a flexible cord or chain or wire, substantially
as described and illustrated on the accompanying sheet of drawings.
Dated this 24th day of November 1896.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Patent Agents.,