Improvements in Instruments for Measuring and Recording Electric Pressures and Currents.
Year: 1893

page_text: Date of Application, 29th Dec., 1893
Complete Specification Left, 29th Sept., 1894-Accepted, 3rd Nov., 1894
PROVISIONAL SPECIFICATION.
Improvements in Instruments for Measuring and Recording Electric
Pressures and Currents.
I WILLIAM THOMSON, BARON KELVIN of Largs, Professor of Natural
Philosophy in the University of Glasgow, Glasgow, North Britain, do hereby
declare the nature of this invention to be as follows:-
I prefer to use electrostatic instruments of the kind described in my Patents
Nos. 4167, A.D. 1883, page 34; 11,106, A.D. 1884 pages 8 and 9; and 18035,
A.D. 1888, in all cases in which sufficient power for giving the proper position of
the indicator can be obtained by such instruments. To increase the power of the
cellular or multi-cellular pattern described in my Patent No. 18035, A.D. 1888, I
use for the movable body three vanes, or three sets of vanes fixed in corresponding
positions at angles of 120° round an axis. Thus when the vanes are in planes
perpendicular to the axis each set of three is a flat trefoil, but pieces in planes
parallel to the axis, or portions of cylindrical surfaces attached to the tips of flat
trefoil vanes, or to the ends of radial bars, may be preferred in some cases.
movable body is mounted so as to turn as freely as possible round its axis, which
may be either vertical, as in the form particularly described in my Patent
No. 18,035, A.D. 1888, or horizontal as in my Patent No. 11,106, A.D. 1884. The
movable body is actuated by electrostatic force depending on difference of potential
between itself and the fixed body which should be so shaped as to give the greatest
condenser-capacity which the circumstances allow when the movable body is at the
end of its range at highest pressure.
The
When the axis is horizontal I use gravity for balancing the electric force; and I
introduce an arrangement by which, when the pressure is less than the least to be
measured by the instrument, a weight, supported on the movable body during the
use of the instrument is detached from it, as it is moving towards zero, by a fixed
stop or stops, and the movable body is allowed to go farther and come to rest in a
zero position of equilibrium without electric force.
may
When the axis of the movable body is vertical, I prefer to use the torsion of a
bearing wire to give the force for balancing the electric force, but in some cases
the bifilar method, or the method by a spiral spring, may be preferred. To test
the zero I add an appliance to the torsion head, by which at any time it may be
immediately turned round through a definite angle, and so, when there is no electric
force, the zero position of the movable body may be seen. It then be corrected
if necessary either by hand or by an endless screw or other convenient mechanism.
When the correctness of the zero has thus been ascertained or effected the torsion
head is turned back precisely the same angle as at first, and the instrument
I use the same methods for correcting the zero in cases in which electro-
magnetic force instead of electro-static force is employed for indicating the
potential.
for use.
ready
For recording the indications I prefer arrangements by which the marker has an
up and down vertical motion. When the instrument is electro-static I suspend the
marker by two or more fine threads or fibres from a 'cylindric drum attached to the
movable body, and I use a fine metal point for the marker, and mechanism to
produce pressure between it and the paper which takes the record at sufficiently
short intervals of time, or I use methods such as some of those employed in my
siphon recorder for submarine signals. With electro-magnetic instruments giving
sufficient power to render the error due to difference of weight of the ink
unimportant, I use for marker a small ink cup with a projecting lip carrying a

page_text: small thread or wire brush or a loop of fine wire pressed slightly against the paper.
I prefer to produce this pressure definitely by gravity, for which purpose I hang
the marker by a hook slightly on one side of the vertical through its centre of
gravity, from a point on the movable body. I guide the marker by a bar projecting
horizontally from it and two fixed vertical bars, against which it is kept pressing by
the dragging force of the paper.
Dated this 28th day of December 1893.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant s Agents.
COMT DETE DI DUITIVATION.
Improvements in Instruments for Measuring and Recording Electric
Pressures and Currents.
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 :-
I prefer to use electrostatic instruments of the kind described in my Patents
Nos. 4167, A.D. 1883, page 34; 11106, A.D. 1884, pages 8 and 9; and 18035,
A.D. 1888 in all cases in which sufficient power for giving the proper position of
the indicator can be obtained by such instruments. To increase the power of the
cellular or multi-cellular pattern described in my Patent No. 18035, A.D. 1888, I
use for the movable body three vanes or three sets of vanes fixed in corresponding
positions at angles of 120° round an axis. Thus when the vanes are in planes
perpendicular to the axis each set of three is a flat trefoil, but pieces in planes
parallel to the axis, or portions of cylindrical surfaces attached to the tips of flat
trefoil vanes, or to the ends of radial bars may be preferred in some cases.
movable body is mounted so as to turn as freely as possible round its axis, which
may be either vertical as in the form particularly described
The
in my Patent
No. 18035, A.D. 1888, or horizontal as in niy Patent No. 11106, A.D. 1884. The
movable body is actuated by electrostatic force depending on difference of potential
between itself and the fixed body which should be so shaped as to give the greatest
condenser-capacity which the circumstances allow when the movable body is at the
end of its range at highest pressure.
When the axis is horizontal use gravity for balancing the electric force; and I
introduce an arrangement by which when the pressure is less than the least to be
measured by the instrument a weight supported on the movable body during the
use of the instrument is detached from it, as it is moving towards zero by a fixed
stop or stops, and the movable body is allowed to go farther and come to rest in a
zero position of equilibrium without electric force.
When the axis of the movable body is vertical 1 prefer to use the torsion of a
bearing wire to give the force for balancing the electric force, but in some cases
the bifilar method, or the method by a spiral spring, may be preferred. To test
the zero I add an appliance to the torsion head by which at any time it may be
inmediately turned round through a definite angle, and so when there is no electric
force the zero position of the movable body may be seen. It may then be corrected
if necessary either by hand or by an endless screw or other convenient mechanism.
When the correctness of the zero has thus been ascertained or effected the torsion
head is turned back precisely the same angle as at first, and the instrument is ready
for use.
I use the same methods for correcting the zero in cases in which electro-
magnetic force instead of electrostatic force is employed for indicating the
potential.
For recording the indications I prefer arrangements by which the marker has an
up and down vertical motion. When the instrument is electrostatic I suspend the

page_text: marker by two or more fine threads or fibres from a cylindric drum attached to the
movable body,
and use a fine metal point for the marker, and mechanism to
produce pressure between it and the paper which takes the record at sufficiently
short intervals of time, or I use methods such as some of those employed in my
siphon recorder for submarine signals. With electro-magnetic instruments giving
sufficient power to render the error due to difference of weight of the ink
unimportant, I use for marker a small ink-cup with a projecting lip carrying a
small thread or wire brush or a loup of fine wire pressed slightly against the paper.
I prefer to produce this pressure definitely by gravity, for which purpose I hang
the marker by a hook slightly on one side of the vertical through its ceutre of
gravity from a point on the movable body. I guide the marker by a bar projecting
horizontally from it and two fixed vertical bars, against which it is kept pressing
by the dragging force of the paper.
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 an elevation of a volt meter of the cellular or multi-cellular pattern.
The movable body consists of three vanes A1 A2 A3 in one plane, or two or more
sets of three vanes in parallel planes fixed in corresponding positions round an
axis. The axis may be vertical or horizontal. In the case illustrated the axis is
horizontal. The fixed body consists of a series of plates B1 B2 B3, forming cells.
into which the vanes are electrically attracted, while they are also repelled from
three fixed repelling plates R R R in metallic connection with the ranes. Thus
the movable body is actuated by electrostatic force depending on difference
between the potential of itself and the fixed repelling plates; and the potential of
the cells being the difference of potentials to be measured. Attached to the axis
is a pointer C, the position of which on the scale indicates this difference of
potential. I use gravity for balancing the electric force. There is an arm D at
right angles to the pointer, at one end of which a weight dis hung. At the other
end of the arm there is another weight d'. When the electric pressure is less than
the least to be measured by the instrument, the weight d' rests on the end of the
arm D and balances the weight d at the other end. When the electric force is
applied the vanes A' A2 A3 are attracted into the cells.
When the pressure
exceeds the least to be measured the end of the arm D leaves the weight d'
hanging on the hook which is attached to a metal shield between the cells and
the pointer. The weight is then left to balance the electric force.
Figure 1 is an end view partly in section of a portion of the arm D and
weight with hook ..
Figure 2 is an engine room volt meter in which gravity is used for balancing the
electric force. The weight hangs from the arm attached to the pointer C. In
the instrument illustrated 100 volts is the lowest to be measured. When the potential
falls below 100 the weight rests on a conical point borne on a platform ď²,
and when there is no electric force the pointer is allowed to come to rest in a zero
position of equilibrium without electric force and without the weight '.
Figure 3 represents a recording voltmeter showing another method of carrying
out the arrangement of detaching the weight when the pressure is less than the
least to be measured. In this case the movable body is a soft iron rod or wire h,
hung from two spiral springs wound in opposite directions, and is drawn in to a
solenoid by the electro-magnetic force to be measured. When the force is less
than the least to be measured the movable body rests hanging from the top of the
solenoid as shown in Figure 4. When there is no electro-magnetic force the
movable body can be unhooked and the spiral springs allowed to come to rest in
their zero position of equilibrium without electro-magnetic force and without the
weight of the movable body.
The method of recording the indications is shown in Figure 3 as applied to
electro-magnetic instruments. For marker, a small ink-cup e, fixed to the lower

page_text: end of a soft iron bar h, is used, with a projecting lip carrying a small thread or
wire brush, or a loop of fine wire pressed slightly against the paper. The pressure
is produced definitely by gravity. For this purpose the upper end of the iron
bar his hung on the lower end of an aluminium link / slightly on one side of the
vertical through the centre of gravity of the iron bar, marker, and movable guide
bar f. Thus the ink-cup falls against the paper drum. The marker is guided ou
the principle of the geometrical slide by a bar, Figures 3 and 5 projecting
horizontally from it and two fixed vertical bars gg2. The horizontal bar is
kept pressing against the fixed vertical bars by the dragging force of the paper.
The upper end of the aluminium link is hung by a hook m on a V-shaped bar,
of which the upper ends n n' are borne by two spiral springs wound in opposite
directions.
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 trefoil electro-static volt meter as described and illustrated on Sheet 1 of
the drawings.
2. In electric measuring instruments the arrangements for checking the zero
and obtaining indications through the range required only, substantially as described
and illustrated on Sheets 1, 2, and 3 of the drawings.
3. In instruments for recording electric pressures and currents, the method of
suspending and guiding the marker, substantially as described and illustrated in
Figures 3, 4, and 5.
Dated this 28th day of September 1894.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.