Improvements in Electrical Measuring Instruments.
Year: 1891

page_text: COMPLETE SPECIFICATION.
[Communicated from abroad by EDWARD WESTON, of Newark, New Jersey,
United States of America, Electrician.]
Improvements in Electrical Measuring Instruments.
1, HENRY HARRIS LAKE of the firm of Haseltine Lake & Co. Patent
Agents 45 Southampton Buildings in the County of Middlesex, 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 invention relates to an electrical measuring instrument intended more
particularly for the measurement of electrical currents of high strength.
The principal features of the instrument are the form and arrangement of the
magnet and the disposition of the coils therein, the devices for transmitting motion
from the moving coil to the index whereby a slight movement of said coil is
caused to produce large movement of the index, and the general disposition of the
parts whereby the instrument is rendered very sensitive in operation, accurate in
measurement, not influenced by induction from exterior sources and capable of
measuring currents of great strength without injury..
In the accompanying drawings,
Fig. 1 is a front view of the instrument;
Fig. 2 is a vertical sectional view on the line X X of Fig. 1;
Fig. 3 is a vertical sectional view on the line Y. Y of Fig. 2;
Fig. 4 shows details of the needle pivot mechanism ;
Fig. 5 shows the laminations of the magnet pole;
Fig. 6 is a vertical section on the line Y Y of Fig. 2, showing the instru
ment provided with a coil of high resistance to adapt it for use as a potential
indicator;
Fig. 7 represents a modification of the instrument in which there is but one fixed
coil which operates as a sucking solenoid;
Fig. 8 is a front view of the instrument in Fig. 7;
Fig. 9 is a sectional view of a modification of the device for transmitting motion
from the moving coil or armature to the needle; and Figs. 10 and 11 show details
of this device.
Fig. 12 is a side elevation of the instrument shown in Fig. 6;
Fig. 13 shows the same instrument and a preferable mode of suspension of the.
same, and
Fig. 14 shows the suspension device in detail.
Similar letters of reference indicate like parts.
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Referring now more particularly to the instrument shown in Figs. 1 to 6
inclusive. A is the back board. Ba cylindrical case secured thereto. Ca glass
plate covering the dial. The magnet consists of two annular disks F and G and a
peripheral wall H. The disks are united by bolts J, Fig. 3. One pole piece D is
secured in the central opening of a disk F. The other pole piece E is received in
a socket formed in a flanged collar K received in the central opening of disk G.
The pole piece E is concentric with, and is surrounded by the pole piece D. In the
annular space L between said pole pieces, there is, therefore, a strong magnetic.
field; and the body of the magnet forms a magnetic shell which shields the
instrument from external inductive influences.
M is a copper core surrounded by the sheath N of insulating material. In the
pole piece E are openings lined with insulating material O, Fig. 3; and through
these openings and into the copper core M extend the ends of copper strips P.
Electrical connection between the said strins and the conver Core M is thus made

page_text: The copper strips are wound parallel to one another around the core M and form a
fixed coil nearly filling the interior of the cylindrical magnet. The outer ends of the
strips, as shown at Q, Fig. 3, are connected to, a metal bar R,which communicates
with the binding post (dotted lines Fig. 2). The copper core M receives at its
end another copper bar Stwhich communicates with the' binding post 2. The
current entering at either binding post 1 or 2, proceeds through the coils P and
thence to the other binding post. T is a light cylinder of copper closed at one
end and entering the annular space between pole pieces D, E. This cylinder carries
a coil U of fine wire, and is supported on a flanged head V carried on a copper or
aluminium tube W. The tube W extends through the core M and has at its
opposite end a cap a.. Secured to the cap a is a leaf spring b. Secured to the
head but insulated therefrom by a band e, is a spring d. Springs and d are
secured to bars e and f which are attached to the upper side of the magnet case and
are insulated therefrom, as shown at g. Extending through the tube W is a spiral
spring w, carrying at one end a threaded rod i which receives a nut j outside the
cap a. The other end of the spring is attached to the yoke k. As shown in Fig. 4,
spring d is received in a groove in the band e and the face of cylinder T is received
between said band c and a flange on the head. The outer end of the spring w
is connected to a threaded rod m, which passes through one arm of a yoke k and
ends in a pivot point n. A threaded pin o passes through the other arm of yoke k,
and serves to secure the needle p between said arm and a washer q. The pin o is
pointed to form a pivot. Between the pivots nand o is a stationary cylindrical
block received in the end of a fixed brackets. Needle p is counterweighted at t
and moves over a scale plate u which is supported by standards attached to the
magnet plate F.
l
When the tube W is moved into the magnet, the spiral spring we therein is sub-
jected to tension and consequently rotates, carrying with it in its rotation the yoke k,
which turns on its. pivot points, o upon the fixed block r. Said yoke thus guides
the needle
to move over the scale. The suspension springs d and tend by their
elasticity to bring tube W back to its original position of rest. A very slight motion
of tube W is, by this construction, quite sufficient to cause a large deflection of the
needle.
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When the instrument is designed for use as an ammeter, a shunt circuit proceeds
as follows-From binding post 1 by wire a to bar f, to spring b, to tube W through
cylinder T and through insulated coil U on said cylinder to spring d, to bar e and by
wire to binding post 2.
The operation of the instrument is as follows:-When the current to be measured
circulates, through the coil P, an intense magnetic field is produced in the annular
space between the pole pieces. At the same time, the current passing through
coil U produces a field around said coil. In accordance with well-known laws, the
interaction of these two fields results in a drawing of the suspended coil U into said
annular space, and the extent of movement of said coil will bear a relation to the
difference of potential in the current circulating through the coils and between the
terminals of the instrument. As the coil U and consequently its supporting cylinder
is moved inward, the spiral spring wis extended and rotates, thus moving, as already
explained, the needle p over the scale plate u, and the extent of movement of the
needle P will depend upon the distance which the coil U is moved. The scale plate
is laid off to show strength of current in amperes.
When it is desired to use the instrument as a potential indicator or as an ammeter
for very weak currents, the thick quadruple copper strips Pare removed and a single
coil of thin copper strip (P Fig. 6) from two to three one-thousandth of an inch in
thickness is substituted the terminal of this coil connecting as shown at P" Fig. 6,
with the copper core..
The circuit in the instrument as thus arranged proceeds as
follows: From binding post 1 (Fig. 6) to wire c', to coil P', to the copper core M,
to the spring, tube W, coil U, spring d, bar e, and thence to binding post 2, by
wire, (Fig. 6). When the instrument is thus constructed, the high resistance
of the coil will cause the suspended coil U.to take a position between the poles

page_text: of the magnet depending primarily upon the difference of potential between the
terminals of the instrument; and the scale plate, in such case, will, of course; be
graduated to indicate this difference of potential in volts.
In order to reduce or prevent magnetic-lag in the instrument, the magnet poles
may be laminated and the laminations separated by strips of insulating material,
as shown in the sectional view, Fig. 5, the magnet pole Ehere-being divided into
laminations, e', e", &c.
Referring now to the modification' of the instrument represented in Fig. 7, A is
the base of the instrument, 13 an enclosing case and C³ a glass cover of the dial.
D' is a brass tube forming a core upon which is wound the insulated coil E2, which
is wholly enclosed in the iron cylinder F. G is an iron tubular armature supported-
at one end by the vertical spring H2 and at the other end by the similar spring I...
Spring is connected to tube G' by a bar J, the end of which is threaded so that
the tension of said springs may be adjusted. The upper ends of the springs are
connected to metal bars K², L, which are secured to the block M of insulating
material on cylinder F. N2 is a spiral spring having on one end a threaded rod
which is received in the extremity of tube G². The other end of spring N' is
attached to a threaded pin P2 secured to the yoke 02. Through the opposite arm
of yoke O passes the threaded pin p, which secures the index needle Q' to said
yoke. The pivot pins are received on opposite sides of the fixed block R which
is supported on the bracket S. The arangement of this part of the apparatus is
the same as already described in connection with Fig. 1 to 6. T is the scale plate
supported on the standard U³. The circuit in the instrument is from one binding
post 1 through the coil E² to the other binding post 2. The coil then becomes a
sucking solenoid of which the tube G2 is the armature. And when the current.is.
established, said tube will be drawn-into the coil in accordance with well-known
laws for a distance bearing a relation to the strength of the current. As the
tube G2 is drawn inward, the needle is rotated over the scale-in-the manner already
described.
"
It will be observed that the cylinder F of magnetic material forms a
magnetic shield for the instrument; and that the armature being disposed hori-
zontally the action of gravity upon it does not interfere to accelerate or retard its
motion.
Referring now. to the device shown in Figs. 9, 10 and 11; this is another::
mechanism for converting the rectilinear movement of the movable armature or coil
in the instrument into rotary movement of a needle over a scale. The parts of
the instrument are the same as are shown in Figs. 1 to 6 inclusive and are similarly
lettered. Upon the extremity of the tube W and beyond the sleeve V are cut two
spiral grooves d³, which receive pins which project inwardly. from the inner sides of
the fork e³, which is formed upon a rod m³ secured to one arm of the yoke k. Upon
the arm is a pin s to which is secured one end of a spiral spring . The other
end of said spring is fastened to the rod m³.
The operation of the device is as follows: -When the coil U moves into or out
of the annular space between the pole pieces D, E, the tube W is, of course,
caused also to move in the direction of its longitudinal axis. The pins upon the
fork e³ are thus compelled to traverse the quick pitch spiral grooves d³ and conse-
quently said fork, and hence the rod m³ and yoke k are compelled to turn on the
pivot pins n, o; and by reason of this rotation the needle is moved over the
scale u.
Obviously, the extent of rotation of the support and hence the extent of
movement of the needle, will correspond to the extent of axial movement of the
tube W and coil U; hence the axial movement of the coil is converted into rotary
movement of the needle over the scale. The spiral spring is wound. in such
direction as to oppose by its elasticity the rotation of the parts when the coil is
thrown into the field between the pole pieces. When the current is arrested, the
effect of the spring is to assist in bringing the needle back to the normal or zero
position.
In instruments of this kind it is desirable to provide means for preventing any

page_text: longitudinal tilting of the instrument, the effect of which might be to cause the coil
supporting cylinder T to move by gravity into or out of the magnet and hence to
cause the spring w to move the needle; thus making a false indication. In order to
allow of the instrument being adjusted truly, I may provide it with a, base
(A Fig. 6) supported on a tripod B₁ C¹ D', one end of which, D', may be made
vertically adjustable, as shown in Fig. 12. Or I may suspend the entire instru-
ment in the mode shown in Fig. 13. In this case, the terminals E' F are secured
to a bar G of insulating material. Two bent brackets H' I' having parallel
arms JK receive the bar G laid upon them. The faces of the terminals E' F¹
then make contact with the arms JK'. Binding posts 3, 4 may be provided so
that one leading in wire may be connected to each bracket. The arrangement of
the two suspension bars E F which are preferably flexible and the supporting.
bracket prevents any material longitudinal tilting of the instrument.
Among the advantages flowing from the construction described
following:
:―
are the
1. The magnet is practically a closed shell and therefore a magnetic screen
protecting the instrument from the effects of outside induction.
2. The spiral spring w or N³ may be adjusted so as to have no initial tension; or
in other words, no pulling force against the action of the supporting leaf springs..
Consequently, the instrument is thus rendered much more sensitive.
3. The construction of the transmitting mechanism between the movable coil or
armature and the needle is such that a very small movement of the coil causes an
extensive movement of the needle over its scale. In the construction shown in
Figs. 1 to 6 inclusive, the coil P offers a conducting channel of large cross-sectional
area and permits of very heavy currents being taken through the instrument without
danger of burning or other impairment; and hence instruments of this class may be
adapted to currents of almost any strength and are especially suited for employment
as station ammeters in electric lighting plants.
Having now fully ascertained and described the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me by.
my foreign correspondent I declare that what I claim is
1. In an electrical measuring instrument, an electro magnet having concentric
poles and a movable coil supported by springs in the annular space between
said poles and suitable mechanism for transforming the axial motion of said
coil into rotary motion of an index needle over a scale substantially as hereinbefore
described.
2. In an electrical measuring instrument, an electro magnet having concentric poles
and a coil of metallic strips enclosed in a magnetic shell of metal, a movable coil
supported by springs in the annular space between said poles and suitable mechanism
for transforining the axial motion of said coil into rotary motion of an index needle
over a scale substantially as described.
3. In an electrical measuring instrument, an electro magnet having a hollow
core, a tubular armature supported therein by springs and suitable mechanism for
transforming the axial motion of said armature into rotary motion of an index needle
over a suitable scale.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.