Improvements in Galvanometers.
Year: 1893

page_text: Date of Application, 16th May, 1893-Accepted, 22nd July, 1893
COMPLETE SPECIFICATION.
[Communicated from abroad by WHITNEY ELECTRICAL INSTRUMENT Co., of
Penacook, New Hampshire, United States of America, a corporation duly
established under the laws of the State of Maine.]
Improvements in Galvanometers.
I, 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:-
This invention relates to a galvanometer or instrument for indicating the strength
of an electric current. The instrument comprises a permanent field magnet and a
needle or armature having a pivotal movement in the field thereof, provided with
a pointer to indicate in connection with a suitable scale the amount of its move-
ment, the said instrument also having a coil or solenoid through which the current
to be measured passes, which coil is located in such position with reference to the
needle as to cause the current therein to tend to move the said needle from the
position occupied while under the directive influence of the magnet, the amount
of this movement thus indicating the strength of the current by which it is
produced.
In order to control or regulate the relative effect of the current and of the field
magnet on the needle, the said solenoid is in accordance with this invention
provided with a core and means to adjust its position in said coil and to thereby
vary the effect produced on the needle by the current passing through the coil.
Another feature of the invention consists in making the end of the said core
diagonal to the axis of the solenoid or in other words, making the said core of
such shape that the part at one side of the axis of the needle approaches nearer
the needle, when in its normal position, than the part at the other side, the
effect of such disposition of the material being to increase its influence upon the
needle as the latter departs from its normal position, thus making the increments
of movement of the needle more nearly in direct proportion to the increments of
current than is usually the case.
The invention consists also in providing means for making the position of the
lines of force of the permanent field adjustable with relation to the armature or
needle so that although the said field may be regarded as permanent or constant
when once adjusted during the observations of the current effect, the directive
effect of said field on the needle may be adjusted from time to time as is found
necessary.
A convenient means for adjusting the field consists of a movable bridge or
keeper in magnetic contact with the poles of the field magnet but being capable
of movement with relation thereto, so that it can be set in different positions,
the said keeper thus being magnetized by the magnet and constituting a part
of the field which is movable with relation to the armature and may thus be
employed to vary the magnetic effect on the armature.
The field magnet may also be provided with a variable or adjustable magnetic
shunt shown in this instance as produced by iron screws or pins passing through
the branches of the magnet at some distance from their poles and extending
towards one another so that they constitute a partial magnetic circuit and prevent
the magnetism at the poles from being so strong as it otherwise would.
This device may be used to compensate for the variations in magnetic strength
which take place in a permanent magnet the said pins being set near one another
when the magnet is highly charged or of maximum strength so that the poles

page_text: receive only a portion of the magnetism they otherwise would, and if the said
magnet is found to weaken, the shunt projections can be separated more widely
so that a larger portion of the magnetism will pass to the poles to afford the field
for the indicating armature or needle.
Thus by proper adjustments from time to time the field of the indicating
armature may be retained constant although the strength of the magnet itself
may vary.
A similar effect may in some cases be more conveniently produced by providing
the field magnet with adjustable polar extensions that co-operate with the needle
and by their adjustment enable the effective field of the needle to be varied with
relation thereto, as may be required for the proper operation of the instrument..
Figure 1 is a plan view of an indicating instrument embodying this invention,
a portion of the enclosing case being broken away to show the parts below.
Figure 2 a plan view of the field magnet, coil, and armature, the pivoted arbor
of the latter being shown in section.
Figure 3 a front elevation of the instrument with the enclosing case removed.
Figure 4 a sectional plan showing a slightly different arrangement of the
needle relative to the field magnet and solenoid or coil for the current to be
measured.
Figure 5 a similar sectional plan showing another modified arrangement, and
Figure 6 an end elevation of the solenoid and device for adjusting the core
thereof as shown in Figure 5.
Like letters of reference indicate corresponding parts throughout the drawings.
The operative parts of the instrument are supported on the base plate a and
enclosed in a cover b a portion only of which is shown in Figure 1, the said cover
having an opening through which the end of the indicating pointer c and the
graduated scale d with which it co-operates may be observed.
The said pointer c is connected with an arbor e pivoted at e² and having fixed
upon it an armature or needle which is subjected to the attractive influence of
a field magnet g shown as of the horse-shoe or U-shape, the said needle f normally
standing lengthwise between the poles of the said magnet.
The current to be measured is caused to pass through a coil h shown as wound
upon a flat tube h² (see Figures 4 and 5) of non-magnetic material the open end
of which tube is adjacent to the needle f which may thus turn from its normal
position transverse to the axis of the solenoid towards the position in line with
the said axis, the amount of its angular movement depending upon the amount of
attractive movement of the solenoid relative to the attractive force of the field
magnet, and varying with the strength of the current passed through the
said coil.
In order to increase and modify or regulate the effect of the current in the coil
on the needle the said coil is provided with a core piece i of iron (best shown in
Figures 4 and 5) which becomes magnetized by the current traversing the coil and
thus acts upon the needle f in conjunction with the direct inductive action of the
current in the coil.
The said core piece is shown as approaching the needle more at one side than at
the other side of the axis of the said needle (when in normal position) the result of
which is that when the needle is turned from its normal position as shown by full
lines towards the position indicated by dotted lines (Figure 5) the effect of the
attraction of the core to turn the needle is greater than it would be if the core were
square across the axis of the solenoid or approached the needle equally on both
sides of the axis of the latter.
The result of this construction of the core is to give a more uniformly graduated
scale d than is commonly attained, because the effective action of the directive
influence to resist the movement of the needle increases as the needle departs from
its normal position, while the effect of the current in the solenoid to produce such
movement commonly diminishes as the needle moves further from its normal position,
so that commonly a given increment in the current produces far smaller movements

page_text: of the needle when it is already at some distance from its original or normal
position, than is produced by an equal increment in current when the needle is at
the beginning of its movement from the normal position, so that the graduations at
the higher numbers on the scale are usually much smaller than those at the lower
numbers on the scale, a defect that is to a large extent corrected by the construction
of the solenoid core herein shown and described.
The relative effect of the current and magnetic field upon the needle may be
varied by changing the position of the core in the coil, the movement of said core
towards the needle increasing the current effect and movement in the opposite
direction diminishing the current effect; and in order to facilitate the adjustment
of the core and consequent control of the relative effect of the current and field
upon the needle, the said core as shown in Figures 5 and 6 is provided with a
threaded shank or stem engaged by a nut which is restrained from longitudinal
movement in the direction of the axis of the solenoid so that the rotation of the
said nut in one or the other direction produces a longitudinal movement of the
shank and core i in the axis of the solenoid.
The said nut is provided with a notched or milled periphery as best shown in
Figure 6, to facilitate its rotation for the purpose of adjusting the position of the
core i.
The invention is not limited to the specific construction and arrangement shown,
as it is obvious that these may be varied without departing from the essential novel
features of the invention.
The invention, so far as relates to the adjustability of the core and means for
effecting the same, is not confined to a core having the construction described for
producing uniformity of movement of the needle, and on the other hand the
invention so far as relates to the construction for producing uniformity of movement
of the needle is not limited to a core which is also adjustable in the solenoid.
The adjustable core piece thus far described acts mainly to modify the effect
produced by the current on the needle but it is in many cases desirable to provide
for modifying the action or directive influence of the field magnet as for example to
compensate for changes that may gradually take place in the strength of the field
magnet.
j
In the construction shown in Figures 2 and 3, the solenoid coil lies mainly
between the branches of the field magnet g the extremities of which are about in
line with the needle f. The said field magnet is provided with an adjustable field
piece shown as a bridge or keeper k of magnetic material extending from one pole
to the other of the magnet and being in magnetic contact therewith. The said
bridge piece is of comparatively light or thin metal so as not to absorb to two great
an extent the magnetism of the magnet g and is curved in shape as shown, forming
an arch around the axis of the needle or armature f. By sliding the said bridge
piece k transversely along the poles of the magnet as indicated by full and dotted
lines Figure 2, the magnet effect upon the needle ƒ will be varied, producing the
corresponding variation in the position of the armature which may thus be
adjusted to bring the pointer c to the desired position with relation to the graduated
scale.
-Thus by sliding the keeper k laterally on the poles of the magnet a small amount,
such as is provided for by the slots see Figure 3, which fit over the fastening
screws k³, a movement of the pointer c over one or more divisions may be effected,
thus affording a convenient means for adjusting the pointer if necessary before
making the current observation.
The curved or arch shape of the field produced by the movement of the curved
keeper k makes the field resistance to the rotation of the armature more uniform in
the different positions of the latter, producing substantially the same result on the
uniformity of movement of the pointer for equal increments in current, that is
produced by the inclined shape of the solenoid core piece i before described.
In order to provide means for keeping the field of force for the armature or
needle substantially constant although the magnet g may vary in strength or fall

page_text: off in magnetism, the said magnet may be provided with an adjustable partial
magnetic shunt, shown in Figure 2, as consisting of two screws or projections m, m³,
extending towards one another between the branches of the magnet at some
distance from the actual poles or extremities of the magnet, the said projections m, m2,
constituting what may be regarded as secondary poles and diverting a portion of
the magnetic effect from the main poles the said portion varying with the degree of
proximity of the secondary poles m, m².
Thus when the magnet is strongly charged the said adjustable shunt poles m, m³,
may be placed quite near together so that only a comparatively small portion of
the full strength of the magnet g is effective at its poles, the instrument being
graduated to indicate properly with such a field.
Then if the magnet is found to weaken, the field may be brought up to normal
strength by drawing the shunt poles m, m2, further apart so that although the
magnet is weaker a larger percentage of its strength is effective at the poles.
Similar effects may in some cases be more advantageously arrived at by the
construction shown in Figure 4, in which the solenoid coil extends at both sides of
the needle for in other words, the said needle is about at the middle of the length
of the solenoid coil and the armature or needle fis located at some distance from
the extremities of the branches of the field magnet g.
The said branches are provided with adjustable pole pieces n, n², shown as iron
screws working in transverse openings in the branches of the magnet g so that they
can be turned in or out so as to bring their inner ends nearer to or further from
the ends of the needle f.
The said pole piece screws are shown as provided with check nuts o to lock
them when properly adjusted and the directive influence of the magnetic field upon
the needle may be varied by adjusting the said pole pieces n, n², the said directive
influence being increased as said pole pieces are screwed inward and diminished as
they are screwed outward, so that it can at any time be brought to the desired
amount, and if the strength of the magnet g should vary its directive influence
might be retained constant by making the proper adjustments of said pole pieces as
such variations occur.
As shown in Figure 4, the extremities of the magnet g are magnetically con-
nected by a thin strip p of iron or steel secured to the poles of the magnet by iron
screws so that it causes a portion of the magnetic influence that would otherwise
be produced by the magnet to be withdrawn from the needle f, thus rendering
the influence of the adjustable poles n, n², on the said needle more delicate.
In the construction shown in Figure 5, the solenoid coil projects outward
beyond the poles of the magnet and the latter is not shown as having devices
for adjusting its influence, and it is to be understood that the movable core
piece or means for varying the influence of the current on the needle may be
employed without means for adjusting the field or on the other hand the devices
for adjusting the effect of the field magnet may be employed in instruments not
having an adjustable core piece, or all of the means for adjustment may be
employed in a single instrument as shown for example in Figure 2.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, as communicated to me by
my foreign correspondents, I declare that what I claim is :-
1. In a galvanometer means for adjusting the effect of the current on the
needle, substantially as described.
2. The combination of the field magnet and needle pivotally supported in the
field thereof, with a solenoid and core co-operating with the said needle, sub-
stantially as and for the purpose described.
3. The combination of a field magnet and needle movable in the field thereof,
with a solenoid and movable core piece therein, and means to adjust the said
core piece relative to said needle, substantially as and for the purpose described.
4. The combination of the field magnet and needle pivotally supported in the

page_text: field thereof, with a solenoid and core therein of greater extent towards the needle
at one side than at the other side of the axis thereof, substantially as and for
the purpose set forth.
5. An electrical indicating instrument comprising a field magnet and an
indicating armature or needle pivoted in the field thereof, combined with a bridge
or keeper connecting the poles of the said magnet, and modifying the effect of the
magnetic field upon the said needle, substantially as described.
6. An electrical indicating instrument comprising a field magnet and indicating
armature or needle pivoted in the field thereof, combined with a bridge or keeper
connecting the poles of said magnet, and laterally adjustable thercon, the said
keeper deviating from the direct line between the poles so that its adjustment on
said poles varies the magnetic effect on the indicating needle, substantially as
described.
7. An electrical indicating instrument comprising a field magnet and indicating
armature or needle pivoted in the field thereof, combined with adjustable secondary
poles constituting a magnetic shunt whereby the effective strength of the field
relative to the strength of the magnet may be varied, substantially as and for the
purpose described.
Dated this 16th day of May 1892
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.