Improvements relating to Galvanometers.
Year: 1893

page_text: Date of Application, 13th July, 1893
Complete Specification Left, 4th Apr., 1894-Accepted, 12th May, 1894
Improvements relating to Galvanometers.
I, CARL LUDWIG RUDOLPH ERNEST MENGES, of 82/84 Balistraat, The Hague,
in the Kingdom of Holland, Electrician, do hereby declare the nature of this
invention to be as follows:-
My invention relates to galvanometers and comprises the improvements herein-
after described.
When an electric current flows in opposite directions through two coils arranged
side by side, the space between the two coils and its lateral prolongation in a
direction at right angles to the axes of the coils remains practically free from
lines of force. Hence if a magnet be placed in this space it will not be influenced,
that is to say, its magnetic state will not be altered, by any current flowing in the
coils, nor will its position be altered relatively to the same.
According to my invention I construct a galvanometer with two coils situated as
above mentioned and fix the controlling magnet in the neutral space between the
same, the moving magnetic needles being placed inside the coils. When a current
passes, the movable needles will be deflected. The magnetic state however of the
fixed magnet is unaltered by the current in the coil neither does the movement of
the needles affect the same since their actions are equal and opposite and practically
destroy each other. The controlling magnetic field therefore in which the movable
needles are swinging is constant.
In order that my invention may be clearly understood I will now proceed to
describe one or two methods of carrying the same into practice.
In the accompanying drawings,
Figure 1 is an elevation, and
Figure 2 a plan of an instrument constructed according to my invention.
Figure 3 is a section on the line bc, Figure 1.
Figures 4 and 5 shew modified details of construction.
Figures 6, 7 and 8 shew further modifications hereinafter explained.
Like letters of reference denote similar parts throughout the drawings.
A is one of the coils. B is the other coil, the wires being joined so that a current
will flow in opposite directions in the coils. NS is the controlling magnet fixed in
the space between the coils.
I provide in each coil a movable iron or magnetic needle s'n' and s² n² these
needles will when no current is flowing place themselves parallel to the controlling
magnet N S, but will be deflected in opposite directions by a current in the
coils A, B. No change of direction of the magnetic axis of the controlling
magnet N S occurs by the action of the movable needles when deflected, because
the actions of the two needles which are equal and opposite practically destroy
each other.
If the two needles ¹n' and s² n² are connected with each other by any constraining
inechanism, so that they must always move in opposite directions the apparatus
becomes astatic and is not affected by external forces. For instance as shown in
Figure 4, one needle s'n' may be connected with a sector 1, toothed externally,
and the other needle s² n² with a sector 2 toothed internally. The two sectors 21, 2,
engage with wheels ¹², fixed on the same shaft, or bevel wheel gearing may be
used as shewn at k', k, Z, Figure 5, the index being fixed upon the axis of the
intermediate wheels, or Z as indicated in Figure 4.
The same object may also be achieved without any mechanical connection of the
needles by the arrangement represented in Figures 1, 2 and 3. The needle s¹´n¹

page_text: carries a ring aa on which the scale is marked, while the index 6' 6' is fixed upon
the other needle..
Under certain circumstances I find it may be advantageous to make the movable
needles s'n' and s³ n² considerably shorter than. the directive magnet NS as shewn
in Figure 6. To obtain as strong a controlling force as possible, bars p' p' and p² p²
of soft iron are provided which conduct the lines of force coming from the
controlling magnet N S to the needles. These bars p' p' and p² p² may also pass
through openings in the coils, so as to be brought near to or even in contact with
the magnet N S.
I sometimes make my improved galvanometer with an astatic needle system of
the ordinary design. For instance I may use what I will call a duplication of
the instrument shewn in Figure 2.. I then provide two pairs of coils each having
a controlling magnet, and in one of the coils of each pair I mount a needle. Said
needles are secured on a common shaft. If the arrangement be such that the
two middle coils are traversed in the same direction by a current these coils may
be replaced by a single coil. Such a galvanometer with three coils A, B and C
is represented in Figure 7 in which figure each coil consists of only one turn.
As herein before mentioned in the space beyond the ends of the magnet NS,
Figure 2, there is practically no field due to any current passing round the coils.
In lieu therefore of one controlling magnet 1 sometimes use two which are placed
opposite each other with their poles of unlike names at N, S.
If these magnets be made long enough the outer ends may be bent and
connected together but at such a distance from the coils A and B that the action
of the electric current there is insignificant, this arrangement is shown in
Figure 8.
In the instrument shewn in Figure 7 this closing of the magnetic circuit is
preferably effected by joining the north pole N¹ of one controlling magnet to the
south pole S2 of the other magnet thus making a horse-shoe as shewn in dotted
lines in the figure.
The bent part of the horse-shoe is outside the range of action of the electric
current in the coils, the magnetic field of said coils extending for a short distance
only, as the current in coil B flows in the opposite direction to that in coils A and C.
My improved galvanometer can obviously be used when properly wound and
graduated as either an ammeter or a voltmeter as desired.
Although I have herein described various methods of carrying my invention
into practice I wish it to be clearly understood that I do not limit myself to those
methods but I reserve the right to modify the same in detail without departing
from the nature thereof.
Dated this 12th dox of Lul 1002
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements relating to Galvanometers.
I, CARL LUDWIG RUDOLPH ERNEST MENGES, of 82/84 Balistraat, The Hague,
in the Kingdom of Holland, Electrician, 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 :--
My invention relates to galvanometers and comprises the improvements herein-
after described.
When an electric current flows in opposite directions through two coils arranged 5
side by side, the space between the two coils and the lateral prolongation of the

page_text: same in a direction at right angles to the axes of the coils remains practically free
from lines of force, for the lines of force are practically concentrated into a single
circuit passing from one coil through the other and back. Hence if a magnet be
placed in the space mentioned it will not be influenced, that is to say, its magnetic
state will not be altered by any current flowing in the coils, nor will it be
magnetized or demagnetized.
According to my invention 1 construct a galvanometer so that the movable
needle or needles is or are placed in a magnetic field produced by a magnet
situated in the neutral space above mentioned. The controlling magnetic field
therefore in which the movable needles are swinging is not affected by the current
to be measured.
In order that my invention may be clearly understood I will now proceed to
describe some methods of carrying the same into practice.
•
In the drawings accompanying the Provisional Specification
Figure 1 is an elevation, and
Figure 2 a plan of an instrument constructed according to my invention.
Figure 3 is a section on the line 6 c, Figure 1.
Figures 4 and 5 shew modified details of construction.
Figures 6, 7 and 8 shew further modifications hereinafter explained.
Figures 9, 10 and 11 which accompany my Complete Specification show still
further modifications of my invention.
Like letters of reference denote similar parts throughout the drawings.
A is one of the coils. B is the other coil, the wires being joined so that a
current will flow in opposite directions in the coils. NS is the controlling
magnet.
In the arrangement shown in Figures 1, 2 and I provide in each coil a movable
iron or magnetic needle s¹ n' and s² n². These needles will when no current is
flowing place themselves parallel to the controlling magnet N S, but will be
deflected in opposite directions by a current in the coils A, B. No change of
direction of the magnetic axis of the controlling magnet N, S occurs by the action
of the movable needles when deflected, because the actions of the two needles
which are equal and opposite practically destroy each other.
If the two needles s¹ n' and s² n² are connected with each other by any con-
straining mechanism so that they must always move in opposite directions the
apparatus becomes astatic and is not affected by external forces. For instance as.
shown in Figure 4, one needle s¹ n¹ may be connected with a sector z³, toothed
externally, and the other needle s² n² with a sector 22 toothed internally. The two
sectors,, engage with wheels 1, 2, fixed on the same shaft, or bevel wheel
gearing may be used as shewn at k¹, k², Z, Figure 5, the index being fixed upon the
axis of the intermediate wheels ', r2 or Z as indicated in Figure 4.
The same object may also be achieved without any mechanical connection of the
needles by the arrangement represented in Figures 1, 2 and 3. The needle s¹ n'
carries a ring a a on which the scale is marked, while the index 16' is fixed upon
the other needle.
Under certain circumstances I find it may be advantageous to make the movable
needles s¹¹ and s² n² considerably shorter than the directive magnet N S as shewn
in Figure 6. To obtain as strong a controlling force as possible, bars p' p²
and p² p² of soft iron are provided which conduct the lines of force coming from
the controlling maguet NS to the needles. These bars p' p¹ and p³ p² may also
pass through openings in the coils, so as to be brought near to or even in contact
with the magnet N S.
I sometimes make my improved galvanometer with an astatic needle system of
the ordinary design. For instance I may use what I will call a duplication of the
instrument shewn in Figure 2. I then provide two pairs of coils each having a
controlling magnet, and in one of the coils of each pair I mount a needle. Said
needles are secured on a common shaft. If the arrangement be such that the two,
middle coils are traversed in the same direction by a current these coils may be

page_text: replaced by a single coil. Such a galvanometer with three coils A, B and C is
represented in Figure 7, in which figure each coil consists of only one turn.
As herein before mentioned in the space beyond the ends of the magnet NS,
Figure 2, there is practically no field due to any current passing round the coils.
In lieu therefore of one controlling magnet I sometimes use two which are placed
opposite each other with their poles of unlike names at N, S.
If these currents be made long enough the outer ends may be bent and connected
together but at such a distance from the coils A and B that the action of the
electric. current there is insignificant, this arrangement is shewn in Figure 8.
In the instrument shewn in Figure 7, this closing of the magnetic circuit is
preferably effected by joining the north pole N₁ of one controlling magnet to the
south pole S2 of the other magnet thus making a horse-shoe as shown in dotted
lines in the figure.
The bent part of the horse-shoe is outside the range of action of the electric
current in the coils, the magnetic field of said coils extending for a short distance
only as the current in coil B flows in the opposite direction to that in coils A
and C.
A com-
If a movable needle be placed in the arrangement shewn in Figure 3 above or
below and near to the coils A and B, thus within the magnetic field produced by
these coils, it will of course also be deflected by the current in the coils.
bination of this arrangement and that shown in Figure 3 is indicated in Figure 9,
where the needle is inside the coil A but in the outside magnetic field in respect to
the coils C and D. The needle is therefore in a much stronger magnetic field than
it would be if the coils A and B alone were present. If also a strong controlling
magnet is used, the outside influences may be neglected and the astatic arrange-
ment dispensed with. Thus in Figure 9 there is only one needle with an index b, b
indicating the deflection on the scale a. A straight controlling magnet may be
used such as indicated in Figures 1, 2 and 3, but generally I prefer a bent magnet
as indicated by the dotted line in Figure 7, or as in Figure 8, as it will occupy less
space for the same magnetic strength. In Figure 9, the magnet N m S is supposed
to be cut at m, the part m S which is taken away, should lie with the pole S
opposite N, so that the coil A is between N and S.
The arrangement with four coils A, B, C and D has moreover, the advantage
that the main object of this invention, that is to say, arranging the electric circuit
in such a manner that it will not influence the controlling magnet, is attained to a
greater degree than in the previous devices for the magnetic field is more confined
to the interior of the coils and the outside field, in the gaps or spaces between
adjacent faces of the coils, being smaller, there is less, leakage to influence the
controlling magnet. These gaps or spaces and therefore also the leakage may be
made still smaller by arranging more than four coils in a closed circuit or by
forming the coils with a bent axis. The arrangement of the needle and index in
the middle of a coil as shewn at A, Figure 9, may be less convenient where small
gaps only exist.
I therefore prefer to arrange the needle in the gap on a spindle
of sufficient length provided with an index which swings freely outside the coils, in
the manner indicated by ns and bb, Figure 11.
With bent coils I may put the adjacent faces of the coils close together so as to
practically avoid a gap, or I may use only a single annular shaped coil, as indicated,
Figures 10 and 11, with a gap just large enough to allow of the introduction of the
needle ns which gap also facilitates the winding of the wire.
The position of the controlling magnet N S in Figures 10 and 11 is different
from that shown in Figure 9, but the same arrangement as in that figure may be
used with a ring coil, and conversely.
"The magnet may also be bent to such a shape that the middle part m, Figure 9,
will lie in the space between the coils A, B, C and D, or in the opening of the ring
coil, Figure 10.
J
14
My improved galvanometer can obviously be used when properly wound and
calibrated as either an amperemeter or a voltmeter as desired.
-St

page_text: Although I have herein described various methods of carrying my invention into
practice I wish it to be clearly understood that I do not limit myself to these
methods but I reserve the right to modify the same in detail, without departing
from the nature thereof.
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. A galvanometer having two or more coils placed side by side and connected
in such a manner that a current will flow in opposite directions through adjacent
coils, with one or more movable iron or magnetic needles adapted to be acted upon
by the current flowing in the said coils and also by one or more controlling magnets
so shaped and disposed relatively to the coils that the line joining the poles of said
magnets is approximately perpendicular to the magnetic circuit set up by the coils.
2. A galvanometer such as described in the preceding claim but having its coil
or coils so shaped and arranged that the axis thereof forms a closed figure, the
direction of the current in the said coil or coils being such that a magnetic field
will be produced, the lines of force in which lie along said closed figure.
3. In a galvanometer constructed substantially as described a pair of movable
needles connected by a restraining mechanism so that when they move, they must
do so in opposite directions, for the purpose specified.
4. In a galvanometer constructed substantially as described a pair of movable
needles one of which carries the scale while the other, which is always deflected in
the reverse direction, carries the pointer, for the purpose specified.
5. A galvanometer having three coils and two needles on the same spindle,
substantially as described with reference to Figure 7 of the drawings, for the
purpose specified.
Date Lhi u 1
C
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.