Improvements in Galvanometers.
Year: 1889

page_text: Date of Application, 22nd Mar., 1889
Complete Specification Left, 22nd Jan., 1890-Accepted, 22nd Mar., 1890
PROVISIONAL SPECIFICATION.
Improvements in Galvanometers.
FREDERIK VILHELM ANDERSEN of 14 Westdown Road Catford in the County of
Kent do hereby declare the nature of this invention to be as follows :-
The improvements consist chiefly in
:-
1) Suspending a needle in such a manner that its magnetic axis is placed obliquely
in relation to the axis of suspension, i.e. to the axis round, which the needle turns
when deflecteil, & not as is commonly the case at right angles to the axis of suspension,
and-
2) Arranging in certain cases special magnetizing coils round the said needle as
described hereafter.
The said obliquely suspended needle may be an ordinary straight magnetized steel.
needle attached to a rigid pivotted spindle, with which it forms' a certain angle,
which may be any angle different to 90°.
If this arrangement is placed with its axis of suspension vertical, the magnetic field
of the earth may be used for directing the needle to zero, and galvanometer coils
may be arranged in any known way, so as to deflect the needle from zero when a
current is passed through them, these coils may consist of a number of turns wound
on any suitable frame, such as a tube placed round the axis of suspension concentric
with the same, or instead of such coils, a split tube placed concentric with the.
suspension may be used, the current being led up one side of the tube, & down
the other, the latter form I prefer to use when strong currents are to be measured.
The said obliquely suspended needle may on the other hand be made of soft iron,
& a magnetizing coil be added to the arrangement, this magnetizing coil being placed
round the axis of suspension of the needle, & concentric with the same, the individual
turns of this coil having their planes at right angles to the axis of suspension, in
order that no deflecting tendency upon the needle shall ensue from a current passing
through them, but such current shall have the effect of magnetizing the soft iron
needle only. Galvanometer coils are used for deflecting the needle in combination
with this arrangement in similar manner to the one above described & such galvano-
meter coils may be placed either close to the needle & inside the magnetizing coil, or
if preferred, further away from the needle, & outside the magnetizing coil, the former
alternative being the one generally adopted.
A controlling force for the needle may be provided in various ways, advantage
may be taken of magnetic fields, as already described, or springs, or bifilar, or
torsional, or other suitable devices may be adopted for the purpose.
To eliminate disturbances from extraneous magnetic influences, I frequently mount
my improved Galvanometer in an iron case.
The oblique needle is generally placed so as to form a comparatively small angle
with the axis of suspension i.e. the magnetic axis of the needle is not very far from
parallellism with the axis of suspension, thus the galvanometer coils & also. the
magnetizing coils when such are used, can be placed in close proximity to the
needle, & a greater efficiency can therefore be obtained from this arrangement than from
any hitherto known form of Galvanometer, the reason being that a comparatively
long & powerful magnetic needle is obtained, which allows of deflecting coils being
arranged very closely round it so as to intercept practically all its magnetic lines, in
whichever position it stands.
Dated this 22nd day of March 1889.

page_text: COMPLETE SPECIFICATION.
Improvements in Galvanometers.
I, FREDERIK VILHELM ANDERSEN, of 14 Westdown Road, Catford, in the County
of Kent, Electrical Engineer, 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 for improvements in galvanometers has for its object to construct
an instrument in which a comparatively long and consequently powerful magnetic
needle is suspended within the deflecting coils in such a manner that said coils
intercept practically all the magnetic lines of the needle in whatever position it takes ;
and consists in mounting a long needle on an axis making a small angle with the
magnetic or longitudinal axis of the needle. The needle may be either a permanent
magnet or magnetised by special coils.
In the accompanying two sheets of illustrative drawings,
Fig. 1 is a vertical section of an instrument for measuring the difference of
potential between any two points of an electric circuit constructed according to my
invention, and
Fig. 2 is a plan of the same;
Fig. 3 shews a method of winding a deflecting coil suitable for use with my
improved needle in an instrument for measuring the difference of potential between
two points of an electric circuit ;
Fig. 4 shows in elevation a method of winding deflecting coils suitable for use with
my improved needle in an instrument for measuring the resistance of an electric
circuit or of a portion of a circuit, and
Fig. 5 is a plan of the same; and
Fig. 6 is a vertical section of an instrument, constructed according to my invention,
for measuring the quantity of current passing in a unit of time in an electric circuit,
the needle being supposed removed, and
Fig. 7 is a plan, and
Fig. 8 a horizontal section of the same.
Referring to figs 1, 2, and 3, the needle is composed of a thin blade 1 of soft
iron to which is secured a non-magnetic spindle 2 making a small angle with the
direction of length of the needle. A recess is shown stamped in the blade 1 into
which the spindle 2 fits and is secured by rivets. The case of the instrument
comprises an outer cylinder 3 preferably of iron and a cover 4 also preferably of
iron. The dial 5 is secured to the cover 4 which also supports the rim 7 for the
glass plate 6 covering the dial. To the underside of the cover 4 and extending
centrally downwards within the cylinder 3 is secured a tube 8 of non-magnetic
material. In the lower end of the tube is a block through which passes a set screw 9
serving as a lower bearing for the spindle 2 of the needle 1. The top bearing of
the spindle is formed by the bracket 10 screwed to the upper side of the cover 4.
A spiral spring 11 has one end attached to the spindle 2 and its other end to a
moveable ring 12 mounted centrally on the underside of the cover 4 and actuated,
by means of a lever 15 from the outside of the case, to give a slight adjustment of
the spring to bring the pointer to zero. The pointer 16 is attached to the spindle ?
and indicates on the scale 17.
The cover 4 of the case also supports centrally an insulating reel 18 carrying the
coils 19 for exciting the needle. The deflecting coils 20 are wound upon the tube S
as clearly shown in Figs. 1 and 3. The circuit of the instrument is from the
terminal 21 through the plate 22 deflecting coils 20 exciting coils 19 and plate 23 to
the terminal 24.
-
.
When this instrument is required to indicate the difference of potential between
two points of an electric circuit, the terminals 21, 24 are connected to the said
points of the circuit; the needle 1 is deffected against the resistance of the spring 11.

page_text: The amount of deflection is indicated by the pointer 16 on the scale 17 which is
suitably graduated to read the difference of potential in volts.
When the instrument is required to measure the resistance of a circuit or of a
portion of a circuit the tube 8 is wound with two sets of coils 25, 26 arranged at right
angles to one another as clearly shown in Figs. 4 and 5 instead of with the coils. 20.
One of these coils, say, 25 is put in the circuit in series with the resistance. to be
measured and the other coils 26 and the exciting, coils 19 are arranged. in series
as a shunt to the resistance. In this arrangement the spring 11 is dispensed with.
The deflection of the needle to either side of its symmetrical position with respect to
the coils. 25, 26 will be indicated on the scale 17 which is then suitably graduated to
read ohms.
When the instrument is required to measure the amount of current passing in the
circuit in a unit of time. the modified construction shown in Figs. 6, 7 and 8 is
adopted. The deflecting coil 27-consists of a tube split diametrically across from the
top to nearly the bottom and formed in one with the bracket 28 and terminal 32.
The needle 1 works within the tube 27 which is secured by the said bracket 28 to the
cover 4. On the opposite side of the split conducting tube 27 to the bracket 28 is
connected the end of a broad copper strip 29 which forms the exciting coil and is
wound round the tube 27 and led to a second terminal 30 on the outside of the
instrument. The strip 29 and split tube 27 are insulated from the casing and the
convolutions of the strip are insulated from one another, the insulating material
being indicated by thick black lines. The lower end of the spindle of the
needle works in a screw 31 fitted in a block secured to the lower end of the
tube 27.
When the instrument is inserted in the circuit the needle is deflected against
the resistance of the spring 11 and indicates on the scale 17 which is graduated to
read amperes.
When the instrument is required to measure the amount of work effected in a given
portion of an electric circuit in a unit of time, the exciting coil 29 is dispensed with
and the needle 1 is made of mica and wound with a fine wire coil. The deflecting
coil 27 is put in circuit with the circuit in which the work is to be measured and
the coil on the mica needle is arranged as a shunt to the portion of the circuit in
which the work is to be measured, a suitable resistance being also inserted if required
in the shunt circuit. The needle is deflected against the resistance of the spring and
the scale is graduated so that the pointer indicates the number of watts.
It will readily be understood that the current passes down one side of the tube 27
and up the other side.
The iron case of the instrument prevents any influence of the earth's magnetism
and allows the instrument to be brought close to powerful currents without affecting
its measurements.
Although the needle is shown in every case arranged to be excited by special
coils it is evident that in many cases a magnetised steel needle of the same shape may
be employed without departing from the nature of my invention.
The angle between the spindle 2 and the magnetic or longitudinal axis of the
needle 1 may be any angle less than a right angle but is preferably not more than
30 degrees.
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. In galvanometers arranging a long needle on an axis making a small angle
with the magnetic or longitudinal axis of the needle substantially as described and for
the purposes set forth.
2. A galvanometer consisting of a long needle mounted on an axis making a small
angle with the magnetic or longitudinal axis of the needle and of a deflecting coil or
coils and an exciting coil symmetrically surrounding the said needle substantially as
described with reference to figs. 1, 2, 3, 4 and 5 of the drawings.

page_text: 3. A galvanometer consisting of a long needle mounted on an axis making a small
angle with the magnetic or longitudinal axis of the needle and of a tube surrounding
the said needle and split diametrically across from one end to near the other and
connected with the terminals of the instrument so that the whole current can be
passed down one side and up the other to deflect the needle the whole constructed
substantially as described with reference to figs. 6, 7 and 8 of the drawings.
4. The construction of galvanometers substantially as described with reference to
the drawings.
Dated this 92nd day of Jonuary 1800
WHEATLEY & MACKENZIE,
40, Chancery Lane, London, W.C., Agents.