Year: 1888

page_text: Date of Application, 6th Jan., 1888
Complete Specification Left, 8th Oct., 1888
Complete Specification Accepted, 14th Dec., 1888
I, JOHN HUBERT DAVIES, of 3 Burry Terrace, Westbourne Square, London, W.
Electrical Engineer, do hereby declare the nature of this invention to be as follows:-
:-
This invention relates to improvements in electrical measuring instruments of the
type wherein a light iron needle, or armature, is caused by the passage of a current
through suitably disposed coils of wire to actuate an indicating needle, and has for its
object the provision of means whereby the needle, or armature, shall be rendered less
susceptible to the influence of magnetic fields outside the instrument, while at the
same time ensuring great simplicity of construction and cheapness of manufacture.
To overcome the difficulty heretoforo experienced with instruments of this class
when working in proximity to disturbing magnetic influences the light needle, or
armature, made of soft iron and preferably of small cross section so as to ensure its
rapid magnetic saturation, is mounted on the same spindle as the indicating needle
and counterbalanced either by a suitable spring or weight in the usual manner.
The ends of the soft iron needle, or armature, project sufficiently from the spindle
on which they are mounted as to allow of their coming within the influence of two
coils of wire placed, diametrically opposite, one on each side of the spindle.
These coils instead of being wound, as is usual, each in the same direction whereby
the opposite ends of the needle, or armature, become magnetised with opposite signs
(i.e. one end N and the other end S) are wound in opposite directions whereby mag-
netism of the same character, or sign, is induced in each of the ends of the needle, or
armature, so rendering the same astatic and overcoming the tendency to be influenced
by outside magnetism which exists in a needle or armature whose ends are differently
magnetised.
It will be understood that in place of using simple coils of wire the object of this
invention may be attained by placing a fixed iron core in the coils in such a way that
it repels the pivotted iron needle, or armature, by reason of like poles being induced
in those ends of the fixed core and the pivotted needle that are in proximity.
T
1036

page_text: I, JOHN HUBERT DAVIES, of Cadby Hall Works, Hammersmith, London, W.,
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:-
This invention relates to improvements in electrical measuring instruments of the
type wherein a light iron needle, or armature, is caused by the passage of a current
through suitably disposed coils of wire to actuate an indicating needle, and has for its
object the provision of means whereby the needle, or armature, shall be rendered less
susceptible to the influence of magnetic fields outside the instrument, while at the
same time ensuring great simplicity of construction and cheapness of manufacture.
To overcome the difficulty heretofore experienced with instruments of this class
when working in proximity to disturbing magnetic influences the light needle, or
armature, made of soft iron and preferably of small cross section so as to insure its
rapid magnetic saturation, is mounted on the same spindle as the indicating needle
and counterbalanced, either by a suitable spring, or weight, in the usual manner. The
ends of the soft iron needle, or armature, project sufficiently from the spindle on
which they are mounted as to allow of their coming within the influence of two coils
of wire placed, diametrically opposite, one on each side of the spindle. These coils
instead of being wound, as is usual, each in the same direction whereby the opposite
ends of the needle, or armature, become magnetised with opposite signs (i.e. one end N
and the other end S) are wound in opposite directions, whereby magnetism of the
same character, or sign, is induced in each of the ends of the needle, or armature, so
rendering the same astatic and overcoming the tendency to be influenced by outside
magnetisin which exists in a needle, or armature, whose ends are differently magnetised.
It will be understood that in place of using simple coils of wire the magnetic effect
of the coils on the needle may be produced with greater intensity by inserting iron
cores in the coils without departing from my invention; but I generally prefer to
construct the instrument with as little iron as possible.
The accompanying sheet of drawings further illustrates my invention.
Figure 1 is a section and Figure 2 a plan of an instrument constructed in accordance
with this invention, the reference letters in both figures indicating like parts.
A, A', are end cheeks of the coil fastened together by the plates B, B', which also
carry the jewel holes for the pivot E of the needle system.
The coils C, C', shown in the figure are formed of copper strip suitably insulated for
carrying large currents; the inside end of both coil strips is attached by rivets and
solder to the insulated copper cross rods D, D¹, which thus electrically join the two
coils, (leaving, a space for the pivot between them) and the outside ends of the strips
are carried to the terminals T, T. The insulation of the copper cross rods is shown
at K, K. If the currents to be measured are small, or if the instrument is to be used

page_text: as a voltmeter, the coils consist of wire more or less fine according to the range the
instrument is intended to have; for a voltmeter No. 38 B.W.G., is a suitable size of
silk covered copper wire.
In this case each coil is provided with two cheeks between which the wire is wound
in the usual way and the copper cross rods D, D¹ can be dispensed with, the connection
between the coils being made with wire. In all cases, however, the conductor is so
wound and the coils so connected together that the current passes round the two coils
in opposite directions as and for the purposo hereinbefore defined; this result would
be attained by so winding the coils shown in Figures 1 and 2 that if they could be
both seen when looking at one side of the instrument they would both appear to be
wound in the same way, and direction, the copper cross bars connecting the two inside
ends together, and the two outside ends going to the terminals.
The needle, or armature, of the instrument is formed of two soft iron wires F, these
are fixed in holes passing through the pivot E, and are so arranged that when the
pointer H is at the zero of the scale on the plate J they lie at about the angle shown
as regards the coils; as the current through the coils increases they assume a position
increasingly approaching coincidence with the magnetic axis of the coils and the pointer
indicates corresponding valves on the scale.
G, G, are two balance weights on the needle system which, in the instrument shown
in the figures, are so adjusted that the force of gravity keeps the pointer at the zero of
the scale when no current is passing through the coils and opposes to the desired
extent the deflecting force of any current which is to be measured. Instead of using
gravity as the controlling force I sometimes completely balance the needle system by
the weights G, G', and attach a coiled spring for opposing the deflective force of the
current, one end of the spring being attached to the needle system and the other to
the plate B, in any suitable manner, as will be well understood.
The instrument is mounted on a base N, preferably of wood, and covered with a
glass topped case M.
Having now particularly described and ascertained the nature of my said invention,
and in what manner the same is to be performed, I declare that what I claim is :-
First. In electrical measuring instruments the use of coils so wound and connected
that the armature, or needle, is so magnetised by them as to have similar poles at its
opposite outside ends substantially as hereinbefore described.
Second. The construction and use of coils of copper strip wound and connected
together by the copper cross rods D, D', in the manner, and for the purpose, sub-
stantially as hereinbefore described and shown in the accompanying drawings.
Third. The construction of electrical measuring instruments in the manner sub-
stantially as herein before described and shown in the accompanying drawings.
Dated this fith day of October 1888.
F. SEATON SNOWDON,
Agent for the Applicant.