Year: 1886

page_text: I, OSCAR FREDRIK JONSSON, Electrician, of Stockholm in the Kingdom of
Sweden, 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 object of this invention is a galvanometer for mensuring electric currents,
which apparatus may be placed near foreign electric currents without being
subjected to wrong indication. The instrument is besides very sensitive and does
not change in the course of time.
On the annexed drawing fig. 1 represents the galvanometer viewed from the side
partly in section, and fig. 2 the same viewed from the front. Figs. 3 and 4 are
diagrams for explaining the working of the galvanometer.
The parts of the instrument are placed upon a wooden platforni A, to which two
plates with pole screws B and C are secured. On the top of the plate A is fixed a
brass plate D which at the bottom is provided with a groove into which a border
of the bobbin E enters, so that, if lifted up therefrom, it may always reoccupy the
same place. The coils of the bobbin are connected with the plate of the pole
screws. In the bobbin is an iron core F fixed at the plate D and thus not
following the bobbin. Above the axis of the core is a little shaft G, from which
projects a hand H of aluminium or other light metal, moving upon a graduated
scale K secured to the plate D. From the shaft G also an iron plate I projects,
which is bent around part of the exterior of the core F. Below the graduated
scale a weight L is suspended for the suspension of the instrument in a
perpendicular position.
If, as shown in Fig. 3, the core a of an electro magnet is divided longitudinally
in two parts each part forms a separate core and both obtain the same poles turned
in the same direction. The parts of the core tend thus to repel one another. Such
a core is in Fig. 4 adapted into a bobbin. The one part b of the core is here
greater than the other c and moreover fixed, while the part c pivots on its one
border. Because the cores obtain the same polarity turned in the same direction
the pivotting part c of the core must be repelled from the fixed one b and thus
turn around its border. In order to render a part of the core more easy of motion
and to concentrate the magnetism in a greater fixed part of the core, so that the
galvanometer may become more sensitive, the smaller movable part c of the core
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page_text: is substituted by a plate I clasping partly the fixed core F. This disposition is
adopted in the above instrument, which works in the following manner.
When the instrument is not traversed by any current, the plate I gets close
along the core F. But if on the contrary an electric current is passing through the
instrument in the direction indicated by the arrows, the core F and the plate I
become magnetic. As both the core and the plate obtain the same poles turned in
the same direction, the core repels the plate, so that the hand is moving along the
scale. The weight of the plate acts as counterweight. On the passage of the
current through the bobbin, the part of the coils to the right of the core will be
principally claimed for generating magnetism in the core, while the remaining part
of the coils acts attracting upon the plate. From this it is evident that the core
as well as the coils on the left side of the bobbin tend to turn the plate in the same
direction.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, declare that what
I claim is
In a galvanometer the disposition in the bobbin (E) traversed by the current
wanted to be measured of a fixed greater iron core (F) and an iron plate with hand
acting as a smaller core and pivotted on a shaft (G), by which disposition the current
in the bobbin acts directly upon the plate (I) and indirectly by magnetizing the
core (F), so that the plate (I) absents itself more or less from the core in proportion
to the power of the traversing current.
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