Improvements in Electric-current Meters.
Year: 1890

page_text: Date of Application, 28th Nov., 1890-Accepted, 3rd Jan., 1891
COMPLETE SPECIFICATION.
Improvements in Electric-current Meters.
We EUGEN HARTMANN and WUNIBALD BRAUN both of Bockenheim Frankfort on
the Maine in the Empire of Germany Electrical Engineers 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 :-
Our invention relates to an improved arrangement hereinafter described whereby
the relatively small elongation of a wire or conductor due to the expansion resulting
from the heat generated by the passage of the current to be measured is converted
into a relatively extensive displacement of the band or pointer indicating the strength
of the current.
And in order that our said invention may be fully understood we shall now proceed
more particularly to describe the same and for that purpose shall refer to the several
figures on the annexed sheet of drawings the same letters of reference indicating
corresponding parts in all the figures.
Figure 1 of the accompanying drawings is a diagram illustrating the principle of
the action of a ineter arranged according to this invention with the wires or conductors
in their normal position and
Figure 2 represents the position assumed when the wires are elongated or expanded
by the passage of a current.
Figure 3 illustrates the application of this principle in a practical form and
Figure 4 illustrates a modification of the arrangement of the parts as hereinafter
described.
According to the combination illustrated in Figure 1 two parallel wires a and b
whose expansion or elongation serves as the measure of the current passing through
them are attached at their extremities to fixed clamps or supports k. These wires are
connected at or near the middle to a rigid or inflexible arm or lever pivoted at s¹ at
or about the centre of the said arm or lever between the wires a and b as represented
in Figure 1. Under these conditions the longitudinal extension or expansion of the
wires a and b tends to cause them to assume the shape represented in Figure 2 thereby
moving the lever s through an angle which is of considerable amplitude relatively to
the amount of longitudinal expansion of the wires a and b and which increases in
inverse proportion to the normal distance separating the latter. By connecting the
levers with a hand or pointer Z as illustrated in Figure 3 the amplitude of the angle
of rotation of this lever is enabled to be read off on a suitably graduated scale and
affords an indication of the current passing in the conductors a and b.
A spring F is provided to control the movements of the pointer as indicated in
Figure 3.
Figure 4 illustrates an arrangement on the same principle in which two pairs of
parallel wires a band a¹ b' are employed. This arrangement has the advantage of
combining the power of two pairs of wires thereby securing greater certainty or pre-
cision in the indications afforded by the instrument which is also rendered less sensitive
to vibration and other external disturbing influences. The indicator is carried by a
spindle or axis a arranged at right angles to the wires a b and a b¹ and receives a
rotary impulse from a helical spring F which acts in opposition to the pull of the said
wires. An arm c is attached to the lever s connected to the wires a b and a similar
arm c¹ is attached to the lever & worked by the wires a¹ b¹. These arms c and c¹ are
connected by threads or flexible connections 9 g₁ to the axis x so that when the
wires a ba¹ expand a rotary motion of x is produced from both sides. The
expansion of the wires enables the spring F to rotate the spindle and wind
the threads g g¹ upon this spindle as far as the expansion of the wires a band a¹ b¹
permits and the hand or pointer on or connected to the said spindle partakes of a
Leics:

page_text: corresponding angular displacement which being necessarily dependent on the
amount of longitudinal expansion of the conductors affords an accurate indication of
the current.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is:
1. In an electric current meter acting by the expansion of a conductor heated by
the current to be measured the arrangement of a rigid or inflexible pivoted arm or
lever connected to wires or flexible conductors heated by the current and enabling
the longitudinal expansion of the said wires or conductors to produce a movement of
a hand or pointer substantially as herein before described with reference to the
accompanying drawings.
2. The combinations and arrangements of parts constituting the improvements in
electric current meters substantially as hereinbefore described with reference to the
accompanying drawings.
Dated this 28th day of Noromban 1800
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.