Improvements in Electric Current Meters.
Year: 1891

page_text: 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:
This invention relates to means for measuring electric currents by the expansion
of a conductor through which the current is caused to flow and it consists in an
improved mechanical arrangement hereinafter described whereby a differential
action is produced and the movement resulting from the expansion of the conductor
is converted into a movement of the indicator of relatively great amplitude.
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 in which represents a
conducting wire whose expansion when heated by the passage of an electric
current enables the said current to be measured. This conductor is attached at one
end to a fixed point p and the other end is attached at 7 to one end of a flexible
bridge the other end of the said bridge being attached to a fixed point pl. This
bridge is connected to one end of a piece of thread or other flexible material
other extremity of which is attached to a pulley or drum for example fixed on
the axis or spindle of a pointer z. This drum is connected to a counter-weight 9 or
other equivalent device such as a spring which maintains the flexible connection f¹
in a state of tension.
the
In this arrangement the expansion and contraction of the conductor s produces
corresponding variation in the tension of the flexible bridge which is. consequently
enabled to deflect and allow the connecting thread f¹ to be coiled or uncoiled on the
drum x.
The resulting rotary motion of the said drum being transmitted to the
pointer z the latter is enabled to give the required indications.
Figure 2 illustrates a more advantageous arrangement in which the conductor s
whose expansion affords an indication of the current is stretched between two fixed
points p and a thread or other flexible connection or bridge fis attached at one end
to the conductor s at 7 being attached at the other end to a fixed point pl. Another
thread is attached at one end to the thread fat or, about the middle of the latter
and is attached at the other end to a pulley or drum on the axis of a pointer z
connected to a counter-weight g or its equivalent such as a spring whereby the
flexible connections and conductor are maintained in a constant state of tension
and rotary motion is imparted to the indicator axis whenever any variation occurs
in the length of the conductor s.
On the passage of the current the temperature of the conductor or wire s is raised
and its expansion enables it to yield to the traction of the connection fas
represented in Figure 3. The distance between the point and the point p' being
thus shortened the flexible connection f is also enabled to yield but is deflected to
a greater extent than the wire s so that a relatively large portion of the thread f
is wound upon the pulley z owing to the action of the counter-weight g and a
corresponding rotary motion through an arc of a circle is imparted to the pointer z
which may be caused to move or deflect from the position represented in. Figure 2
to that represented in Figure 3 for example. The movement of the connection fl
being considerable in proportion to that of the wires it is possible with this
arrangement to make the pulley of larger diameter and the apparatus.is thus
enabled to act with greater: precision than would otherwise be the case,

page_text: "
A still greater difference in the relative movements of the heated conductor and
the indicator can be obtained when the end of the flexible connection or bridge f
in place of being attached to a fixed point p¹ is attached to a second conductor or
wires as represented in Figure 4. In this case both the wires and s¹ being
heated by the passage of the current are deflected as represented in Figure 5 and
their combined movement is transmitted to the connection acting on the pointer.
In the arrangement illustrated in Figure 6 three conducting wires 3, s¹, ³, are
employed in combination with two flexible connections or bridges f, f, acting on a
third or supplementary bridge f*. The combined deflections of the wires s, s', 8³,
shorten the distances between the points e at which the connections ff are attached
and the combined deflections of these connections are transmitted to the supple-
mentary bridge f which is deflected to a proportionately greater extent and
transmits a correspondingly augmented movement through the thread f¹ to the
pointer z.
Figure 8 represents another arrangement in which two parallel conducting
wires are employed in combination with a series of flexible connections f
whereby a differential motion is obtained resulting in a relatively long movement
of the pointer as may be readily understood by referring to the drawing. For
measuring powerful currents a number of parallel conducting wires may be
connected with one flexible connection as represented in Figure 7. All these
arrangements are merely given as examples of the way in which our invention may
be performed in practice.
In order to render the instrument independent of variations of atmospheric
temperature the measuring wires s are supported upon bars p³ of the same material
as represented in Figure 9. and these bars are supported at the middle upon zinc
plates a attached to a brass ring M. The bearings of the axis of the indicator
pulley are supported on a zinc plate a likewise secured to the ring M. By
means of this arrangement the brass ring and the zinc plates are caused to expand
and contract in opposite directions, so as to compensate for the effects of expansion
and contraction due to variations in the atmospheric temperature and the rate of
expansion of the zinc being greater than that of the brass a uniform normal
distance is maintained between the points of support of the flexible bridge or
connection f. The axis of the indicator being supported in like manner upon a
zinc plate the indications given by the instrument are in no way influenced by the
external temperature. When a number of measuring wires are employed they
may be supported in a similar manner. When the rate of expansion of the bridge
is greater than that of the brass, rods or plates having a lower rate of expansion
may be attached to the brass ring in order to maintain a constant normal tension of
the bridge.
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 :-
1st. In an electric current mcter worked by the changes produced in one or
more conductors by the heating action of the current, the arrangement consisting
´ of one or more flexible mechanical connections or bridges placed between wires or
conductors receiving the current (Figures 4 to 8) or between such wires or
conductors and a fixed point (Figures 1, 2 and 3) the said connections converting
the variations or deflections of the said conductors either directly (Figures 1, 2, 3,
4, 5 and 7) or through the intervention of one or more similar supplementary.
bridges (Figures 6 and 8) into a rotary or circular motion of relatively great
amplitude substantially as hereinbefore described with reference to the accompanying
drawings.
2nd. In an electric current meter an arrangement in which the measuring wire
and the indicator axis or spindle are supported upon pieces of metal having
unequal rates of expansion so combined that they expand in opposite directions
and maintain a normally uniform tension of the flexible connections or bridges

page_text: independently of external or atmospheric temperature substantially as hereinbefore
described with reference to Figure 9 of the accompanying drawings.
3rd. The general arrangements and combinations of parts constituting the
improvements in electric current meters substantially as hereinbefore described
with reference to the accompanying drawings.
Dated this 16th day of July 1891.