Improvements in or relating to Apparatus for Indicating the Strength of Current upon an Electric Circuit.
Year: 1888

page_text: COMPLETE SPECIFICATION.
Improvements in or relating to Apparatus for Indicating the
Strength of Current upon an Electric Circuit.
I, OLIVER BLACKBURN SHALLENBERGER, of Rochester, in the county of Beaver,
and State of Pennsylvania, U.S.A., 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 :-
The invention relates to the class of electrical apparatus employed for indicating the
strength of currents upon an electric circuit.
The object of the invention is to provide convenient, effective and reliable means
for determining the difference of potential existing between two given points in an
electric circuit supplied with alternating, intermittent or pulsatory electric currents.
The present invention relates particularly to that form of indicator in which a
Wheatstone bridge or equivalent circuit is so organized that when currents of the
character named are caused to traverse it a counter electromotive force will be
developed in one or more of the conductors, which will increase the apparent
resistance thereof. This counter-electromotive force will increase and decrease as the
applied electromotive force varies. By properly organizing the indicating circuits
such changes in the distribution of the differences of potential may be secured as to
effect the proper operation of the indicating apparatus.
In a bridge arranged in this manner, current flows across the indicator circuit when
the difference of potential of the line is either above or below normal, but since this
current is alternating, its effect upon such instruments as are ordinarily used as
indicators would be the same, whether the difference of potential of the circuit be too
high or too low. This invention provides an organization such that the indicator is
deflected in a definite manner such as will indicate either an increase or decrease from
normal difference of potential. Although the invention is especially applicable to a
bridge containing inductors as described, it is evident that other equivalent devices as
incandescent lamps may be used in their stead.
In the accompanying drawings different organizations of apparatus for carrying out
the invention are shown.
Referring to figure 1, A represents a source of alternating, intermittent or pulsatory
electric currents, and L1, L2, represent main line conductors derived therefrom and
leading to any desired work circuit.
Between the lines L1, L2, there is connected an indicating apparatus for determining
the difference of potential existing at the points-1, 2, upon these conductors. Two
conductors 3 and 4 connect the points 1 and 2. From a point 5 in the conductor 3,
to a point 6 in the conductor 4 there leads a conductor 7; this conductor includes in
its circuit a coil & of the indicating device D. It is designed that this coil & shall be
turned in one direction or the other accordingly as the difference of potential rises
above or falls below the desired normal point. The coil d is supported in any
convenient manner and carries an indicator e.
In the conductor 3 between the points 1 and 5 there is included a coil of high self
induction M', having a given law of variation of counter electromotive force under

page_text: changes in the current traversing it. A similar coil M² is included in the conductor 4,
between the points 2 and 6. The coils are respectively provided with cores m² and m²
of soft iron.
Two resistances R' and R2 are respectively included in the conductors 3 and 4,
between the points 2 and 5 and 1 and 6. The respective coils and resistances are
located in a manner similar to the four arms of a Wheatstone bridge. The parts are
so organized that when the difference of potential between the points 1 and 2 is normal,
the points 5 and 6 are at the same difference of potential, and therefore no current
will traverse the conductor 7. If, however, the difference of potential at the points 1
and 2 is increased, then a corresponding change in the counter-electromotive force of
the coils M and M² will take place; thus their apparent resistance may be decreased
in a greater ratio than that of the resistances R' and R2, the latter remaining
approximately constant. Therefore, a difference of potential will exist between the
points 5 and 6 which will cause currents to traverse the conductor in a given
direction with reference to the main current at that moment. If, on the other hand,
the difference of potential decreases, then the apparent resistance of the coils M' and M²
will increase in a greater ratio than that of the resistances R¹ and R2, and consequently
a current will traverse the conductor 7 in the opposite relative direction.
For the purpose of causing the currents which thus traverse the conductor 7 and
the coil d to indicate whether the potential has increased or decreased, a second coil f
is placed in inductive relation with reference to the coil d. This coil f may be
included in some portion of the circuit where the direction of the current will remain
the same with relation to that in the circuit L, L2, notwithstanding the change in the
relative direction of current through the conductor 7; thus, in figure 1, it is placed
in the conductor 3 between the points 2 and 5. From this it will follow that if the
coil d is normally placed at right angles to the coil f and is free to turn, it will move
in one direction if the currents through the conductor 7 are in a given direction, and
will move in the opposite direction when the currents through the conductor 7 are in
the other direction. In other words, the coil has a fixed relation to the currents in
the general circuit, while the coil d is traversed by currents in the same direction or
the opposite at any instant, accordingly as the difference of potential is above or
below the normal.
Instead of connecting the coil f in the conductor 3, as described with reference to
figure 1, it may be connected between the points 1 and 2, as shown in figure 2, by an
independent conductor 8. In other respects the organization in figure 2 is essentially
the same as that described with reference to figure 1.
The cores of the self-induction coils M¹ and M² may be made adjustable if desired.
Thus the core m², figure 1, is shown as being capable of being withdrawn from the
coil, and a scale n and pointer n¹ serve to designate the degree to which the core is
withdrawn.
Instead of the coils M³, M², any equivalent device may be employed, provided a
change in the difference of potential across 5, 6, is produced by variation of the
difference of potential of the line L, L.
Instead of making the coil M² adjustable, one of the resistances as R³, figure 2, may
be adjustable.
Referring now to figure 3 a slightly different organization will be described. In
this figure only one self-induction device M' is shown and this is located in the branch 3
between the points 1 and 5. In the branch 4 between the points 1 and 6 an adjustable.
resistance M is shown. This is provided with a pointer m' applied to the scale m for
determining the amount included in the circuit. The resistances R' and R2 are
respectively included in the branches 3 and 4 as shown. Normally the several
resistances are so adjusted that with a given difference of potential between the
points 1 and 2 the difference of potential at the points 5 and 6 will be equal and no
current will flow through the conductor 7 and the indicator D¹ included therein. But
if there is a change in such difference of potential the counter-electromotive force of
the device M' will be changed while the resistances at R1 and R2 will remain
approximately constant. This will cause a difference of potential between the points 5

page_text: and 6 and the current will flow in a corresponding relative direction through the
conductor 7 or the indicator will show if the electromotive force has risen too high or
fallen too low.
By adjusting the resistance M and noting the result upon the indicator D¹, the
direction in which the change has occurred may be determined and also the amount.
In figure 4 an organization is shown in which four self induction devices are
employed as shown at M1, M2, M3, and M. These have different laws of change under
given changes in difference of potential, but each possesses a certain amount of self-
induction. The distribution of the differences of potential is effected by any change in
the difference of potential on the circuit to which it is applied in the general manner
already described. In this instance the indicator D is shown with two coils and d
connected in somewhat the manner shown in figure 2. The coil fis included in the
conductor leading to the point 2, so that all the current which traverses the two
branches must traverse the coil f. This current will always be in the same relative
direction to the currents in the arms of the branch, notwithstanding the changes in
direction of the current through the conductor 7, and therefore the indicator will
readily show in which direction the difference of potential has varied.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that
what I claim is :-
1. The combination of an indicator acted upon by variations in alternating, inter-
mittent, or pulsatory electric currents to indicate such currents, two self-induction
devices, and two resistances respectively in branch circuits spanning one of said self-
induction devices and said indicator, and the other of said self-induction devices and
the indicator.
2. The combination of two branch conductors, a self-induction device and a
resistance in one branch, the former being adjacent to the branching point, a self-
induction device and a second resistance in the other branch, the latter being
adjacent to said branching point, a conductor uniting points in the respective branches
between the corresponding self-induction device and resistance, and an electric
indicator operated by alternating, intermittent, or pulsatory currents connected in the
last-named conductor.
3. An indicator for alternating, intermittent, or pulsatory electric currents,
consisting of a movable and a fixed coil in inductive relation to each other, a Wheat-
stone bridge, in the bridge conductor of which one of said coils is situated, a self-
induction device and a resistance in one arm of the Wheatstone bridge, and upon
opposite sides of the point at which the bridge conductor is united therewith, a
resistance in a portion of the other arm which spans the coil thus situated and said
self-induction device, and a second self-induction device in a portion of the second
arm spanning said coil and the first named resistance.
4. An indicator for alternating, intermittent, or pulsatory electrical currents,
consisting of two resistance circuits having points of equal normal difference of
potential, an indicating coil connected between said points, and a second coil
establishing a field of force connected in circuit between points at which the direction
of flow of current is independent of the direction of flow of the current in the
resistance circuits.
5. The combination of a circuit traversed by alternating, intermittent, or pulsatory
currents, two branch circuits connected therewith and adapted to vary their relative
distribution of difference of potential under variations in the difference of potential
of the main circuits, a coil of wire connected across two intermediate points on said
branch circuits, a second coil connected in shunt to the main circuit, and an indicating
device affected by the combined currents in the two coils.
6. An indicator for alternating, intermittent, or pulsatory electric circuits consisting
of two branch conductors, one branch containing a device of variable self-induction
under variations in the difference of potential applied thereto, a device in the other
branch opposing the flow of current therethrough, a conducto: connecting points in

page_text: said branch conductors and an indicator affected by currents traversing said connecting
conductor, substantially as described.
7. An indicator for alternating, intermittent, or pulsatory electric circuits consisting
of an electric conductor having two branches, a self-induction device and an artificial
resistance included in one branch, a second resistance and an adjustable resistance
device included in the other branch, an electric conductor uniting intermediate points
in the two branches, an indicating coil in the last-named conductor, and a second
indicating coil included in the first-named conductor and applied to the other indicating
coil, substantially as described.
WM. P. THOMPSON & Co.,
Agents for the Applicant.