Improvements in Indicators for Telephone Exchanges.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improvements in Indicators for Telephone Exchanges.
We, SIEMENS BROTHERS & Co., Limited, of 12, Queen Anne's Gate, West-
minster, in the County of London, Electrical Engineers, do hereby declare the
nature of this invention (as communicated to us from abroad by Siemens and
Halske, 94, Markgrafenstrasse, Berlin, in the German Empire, Electrical En-
gineers,) to be as follows:-
In the indicators of present construction for telephone exchanges the incon-
venience arises that the operator requires to stretch his arm inconveniently in order
to restore the indicator drop, difficulty is experienced in effecting this electrically
by a conveniently situated press-button.
The present invention relates to an improved construction of indicators whereby
this inconvenience is avoided. It consists in providing two opposite horizontally
placed electromagnets, the outer ends of whose cores are joined together by a yoke,
the middle of which has pivotted to it an upright armature tongue which rocks
between the two opposite poles of the electromagnets, and which tends to tumble
over into the one position or the other when passing the vertical centre line. To
the side of the tongue is fixed a light double ended bar to one end of which is
fixed the indicator drop at right angles to the bar, this being so arranged rela-
tively to the tongue that when the latter assumes the one angular position in
contact with the pole of the one magnet, the bar is in the horizontal or dropped
position, with the drop shewing through opening of the glass indicator frame,
while when the tongue is in the opposite angular position, the bar is turned into
a corresponding angular position in which the drop is removed from the opening
of the frame.
The coils of the two electromagnets are included in two different electric circuits,
that of the one which brings the drop into the visible position being in the sub-
scribers circuit, while that of the other is in the exchange circuit.
Thus on a subscribers circuit being closed for calling, the tongue is attracted
so as to bring the drop before the opening of the frame, while when the exchange
circuit is closed, the tongue is moved over to the other electromagnet, and the
drop is raised away from the opening.
According to another modification the apparatus is arranged as a polarised
ringing-off drop.
For this purpose there is combined with the above device a permanent magnet,
one pole of which is fixed to the middle of the before mentioned soft iron yoke
connecting the cores of the electromagnets while the other end carries the pivots
of the armature tongue to which the bar of the indicator drop is fixed. The
electromagnet cores are so arranged that the two opposite poles thereof are of the
same sign, say north, while the armature tongue is polarised by the permanent
magnet so as to be of the opposite sign, say south. The coils of the two electro-
magnets are in series on the same circuit. The armature tongue has on each side
of it an arc shaped piece that slides in contact with a corresponding curved surface

page_text: on the electromagnet poles as it tumbles over from the one position to the other.
By this means there is no stray field since the magnet circuit is always effectually
closed through the armature and when the tongue is lying against the one pole,
its free curved projection is situated quite close to the other pole so that even with
a weak current it has a very sensitive action.
The tongue, and consequently the indicator arm and drop are actuated by pass-
ing currents first in one direction and then in the opposite direction through the
electromagnet coils, so as to reverse the polarity of the cores.
Improvements in Indicators for Telephone Exchanges:
We, SIEMENS BROTHERS & Co., Limited, of 12, Queen Anne's Gate, West-
minster, in the County of London, Electrical Engineers, do hereby declare the
nature of this invention (as communicated to us from abroad by Siemens and
Hale, 91, Markgrafenstrasse, Bulin, in the German Empire, Electrical En-
gineers), and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
In the indicators of present construction for telephone exchanges the incon-2
venience arises that the operator requires to stretch his arm inconveniently in order
to restore the indicator drop, and difficulty is experienced in effecting this electri-
cally by a conveniently situated press-button.
The present invention relates to an improved construction of indicators whereby
this inconvenience is avoided. It consists in providing two opposite horizontally 2
placed electromagnets, the outer ends of whose cores are joined together by a yoke,
the middle of which has pivotted to it an upright armature tongue which rocks
between the two opposite poles of the electromagnets, and which tends to tumble
over into the one position or the other when passing the vertical centre line. To
the side of the tongue is fixed a light double ended bar to one end of which is 3
fixed the indicator drop at right angles to the bar, this being so arranged rela-
tively to the tongue that when the latter assumes the one angular position in
contact with the pole of the one magnet, the bar is in the horizontal or dropped
position, with the drop shewing through opening of the glass indicator frame,
while when the tongue is in the opposite angular position, the bar is turned into 3
a corresponding angular position in which the drop is removed from the opening
of the frame.
The coils of the two electromagnets are included in two different electric circuits,
that of the one which brings the drop into the visible position being in the sub-
scribers circuit, while that of the other is in the exchange circuit.
The accompanying drawing shews an indicator constructed according to the
present invention.
Figure 1 shews a longitudinal section and Figure 2 a cross section of one arrange-
ment. Figure 3 shews a longitudinal section, Figure 4 a cross section and Figure
5 an end view of a modified construction.
Two electromagnets E Es Figure 1 have their outer pole ends connected together,
the connecting piece carrying an armature A pivoted at a so as to rock between
the poles P's. The pivot is situated below the centre of gravity so that the
armature has a bias to one side or the other. The armature is connected laterally
4

page_text: to the arm K of an indicator flap, which moves up and down behind the glass plate
of an indicator case, which carries the subscribers number. The coils of the
magnets are included in two different electric circuits, the right hand coil being
in the subscribers circuit, and the left hand coil in the exchange circuit.
Thus on a subscribers circuit being closed for calling, the tongue A is attracted
by the electromagnet E, so as to bring the indicator drop before the opening of
the frame, in which position the parts are held by gravity until the exchange cir-
cuit is closed, when the tongue will be moved over to the other electromagnet E¹,
and the drop K is raised away from the opening, as shewn at Figure 1.
According to the modification shewn at Figures 3 to 5, the apparatus is arranged
as a polarised ring-off drop.
For this purpose there is combined with the above device a permanent magnet M
one pole of which is fixed to the middle of the soft iron yoke R connecting the cores
of the electromagnets E¹E while the other pole carries the pivots of the armature
tongue A to which the bar of the indicator drop K is fixed. The coils E¹ E of
the electromagnet are connected in series, and the yoke is interrupted at one point
by a slit so that the opposite poles thereof are of the same sign, say north, while
the armature tongue A is polarised by the permanent magnet so as to be of the
opposite sign, say south.
The armature A is formed as a segment of a cylinder, at the middle of whose
cylindrical surface projects a tongue situated between the poles of the electro-
magnets, while the curved surfaces on either side move under correspondingly
hollowed surfaces of the said poles. By means of this form of the armature the
advantage is gained that there can be no magnetic dispersion between the poles
of the electromagnet, as the magnetic circuit is always closed by the armature.
Also, there can be no magnetic dispersion between the permanent magnet and the
electromagnets as the space in which the lines of force can pass from the poles of
the electromagnets to the poles of the permanent magnet is entirely filled out by
the armature body.
The construction furthermore affords the advantage that while the armature still
has its tongue bearing against the one pole, the other part thereof is already
situated in the sphere of influence of the other pole. By this means a very effective
and sensitive action is obtained even with very weak current impulses.
The entire arangement of the indicator is very flat, and consequently only a
small space is required for it, which is of great advantage.
The entire construction of the indicator is very simple, as nearly all the metal
parts can be produced by stamping, and the ring off drop is not subject to external
influences, on account of the compact form of its armature, which is firmly sup-
ported on point centres.
The indicator is operated by passing currents through the coils alternately in
opposite directions.
The cores of the electromagnets being polarised by the permanent magnet and
armature it follows that when no current is passing both poles will be of the same
sign, and the armature will be held over by the magnet with which it is in contact;
when a current is passed through the coils in one direction, it will strengthen
the one pole, say the left hand one, causing the armature to remain in its attracted
position while the other pole will be weakened or reversed. On passing a current
through in the contrary direction, the polarity of the left hand magnet will be
reversed while that of the right hand one will be strengthened, causing the armature,
and consequently the indicator drop to move over into the opposite position.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, we declare that what we
claim is:-
1. An indicator for telephone exchanges, having a pivoted armature rocking
in the neutral zone of two opposite electromagnets, which armature has a tongue
moving between the poles of the magnets and on either side thereof projections

page_text: with cylindrical surfaces which fit into corresponding hollows of the poles, so that
on the one hand there is no magnetic dispersion between the poles of the electro-
magnets and on the other hand the armature is always within the sphere of in-
fluence of the magnets, substantially as described.
2. An indicator such as is referred to in the first claim wherein the armature 5
is pivotally mounted upon a permanent magnet, so as to be polarised thereby,
substantially as described.
ABEL & IMRAY.
Agents for the Applicants.