Improvements in Telephone Systems.
Year: 1899

page_text: Date of Application, 17th Feb., 1899-Accepted, 5th Aug.,
1899
Improvements in Telephone Systems.
I, LARS MAGNUS ERICSSON, of Thulegatan 5, Stockholm, Sweden, Manufacturer, 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 the present apparatus is to automatically connect metallic circuits of
telephone-subscribers with a similar metallic circuit leading to a central exchange
station. The apparatus is primarily intended to be installed in places having a
small number of telephone-subscribers connected by a main circuit with a central
exchange of some size; it is evident, however, that it can be used in any other
telephone-system, even a single wire or earth system, if it is desired to save wire.
Its greatest significance, however, lies in the fact that in very small systems with
but slight chances of development it completely fills the place of a manually operated
switch-board, thus doing away with the operating cost which is usually quite
burdensome in plants of the kind.
In order to fill its said main purpose the apparatus must be so arranged that a
complete metallic circuit is obtained; consequently it works with no earth connection
whatever. In its construction attention has, moreover, been paid to a strict
adherence to the principle of maintaining an electric equilibrium of the two
branches of the line, which principle is more especially of importance in long telephone
lines, as well as to avoiding a reduction in efficiency by the presence of a shunt
between the branches or a resistance coupled into them.
There is no theoretical obstacle to constructing the apparatus for any number of
subscribers' circuits; as only one main-line can enter into it, however, it is a good
plan to limit the number of subscribers to a few only. The apparatus described in
This number has been chosen
the following is constructed for 6 subscribers' circuits.
for the reason that in systems with a greater number of subscribers a single main-
circuit, no doubt, must be regarded as insufficient. There is, however, no absolute
hindrance to the apparatus being used also for systems having several main-lines; it
is only to be taken into account that one switch apparatus must be provided for each
main-line.
The location of the apparatus in the system may, of course, be varied in many
ways. The best plan, however, is undoubtedly to install it with the subscriber who is
most centrally located, the main line being accordingly drawn to this point as well
It should be mentioned that the length of
as the wires of all the other subscribers.
a subscriber's circuit has no effect on the working of the apparatus which is perfectly
sure even though the resistance of the subscriber's circuit amount to 10,000 ohms.
After all the apparatus and wires of the system have been connected the latter
operates as follows. Any one of the subscribers connected can immediately obtain
communication with the central exchange station by signalling by means of the
inductor belonging to his apparatus. The limitation must here be made, however,
that if one subscriber is already in connection through the switch with the central
exchange-said connection may have been brought about by the subscriber himself
or by the said exchange-none of the other subscribers belonging to the switch-

page_text: apparatus in question can obtain connection with the main line. Should a sub-
scriber make an attempt to obtain such connection he immediately discovers that the
main line is engaged, by the fact that his own call bell does not sound.
The central exchange is enabled, by sending off current impulses of a certain
direction, to obtain connection with any one of the subscribers' circuits attached to
the switch-apparatus and thus to place outsiders in connection with the subscribers
belonging to the said switch.
A subscriber of the switch is likewise able to obtain connection with another
subscriber of the same switch, but only by the assistance of the central exchange.
The main line is thus engaged also in this case. This may be regarded as a disad-
vantage, but on the other hand it involves important advantages. For, only in this
manner the central exchange can exercise complete control over the switch and the
subscribers' circuits attached to it. The necessity of such control is readily
perceived, when it is borne in mind that the central exchange should not only
be able to bring about connection with any one of the subscribers of the switch
but also, when a conversation is ended, even if this be held between two sub-
scribers of the small system, be able to immediately effect the return of the
switch to its normal position. Besides, they should be able from there if need be,
to plunge into a conversation while going on, for transmitting messages of im-
portance, etc. Moreover, the central exchange should always have such control of the
switch that it will be impossible for a subscriber to hold either the main line or the
circuit of another subscriber engaged for an arbitrary period of time. In order to
perform said duties the central exchange must always by means of the main line have
control over the switch and the conversations carried on through it.
The apparatus is composed of three principal parts which may here be termed the
réversing-apparatus, the connecting-device, and the relay-apparatus. Between these
three parts there is no mechanical, but only an electric, connection. Figures 1-4 in
the accompanying drawings show the reversing-apparatus, Figures 5 and 6 the
connecting-device, while Figure 7 shows diagrammatically the apparatus as a whole
including the relay apparatus.
The function of the reversing-apparatus is to conduct a constant current through
its winding into the one or the other of two different paths or branches according to the
direction of the passing current. Each of these two current branches passes
through a relay. One of the said relays effects the connection of the main-line with
any one of the subscribers' circuits by means of electromagnets actuated by a local
battery. The other relay in similar manner effects the return of the apparatus to its
normal position.
In order to obtain a rotary movement the direction of which is determined by the
direction of the current in a circuit, there have heretofore been employed sensitive
and permanent magnetic needles influenced by the current in the said circuit which
is fixed. As experience, however, has shewn that such a magnetic needle is easily
liable to lose its magnetism under the influence of the atmospheric currents which
frequently appear, more especially in long circuits, the reversing-apparatus here
referred to has been constructed on quite a different principle.
Figure 1 shows a front view of the reversing-apparatus, with one contact-arrange-
ment removed.
Figure 2 shows the said contact arrangement.
Figure 3 shows the reversing-apparatus viewed from one side; and
Figure 4 a top view of the same apparatus.
In the different figures the same letters everywhere designate the same parts.
Between pole-shoes H fixed to a system of permanent magnets A there are secured
on a shaft B pieces C forming a framing on which a wire D is wound. On a forward
frame-piece E, and a rear piece E, cross-bars G, and G, are respectively fixed by
means of studs or brackets F and F. The shaft B is journalled in the said cross-
bars. An electric current passed through the wire or coil D will, owing to the inter-
action taking place between it and the magnetism, produce a turning-moment which
according to the direction of the current will rotate the wire coil in one direction or

page_text: 2
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the other. On the forward end of the shaft B is rigidly mounted a disc K of insulating
material. In this disc is formed a concentric channel I. In the said channel is
placed a body Qu of mercury which is prevented by a glass disc M from running out
of the channel in which enter three contacts Q, R₁, and R¹, of platinum one of which
Q is, by means of a platinum wire q, in electric connection with the shaft B and the
framing while the contacts R₁, and R₁₂, by means of contact-pieces 2₁ and 2 and
insulated cords 8, and sa, are respectively connected with terminals v₁ and v. The
distance between the contacts Q, R¹, and R₁₂ are such that when the wire-coil occupies
its normal position the body of mercury is in contact only with the contact Q.
When the wire-coil is revolved the mercury will connect the last-mentioned contact Q
with the one or the other of the contacts R¹, and R¹, depending on the direction of
rotation. To keep the wire-coil in its normal position when no current is passing
through, i.e. in such a position that the contacts Q, R₁, R¹, will not be in contact
with one another, the following contrivance is provided. On a bracket S fixed to the
forward frame-piece E, there are mounted on shafts i bell-crank levers P, U, the arms
U of which carry adjustable weights T₁ and T2 respectively. On the shaft B is fixed,
behind the contact-disc K, a metal-piece N with a roller O. In the normal position
of the wire-coil the said roller rests freely between the arms P, because the arms U
then rest on pins Z; on the other hand, if the wire-coil be revolved in one direction
or the other the roller C will press against either of the arms P, the corresponding
arm being thereby lifted. By the weight T₁ or T, there is consequently produced a
turning moment counteracting the motion of the wire-coil and forcing the
latter back into its normal position as soon as the current ceases to flow in the wire.
For reasons to be given below it is of importance that the reversing-apparatus
should operate only for continuous currents; an alternating current should have no
influence on it. For this reason the contact Q is made in the shape of a plate filling
the greater portion of the cross-section of the channel L, this having for result that
the movement of the body of mercury is impeded so that only a current impulse of
comparatively long duration, and thus not one forming an element of an alternating
current, is able to produce a noticeable rotation of the wire-coil. This choking of
the channel I may of course be produced in some other manner and occur in more
than one place.
In the connecting-device there are three principal parts. By means of one of said
parts the central exchange can obtain connection with any one of the subscribers'
circuits entering the switch and at the same time shut out all the other subscribers
from the possibility of disturbing the connection effected. By means of the second
part any subscriber of the switch can place his circuit in connection with the main
line while simultaneously shutting off all the other subscribers of the switch from
the possibility of reaching said main line; the third part serves to return the switch
to its norinal position when a conversation is finished.
Figures 5 and 6 show the parts belonging to the connecting-device. For the sake
of clearness, all connections needed for the electric action of the apparatus, as well as
all electromagnet windings, have been omitted in these figures.
The parts brought into service when a subscriber belonging to the automatic switch
is to be connected from the central exchange are the electromagnet-contrivances A,
and A,, and the connecting-drum X. The electromagnets are made of horse-shoe
shape and each is provided with an armature 142. In a hole drilled in one branch
of each magnet a pin 126 is movable vertically. The connecting-drum X is com-
posed of two metallic portions X, and X, deposited in insulating material and in-
sulated from each other, in which portions there are inserted in drilled holes pins or
pegs N¹N, M₁-M³, K₁₁-K, and L-L'. The pins N₁₁-N¹ and M₁₁-M
are in electric connection with the metallic portion X1, the pins K¹,
-K¹, and L-L
on the other hand being in electric connection with the metallic portion X. On an
insulating piece 135 fixed to a metal plate 100 there are located brackets 137, one
at each end of the drum. In these brackets the drum X is journalled. A ratchet-
wheel 133 is secured to the drum. The pins 126 previously mentioned bear against
adjustable screws 127 placed on arins 123. The arms 123 are secured to a shaft 122
6
7

page_text: journalled in the brackets 120. With one of the arms 123 is connected a feed-
pawl 128, said connection, however, not being rigid but such that the pawl can move
in relation to the arm and engage with the teeth of the ratchet-wheel 133, By
means of a screw 134 the feed-pawl can be adjusted to proper engagement with the
ratchet 133. 139 is a spring-box containing a coil-spring connected with the drum
and the tension of which is increased when the drum is turned from its normal
position. As will be explained in the description below of the electrical action of
the apparatus, the coils of the magnets A, and An will be simultaneously traversed
by currents of equal strength when the central exchange connects a subscriber
belonging to the switch. They will then cooperate in their respective functions.
The task to be performed by them is as follows:-During the passage of the current
the armatures 142 depress the pins 126, thus causing the arms 123 to be
depressed. The result is that the feed-pawl 128 is drawn downward and causes the
ratchet 133 and drum X to rotate. When the current ceases, the arms 123 are
raised by a spiral spring 124 actuated by a screw 125, thus bringing the feed-pawl
in engagement with the next tooth of the ratchet. In order that, in this action, the
drum may not under the influence of the coil-spring in the spring-box 139 return
to its original position, there is provided another pawl 129 similar to the pawl 128
but independent of it, the said pawl serving to retain the drum in the position given
to it by the feed-pawl 128. The effect of this rotation is that the pins or
pegs NN and K-K¹, are brought out of contact with contact-springs 1-V I₁
and 12-VI and V II fixed on the insulating-piece 135 and that of the springs 1—6
and 11-66 fixed on the same insulating-plate, the spring 1 is brought into contact
with the pin M¹, and the spring 11 in contact with the pin L. The object of this
is stated in the description below of the electric action of the apparatus. A succeed-
ing current-impulse sent through the coils of the electromagnets A, and A, will
advance the ratchet and thus the drum another step, etc.
0
The springs 1-6 and 11-66 above the drum serve to connect any one of the six
subscribers with the central exchange, while the springs 1-VI, and 1-VI2 at the
underside of the drum serve to make it impossible for the other subscribers to
influence the apparatus as soon as such connection has been made.
To enable a subscriber of the switch to place himself in connection with the central
exchange, six electromagnets are provided, one for each subscriber. K, designates
the cores of these electromagnets which are constructed as follows. On each core K,
is screwed a pole-piece 105 of soft iron. On this pole-piece bears one end of a perma-
nent magnet 101 bent at an angle and bearing with its other end against a pole-
piece 109 likewise of soft iron. The latter pole-piece has its end shaped as an edge
on which rests an armature A₁. By means of a screw 108, a bell-crank 106 and a
spiral spring 107 the armature As is given a certain tendency to release itself from the
core K, by which it is held fast under the influence of the magnet 101.
The mag-
netism is so strong, however, that a release cannot take place until favoured by an
outer impulse. This impulse is furnished when a subscriber by means of his inductor
sends out an alternating current. In the inactive position of the switch each sub-
scriber's circuit is connected with the winding or coil of the corresponding magnet.
Either of the current-directions in the alternating current will counteract the mag-
netism of the magnet 101 and this to such an extent that the spiral spring 107 will
have power enough to release the armature As from the core Ks. Owing to the
construction of the electromagnet the magnetism after such release is unable to again
attract the armature into contact with the magnet. Under the influence of the spiral
spring 107 the armature As will now perform the operations necessary for connecting
the subscriber with the main line and shutting off the other subscribers from said
line. This is accomplished in the following manner. In the sleeve 143, which
is inserted in an insulating-piece 112, a pin B, is movable vertically. One such
pin is provided for each of the six electromagnets. Springs e₁-e, normally bear
on contacts a-a. By means of adjustable screws 113 insulated from the
springs ee the said springs can be acted on by a bar ST sustained by
arms 116 which are rigidly connected with each other by means of a shaft 114

page_text: journalled in side-pieces 145. When a call is made and one of the armatures A
consequently is released, its upward movement will be transmitted by means of the
pin B, to the bar ST. The latter will then likewise move upward, causing all
the springs e and ea to be removed from the contacts a and a. By this means the
other subscribers are shut out from all possibility of influencing the apparatus.
In the upward motion of the armature A., moreover, springs fi and fa are pressed
by means of two screws 110 against contacts b, and b.. This, however, takes place
only at the electro-magnet influenced by the current and has for result that the
apparatus of the calling subscriber is placed in direct connection with the main
line.
By the construction here given to the subscribers' electromagnet important advan-
tages are gained. As the influence of the permanent inagnetism on the armature
when the latter is in direct contact with the core is very great, while it is greatly
diminished as soon as the armature has become slightly removed from the core, a
This is of
considerable amount of energy can be stored in the spiral spring 107.
importance as producing a very powerful and sure action in the release of the arma-
ture. If the electromagnet be provided with many coils or windings the apparatus
will at the same time be very sensitive. As mentioned above, the apparatus in
question, the electromagnet coils of which have a resistance of 3000 ohms, is per-
fectly reliable in its action for subscribers' circuits reaching 10,000 ohms resistance.
The parts forming the replacing-motion are: the electromagnets A, and An, the
arms 116 with the bar ST and the arm 115. As will be hereinafter explained the
operator at the central exchange in replacing the apparatus sends out a current of
opposite direction to that used in making the connection. By the aid of a relay a
local current is thereby passed through the coils of the electro-magnets A, and Aa
which co-operate in the sune manner as the magnets A, and An in making the
connection. The construction of the electro-magnets As and A, is the same as that
With the armatures 118 of the former are con-
of the electromagnets A1 and A2.
nected draw-rods 117 fixed to each of the bar ST which consequently is drawn down
when a current traverses the coils of the maguets A and A. The tension of the
springs and e, will then bring said springs to bear against their respective con-
The bar ST simultaneously depresses by means of the pin B, the
armature As of the magnet belonging to the calling subscribers. Owing to their
tension the springs fif, then resume their normal positions.
tacts g
con-
On the other hand, if the replacement is to be done subsequent to a
nection made by the central exchange, in which case nothing pertaining to the
subscribers' magnets has been disturbed, but only what belongs to the connecting-
drum X, the bar has no other function to perform than to rotate by means of the
arms 116 the shaft 114 on which the arm 115 is fixed. The latter arm presses on the
lower end of the pawl 129 which is made in the shape of a bell-crank, the result
being that the pawl is brought out of engagement with the ratchet 133. The feed-
pawl 128 is likewise compelled, by means of the pin 132 secured to the pawl 129, to
disengage itself from said ratchet, and the druin X thus released resumes its normal
position under the influence of the coil-spring in the spring box 139.
When two subscribers connected by the aid of the automatic switch have had a
conversation with each other, one of the subscribers' electromagnets as well as the
connecting-drum X have been actuated. The replacement is then effected as
described, two operations, however, being involved, viz., the replacing of the magnet
and the replacing of the drum.
Figure 7 shows diagrammatically the entire apparatus. To make its mode of
operation clear, the latter is described for the three cases which can be assumed in
practice, viz.,
1: A subscriber having a circuit attached to the automatic switch wishes to
obtain connection with the central exchange or a circuit entering the
latter;
2: The central exchange or a subscriber having a circuit entering the latter
wishes for connection with a circuit attached to the automatic switch;

page_text: 3: A subscriber having a circuit attached to the automatic switch wishes to obtain
connection with another circuit attached to the same switch.
1: A subscriber having a circuit attached to the automatic switch wishes to
obtain connection with the central exchange or a circuit entering the latter.
Let this subscriber be the one, for instance, who has apparatus No. 3 (see Figure 7).
This subscriber accordingly makes a call by means of the inductor of his telephone.
The circuit of the alternating current generated will be as follows: Apparatus No. 3,
the line-branch L₁, the wire 20, spring 3, which will not be traversed because in
the normal position of the switch it is not in contact with the connecting-drum X,
the wire 21, contact a₁, and spring ₁, the wire 45, coil 46 of the magnet M3, the
wire 23, spring III,, the pin N, the metal part X, in the connecting-drum X, wire 24,
branch-point 75, wire 39, one branch 25 of the coil D of the reversing-apparatus, the
wire 27, one of the branches HL2 of the main line indicator-drop or other correspond-
ing device of the central exchange, the other line-branch HL of the main-line, the
wire 28, the other branch 26 of the coil D of the reversing-apparatus, the wire 29,
the metal part X2 in the connecting-drum X, the pin K¹, spring III, wire 30,
spring ea and contact a2, wire 31, spring 33, which is not traversed because in the
normal position of the switch it is not in contact with the connecting-drum X, the
wire 32, line-terminal of the switch Y2, the line-branch L2, and the subscriber's
apparatus No. 3. As the springs I, II, III, IV, V, VI, are in contact with the
pins N1, N2, N1, N1, N1, N1, respectively and thus also with the metal part X₁, and
the springs I, IÏz, III, IV, V, VI, are in contact with the pins K₁₁, K¹, K, K¹,
K, K, respectively and thus also with the metal part Xa, there is between X, and X
besides the circuit just pointed out through 24, 75, 39, 25, 27, HI, the exchange-
apparatus Hл, 28, 26, 29, five additional branch-circuits by which the call-current
from the apparatus No. 3 can pass, viz., the circuits of the subscribers No. 1, 2, 4, 5,
6 which circuits issue from the springs I, II, IV, V, VI, reach the springs I, II,
IV2, V2, VI2, and in every way correspond to the circuit 23, 46, 45, c, d, 21, 3, 20,
Y₁, I, No. 3 I.z, Y2, 32, 33, 31, 2, 2, 30. As, however, in each of the said circuits
among other resistances enters that of 3000 ohms of the coil of a magnet corre-
sponding to the magnet M, which resistance is greatly self-inductive, the branch-
current arriving at each subscriber's apparatus will be so much reduced in strength
that it will not have power enough to actuate the bell of the apparatus.
6
There is, however, another circuit, coupled in parallel to the main line, for the
current from the subscriber's apparatus. This branch-circuit passes from the brauch-
point 75 through the wire 38, the resistance 47, wire 37, contact c, wire 36,
spring VII, pin K₁₁ to the metal part X, in the connecting-drum X. As the resist-
ance of 47 is made equal to but 200 obins, the greater portion of the call-current
from the subscriber's apparatus will take this path, more especially if the main-line
is of any considerable length, and in this manner a sufficiently powerful action of the
current in the coil of the electro-magnet M, is produced. Without this branch-
circuit and if the resistance of the main-line were considerable, it might occur that
the call-current suffered so great a loss of strength that in passing through the coil
of the magnet M, it would be unable to perform the work required of it at this point.
With the construction here used such failure cannot occur.
The branch-circuit through the resistance 47 might, however, produce such weak-
ness in the current traversing the central exchange that the indicator of the latter
cannot be brought into action. This is of no consequence, however, as will be now
shown.
The call-current sent out from the subscriber's apparatus No. 3 passes undivided
through the winding of magnet Ma. This being an alternating current, however,
which, as is well known may be defined to consist of a series of impulses, every
alternate one positive and every alternate one negative, either of the two first im-
pulses must, owing to the construction of the magnet M₁, release the armature A,
from the core K₁. The effect produced is as follows; The pin B, will raise the
bar ST, thus breaking connection between the contacts and e, and between the
contacts as and ea, not only for the subscriber's magnet in question but simultaneously

page_text: for all six of the magnets. The contacts b, and f, and b, and f, are also respectively
brought to touch each other, but only as regards the magnet in question. Finally,
connection is broken at c. The circuits previously pointed out for the call-current
from No. 3, viz. partly through the resistance 47, partly through the main line, and
partly through the five remaining subscribers' circuits, thus exist only during the
first or, at the most, during the first and second of the current impulses. During
the succeeding ones the circuit will be the following: Apparatus No. 3, the line-
branch I, the line-terminal of the switch Y₁, the wire 20, spring 3, wire 21, con-
tact b₁, spring f, wire 34, metal part X, in the drum X, the wire 24, branch-point 75,
wire 39, one branch 25 of the coil D of the reversing-apparatus, the wire 27, line-
terminal HY., one branch HL, of the main line, the exchange, the other branch HL,
wire 28, the other branch 26 of the coil D of the reversing-apparatus, the wire 29,
metal part X2 in the connecting-drum X, the wire 35, spring f₁, contact b, wire 31,
spring 33, wire 32, line-terminal of the switch Ya, the line-branch I, and the sub-
scriber's apparatus No. 3. The springs 3 and 33 which are not in contact with the
metal parts of the connecting-drum X do not enter directly in the circuit. There
are no branch-circuits to the circuit last mentioned, partly because all the other
subscribers' circuits have become broken by the breaking of the contacts between
the respective parts e, and a, and ea and aa, partly because of the breaking at c of
the branch-circuit through the resistance 47. The result is that, as soon as a sub-
scriber has made a call, none of the remaining subscribers can make one. It is
evident that, even if the two first current impulses should have proved too feeble
to actuate the indicator-flap of the exchange, the succeeding ones will surely do so,
as no weakening branches or unnecessary resistances are present. Only the line
resistance of the subscriber's line and the main line and the resistance of the coil D
of the reversing apparatus enter into the circuit mentioned. As already mentioned,
the reversing-apparatus is so constructed that it is not influenced by alternating
currents. On having called the central exchange in the manner stated the sub-
scriber No. 3 can freely converse with the latter and obtain connection with the
subscriber desired. From the diagram it is evident that, on the one hand, no
unnecessary resistances enter this connection with the exception of that of the coil of
the reversing apparatus and on the other hand that there are no shunts nor earth-
circuits. As regards the resistance of the reversing-apparatus, this is so small, (some
60 or 70 ohms), and besides, practically speaking, so free from self-induction that it
cannot interfere with the transmission of speech in any perceptible degree. In order
to make the telephonic circuit completely symmetrical, the said resistance, more-
over, has been divided into two equal parts between the two branches of the circuit.
When the conversation carried on is concluded, a "ringing-off" signal is given from
the subscriber's apparatus to the central exchange. The operator here has then to
break the connection and return the automatic switch to its normal position. The
description of the replacing-operation is deferred, however, and will be given in
connection with the second case, viz.
2 The central exchange or a subscriber having a circuit entering the latter wishes
for connection with a circuit attached to the automatic switch.
As the connection between a calling subscriber's circuit and the main line to the
automatic switch is brought about in the usual manner by the operator at the central
exchange, I will only describe how the latter obtains connection with some particular
subscriber of the said switch. Assume that the central exchange desires to converse
with, for instance, subscriber No. 3 of the automatic switch. The operator then sends
through the main line a continuous current of a certain direction which may be
assumed to be that indicated by the arrow in the diagram, .e. positive in the
line-branch HL, in the direction of the switch. The circuit of this current will be as
follows the line-branch HL₁, line-terminal of the switch HY,, the wire 28, one
branch 26 of the coil D) of the reversing-apparatus, the wire 29, metal part X, in the
connecting-drum X, the pin K¹, spring VII, wire 36, contact c, wire 37, resistance 47,
wire 38, branch point 75, wire 39, second branch 25 of the coil D of the reversing-

page_text: 0
apparatus, the wire 27, line-terminal of the switch HY, line-branch HL, of the main
line, and the central exchange. As all the springs I-VI are connected respectively
by means of the pins K₁₁-K, with the metallic part X,, and all the springs I-VÏ₁
are connected respectively by means of the pins N₁₁-N, with the metallic part X₁,
there will still be between the spring VII and the branch-point 75 six current paths
running parallel through the coils of magnet M, and the remaining subscribers'
magnets and subscribers' wires. As, however, the resistance of each of these current
paths is very great in comparison with the resistance of the branch-circuit
through the resistance 47, the current in each of them will be so weakened that it
cannot actuate the bell of the subscriber's apparatus. As this is designed to be
operated by alternating currents, the worst that can happen is that its armature makes
one single stroke.
2*
The effect of the current in passing through the coil D of the reversing-apparatus
is to cause the said coil to rotate in one direction or the other, the body of mercury
being thereby made to connect electrically the middle contact with the one or the
other of the side-contacts. Assume that in the diagram Q designates the middle
contact and R₁, and R¹, the two side-contacts. The result will then be according to
the diagram, that the contact Q is brought in electric connection with the
contact R¹, or R¹, depending on the direction of the current passed through the coil
of the reversing-apparatus. Assume that a positive current in the branch HL, in
direction of the switch effects connection between the contacts Q and R₁₂, and that a
positive current in the branch HL in direction of the switch effects connection between
the contacts Q and R₁₁. If it be further assumed that the connecting of a subscriber's
circuit is to be brought about by sending out from the central exchange a positive
current through the branch HL₁, the contact Q will in this case be brought into
connection with the contact R¹. A circuit parallel to that through the resistance 47
will then be opened for the current sent out, viz., from the contact Q which is
connected with the branch 26 of the coil of the reversing-apparatus, through the
contact R¹, the wire 42, magnet-coil of the relay R, wire 77, branch-point 76, wire 41
to the branch-point 75. The relay R, having a winding of 200 ohms resistance and
possessing a high degree of sensitiveness will, when a current traverses its magnet-
coil, close the contact D. and the battery BT located at the automatic switch which will
then work in a circuit consisting of: the battery BT, wire 79, wire 87, contact D., wire 88,
the parallel branches: viz. the wire 89, coil of magnet A₁, wire 90 and wire 91, the
coil of magnet A₁₁, wire 92 and the wire 86 which conducts the current back to the
other pole of the battery. As already mentioned, A, and A,, (see Figure 6) are two
electromagnet-devices co-operating with each other." When their coils are traversed
by a current, the connecting-drum X will be revolved by means of their armatures.
The rotation is assumed to take place in the direction indicated by the arrow
on the drum. The first impulse emitted from the central exchange in the direction
assumed will rotate the drum one step. The result produced is that the contact of the
springs IVI, with the respective pins N₁₁-N1, and that of the springs I-VI, with
the respective pins K-K¹ are broken. As a consequence all the subscribers' circuits
but one will remain cut out and will be unable to actuate the switch.
One single
circuit, viz. No. 1, is connected with the main line by the spring 1 being in contact
with the pin M₁, and the spring 11 being in contact with the pin L. In the
rotation of the drum the contact is also broken between the spring VII and pin K¹7.
As the shunt-circuit through the resistance 47 passes through this contact, the said
circuit will be broken and therefore cannot enter into the circuit of the succeeding
impulses emitted from the central exchange. However, as the connection between
Q and R¹, will remain as long as the first impulse lasts and also owing to the above-
mentioned inertia of the body of mercury, the said circuit will be closed during the
interval between the two impulses mentioned, if the said interval be made short.
The circuit is then closed by means of the relay R.. Should the connection cease
between the contacts Q and R¹, for instance owing to carelessness in sending out the
current impulses, there is nevertheless the possibility of producing a current through
6

page_text: the coil of the reversing-apparatus, since the subscriber's apparatus No. 1 enters into
the circuit. The second impulse emitted from the central exchange, which impulse
must pass in the same direction as the first, will revolve the drum and thereby break
the contacts 1-M¹, and 11-L¹, while the contacts 2-M¹, and 22-L¹, are produced
instead. The third impulse finally breaks these two contacts and, instead, brings
about the contacts 3-M, and 33-1. The object in view, viz., effecting the
connection of apparatus No. 3 with the main line, has now been attained. Had the
intention been to make connection with apparatus No. 6 the central exchange would
have had to emit six impulses of the same direction. During the whole time the
springs I-VI, and I-VI, remain out of contact with the metallic parts of the
connecting-drum, and consequently all the subscribers' circuits but that temporarily
connected will remain cut out.
As soon as the operator at the exchange has sent out the three impulses mentioned
he will be able to call and converse with subscriber No. 3 by means of a circuit
composed of the parts: HL, HY₁, 28, 26, 29, X, L¹, 33, 32, Y₁, L2, No. 3, I₁, Y₁,
20, 3, M¹, X₁, 24, 75, 39, 25, 27, HY,, HL,. As the contact is broken both between
the parts VII and K, and between the parts Q and R₁₂ when the reversing-
apparatus has resumed its normal position, there will be no branches to this circuit.
Neither are there any extra resistances in it with the exception of the coil of the
reversing apparatus, but as the latter, as mentioned, is small and practically free
from induction, it will not interfere with the transmission of speech. The rest of the
subscribers, whose circuits are broken in two places, viz., at the respective springs I₁,
II₁, IV₁, V₁, VI₁, and I, II, IV, V, VI, are deprived of every means of disturbing
the conversation. When the conversation is ended and the conversing subscribers
consequently have rung off, the operator at the central exchange must remove the
connection. This must be preceded, however, by the return of the switch to its
normal position. To effect this the operator sends out a current of opposite
direction to that used for making the connection. This current traverses, of course,
When passing through
the circuit which has just been used, for the conversation.
the coil D of the reversing-apparatus it brings about connection between the
contacts Q and R₁₁, thus creating a branch-circuit through the contacts Q and R₁₁.
the wire 40, the coil of the relay R₁, the wire 78, branch point 76, wire 41 and
branch-point 75. The relay R, has exactly the same properties as the relay Ra
previously mentioned and, when a current traverses its coil, it closes a circuit to
the battery BT, which circuit consists of: battery BT, the wire 79, wire 80,
contact D,, wire 81, the parallel branches: wire 82, the coil of magnet A, wire 85
and wire 83, the coil of magnet A22 the wire 84 and the wire 86 and the other pole
of the battery. The magnet-devices A, and A₂ co-operate as already mentioned
and bring the switch back into its normal position by means of their armatures,
no matter whether it has been disturbed from the said position by switching from
the central exchange or by a call made by a subscriber, which case has been treated
with under No. 1.
1
3. A subscriber having a circuit attached to the automatic switch wishes to obtain
connection with another circuit attached to the same switch.
This case is a combination of the two cases previously mentioned. The calling
subscriber first calls the central exchange, the course of events being then the same
as mentioned under 1. The central exchange subsequently in the manner described
under 21, places itself in connection with the desired subscriber of the switch. This
being done the two subscribers will be in connection with each other. Connecting
the desired subscriber by the central exchange differs as regards the circuit from the
course outlined under 21 in that the first impulse does not pass through the
resistance 47 which is cut out at c by the subscriber's calling-operation, but through
this subscriber's apparatus. The circuit in a conversation between two subscribers―
-for instance No. 3 and No. 5-by the aid of the automatic switch, when No. 3 is
the calling and No. 5 the called subscriber, will be No. 3, L., Y, 20, 3, 21, b₁, fi,
34, X₁, M³, 5, 50, Y, L, No. 5, L, Y, 51, 55, I, X2, 35, ƒ₂, b₂, 31, 33, 32, 12, 2,
R

page_text: and No. 3. Between X, and X, the main-line is coupled in the circuit as a branch-
circuit and consequently it is able, as mentioned in the beginning, to exercise
complete control over the connection. In replacing the switch the procedure consists
of a combination of those in cases 1 and 2.
As stated in the beginning of this Specification, the prime purpose of this switch-
apparatus is to replace the hand-operated switch-board in small country systems
connected with a larger central exchange station. As circuits of great length and
consequently of great resistance may here frequently be involved, it is of importance*
that the apparatus should combine great sensitiveness with sure working. As
already pointed out, the subscribers' magnets possess a high degree of sensitiveness
while at the same time being capable of performing the work required to them with
great power. By the construction given to the reversing-apparatus this is also made
very sensitive which, of course, is of great importance since by this means the
required quantity of current in the lines for switching will be small even for a main
line of quite a great length. The work to be performed in the switch, morever, is
executed as is evident from the above description, by electromagnets supplied with
current from a local battery, which electro-magnets are set in action by extremely
sensitive relays. By this means great power and sureness of action are obtained.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:-
1. In automatic telephone switch apparatus composed of a reversing-apparatus
for effecting the connection of the main line leading to a central exchange station
with any one of the subscribers' circuits attached to the switch apparatus, which
reversing-apparatus is provided with a wire coil connected with the said maiu-
line, and of electromagnets by the aid of which the subscribers' circuits are
connected with the main line and the coils of which are respectively coupled in a
corresponding subscriber's circuit, the arrangement of reversing-apparatus consisting
of a fixed permanent magnet (or group of permanent magnets) between the pole-
shoes of which is located a wire coil carried by a rotatable frame and coupled in
the main line from the central exchange station, each subscriber's magnet being
connected with a permanent magnet one pole of which, or a pole-piece connected
to it, is in contact with a piece of iron serving as an armature and acted on by a
constant force (developed, for instance, by a spring), all for the purpose partly of
preventing injurious influence of atmospheric currents in the lines, partly of producing
such great sensitiveness to the current impulses emitted, whether from the central
exchange or from the subscriber's apparatus, combined with sureness of action, that
the apparatus will be applicable even to metallic circuits of considerable length,
substantially as set forth.
2. In automatic telephone switch apparatus of the kind described in Claim 1; the
arrangement of coil located on the rotatable frame of the reversing-apparatus and
divided into two branches having the same electrical properties and coupled each in
one of the branches of the main line, for the purpose of evenly dividing the electrical
properties between the two line-branches, substantially. as set forth.
3. In automatic telephone switch apparatus of the kind described in Claim 1; 4
the arrangement of movable body of inercury (Qv) enclosed in a channel (L),
made in a disc of insulating material and rigidly connected to the shaft of the
frame supporting the aforesaid coil, and so adjusted that, according to the position
of the coil depending on the direction of a current emitted from the central
exchange, it will connect an intervening contact-piece (Q) with one or the other
of two side-contacts (R₁, and R₁₂), for the purpose of enabling connections to be
made and the switch to be replaced with a minimum of labour, substantially as
set forth.
4. In automatic telephone switch apparatus of the kind described in Claims 1
and 3, the arrangement of channel (L) choked or made narrower in one or more 5
places, for instance by the intervening contact (Q) being made in the shape of a

page_text: plate extending almost across the channel, for the purpose of preventing the
reversing-apparatus being influenced by an alternating current, substantially as set
forth.
5. The improved automatic telephone switch apparatus herein before described and
illustrated in the accompanying drawings.
ديو
1000
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.