Improvements in Telephone Exchange Systems.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in Telephone Exchange Systems.
We, DANIEL SINCLAIR, Engineer-in-Chief to the National Telephone Company,
Limited, Oxford Court, Cannon Street, in the City of London, and WILLAM
AITKEN, Engineer with said Company, at above address, do hereby declare the
nature of this invention to be as follows:-
Our invention relates to telephone exchange systems and has for its object the
improvement of the present systems using either series of jacks and ordinary drop
indicators, or branching jacks and self restoring indicators, and also what is known
as the common battery system, by introducing in conjunction therewith a new and
simplified arrangement of clearing out signals operated automatically by the
apparatus at the subscribers' station and automatic apparatus at the exchange
jointly controlled at the exchange and the subscribers' station for including the
calling generator in circuit with the signal bell at the called subscriber's station
and removing them therefrom by the action of lifting the receiver from the
switch-hook at the subscriber's station.
The working of such a system will be as follows: —
After
The subscriber will call the attention of the operator at the exchange by turn-
ing the handle in connection with the generator of his instrument, and the
operator will answer and then test the line wanted in the usual way.
inserting the plug in the jack of the line wanted, the operator will depress a
plunger which will remain down and bring into circuit a generator which will
continue to ring, preferably intermittently the wanted subscriber until he replies
when the taking off of the receiver from the switch-hook of the called subscriber's
instrument releases the generator and causes the plunger to rise thereby giving
a signal to this effect to the operator. Should the called subscriber not reply
from any cause, the calling subscriber can still get the attention of the operator
for he has the control of the clearing signal, as either subscriber placing the receiver
on the switch-hook will give the signal to clear or a separate signal can, if neces-
sary be fixed for each subscriber.
Such a system has also this advantage that it acts as a check upon the test
circuit for when two subscribers are talking together there is no earth at either
end of the circuit, therefore the plunger of the relay in the cord of the third
subscriber (who has called for one or other of the lines engaged and been wrongly
connected owing to the test failing) will not remain down and the operator will
know there is something wrong will not complete the connection and thus avoid
triple conversation.
ce
JT.... 1908
DANIEL SINCLAIR,
WILLIAM AITKEN.

page_text: Improvements in Telephone Exchange Systems.
We, DANIEL SINCLAIR, Engineer-in-Chief, and WILLIAM AITKEN, Engineer to
National Telephone Company Limited, of Oxford Court, Cannon Street, in the
City of London, 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 telephone exchange systems and has for its object
the improvement of the present systems using either series jacks and ordinary
drop indicators or branching jacks and self restoring indicators by introducing
in conjunction therewith a new and simplified arrangement of clearing out
signals operated automatically by the apparatus at the subscriber's station and
automatic apparatus at the exchange jointly controlled at the exchange and the
subscribers station for including the calling generator in circuit with the signal
bell at the called subscriber's station and removing them therefrom by the action
of lifting the receiver from the switch-hook at the subscriber's station.
Our invention is illustrated by the following drawings:
Fig. 1. A diagram of connections showing our invention applied to a multiple
switchboard having branching jacks and self restoring indicators.
Fig. 2. Shows one form of ringing relay or electro magnetic control with
springs attached.
Fig. 3. Shows our invention with two clearing signals.
Fig. 4. Shows an electromagnet controlling an existing form of ringing key,
and also shows a translator or repeater used instead of a bridging coil to connect
the battery to the lines.
Fig. 5. Shows an electromagnet controlling another form of ringing key.
Fig. 6. Shows a double wound armature used in the generator so as to do away
with the bridging coil.
The working of such a system will be as follows:-
The subscriber will call the attention of the operator at the exchange by turn-
ing the handle in connection with the generator of his instrument, and the
operator will answer by inserting the answering plug of a connecting set in the
answering jack of the line calling, and then test the line wanted in the usual
way. After inserting the calling plug of the same connecting set in the jack of
the line wanted, the operator will depress a plunger which will remain down
(or pull over a ringing key lever which will remain over) and bring into circuit
a generator which will continue to ring, preferably intermittently, the wanted
subscriber, until he replies, when the taking off of the receiver from the switch-
hook of the called subscriber's instrument releases the electromagnet and causes
the plunger to rise (or the lever to return to the vertical) thereby giving a signal
to this effect to the operator. Should the called subscriber not reply from any
cause, the calling subscriber can still get the attention of the operator for he
has the control of the clearing signal. Either subscriber placing the receiver on
the switch-hook will give the signal to clear, or a separate signal can, if neces-
sary, be fitted for each subscriber.
Such a system has also this advantage that it acts as a check upon the test
circuit, for when two subscribers are talking together there is no ground or earth
at either end of the circuit, therefore, the plunger of the relay in the cord of the
third subscriber (who has called for one or other of the lines engaged and been
wrongly connected owing to the test failing) will not remain down, and the
operator thereby knowing there is something wrong will listen on the circuit,

page_text: and if a conversation is heard will withdraw the plug and thus avoid a triple
connection.
In the drawings which illustrate our invention C and D Fig. 1 represent two
subscribers lines according to the well known system using branching jacks and
self restoring indicators, with however the centre point of the bell coils d and d
connected through springs e and el direct to earth E at the subscribers instru-
ment. These switches or springs being operated by the switch-hooks s and s
the earth being cut off when the receivers r and are in use, as the switches
are then raised, t and are the ordinary form of ringing generator; and are
receivers; and q and the secondaries of the induction coils, the primary and
microphone circuits not being shown; and el represent the line indicators;
and a and a and b and the spring jacks. E always represents the earth. Sub-
station C is shewn with the receiver off the switch-hook, and therefore with the
ground connection E cut off; sub-station, D is shown with the receiver on the
switch-hook with centre point of bell to ground E.
Across the answering cord in connection with plug u Fig. 1 is bridged a listen-
ing key o having on its inner contacts a differential coil f of suitable resistance
and high self induction, the centre point being connected to a suitable battery
indicator (or relay with lamp in a local circuit) and the other side of this to
battery and earth E. The outer contacts of the listening key are joined
to a ringing back keyn and telephone in the well known manner.
The two conductors from the calling plug are connected to springs h and i
respectively of the ringing key, the inner contacts of which pass to listening key
springs, and tip and sleeve respectively of answering plug 76. The outer contacts
of springs h and i are connected through the two windings of the coil g of the
ringing electro-magnet to generator and interrupter or circuit breaker / re-
spectively. The latter breaks the ringing current into 2 seconds ring and 4 seconds
silence or other suitable period. Between the lines to and a differentially wound
bridging coil m of suitable resistance and self induction is connected, with its
centre point to battery and earth E.
Supposing a connection being made between lines C and D the answering plug
will be in jack a, and calling plug in jack 61. To ring the wanted subscriber 1)
the operator will pull over lever of the combined ringing key and electro-magnetia
control which is in the calling cord circuit, thereby mechanically closing the
magnetic circuit at z of the electro-magnet (this is better shown at z Fig. 5,)
and thereby pressing the springs h and against the outer contacts.
There is now a circuit from earthed battery through both windings of bridging
coil m through the two windings of the coil g through springs and over both
conductors of the cord to tip and sleeve of plug v, through bush and short springs
of jack over A and B wires to subscriber's instrument where it passes through
the two coils of bell in parallel to centre point and through spring e¹ to earth.
The armature therefore remains attracted, and as the generator and inter-
rupter are joined together in series, but jointly in parallel with bridging coil m, the
called subscriber 1 will continue to be rung intermittently until he removes
the receiver from the switch-hook s¹. The path of the ringing current is round
the metallic circuit from one pole of generator through one winding of coil g
to outer contact of spring h, through spring to tip of plug v, to short spring
of jack b', over A wire to contact and switch-hook through coils of bell d',
through spindle of generator and back by B wire to bush of jack ¹, sleeve of
plug v, spring i and outer contact, through the other winding of coil g, through
interrupter to generator k.
The electro-magnet coil g is so wound that the ringing current from generator k
has no magnetic effect on the core.
When the receiver is lifted, the earth is cut off at switch e¹, and the arma-
ture z rises, and lever y returns to the vertical, which indicates to the operator
that the subscriber has answered. After conversation either subscriber placing
the receiver r or r¹ on the switch-hook s or s gives the signal to clear, the circuit

page_text: then being from earthed battery a through relay or indicator j to centre point of
coil f, through listening key o plug u and jack a over the two wires A and B of
one or both lines through the two bell coils of d and in parallel to centre
points and through switches e and el to earth E. The indicator or lamp there-
fore gives a distinctive signal to clear, this indicator being restored to its nermal
condition by the withdrawing of the plugs, one side of the grounded battery a
thereby being insulated.
It is necessary to join the battery a to the lines in such a way that the current
does not prevent the armatures of the polarised ringers d and d¹ responding to
the ringing current from generator k. The direction of the current depending
on the polarity of the ringer.
Fig. 2 shows one form of construction of electro-magnetic ringing control-
ling apparatus, the double wound coil g being inside the iron tube or sheath g
The armature is hinged to the tube and has an extension to the plunger y'.
When the plunger is depressed the armature is carried with it, and the
magnetic circuit of the tube closed, springs and (is behind ¹) at the
same time make contact with the outer springs, and the battery current has a
path to ground at the sub-station so that the armature z¹ remains attracted after
the finger has been removed from the plunger y', until the continuity of the
battery circuit has been broken by the lifting of the receiver from the switch-
hook at the sub-station.
Fig. 3 shows diagrammatically the cord circuit with two clearing signals. A
translator, divides the circuit into two sections, the centre points being
connected through clearing indicators and 2 as before described. The ring-
ing and controlling apparatus is connected as before in the calling cord circuit, g
being the double wound coil, and ¹ and the moving springs connected with
the tip and sleeve respectively of the plug ; m' is the bridging coil with centre
point to battery and earth E; is the ringing generator and 7 the interrupter.
Figure 4 shows our invention with an electro-magnet controlling a well known
form of ringing key. Coil g¹ in this case has its magnetic circuit normally closed,
spring holding armature against the core. The inside of armature z is suit-
ably cut to receive and hold the barbed head 2,2 being an extension attached
to plunger y. When the plunger y is depressed springs and make contact
with the outer contacts, at the same time the barbed head y has displaced the
armature sufficiently to allow the barbed head to enter the cavity in the inside
of armature when the spring gagain presses the armature against the core.
There is now a circuit from earth E through battery a to centre point of the
secondary winding of a ringing transformer m', through both windings of m',
both windings of coil g', through cuter contacts and springs h¹ and to tip and
sleeve of plug, over both lines (to centre point of bell) and earth E at sub-
station D. The current through the coil g holds the armature so that the
barbed heady cannot be withdrawn, and plunger therefore remains down until
the circuit is broken by the lifting of the switch-hook severing the ground con-
nection at sub-station D. The generator and interrupter 7 are shown in the
primary circuit of a transformer.
Fig. 5 shows the construction of the electro-magnetic ringing and controlling
apparatus shown diagrammatically in Figure 1. A combined listening and ring-
ing key of a well known form has attached the double wound coil g both ends
of the core being extended and returned as shown. The lever y has a soft iron
extension or armature which when the lever y is pushed to the ringing position
causes the armature z to join together the two poles, thereby completing the
magnetic circuit, and armature is firmly held when the circuit passes through
the coil until the continuity of the circuit is broken by the lifting of the switch-
hook at sub-station D).
Fig. 6 shows a generator k with a double wound armature with its centre
point connected to earthed battery a this makes unnecessary the bridging coil m.

page_text: This invention admits of other modifications in the arrangements which would
readily suggest themselves to those skilled in the art. We therefore do not
limit ourselves to the precise arrangements shewn or described herein.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed we declare that what
we claim is ;-
1. An electro-magnetic ringing and controlling device with double wound coil,
one winding of which is connected to the circuit of each wire. The windings being
so arranged that ringing currents from a magnetic generator pass in opposite
directions and neutralizing each other have no magnetic effect on the core, a
battery current however passing through the two windings in similar directions
magnetise the core and hold the armature, when it is placed against its ends
mechanically substantially as described.
2. The combination of a double wound electro-magnetic ringing and control-
ling device with a ringing generator and interrupter so arranged in relation to
each other and to the bell at the sub-station that the ringing current is round
the metallic circuit and therefore less likely to cause disturbances in neighbour-
ing circuits, substantially as described.
3. The combination of a double wound electro-magnetic ringing and control-
ling device with a double wound bridging coil common to a number of circuits
with the centre point connected to an earthed battery, so arranged in relation to
each other and to the bell coils at the sub-station with their earthed centre points
that when connected together the coils of the control magnetise the core and hold
the armature until the earth connection is severed at the sub-station, substan-
tially as described.
4. The combination of a double wound electro-magnetic ringing and control-
ling device with a transformer common to a number of circuits, the centre point
of which is connected to an earthed battery, substantially as described.
5. The combination of a retardation coil with its centre point connected through
a battery indicator or relay to earthed battery as a clearing signal when the sub-
station receiver is returned to its rest with a double wound ringing relay or ring-
ing key contolling device, so arranged that the lever will remain over until the
called sub-station answers, and connects the lines through when the sub-station
receiver is taken from its rest. A current from the generator between these
times ringing the sub-station at predetermined intervals substantially as described.
6. The combination of a telephone switchboard and sub-station apparatus with
a double wound ringing relay or ringing key electro-magnetic controlling device
so arranged that when the plunger is depressed an earthed battery is connected
through the two windings of a bridging coil and the two windings of the coil of
such electro-magnetic controlling device to both wires and earth at sub-station
and an alternating current from a generator connected with an interrupter in
parallel with a bridging coil at the central and a bell at the sub-station. The
bell therefore responding until the earth at the sub-station is removed by the
switch-hook being raised, thus allowing the relay plunger to rise, which is a
sigual to the operator that the subscriber has answered and joined the connection
through, and cut off the generator, substantially as described.
7. A ringing generator with a double wound armature in combination with
an earthed battery, a double wound electro-magnetic ringing control, and an
instrument at the sub-station with the centre point of the bell to earth substan-
tially as described.
Dated this Twenty-first day of Annil 1000.