Improvements in Telephone Systems.
Year: 1898

page_text: Improvements in Telephone Systems.
We, DANIEL SINCLAIR, Engineer-in-Chief to the National Telephone Company,
Ltd., Oxford Court, Cannon Street, in the City of London, and WILLIAM AITKEN,
Engineer, with said Company at above address, do hereby declare the nature of
this invention to be as follows:-
The object of this invention is to improve the efficiency of telephone exchange
systems generally and that known as the central battery system in particular.
In some of the present known central battery systems, there is a great loss of
electrical energy, for the reason that the current is continually discharging round
the metallic loop or over both lines to earth.
In others this loss of energy is
avoided by the signals transmitted to the exchange being of a transient nature;
this renders it necessary to have at the exchange a drop indicator which has to be
restored by hand or by a complicated electrical movement, with a special circuit
through all the jacks of tlie switchboard.
In the new and improved system worked according to our invention, the elec-
trical energy is only operative from the time the subscriber removes his receiver
from the switch hook to call the attention of the exchange until the operator has
replied: the act of inserting the plug to reply breaks the continuity of the battery
circuit. Again with the clearing signal, the current is only flowing from the time
the subscriber replaces the receiver on the switch-hook until the operator has
withdrawn the plugs, this act again breaking the continuity of the battery circuit.
To attain this end a relay of considerable resistance is provided in each sub-
scriber's instrument and fixed in such a position that the switch-hook in being
raised or depressed, will automatically press the armature against the inner con-
tact, the armature being connected preferably to the centre point of the call bell
and the inner contact of the relay being connected thro' the coil or coils of the
relay to earth.
At the exchange the circuits are preferably as follows:-
The subscribers lines are bridged by resistance coil or coils of high self-induc-
tion (if one coil is used we prefer to wind it differentially) and the centre point
connected to spring provided in the jack which in its normal position is in con-
tact with a stud connected with the subscriber's calling indicator, battery and
earth. The line springs may be connected in series or in parallel as is commonly
the case and so arranged in relation to the spring before mentioned that on the
insertion of a plug one of the line springs presses on an insulating stud fixed on
the spring in connection with the centrepoint of the bridging coils and causes it
to break circuit with the indicator stud, and make contact with the test spring
which is in connection with the barrel or bush of all jacks of that line in the
exchange.
The separation of the spring and stud removes the current from the line, and
the connection of the spring to the test-spring joins the centre point of the bridg-
ing coils to the barrel or bush of the jack.
The apparatus for connecting subscribers' lines together at the central station
may be of any of the well-known designs and the arrangement of the same is as
follows:-
The tips and rings of each pair of three-way plugs are respectively connected

page_text: through listening keys and ringing keys in the usual way. The sleeve of the plug
however, is joined to special contacts on the listening key, ring off indicator,
through battery to earth.
The operation of our system is as follows:-
A subscriber wishing to call the exchange removes his receiver from the switch
hook, this mechanically closes the relay as previously described, the relay being
held in that position by the current from the central battery through indicator,
through spring and stud in jack, through bridging coils, over both lines, through
bell coils in parallel to the inner contact of relay and through relay coils to earth.
Simultaneously the indicator at the exchange shows that attention is required.
The insertion of the operator's answering plug disconnects the line indicator and
central battery from the lines, thus restoring both the subscriber's indicator and
the relay to their normal condition. The operator is then in a position to com-
municate with the subscriber and on learning the number wanted inserts the call-
ing plug of a pair of cords into the jack of the wanted subscriber.
On the completion of the conversation the act of one or both of the subscribers
placing the receiver on the switch-hook again mechanically closes the relay, and
the current now has a path through the ring-off indicator, the third conductor of
the cord, barrel of the jack, test spring, bridging coils, lines, bell coils and through
relay contact and relay coils to earth, thus causing the ring off indicator to show
a definite signal, this signal continuing to show until the operator has withdrawn
the plugs.
The fore-going invention with slight modifications may be adapted to work
with most of the apparatus at present in common use.
For example:
=:
With what are commonly known as three point jacks, the connection from the
centre point of the bridging coils would be taken to the armature of a special relay
for each line in the exchange, the outer contact being connected to line indicator,
battery and earth, the inner contact being connected in parallel to the coils of the
relay to earth and to the test wire, instead of to the spring and stud, as before
mentioned.
"
Our invention may also be applied to non-multiple boards. In this case no line
bridging coils are necessary, the current being connected with the lines direct
through calling indicator and inner contacts of spring jacks. The connecting
cords, however, must be bridged by coils of the pattern before specified, the centre
point being connected to ring off indicator, battery and earth. The apparatus at
the subscriber's to be as before described.
The principle of our invention may also be applied to operators' connecting sets
so as to lessen the work of the operator, by the following means:-A relay of con-
siderable resistance is introduced into the cord circuit and so arranged in relation
to the ringing key button that when the operator presses the button to call a sub-
scriber the circuit of the relay is closed. This causes two contacts that are con-
nected with the tip and ring of the calling plug, to be held against two generator
contacts, thus joining the wanted subscriber's line to a generator, or other source
of electrical energy. The relay remains energised until the subscriber removes
his receiver from the switch-hook to reply.
Dated this 10th day of February 1898.
DANIEL SINCLAIR,
WILLIAM AITKEN.

page_text: AITKEN, Engineer with the said Company at above address, 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 this invention is to improve the efficiency of telephone exchange
systems generally and that known as the central battery system in particular."
In some of the present known central battery systems, there is a great loss of
electrical energy, for the reason that the current is continually discharging round
the metallic loop or over both lines to earth. In others this loss of energy is
avoided by the signals transmitted to the exchange being of a transient nature;
this renders it necessary to have at the exchange a drop indicator which has to be
restored by hand or by a complicated electrical movement, with a special circuit
through all the jacks of the switchboard.
In the new and improved system worked according to our invention, the elec-
trical energy is only operative from the time the subscriber removes his receiver
from the switch hook or depresses a plunger to call the attention of the exchange
until the operator has replied; the act of inserting the plug to reply again breaks
the continuity of the battery circuit. Again with the clearing signal, the current
is only flowing from the time the subscriber replaces the receiver on the switch-
hook until the operator has withdrawn the plugs this act again breaking the con-
tinuity of the battery circuit.
The invention is illustrated by the accompanying drawings:-
Figure 1 is a diagrammatic representation of the circuits and apparatus at the
central and sub-stations according to our invention, for use in small exchanges,
and using in conjunction therewith the automatic ringing.of the sub-station.
Figure 2 shows in elevation a suitable form of ringing relay for use in con-
nection with our invention.
Figure 3 shows diagrammatically the differentially wound coils of the relay.
Figure shows diagrammatically the circuits and the apparatus at the central
and sub-station in conjunction with large exchanges having complete branching
jacks and without automatic ringing.
Figure 5 shows the relay at the sub-statiion mechanically closed by a plunger
for calling the exchange and automatically closed by the replacing of the receiver
on the switch hook for clearing.
Figure 6 shows the circuit of the relay at the sub-station closed by a plunger
both for calling and clearing.
Figure 7 shows a simple arrangement at the exchange end of a line for small
exchanges.
Our invention according to Figure 1 uses a spring jack which is branching as
far as the speaking circuit is concerned but which has a spring which makes
with and breaks from other springs in the signalling and test circuits; springs a
and a, b and b are the springs in the speaking circuit, springs c and d are the
springs in the signalling circuit, which break from the inner contacts which are
connected to the line indicators g and g¹. the other side of these indicators being
connected to the central earthed battery. The indicators may be of any of the
well known forms of battery indicators or a relay with lamp in its local circuit.
To the bushes or barrels of the jacks d and, the test wire attached. Between
the springs a and b a coil of suitable resistance and self-induction is connected
the centre-point having a connection to spring Plugs and are used to
connect lines together and preferably have three points, a tip, ring and sleeve.
The listening key k connects in circuit either the operator's telephone or the
clearing indicator m, whose other side is connected to the earthed central battery p.
The operator's telephone circuit has a ringing key h which allows the operator to
ring by generator n on the answering plug when necessary. The ringing on the
calling plug may be done by a similar key to h in the well known manner or by
ringing relay as shown. The depression of the armature (see Fig. for detail)
causes the springs 1, 2, 3, 4, 'to break from under contacts and make with outer
ones. In the normal position, with the armature up, the three parts of the
C.

page_text: 0
plugs, and are respectively connected together as when a telephonic connection
has been made. When the armature is depressed, the calling plug has the tip
and the ring joined to generator and circuit breaker respectively, the sleeve
being joined through one winding of the relay coil to battery (the polarity
being opposite to that which is joined to the clearing indicator and earth. The
other winding of the relay coil being joined direct or through a resistance to earth.
These two windings are differential so that the magnetic effect produced by one
is neutralised by the other.
At the sub-station any of the well known forms of instruments may be used and
either with or without a ringing generator. The drawing shows the instrument
without a generator. The centre point of the call bell or the B line at the
instrument is connected to the armature of a polarised relay. The contact which
it meets when depressed being connected through the coils of the relay to earth.
The relay is polarised so that it will be held by the clearing current but not by
the current used in connection with the ringing relay at the central.
to
7 are
In Figure 4 three-point branching jacks are used, the a and b springs have a
suitable bridging coil r as before described, the connection from the centre point
being connected through the armature and outer contact of the cut-off relay
calling indicator g and earthed battery p. The coils of the cut off relay
connected, one side to earth and the other to test wire and bush of jack d. The plug
connections differ from those in Figure 1 in that an ordinary ringing key is
shown instead of the ringing relay and that the outer contacts on the listening
key are connected to a retardation coil w (similar to r) the centre point being con-
nected to clearing indicator m battery p and earth and the inner contacts to the
operator's telephone i The sleeves of the plugs j and j¹ are connected to battery
and earth.
21°
At the sub-stations the instruments are as before described and the relay may be
polarised and operated only by the switch-hook as before described or as shown at
Figure 5 an ordinary relay may be fitted and a plunger used for calling the ex-
change, and the placing of the receiver on the switch-hook after a conversation
giving the signal to clear, the relay being so arranged, that when the switch-
hook frises when the receiver is removed it lifts the front pivotted part of the
armature but when the switch-hook is again depressed by the weight of the
receiver the armature is brought down and remains down until the cords are with-
drawn at the central.
Figure 6 is preferably used when the generator is retained at the sub-station and
the subscribers allowed to call each other, the ringing key y then being omitted
at the central.
Figure 7, is for non-multiple exchanges, the calling indicator 9 being joined
direct to the inner contacts of a break jack, the plug circuit and the sub-station
being similar to any of the before described arrangements.
We will now describe the operating of our invention with special reference to
Figures 1 and 4.
In the operation of the system the earth battery is normally connected to line,
but there is no discharge as the electrical circuit is not complete. When however
the subscriber takes the telephone from the switch-hook as in Figure 1, or depresses
the plunger as in Figure 5 and 6 the circuit is completed from the earthed battery
p, through calling indicator g to centre point of bridging coil over both lines in
parallel to centre point of bell u as in Figure 1 or through one half of coil r and
over the B line as in Figure 4 to armature of relay e across the contact and through
the coil or coils to earth. The armature e is therefore held attracted and the call-
ing indicator or relay g at the central is energised. The operator knows thereby that
the subscriber desires attention and inserts plug into the answering spring jack.r.
The continuity of the battery circuit is thereby broken as the spring has been
lifted from its under contact in the case of Figure 1 and in case of Figure 4 a
circuit has been established from earthed battery p.through sleeve of plug and
bush of jack over test wire and through coil of cut off relay g to earth, the arma-

page_text: ture of relay is therefore attracted and the calling circuit broken, and the
relay e is restored to its normal position.
The operator tests the line wanted in the well known manner and if the line
wanted is disengaged inserts the plug in multiple jack y. The circuit of the
calling indicator of that line is broken in a manner similar to that just described.
The operator then rings in the well known manner for Figure 4 but for Figure 1
she depresses by a plunger the armature of ringing relay momentarily. The
armature remains attracted as there is a circuit from earthed battery
one of its coils to earth by spring 3 and its outer contact.
through
The subscriber is at the same time rung intermittently as there is a circuii from
the generator n through spring 2 of relay and its contact to tip of plug j to
spring al of jack over the A line through the bell u of the subscribers instrument
back by B line to b spring of jack, ring of plug to spring of relay / and outer
contact through circuit breaker e to other side of generator n. The circuit
breaker o is driven by motive power and the bell at the subscriber instrument rings
for say two seconds with intervals of four seconds. When the subscriber removes
the telephone from the switch-hook the ringing ceases because the armature of
the relay rises, a momentary circuit was formed at the time for lifting the
receiver from the earthed battery p through the inner coil of relay through
spring 4 and its outer contact to sleeve of plug through bush and spring c
of jack, to centre point of bridging coil over both lines and through bell coils u
in parallel to centre point and through relay e¹ to earth. The opposing magnetic
effect of the two coils of the relay cannot hold the armature and the springs 1, 2,
3, 4, leave their outer contact and make with the inner ones, and thereby connect
the lines together. The current from the battery p is of such a polarity that it
does not affect the relay e¹. The operator after depressing the plunger controlling
the armature of ringing relay pulls over listening key this in the case of
Figure 1 connects the clearing indicator m to the lines through the test circuit
so that when the telephone is returned to the switch-hook after a conversation,
the circuit is from the earthed battery through clearing indicator or relay m
through inner contact of listening key to sleeve of plug and in parallel to
inner contact and spring 4 of relay to sleeve of plug and over both lines in
parallel by bushes of jacks d and d springs e and to centre point of coils ▸
and rover both metallic circuits and bell coils u and u¹ in parallel to centre
points and then through relays e and e¹ to earth. Either subscriber therefore
placing his telephone on the switch-hook gives the signal to clear, the clearing
indicator m remaining energised until the operator withdraws the plugs, that act
again breaking the continuity of the battery circuit and restoring the relays e
and e' to their normal condition. In the case of Figure 4 the manipulating of the
listening key places the bridging coil w across the metallic-circuit the centre point
being connected to clearing indicator m and earthed battery p. When the tele-
phone is returned to the switch-hook, the circuit is from the earthed battery p
through clearing indicator m to centre point of coil w through both its winding
and both subscribers lines and bells in parallel and through relays e and e¹ to
earth.
The
In the case of Figure 6, the clearing signal would be given by depressing the
plunger after a conversation, the circuit then being as before described.
cord circuit in connection with this arrangement would be similar to Figure 4 but
the ringing key would be omitted as after the operator has made the connection
one subscriber rings the other by the generator provided on the instrument, this
ringing does not indicate in the exchange. The wires joined together become prac-
tically private wires and the subscribers may return the telephone to the switch-
hook and ring each other as required.
In Figure 7 no bridging coils are necessary as the boards are non-multiple and
the calling indicator g is connected direct to the inner contact of a make and
break jack, the other side being connected to earth battery p.
The instruments and cord circuits may be of any of the before described
arrangements,

page_text: The ringing relay in the cords formerly described may also be used in con-
nection with ordinary systems having the centre point of the magneto bell of the
subscribers instrument connected to earth through a switch operated by the
switch-hook. In this case the relay has only one coil with an earthed battery on
one side. When a connection is made and the armature depressed, it remains
attracted as the battery finds earth at the subscribers office, and this earth is cut
off when the subscriber takes the receiver from the switch-hook, allowing the
armature to restore and so joining the lines through. This application of our
invention has been amplified in a subsequent Provisional Patent No. 16164
date 25th July 1898.
This invention admits of modification in the arrangements which would readily
suggest themselves to those skilled in the art. We, therefore, do not limit our-
selves to the precise arrangements shown 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. The improved system of automatic and mechanical signalling on telephonic
systems as hereinbefore described under several modifications with reference to
the annexed diagrams.
2. The improved system of automatic ringing of the wanted subscriber, after
the depression of a plunger substantially as described.
3. A relay at the sub-station which keeps a battery circuit normally open and
which after the armature has been depressed by the action of the switch-hook or
plunger to call or clear remains energised until the battery circuit has been
broken at the exchange.
41 10
day of Vacamha 1909
DANIEL SINCLAIR,
WILLIAM AITKEN.