Improvements in Telephone Exchange Systems.
Year: 1899

page_text: Date of Application, 27th June, 1899
Complete Specification Left, 27th Mar., 1900-Accepted, 23rd June, 1900
Improvements in Telephone Exchange Systems.
We, DANIEL SINCLAIR, Engineer-in-Chief and WILLIAM AITKEN, Engineer to
National Telephone Co. Limited, of Oxford Court, Cannon Street, in the City
of London, do hereby declare the nature of this invention to be as follows:--
The object of this invention is to simplify and improve the efficiency of tele-
phone exchange systems by converting fleeting signals from the sub-station into
permanent signals at the central exchange.
In the new and improved system worked according to our invention the
electrical energy from the central battery is only operative from the time the
subscriber removes his telephone from its rest to call the attention of the exchange
until the operator has replied; the act of inserting the plug to reply breaking
the continuity of the battery circuit. Again with the clearing signal, the current
is only flowing from the time the subscriber replaces the telephone on its rest
until the operator has withdrawn the plugs, this act again breaking the con-
tinuity of the central battery circuit. The current over the lines is only
momentary viz; during the rising or falling of the telephone rest, the signal in
the exchange being kept energised by a local circuit.
To attain this end a spring in connection with the telephone rest (which forms
part of the line circuit) makes contact when rising or falling with another
spring which is connected to earth, the telephone rest spring being clear of this
earth contact in its upper and lower positions. Any of the well known forms of
instruments may be used with this simple arrangement added, preferably without
ringing generator but with polarised ringer.
At the exchange I preferably use branching three point jacks, i.e. with two
line springs and a test spring attached to the bush or barrel, with three-way
plugs and cords and listening and ringing controls of the well known patterns
modified as will be described.
The special apparatus consists of a line relay constructed and connected as
follows:
The coil has one side connected through the armature and contact of a cut off
relay to one wire of a metallic circuit, (preferably the B wire) or it may be con-
nected to the centre point of a bridging coil joined across the metallic circuit,
the other side being joined to the earthed central battery. The line side of
the coil is also joined to one circuit of the armature which has two springs or
tongues and two under contacts, one being connected through the armature and con-
tact of the cut off relay and through supervisory relay to earth and the other to a
battery and thence to the line or calling lamp signal to the other circuit on the
armature of the line relay. The supervisory relay has two local circuits in one
of which is a lamp and the other an alarm bell.
The coil of the cut off relay has one side joined to the test wire and the other
to earth. To the inner contacts of the listening keys are connected bridging
coils, preferably differentially wound, with the centre point connected through

page_text: the coils of a relay (similar to the line relay) to earthed central battery. One
local circuit is broken by extra springs on the listening key so that the circuit is
broken when in the listening position. The outer contacts of the ringing key are
connected in circuit with a generator, circuit breaker and a. double wound electro-
magnet controlling the ringing key, one side of the generator being earthed. The
sleeves of the plugs are connected to an earthed battery. The operating is as
follows:-
When a subscriber removes the telephone from its rest to call, the line is
momentarily earthed and the earthed central battery discharges energising the
line relay and causing the armature to be attracted. Although the earth contact
has been removed at the sub-station, the armature does not fall back because a
local circuit has been formed from the earthed central battery through the coil
of line relay to one armature circuit and under contact and through supervisory
relay to earth, causing the lamps in the local circuits to glow. When the operator
plugs in to answer, with the key in the listening position the earthed battery
connected to the sleeve of the plug has a circuit through the cut-off relay to
earth and its two armatures are attracted breaking the calling relay from the
line and breaking the calling lamp local circuit so that the lamp ceases to glow.
When the other plug of a connecting set is inserted in the jack of the line wanted
that line relay circuits are similarly cut.
When the ringing lever is put over to ring the subscriber wanted it is
mechanically held in that position and as the generator current is through the
two windings of the electromagnet there is no magnetic action and the subscriber's
bell is rung at intervals until he answers. When the telephone is removed from
.its rest and the line momentarily earthed there is a circuit from the earthed
generator, through one winding of the electromagnet and over one wire to earth
at the sub-station and the armature of the control is attracted and the lever
released and the connection joined through. The interrupter or circuit breaker
has a second circuit which joins up an earthed battery which releases the control
if the telephone should be removed while the generator not ringing.
Either subscriber now returning the telephone to its rest and therefore again
momentarily earthing the line will energise the clearing relay and the lamp will
glow in a manner similar to that described for the calling apparatus when the
operator will withdraw the plugs and return the listening key to the to the listen-
ing position thereby cutting the clearing lamp circuit and causing it to cease to
glow, this movement at the same time restoring the apparatus to the best possible
position for attend to another call.
Preferably two clearing out signals should be used, the cord circuit then being
divided by a translator or by two condensers with a bridging coil across the
cords on each side of the condensers, the centre points of the two windings of the
translator on the centre points of the two retardation coils being connected to
separate clearing out relays as before described.
Dated this 26th day of June 1899
DANIEL SINCLAIR.
WILLIAM AITKEN
Хоторное вжене увсета.
We, DANIEL SINCLAIR, Engineer-in-Chief and WILLIAM AITKEN, Engineer to
the National Telephone Co. Limited, of Oxford Court, Cannon Street, in the City
of London, do hereby declare the nature of this invention and in what manner 5

page_text: he same is to be performed, to be particularly described and ascertained in and
y the following statement:-
The object of this invention is to simplify and improve the efficiency of tele-
hone exchange systems by converting fleeting signals from the sub-station into
permanent signals at the central exchange.
In the new and improved system worked according to our invention the
electrical energy from the central battery is only operative from the time the
subscriber removes his telephone from its rest or depresses a plunger, or revolves
a generator to call the attention of the exchange until the operator has replied,
the act of inserting the plug to reply breaking the continuity of the battery
circuit. Again, with the clearing signal, the current is only flowing from the time
the subscriber replaces the telephone on its rest or again depresses the plunger
or revolves the generator until the operator has withdrawn the plugs and returns
listening key to the normal position, this act again breaking the continuity of
the central battery circuit. The current over the lines is only momentary, viz:-
during the rising or falling of the telephone rest, the depressing of the plunger or
the revolving of the generator, the signal in the exchange being kept energized
by a local circuit.
Our invention is illustrated by two sheets of drawings (A) Sheet 1, Figure 1,
illustrating the use of a fleeting contact for calling and clearing purposes operated
A low voltage
by the rise and fall of the telephone rest at the sub-station.
battery for lighting the calling and clearing lamp signals in the local circuit at
the exchange, and apparatus to enable the operator to ring the subscriber wanted.
(B) Sheet 1, Figure 2, shows the cord circuit divided by translator for two
clearing signals.
(C) Sheet 1, Figure 3 shows the cord circuit divided by condensers for two
clearing signals.
(D) Sheet II, Figure 1, illustrates the use at the sub-station of a plunger for
calling and clearing purposes and a generator provided so that the calling sub-
scriber.can after the operator has made connection ring the subscriber wanted.
At the exchange the line relays and calling and clearing relays and other apparatus
are energised by a common battery.
(E) Sheet 11, Figure 2, illustrates the use of a generator at the substation for
calling and clearing purposes, no current then being normally on the lines.
To attain the result described at (A) a spring in connection with the telephone
rest or the telephone reste (which forms part of the line circuit) makes contact
when rising or falling with another spring f which is connected to earth, the
telephone rest or spring e being clear of this earth in its upper and lower positions.
Any of the well known forms of instruments may be used with this simple
0 arrangement added, preferably without ringing generator but with polarised
ringer d.
At the exchange we preferably use branching three point jacks i.e. with two
line springs a, b, and a test spring attached to the bush or barrel c with three-
way plugs and cords and listening key r and ringing controls u, t of the well
15 known patterns modified as will be described.
The special apparatus consists of a line relay k constructed and connected as
follows:
The coil has one side connected through the armature ³ and contact h¹ of
a cut-off relay to one wire of a metallic circuit, (preferably the B wire) or it may
50 be connected to the centre point of a bridging coil joined across the metallic
is also joined to contact with which
circuit. The line side of the relay coil
one of the armature springs or tongues makes contact. Tongue k connected
through the armature hand contact h² of the cut-off relay h and through super-
visory relay to earth. The other tongue 3 and contact are in circuit with a
55 battery and the line or calling lamp signal j. The supervisory relay has
two local circuits in one of which 121 are a lamp m and battery ¹, and in the
other an alarm bell n and battery ².

page_text: The coil of the cut-off relay h has one side joined to the test wire in connection
with c and the other to earth.
To the inner contacts of the listening key r is connected bridging coil z
preferably differentially wound, with the centre point connected through the
coil of a relay o similar to the line relay, to earthed central battery it. One
local circuit oo is broken by extra springs on the listening key r so that
the circuit is broken when in the listening position; the other local circuit 0² o*
is in connection with lamp p and battery 23. The outer contacts u³ u of the
ringing key are connected in circuit with a generator and circuit breaker w
and the two windings of a double wound electromagnet t controlling the
ringing key u one side of the generator being earthed." The sleeves q q' of
the plugs qq are connected to earthed battery it.
The operating is as follows:-
When a subscriber removes the telephone y from its rest e to call, the line is
momentarily earthed by making contact with spring f and the earthed central
battery discharges, energising the line relay k and causing the armature to
be attracted. Although the earth contact has been removed at the sub-station C
the armature does not fall back, because a local circuit has been formed from
the earthed central battery through the coil of line relay k to contact k¹ and
armature and through armature and contact h of cut off relay h and through
coil of supervisory relay to earth. The lamp j in the other local circuits
therefore continues to glow. When the operator inserts plug in jack
answer with the key in the listening position (that is in contact with r¹ and
with the earthed battery connected to the sleeve q' of the plug q, has a
circuit through the cut-off relay to earth and its two armatures ³h are
attracted, breaking the calling relay from the line at and breaking the
local circuit at 2 so that the coil k is no longer energised and the local circuit
is therefore broken at and so that the lamp ceases to glow. When the
other plug of a connecting set is inserted in the jack of the line wanted that
line relay circuit is similarly cut at relay h³.
to
When the ringing levers is put over to ring the subscriber (D)) wanted it is
mechanically held in that position by pointer 1 passing over barbed head of
spring spring makes contact with u, and with and as the generator
current is through the two windings 2 and 3 of the electro-magnet there is
no magnetic action, and the subscriber's bell is rung at intervals until he
answers. When ne telephone g¹ is removed from its rest e¹ and the line
momentarily earthed there is a circuit from the earthed generator through one
winding of the electromagnet and over one wire B to earth at the sub-station D
and the armature of the control t is attracted and the lever s released and the
connection joined through. The interrupter or circuit breaker w has a second
circuit which joins up an earthed battery which releases the control if the
telephone gl be removed while the generator is not ringing owing to the springs
being on the insulated section of the interrupter w. Either subscriber now return-
ing the telephone to its rest and therefore again momentarily earthing the line
will energise the clearing relay and the lamp 7 will glow in a manner similar
to that described for the calling apparatus, when the operator will withdraw the
plugs and and return the listening key to the listening position, thereby
cutting the local circuit 7, 8 and causing the lamps to cease to glow, this move-
ment at the same time restoring the apparatus to the best possible position for
attending to another call.
Preferably two clearing out signals should be used, the cord circuit then being
divided by (a) Sheet I, Fig. 2, translator z¹, 2, or by (b) Sheet I Fig. 3 two
condensers, 5, 6 with a bridging coil across the cords on each side of the
condensers, the centre points of the two windings of the translator or the centre
points of the two bridging coils being connected through separate clearing out
relays o, o, 07, 08 to earthed central battery.
(d) on Sheet II, Fig. 1 is shewn the modification before described. The instru-

page_text: ent at the sub-station has a plunger or switch, e, e¹ for calling and clearing,
e spring e, el being depressed until it makes contact with f, f', and then
eleased. The instrument has also a generator whose armature is revolved to
ing the bell of the subscriber wanted. The placing of the telephone on the
est at one substation causing relay 05 or 07 to be energised and give a clearing
igual and the placing of the telephone on the rest at the other sub-station
ausing relay 0 or 08 to be energised and give a clearing signal--the operator
nly disconnecting after both relays have been energised.
At the exchange the coil k of the line relay has the lamp j in parallel with it,
one side being connected through the armature h² and contact h₁ preferably, to
the B wire of the metallic circuit. The contact has a parallel connection to
the armature of the line relay. The other side of relay coil and lamp j
are connected to one side of battery i, and the contact k¹ connected to the other
side. One side of the cut-off relay coil is connected to the test circuit c, while
the other side is connected to earth side of battery.
The cord circuit has a listening key r in circuit, the inner contacts ³, being
The outer contacts 71. 76 are connected
connected to the operators telephone y.
to differentially wound bridging coil z which has its centre point connected to
relay o and lamp p in parallel, and another connection to contact o². The other
sides of lamp and relay coil o are connected to one side of the battery i and
the armature o connected through contacts 7, 8 of listening key to earthed side
of battery i, the contact ri, being open in the listening position. The sleeves
of the plugs q', are connected together and through resistance to battery i.
The operation is as follows:-
Subscriber e depresses call key e, and earthed central battery i has then a
circuit through relay coil k and lamp ; in parallel through armature ½² and
contact h¹ of cut off relay h over B wire and one bell coil, or from line direct to
Relay is therefore energised, and arm-
earth through switch e and contact f.
ature attracted, when a local circuit is established from central battery through
coil and relay lamp in parallel through armature h² and contact h¹ of cut-off
relay through armature and contact of line relay to earthed side of central
battery and armature therefore remains attracted and lamp j glows after call
keye has been disconnected from earth. Answering plug q is then inserted in
jack c when a circuit is established from earthed central battery through and
sleeve of plug q', through bush and test wire c, through coil of relay h, back to
earthed side of battery. Relay his therefore energised and armature h³ is
attracted away from contact hand as line coil and lamp have thereby been
disconnected from the earthed side of battery the relay is de-energised and
lamp ceases to glow. After the operator has learned the subscribers require-
Uments the plug q is inserted in jack when another local circuit is established
through coil of cut-off relay h³, and the line relay and lamp j¹ disconnected
from line in a manner similar to that of the calling line. Operator then puts
listening key to the through position that is with spring in contact with
and spring, in contact with and spring in contact with 78. Subscriber C
5 then calls d by revolving armature of generator when bell d' responds. This
ringing current does not indicate in the exchange. After conversation is finished
one or both subscribers depresses call key e, e when the earthed battery has a
circuit through lamp p and relay coil o in parallel to centre point of bridging
coil z over both wires and bell coils in parallel to earth through call key ef and
30 e, f. A local circuit is again established from one side of central battery
through lamp p and relay coil o in parallel to contact o2 and armature o' through
contacts, of listening key to earthed side of battery i and relay o remains
energised and lamp p glows until operator withdraws plugs and returns listening
key to the listening position.
55
(e) Sheet II Fig. 2 illustrates the modification before described with a generator
at the sub-station for calling and clearing. At the exchange the A and B wire
pass through armature h¹; h³ and contacts h², h* of cut-off relay h, to caling lamp j

page_text: and coil of relay k in parallel. The A line also has a parallel connection to
contact and armature of line relay with connection to battery and earth.
One side of lamp and relay coil k also have connection to earth as also has coil
of cut-off relay. The operating is as follows:-
When the armature of the generator is revolved, relay & is energised and
armature is attracted. A local circuit is then established from earthed battery i
through armature ², contact karmature and contact ² of cut-off relay through
lamp and relay coil k in parallel to earthed side of battery and lamp therefore
glows until operator inserts plug in jack 3 to answer, when relay coil his energised
and armatures h², h are attracted and local circuit broken.
Any of the well known cord circuits may be used with this combination.
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 combination of two relays, one breaking one contact and the other
making one contact with the two armatures, or one armature and one contact
connected in parallel for use as a line and cut off relay.
(2) The combination of two relays, one breaking one contact and the other
making one contact with the two armatures, or one armature and one contact
connected in parallel, with an incandescent electric lamp in parallel with the
coil of the line relay as an indicator.
(3) Two relays one breaking one contact and the other making one contact,
with the two armatures or one armature and one contact connected in parallel,
with an incandescent electric lamp in parallel with the coil of the line relay
as an indicator, in combination with an earthed central source of electricity.
(4) Two relays one breaking one contact and the other making one contact,
with the two armatures or one armature and one contact connected in parallel,
with
the
electric lamp in parallel with
coil of the
line relay
as an indicator, and an earthed central source of electricity in combination
with a switch at the sub-station to make and break circuit with earth substantially
as described.
an
(5) A. line or calling relay in combination with a cut-off relay with the con-
nections such that when the coil of the line relay is energised by a current to
line of short duration and the armature attracted a local circuit through the line
coil is established and the armature held attracted after the earth on the line
has been removed, substantially as described and shown on the accompanying
designs.
(6) A line or calling relay with an electric lamp as an annunciator in parallel
with the coil, and a cut-off relay in combination with a call key or earthing switch
at the sub-station, with the connections such that when the coil of the line relay
is energised by a current of short duration, when the call key is connected to
earth, the armature is thereby attracted and held attracted by a local circuit
established through the line coil, after the call key is released from earth, sub-
stantially as described.
(7) A line or calling relay in combination with a cut-off relay with the con-
nections such that when the coil of the line relay is energised by a current to line
of short duration and the armature attracted and held by a local circuit established
through the line coil so arranged that the coil of the cut-off relay is energised, the
line and the local circuits being cut and the line relay de-energised substantially
as described.
(8) The combination of a relay with a lamp in parallel with the coil with a local
circuit in combination with springs on a listening key so arranged that when
the listening key is in the through position and the call key at the sub-station
is depressed and released, the current of short duration attracts the armature of
the clearing relay, and the local circuit retains the armature attracted until the

page_text: connection is severed and the listening key returned to the listening position,
when the local circuit is broken and the relay de-energised, substantially as
described and shewn in the accompanying drawings.
DANIEL SINCLAIR,
WILLIAM AITKEN.