Improvements in Telephone Exchange Systems.
Year: 1899

page_text: Date of Application, 27th June, 1899
Complete Specification Left, 27th Mar., 1900-Accepted, 5th May, 1900
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 to be as follows:-
The object of this invention is to simplify and improve the efficiency of tele-
phone exchange systems and consists primarily of improvements on the exchange
system described in connection with Fig. 3 of our Patent 14064 of 1896.
In the new and improved arrangement worked according to our invention,
branching jacks (preferably 3 point) are used instead of make and break jacks,
the line signal, (consisting of a relay and lamps) being disconnected from circuit
when two lines are joined together, by a cut-off relay connected to the test wire
and to earth. At the sub-station, the centre point of the telephone or the bell
or a bridging coil is connected to earth when the telephone is off its rest.
The line or calling signals are connected to earthed central battery.
Preferably three-way connecting plugs and cords are used with the usual
listening and ringing keys, we preferably however control the ringing key by
a double wound, electromagnet, having in connection therewith a generator
having one side earthed, and an interrupter so constructed as to intermittently
break the ringing circuit.and when this is done to connect up an earthed battery
to actuate the control.
To the inner contacts of the listening key a bridging coil is connected, the
centre point being connected to clearing relay and earthed central battery. The
armature is normally against the outer contact connecting up a lamp and
battery whose circuit is however broken at the armature and inner contact of
the cut-in relay, the armature being normally against the outer contact, and
the coils of the cut-in relay joined to the third conductor of the cords and to
earthed battery.
Preferably however, we use two clearing out signals and connect between the
inner contacts of the listening key, and ringing key a translator or two con-
densers, in the first case the centre points of the two windings are connected to
separate clearing out relays as before described, in the latter case the cords are
bridged by differential retardation coils one on each side of the condensers, the
centre points being connected to separate clearing out signals before described.
The operating is as follows:-
When the sub-station telephone is removed from its rest, the latter connects
the lines to earth, there is therefore a circuit from the earthed central battery
through the clearing out relay coils and over one line to earth at the sub-station
the lamp in the relay local circuit therefore glows. When the operator inserts
the answering plug into a jack in connection with that line. there is .another
circuit from the earthed central battery through the coils of the cut-in relay
through the third conductor of the cord and plug and the test circuit of the
jacks and through coil of cut-off relay to earth, the line relay is therefore out

page_text: out of circuit, and the cut-in relay has joined up the clearing lamp circuit.
When the other plug of the connecting set is inserted in the jack of the line
wanted, that line relay is similarly cut out of circuit. The lever of the ringing
key is now thrown over and it remains in that position and the wanted sub-
station is intermittently rung until the telephone is taken from its rest. When
that is done, there is a circuit from the earthed generator through one winding
of the coil of the control, and over one line and coil of bell to earth and this
current releases the control and the lever returns to the vertical. Should the
telephone be lifted during one of the intervals of ringing the earthed battery
through the interrupter will do the same thing. During conversation the central
earthed battery is discharging through the clearing relays through translator
windings on retardation coils over both wires through bell coils to centre point
to earth at the substation, the clearing relay armatures are therefore attracted
and the clearing lamp circuit broken.
With one clearing signal it is necessary for both sub-stations to replace the
telephones before the clearing signal is given. With two signals the operator
has better control of the circuits. When the sub-station replaces the telephone
the circuit of the central battery is broken at the sub-station, and the clearing
relay armature returns to the outer contact thereby completing the clearing
lamps circuit.
Both lamps glowing is the signal to clear
DANIEL SINCLAIR.
WILLIAM AITKEN.
provement pro
We, DANIEL SINCLAIR, Engincer-in-Chief, and WILLIAM AITKEN, Engineer to
the 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:
The object of this invention is to simplify and improve the efficiency of tele-
phone exchange systems and consists primarily of improvements on the exchange
system described in connection with Fig. 3 of our Patent 14064 of 1896.
In the new & improved arrangement worked according to our invention
bianching jacks (preferably 3 point) are used instead of break jacks, the line
signal (consisting of a relay & lamp) being disconnected from circuit when two
lines are joined together by a cut off relay connected to the test wire and earth.
At the substation the centre point of the telephone bell or bridging coil is con-
nected to earth when the telephone is off its rest.
The line or calling signals are connected to an earthed central battery.
Preferably 3-way connecting plugs & cords are used with the usual listening
and ringing keys, we preferably however control the ringing key by a double
wound electromagnet, having in connection therewith a generator having one
side earthed, and an interrupter so constructed as to intermittently break the
ringing circuit.
To the inner contacts of the listening key a bridging coil is connected, the
centre point being connected to clearing relay, and earthed central battery.
The armature is normally against the outer contact connecting up a lamp and
battery whose circuit is however broken at the armature and inner contact of

page_text: e cut in relay, the armature being normally against the outer contact,
e coils of the cut in relay joined to the third conductor of the cords and earthed
attery.
Preferably however, we use two clearing out signals and connect between the
aner contacts of the listening key, & answering plug,. a translator or two con-
ensers, in the first case the two centre points of the two windings are còn-
ected to separate clearing out relays as before described, in the latter case the
ords are bridged by differential retardation coils one on each side of the con-
ensers, the centre points being connected to separate clearing out signals as
before described.
The invention is illustrated in the diagrams attached which represent two
sub-stations connected by telephone lines with spring jacks, and signal con-
rolling relays in a telephone switchboard together with a pair of plugs for uniting
the lines & signals associated with the plugs.
Fig. 1. At the station C the contact point of switch lever f is connected to
earth, the lever f being connected to centre point of bell coils d one side of the
bell to the A line of the metallic circuit thence to spring a of spring jack, a
being joined to spring a¹ of another jack z¹ of the multiple, the other side of bell
is connected to the B line of the metallic circuit thence to spring of spring
jack z, b being connected to spring b¹ of another jack of the multiple a tap
off the B line is led to contact point h¹ of cut off relay h the tongue h² of h to
line relay k, the other side of k leading to earthed battery the bushes c, c¹ of
the spring jacks are connected together and led to cut off relay h, the other
side of h being to earth, the contact point k of relay k is connected to pilot
relay coil which is led to calling lamp thence to battery and to tongue 2
of relay k, the relay coil is doubled tongued, the tongue being.connected to
battery the other side of being led to night bell g thence to contact point /3
the other tongue of 7 is connected to battery i, the other side of i to pilot lamp i
and thence to contact point 3, a suitable 2-way switch is inserted in the local
circuits of pilot relay, in order that bell can be used for night work, and pilot
lamp in the day, the circuits of substation D are similar to those of C, where
the same letters with indices refer to similar pieces of apparatus, the cord circuit
consists of an answering plug m, and calling plug m³, the tip m² of m is con-
nected to one side of translator coil the other side of the coil to m³ of m, the
5 centre point of n¹ is connected to clearing relay coil the other side of u is
divided into two branches one branch being connected to earthed battery it, the
other passing to coil of cut in relay t, the other side of t to sleeve of plug m, the
tongue of relay u to battery thence to clearing lamp, to tongue t¹, of relay t
the contact pt of t is connected to contact point u¹ of u, one side of translator
coil n to spring o³ of combined listening and ringing key, a tap off spring o
to spring of ringing key, the other side of n to spring o³ of listening key, a
tap off spring o³ to spring p of ringing key, spring på of ringing key to tip m
of plug m spring m³ to ring me of plug m spring p to one coil of magnetic con-
trol thence to generator (one side of which is connected to earth), thence to
5 interrupter 1, to other coil of ringing control q back to spring 76, springs o¹ &
are connected to coils of operators telephone S the centre point of which is in
earth, the centre point of n2 is connected to clearing relay coil v, the other side
of is divided into two branches one branch being connected to earthed battery 4,
the other passing to coil of cut in relay.w, the other side of w to sleeve of plug m
the springs
50 the tongue of relay through clearing lamp to battery to tongue 2 of
relay the contact point of is connected to contact point w² of w,
of the combined ringing & listening key are operated by means of wedge g
to which is attached a handle q', when the wedge is forced in the position so as to
make contact between springs p¹ & p², p³ & p6 of ringing key it is held in this
55 position as long as magnetic control is inert, but immediately the control is
energised its armature 3 is attracted releasing the wedge which falls back to its

page_text: normal position thus cutting the ringing current off the line when the wedge is
forced in the position so as to make contact between springs o¹ and o³ o³ and o
of listening key, when released by operator it returns to its normal position. .
In order to illustrate the working of our invention we will suppose a person
at sub-station C, wishes to communicate with sub-station 1), C takes his telephone
off the lever f, making contact between contact point and f a current flows
from earthed battery through line relay k contacts of relay line B one coil of
bell to f, to earth, thus energising relay k closing contacts & thus light-
ing calling lamp which is the signal to the operator that C requires attention,
the closing of contact & also energises pilot relay 7, closing contacts &
&, thereby either lighting pilot lamp (if day working) or ringing bell g
if night working, the operator then inserts answering plug m in either jack z
or thereby completing a circuit from earthed battery through cut in relay,
sleeve m³ of plug m, bush e or el of jacks z or ', through relay coil- to earth,
thereby closing contacts, of relay and breaking contacts h', h of relay h which
breaks the circuit of relay and in consequence lamp goes out, and pilot relay
is rendered inert thus causing either bell g to cease ringing or pilot lamp to go
out, the insertion of plug m completes another circuit from earthed battery i
through clearing relay u to centre point of translater coil n', in parallel through
ring and tip of plug m line springs of spring jack to lines A & B coils of bell d.
to centre point switch-lever contact point to earth thus breaking contact u
&u²of relay in consequence of this clearing lamp does not light on the
insertion of plug m in the jack, the operator having ascertained the number
wanted by means of listening key O, inserts calling plug m² in jackor,
forces wedge q in position so as to cause springs 1 & 2 and and to come in
contact (the wedge is held in this position by armature 3 of magnetic control q²)
the current from generator flows through interrupter 1 one coil of magnétic
control springs p&p of ringing key ring m of plug m³, spring or 3 of
spring jack, B line bell to A line springs a or a³, tip m of plug m² springs 3
&p of ringing key other coil of magnetic control to other side of generator r,
the bell therefore intermittently rings, the insertion of plug m has also com-
pleted the circuit of relay c and in consequence clearing lamp lights indicating
to the operator that the subscriber has not attended to his call, on the telephone
at I being removed from the switch lever the condition of the generator circuit
is altered, the current from the generator now flowing through one coil of mag-
netic control, to springs 5 & 6 of ringing key to ring ms of plug m'; to spring .
&of spring jack B line through one coil of bell switch lever contact c¹
to earth and thus back to generator thus one coil of the control being deprived of
current, the control is energised its armature q3 is attracted and in consequence
the wedge is released, and breaks contacts and p³, p5 and 76 of ringing key,
the ringing current is thus cut off the line circuit, taking telephone off the
switch-lever also completes circuit from earthed battery through clearing
relay to centre point of translator coil n thence in parallel through contacts
and and to tip and ring m³ and m of plug m² springs a², or to
lines A and B coils of bell centre point of bell switch lever f¹ contact & to
earth and in consequence contact and is broken.clearing lamp goes out thus
indicating that the subscriber has attended to the call the signal to clear is when
both clearing lamps and light this is accomplished when both telephones are
replaced on the switch-levers (it will be noticed that if either telephone is
replaced alone the clearing lamp associated with that line lights but one lamp
alone alight is not the signal to clear) the earths being cut off centre points of
bells d, the current through clearing relays and is cut off and in conse-
quence contacts u¹ and u³ of clearing relay . and 3 of clearing relay & make
contact respectively the local circuits of both clearing lamps are thus completed,
(both contacts t¹, 2 of cut in relay t, and 101, 10 of relay to are made as both relays
are energised as plugs m and m² are in their respective spring jacks) the operator
now withdraws both plugs.

page_text: Fig. 2 shows a modification of Fig. 1, the bridging coil n taking the place or
translator n in Fig. 1.
Fig. 3 is a further modification of Fig. 1, in which we use condensers and ¹
one in each line of the cord circuit, bridging coils n and n¹ being bridged across
the lines one on each side of the condensers.
It will be noticed that when the circuit is arranged as in Fig. 2 only one
clearing signal is used, and that the clearing signal is only given when both
telephones are on the switch levers at the respective sub-stations.
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:
―
1st. The combination with a telephone line extending from a subscribers station
to a central office, the association there-with at the central office of a cut off relay
and line relay, one side of the line being connected to a contact point of the
cut off relay, and the centre point of subscribers bell connected to earth when the
telephone is off the switch lever substantially as described.
2nd. The combination with two plugs at the central office of cut in and clear-
ing relays, the contact of the cut in relay being normally opened, the contact of
the cut off relay normally closed, arranged substantially as described and shewn
in accompanying drawings.
der of March 1900.
DANIEL SINCLAIR.
WILLIAM AITKEN.