Improvements in Central Battery Telephone Exchange Systems.
Year: 1899

page_text: Date of Application, 12th Sept., 1899
Complete Specification Left, 12th June, 1900-Accepted, 18th Aug., 1900
PROVISIONAL SPECIFICATION.
Improvements in Central Battery Telephone Exchange Systems.
I, WILLIAM AITKEN, Engineer, with the National Telephone Company, Limited,
Oxford Court, Cannon Street, in the City of London, do hereby declare the nature
of this invention to be as follows:-
To simplify and improve the efficiency of telephone exchange systems, particu-
larly those having the calling and clearing signals energised by a central source
of electricity in conjunction with the removing of the telephone from the rest
or switch-hook of the instrument at the sub-station and the replacing of the same.
In all known systems having two clearing lamps per pair of connecting cords-
one to indicate the condition of the calling subscriber's circuit and the other to
indicate the condition of the circuit of the subscriber with whom he has been con-
nected it has been necessary to divide the connecting circuits into two sections
by condensers or translators so that as far as signalling is concerned there are two
distinct circuits, the condensers and translators, however, repeating the wave-
like speech currents from the one circuit to the other. The necessary retardation
coils and relays being then fitted in conjunction with the two circuits on each
side of the condensers or translators.
The principal feature of my invention is that two distinct and individual
signals are obtained from the two subscribers' lines connected without any
division of the connecting cord circuits whatever. There is, therefore, no diminu-
tion in the volume or intensity, nor is the formation of the speech wave in any
way interfered with, which is the case in the before mentioned systems, particu-
larly when (as is commonly the case) the translator is employed. By my in-
vention the cost is also materially decreased.
To attain the end described, I connect the two plugs of a connecting set to-
gether with the usual listening and ringing keys, the latter being slightly modified
as will be described hereafter. Instead, however, of joining the plugs tip to tip
and ring to ring as is usual, I connect the tip of one plug to the ring of the other,
thereby crossing the cords.
To the inner contacts of the listening key I connect two suitable relays or
indicators in series and so in bridge across the cords. The relays preferably have
lamps and battery in the local circuits. The main signalling battery I connect
one side to earth and the other to a point between each pair of relays.
A double wound ringing control electromagnet (which mechanically locks and
keeps the ringing current on until it is electrically released when the telephone
is taken from its rest at the sub-station) I connect to the ringing key, after pro-
viding the latter with an extra spring, one outer contact being connected through
a resistance equal to the average line and bell to earth; two ends of the differenti-
ally wound coil are connected together and joined through an interrupter ringing
generator and earth.
The lines in the exchange are connected through spring jacks in the usual way.
but with one wire only-preferably the A wire-connected through the armature

page_text: and contact of a cut off relay (whose coil is connected in the usual way to the
test circuit) to relay with lamp and battery in the local circuit, or to ordinary drop
indicator and to earthed main battery. The line relay has two coils, one in the
circuit above described and the other the retaining coil, when the armature is
attracted in the local circuit. The line relay local circuit has also a circuit through
a second tongue on the armature, and contact of the cut-off relay, which when the
latter is energised breaks the circuit and allows the line relay armature to fall
back to its normal position.
The instrument at the sub-station may be of any of the well known forms
with the connections modified as follows:-
The wire to which the line indicator with earthed battery is attached to be
normally insulated, the other wire to have a connection through the switch-hook
to bell coils and earth, so that when the switch-hook is up the bell is out of circuit
and the two wires joined together through the receiver and secondary of the indi-
cator coil. As the switch-hook rises a momentary contact is to be made between
the A wire and earth, this contact being so arranged that the line is not earthed
when the telephone is replaced.
When the telephone is taken from its rest to call, the line is momentarily
earthed and line relay armature is attracted and held attracted by the retaining
coil. When the answering plug is inserted the cut-off relay is energised and
line relay is cut off and local circuit broken and lamp goes out. The answering
plug is then inserted in the jack of the line wanted and the ringing key depressed
or pushed over when it is mechanically held over and the sub-station bell is rung
at intervals, the circuit being from earthed generator, through interrupter, both
windings of electromagnet in such a way that the current effects neutralise each
other. One winding is connected to one wire of line and bell of instrument and
earth and the other through a resistance approximately equal to that of wire and
bell to earth the resultant current from difference of resistance not being sufficient
to release the control. When, however, the telephone of the sub-station being
called is removed from its rest the earth is removed so there is then a circuit
through one coil only and the control is released.
When the calling subcriber places the telephone on its rest, the earthed
bell is again connected up and the earthed main battery has a circuit through one
clearing relay to ring of answering plug, over B wire and through bell coils to
earth; and when the subscriber called places his telephone on its rest the main
earthed battery has a circuit through the other relay to the ring of the calling
plug and over the B wire through bell to earth. Either subscriber may, therefore,
place the telephone on its rest and the operator will not interfere, but both
telephones being placed on their rests, and therefore both lamps glowing, will
be a signal to the operator that the connection must be severed.
A modification of my invention consists in retaining the generators in the
instruments and line drop indicators in the exchange preferably in combination
with break jacks. The clearing system on the cords being as before described.
Dated this 19th of Cantanhas 1000
Improvements in Central Battery Telephone Exchange Systems.
I, WILLIAM AITKEN, 2, Oxford Court, Cannon Street, in the City of London,
Electrical Engineer, 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 my invention is to simplify and improve the efficiency of telephone

page_text: exchange systems, particularly those having the calling and clearing signals
energised by a central source of electricity in conjunction with the removing of
the telephone from the rest or switchhook of the instrument at the sub-station
and the replacing of the same.
In all known system having two clearing lamps per pair of connecting cords,
one to indicate the condition of the calling subscribers circuit and the other
to indicate the condition of the circuit of the subscriber with whom
he has been connected, it has been necessary to divide the connecting circuits
into two sections by condensers or translators so that as far as signalling
is concerned there are two distinct circuits, the condensers and translators, how-
ever, repeating the wave-like speech currents from the one circuit to the other.
The necessary retardation coils and relays being then fitted in conjunction with
the two circuits on each side of the condensers or translators.
The principal feature of my invention is that two distinct and individual signals
are obtained from the two subscribers lines connected without any division of
the connecting cord circuits whatever. There is, therefore no diminution in the
volume or intensity nor is the formation of the speech wave in any way interfered
with, which is the case in the before-mentioned systems, particularly when (as
is commonly the case) the translator is employed.
To attain the end described, I connect the two plugs j k of a connecting set
together with the usual listening and ringing keys & m respectively. Instead,
however, of joining the plugs tip to tip and ring to ring as is usual, I connect
the tip of one plug to the ring of the other and the tip to the ring
thereby crossing the cords. To the inner contacts of the listening key I
connect two suitable relays p q or indicators in series and so in bridge across the
cords. The relays preferably have lamps and battery s in the local circuits.
The main signalling battery s has one side connected to earth E2 and the other
to a point between each pair of relays 2 & g.
The line connections may be arranged in any of the well known ways, with
on line (the A wire) insulated at t or at the sub-station and the B wire con-
nected through the switch hook or to bell or to earth E, at C. An
insulated extension of the switch hook connects spring to earth momentarily
as the switch hook rises or falls. The line connections with calling apparatus
at the central are not essential to the working of my invention and as they may
be modified in many ways, I have not described them all but I have illustrated
two methods which are suitable for working with my invention.
When two lines are connected together for conversation plug j is in jack e or el
and tip is in contact with spring or a¹ and ring in contact with springs b
or b and plug kin jack or and the tip 1 in contact with spring 2 or 3 and
ring in contact with spring 62 or the calling relays f, f and lamps g, g¹ are
cut out of circuit by cut off relays d, d tongues breaking contact with
and tongues breaking contact with ds when the relays are energised.
The circuit then being from earth to central battery s through resistance . to
sleeves of plugs bush of jacks through coils of relays d, do, to earthed
side of battery .s.
The relay has retaining coil fl in parallel with lamp the circuit being from
earthed battery s coil f and lamp g in parallel, contacts d, of cut off relay
through pilot relay y to earth . The pilot relay has lampy and battery 2
in its local circuit.
The ring key m is shewn in the drawing, springs m², m³ breaking from the
springs m. m, when lever is pushed over and making contact with springs m,
m6, m being insulated and m" connected through generator o to earth E.
When lever is pushed towards listening key springs 25 break from 13
and make with 16 thus bringing into circuit telephone secondary of induction
coil with the primary microphone and battery.
When the telephones V V are off their rests the earthed bells t, w¹ are insulated
When the calling subscriber C places the telephone on its rest the earthed

page_text: bell is again connected up and the earthed main battery s has a circuit through
one clearing relay springs of listening key to ring of answering plug
spring b of jack cover B wire and through bell coils t to earth, relay p is there-
fore energised and tongue p attracted against contact p thereby completing
circuit of battery s through lamp r, tongue p₁ is attracted away from contact ²
thereby preventing the circuit of battery s being completed through the tele-
phone of the called subscriber.
When the called subscriber D places his telephone V1 on its rest to the main
earthed batterys has a circuit through the other relay g, listening key con-
tacts, to the ring of the calling plug, spring 2 of jack and over the B1
wire through switchhook & contact w¹ through bell w¹ to earth. The relay
closing the lamp l circuit, at q¹, q2 and cutting the line circuit at 3. Either
subscriber may, therefore, place the telephone on its rest and the operator will
not interfere, but both telephones being placed on their rests, and therefore both
lamps glowing will be a signal to the operator that the connection must be severed.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed I declare that what I
claim is-
(1) A telephone system having two clearing signals for each pair of cords, one
identified with the calling subscriber's circuit and the other identified with the
called circuit, without the division of the circuit into two sections by condensers,
translators or the like, substantially as described.
(2) Two relays in series across a pair of connecting cords with an earthed
central battery connected to the junction between the two, the conductors of the
cords being crossed so that the tip of the one plug is connected to the ring of the
other, substantially as described.
(3) Two relays in series across a pair of cords in combination with a central
battery each having contacts which break the line circuit beyond the relay being
operated so that the battery circuit cannot be completed over the line connected,
substantially as described.
(4) A telephone system with instruments at the sub-station having normally
one line insulated and the other earthed through the call bell in combination
with two relays in series across the cords operating two clearing signals all
energised from a central battery, the cord conductors being crossed so that one
sub-station connected energises one relay and the other sub-station energises the
other relay when the telephone is placed on its rest, substantially as described.
Dated this 12th day of June 1900.
WILLIAM AITKEN.