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Патент USA US2114253

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April 12, 1938.
w. v. K. LARGE ET AL
5 Sheets-Sheet 1
Filed Oct. 29, 1936
April 12, 1938. '
w. v. K. LA'RGE ET AL
2,114,253 ‘
‘Filed Oct. 29, 1936
5 Sheets-Sheet 2
llvmvmns: W VKLARGE
3 (Wit/QM
April 12, 1938.
Filed 001:. 29, 1936
5 Sheets-Sheet s
Q205. 3‘
Apgil 12, 1938.
w. v. K. LARGE‘. ET AL
Filed Oct. 29, 1956
5 Sheets-Sheets
1 1K131
(‘J-m. /
W L/K’.
Patented Apr. 12, 1938
Wayne V. K. Large, Hollis, and George A. Locke,
assignors to Bell
Glenwood Landing,
Telephone Laboratories, Incorporated, New
York, N. Y., a corporation of New York
Application October 29, 1936', Serial No. 108,154
7 Claims. (01. 178-2)
basis, that is, it is more particularly intended for
This invention relates to switching and ex
use in small o?ices where the number of operé
change circuits for telegraphy.
An object of the invention is to improve and ators does not ordinarily exceed three and where
simplify manual exchange circuits; to improve the ultimate number of lines terminating at the
5. the operation thereof and to make the cord circuit
and supervisory equipment interchangeably oper
able with a variety of types of lines under a variety
of conditions.
A feature consists of relays in a cord circuit
which are connected with battery instead of
ground at the arti?cial line to provide a marking
holding effect through their bias windings when a
spacing signal is transmitted into the “apex” con
nection. This eliminates the need for an anti
The desirable feature of home and team opera
tion is provided whereby a call may be answered
and supervised by more than one operator _ f‘
The physical appearance and location, ofuj‘the
various elements of the switchboard, including
jacks, key-shelf arrangement, etc., may bevaried
local loops and lengths of loops will therefore have
to ?t circumstances. One switchboardshowing
the physical arrangement which may be conven
iently employed is disclosed in the patentQof
Burgess and Knowlton, No. 2,037,193, granted
the same switchboard termination except for the
value of whatever current regulating resistance
at the central o?ice is concen-‘
15 kick-off network at the central o?ice end of the
may be necessary.
A further feature is that a single cord circuit is
20 universally utilizable for interconnecting short
subscribers’ lines, toll lines to other exchanges
and long subscribers’ lines including long line
equipment. In combination with this feature is
the feature that the supervisory equipment is in
corporated in the cord circuit rather than in the
line circuits. The selectors required for toll line
supervision and the differential relays needed for
local supervision are in the cord circuit. Al
though this increases the amount of equipment in
the cord ‘circuit, it reduces the amount of equip
ment required in the subscriber’s line circuit, the
toll line circuits and the toll subscriber line cir
A further feature is that the toll line circuit is
so designed as to be slow to operate on calling
signals, which eliminates false toll line call signals
due to short impulses.
A further feature is that a permanent open
40 trouble condition upon the toll line causes a signal
indication at the exchange.
A further feature is that of automatic?ashing
recall signals in connection with local subscribers’
lines as well as with toll subscribers’ line and toll
trunk lines.
A further feature is that certain well-known
unattended as well as attended subscriber equip
ments may be utilized on subscribers’ lines as
well as subscriber and toll lines.
As in the case of certain previous telegraph
switching arrangements, regenerative repeaters
may be utilized in the cord circuit by a simple sub
stitution‘for the non-regenerative repeaters more
usually employed.
o?ice is not to be in excess of about eightyto one
The switchboard is designed on a non-multiple
trated in or associated with the cord circuit; ‘ The
cord circuit includes various keys. The general 20
functions of the various keys associated with the‘.
cord circuit (Figs. 4 and 5) may be outlined as
Typing key TK is a locking key and when operl
ated in one position connects the operator’s cir 25
cuit to the cord with which it is normally associ
ated; when operated to the other position it con
nects the cord circuit to an operator’s circuit to
the right or the left.
Key RC (Fig. 5) when operated to the left 30
transmits a ten-second open signal to a circuit
connected to the plug 6 and supplies a holding
circuit for a circuit connected to the plug ll; when
operated to the right with a calling cord plug 6,
connected to a subscriber ringing current is trans 35
mitted to the subscriber's line connected to‘the'
plug 6 and holding battery is connected to acirv-l
cuit connected to the plug 4; when the“ cord plug
6 is connected to the toll line and the key RC is
operated to the right for a couple of seconds a toll 40
call signal is transmitted and the circuit con?‘
nected to the answering plug 4 is held closed;j'and
when the calling plug 6 is connected to atoll line
and key RC is held operated to the right for seven
secondsv until the cord lamps ?ash a recall signal 45
is transmitted over the toll line and‘ any circuit
connected to the answering plug 4 is held closed. ‘
The splitting key SK may be operated‘ either to
the right or the left to connect the operator’s
teletypewriter to a circuit connected either ‘to the
answering plug 4 or calling plug 6 and the circuit
in the opposite direction is held closed.‘ ‘ '
The ringing key RK when operated to the'left'
with a typing key operated supplies-ringing cur-7
rent to the circuit connected to the plug 4 and‘
holds the circuit connected to the plug 6 closed;
When the answering plug 4 is connected to a
toll line with a typing key operated and the ring
ing key is operated to the right for two- seconds a
break signal effective as a toll call on a toll line
is transmitted; when operated to the right under
similar conditions for seven seconds until the cord
lamps ?ash a recall signal is sent to the toll line
and the circuit connected to plug 6 is'held closed.
When no operator is using a position the key
K may be operated to disconnect ground from
both of its contacts which prevents unnecessary
current ?ow and power consumption during idle
Conventional features which would be well un
derstood by those skilled in the art, such as fuses,
test jacks, current limiting resistances, power
supply connections, night alarm circuits, etc., are
25 either omitted from the description in order to
simplify the disclosure of the more fundamental
features or disclosed only fragmentarily and in
In the accompanying drawings:
Fig. 1 indicates how the circuits of the various
sheets ?t together for convenient description;
Fig. 2 shows a simple form of subscriber’s line
and station circuit;
Fig. 3 illustrates diagrammatically one terminus
of a toll line;
Figs. 4 and 5 together diagrammatically illus
ing key TK is now operated to home which ex
tends the subscriber’s circuit through the polar
ized relay PR and sending contacts of the oper
ator’s machine which enables the operator and the
the information that a connection to a local sub
scriber is Wanted. the operator connects the call
ing plug 6 of the cord circuit to the jack of a sub
scriber’s line similar to that of Fig. 2. The sleeve
circuit causes the relay SC to operate but the
relay MC is a marginal relay and does not oper 20
ate because of the resistance 5 in the ground con
nection of the sleeve. Because the line of the
called station is open at the subscriber’s station
the differential relay DC operates and causes the
cord lamp CL to light and operates relay FC to 25
hold the calling subscriber’s line closed. The op
erator rings the called subscriber by moving the
key RC to a position corresponding to the right
on the drawing. The key has a contact to main
tain the communication circuit towards the sub 30
scriber making the call. Moreover after the re
lease of the key and inasmuch as the relay R op
erates and locks operated under control of the
relay DC‘, and. causes the relay FR to operate, the
line of the subscriber making the call is closed 36
from the left lower normally made contact of
trate the equipment of one cord circuit and the
key RC to battery on the right-hand make con
equipment of one operator’s position together with
tact of relay C through the inner upper contacts
of relay FR. The line of the calling subscriber is
also closed and 20-cycle ringing current is sup 40
various interconnecting keys;
the armature thereof is operated to the left. The
ring side of the subscriber’s line extends over the
back contact of relay MA, make contact of relay
SA, to battery on the left armature of relay C.
The differential relay DA is included in both
sides of the line and does not operate. The typ
subscriber to intercommunicate. Upon receiving
The remaining elements of the system will ‘be
su?iciently understood by reference to the follow
ing outline of operations in which the methods of
making, establishing, and terminating calls be
tween various types of lines will be described in
20 detail.
lay H, back contact of relay T, through the upper
Winding of relay RA to the armature of repeater
relay RC and thence to negative battery When
Fig. 6 illustrates the line termination equip
' ment and repeater of a subscriber’s line provided
with long line equipment commonly referred to
as a toll subscriber’s line circuit for differential
duplex operation;
Fig. '7 illustrates a subscriber’s station to be
connected to Fig. 6;
Fig. 8 illustrates a modi?ed arrangement of
plied from a source of ringing current ‘I over a ' "
make contact of relay FR to the tip of the called
line which causes the ringer l to be actuated.
The called subscriber answers by actuating the
key 3 thereby applying power to his teletype 45
writer motor (through contacts and mechanism
not shown) and closing the line. When the line
closes the differential relay DC is deenergized and
the lamp CL goes out. All supervisory lamps are
now extinguished and the differential relays in
each side of the cord circuit do not operate as the
subscribers communicate. The operator may
monitor and then retire from the circuit by re
storing the key TK to the normal position.
tip side of the subscriber’s line Fig. 2. The tip
of the line is grounded at the subscriber’s station.
Recall or disconnect signals from a local sub
Consequently, no current flows in the line when
it is idle. In order to make a call the subscriber
operates the power switch 3 which closes the loop
In order to signal the operator a subscriber may
momentarily open and reclose the power switch
3. For obvious reasons this causes the differen 60
tial relay DA or DC associated with the line to
Fig. 6 adapted for two-path polar operation; and
Fig. 9 illustrates a subscriber’s station to be
connected to Fig. 8.
Connection of one local station to another local
In the idle condition the subscriber’s circuit
includes ringer l in series with a condenser in the
and shunts the ringer. The current ?owing
through the loop causes the relay A to operate
and light the line lamp LL.
To answer the call the operator places the plug
4 in the jack of the subscriber’s line which ‘opens
the circuit of the relay A and extinguishes the
lamp LL. The sleeve of the cord is connected
through a resistance 5 to ground. The relay SA
is operated over the sleeve circuit but the marginal
70, relay MA is not operated. The operation of re
lay SA causes relay C to operate which closes
battery supply to the contacts of the’ repeater
relays RA and RC.
The subscriber’s line now
extends from the tip of the plug 4 through the
75 make contact of relay SA, back contact of re
operate which lights the associated cord lamp
AL or CL and also causes the relay FA or F0 to
operate. The operated one of these relays locks
up. Assuming the relay FC to operate, for ex 65
ample, the locking circuit extends from battery
over back contact of relay FR, winding of relay
FC, the make contact thereof through the back
contact of relays H and T and thence to ground
on the upper inner make contact of relay SC. 70
When the line circuit is closed again the particu
lar relay DA or DC which has been operated. re
leases and removes the ground connection from
the lighted lamp AL or CL. However, the locked
up relay FC supplies a periodically interrupted 75
ground to the lamp which causes it to ?ash until
the operator operates a typing key, such as key
'I'K, to the left to connect her machine to the
recalling line which causes the operation of the
Cl relay H or the relay T to release the relay FC and
extinguish the lamp CL.
For a disconnect signal the subscriber opens
the power switch permanently which operates the
differential relay DA or DC nearest his line which
10 causes the associated lamp AL or CL to light and
remain lighted. Although the relayFC operates
and supplies interrupted ground to the lighted
lamp it does not flash because a steady ground
connection is also supplied from a lower make
contact of whichever relay DA or DC happens to
be operated.
Connection of a local line to a toll line
The operator receives a call from a local sub
scriber as previously described and connects the
calling plug 6 to the toll line jack 8, such as shown
in Fig. 3. The sleeve of the toll line jack is
grounded with no series resistance and this causes
both the relays SC and MC to operate. The relay
MC‘ short-circuits the upper winding of the relay
DC and connects the ring side of the plug 6
through the winding of the relay ST to negative
battery. The relay MC also disconnects the lamp
CL from its path to the winding of relay FC
and connects it over a path through the back
contact of the relay ST to the left brush arm of
the supervisory selector SEL. The relay SC closes
the tip» of the transmission path from the toll
line 9 through the make contact of the relay MC
and a make contact of the relay SC, which is now
operated, over contacts of the key RC to the re
peater Ra, R0 in the cord~ circuit. The operator
calls the distant office by operating the key RC
to a position corresponding to the right in the
drawing for about two seconds. This opens the
toll line but holds the communication circuit
closed towards the answering side of the cord.
At the distant exchange the line is terminated
in a toll line circuit similar to that of Fig. 3 or its
equivalent. The line relay L releases and the re
lay TA which normally stands with its armature
on its left-hand contact is operated to its right
hand contact after the current in the upper
winding has charged the condenser l 0 sur‘?ciently
so that the current in the lower winding takes
control of the armature. The object of this con
denser and winding arrangement on the relay
TA is to delay the operation of the relay TA so
that short line interruptions of less than about
one second will not cause a false call upon the
line. Operation of relay TA to its right-hand
contact puts ground upon the lead II extending
to the toll line lamp TL thereby causing that
lamp to light. The distant operator connects an
60 answering plug 4 into the jack of the toll line
thereby opening the circuit of the lamp TL and
extinguishing the lamp and extending the com
munication circuit into the cord of the distant of
?ce from a toll line connection. Inasmuch as re
lays MA and SA at the distant station will both
operate, the communication circuit will proceed
from the tip of the plug and jack through a con
tact of relay MA shunting the differential relay
DA over the upper make contact of relay SA, a
back contact of relay H, a back contact of relay
T and through the winding of repeater relay Ra
to the armature of repeater relay Rc. As will be
understood from the previous description the dis
tant operator may operate a typing key TK and
connect the cord circuit teletypewriter for com
munication and will thereafter proceed to ex
tend the call through the station as may be de
Transmission and reception of recall and discon
nect signals over a toll Zine
Returning now to the central of?ce originating
the call and assuming that the operator wishes
to recall the operator at the distant central of
?ce, this will be accomplished by operating the 10
key RC to a position corresponding to the right
on the drawing until the cord lamp CL ?ashes.
This will occur in about ?ve or seven seconds after
which the key should be released. The operation
at the station originating the recall signal is that 15
the relay L (Fig. 3) releases and one second later
the relay TA operates to the right. This supplies
ground to the ring of the plug and jack, thereby
causing the relay ST to operate and connect the
stepping magnet ROT on the selector SEL over a 2.0
contact of relay ST to a source of interrupted
ground operating at about sixty interruptions per
minute. The selector steps up and when the
right-hand brush arm thereof reaches contact
No. 6 the relay RD operates and short-circuits 25
the contacts of the key RC which were opening
up the line, thereby reclosing the line, reoperat
ing the relay L and releasing the relay ST. The
selector remains on the sixth contact and the
lamp CL continues to flash because it is con-' 30
nected in a circuit extending from battery
through the lamp CL, a make contact of relay
MC, a back contact of relay ST, left-hand brush
arm of selector SEL to interrupted ground. The
lamp continues to ?ash until the operator con 35
nects her teletypewriter instrument to the circuit
by means of a typing key TK.
Operation of the
typing key closes the circuit through the relay
RR which upon operating closes the circuit which
extends from battery on the release magnet RLS 40
of the selector over the make contact of the relay
RR to ground, thereby causing the selector to re
turn to normal. The same ground which operates
the release magnet RLS also operates the relay
RR which again opens the ground connection to 45
the release magnet and thus makes it possible for
an operator to receive a recall or disconnect sig
nal from a toll line even though the typing
key is already operated.
The transmission of a disconnect over a toll 50
line is accomplished by operating the key RC‘ to a
position corresponding to the left in the drawing
until the cord lamp CL lights steadily. Since the
relays SC and MC are operated the operation of
the key terminates the cord circuit of the re 55.
peater and opens the circuit towards the toll line.
The release of relay L, operation of relay TA to
the right and operation of relay ST causes the
selector to step and inasmuch as the circuit of
the relay RD is not completed on the sixth con 60.
tact of the selector the selector continues to
step until it reaches the tenth contact at which
time relay RD operates. The cord lamp CL be
comes continuously lighted over a circuit extend
ing through the left-hand brush arm of the se
lector to ground upon the tenth contact and con
tinuously lighted until it is extinguished by re
moval of the plug cords from the associated
jacks, whereby the upper of the two off-normal
contacts of the selector closes a circuit through 70?
the release magnet RLS to a back contact of the
relay C which is released when the cord is idle.
The reception of recall and disconnect signals
over a toll lineeis as follows: Inasmuch as the line
is opened the relay TA is operated to the right 15
and the relay ST in the cord is operated.
causes the selector to step to a position corre
sponding roughly to the length of the open sig
nal after which release of the relay ST causes
the signal lamp to appear. In the case of a re
call signal the lamp is extinguished by operating
the typing key TK and in the case of a discon
nect signal the removal of the plugs from the
jacks extinguishes the lamp.
Sending a recall signal from the answering end
of the cord circuit
When the plug 4 is connected to a toll line a
recall signal may be transmitted to a distant
15 central o?ice by operating the recall key RK to
the right with the operator’s teletypewriter cir
cuit connected to the cord by the throwing of the
key TK, and holding the key RK in the operated
position until the cord supervisory lamps flash.
20 Battery on the right-hand contact of the key
RK maintains the circuit toward the plug 6 closed
and the left-hand side of the key interrupts the
communication circuit toward the plug 4. When
the selector reaches the sixth contact the right
25 hand brush arm thereof causes the relay RD to
operate and shunt the left-hand contact of key
RK which is opening the line, thereby closing up
the line and reoperating the relay L in a toll
line circuit. The relay operation is otherwise
30 generally the same as previously described in con
nection with sending a recall signal over the toll
line by means of key RC except that the opera
tions take place with respect to the other end
of the cord.
Ringing subscriber an answering side of cord
Provision is made for ringing on a subscriber
line from the answering side of the cord, that
is, the side connected to the plug 4. This is ac
40 complished by connecting the operator’s machine
to the circuit by means of the typing key TK and
then operating the key RK to the left. This
causes ringing current to proceed from the ring
ing generator ‘I over the tip‘ side of the sub
45 scriber line and at the same time the battery on
the operated contact of key RK maintains the
communication circuit closed toward the plug 6.
Under this condition upon ?rst connecting the
plug 4 to the subscriber’s line the relay DA op
50 erated and caused the relay FA to operate. Like~
wise, a typing key TK was operated which opens
the locking path for the relay FA so that when
the subscriber answers the relay FA will release.
In all cases where a cord is connected to an
55 idle subscriber line it is necessary to hold the cord
repeater closed on that side until the subscriber
answers in order that the subscriber’s machine on
the other side of the cord will not run open. The
upper contacts of relay DA provide this holding
60 path with the typing key either operated or non
operated and open the path as soon as the sub
scriber answers. In addition, when a subscriber,
connected to a toll line, disconnects, provision
must be made to insure that the open condition
is not transmitted through the cord to the toll
line. The upper contact of relay DA also per
forms this function.
Connection of a toll line to a local line
The toll line call is acknowledged by connect~
ing the plug 4 to the jack of the calling line
which arranges the side of the cord next to the
plug 4 for a toll line connection. The calling cord
is connected to the subscriber line jack by means
75 of the .plug 5 and the sideof the cord adjacent
the plug 6 is then arranged for a local connection.
A ringing signal is sent to the subscriber in the
same manner as previously described in connec
tion with a local to local connectionv and when
the subscriber answers the cord lamp is extin
guished. Supervisory signals are sent from and
received in the cord circuit in the same manner
as previously described.
Toll line to toll line connection
When a through connection is to be established
the marginal sleeve relays MA and MC at both
ends of the cord operate and thereby arrange the
cord for toll line connection on the answering and
calling sides. Any incoming supervisory signals, 15
such as recall and disconnect, operate both super
visory lamps and are repeated through the cord
repeater. These signals are extinguished by mo
mentary operation of the teletypewriter key TK.
Toll, line subscriber connections—-Geneml
In furnishing service to subscribers it occasion
ally happens that certain subscribers are too far
from the exchange o?ice to be furnished service
over a simple loop. For example, with certain 25
types of cable the maximum physical mileage of
cable which may be included with satisfactory
operation is of the order of forty miles. In such
cases service may be furnished to such subscrib
ers over line circuits operating on an upset du
plex, two-path polar, or differential duplex basis.
A terminating circuit suitable for use with such
a toll line is required at the central oil‘ice in ad
dition to the toll telegraph repeater. There is
described herein and illustrated in Fig. 7 the
equipment for cooperating with such a toll line
subscriber’s circuit as shown in Fig. 6.
This ar
rangement is adapted for diiferential duplex op
eration. With a slight modi?cation, namely, the
utilization of .a single additional armature and‘ 40
contact on a relay as will hereinafter be de
scribed, the transmission may be accomplished
by a two-path polar circuit as shown in Figs. 8
and 9.
Toll subscriber line equipment for differential
duplex operation
Consider now the operation of a cord circuit
such as shown in Figs. 4 and 5, a subscriber’s line
termination such as shown in Fig. 6, and a sub
scriber’s station equipment such as shown in Fig.
7 connected to the line termination equipment
by means of the line l3.
To make an incoming call the subscriber closes
switch II. This supplies power to the station 55
equipment and causes relay I2 to be operated.
This connects marking battery to the line 13. In
this case marking battery is arbitrarily chosen as
positive battery. In Fig. 6 the polar relay E is ap
erated by positive potential upon the line it and 60
the ordinary relay D is also operated. Relay E
operates relay F which operates relay C6. Relay
C6 closes a circuit to ground to operate the relay
J and to cause lamp TLB to light under the con
trol of .a contact on the line jack l6. Relay J re
places the positive battery on windings of relays
D and E with negative battery over a circuit ex
tending from negative battery over the upper
make contact of relay J to winding of relay E.
Relay C6 also connects line lead l3 to the re
peater R over conductor 14 which closes the loop
and applies marking battery to the line relays of
the repeater. A circuit is then closed through the
upper winding .of relay B over the back contact
of relay A6, thusoperating relay B to close con 75
tact l5 to maintain the operating circuit for relay
F which is a slow release relay.
When the operator answers she places the plug
4 into the jack IS with the same effect in the cord
circuit as in answering a subscriber line call.
This also prepares a path for the relay A6 over
the jack terminals. The termination circuit from
the repeater R is now closed to the tip of the plug
and cord and the lamp TLS is extinguished. Com
ll) munication may take place between the sub
scriber station and the operator or another sub
scriber. Relay B follows the teletypewriter sig
nals but relay F is slow to release and relays C6,
D and J remain operated.
Relay B follows the signals and supplies ground
and open-circuit alternately to the ring of the
jack to balance the relay DA or DC in the cord
circuit. In this manner signal transmission is
prevented from causing operation of relay DA or
Consider now a break signal from the sub
scriber at the station of Fig. '7. This opens the
path through the relay B which causes the relay
B to open the contact I5 for a time sufficient
to allow relay F to release. This releases relay
C6. This connects the line I3 over a contact of
relay J to ground by way of a back contact of
relay G6, a front contact on the lower armature
of relay J, through the high resistance I611. The
30 charge stored in the capacity of the line passes
through the high resistance l?avbefore the slow
release relay J releases. Upon release of the relay
J the operating path for the relays D and E is
transferred back to the line circuit 13 but inas
35 much as negative or spacing potential is now ap
plied to the line circuit the relay D is held op
erated but relay E remains released during the
continuance of the break signal. Upon comple
tion of the break signal marking potential is
again applied to the line [3 which holds relay D
operated, causes relay E to operate, which causes
relay F to operate, which reoperates relays CB
and J to restore the transmission circuit, after
which the relay F is held operated by the relay
B. Relay B is reoperated to close contact l5.
Consider now a break signal originating in or
beyond the cord circuit of Figs. 4 and 5. Relay
B opens contact l5, which releases relay F, which
releases relays C6 and J. Relay J connects the
operating path for relays D and E to the line l3
but inasmuch as marking potential is applied
from the line 13 during the break period the relay
E is operated, which in turn reoperates relays F,
C6 and J. Upon reoperation, relay J causes relay
55 E to release by virtue of negative battery sup
plied locally from the source I‘! over a back con
tact of relay C8 and front contact of relay J. If
the break signal is continued beyond this time,
this cyclic operation and reoperation may con
60 tinue as relay F again releases upon the release
of relay E because relay B maintains contact [5
open and, therefore, the break signal condition
is continued until the loop circuit is reclosed to
operate relay B which reoperates relays F, C6
and J.
Consider now a disconnect signal transmitted
into the cord circuit of Figs. 4 and 5 from the sta
tion of Fig. 7. The attendant at the station of
Fig. 7 opens the switch II which sends an open
70 signal through the repeater R to the cord circuit,
thereby releasing relays B and F, which there
upon releases relay CB. Upon release of relay
C6 and during the holding time of relay J the
charge on the line will be discharged to ground
the high resistance 16a. Upon release
of relay J the relay‘ D will release and cause the
operation of relay A6 over a circuit from battery
through the winding of relay A6, a contact upon
jack E6 to ground upon the back contact of relay
D. When relay A6 operates it connects ground to
the ring of jack to operate the differential relay
DA or DC in the cord circuit because at this time
the tip lead through the differential relay is open.
Relay A6 also closes the loop circuit to the re
peater from a source of plus 130 volts over an 10
upper make contact of relay A6 through the up
per winding of relay B and conductor Ha to the
repeater. The lighting of the disconnect lamp in
the cord circuit in the manner previously de
scribed will call the attention of the operator to 15
the disconnect signal and appropriate action will
be taken as previously described.
If the subscriber station attendant disconnects
during the time a break signal is being trans
mitted from the cord circuit, relay B will already 20
have been released and the release of relay D will
cause the operation of relay A6. Since relay A6
upon being operated maintains ground on the
ring lead to the jack and plug of the cord circuit,
a disconnect signal will be produced.
Consider now the transmission of a recall sig
nal from the station of Fig. 7. The line circuit
is temporarily opened as in the transmission of a
disconnect signal which causes the release of
relay B to open contact I5, and the release of re 30
lays F, C6 and J so that relay D is connected to
the line l3 and is released, which connects ground
over the jack to operate the relay A6, which con
nects ground to the ring of the plug and jack of
the cord circuit. When the recall key I8 is re 35
leased, relays D and E reoperate and relay E re
operates the relay F, which in turn operates re
lay C6 to close the line circuit and also reoperates
relay J and the repeater R acts over the con
ductor to reoperate relay B. When the line cir
cuit is reclosed the relay B holds the relay F
reoperated. Inasmuch as relay D is operated re
lay AB is released which removes the ground con
nection from the ring lead to the cord. The
momentary connection from ground to the ring 45
lead of the cord with the tip of the cord open
causes the differential relay DA or DC of the
cord circuit to operate. Upon release of the dif
ferential relay when the cord circuit is again
closed the cord circuit supervisory lamp AL or CL 50
will ?ash in the manner previously described.
The recall signal from the station of Fig. '7
may be transmitted and indicated correctly even
though a break signal is being transmitted from
the cord circuit or from a station beyond the 55
cord circuit.
Consider now the operation in calling the
subscriber’s station. The plug 6 of the cord cir
cuit Will be inserted in the jack I6. Relay A6
will be operated by virtue of ground at the back 60
contact of relay D. Relay A6 connects ground
to the ring of the jack and plug to operate the
differential relay in the cord circuit and hold the
cord supervisory lamp lighted.
The operator
transmits ringing current in the manner previ 65
ously described from the cord circuit over the tip
of the plug and jack through contacts of relays
A6 and C6 to operate the relay H6 in series with
a condenser to ground. In operating, relay H6
operates relay J and connects the ringing cur 70
rent generator ‘I over the contact of relay H6
and contact of relay J and back contact of relay
C6 to the line I3 which causes the ringer l at
the subscriber’s station of Fig. '7 to operate.
Upon cessation of the ringing current relay H6 75
releases and during the time required to allow
slow release relay J to release the resistance Ilia
discharges the line and prevents momentary
operation of relays D or E when they are re
connected to the line.
When the subscriber answers the relays D and
E operate, relay E operates relay F, which oper
ates relay C6, which closes the line up to the
repeater R and operates relay J, which closes a
10 holding path for relay D over the back contact
of relay A6, which was released when relay D
operated upon the closure of the line circuit.
Upon the release of relay A6 it closes the tip of
the plug and jack through the upper winding of
relay B to the repeater R and. opens the ground
connection from the ring of the plug and jack
to extinguish the supervisory lamp AL in the
cord circuit.
Two-path polar toll subscriber line
For two~path polar operation the subscriber’s
station will be in accordance with Fig. 9 and the
line circuit in accordance with Fig. 8. Operation
of relay H2 in Fig. 9 connects the subscriber’s
set for operation over a two-wire line comprising
a receiving leg l3 and a sending leg BA. The
ringer I, the sending relay 20, the receiving
relay 2!, the sending contacts 22, the recall key
it’, the power supply switch II and other equip
ment will be generally the same in Fig. 9 as in
so Fig. '7.
Consider now Fig. 6 in comparison with Fig. 8.
It will be seen that Fig. 8 includes two additional
leads connected to one armature and one con
tact respectively of relay C6. These leads are in
cluded in the transmission conductor 13A. A
resistance 24 is connected from the inner lower
make contact of relay C6 to the outer lower
armature thereof. Except for these differences,
Fig. 8 is the same as Fig. 6. When relay C6 is
operated its armature closes the transmission
conductor [3A and when relay C6 is released
the conductor I 3A is opened. The repeater R
of Fig. 8 is generally similar in function and
_ mode of operation to repeater R of Fig. 6 except
that it is designed for two-path polar operation.
It will be seen that the transmission conductor
I8 is extended to the repeater R in Fig. 8 through
the transmission conductor I4 in Fig. 8 in the
same manner as in Fig. 6 and that it extends
through the windings of relays E and D in Fig. 8
over the back contact of relay C6 and back con
tact of relay J in the same manner as in Fig. 6.
Consequently, a subscriber’s line equipment may
be furnished so that by leaving the extra arma
55 ture and contact of relay C6 idle it may be
employed for differential duplex transmission as
in Fig. 6 or by connecting up the armature and
contact to the line of conductor I3A it may be
used for two-path polar operation as in Fig. 8.
When relay C8 is released under the condition
of two-path polar operation the line receiving
relay of the repeater R is held to its spacing con
tact by negative battery supp-lied from the source
I‘! through resistances 23 and 24 over the back
65 contact of relay C6.
The operation of the recall key [8 at the sub
scriber’s station connects the line l3 to the line
18A at the subscriber’s station and isolates them
from the transmission circuit at the subscriber’s
70 station. Under this condition when resistance
[8a of Fig. 6 discharges the line as hereinbefore
described it discharges both conductors l3 and
MA and thus prevents false operation of relay
E in the case of transmission of recall signals
75 or ringing signals.
One other condition remains to be discussed;
this is the case known as upset duplex trans
mission. Marking battery on line 13 is negative
at the subscriber’s station of Fig. 8. Now refer
to Fig. 6. To make the circuit operate under
this condition it is necessary that the polar relay
E be connected reversely and that provision be
made to supply positive current rather than
negative to the relay E under the break signal
condition. To do this the upper end of resist
ance 23 may be disconnected from the negative
terminal of battery I‘! and connected to the posi
tive terminal of a grounded battery or source
(not shown).
It will thus be seen that essentially the same
circuit with slightly different wiring will serve
to terminate subscribers’ toll (repeatered) lines
working on the differential duplex, upset duplex,
or two-path polar basis.
In addition to attended stations a subscriber
may be provided with unattended service which
enables him to receive messages when no one is
present at the station by utilizing a subscriber’s
line and station, such as shown in Fig. 3 of the
application of Singer, Serial No. 89,828, ?led July 25
9, 1936 to which speci?c reference is made as a
part of the present disclosure.
To utilize a regenerative repeater in the cord
circuit as hereinbefore mentioned may be done;
the relay Ra and its contacts are removed from 30
the circuit and its two leads on the left of its
winding transferred to a regenerative repeater
such as shown in Fig. 2 of Vernam Patent
1,619,897, March 8, 1927; relay Re and its con
tacts are removed and its two leads on the right
of its winding are also transferred to the re
generative repeater; the inner left armature of
relay C may control the motor start circuit of
the regenerative repeater. The four transmis
sion leads and the motor start lead. are so shown 40
in the Vernam patent, although of course, in the
present arrangement the regenerative repeater
will start on open line and repeat open and close
signals rather than polar signals.
What is claimed is:
1. In a telegraph exchange system, a link cir
cuit for manual lines, a differential relay in each
end of said link circuit having opposing wind
ings for the flow of signaling currents, a single
conductor transmission line to- which an end of
said link circuit may be connected, a relay in
and controlled by signal current traversing said
transmission line, a path controlled by said relay
extending to said differential relay over a termi
nal of said link circuit whereby current is sup
plied to said di?erential relay in one winding to
balance the signal current in another winding
and prevent the operation of said differential re
1ay by signal current.
2. In a telegraph manual exchange system, a 60
link circuit, an operator’s circuit connectable at
will to any one of a plurality of link circuits, a
ringing key individual to a link circuit and a
ringing key individual to an operator’s circuit.
3. In a telegraph manual exchange system, a
cord circuit including a cord lamp, two types of
line circuits to which said cord circuit is connect
able, a selector in said cord circuit, a relay selec
tively responsive dependent upon the type of line
to which said cord circuit is connected for con
necting said lamp to an energizing circuit di
rectly or under the control of said selector.
4. In a communication circuit, a selector, a key
under the control of an operator, means whereby
recall conditions established at a remote point 75
actuate said selector, a recall signal produced by
actuation of said selector to a given point, a re
lease winding for said selector, said winding be
ing energized by actuation of said key to a given
position, and means whereby if said key is already
operated to said given position prior to the actu
ation of said selector to said given position said
release winding is not energized.
5. A system according to claim 4, including
10 means whereby if said key is already operated
when said selector is actuated, release and reop
eration of said key energizes said release winding.
6. In a supervisory circuit arrangement for a
telegraphic line, a relay (A6) included in a path
15 closed at a jack when a cord circuit is connected
to said jack, another relay normally opening said
path when said line is closed for intercommuni
cation, a relay chain for actuating said relay
to maintain said path open upon change of po
larity of break signal length upon said line at a
distant point, means whereby said path is closed
upon an opening of said line of break signal du
ration at a distant point, and asupervisory signal
established by actuation of said ?rst named relay
by closure of said path.
'7. In a telegraphic exchange system, a cord cir
cuit, a selector therein, means for connecting said 10
cord circuit to single conductor or two-conductor
lines interchangeably, and means whereby said
selectors control the sending of supervisory sig
nals over said single conductor lines.
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