US1504296A - Telephone system - Google Patents

Description

m@ um, I www@ 5. E. WILLIAMS, JR., E''

TELEPHONE SYSTEM Filed May 14 1.921 6 Sheetf-Sheet 1 Am@ 'im m24@ v Lm@ S. E. WILLIAMS, JR., E? AL TELEPHONE SYSTEM Filed May 14 1921. 6 SheeS-Shee'i 2&2

OOOOOOO Aug., 1&2, 1924,. @5,504,296

S. E. WILLIAMS, JR.. ET AE.

TELEPHONE SYSTEM OOOO OGOOO S. ES. WILLIAMS. JR., ET AL TELEPHONE SYSTEM Filed May 14 1921 6 Sheets-Sheet 4 Au@ l2., 1924. 3,594,296

S. B. WiLLMS, JR., ET

TELEPHONE SYSTEM Filed May 14 1921 6 Sheets-Sheet 5 S. E. WILLIAMS, JR., ET AL Aug, m wm TELEPHONE SYSTEM Fileu May 14 i921 6 Sheets-Sheet 6 www F Q2 .i mw%)\ m www. w L@ p @am Sm OOOOOMIIIn h. oooooooonwlo. @nw IIHII. UNQ www g new OOOOOOQOMQ@ n www Patented fitug. l2, lQZdl.

SAMUEL B. WLLIAMS, JR., l? BROOKLYN, All?) EBWARD E. HINBCHSEN, 0F NEW YORK, N. Y., ASSIGNOR-S T0 TESTERN ELECTRC COMPANY, :ENCORCPOR-ATED, OIF NEX/V YORK, N. Y., A CORPORATION O33' NEW' TELEPHONE SYSTEM.

Application filed May lll, 1921.

T0 all fio/tom it may concern:

Be it known that we, SAMUEL B. Win-- LrAMs, J r., and EDWARD E. llnvnieiisnn, citizens of the United States, residing at Brooklyn, in the count-y of Kings, State of N ew York, and at New York, in the county of New York, State ot New York, respectively, have invented certa-in new and useful Improvements in rlelephoner Systems, of which the following is a full, clear, concise, and exact description. f

This invention relates to improvements in telephone systems and has particular reference to a private branch exchange sys tem which may be used in conjunction with either manual or machine switching central otlices.

An object of the invention is the provision ot an automatic switch wherein novel means are employed for preventing response oit the switch. to false impulses produced sometimes bythe accidental depression et the switchhook.

ln accordance with the above object, use is preferably made of a relay in the switch circuit the operation ot which is so controlled that when the lirst'oi a series ot impulses is trai'isniitted to Ya switch, said relay will prevent the stopping,` olt the brushes ci the switch until the second inipulse is received,y whereupon the relay opcrates to allow the switch to respond to said second and subsequent impulses.

Another object is to provide novel nfieans which will permit an attendant to secure 'a connection to a subscribens line through a connector switch on a call incomingfrom a cent-ral otlice even though said line be busy'.

A'it'urt-her object is the provision oit a. ringingl circuit for a connector switch wherein a ringing tone is transmitted te a calling subscriber when a called substation is being signaled and wherein a premature application ci' said ringing tone is prevented while the switch is being,l moved over terminals individual to subscribers lines in different groups.

@ther objects will appear in the Vcourse of the following description when taken in connection with the accompanying` drawings wherein Figures l tov 6, when taken together and arranged shown in Figure 7, diagi'vnmatically illustrate a preferred ein bodiment oit the inventive 1 Serial No. 469,650.

Briefly stated, the invention pro-vides a private branch exchange lin which line linder switches are employed for extending calling; subscribers lines over link circuits to selector switches. These latter switches have access to connectors for establishing calls between subscribers within the er,` change; and also to attendants and central ottice trunks, whereby subscribers may secure connection with an attendant or a direct connection to a. central ofce. The terminals assigned to the various connectors and trunks in the bank of each selector may be arranged in any desired manner, means being provided in the switch for stepping the brushes thereof over undesired terminals when seeking terminals individual to idle connectors, attendants trunks or central oflice trunks.

An incoming call from central oli'ice to a subscriber withinthe exchange is routed through the attendant who connects the central cnice trunk to an idle connector and then operates the latter by dial impulses to select a desired line.` lf this line is busy, the attendant may nevertheless obtain connection thereto by t-he operation of a key in the central oiiice trunk.

rin attendant may originate a call to the subscriber within the exchange or she may initiate a call to central otlice and, it desired, extend it to a station in the same manner that an incomingcall from the central otlice is extended thereto.

The trunks leading to the central otlice may terminate in a manual exchange or in a machine switching' office and, in the latter instance, provision is made whereby the attendant may have supervision over cert-ain connections such as when a toll call is initiated. For this purpose, use is preferably made of a` code switch, shown in Figure 6, which upon the seizure of ay central oflice trunk by a calling subscriber" establishes a condition whereby, when impulses are transmitted by said subscriber, said impulses will operate the code switch and be simultaneously repeated at the central oliice to actun ate the switches thereat. The code switch, in this operation, discriminates between the character ot calls initiated by subscribers by setting up certain conditions in the circuit of the switch in response to the in WiSe/S transmitted, 1f a-all iS such require supervision by the attendant, discrin'linating relays in the code circuit operate in response to the dial operations to effect a condition whereby a signal before the attendants position individual to the seized trunk will be opera-ted. On the other hand, if the call does not require supervision, the code switch Will nevertheless operate, but the discriminating relays Will fail to establish the condition Which causes the operation of the signal at the attendants position.

It is believed that the invention will noyv be fully understood from-the following detailed descriotion of the operation in establishingA various connections.

Assuming that the link circuit L, shown in Figure 1, is the rst idle linlt circuit to which the calling lines of a group have access, when a subscriber at substation A initiates a call, a line relay 100 individual to the calling line is energized over a path 1127 the outer extending from battery through the Windin of said relay, thc back contact and lefthant armature of cut-olf relay 101, the apparatus at substation A and the outer righthand armature and back contact of relay 101 to ground. rlhe energization of line relay closes a circuit for the relay 102 of the `line finder switch B associated With the vlink circuit. L, said circuit extending from grounded battery through the Winding of relay 102, the brush 103 of the line finder, back contact and inner lefthand armature of relay 104i, conductor 119, the front contact andarinature of line relay 100 and from thence over the common conductor 105 to ground at relay 106. The energization of relay 102 establishes an obvious circuit for sloiy to releaseV relay 107, whereupon an energizing circuit for the motor magnet 108 of the line iinder is closed, said circuit eX- tending from grounded battery through the Winding, arinatureand bach contact of the magnet 108, the inner 'left-hand armature and front contact Aof relay 102, the left-hand aig'n'iature and front contact of relay 107, brush 109 of the selector switch C and its associatedfnorinal contact, the back contact and outer left-hand armature of relay 1011 and the left-hand normal contacts of sloiv to release relay 110 to ground. At the saine time, a circuit is established extending from grounded battery through the left-hand wind of relay 111, the Winding of relay right-hand armature and back contact of relay 104, the front Contact and right-hand armature of relay 107, and from thence over the energizing circuit of relay 102 through the brush 103 to ground. Relays 111 and 112 energize, but the operation of relay 111 at this 'time has no useful function. The energiZ-ation of relay 112 dis-V connects the battery supply through the windings or" the line relay 113 from the brushes 114 and 115 of the line linder. The stepping magnet 108 is operated by the circuit described therefor and the brushes olE the line finder are stepped from their nor mal positions. Upon leaving these positions the operating circuits for relays 102 and 112 are opened at the brush 103 but said relays are maintained energized during the stepping operation of the line finder due to a holding circuit extending through the front contact and inner right-h and armature. of relay 102 to brush 110 of the line linder to back contacts of the line relays of the lines connected to terniinals over which said brush passes. The circuit of the stepping` magnet 108 being self-interrupting, the line linder Will continue to step as long as brush 110 encounters ground on the terminals over which it passes. Vylhen the terminal of the calling line is reached no ground will be found upon that terminal engaged by brush 116 due to the fact that the line relay 100 is operated. Relays 102, 111 and 112 will therefore release as the holding circuit for these relays is no longer closed. The release of relay 102 permanently opens the circuit of the stepping magnet 10S and the brushes of the line finder come to rest upon the terminals of the calling line. ist circuit is now established for the cut-oli' relay 101 of said line extending from grounded battery through the Winding of said relay, the sleeve brush 11iand its associated terminal and the back contact and outer lett-hand armature of relay 102 to ground. Relay 'lill operates and thereby opens the energizing circuit for relay 100 which then restores. The ground from the outer lett-hand urina ture and back contact oi" relay 102 etended to the test terminal 11S of the calling line and causes this line to test busy if engaged by the test brush ot a connector switch. The release of relay 112 establishes a circuit for relay 1123 traceable from grounded battery through the lettdiand Winding of relay 113, back Contact and outer left-hand armature of relay 112, brush lll and its associated teriniinil.` the calling` substation line circuit, the brush and its associated terminal, the inner left-hand armature and bacl-z contact and relay 112 and the right-hand Winding of relay 11R to ground. Relay 113 energizes in the circuit described therefor and establishes an obvious operating circuit for slow to release relay 110. Upon the energization of the latter relay, a circuit is closed for relay 10sL et;- tending from grounded battery through the right-hand Winding of said relay 101-h the outer right-hand armature and back contact of relay 102, the left-hand armature and front Contact of relay 110 to ground. The energization of relay 104i in thecircuit just traced disconnects the com ion lead 110 from the inner left-hand back contact of llo relay 104 so that a second call initiated in the group ot' which line A forms a part will be extended through the inner lett-hand armature and bach contact ot the relay 10ft of the next idle line finder to the normal terminal of said finder engaged by brush 103. The release of relay 102 at the time the brushes of the line finder engage the terminals ot the calling line also causes the release of relay 107, but, owing to the slow release nature of the latter relay, the circuits for relays 104, and 113 are established before relay 107 retracts its armatures. This is for the purpose of preventing premature release of the line linder as will be more i'ully understood in the course ot the iollowing description. A dial tone from the apparatus is now connected to the calling line through the brushes 121 and 122 of the selector switch and their associated normal contacts. Upon hearing this tone, the subscriber may proceed to dial the number desired.

A connection from a` subscriber at substation A to another subscriber within the pri- It will be assumed that the subscriber is in the lirst group and it will, therefore, be necessary to dial 8 as the first digit.

Before proceeding with the description of this connection, it is to be noted that, 'for purpose ol simplicity and economy or' space, several of the terminals in the ba' lr of the selector C have been omitted, es shown, there is provided a normal terminal followed by three terminals that are allotted for central office trunks. The next tr-o terminals are assigned to connectors employed in establishing connections between the two groups of subscribers within the exchanue. However, between these two sets of terr inals other terminals allotted 'for centul oilice selection may be provided and in accordance with the followingl description there are three more terminals to which central oce trunlrs may be connected. The system thus makes provision for sin central office trunks, the terminals tor three of which are shown. rlhe next two terminals shown in the selector banlr following those allotted to connectors areassigned to atten'dants trunlrs and the succeeding terminals, with the exception oit the last, are also allotted to the groups .of connectors ein pl'oved to establish connections within the exchange. The terminals of the two groups of connectors are 'preferably arranged alternately and provision is made whereby only an idle connector assigned to the group of lines in which the called line is located will be selected, the ter iinals ol1 the connectors ser viV g the other group ot lines being automatically passed over in the selection ol said idle connector. lt will be understood, ot course, that the number ot connectors and trunlrs to the central oil/ice depend solely upon the size ot the exchange and may vary without departing 'from the spirit or scope oll the invention.

Proceeding now with the description oi' the above noted connection and taking up the operation'itrom the point where relay 110 is operated by the energization o'li relay 113, a cir-cuit is now established from grounded battery through the resistance 126, the lett-hand winding1 of the stepping` relay 127, the brush 125, right-hand normal contacts of relay 128 and the right-hand armature and liront Contact of relay 110 to ground. Relay 127, however, does not operate in this circuit due to the ground extending :trom the right-hand armature or' relay 110 through the right-hand armature and t'ront contact ot relay 113, the outer right-hand armature and back contact of relay 129, the brush 12fl'to the lett-hand winding of relay 127. This ground short circuits the relay 127 and prevents the same from operating until the in'ipulse receiving relay 113 releases in response to the impulses transmitted trom the callingsubstation.

Upon the release olf relay 118 in response to the iirst impulse transmitted, relay 127 energizes and thereby establishes an obvious circuit tor operating slow to release relay 130. rlhe energization of the latter relay causes the operation of relay 129 to disconnect the brushes 121 and 122 of selector C from the remaining portion of the link circuit, the circuit for relay 129 being traceable from grounded battery through the lett-hand winding ot said relay, the lett-hand front contact and armature ol relay and the right-hand armature and liront Contact of relay 110 to ground. The right-hand contact o1 relay 113 is now connected, by the operation relay 129, directly to the resistance 126 instead of being extended through the brush 124c-= rlhe operation oit relay 130 also establishes an energizing circuit for relay 128 which extends trem grounded battery through the winding` of relay 128 and the right-hand armatures and front contacts of relays 130 and 110 to ground. However, relay 128 does not energize at this time due to a short circuit provided by ground at the lei'tehand armature of relay 127 and extending through the inner lett-hand armature and bach contact of relay 128. The circuit 4for motor magnet 131 of the selector C extends through the iront contact and inner leftllt) lli.

hand armature of relay 128, but inasmuch as this relay does not energize at this time it is apparent that the motor magnet will not operate to step the switch from its normal position in response to the first impulse transmitted. Thus relay 128 delays placing the operating mechanism of the selector switch under the control of the stepping relay 128 until the end of the first selecting impulse so that the switch takes its rst step in response to the second impulse of a series. Therefore, should a false impulse be transmitted to the switch by the calling subscriberv accidentally depressing the switch hook, or otherwise, the switch will not respond to this impulse nor to any other false impulsetransmitted before the dial at the substation is operated. When relay 113 operates at the termination of the first impulse, relay 127 is again sho-rt circuited and releases. This permits relay 128Y to operate over the energizing circuit described therefor and in so doing said relay places the motor magnet 131 under the control of F. relay 127. The operation of relay 128 also connects the operating winding of relay 127 direct to ground through the right-hand armature and front contact of relay 110 instead of through the brush 125. The next release of relay 113 in response to the second impusle permits relay 127 to operate thusconnecting the ground at relay 127 to the winding of motor magnet 131. Relay 127 is locked up through its right-hand contact and armature, the contact and armature of Vmotor magnet 131, the front contact and inner left-hand armature of relay 128, which now remains operated, and the front contact and left-hand armature of relay 127 to ground. The construction of the motor magnet 131 is such that its contact and armature are not separated until the motor magnet has completed its stroke and therefore relay 127 will Vremain locked until such time that said armature and contact are separated notwithstanding the fact that the short circuit for the left-hand winding of relay 127 may be closed by the operation of relay 113 before the motor magnet advances the brushes of selector C to the second terminals associated with said brushes. In response tothe further impulses the switches advance in the same manner as just described until the brush 125 engages the terminal 132` and the remaining brushes of the switch engage associated terminals located in the same vertical row with the terminal 132. It is to be noted that during the transmission of impulses relays 110 and 130 remain operated, due to their slow to release nature, while the circuits therefor are being momentarily interrupted. After the last impulse, relay 113 remains operated whereupon relay 127 releases thereby vcausing, after an interval, the release of relay 130. The deenergization of the latter relay opens the circuitl for relay 128 which also releases.

The brushes of the switch are now en gaged with terminals assigned to the t rst connector of the first group which is ein` ployed for establishing connections to the called lines served by said group of connectors. lf this first connector is busy this condition is denoted by ground upon the terminal engaged by brush 123 ot the selector and relay 129 will therefore remain operated and cause the operation o 1 relay 133 over a circuit extending from grounded battery through the left-hand winding ot relay 129, left-hand normal contacts of relay 130, the right-hand winding of relay 133, the front contact and inner right-hand arma4 ture of relay 129 and the brush 123 to ground. Also, the release of relay 128 connec-ts ground at the right-hand normal con tacts of relay 128 to brush 125 and terminal 132 and from thence through the inner righthand armature and back contact of relay 111 and winding of relay 134 to t grounded battery. Relay 134- energizes and establishes an operating circuit for relay 135 extending from. grounded battery through the winding of relay 135, the front contact and inner right-hand armature of relay 134;, t-he right-hand normal contacts of relay 130 and the right-hand arnniture and contact of relay 110 to ground. Both relays 134; and 135 lock up through their front contacts and inner left-hand armatures and from thence over the energizing circuit of relay 135. The operation of relay 13st disconnects the first of the terminals assigned to the second group of connectors, that is the terminal following terminal 132, from the winding of relay 135 and connects said terminal to thel right-hand winding of relay 129 and the left-hand winding` of relay 133 in parallel. The operation of relay 135 establishes a self-interrupting circuit for motor magnet 131 extending from `ground through the outer left-hand armature and front contact of relay 135 and the lett-hand inner armature and frontA contact of relay 133 and the contact, armature and winding of motor magnet 131 to grounded battery, thus causing said motor magnet to operate and advance the brush 125 of the switch from terminal 132 te the next succeeding terminal. Inasmuch as the relay 13st is now operated the ground on t-he brush 125 will be extended through the outer right-hand armature and front cont-act of relay 134e to the right-hand winding of relay 129 and the left-hand winding of relay 133 to maintain these two relays energized whereby the motor magnet 131 will be caused to advance the brushes of the switch another step. This engages the brush 125 with the first of the two terminals 137 allotted to attendants trunlzs and the ground on brush 125 will then be extended through the inner righthand armature and front contact of relay 135, the left-hand armature and back contact of relay 138 to the before-mentioned windings of rela-ys 129 and 133. The switch therefore continues to step over the terminals assigned to attendants trunks until the next succeeding terminal is reached which is the one allotted to the second connector of the group serving the group of lines in which the called line is located. 1f this second connector is also busy, the relays 129 and 133 will not be maintained energized through the brush 125 since the terminal, following the second terminal 137, is not connected to the right and left-hand windings of said relays, respectively, due' to the fact that the outer right-hand' armature of relay 1311 is separated from its back contact. However, relays 129 and 133 will remain energized through the brush 123 which finds ground at the busy connector. The motor magnet 131 will therefore advance the brushes of the switch C to engage t-he next succeeding terminal. The brushes of the switch will therefore be again advanced and this operation will continue until the terminals of an idle connector in the first group are located. l/Vhen this occurs ground will no longer be connected to either of the windings of either of the relays 129 and 133 and these relays will therefore release. 1nasmuch as relay 112 is not operated, relay 113 remains under the control of the calling subscriber and relay is maintained operated. 1t will be recalled that the operating circuit of relay 127 is removed from control of brush when the selector takes its initial step and from the control of relay 128 at the termination of the first series of impulses. f'l`herefore, the relay 12? and consequently the selector switch will not respond to any further impulses transmitted. Upon the release of relay 129 after the selection of the trunk leading' to the idle connector, and assuming this connector to be the one to .which terminal 136 is assigned, ground is extended to the connector through the right-hand armature of relay 110, the 1iglit.-liand armature and contact of relay 113, the outer right-hand armature and back contact of relay 129 and the brush 124. Ground is also connected to the brush 123 from the left-hand armature and front contact of relay 110, the inner right-hand armature and front contact of relay 104, and the baclrcontact and inner right-hand armature of relay 129.

`With the brushes of the selector C in engagement with the terminals of the trunk extending to the idle connector switch E shown in lFigure 2, the relay 200 of the switch operates over circuit extending Vfrom grounded battery `through the wincground on the conductor 202.

ing of said relay, the brush 201 and its normal terminal and the conductor 202 to above mentioned ground on the brush Relay 200 operates and locks through its outer left-hand armature and front contact to The operation of relay 200 establishes an operating circuit for stepping relay 203 extending from grounded battery through the resistance 219, the left-hand winding of said relay, the brush 204'and its associated normal contact, the right-hand normal con* tacts of the slow to release relay 205 and the front Contact and inner right-hand armature of relay 200 to ground. Relay 203, however, does not operate due to the short circuit established by the ground extending from brush 1241 of the selector to the conductor 206, the application of this ground heing controlled by the relay 113. The ground extended from the outer right-hand armature and front contact of relay 2007 upon the operation of the latter relay, is applied to the brush 207 of switch E through the nor mal contact and outer right-hand armature of relay 208 and is connected to the righthand winding of slow to release relay 209 which thereupon operates to disconnect the source of ringing current 210 from the brushes 211 and 212 of the connector. Relay 209, by operating, also prevents the transmission of a ringing tone to the calling suhscribers line through the back contact and inner left-hand armature of relay 209, the back contacts and outer left-hand armatures of relays 208 and 215, the condenser 218, and the back contact and outer left-hand armature of relay 216. The connector switch is now ready to receive impulses transmitted from the calling substation and upon each deenergization of the relay 113, in response to said impulses, the short circuit for the left-hand winding of relay 203 is removed/and said relay operatmand locks through its front contact and ner right-hand armature and the cont and armature of the motor magnet 213 described in connection with the relayr of the selector switch, the locking circuit for relay 203 remains closed until the motor magnet has completed its stroke.

The second digit of the numbers ot v5r-.c subscribers within the exchange is eithe" 'l or 0 and in the establishment of the c nection shown in Figure 2, the subs line D is shown in the group of lines having 0 as the second digit. For the same reason as referred to in connection with the terminal "bank of selector C, a number of the terminals of the bank of switch E have been omitted. By referring to the row of terminals associated with brush 2041, it ifi-:ill be seen that only two terminals are shown to indicate the group of subscribers lines, the second digit of'which is 1. These terminals over the associated follovvl the second or intermediate terminal associated with the brush 204: which engages said second terminal when one impulse is transmitted to the selector switch. rlhe terminal in the row referred to following the last terminal assigned to the subscribers7 lines in the iirst group is the next intermediate 'terminal upon Which the brush 201i, comes to rest when ten impulses are transmitted to the connector switch. Following this terminal are others assigned to the second group of subscribers lines having 0 'lor the second digit. As shown in the drawing, the su-bscribers line D is associated with the rst vertical row of terminals in the second group of subscribers lines and there- :tore in order to secure connection to this line, it will be necessary to dial 0 and 1. as the second and third digits of the called line. Each operation of the motor magnet 213 in response to the energization of relay 208 advances the brushes of the switch E terminals Vuntil the brushesv engage the vertical row of terminals in which the terminal 214 is located. The first operation of relay7 208 establishes an energizing circuit for relay 205 which remains operated during transmission ot impulses from the calling substation. The operation of the relay 205 establishes a circuit tor relay 208 extending from grounded battery through the left-hand winding ot relay 208, front contact and lett-hand armature ot relay 205, and the front contact and outer left-hand armature of relay 200 to ground on the conductor 202. Relay 208 operates and disconnects the trunk from the brushes 211 and 212 and also opens. at its outer right-hand armature and back centact, the energizing circuit tor relay 209 which thereupon releases. During the transmission of impulses, the dial at the calling substation opens the vreceiver circuit and Yhence the calling subscriber will not hear the ringing tone while the dial is operating land the relay 209 is released. The operation lof relay 205 disconnects the ground at relay 200 from the brush 205iand` connects said ground throughv the Atrout contact and right-hand armature of relay 205 directly to the left-hand Winding of stepping relay 203, so vthat the operating circuit ot the latter relay will not be open when the switch moves lirom its normal position.

At the termination of `the first series of impulses, relay 203 remains deenergized suticiently long toi permit the release of relay 205. Brush 207 is now engaged with an intermediate terminal et its associated row. The restoration of the latter relay opens the energizing circuit for relay 208 which thereupon releases. Ground is again connected tobrush 20.7 through contacts of rela-ys 200 and 208 whereupon relay 209 again operates through its right-hand Wind- 'ng to again prevent the application oi ringtone to the calling line. The release ot relay 205 again closes the operating eircuiit for stepping relay 203 through the brush 204 and terminal 214. It will thus be seen from the foregoing description, thatl while the brushes of the switch are in engagement with either the normal or intermediate terminals, ringingtone is disconnected from the calling subscribers line by the operation oi relay 209.

The impulses are new transmitted corresponding to the lastdigit of the called number and in the example shown, its digit being l.. the brushes of the switch are stepped in the same manner as previously described to engage the terminals individual to the called line. Relay 208 is again operated upon the first operation oi relay 203 to o )en the circuit for relay 209 which releases et'ore the magnet 218 can step the brushes et the s *itch onto the next set of terminals. lf the line is busy, the release of relay 205 at the termination ot the impulses transmitted establishes a circuit extending 'from grounded battery through the letthand winding oi' relay 208, the. left-hand normal contacts of the relay 2057 winding and inner lett-hand normal contacts ot the relay 215. the inner lett-hand armature and 'Front contact otrelay 200 the front contact and enter right-hand armature ot relay 208 to the brush 20T. The busy condition ot the called line is denoted by lground upon the terminals associa-ted with the brush 207, such as the terminal 118, of Figure 1, and this ground causes the relay 208 to remain operated and relay 215 to energize. A. holding circuit is established Vlor relays 208 and 215 by the operation ot' the lutter. said circuit extending through the iront contact and inner left-hand armature of relay 215v` the right-hand normal cent-acts of relay 216 and the front cont-act and outer right-hand armature of relay 200 to ground. Relay 209 is not operated at this time since its right-hand winding is not connected to the terminal engaged by the brush 207. However. the operation ot relay 208 prevents 1the application ringing current to the called line and ringing tone to the callingline. The operation ot relay 215 connects the busy tone apparatus 21T through the front contact and outer right-hand armature ot said relay, the condenser 218 and lthe bach Contact and outer lett-hand arma ture et relay 216 tothe tip side ot the trunk and from thence to `the calling subscrihefs line. rllhe sulgiscriber, upon hearing` this tene replaces his receiver on the switch hook to restore the apparatus to normal in a manner which will presently be described` At the time ot the applica! tion of the busy tone. a circuit is cle.. d `for relay 216 extending from grounded batlill) tery through resistance 219 at. relay 203, winding oi relay 210, front contact and inner right-hand armature of relay 215, brush 204, the right-hand normal contacts of relay 205 and the. front contact and inner right-hand armature olf relay 200 to ground. Relay 216 does not operate at this time due to the ground on the conductor 206 which. is connected to the brush. 204 of the selector, this ground short ci rcuiting the relay 210,

Assuming now that the called line is not busy, the relay 215 fails to operate and relay 208 releases due to the lack of ground on the brush 20T. rllhe release of relay 208 connects ground through its back contact and outer righthand armature from the relay 200 to the brush 20'? and this ground extends tlirough the winding of the cut-oli" relay 220 of the called line which thereupon operates, The multiple test terminals of the called line, similar lto the terminal 118, are now groundedl and will test busy to any other connector switch engaged therewith. Due to the tact that relay 215 does not operate when the terminals of the idle line are engaged, a circuit is established troni relay 221 extending from grounded battery through the winding of said relay, the riglithand armature and bach contact off relay 209, the back con-tact and inner righthand armature of relay 215, the brush 204, the riglrt-hand no 1mal Contact ot relay 205 to ground at the inner right-hand armature and front contact ot relay 200. The relay 221 is similar to relay 433 shown in the co-pending application of' Edward E. Hinrichsen, filed July 14, 1920 and bearing `Serial No. 390,143. Said relay is designed to control the generation of ringing current in the source 210 yin the manner described in said co-pending application and this source of ringing current is thereupon connected through the legt-hand winding of relay 2091 to the substation appara-tus of the called line through bach contacts of relays 209 and 208 and the brushes 211 and 212. il. portion. ot this ringing current is diverted through the outer lett-hand armatures and bach contacts ol? relays 215 and and condenser 218 to the calling line to notify the subscriber thereat that the called line is being ,signaled When the called subscriber removes his receiver trom its switch hooln sullicient current passes through the lett-hand winding of relay 209 to operate the same and said relay thereupon loclfs up to ground on conductor 202 through brush 201 and the front contact and inner right-hand armature ot said relay. The operation of relay 209 disconnects ringing `current from the called line and connects said line to the calling line through the selector switch C. The calling line is now supplied with talking current troni the relay 113 and the calle-d line has talking current connected thereto from relay 138 through the right-hand normal contacts ot' relay 112. Conversation may now proceed between the subscribers at substations il, and D.

At the termination of the conyersatioi'i, the replacing of the receiver upon its switch hook at the calling substation releases rek lay 113, whereupon relay 110 deenergies. The restoration of the latter relayl opens the energizing circuit 'l'or relay 104 extending through the left-hand armature aud front contact of relay 110 and the outer right-hand armature and back Contact of relay 102. Ground from the lett-hand ncrmal contacts of relay 110, the outer lett-hand armature and bach Contact of relay 1 0-l; and brush 109 of the selector is now extended in parallel to the right and lett-hand windings respectively of relays 129 and 133 and said relays thereupon operate. 1Upon the operation of relay 133, a circuit estal lished from ground through the right-hand normal contacts of relay 1107 the inner letthand armature and front contact of relay 133, the Contact, armature. and winding ot motor magnet 1.31 or' the selector to grounded battery, This is a self-interrupting circuit and upon each closure thereof, the

motor magnet operates to step the brushes operating circuitJ for the motor magnet and the brushes of the selector switch come to rest upon their normal terminals. The release of relay 110 also opens the locking rircuits for relays 1.34 and 135 which thereupon restore to normal,

A circuit is now established for re1 ay 102 extending from grounded battery through the winning of said relay, the brush 103, ot the line linder, the left-hand normal contacts of relay 107, brush 109 and its normal erminal, the baclr Contact and out-er letthand armature ot relay 104 and from thence to ground at relay 110. Relay 102 energ if in this circuit and locks through its 1'1 ,nt Contact and inner right-hand armature to the brush 110, and the terminal o'f the cult ing line engaged thereby, the bach contant and armature of the line relay 100.y which. released when the calling subscriber replaced his receiver upon its switch hook, the back contact and armature of relay to ground. The operation of the relay 'l0 again establishes the operating circuit for relay 107 and a circuit is vthereupon estahlished for relay 1,12 extending from soun-lf ed battery through the lett-hand winding of relay 111, winding of relay 112, the outer right-hand armature and bach contact of relay 104, the front Contact and right-lr nd armature of relay 107 and trom thence over CCA front contact ot relay 102, the lett-handv` armature and front contact of relay brush 109 and from thence over the previously described circuit to the ground at n the relay 110. The motor magnet 108 opcrates to step the brushes of the line tindcr B until the brush 116 encounters a terminal having no ground thereon. rlhis might be the normal terminal oit the brush or i* might be a terminal of a line which may originate a call While the switch is returning to normal. ln the latter event the line` finder Will stop upon the terminals individual to, this calling line and the operation Will be the same as previously described. lhen the brush 116 encounters an open terminal in the return of the switch towards its normal position, the locking Ii'fciiit of relay 102 is opened thus permanen bresil;- ing the operating circuit of the motor niagnet 108. The release of relay 102 also opens the circuit for relays 111 and 112 which thereupon release, thus completely rcstoru the apparatus of thefline finder and selec switch to normal.

At the time of the release of relay 110 of the selector the ground, which was extended to the conductor 202 through the brush 123 to main-tain the relay 200 of the connector switch energized, is removed and said relay 200 thereupon releases. The

vbrush 222 of the connector E is thereupon the contact, arma-ture and Winding et stepping magnet 213 to grounded battery. This being a self-interrupting circuit, the motor magnet Will operate to step the brushes of the connector until their normal termin are reached, whereupon the circuit for si motor magnet will be permanently opened. rlhe release of relay 200 also establishes an operating circuit for relay 208 extending through the right-hand Winding thereof to the grounded brush 222. The operation oi relay 208 extends the ground from the brush through the inner right-hand armature and front Contact of relay 208, theV outer left-hand armature and back contact oi' relay 20() and the conductor 202 to the terminal individual to the connector over which the brush 123 of the selector passes.

The ground on this terminal is multipled to other similar terminals and will prevent a selector trom seizing the trunk extending to connector E while the latter switch is returning to normal.

A sul'iscriber within the exchange may secure connection to the attendants position by dialing 0. ln response to the removal of the receiver trom its switch hook at the callingsubstation. Ithe line finder B will operate to engage the terminals of the calling line in the same manner as previously described and in response to ten impulses transmitted a selector C will operate as hereinbefore set forth to step its brushes to engage. the tirst set of terminals in the selector bank which are assigned to the iirst trunk leading to the attendants position. ln the present showing, provision is made 'tor tive olE such trunks and the terminals of rthese trunks over which brush 125 of the selector' passes are indicated as 137. At the termination of the ten impulses transmitted brush 125 is in engagement With the first ot the terminals 13T and a circuit is established for relay 138 extending from ground ed battery through the left-hand Winding of said relay, the back contact and inner right-hand armature of relay 135, the brush 12.3, the right-hand normal contacts ot rclay 128, which` released at the termination of the impulses as previously described, and the right-hand armature and front contact of relay 110 to ground. lelay 138 operates and locks through its front contact and inner left-hand armature and from thence over the ener i2zing` circuit therefor. The cnergization ot relay 138 establishes an operating circuit for relay 111 extending from grounded battery through the lett-hand Winding of relay 111, Winding ogt relay 112, the outer right-hand armature and Jfront Contact of relay 1.01-, the right-hand armature and front Contact oi' relay 138, the back contact and inner left-hand armature of relay 185, the right-hand normal contacts of relay 130, and the right-hand armature and front contact of relay 110 to ground. Relay 111 locks through its outer left-hand armature and Yfront contact, the outer leithand armature and back Contact or' relay 128 and the lett-hand armature and E1-ont Contact oi? rela-y 110 to ground. 'lhe operation of' relay 111 establishes, as previously described, energizing and locking` circuits for relays 134 and 135.

lic, the First trunk extending to the attendants position is busy, this condition is denoted by ground upon the test terminal which brush 123 engages. lt Will be recalled froin the previous description of thc ope-ration of the selector circuit that at the time oiE testing, the relay 129 is energized through its right-hand Winding. lVith ground upon the brush 128, a circuit is esiii@ the lamp 305 will light. The operator releases the connection by restoring either key 303 or 304 and the removal ot ground from the terminal engaged by brush 123 and the restoratio-n of-'the receiver at the calling substation causes the release of the selector switch as previously described.

' The attendant may originate a local call to any substation within the private branch exchange by operating key 307 which connects her head set in circuit with the line relay 308 through contacts of the cut-off relay 309. In the same manner as hereinbefore described, an `idle line finder similar to the finder B is caused to hunt for the terminals individual to the attendants position after which the attendant may complete the connection in the same manner that a call is established between subscribers.

A subscriber within the private branch exchange may secure a direct connection to the central office by dialing the` digit 2. Upon the initiation of the call the line iinder B operates in the same manner as before described and associates a selector C with the `calling line so that in response to the two impulses transmitted, the brushes of the selector will take one step to engage the brush 125 with the second terminalY in its row. Upon the release of the relay 123 and consequent grounding of the brush 125, an'

energizing circuit is established for the relay 111 through the right-hand winding thereof. Relay 111 locks up in series with relay 112 as before described but it relay 133 is operated due to the engagement ot' the brush 1.23 with a terminal of a busy trunk, relay 112 is short-circuited. The operation of relay 111 also causes the energization of relays 134 and 135 as previously described. The test for an idle trunk is made in the same manner as hereinbefore set. forth and if none ot the trunks leading to the Central 'office are idle, the switch will continue to step until the last terminals of the bank are reached whereupon the calling subscriber is given. a. busy tone. The replacing ot the receiver upon its switclihook at the calling substation will then release the switches in the same manner as previously described.

It an idle trunk is found, no ground being on the test terminal thereof, relay 133 will tail to operate, thus stopping the switch on the terminals of the idle trunk. Relay 112 will energize to open the circuit for relay 113 and connect the calling line direct to the trunk and around the condensers 142.

1t will iirst be assumed that all of the trunks leading from the private branch exchange terminate in a manual central oice F conventionally illustrated at the right ot Figure 4. Upon the operation of relay 112, the subscribers line is extended through normal contacts of relay 400 in the central otlice trunk circuit and the windings ot line relay 401. This latter relay energizes to establish an obvious energizing circuit Yfor slowto-release relay 402 which, in closing its letthand armature and front contact, extends busy ground y'from the lett-hand normal. contacts ot slow-to-release relay 403 to the test terminal engaged by brush 123 of the selector to cause the multiple terminals of the trunk to test busy to all other switches C. The busy lamp 404 is lighted by the energization of relay 402 over an obvious :ircuit to indicate to the attendant that. a particular trunk has been taken for use. rThe encrgization of relay 401 grounds the tip side of the trunk extending to the central oiiice F through the righthand armature and front contact ot relay 401 andinnermost right-hand armature and back contact of relay 405. This ground, in the present instance, is shown as extending from the back contact and left-hand armature of relay 600 but, inasmuch as the apparatus including the code switch shown in Figure 6 is not employed where the trunks of the private branch exchange extend to a manual central otiice, it will be understood that this ground may be directly connected to the right-hand armature of relay 401. The operation of relay 401 also establishes a circuit for relay 406 extending from grounded battery through the winding of relay 40G, the upper contacts of release key 407, the normal contacts ot the dialing key 408, lett-hand normal contact of relay 40G and front contact and lett-hand armature of relay 401 to ground. Relay 400 energizes and locks in a circuit through its iront contact and inner left-hand armature to ground at the right-hand armature and liront contact of relay 402.

The grounding ot the tip side of the trunk by the operation of relay 401 causes the energization of line relay 40S at the central oilice F whereupon the usual line lamp at said oiiice individual to the seized trunk is lighted. The operator then answers the call by inserting a plug into the ack ot the trunk in the usual manner. This operation closes a circuit extending from grounded battery in the cord circuit employed by the operator. through the right-hand normal contacts ot the flashing or disconnect key 400 which may be used for recalling the central oiiice operator or giving a disconnect signal, the right-hand armature and normal contacts of relay 410, the winding oit' line relay 411, the upper normal contacts ot key 412 and the lett-hand normal contacts of keyv 409 to ground in the operators cord circuit. Relay 411 energizes in this circuit and establishes an obvious operating circuit for relay 403 which, in attracting its left-hand armature, disconnects the ground potential from the lett-hand armature and front contact of relay 402 and extends it directly through the left-hand armature of relay 403 to the brush 123 and lamp 404.

Relays 403 and 406 now being energized, a circuit is established for relay 400 extending .trom grounded battery through the winding of said relay, the lower normal contact ot hey 412, conductors 413 and 414 which are strapped together when the trunks lead to a manual oliice, the front contact and inner left-hand armature of relay 406 and the right-hand armature and 'front contact ot relay 403 to ground. Relay 400 energizes to entend the calling line over the trunk to the central oilice through the winding of supervisory relay 415 which is bridged across the trunk. Conversation may now proceed between the calling subscriber and the central oliice operator. The operation of relay 400 causes the release of relay 401 but relay 402 remains operated due to ground at the front contact and outer left-hand armature of relay 400. rlhe operation ot the su pervisory relay 415 establishes an obvious energizing circuit- ;tor relay'410 which relay, upon operating, opens the energizing circuit ot relay 411 which then releases. Relay 410 also bridges the non-inductive shunt 416 around the active winding ot the supervisory relay 415.

fit the termination of lthe conversation, the restoration of the receiver upon its switch hool at the calling substation releases the supervisory relay 415 whereupon relay 410 deenergizes. Relay 411 is then operated over its previously described circuit thus preventing the release of relay 403. As a winding ot relay 411 is ot a high resistance, the supervisory relay at the central oflice is released thus giving the operator thereat the disconnect signal in the usual manner. llllhen the operator removes the plug from the jack, relay 411 releases and causes, in turn, the release ot relays 403, 400, 402 and 406 and the extinguislnnent of the busy lamp 404. rllhe trunk circuit is now restored to normal and the removal ot ground from the brush 123 causes the release ot relay 104 which ellects the return to normal oit the switches B and C in the same manner as previously described.

Should the central oflice operator discon-l nection to the central. ottico, the inner righthand armature of the cutofl' relay 101 ot the subscribers line is connected by a conductor 139 to the terminal in the line linder bank individual to said line over which brush 140 passes. llllhen the cut-oil' relay 101 is operated by the finding of the calling line and theiinpulses have been transmitted to onerate selector C, a circuit is established eirtending from grounded battery through the inner armature and front contact of relay 101, conductor 139, the brush 140, the letthand winding of relay 141, the brush 1:25, the right-hand normal contacts ol relay 128, the right-hand armature and ,trontconm tact of relay 110 to ground. Relay 141 euergizes and locks through its right-hand wlnding, front contact and inner right-hand armature, the outer lett-hand armatmfe and back contact of relay 128 and the lett-hand armature and :tront contact ot relay 110 to ground. The operation of relay 141 connects the terminals individual. to the central. olice trunks over which brush 125 passes to the right and left-hand windingsl respectively, ot relays 129 and 133 through the 'iront contact and outer right-hand armature ol said relay 141. Bela-ys and therefore rcmain operated and vthe selector switch C continues to step over the terminals of the central oiiice trunk even though these trunlr are idle. The brushes ol the switch C are also stepped over the other terminals in the same manner as previously described and upon reaching the last vertical row ot terminals, which is the all-busy position, the brush 123 encounters ground which extends from the right-hand armature and front Contact` ot relay 110, the right-hand normal contacts of relay 130 and the inner lett-hand armature and front contact ot relay 141. llelays.

129 and 131 are thereby maintained ene;V gized and the brushes .of the selector C therefore do not stop upon the last row oit tei1H minals but continue on to their normal positions.

The attendant at substation 306 may call the central oiiice 'F by operating the listening` key 417 which extends ground. trom the right-hand normal contacts of relay 403 through an alternate contact ol key 417, and the right-hand normal contarte ol relay 421 to the tip side of the trunk with the result that line relay 40S/ at the central. office will operate to light the line lamp thereat. The closure ot the lowermost alternate Contact ol key 417 extends ground through the middle normal contacts oil' 1rey 409 and troni thence in parallel through the guard lamp 420 and the winding of relay 405 to grounded battery. The lamp 420 is lighted and the energization of relay 405 extends the last mentioned ground through its liront contact and outer right-hand armature and the right-hand normal contacts ot relay 418 to the multiple test terminals appearing in the banks of selector switches C whereby the trunk will test busy to these switches. The lamp 404 is also lighted by the above nientioned ground to indicate the busy condition of the trunk. The central o'tlice operator, observing the lighted condition ot the line lamp individual to the trunk, answers the call by inserting a plug into the jack of Asaid trunk whereupon the supervisory rela-y 415 is energized. rhe operation ot this relay causes the energization of relay 410 which, in closing its right-hand front contact, includes the non-inductive winding 410 ot the supervisory relay in the circuit tor talking purposes. The energization of re lay 415 also closes an obvious circuit lfor relay 403 which, when energized, disconnects ground from the tip side of the trunk.

The attendant may release the central ot- Jtice trunk by operating the disconnect key 409 and by restoring listening key 417 which removes ground at key 417 from the multiple test terminals and causes the release ot relay 405 and the extinguishment of lamp 420. The replacing of the receiver upon its switch hook at the attendants substation 206 opens the circuit to supervisory relay 415 which thereupon releases to cause the deenergization ot relay 410 and the consequent release ot relay 403. rlhe lamp 404 is extinguished and ground removed troni the test terminals ot the trunk upon the release of relay 403. The central office operator upon receiving the disconnect signal in the usual manner removes the plug 'from the jack.

For an incoming call trom the manual central ottlce l) to the attendant at substation 305, the operator at the central otlice inserts the plug of the cord circuit in the jack and thereby energizes the relay 411 over the previously described circuit therefor, whereupon the relay 403 operates to ground the multiple test terminals ot the trunk, and the busy lamp 404 is lighted. lll/hen a central oliice operator applies ringing current to the line, said current extends Ytrom the ring side ot the trunk through the outer right-hand armature and back contact ot relay 406,` the lett-hand winding ot relay 422 and the upper normal contact ot key 412 to the tip side of the trunk. Relay 422 energizes and locks through its right-hand winding, front contact and armature, the back contact and outermost armature of relay 405, and the right-hand normal contacts of relay 413 to ground at the lett-hand armature ot relay 403. A circuit for lighting the line lamp 423 is also established which extends through the lett-hand armature and front contact of relay 422 and from thence over the locking circuit of said relay. The attendant at substation 206, observing that a call is awaiting attention, lirst operates the listening key 417 which energizes relay 405 and lights the guard lamp 420 as previously described. The energization oi relay 405 opens the locking circuit ot relay 422 and extinguishes the lamp 423. The energization of relay 405 also bridges the upper and lower windings ot the retardation coil 424 across the trunk through the high resistance winding ot relay 411 to hold said trunk, the middle winding ot said coil being normally shunted through the outer left-hand armature ot' relay 410. The attendant now removes the receiver trom its` switch hook at lier substation whereupon the supervisory relay 415 operates in series` in the central oliice operatons telephone set. rllhe operation ot relay 415 again operates relay 410 to close the talking circuit and open the shunt around the middle winding ot the retardation coil 424. Relay 411 releases to remove the coil 424 lrom the line and opens the original energizing circuit for relay 403 but this relay is maintained energized by ground at the lett-hand armature and contact of relay 415.

The attendant .may now converse with the central otiice operator and it the call is to be extended to a subscriber within the eX- change the attendant leaves the listening key 417 operated and actuates the dialing` key 403. Relay 400, the circuit ot which extends through the lower contacts ol relay 403, will not energize.

Upon the operation of relays 421 and 402, following the actuation oic the listening key 417 and energization of relay 401, a circuit is established tor stepping relay 500 ot the selector switch shown in Figure 5, which circuit is traceable from grounded battery through the left-hand winding of said relay, the brush 501 in its normal position. the right-hand normal contacts ot relay 502, the front contact and inner left-hand armature ot relay 421 and the right-hand armature and contact of relay 402 to ground. Relay 500, however, does not operate due to a short-circuit evtending from ground on the right-hand armature and front contact ot relay 401, the innermost armature and front contact ol relay 405 which is operated by the actuation ot key 417, the no-test key 440 and the outer right-hand armature and back contact of relay 503. The selector switch is now ready to receive impulses from the attcndants position and since relay 401 is now under the control ot the attendant/'s telephone set, said relay will respond to the impulses transmitted. The opening of the contact and right-hand armature ot relay 401 in response to the lirst impulse removes the short circuit from the leitt-hand winding ot relay 500 whereupon this relay operates to close an obvious circuit for slow-toerelease relay 505. The latter relay establishes an energizing circuit for re.-

lay 503 extending from grounded battery through the righthand winding of said relay, the front contact and left-hand armature of relay 505, the lower contacts of key 407 and the' left-hand armature and front contact of relay 403 to ground. Relay 505 also establishes, through its right-hand armature, an energizing circuit for relay 502 but the winding of this relay is shortcircuited through its back contact and lefthand armature to ground at the left-hand armature ot relay 500. lhen the latter relay releases at the termination of the first impulse, the short circuit for relay 502 is removed and this relay operates to place the motor magnet 506 under the control of the relay 500. It will thus be apparent, as in the case of the selector C, that the irst impulse transmitted to the selector of Figure 5 is absorbed by the action of relay 502 for the same purpose as previously described. lin response to the subsequent impulses relay 500 operates to close a stepping circuit for magnet 506 which advances the switch to a trunk leading to a connector switch such as shown in Figure 2. During the transmission of the impulses, relay 505 remains operated but at the end of a series ot' impulses said relay releases after an interval and connects the right-hand windings oi' relays 503 and 507 in series through the inner right-hand armature and back contact of relay 503 to the brush 508. The release of relay 505 also causes the deenergization of relay 502 which, in releasing, eX- tends ground from the right-hand armature of relay 402 to the brush 501.

lf the wanted subscribers line is in the groups served by the first group of connectors, the brushes of the selector switch will be stepped until the brush 501i engages the terminal 509, certain of the terminals of the selector bank being omitted as in Figure 1. Ground on the brush 501 will thereupon operate relay 510 and this relay will lock through its front contact and rightehand armature to ground, at the left-hand armature of relay 403. The operation of relay 510 connects the terminals of the second group of connectors, such as terminals 511, to the leitt-hand windings of relays 503 and 507 in parallel. The selector' will-hunt for an idle trunk leading to a connector switch in the samemanner as previously described in connection with switch Gand if the first trunk encountered is busy the terminal engaged by brush 508 will be grounded to maintain relay 503 energized and to operate relay 507. The operation of relay 507 eX- tends ground from they armature and contact'thereo'f through the back contact of relay 500 to the back armature and winding of the motor magnet 506 to cause the latter to step the brushes of the switch to the terminals of the next trunk. This operation continues until an idle trunk is found but it all trunlrs leading to the first group of connectors are busy, the switch will continue to step over all of the terminals until the last terminals are reached whereupon the switch will bevbrought to rest in the same manner as described in connection with switch C. A busy tone from the apparatus 512 will then be transmitted to the attendants telephone set.y

As shown in .Figure 5, the trunk leading to the connector of Figure 2 is connected to terminals assigned to the second group of connectors so that it will be necessary for the attendant to send suticient impulses to step the brushes of the selector until brush 501 is brought in engagement with the iirst of the terminals 511, In this instance, relay 510 will not operate and when brush 501 is grounded, as previously described, this ground will be extended to all of the terminals assigned to the first group of connectors through the back contact and left-hand armature of relay 510 to maintain relay 503 and 507 operated during the trunk hunting operation ot the switch. The test for an idle trunk leading to a connector in the second group therefor takes place in the same manner as described in connection with the iirst group of connectors and upon encountering an idle trunlr such as the one` shown, relays 503 and 507 release when ground is not present upon the terminal engaged by brush 508. rlihe release of relay 503 extends the trunk leading from the attendants position through to the brushes 515 and 514; supplies ground to the brush 508 from the lett-hand armature and front contact of relay 403; and connects ground to the brush 515 from the right-hand armature and 'front contact of relay 401 through the innermost right-hand armature and front contact of relay 405 and the no test key 440. These two grounds are connected to the conductors 202 and 206 of the connector circuit and perform the same functions as the ground supplied to these conductors from the switch C.

After the connector has been seized it is operated under the control of relayf401 to select the desired line. The connector functions in the same manner as described in connection with a local call and it the line is found to .be idle the bell at the substation is rung and a portion of the ringing current is transmitted back to the attendants telephone set in the same manner as described with respect to the call initiated at the substation A. Upon hearing this ringing curF rent the attendant restores the listening and dialing keys 417 and 408 and thereby causes the release of relays 421, 401 and 402. Relay 405, however, remain locked up to` ground at the lett-hand armature and front contact of relay 403 and the central oilice supervisory relay is maintained operated throughY the low resistance winding of relay 411 and windings of the retardation coil 424. At the time the listening key 41T was operated and relay405 energized, a circuit for guard lamp 420 was also established in parallel with relay 405 and said lamp remains lighted during the selection of the called line by the attendant and the ringing of said line to indicate to the attendant that the subscriber has not answered. Villen the called subscriber `removes his receiver `from its switch hook his substation apparatus is connected through brushes 513 and 514 and normal contacts of relays 503 and 400 to the winding of relay 401 which relay thereupon operates and causes the energization of relays 402 and 406, the circuit Jfor the latter relay being now closed at the dialing key 408. Relay 406 locks up inthe same manner as previously described. 14s relay 403 is already operated and the conductors 413 and 414 are connected together either permanently as previously referred to or by means of a relay in the code circuit of Figure 6, relay 400 operates in the same manner as previously described and connects the called subscribers substation through front contacts of the relay 400 to the central ofice trunks. The operation of the relay 400 releases relay 401 but relay 402 is maintained energized by ground at the outer lett-hand armature and front contact ot relay 400., Relays 415 and 410 now operate and in so doing the latter relay removes the short-circuit from the middle winding ot' retardation coil 424 and places the non-inductive shunt 416 across the winding ot the relay 415. The operation of relay 410 also establishes a circuit for relay 41S extending from grounded battery through the righthand winding o't said relay, the lett-hand armature and front Contact of relay 405, the front contact and outer lett-hand armature of relay 406 and the Jfront Contact and inner lett-hand armature of relay 410 to ground. Relay 418 locks up through its lefthand winding, front contact and inner lefthand armature, the lower normal contacts of key 407 and left-hand armature and tront- Contact of relay 402 to ground. rlhe operation of relay 418 places the locking circuit oit relay 405, which extended through the front contact and outermost armature or said relay, under the control of relay 410. The operation of relay A418 also causes the energization of relay 427 over a circuit extending from grounded battery through the winding of said relay, the front Contact and inner right-hand armature ot relay 418 and from thence over the energizing circuit for the latter relay to ground at the front centact andl inner left-hand armature of relay 410. The operation of relay 427 opens the circuit for lamp 420 which is thereupon extinguished.

It is to be noted that when the attendant operates the listening key 417 in response to a call from the central oiiice, the closureI of the next to the lowermost contact and associated spring` of said key grounds the conductor 431 so that in cases where the code switch oit Figure G is employed, relay 614 of said switch will be operated through its lett-hand winding. The operation ot this relay connects the conductors 413 and 414 to prevent the code switch trom responding to the impulses transmitted from the attendants position, in a manner which will hereinafter appear.

After the connection has been established from the central otlice to the ycalled subscriber, ii" the latter desires to recall the attendant he may do so by depressing his switchhook momentarily or by operating the dial. This causes the momentary release of relays 415 and 410 whereupon relay 405 releases. Relay 427 being slow to release, maintains its armature attracted during the interruptions inthe line circuit which cause the release of relay 410 and thereby prevents the opening of the holding bridge across the line through the retardation coil 424. lwhen relay 410 again operates, a circuit is established tor the line lamp 423 extending from grounded battery through said lamp, the lett hand armature and back Contact ot relay 422, the outer lett hand armature and liront contact of relay 418, the outermost right. hand armature and back contact of relay 405, the liront contact and outer right hand armature of relay 418, the front contact and left hand armature of relay 406 and the inner lett hand armature and iront contact of relay 410 to ground. lu answer to thev lighting ot the lamp 423, the attendant operates the. listening key 417 which again operates relay 405 thereby opening the eircuitfor lamp 423 and extinguishing the same.

lt the attendant has occasion for any reason to transfer a call to another line than the one originally selected, she may do so by operating` the key 40T. This opens the circuit t'or relays 406 and 418 permitting these relays tore-lease provided they have been operated by the 'called subscriber answering the call. The operation ot release key also grounds the oil normal brush 516 through the lower alternate contact ot key 40'( and the lett hand armature and trout. contact ot relay 403. The ground on brush 516 causes the operation ot relays 503 and 507 through their lett hand windings in parallel and the operation of the latter relay establishes a selt-interrupting` circuit for thel motor magnet 506, which will thereupony operate to return the lunshes ot the switch to their nor-

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