US1580951A - Telephone system - Google Patents

Description

A ril 13,1926. 4 1,580,951 L. J. BOWNE Er AL TELEPHONE SYSTEM Filed Dec. 31, 1924 3 Sheets-Sheet 1 &

/n vemars: I lanyfardJBoqme Horace W Ulric/7.

by ,my

L. ,1. BOWNE ET AL April 13 1926.

TELEPHONE SYSTEM 3 Sheets-Sheet 2 Filed Dec. 51 1924 Horace W (l/r/ch.

April 13 1926. 1,580,951

| J. BOWNE Er AL TELEPHONE SYSTEM l' ilecl Deb. 31. 1924 :5 She ts-Sheot 5 hue/Wars.- lanqrbrd J flow/1e. Horace W Ulrich.

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Patented Apr. l3, 1925?.

UNITED STATES 1 ,580,951 PATENT OFFICE.

LANGFORD J'. BOWNE, OF HOWARD BEACH, NEW YORK, AND HORACE ,W. ULRICH, OF

EAST ORANGE, NEV JERSEY, ASSIGNORS TO WESTERN ELECTRIC COMPANY, IN- CORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed December 31, 1924. Serial No. 759,195.

To (ZZZ whom it may concern.

Be it known that we, Lnnsronn J. Bownn and Homes W. ULRICH, citizens of the United States of America, residing at Howard Beach, Queens County, New York, and East Orange, Essex County, New Jersey, respectively, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full, clear, conelse, and exact description.

This invention relates to telephone systems and more particularly to two-way intercxchange trunk lines and connecting cord circuits therefor adapted to be used in a multi-exchange system.

T he object of the invention is to provide improved m ans for increasing the operatefiiciency, and effecting installation economies in systems of this character.

The invention hereinafter described is particularly applicable to a system comprising a plurality of private branch exchanges. In such systems it is desiraole to be able to interconnect any one subscribers line with any other subscribers or central office line, terminating either at the same or at different switchboards of the system. For the purpose of describing this invention, the circuit arrangement hereinafter described for interconnecting any two of such private branch exchange switchboards will be called a through and terminating tie line and a connection of two such tie lines at any private branch exchange will be referred to as a through tie line connection.

A feature of the invention resides in a circuit arrangement for tie lines of he char acter described which automatically discriminates between tie line to station, tie line to central office and through tie line (tie line to tie line) connections wl'iereby a repeatingcoil ,is included in. the tie line to station and in the tie line to central oilice connections and a direct talking path, from which the repeating coils and associated equipment are absent, is pro dried for through tie line conncctions.

The tie line of the present invention is adapted to function under all conditions with standard private branch exchange cord circuits similar to the one disclosed in Patent No. 1559,5297, granted October 27, 1925, t lter P. Albert, thereby making it uny to provide at each switchboard socalled universal cord circuits or other special equipment heretofore employed for making through connections from one tie line to an other.

More specifically, when the back plug of a standard P. B. X. cord, similar to the cord circuit described in the aforementioned copending application, is inserted in a jack ass ciated with a tie line according to this invention the tie line descriminates between battery normally supplied'by the cord for station connections and the battery supplied by a line to which the front cord may be connected, that is, acentral ofiice trunk line or another through and terminating tie line, and it further discriminates between the battery current supplied by these two latter types of lines. In case a cord circuit is connecting two through and terminating tie lines battery current from the tie line to which the front cord is connected causes apparatus associated with both tie lines to function to remove the normally connected repeating coils and associated equipment from both tie lines and to connect the tie lines through as hereinbefore mentioned.

Another feature of the invention resides in the provision of means, associated with a standard P. B. X. cord circuit, responsive to the operation of a monitoring key associated with saidcord circuit, to disconnect the low impedance talking circuit of the opera tors telephone set from the cord in case any talking key at the position is operated; to connect the operators receiver to the cord through a high impedance transformer for the purpose of minimizing transmission losses during monitoring and to prevent the connection of a second cord circuit with said first cord circuit in case the talking key of the second cord circuit is operated during the period the monitoring key of the first cord circuit is operated.

fitill another feature resides in the provision of means comprising a selector and a relay associated with the incoming end of a railway message telephone line which terminates at a P. B. X. in a tie line circuit in accordance with this invention whereby selective impulses transmitted over the message line from an outlying station cause said selector to function to cause said relay to initiate a call over the tie line equipment in the usual manner herein described.

Other features, not specifically mentioned, including further discrimination means and provision for supervision under all conditionsot the line, will more readily appear from the following description of the invention in conjunction with the accompanying drawings in which a tie line embodying the invention is shown together with sufficient connecting apparatus to properly illustrate the invention.

Referring to the drawings:

Fig. 1 shows one end of a tie-line according to the present invention terminating in a private branch exchange switchboard with which may be connected a cord circuit shown in Fig. 2.

Fig. 1 represents a trunk to a central office, terminating at the same private branch exchange as the tie-line herein described,

with which connections may be made ashereinbei'ore mentioned.

Fig. 1" represents the circuit arrange,- ments for th-e extension of the tie-line of Fig. 1 to another private branch exchange where it terminates in a similar circuit arrangement; and Fig. 1 represents an arrangement for connecting the tie-line circuit of Fig. 1 to a railway message telephone line equipped with selector equipment.

Figs. 3, 3 and 3 are duplicates of Figs. 1, 1 and 1", except that the circuit arrangement is shown in reverse order. The cord circuit in Fig. 2 is designed to interconnect the tie-lines illustrated in Figs. 1 and 3.

Fig. 3 represents a subscribers line served by the private branch exchange.

It should be understood that the system is readily adaptable for extending dial station lines terminating in automatic switches, not shown, which switches have access to the P. B. X. attendant. Also, central ofiices associated with the private branch exchange, as for example in Fig. 1, may either be semi-automatic or automatic, as well as manual. For purposes of this description, the drawings have included only that necessary to an understanding of the invention.

Fig. 2 is a schematic of an intercommunicating multi-exchange telephone system to which the invention is particularly applicable. Private branch exchanges at five cities, Boston, New Haven, New York,

Philadelphia, and Washington, are shown linked together by tie lines. The rectangular boxes on either side of the circles representing the respective P. B. X.s at each city indicate an end of atie-line capable of forwarding or terminating a connection from another private branch exchange. The

small circles designated V, N, X, Y and Z represents central ofiices, the smaller circles a, Z), 0, etc. to 9 represent subscribers of a central otfice or stations of a private branch exchange and the small square h a rallway train dispatchers station on a railway message telephone line terminating in tie line equipment at the Washington P. B. X.

A detailed description of the operation of the system will now be given.

Considering Fig. 3, on incoming calls from a distant private branch xchange, relay 10 operates in a circuit from the distant loop, tip of the line, contact 15 of relay 11, upper contact of relay 12, upper right-hand winding of repeating coil 13, condenser 14, winding of relay 10, lower right hand winding of repeatingcoil 13, lower normal contact of relay 12, contact 16 of relay 11, ring of line, to distant P. B. X. Relay 10 causes relay 17 to operate in a circuit comprising ground .18 of lead B of Figure 3 which is the normal arrangement, contact 19 of relay 10, contact 21 of relay 20, winding of relay 17, normal contact 22 of relay 23 and battery 24. Relay 17, upon its energization locks up to ground 25 at its alternate contact 26, and lights line lamp 27 in an obvious circuit including battery 28, and contact 29 of relay 17, to ground 31 at the lamp. Busy signal 32 will also be set in a circuit from battery 28, contact30, to ground at the signal.

It the call, on the other hand, be considered incoming to the end of the tie-line shown in Fig. 1, a similar operation would take place, relays 210 and 217 operate, lamp 227 lights, and make busy signal 232 is set.

For simplicity, however, the operation in the answering of an incoming call will be described only in conjunction with Fig. 3. As the tie-line is handled on a station basis, it is answered with the rear cord of the cord circuit (shown in Fig. 2). The attendant upon noting the illumination of lamp 27 will insert the rear plug of the cord into jack 33 of the tie-line. The tip spring of the jack will, therefore, serve to close the.

local contact to ground 34. Thereupon relay 35 will operate in a circuit as follows: battery at relay 35, winding of relay 35, resistance 36, armature and contacts 59 of relay 23, contacts 37 and armature of relay 38 to ground 34. Relay 35 by closing its contacts 40 thereupon causes relay 39 to operate in a circuit from battery of relay 39, outer normal contacts of relay 41, normal back contact of relay 42, contacts 43 of relay 39, contacts 40 of relay 35 to ground 34.

Relay 39 looks up to ground 34 through its contact 44, in a circuit including outer normal contacts of relay' 41, outer normal contacts of relay42, contacts 44 of relay 39 and contacts 37 of relay 38. Relay 39 also closes the circuit to relay 45 at its contacts 46 which may be traced from battery of relay 45, outer right-hand normal contact of relay 23, contacts 46 of relay 39, 37 of relay 38 to ground 34 at the jack.

Relay 45 will then lock up in a circuit in- Ill) relay 23, contacts 50 of relay 45 to ground 34; and lock up to ground 34 through its alternate outer left-hand contacts and contacts 37 of relay 38. Relay 23 will then -cause relay 17 to deenergize by pulling over its inner ri ht-hand armature and openmg contacts 22 to disconnect battery 24 therefrom. The pulling over of this armature will connect battery 24 to hold busy signal 32 operated after relay 17 releases. Relay 17, in releasing extinguishes the line lamp 27 to note the answering of the call. Cut off relay 23 in pulling over its outer right-hand armature opens the path from the make contact 46 of relay 39 to the winding of relay 45 to prevent future false operation of re lay 45. Relay 45, however, will not release at this time, being locked up at ground 34 through its contacts 47 and contacts 40 of relay Relay 23, in operating, also opens the operating path to the winding of relay 35 throu 'h resistance 36 at contacts 59. Relay 35 will, therefore, be cut off from ground 34 and failing to find a holding ground, releases. It should be noted that With the rear cord in the jack there is no ground on the sleeve of the cord. Relay 35 in releasing, opens contacts 40, in turn releasing relay 45. Relay 23 also closes the circuit through winding of relay 20 at its contacts 52 from battery 51. The circuit finds a holding ground at 34 through contacts 37 of relay 38. Relay 20 operates slowly. Finally, relay 23 by closing its inner left hand armature contacts connects ground 34 through the normal contact of relay 35, when it releases, to the sleeve of the jack through contacts 37' of relay 38. This ground on the sleeve of the jack provides a ground for supervisory lamps 101 and 102 in the cord circuit, and serves for an audible busy signal when a busy test is made on the sleeve of a multiple jack.

Relay 20 in operating opens at its contacts 21 the path fronr the front contact 19 of ringing relay 10 to the winding of relay 17, to prevent the possible operation of this relay on a re-ring. It also opens the short circuit of the winding of relay 53 by pulling over its left-hand armature. Primarily, relay 20 connects the ring side of the jack through the lower left-hand winding of repeating coil 13, left-hand make contacts of relay 20, normal left-hand contacts of relay 45 to Winding of relay 54, winding of relay 55, then back through the right-hand normal contact of relay 45 to the tip of the line through upper left-hand winding of repeating coil 13. The result of connecting relays 54 and 55 across the rear cord is to cause the operation of the rear supervisory relay 103 and the extinguish ment of rear lamp 101, in a circuit as follows z-grounded battery 104, inner lefthand normally closed contacts of relay 105, winding 106 of retardation coil 107, contacts 108 of through dial and night key 109, winding of relay 103, to ring of the plug and jack, through the loop including relays 54 and 55, as hereinabove described, back through the tip of the jack, tip of plug, contacts 110 of key 109, winding 111 of coil 107 right-hand normal contacts of relay 105, to ground.

Front lamp 102 remains lighted inasmuch as front supervisory relay 112 remains normal, the circuit path running from grounded battery 113, through the lamp, outer left hand contacts of relay 105, normal contacts of relay 112 to ground on sleeve of jack.

It may now be noted that on calls to stations, the station receives a greater amount of transmitter battery than on average station to station calls, due to the comparative high resistance of relays 54 and 55 in the loop.

Polarized relay 54, in operating on the cord battery 104, closes the circuit to the windings of the relays 41 and 56 in apath as follows :battery and windings of relays 41 and 56, make contact of relay 54, normal armature contact of polarized relay 55, which is not operated on the cord battery, to ground 34. Relay 41, thereupon opens the circuit to the winding of relay 39 which releases. No further operation of the circuit takes place on calls to stations or calls to central office trunks on which the battery is poled the same as the cord circuit battery. On calls to other through and terminating tielines or to central oflice trunks which supply reverse battery before or after the called party answers; and hence variously and differently affect polarized relays 54 and 55, there is further functioning of this circuit, as will hereinafter be explained.

Considering now the ope-ration of the circuit on outgoing calls from stations or other types of tie-lines; such stations as for example or f as illustrated in 2 are answered with the rear plug of the cord and their extension is affected by the insertion of the front plug in the forwarding tie-line (as 302 or 303 depending on the extension desired) \Vhen the front plug of the cord is inserted. in the tie-line jack of Fig. 1 (the same operation taking place if the circuit arrangement per se in Fig. 3 were considered) the auxiliary contact on the jack closes the circuit from ground 234 to the winding of relay 235 through resistance 236. The circuit extends from battery, winding of relay s35, resistance 236, contacts 259 of relay 223, contacts 237 of relay 238 to ground 234. Relay operates and connects the sleeve of the jack to a point 297 between the winding of relay 235 and resistance 236, through its alternate left hand contacts. It should now be observed that relay 105 of the cord circuit is connected from ground to thesleeve of the front cord, and therethrough to battery of the relay 235. As a result of the difference of potential between the sleeve of the front cord and the point 297 between relay 235 and resistance 236, relay 105 of the cord will operate; the winding of relay 235 is shunted by resistance 270 to provide sufiicient current from battery of relay through relay 105 to cause said relay to operate. Relay 105, in operating removes the battery on the ring and ground on the tip of the line; and bridges winding 111 of retardation coil 107 across the cord circuit in a path from tip of the cord, upper normal contacts of relay 114, contacts 110 of key 109, winding 111 of coil 10?", make right-hand contact of relay 105, normal contacts of relay 115, contacts 116 ofkey 109, normal back contacts of relay 114 to ring of the cord. -When relay 235 operated, it closed the circuit at its outer right-hand contacts to relay 239, through contacts of relays 241, 242 and 239. Relay 239 thereupon operates, locks up to ground 234 through its alternate left-hand contacts, and in turn closes the circuit to the winding of relay 245 :from battery, winding of relay 245, outer normal left-hand contacts of relay 223, inner left-hand alternate contacts of relay 239 to grounc 234 as herein before described. Relay 239 also closes the circuit at its outer right-hand alternate contacts to relay 248 which operates, but performs no useful function at this time. Relay 245 locks up to ground 234 through its inner left-hand contacts and outer righthand contacts of relay 235. Relay 245 in pulling up its outer contacts on either side, now disconnects relays 254 and 255 from windings of the repeating coil 213 and instead transfers the tip and ring of the line through the windings of the repeating coil to the windings of retardation coil 25'? and the winding of relay 258. The detailed circuit changes will be later described. It should be observed, however, that the circuit path from the upper right-hand winding of repeating coil 213 proceeds from battery of etardation coil 25?, and that the lead from lower right-hand winding of repeating coil 2l3, is opened at the contacts of relay 220. It is due to this breal: in the circuit that the loop from the cry bridge including winding 111 of the retardation coil in the cord circuit, and including relay 258, is not completed at this time. It may also be noted that relay 242 is short circuited by the armature normal contacts of relay 258 in an obvious circuit. Relay 245 upon energizing closes the circuit at its inner right-hand contacts from ground 234 to the winding of relay 223 which operates, and locks up to ground 234 through its inner operated contacts 259 and contacts 237 of relay 238.

Relay 223 in operating opens at contacts 259 the ground through resistance 236 to relay 235, which does not release at this time but now holds up in series with relay 105 in the cord circuit. Relay 223, incidentally connects battery at its left-hand alternate contacts to the winding of the busy signal to operate it. Also, in pulling over its outer left-hand armature relay 223 opens the connection between the winding of relay 245 and the inner left-hand contacts of relay This is to prevent future false operation of relay 245. Its main function, however, is to close the circuit to the winding of relay 220 which opens the obvious short circuit on the winding of relay 253 and closes the loop consisting of the dry bridge of the cord and the windings of relay 258 as follows :-battery and winding of retardation coil 25?, alternate left-hand contacts of relay 245, upper right-hand winding of repeating coil 213, tip of jack and plug, upper normal contacts of relay 114 in the cord, throughthe upper normal contacts of key 109, winding 111 of coil 107, right-hand inner alternate contacts of relay 105, through obvious contacts of key 109 and relay 114, ring of plug and jack, lower right-hand winding of repeating coil 213 alternate right-hand contacts of relay 220, outer right-- hand alternate contacts of relay 245, upper winding of retardation coil 257 winding of relay 258 to ground at 234. Upon the energization of relay 258 and the attraction of its armature the obvious short circuit on relay 242 will be removed, and relay 242 will as a result operate. Relay 242, then opens the circuit at its outer contacts serving relay 239, which thereupon releases. Incidentally upon the release of relay 239 and the return of its outer right-hand armature to normal, relay 248 will release. Relay 242 also is designed to close the circuit at its inner contacts from its secondary winding and the winding of relay 211 to normal contacts of relay 258. Relay 258 however, is' purposely operated at the same time, as above described, and serves to prevent relay 211 from operating and relay 242 from looking up to ground 234.

Transmitter battery for the station on the rear cord as for example that illustrated in Fig; 3 is fed'from the battery at retardation coil 25'? in the loop including the windings of relays 242 and 258 which remain operated.

The part of the loop circuit in the cord may be traced as follows :t-ip of front ack and cord, tip of rear cord and jack, through the station, back through rear jack and cord, winding of relay 108, (which energizes and closes a circuit for relay 115 from battery 104 through inner left-hand armature of 0perated relay 105), contacts 108 of key 109, right contacts of relay 115 now energized and closing a short circuit on the winding of relay 112, contacts 116 of key 109 back to ring of plug and jack to ground in the tieline as hcreinbefore described.

It may here be explained that on calls from tie-line to station or station to tie-line as just described, the repeating coils and associated equipment i. e., the retardation coil, the relays 242 and 258, etc., are so arranged, that talking battery from current source 257 is supplied to the station, and for supervision in the cord circuit, while at the same time, static-n battery is eifectivelyprevented from reaching the toll line and from interfering with toll line apparatus.

Provision is made for re-ring supervision from the tie-line when either the front or rear plug is in the jack as follows :When the rear plug is in the jack, (using Fig. 3 for illustrative purposes), relay 35 is normal and relay 20 is operated, as hereinbefore described. On a re-ring from the tie-line by the operation of the usual ringing key, at the distant station (not shown), relay 10, bridged across the line, will obviously operate, and shunt down relay 20 by closing a circuit from battery 51, through its contacts 19 to ground 18 of lead B. The shunting of relay 20, and the restoration of its left-hand armature causes the opening of the super visory bridgeon the inside of the repeating coil. which as hereinbefore completely traced, includes relays 54 and 55, and as a result supervisory relay 103 in the cord circuit is released. In consequence lamp 101 lights. Upon the completion of the ring, relay 10 releases, whereupon relay 20 again operates, pulls over its left-hand armature to complete the loop and thus causes supervisory relay 103 to reenergize and lamp 101 tobe extinguished.

Vhen the front plug is in the jack (again using Fig. 3 for illustrative purposes, although Fig. 1 might equally be used) relay 35 remains operated, as described above, and prepares an operating path through its inner left-hand closed contacts for relay 60. On the re-ring from the tie-line, relay 10 is operated and relay 20 releases as hereinbetore described. Relay 60 then operates in a circuit from battery, winding of relay 60, inner left-hand contacts of relay 35, normal right-handv contacts of relay 17, restored contacts 21 of relay 20, inner contacts of operated relay 10 to ground 18 of lead B. Relay 60 in operating pulls up its armatures and connects ringing current to the tip and ring of the line, and thus to the cord circuit to operate ringing supervisory relay 40, in an obvious circuit. Relay 159, in series with condenser 160 controls lamp 102. As long as ringing current is supplied relay 60 in the tie-line, and relay 159 in the cord remain 0pcrated and hence lamp 102 will light in an obvious circuit to ground at relay 159. At the end of the ring, relays 60 and 159 will release and lamp 102 go out. It may be remarked that relay 20 is made slow releasing so that it will not release in case relay 10 operates momentarily due to disturbance or on surges from the tie-line. Only the application of steady ringing current will effect the operation outlined. The purpose of heavy resistance shunt 61 on the winding of relay 10 is to make relay 10 unresponsive to morse thumps which may be impressed on the line and thus on the relay, when the tieline is composited. Resistance 61, is arranged to effectively absorb the peaks of any inorse impulses, so as to prevent relay 10 i from operating long enough to effect the restoration of slow-to-release relay 20.

The circuit operation, on an outgoing ring, with the front cord in the jack will now be described. (For consistency with the previous description, Fig. 1 will now be used for illustrative purposes). As shown hereinbefore, relays 235, 245, 223, 220, 242, and 258 are all operated in the tie line associated with the front cord. In order to ring over the line, the attendant will operate the usual ringing key in the cord circuit, associated with the front cord. Relays 242 and 258 will release on the opening of the cord circuit bridge by the actuation of the ringing key. Also this release takes place immediately before the ringing current is applied; i. e., immediately after the opening of the cord circuit bridge and during the in finitesimal interval before the key contacts to connect ringing current to the line. Relay 242 releases first and breaks its locking circuit when its inner armature restores, be fore relay 258 closes its back contacts. This is due to relay 258 being slower to release than relay 242. As a result, relay 242 is assured restoration without danger of finding a holding ground through the back contacts of relay 258.

When the ringing current is connected by the ringing key contacting, ringing relay 253 operates in an obvious circuit through the jack, plug, and repeating coil 213 and closes the circuit to relay 212, through the inner contacts of relay 253 and ground through the jack. Relay 212, upon operating, obviously opens the line from the repeating coil and connects it to the associated ringing circuit. Ringing will thus be efiected by the attendant. On the complete restoration of the ringing key in the cord, re

lay 258 will again operate and will remove the obvious short circuit on relay 242, thus allowing it again to operate in series with relay 258 and the dry bridge of the cord circuit, as hereinbefore explained and .de scribed.

The circuit condition of the line termed a through tie-line connection with the rear cord in the tie-line jack, will now be considered. If a tie-line, for example, one from Philadelphia as illustrated in Fig. 2, which had been answered by a rear cord at tie-line 300 in New York is to be connected to another tie-line, NewHaven, the connection is known as a through tie-line connection, and there is no need for battery, or ground, or for the repeating coils to be in the circuit at the New York exchange. The circuits at the New York office, are therefore, designed to recognize each other and to advance in condition to their through tie-line positions in which relays 211 or 11, respectively, in Figs. 1 and 3 are operated and effect a through, clear unimpeded line, obviating the usual transmission losses.

l/Vith the answering rear cord of the cord circuit in the tie line jack (of Fig. 3) relays 54 and 55 are bridged across the line in a circuit including battery source 104 in the cord, etc., all as hereinbefore explained in the description dealing with the answering of incoming calls with the rear cord. As described relay 54 operates on the straight cord battery, whereas relay 55 in series therewith but of opposite polarity does not operate. Upon the actuation of relay 54, relays 41 and 56 operate from the battery sources associated therewith, through the alternate contacts of relay 54 to ground 34 as hereinbefore described.

Now, when the front cord of the cord circuit is inserted in another tie line jack (as for example that of 301 at New York in order to forward the call) as represented in Fig. 1, relay 105 operates in the cord circuit, as explained in the description dealing with outgoing calls from station or other tie lines. This removes battery 104 and ground normally connected to the inner right hand armature of relay 105, from the cord circuit, and allows the relay 54 to release,

which in turn releases the relay 41 (which performs no useful function at this time) by breaking the path to holding ground 34. Upon the restoration of relay 54 and the breaking of its alternate contacts, relay 56 starts to release very slowly, it being a slow release relay. Relay 54 closes its back contacts before relay 56 releases, in turn closing the circuit through the operated contact of relay 56 to the winding of relay 39 which operates and locks up in a path as follows: battery and winding of relay 39, outer normal contacts of relay 41, outer normal con tacts of relay 42, contacts 43 of relay 39,

operated contacts of relay 56, normal contacts of relays 54 and 55, to ground at 34.

When relay 220 in the tie line circuit on the front cord operates, as was described, it closes ground through the windings of relay 258 and the repeating coil in that circuit to the ring side of the line and battery through a winding of the retardation coil to the tip side of the line. This battery it will be noticed is reversed to that received from the cord (i. e. the battery received from the cord circuit is connected to the ring side of the line, and ground is on the tip side). As a result polarized relay 55 in the tie line circuit on the rear cord, while unaffected heretofore, although included in the loop, is now affected by the reversal in polarity and. will operate. Relay 55, in operating, opens the operating path of relay 39,'above described, in connection with its operation due to the slow release of relay 56. Relay 39, however, will still remain locked up to ground 34. Relay 55 closes through its contacts the ground 34 to the winding of relay 49 which operates.

It, may here be explained that upon operating, relay 49 prepares a ground circuit through its outer right hand armature contacts to the winding of relay 23 to prevent relay 23 releasing later when relay 38 operates and opens its contacts 37. Relay 49 also prepares a locking path for itself through the normal left hand contacts of relay 48 and inner right hand alternate contacts of relay 38, (relay 48 being operated through the outer left hand operated contacts of relay 39 when relay 39 operated). Relay 49 in operating now opens the operating path of relay 48 by pulling up its inner right hand armature and closes a path to the winding of relay 38 which operates in the following circuit: battery, winding and outer right hand normal contacts of relay 38, inner left hand operated contacts of relay 39, middle right hand operated contacts of relay 49, alternate contacts of relay 55 to ground at 34 through the usual path. Relay 38 will immediately lock up to ground 34 through its outer alternate right hand contacts.

The'operation of relay 38 closes ground at its inner right hand alternate contacts through the operated contacts of relays 48 and 49 to a point 63, between relays 54 and This condition exists as long as relay 48 remains operated, after its operating path is opened by relay 49, relay 48 being slow to release. The function. of this ground in shunting down relay 258 in the tie line on the front cord will be hereinafter shown.

Now will be described the circuit condition in the tie line with the front cord in the tie line jack, i. o. the tie line forwarding the call on a through tie line connection, the incoming cell having been answered with the rear cord as just described. As hereinbetore observed, when the front cord is in a as sociated tie line jack, relays 235, 24.5, 223, 220, 258 and 2 12 are operated. l t hcn the rear cord is in another tie line jack, relay 103 in the cord circuit is operated in the circuit from the current source at 257 in the tie line associated with the front cord, through the cord and the dry bridge of relays 5 1 and 55 in that tie line circuit (i. e. on the rear cord), as hereinbefore explained. Relay 103 in operating closes the circuit in the cord, to relay 115 which operates from battery 10% to ground at the jack through the alternate contacts of relay 103. The oper ation of relay 115, changes the comparatively low resistance bridge in the cord circ .it C0111- prising winding 1.11 of coil 16?, to a much higher resistance bridge now including windings 111 and 161 in series. This bridging circuit, in the cord alone, includes the tip conductor, contacts 110 of key 109, windings 111 and 161 of coil 107, alternate left hand contacts of relay 115, contacts 116 of key 109, to ring of the line. This bridge in the cord, it may be observed, bridges the circuit heretofore described that extends from the battery associated with coil source 257 in the line on the front cord, through the cord, and relays 54 and 55, etc. in the tie line on the rear cord, back to ground 23 1. As a result, relays 2412 and 258 in the tie line on the front cord are, held by the dry bridge consisting of relays 5 1 and 55 in the tie line on rear cord, in multiple with the dry bridge in the cord circuit comprising windings 111 and 161; and also by retardation coil 162 in the attendants talk and dial front circuit, which is also bridged across the line due to the actuation of key 161 and the consequent operation of relays 163 and 114: as follows: Upon the necessary opera tion of talk and dial front key 16 1 (in order to ascertain what disposition is to be made of the call going through) relay 163 will close a circuit from battery and winding thereof, normal contacts of monitoring key 165, lower operated contacts of key 16 1, lower normal contacts of relay 166 to ground at armature of relay 167. Relay 11s will thereupon operate through upper operated contacts of relay 163, upper contacts of of key 1641 to ground at inner arma ture of relay 167. The operation of relay 114 closes ground to relay 166, which causes the energization of the secondary winding of relay 163. As a result, retardation coil 162 is bridged across the cord, the obvious paths including normal contacts of relay 168 and the outer alternate contacts of relay 163.

To proceed with the through tie line circuit operation, when relay 55 in thetie line circuit on the rear cord operated (on reverse battery), and caused the operation of relays 19 and 38,-ground was connected to the rear tie line circuit as above related, to a point 63 between relays 51 and 55. The relay 258 in the tie line on the front cord will value. Belay 242, however, is not so afiected and remains operated on this current. Re-

lay 258 releases slowly and closes ground through the ope *ated contacts of relay 24-2. Relay 242 then locks up as follows: Battery, secondary winding and inner contacts of relay 242, normal armature contacts of restored relay 258 to ground 2341-. Relay 258 by restoring also and principally serves to connect groundto relay 211 after it short circuits the primary winding of relay 2 12 in an obvious circuit. incidentally, it may be noted that relay 242 remains operated on its short circuited primary long enough for the contact on relay to close the circuit toits secondaryas above described. Relay 211 operates slowly in circuit through the inner operated contacts of relay 24.2 and normal contacts of relay 258 to ground 234. Upon its energization, it obviously opens the repeating coil 213 from the tip and ring of the line. In consequence, the dry bridge of the cord circuit is disconnected from the winding of relay258. This operation con sisting of the release of relay 258 and the operation of relay 211 occurs before slow to release relay 18 in the tie line on the rear cord releases.

When the battery associated with coil 257 is removed by the operation of relay 211 on the front cord, relay 55 in the tie line on the rear cord releases and thus opens the operating circuit of relay 4 9. Inasmuch as relay d8 has not yet released up to this time, relay 49 fails to find a holding ground through the normal contacts of relay 418, and will therefore release. Relay 4-9 by opening its outer right hand contacts opens the ground to the winding of relay 23. Relay 23, however, will still find a holding ground at 34 as long as relay 62 remains normal, tl'irough the inner left hand alternat-econtacts of relay 38, normal contacts of relay 62, inner right hand alternate contacts of relay 37, to ground 3% through the usual path. However, as soon as relay 19 completely releases, relay 62 operates through its outer lefthand restored contacts and the inner right hand alternate contact of relay 38 to ground 341. Upon the operation of relay 62, it opens the ground connected to the sleeve of the tie line circuit and to. relay Relay 38 as a result loses its holding ground and releases, thereupon obviously causing relay 20 to release also. Relay 23, in releasing and opening its outer left hand operated contacts opens the ground to relay 39 which releases. When slowly releasing relay 48 finally releases, it opens the ground connected to the line (i. e. from point 63 at relay 55 through operated contacts of relays 48, 19 and 38 as heretoforeexplained) and consequently causes its connection (i. e. from ground through the inner right hand alternate contacts of relay 38, normal outer right hand contacts of relay 48, inner right hand normal contacts of relay 19, to winding of relay 11, which operates and obviously disconnects the repeating coil 13 and associated equipment from the tie line on the rear cord.

Thus, with the operation of relays 11 and 211 in the tie lines on the rear and front cords respectively, the repeating coils are out out and the tie lines are connected directly through the local cord. It may be noted that it was by the mere insertion of the front plug in the tie line jack, that this condition was brought about due to the reception, recognition, and proper execution in the tie line on the front cord of the particular affecting operating condition of the tie line on the rear cord.

Vith the through tie line condition brought about, a description will now be given relative to flashing of the supervisory lamp in the cord circuit while this through connection is being set up. When the front cord is inserted in a second tie line jack, after the rear cord has been inserted in a tie line jack, the supervisory relay 103 in the cord circuit is operated. As a result, supervisory lamp 101 is kept extinguished. However, when the relay 105 in the cord circuit operates in series with starting relay 235 in the sleeve of the tie line on the front cord as heretofore described in detail, and as a result of said operation battery 10 1 and ground at the right hand armature of relay 105 are reversed from the cord circuit, relay 103 releases and causes supervisory lamp 101 to light.

Soon after, as was observed, relay 220 in the tie line on the front cord operates, and connects the reverse battery 25? to the cord circuit. This operates relay 103 again, and thus extinguishes lamp 101. Then, when the ground is connected by relay 38 to the ring of. the tie line on the rear cord, relay 103 is shunted down momentarily due to a reversal of current flow through it caused by the shunting of the ground from the front cord, by the rear cord tie line. This sudden lapse prior to its operation on reverse battery, is sufiicient to momentarily light the supervisory lamp. However, as soon as relay 103 operates on the reverse current it extinguishes the lamp again. From a practical standpoint this flash may not be noticed. There is another flash due to battery 257 being removed by relay 211 in the front cord. This allowsrelay 103 to release before the sleeve ground serving lamp 101 is removed by the operation of relay 62 in the rear cord tie line. When however, this ground is taken off the sleeve, lamp 101 is extinguished and remains so until either distant interconnected exchange re-rings, as will now be explained.

Clearly, on an outgoing ring on through tie line connections, the ringing current is applied directly to the line by means of the usual ringing key bridged thereacross in the cord. No relays, therefore function under this condition. However, on re-rings from either distant tie line on through tie-line conneotions, after relays 11 and 211 have operated in the respective tie lines and the ground is removed from the sleeve of the rear cord by the operation of relay (52, nonlocking supervision is given to the cord circuit as follows: relay 6 1 is bridged across the tip and rin of the rear tie line through the inner middle left hand contacts of relay 38 which is connected directly through to the tie line on the front cord. Relay (Set will operate on a ring from either tie line and will, by pulling up its armature, restore relay 62, which in turn connects ground from 34; to the sleeve of the rear cord through the operated inner right hand contacts of relay 38, restored contacts of relay 62, inner left hand alternate contacts of relay 38, through normal right hand contacts of relay 35 to the sleeve of the rear cord. As a result, rear supervisory lamp 101 will find a ground and remain lighted as long as relay 64 is operated, thus signaling the attendant.

In considering the use of this tie line with reverse battery central oliice trunks, it may be noted that as a general rule in manual and full mechanical power driven machine switching systems, negative battery is supplied over the ring of the line and ground, 1. e. positive battery is connected to the tip, whereas in the usual step-by-step machine switching system, negative battery is connected to the tip, and ground is connected to the ring of the line. As has been noted, the tie line circuit arrangement hereindescribed is designed to operate equally well with battery fed in'either direction. Considering the forwarding of a call from a tie line to a reverse battery central otlice trunk, it should be noted that when the rear cord is in the tie line jack, relay 5 1 (using Fig. 3 for illustration purposes) is operated on the battery 104 from the cord circuit, in turn holding relays 11 and 5G operated. Relays 35, 15 and 39 operate and release, and relays 23 and 20 operate and lock up, all as heretofore particularized. Relay 54- is, as also explained, held up due to the rear cord being in the jack. Now, when the front cord is inserted in a central ofiice jack, as for example, 301 of Fig. 1 which illustrates a central offlce trunk, Y, terminating in the private branch. exchange; and. adapted to be connectedzto-an:associated central oflice, for. example X; relay. 105. in the cord operates inserieswith relay 302. in the central office trunk,whichcloses and supplies battery to the. sleeve of the trunk: jack. The circuit pathxisizxbattery and windinggof relay 302,.

sleeve'of the ack (into which the frontplug' of? the cord=circuit isinsertedto close the. localcont'act) through the winding of relay 105 to-ground. Relay 105thereupon energizes and. removes battery 10 1 and ground at its lnner right" hand armature fromthe.

cord,.thus allowingrelay 5 1 in rear tie line to release.

At this time or immediately" after, relay 302I-by operating. obviously connectsbattery on the tip. and ground on the: ring. of the;

cord. circuit from. the central office. This reversal of battery and ground causes the polarized relay 54: to release. if'it. is still operated, and.in.turn causes relay 55 which functionson current of opposite polarity to operate. The turnover is so. rapid that relay 54in:releasingtcloses the circuit to rela.y39' (as has. heretofore been. described) only momentarily, .and therefore relay 39 does not have time to-operate. and. lock up before relay 55 inoperating,.opens (as has-been1 shown heretofore) the. operating circuit for relay 39. This is eli'ectedfpurposely in order to prevent relay 39 andthence relay 38 from operating. andthus'to keep. relay 11 from functioning to cut: out@ the repeating coil.

' By this device, relay 11 remains-normal.

To proceed, relay 55 closes the circuit. to relay d9 whichoperates through the alter? natecontact ofrelay 55 to ground 31.but

inasmuch as relay39 has not. operated, relay LSdoesnot perform any function at this time. Thebridge in thetie line, consisting offrelays. 54; and 55. holds supervisory relay 103 in the cord circuit operated,thus-keeping lamp 101'. extinguished, and causingrelay 115 to operate. Ashas be-enfully eX- plained, the operationofcrelay 115 changes the bridge inthe cord'circuit fromv one'of low. resistance. including. only resistance 111, to one ofivery highxresistance includinglll andr161 of coil.107. Because of this, as has been analogously. shown heretofore, the

bridges in the cord circuit and tie line hold the. central oflice connection operated.

Supposingthat a distantprivate branch 1 exchange connected as-justdescribed to a central office, wished to re ring the attendant at .the local 1 B. X. (as for example Boston in. Fig. 2e desiring to re-ring New Haven when connected therethrough to'central office V) the following operation could take place:The distant operator, on arecall or,

disconnect"re-ring,.when the rear cord is in the tie l1ne 1ackrand the front cord in the centraloflice jaclgtwould actuatethe usual.

ringing key, whereupon relay 10 operates and'iconnectsf ground from lead B te 1 a point 65 between reslstance 66 and relay 20. This,

in effect: causesrelayto restore inasmuch as it isnow short circuited,.by the battery 51! proceeding. directly to ground at lea'd B Fig; 1?, the normal arrangement, (in-- steadlof through the. winding of relay 20'etcto ground 34, as hereinbefore shown). The release of relay QO opens the dry bridge consisting. of: relays 54;: and 55,- from" across thecord circuit (thusiopening'the loop from thecont-rol ofhce battery) in turn causing relay 1O3 to release This closes the circuit for supervisory'lamp 101, which consequently remains lighted as long. as-the ring is'coming. in from the'distant exchange; The relays 54 a11d55 in'releasing: perform no=use1= fulfunction. At the end of: the ring,.relay 10 releases, thereby removingthesh'ort cir-' cuit. from battery 51 and:allowing relay 20.

again to operate and restore theoircuit to its CODClltlOllPIlOlltO the. re-ringix The condition and'operation of the tie line" on an outgoingcall thereto from a reverse battery central office, Wlll. 1n;turn, now be described; Upon the'flash from the central office, the front cord is connected to thercentral offic-etrunlnas' that shown in Fig. 2 The connection of the call to a tie line-.isr then effected by inserting. the. rear. cord in'* the tie line jack,.for illustration, that of Fig. 3. After the front cordis. connected to said central office trunk, .whichfeeds reverse. battery to thecord circuit,.relays 35,.

39, 4:5, 23 and; 20v operate consecutively as heretofore describedin that part of the. description dealingswith theanswering. of in-n coming. calls with the rear" cord. As shown, relays and release, relay 23locksupandholds relay 2O operated, and relay 39 looks up under; the control of relays 41 and 42.

Due to the reversebattery onthe tip and ring. of the rear cord from the central office trunk, polarized relay willanow operate (instead of relay 54),.and inturn operate relay 49 to ground Mas-heretofore.shown;

Relay 39,"in lockingup, .closesthe circuit to from battery and the windingof relay 38-to the middle right :handalternate contacts-of relay 19, through alternate contactsofrelay. 55 to ground 34-, as heretofore: described. Relay. 38', therefore; operates and.- connects! ground to the line through the operated con tacts of relays 48 and 49 as long as relay 48 remains operated after relay 49 opens its energizing circuit, as heretofore explained. This ground is connected from 34 through the inner right hand alternate contact of relay 38, outer left hand alternate contact of relay 49 and left hand alternate contact of relay 48 to the line through relays 55 and 54 etc. When slow to release relay 48 finally releases, it removes the ground from on the tie line is effected as follows: The

operation of the ringing key in the cord circuit, after relay 48 has released, causes ringing relay 53 to operate in an obvious path, which in turn causes relay 12 to operate in a circuit from battery and winding of relay 12, inner alternate contacts of relay 53, inner operated contacts of relay 23, outer operated contacts of relay 23, outer right hand alternate contacts of relay 49 to ground at 34. The operation of relay 12 thus connects ringing current to the line circuit to ring the distant exchange. It may be observed that the ringing current causes relay 64 to function but no useful result is performed as the circuit to relay 62 is open at the outer alternate contacts of relay 49. When the ringing key is restored in the cord, relay 53 restores, allowing relay 12 to release, and the ringing of the distant exchange to cease.

If, however, the ringing key is operated before the relay 48 has completely restored, relay 55 releases, in turn releasing relay 49, inasmuch as the locking circuit for relay 49 is open at relay 48 (at its left hand operated contacts). Hence, if relay 49 releases before slow to release relay 48 closes its back contact, the circuit to relay 11 heretofore traced through the inner right hand normal contacts of relay 49 etc. is open at the contact of relay 48. Again, when relay 49 releases it closes an operating path for relay 48 from an operated contact of relay 39. This circuit path runs from battery and winding of relay 48, inner right hand normal contacts. of relay 49, outer left hand alternate contacts of relay 39, inner right hand alternate contacts and armature of relay 23, inner left hand alternate contacts of relay 38, normal contacts of relay 62 and inner right hand alternate contacts of relay 38 to ground 34.

In case, however, slow to release relay 48 perchance releases before relay 49 releases, it closes the looking circuit of relay 49, hereinbefore explained, and thus prevents relay 11 from operating on the opening of the central oflice battery by the ringing key.

It may be explained that it is the purpose here to prevent relay 11 from operating, and thus to prevent the cutting out of the associated repeating coil. This is accomplished by keeping either of relays 48 or 49 oper' ated. The repeating coil is inserted in the tie line circuit in terminating connections with central offices, to prevent the central office from reaching the toll line, and from interfering with toll line apparatus. The releating coil in association with its auxiliary apparatus (1. e. relays 54, 55, etc.) also provides a holding bridge for the supervisory signal in the cord circuit; and, in addition serves to hold the line central ofiice equipment, in its operated position until the connection is taken down.

To proceed when ringing current is applied by the ringing key in the cord, relay 53 operates and closes the circuit to relay 12 which operates and obviously connects ringing current to the line. Relay 53 also closes a circuit to the back contacts of relay 39 to hold relay 48 operated when relay 39 releases later. Upon the connection of the ringing current to the line, polarized relay 54 will follow the ringing current, and will operate on each half cycle of the ringing current. (Polarized relay 55 will also operate but performs no useful function as its back contact is closed when the contact of relay 54 is operated.) The operation of relay 54, as just described caused relay 41, under its control, to operate as long as the ringing continues. Relay 41 thereupon opens the locking circuit of relay 39 which as shown was held up by ground 34, thus causing relay 39 to release. This transfers the operating circuit of relay 48 from under control of relay 62 to the control of relay 53. In detail, the circuit for relay 48 formerly extended from battery and winding of relay 48, left hand normal contacts of relay 49, outer left hand alternate contact of relay 39, inner right hand operated contacts of relay 23, inner left hand operated contacts of relay 38, normal contacts of relay 62, inner right hand alternate contacts of relay 38 to ground at 34. Relay 48, will now, upon the operation of relay 39, be under the control of relay 53 in a circuit as follows: bat tery and winding of relay 48, inner left hand normal contact of relay 49, outer left hand restored contacts of relay 39, outer left hand operated contacts of relay 53, inner operated contacts of relay 53, inner left hand op erated contacts of relay 38, normal contacts of relay 62, to ground 34 through inner right hand contacts of relay 38. Relay 48 thusstays operated until relay 49 again operates. It may be observed that relay 41, in addition to effecting the release of relay 39, closesv the circuit at, its inner contact from groundthroughthe make contacts of relays 48- and, 38- to the winding of relay 19' dition of the line, the, desired result, that is, of keeping the relay 11 from operatlngand cutting out the associated-repeating c011 and loop, is accomplished.

Further, in case the ring ng key is restored before slow to release relay 18 releases, relay 55 operates on the central office battery and closes the operating path, as describechior relay 19. hen relay lfifinally releases, relay 49- locks up directly to the jack ground through contacts of relay 48 and 38 and will not release on further operationsof the ringing key.

The circuit arrangement herein outlined may be used with railway message telephone lines equipped with selector apparatus. If themtor example, a train dispatcher at station 71., Washington, Fig, 2?,desires to make connection with another station anywhere in the system, lie-will accordingly transmit by means of an impulse sending key (not shown) a code which would actuate the selector68 (Fig- 3) at the inward end of, the line at the Washington private branch exchange. It will be assumed that selector 68 moves its arm 69, under-control of the transmitted impulse code, into engagement with terminal TO-thereby connecting ground to, the right-hand winding of relay 67 and causing its operation. Relay 67 in operating connects ringing current to the Winding of relay, 10,- and ground to the armatures thereof. Upon. the operation of relay 10,

the circuitis closed to relay 17, asjpreviously described to light the line lamp and set the busy signal, etc. The call isthen answered and forwarded as previously described in detail in that part of theforegoing description dealing with the answering of incoming calls.

In accordance with the monitoring feature-ot this invention, when monitoring-key.- 165 IS operated, the circuit to relayv 167 is obviously closed. Relay 167 thereupon 0p,- erates and opens the ground onlead169, This is done for the purpose of releasing relay 1141, (01" this or other strappedccords) which may be operated if the attendant-has failed to release all the talking keys,- as 164. Relay 167, by pulling up its outer armatures, obviously disconnects thetelephone receiver from induction coil 170 and connects it' across the low impedance winding 172 of themonitoringtransformer 171., Relay 167 also connectsground to relay 168 at: its in,:- ner; left. hand. armature;

Relay 1.68 operates and, connects ground.

at" its; middle left: armature to, cause the op.- erationof1elay;l63.. The operation oat-relay 168; however, opens,- its inner and outernor mal contacts to preventtheconnection oiithe inductioncoil 1r 0, of the operators telephone set; to the talking conductors ofthe-cord and by closing itsycontactslie and 17 5 connects the three serially connected high impedance windings. 176,177 and 178- of transformer 171;theret0,instead.c The operatorsreceiver 173is thereby connected, through the monitoringtransformer. 171,.tothe talking cons 'ductors: of the cord, without the incident;

transmission loss which takes place when-the operator listens in with the regular talking andlistening circuit which includesthe rela tively low-impedance induction coil 170.

It will be noted that the operation of relay. 16.7, removes groundzfroni conductor 169 as hereinbefore mentioned. thereby preventing theoperation of relay 168 of another c0rd,. key is opwhen the corresponding talking eratechthus inturn preventing the connection of this cord to the cord: on which the monitoringkey isoperatedthrough the operators, telephone set circuit;

On receipt oi: the disconnect signal as "described, the connectionis .takendown in the usual manner, and; the circuitrestores to normal.

What is, claimedis:

1. In a telephone: system, a; plurality of private branch exchanges, tie lines-extending therebetween, repeating coils normally, included in, each tie line at each, exchange, a link circuit. at one of said exchanges for interconnecting two of said lines, and; means includedin said two lines responsivetm their interconnection for excluding: saidrepeating coils from the con.- nectedendsof; saiditwo lines 2. In; a. telephone, system, a plurality of private branch exchanges, tie, lines; extending therebetween, repeating coilsnormally included in each tie line at each exchange, a llnkrcircuiti. atone of said exchanges for interconnecting tWo off said lines, and means;

included in said'lines responsive to the intel-connectionv ofsaid two linesby said link oflicelines also terminating at certain of said exchanges, cord circuits at said certain exchanges. tor; lnterconnecting; certain of sald. lines and sand. t1e llnes, repeating 0011s 5 normally included in each end 01"- each of said tie lines, means also included in each of said tie lines responsive to the interconnection of two such lines by one of said cord circuits for excluding said repeat- 1ng coils from the interconnected ends of said lines, and other means also included in said tie lines and cooperating with said cord circuit, responsive to a connection between one of said tie lines and a "subscribers line for supplying talking battery through said tie line to the connected subscribers line when a particular end or" the connecting cord circuit is associated with the tie line and for excluding said battery when the other end of said cord is associated with said tie line.

l. In a telephone exchange system including a plurality oi private branch exchanges, tie lines extending therebetween and terminating thereat, subscribers and central oliice lines also terminating at certain of said exchanges, cord circuits at said certain exchanges for connecting certain of said lines with said tie lines, and means included in one of said tie lines responsive to its connection with one of said subscribers lines for supplying talking battery through said tie line to the connected subscribers line when a particular end 0t said cord is connected with said tie line.

5. A telephone system comprising a plu-- rality of private branch exchanges, interexchange tie lines therebetween, and terminating thereat subscribers and central oilice lines also terminating at said exchanges, cord circuits at said exchanges for interconnecting said various lines, said tie lines being arranged to include a repeating coil in the talking path on a tie line to subscribers line or tie line to central oiiice line connection via one of said cord circuits and means individual to each tie line responsive to the connection of one tie lineto another tie line for providing a through talking path tromsaid one tie line to said other tie line exclusive of said repeating coils.

6. In a telephone system, a private branch exchange, a plurality of tie lines terminating thereat, subscribers lines and central oliice trunks also terminating thereat, a cord circuit tl'iereat adapted to interconnect two of said tie lines and for connecting one of said tie lines with one of said subscribers lines or with one of said central ollice trunks, and for connecting one of said subscribers lines with one of said central oilice trunks or with another subscribers line, repeating coils associated with each of said tie lines at said exchange and included therein on connections between said tie lines and said subscribers lines or central ofiice trunks, and means included in each of said tie lines responsive to the interconnection of two of said tie lines for estab= lishing a through low impedance talking path from one tie line to the other to the exclusion of said repeating coils.

7. An intercommunication system including a plurality of private branch exchanges interconnected by tie lines, cord circuits at each of said private branch exchanges for interconnecting the lines connected thereto and those outgoing therefrom, means actuated upon the connection of one end of one of said cords with one of said tie lines, whereby upon the connection of the other end of said cord with another of said tie lines, the repeating equipment in both said tie lines is cut out, and the tie lines connected directly through the cord.

8. An intercommunication system including a plurality of private branch exchanges,

tie lines for interconnecting said exchanges,

cord circuits at each said exchange, repeating equipment included only in said tie lines and means whereby upon the interconnection of two said tie lines by one of said cord circuits, said repeating equipment in each of said interconnected tie lines is excord circuits at each said exchange for extending said tie lines to associated subscribers lines, to central oflice lines and to other tie lines, repeating equipment in said tie lines, and means actuated only upon the connection of one tie line by one of said cords to another tie line, for removing the repeating equipment in both said interconnected tie lines.

10. A telephone line, a cord circuit including a supervisory signal therefor, a repeating coil normally included in said line, polarized relays adapted to be bridged across said line, and means actuated upon the connection of said line and cord circuit for bridging said relays across said line to control said signal.

11. A telephone system including a private branch exchange, tie lines terminating thereat, a repeating coil individual to each of said tie lines, a cord circuit for interconnecting said tie lines, means responsive to the connection of one end of said cord cir' cuit with one of said tie lines for connecting a dry bridge including a winding of the repeating coil individual to said line thereacross, and other means responsive to the connection of the other end of said cord circuit with another of said tie lines for xcluding said bridge of said first tie line.

12. In a telephone system, in combination, a telephone line, a cord circuit, repeating equipment normally included in said line,

polarized relays adapted to be connected in bridge of said repeating equipment, a current source associated with said cord circuit, means responsive to the connection of said cord circuit with said tie line for operating'one of said polarized relays from sa1d current source, two other relays connected in parallel and controlled by said one polarized relay, and another relay controlled by one of said relays in parallel.

13. In a telephone system a tie line, a cord circuit for connecting therewith, a relay in said'tie line, a resistance in association with said relay, a relay in said cord circuit, and

means actuated upon the connection of a particular end'of said cord circuit with said tie line for causing the shunting of the sa1d relay in said tie line by said resistance and the operation of said relay in the cord circuit.

14. In a telephone system, a tie line, a cordcircui-t adapted to be connected thereto,

a current source in said cord circuit normallyconnected thereto, a current source an said tie line, repeating coil in said tie line,

a plurality of polarized relays in bridge of said tie line, and means controlled upon the connection-of a particular end of said cord circuit to said tie line for causing the disconnectionof said current source in the-cord circuit therefrom, and-means .tor causing the disconnection of said bridged polarized relays from said tie line and the connection of said-currentsource insaid tie line to said repeating coil.

15. .In a private branch exchange telephone system, an exchange, a tie line anda subscribers line terminating thereat, va cord circuitthereat, saidcord circuit being adapted to connect said lines, switching means in said cord circuit, -.a dry lbridge adapted to be connected across said cord circuit by said switching means, a battery source normally connected to said cord circuit bysaidswitching means,a bat- .terysource assoclated w th sa1d t1e line, repeating equlpment H1 saldtie line, and other means in cooperation "with said switching means in the cord responsive 'to the interconnection of said lines .for disconnecting said current source in the cord circuit, for connectingsaid dry bridge'across said cord, and for connecting said repeating equipment to the current source associated with said tie line.

16. In:a telephone system,"a tie line, a-cord circuit, a relay in said tie 'line operated in response to :the connection of said cord :to

said tie line, said relay controlling a super visory bridge across said tie line, super- 7 visory signals associated with both ends of said cord circuit, means responsive to a rering incoming over said tie line vfor releas- .ing sa1d operated relay to cause the opening of said supervisory bridge to effect a change in the condition of oneof said supervisory signals. g

17. In a telephone system, a cord circuit, a tie line, a pair of polarized relays in said tie line, means for causing the operation or one 'ofsaid relays upon the connections of said tie line to one of the ends of said cord circuit, a second tie line, and means actuated with one of said subscribers or'central oifice lines, battery sources respectively associated with said cordcircuit, said trunk lines, and said central ofiice lines, and means included in each of said trunk lines for discriminating between said respective battery sources, responsive to the interconnection of one 01 said trunk lines with another of any of said lines. 7

19. In a telephone system, a cord circuit,

afirsttelephone line, asecond telephone line, clrcult controlhng means in said first telephone line, repeating equipment normally included in said second telephone line, a relay in sa1d second telephone line controlling the connection of said repeating equipment therewlth, and means responsive to the connection of said lines by said cord circuits and controlled by said circuit controlling means in said first telephone :line for causing the operationot sa1d relay in the second telephone line tocause "the disconnection therefrom of said repeating equipment.

20. In a telephone system a first telephone line, a second telephone line, arepeating coil normally included in-eachof said telephone lines, a source of current associated with :eachot said lines, a cord circuit adapted to interconnect sa1d lines, a 011131111? including two polarized relays connected in opposite direction therein associated with eaclrof said llnes, means responsive to the connection of said cord circuit with said first line for con- =IlCt1Ilg across sa1d first line-sa1d circult as sociated therewith including sa1d polarized relays, a source of current associated with said cordcircuit adapted to-operate one only of said vpolarized relays upon their connection acrosssaid first line, means associated with said second line responsive to the connection of the other end of said cord circuit therewith for causing said cord battery to be disconnected and said operated polarized :relay in said first line to be released, means causing'the said source associated therewith to be bridged thereacross to cause the operation of the other of said two polarized relays in the first line, a relay in said second line, means controlled by the operation of said other polarized relay in said first line for actuating another relay in said first line to shunt said relay in the second line, means including another relay in said second line operated upon the shunting of said first relay in said second line for causing the dis connection of the said repeating'coil from said secondline and the disconnection of the said source therein from said line, means responsive to the exclusion of said repeating coil from said second line for causing the release of said other of said two polarized relays in said first line, and means actuated thereupon for causing the disconnection of the other of said repeating coils from said first line.

21. In a telephone system, two telephone lines, a cord circuit adapted to interconnect said lines, repeating equipment normally connected in and adapted to be disconnected from said tie lines, means in one of said lines for disconnectingthe repeating equipment therefrom in response to the interconnection of said second line, means in the other of said telephone lines for disconnecting the repeating equipment from said telephone line, said means being actuated upon the exclusion of the repeating equipment from the first of said tie lines.

22. In a telephone system, a cord circuit, a tie line adapted to be connected to one end thereof, a central ofiice line adapted to be connected to the other end, a pair of polarized relays in said tie line, a current source associatedwith said cord circuit, a current .source of polarity opposite thereto associated with said central ofiice line, means actuated upon the connection of said cord circuit and tie line for causing the operation of one of said polarized relays from the current source in said cord-circuit, and means actuated by the connection of the other end of said cord circuit with said central office line for causing the release of said operated polarized relay, and the operation of the other of said polarized relays.

23. In a telephone system, a. cord circuit, a tie line adapted to be connected to one end thereof, a central ofiice line adapted to be connected to the other end, a first relay in said tie line, two polarized relays associated with said tie line, one of said polarizing relays controlling the operation of said first relay, means responsive to the connection of one end of said cord to said tie line for connecting said polarized relays in series across said tie line and for operating one of. said polarized relays, a repeating coil in said tie line normally connected therein and adapted to be disconnected therefrom by said first relay, means responsive to the connection of the other end of said cord to said central ofiice line for causing the release of said first polarized relay and the operation of the other of said polarized relays, and other means responsive to the operation of said second polarized relay, whereby said first relay is effectively prevented from causing the disconnection of said repeating coil from said tie line.

24. In a telephone system a cord circuit, a tie line adapted to be connected to one end thereof, a central oflice line adapted to be connected to the other end thereof, signaling means in said cord circuit, a dry bridge associated with said tie line, a dry bridge associated with said cord circuit including resistance means adapted to be varied, means for assuring the maintenance of said signaling means in a desired condition, and means responsive to the interconnection of said lines by said cord for changing the resistance in said bridge across the cord to assure the maintenance of the connection of said tie line with said central ofiice line.

25. In a telephone system, a tie line, a central oiiice line, cord circuit for interconnectingsaid lines, a relay in said tie line responsive to ringing current, a second relay in said tie line, a dry bridge associated with said tie line and connected thereacross responsive to the connection of said cord to said tie line, signaling means in said cord circuit, and means actuated upon the connection of the other end of said cord with said central office line whereby upon the operation of said relay responsive to ringing current said second relay is caused to open said dry bridge to control the operation of said signaling means.

26. In a telephone system, a cord circuit, a current source associated therewith, a tie line and a central ofiice line adapted to be interconnected thereby, polarized relays associated with said tie line, means including a current source associated with said central office line connected in a reverse direction to that in the cord circuit for causing the actuation of certain of said polarized relays, a second relay caused to operate by the actuation of said polarized relay, said second relay causing the operation of a third relay to close a locking path for said second relay. upon the release of a fourth relay controlled by said second relay.

27. In a telephone system, a tie line, a central office line. a cord circuit adapted to interconnect said lines, means in said tie line including a first relay under the control of a second relay therein, another relay in said tie line responsive to ringing current, repeating equipment .in said tie line, means for disassociating said repeating equipment from said tie line, and means responsive to the operating of said ringing relay for assuring the operation of either of said first and second relays to maintain the connection of said repeating equipment to said tie line.

28. In a telephone system, a private branch exchange, interexchange tie lines and a railway message line terminating thereat, a line signal for said railway line at said exchange, a cord circuit thereat adapted to interconnect said railway line and one of said tie lines, repeating coils normally included in and individual to each of said lines at said exchange, means including a selector in said railway line, responsive to selective impulses transmitted thereover to cause the operation of said line signal, and means responsive to the interconnection of said railway line and one of said tie lines by means of said cord circuit for excluding said repeating coils from said interconnected lines.

29. In a telephone system a first tie line, a second tie line, acord circuit for interconnecting said tie lines, a signal in said cord circuit, and means in said first tie line operative responsive to the application of ringing current in said second tie line for causing the actuation of said signal.

30. In a telephone system a tie line connecting a first and a second P. B. X., another tie line connecting said first and a third P. B. X., a cord circuit for intercon necting the ends of said tie lines terminat ing at said first P. B. X., a signal in said cord circuit, and means in the end of one of said tie lines associated with said cor'd circuit operative responsive to the application of ringing current at the ends of the tie lines terminating in said second or third P. B. X.s for causing the actuation of said signal in the cord.

31. A P. B. X. telephone system comprising a plurality of tie lines interconnecting a first P. B. X. with other P. B. X.s, equipment in said tie lines at each of the terminating ends thereof including repeating coils, a cord circuit and means responsive to the interconnection of two of said tie lines by said cord circuit for excluding the repeating coils from the interconnected ends of said tie lines and preparing other means in the connected end of one of said interconnected tie lines operative thereafter responsive to the application of ringing current in the distant end of either of the interconnected tie lines for causing the actuation of a signal in said cord circuit.

32. In a telephone system, a first trunk circuit terminating at exchanges A and X, a second trunk circuit terminating at exchanges A and Y, a cord circuit for interconnecting the ends of said circuits terminat-- LANGFORD J. BOVVNE. HORACE W. ULRICH.

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