US2145127A - Telephone system - Google Patents

Description

Jan. 24, 1939. E. SJPETEISON TELEPHONE SYSTEM Filed May 29, 1957 5 Sheets-Sheet 1 $225 EEEG 1N VENTOR.

PETERSON EDWARD 5 ATTORNEY5.

Jan. 24; 1939. E. s. PETERSON TELEPHONE SYSTEM:

Filed May 29, 1957 5 Sheets-Sheet 3 Jan. 24, 1939. 4 E. s. PETERSON 2,

TELEPHONE SYSTEM I File'd May 29, 1937 v 5 Sheets-Sheet 4 MAGNETO 43 SUBSTATION A .l

MAeNETd SUBSTATION B MAGNETO sussmrou c G 4 INVENTOR.

EDWARD s. PETERSON BY ATTORNEY Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application May, 29, 1987, Serial No. 145,543 39 Claims. (01. 179-20) The present invention relates to telephone systems and more particularly to improvements in semi-automatic systemsot the type adapted for use in communities, as, for example, in rural 5 areas, wherein the telephone traflic is small.

In the type of system noted, separate exchanges or oiiices commonly known as satellite or subofllces are usually provided-for supplying telephone service to small groups of subscribers l substations, when for economic reasons it is impractical to extend the subscribers lines to the nearest main or central exchange. Such an oflice is illustrated and described, for example, in applicants copending application Ser. No. 107,- 16 581,-fl1ed Oct. 26, 1936, of which the present application is in part a division. Economy oi. system construction is further attained by routing all calls between the subofilce subscribers lines and the central-ofllce subscribers lines by 20 way of a tandem ofllce over trunlg lines individually extending between each of the subofflces and the tandem oflice and between the tandem and central omces. The tandem oflice is usually conveniently located to serve a small group of sub- 25 scribers lines extending thereto from subscribers substations located in the area immediately adjacent this oflice. This latter group of lines is usually quite small, consisting only of a few subscribers lines of the party line variety having 30 connected thereto magneto type substations of one form or another. The quality of service required by the few subscribers having substations on lines extending, respectively, to the tandem and satellite oflices is inevitably quite low and 35 insuflicient economically to justify the form of equipment usually provided for serving the subscribers needs.

It is an object of the present invention, therefore, to provide a telephone system of the general 40 form noted which is extremely simple and economical in construction and arrangement, and which is entirely capable of providing adequate service to a limited number of rural subscribers.-

More specifically, it is an object of the inven- 45 tion to provide in a system of the character specified small oflices individually having automatic switching equipment arranged in an improved and simple manner, which equipment is capable of operating, to set 'up the usual connections to 50 and between any ofllce line and the central exchange, and also, to set up any desired connection between any pair of subscribers lines individually extending to individual ones of-'the small ofiices.

In general, the objects as setiorth above are 5 attained in accordance with the present invention by providing a system of the form described wherein a'trunk line extends between the central omce and the tandem oflice, which trunk line is accessible to the subscribers lines and suboflice trunk lines and to an operator's telephone at the I central oillce. and, in which control means are provided in the tandem and suboflices responsive to impulsing means controllable by the central exchange operator for setting up connections between any pair of subscribers substations included in the system. For the purpose oi completing calls to and from the tandem oflice lines, 1. e., the tandem oflice subscribers lines and the subomce trunk lines, line relays are included in the control means associated with the central exchange trunk line, which line relays are individually associated with the lines terminating at. the tandem exchange and with the automatic switching means of the central exchange trunk line. The line relays individually comprise windings included in the primary and secondary energizing circuits of the corresponding relays and are individually responsive to the initiation of a call on the associated line to connect the calling line to the central exchange trunk line. The control means associated with the central exchange trunk line also include a stepping switch having a bank of contacts, one of which is included in each of the secondary energizing circuits of the line relays so that, when the wipers of the switch 80 are stepped to any one of a number of predetermined positions, the line relay corresponding to this position becomes energized to complete a connection between the calling and called lines. The stepping switch wipers are controlled by a 85 relay network wherein the relays thereof are so interrelated as to be responsive to impulses transmitted over the central exchange trunk line from the central exchange operators impulsing device. Similar control means are included in each of the 40 subofllces, which means are individually associated with each of the'subofllce trunk lines as pointed out in greater detail hereinafter. These control means are substantially similar to those disclosed in' the above referred to copending application, but all of the novel features common I thereto and to the present application are claimed herein.

The system arrangement'is such that the central exchange trunk line is accessible to all of the lines oi. the system for setting up connections therebetween. Since each connection is established by way of the central exchange trunk line and under the supervision of the central exchange operator, it is obvious that only a single call can be handled by the tandem ofllce equipment associated with the central exchange trunk line at any given time. To insure this result there are provided means responsive to the connection of the central exchange operators tele- 0 phone, any one suboflice trunk line, or any tandem ofllce subscriber's line to the central ofllce trunk line for preventing any 01' the remaining lines accessible to this line from being connected thereto in response to the initiation oi! a call thereon. This means, in the system to be described in detail hereinafter, comprises common cut-ofl relays responsive to the operation of any one of the line relays associated with the lines accessible to the central exchange trunk line, for interrupting the primary energizing circuits of all of these line relays, thereby to prevent these line relays from operating to connect their respective associated lines to the associated central ofllce trunk line when calls are initiated on the associated lines. As pointed out in detail hereinafter, these common cut-oil relays also comprise means for preventing the subofllce subscribers lines from being connected to their respective associated suboflice trunk lines when the central exchange trunk line is seized by one of the tandem oflice subscribers lines or at the central exchange operators station. Also responsive to the operation of any one of the line relays associated with the central exchange trunk line is means for sending a signal back over a calling line to indicate to the calling party that the trunk line is idle, and timing means for releasing the connection between the calling line and the trunk line in case the operators telephone is not connected to the trunk line within a given time interval after the operation of the line relay associated with the calling line. It is evident that the latter means is necessary in order to prevent any individual subscriber from permanently appropriating the single central exchange trunk line to the exclusion of all of the other lines having access thereto.

As noted above there are also provided control means in each of the various subofilces individually associated with the respective subofllce trunk lines, which means are responsive to operation of the central exchange operators impulsing means to complete connections between the subscribers lines common to the respective offlces and between these lines and the subscribers lines of the other ofllces. The nature of the equipment comprising these means is essentially the same as that included in the tandem office. This equipment differs slightly in that the subscribers lines are arranged in two groups and the control means and stepping switch for selecting a particular called group is arranged to be responsive to two series of impulses or digits dialed at the central exchange operators station, the first digit causing the selection of the group of lines including the called line and the second digit causing the selection of the particular called line in the selected group of lines. Aside from this difference in arrangement, the equipment in each of the subofllces is essentially the same as that embodied in the tandem office.

Various additional improvements in the circuit arrangement of the satellite and tandem office equipment are included in the system, which improvements are not specifically mentioned above and are for the purpose of simplifying the connections between the various relays of the control means and for reducing to a minimum the amount of apparatus employed.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figure 1 illustrates in partially schematic form a system of the type to which the present invention is applicable: Figs. 2 and 3, considered together, illustrate the apparatus and control circuits included in one of the satellite oflices of Figure l; and Figs. 4 and 5 illustrate the apparatus and control circuits embodied in the tandem oilice and the central exchange of Figure 1.

Referring now more particulaily to Figure l of the drawings, the telephone system there illustrated comprises a central oiiice III, a plurality of satellite or suboilices, two of which are shown at H and I2, a tandem oflflce indicated generally at l3, subofllce trunk lines l4.and l5 extending from the ofllces H and I2, respectively, to the tandem ofllce l3 and a central ofilce trunk line l8 connecting the tandem ofllce I3 with the central exchange Ill. The latter trunk line terminates at a repeater 20 associated therewith. The repeater 20 comprises secondary windings 22 and 23 coupled to primary windings 24 and 25, respectively,

which primary coils are connected in series across conductors 28 and 21 comprising an intraoflice link line 28. This link line, which is considered as a part of the trunk line I8, is accessible through suitable switching means to each of the subofllce trunk lines 14 and I5 comprising, respectively, conductors 29, 30 and 3|, 32, and also to a group of subscribers lines extending to the tandem office, two of which are shown at 33 and 34 as including, respectively, conductors 35, 36 and 31, 38. With the arrangement shown a total of ten lines, irrespective of the distribution of tandem omce subscribers lines and subofilce trunk lines, may be accessible to the line l8.

In order to isolate the local batteries of the substations connected to the subscribers lines, such, for example, as the lines 33 and 34, from the higher voltage common battery of the tandem ofilce, these lines are not connected directly to the conductors of the line 28 but are connected to a link line 39 comprising conductors 40 and M which are respectively connected to the conductors 26 and 21 through direct current blocking condensers 42 and 43. The subscribers lines, in the type of system described, are of the party line variety having connected thereto at least one and usually two or more subscribers substations of the well-known local-battery type employing a magneto or hand generator for initiating calls therefrom. Thus, the line 33 has connected thereto a subscribers substation A of this type and the line 34 has connected thereto two substations of the same type, indicated at B and C. Since this form of substation is well known in the art and the details thereof form no part of the present invention, the three substations noted have been shown schematically only.

Each of the suboffices II and I2 has extending thereto a plurality of subscribers lines such, for example, as those indicated at 42', 43' 44 and 44' for the suboflice II, and 45, 46 and 41 for the suboifice l2. These lines individually and respectively terminate at subscribers substations shown schematically at D, E, K and F for the oflice II and G, H, and I for the office I2 and may individually be of the party line variety or the single substation variety, depending upon the type of service required by the individual subscriber.

In addition to the portions of the system al- -ready described, there are provided control means vidual ones of which individually terminate at any of the four oillces shown. This means comprises automatic switching means included in the tandem ofllce l3 and associated with the central exchange trunk line i8 thereof, as shown in Figs. 4 and 5, and switching means embodiment ineach of the suboflices II and lrand individually associated with the respective subofllce trunk lines I and I5 thereof, as shown in Figs. 2 and 3.

Neglecting for the present the details of the control means as shown in Figs. 2 to 5, inclusive, and considering the operation of the system generally, it is pointed out that the establishing and releasing of connections between any pair of the various subcribers lines terminating at any of the four offices is entirely under the control of the operator located at the central exchange ill. Thus on a call from one of the tandem oflice subscribers lines to another of the tandem omce subscribers lines such, for example, as a call from the substation A to'the substation B, the party at the substation A removes his receiver from its hook and operates in a well-known manner his hand generator to apply ringing. current to the line 33, which current causes a line relay to connect the calling line to the line 39, in case the central exchange trunk line I8 is. idle, and is thereafter conducted over the lines 38, 28 and I8 to operate a signal device at the. operators station. When the operators attention is attracted by operation of the signal device she connects her telephone to the line l8 to converse with the calling party and obtain the name or number of thev called party, following which the calling party hangs up'and the operator actuates the impulsing device at her station in accordance with the number of the called line. Such impulsing causes the automatic switching means associated with the trunk line l8 to respond and connect the line 34 to the link line 39, thereby establishing a loop between the calling and called parties over the lines 33, 39, and 34. The operator then applies ringingcurrent by way of the lines It and 28 to both the lines 33 and 34, thereby to signal the calling party that a connection has been established and the called party that his telephone is being called. Since the line 34 is a two-party line, code ringing obviously must be used to inform the party B that he is being'called and the party C that the call is meant for the party B.

Alternatively, if the call is to be extended to a subscriber's line in the central exchange or to a toll line, the operator may establish the required connection in the well-known manner through the operator's apparatus embodied in the central exchange. As a further alternative, if the call is intended for a subscriber in one of the subofiices Ii or i2, the operator, upon dialing a predetermined digit causes a suboflice trunk line such, for

example, as the line I4, to be connected to the trunk line l8, following which additional digits are dialed to cause the automatic equipment in the called subofflce to extend the connection to the desired subscriber's line. Following this, ringing current is applied to the conductors of the trunk line l8 to signal the calling and called i x 3 parties that a connection has been established therebetween.

The operation of the system during calls in itiated on one of the subscribers lines terminating at the subomces II and I2 is similar to that briefly described above, the primary diflerence being that the operation of the hand generators at any one of the substations associated with these lines causes successive operations of the automatic switching means in the associated subofllce and the tandem ofilce, thereby to establish a connection between the calling'partys substa tion and the operator's station and to signal the operator in the central exchange. Following this, the operator can, in a manner similar to that described above, extend the connection to the desired party regardless of the oifice in which the called line terminatea' As will be pointed out hereinafter, the release of all connections except those involved in reverting calls is under the supervision of the central exchange operator.

Referring now to Figs. 2 to 5, inclusive, thereare illustrated the control means or automatic switching means whereby the various operations as briefly described above may be carried out. As shovrnunore particularly in Figs. 4 and 5, the control means in the tandem ofllce-l3 comprises means in the form of line relays such as the relays 3M and 320 individually associated with each of the subscribers lines such as the lines 33 and 34 and line relays 330 and 340 individually associated with the trunk lines l5 and M, respectively, for connecting the respective associated lines to the central oflice trunk line l8. Additional or secondary line relays 310 and 380 individually associated with the suboffice trunk lines l5 and M, respectively, are provided, which are controlled by the relays 330 and 340, respectively, and serve a purpose to be described hereinafter. Each of the line relays 318, 320, 330, and 340 comprises a primary or first-operating circuit including one winding thereof bridged across the line conductors and energized during the initiation of a call on the associated line by thecurrent from the hand generator at one of the substations on the line, a secondary or second-operating circuit including a second winding, and means comprising contacts responsive to the energization of the primary circuit for completing the secondary circuit. Thus, the line relay 3|,0 has a primary circuit including the conductors 35 and 3B and ,the upper winding of the relay, a secondary circuit comprising the a the secondary circuit.

The individual secondary circuits of the several line relays comprise two branches, one branch being individual to the corresponding circuit and extending by way of a contact and associated wiper of an automatic or rotary stepping switch 401 and the other branch being common to all of the secondary circuits and extending over the conductors 3i8 and 3I9 through the winding of an additional relay 400 to battery. From the foregoing description it will be apparent that the primary and secondary circuits of each of the line relays are so connected and arranged that the operation of each relay is initiated by energization of its primary circuit, following which its secondary circuit is completed to comp1ete the operation of the corresponding relay and to hold the operated relay in its operated position independently of its primary circuit. It will further be seen that the additional relay 400 is energized in response to the completion of the secondary circuit of any one of the line relays.

The last-mentioned relay, namely, the relay 400, comprises means for initiating the operation of; means for transmitting a waiting tone to a calling subscriber, timing means for disconnecting the trunk line from a calling subscriber's line in case the central exchange operator fails to answer a call by connecting the operator's telephone to the trunk line 18 within a predetermined time interval after a calling line is connected to the trunk line, and means for interrupting the primary energizing circuits of all the line relays in response to the operation of any one of these relays, thereby to prevent more than one calling line from seizing the trunk line 18 during any given time. Thus, the relay 400 includes an armature 401 for completing the energizing circuit of a tone relay 410, an armature 405 for completing a circuit for energizing the thermal relay 413 and an armature 403 for completing a circuit for energizing the common cutoff relay 350, which latter relay when operated completes at its armature 351 the circuit for energizing a second common cut-ofi relay 360. As will be noted, the second cut-off relay 360 includes armatures 361, 363, 365, 361, 369, etc., for interrupting the primary energizing circuits of the line relays associated with the subscribers lines such, for example, as the lines 33 and 34 terminating at the tandem office, and the cutoff relay 350 includes armatures 353 and 356 for interrupting the primary energizing circuits of the line relays 330 and 340, respectively, associated with the suboffice trunk lines 15 and 14, respectively.

In the central exchange, the trunk line 18 terminates at a repeater 446. This repeater comprises primary windings 441 and 448 connected in series across the conductors of the trunk line 18 and coupled to secondary windings 456 and 451 which are connected in series between the tip and sleeve contacts 458 and 459, respectively, of a jack 465. These windings are also connected across the windings of a signal device such, for example, as the drop 466. In addition, there is provided at the operator's station an impulsing device 461 for controlling, through the medium of a group of relays, the operation of the rotary switch 401. This device includes contact springs 468 and 469 for shunting, during a dialing operation, the windings of the drop 466 and interrupting or impulsing springs 418' and 419' extending, respectively, to a contact 464 included in the jack 465 and to the junction point between the primary windings 441 and 448 of the repeater 446.

As pointed out above, the equipment associated with the trunk line 18 comprises automatic switching means including the rotary stepping switch 401 and means for controlling this switch comprising the relays 420, 430, 450, 410, 480, 480', 485 and 485'. The enumerated relays are adapted to be responsive in a particular sequence or sequences to operations performed by the operator in the central exchange 10 and, more particularly, to operation of the operator-controlled impulsing device 461. The rotary switch 401 may be of any desired construction which comprises two sets of contacts, 418 and 419, wipers 428 and 429 for engaging the contacts of the contact sets 418 and 419, respectively, a rotary magnet 460 for stepping the wipers 428 and 429 to predetermined oil-normal positions individually corresponding to the line such, for example, as the lines 14, 1'5, 33 and 34 extending to the tandem oillce, and a release magnet 462 under the control of ofi- normal springs 488, 488 for returning the wipers to their normal positions when an established connection is cleared out. As pointed out above, each of the contacts of the lower set 419 extends to one terminal of one of the windings included in the secondary energizing circuit of an associated relay, and each of the contacts of the upper set 418 extends to the winding terminal of one of the line relays associated with the trunk lines 14 and 15. Thus, the first, second, third, and tenth contacts of the lower contact set 418 are individually connected by conductors 414, 415, 416 and 411, respectively, to the terminals of the windings of the line relays 340, 330, 310 and 320, and the first and second contacts of the upper contact set 418 are individually connected by conductors 418 and 419 to the lower terminals of the windings of relays 490 and 495, respectively. As

will be described in detail hereinafter, when the automatic switch 401 is stepped to any one of its predetermined positions, the secondary circuit of the line relay associated with the line corresponding to such position is energized, causing the relay to operate to connect the associated line to the trunk line 18. Thus, the line relays individually comprise means operated in response to the operation of the automatic switch 401 to predetermined positions individually corresponding to the associated lines.

It is pointed out here that the line relays 420 is energized in response to the connection of the operator's telephone to the trunk line 18, over a circuit extending from battery at the contact spring 464, through the interrupting contact springs 418', 419' and the repeater winding 448, over the lower conductor of the trunk line 18, and through the lower repeater winding 23 and the winding of the relay 420 to ground. This relay, in combination with the relays 430 and 440, comprises means for interrupting the operation of the tone relay 410 and for arresting the operation of the timing means comprising the thermal relay 413. Thus, when the relay 420 operates, it causes the sequential operation of the relays 430 and 440, the first of which interrupts at its armature 431 and associated contact 432 the circuit for energizing the thermal relay 413 and the last of which interrupts at its armature 441 the circult for energizing the tone relay 410.

As indicated in Figure 1, the subofilce trunk line 14 terminates at the subofllce I 1 to which extend subscribers lines such, for example, as the lines 42' and 43' and the trunk line 15 terminates at the subofllce 12 to which extend subscribers lines including the lines 45, 46 and 41. The switching and control equipment included in these two oflices is identical and for that reason only the equipment included in the office I 1 has been shown in detail. Each subofllce is capable of serving two groups of subscribers lines, each including ten lines, and the control equipment is arranged to be responsive to two digits dialed at the central exchange operator's station to select the desired group of lines and the desired called line in the selected group of lines As shown in Fig. 3, the line 14 terminates in the suboflice 11 at a repeater 209 having secondary windings 211 and 218 connected in series between the conductors 29 and 30 of the line 14 by means of a condenser C8, and primary windings 201 and 208 connected in series between the line conducsubscribers lines terminating at the suboflice II is adapted to be connected to the link line II5 through the medium of a line relay associated with the corresponding subscriber's line. Thus, the subscribers line 42 may be connected to the line 5 by means comprising a line relay I20. Similarly, the subscribers lines 43', 44 and 44' may be connected to the line H5 by means comprising the relays IIO, I40and I50, respectively. Each of the enumerated line relays comprises a primary or first-operating circuit including the talking conductors of the associated line, and a secondary or second-operating circuit which is completed in response to completion of the primary energizing circuit or the same relay and also in response to the operation of a minor or rotary stepping switch 225 to a predetermined position. It will be seen that the line relays for individually connecting the subscribers lines such, for ex-- ample, as the lines 42', 43' and 44 to the link line I I5 constitute a group of relays, only one of which should, at .any given time, be responsive to the initiation of a call on its associated line. For this reason,'the primary energizing circuits for the group of line relays associated with the lines 42, 43', etc., included in the first group of ten subscribers lines, individually include means responsive to the operation of common cut-ofi relays for permanently interrupting the primary energizing circuits so long as the associated cut-off relay is operated. Thus, each of the line relays III), I20, etc., has a primary energizing circuit which includes an armature such, for example, as the armatures I3I, I32, I33, etc., under the control of a common cut-off relay I30. Similarly, the line relays, such as relay I40, associated with the lines of the second group of ten subscribers lines, include, in their respective primary energizing circuits, armatures such, for example, as the armatures I6I, I62, I53, etc., under the control of a common cut-off relay I60.

The secondary circuits for the line'relays IIO, I20, I40, I50, etc., have a common portion which includes the winding of an additional relay 200. This latter relay comprises contacts for completing, when the relay 200- is operated, the energizing circuit of the common cut-off relay I30. Also responsive to the operation of the relay 200 is timing means comprising a thermal relay 294 for effecting the release of the trunk line I4 from a calling subscribers line in case the operator at the central exchange fails to answer the call within a predetermined time interval after the calling line is connected to the trunk line I4. Thus, when the relay 200 operates, it completes, at its armature 202, an obvious circuit for energizing the thermal relay 294. In addition, the relay 200 includes contacts for controlling the operation of a tone relay 205 having self-interrupting contacts for periodically short-circuiting one winding thereof such that, when energized,

this relay operates in the manner of a buzzer to cause, by induction, an alternating voltage to be comprising the thermal relay 294 is interrupted by means including the relays 290, 280, and 210, which operate, in the order named, in response to the operation of the switch 401 in the tandem oflice to a position corresponding to the suboffice trunk line I4. Thus, when the relay 290 operates it completes, at its armature 29I and associated upper contact, a circuit for energiz- 210. When the last-mentioned relay operates it interrupts at its armature 214 the circuit for energizing the tone relay 205 and,'at its armature 213, interrupts the. operating circuit for the thermal relay 284, thereby arresting the operation of thisrelay.

In order to eflect the connection of a called line to the trunk line I4 there is provided auto- :matic switching means in the suboflice lI associated with this trunk line and responsive to impulses transmitted over this line irom the impulsing device 461 at the operator's station. This means comprises the minor switch 225 for controlling the operation 01! the two groups oi! line relays and is of the rotarylstepping type including wipers 2I3 and 2 I4 adapted to be stepped, by an operating magnet 2I2, to,predeterm.ined positions individually corresponding to the in- .dividual subscribers lines such, for example, as the lines 42, 43' and 44, and to be restored to normal by means including a release magnet 2I5 and oil-normal springs 2I6. The wipers 2I3 and'2I4 are adapted to engage, respectively, contacts included in contact sets 226 and 221. Each 'cont-act of-each of the two contact sets corresponds to one of the predetermined positions of ing any one of twenty subscribers lines to the trunk line I4.

The contact wipers 2I3 and 2 of the minor switch 225 are adapted to-be connected to ground selectively to complete the secondary energizing circuits of the various line relays through the armatures 222 and 2 of relays 220 and 2I0, respectively, and the armature 215 of the hold relay 210. With this arrangement, the armature 222 is adapted selectively to connect ground to one of the two wipers 2I3 and 2I4, depending upon the condition or the relay 220, which latter relay is energized in response to the dialing 01' one predetermined digit at the central exchange toperators station, and is in a de-energized condition when another predetermined digit is dialed at the operator's station. From the foregoing description it will be apparent that the line relays such, for example, as the relays H0 and 'I20, individually comprise means responsive to the operation of the automatic switch 225 to a predetermined position for connecting the subscribers' lines corresponding to these line relays -to the trunk line I4 of which the'link line H5 is considered a part.

The automatic switching equipment associated with the trunk line I4 includes, in addition to the minor switch 225 and theenumerated relays 2I0, 220, 210, 280, and 290, relays 230, 240, 250, I

and 260, all of which comprise means for controlling the operation or the, minor switch 225 and operate in a predetermined sequence or predetermined sequences in response to operations performed by the central exchange operator, and, more particularly, in response to the operation of the impulsing device 461.

From the foregoing description it willbe apparent that the lines such, for example, as the lines I4, I5, 33, and 34, constitute a group oi! lines accessible only to the central omce trunk line I8. Also accessible to this line are the central exchange operator's telephone and a group of lines in the suboflice II comprising the lines 42' and 43. In order to prevent any one oi! the last-mentioned group of lines from being connected to the central ofllce trunk line I8 when the latter line is busy in connection with a call in which the suboflice trunk line I4 is not involved, there is provided means for interrupting, under the conditions stated, the primary circuits of the line relays IIO, I20, etc., associated, respectively, with the twenty suboffice subscribers lines. This means comprises the common cutofi relay 350, which, upon operating, opens at its armature 356 the primary circuit of the relay 340 and closes an operating circuit for the line relay 290. The relay 290, upon operating initiates the sequential operation of the relays 280, 210, I30, and I60, whereby the primary circuits of all the line relays IIO, I20, I40, etc., are interrupted.

Each of the common batteries included in the individual subofiices is of a lower voltage than the common battery included in the tandem ofilce I3, and provisions are made whereby the suboilice batteries may be charged from the tandem ofllce battery over the subofllce trunk lines. Thus, when the line I4 is idle, the line relay 380 and the common cut-off relay I60 associated therewith are in their respective restored positions so that the conductor 29 of this line is connected by way of the armature 38I and the lower contact 382 of relay 380 to the tandem oflice battery, and is also connected by way of a conductor I0! and the armature I64 of the common cut-oif relay I60 to the battery of the subofiice II. This circuit constitutes a circuit for charging the battery located in the subofilce II' from the tandem ofiice battery during those periods when the trunk line I8 is inactive.

As pointed out previously, the control equipment of the system as described in detail above is capable 01' operating under the central exchange operators supervision to connect any one of the lines terminating at any one of the four exchanges to any other line terminating thereat, thereby to establish a talking loop between the telephones associated with the connected lines.

Initiation of a call on a tandem omce subscribers line two steps. Thus, with the substation B idle,

the primary circuit of the relay 320 including the conductors 31 and 38, is prepared. This circuit extends from the conductor 31 through the upper winding of the relay 320 and the armature 369 of the common cut-off relay 360 to the armature 325 connected to the conductor 38. When the subscriber at the calling substation B operates his hand generator in the conventional manner, ringing current flows over the above circuit causing the relay 320 partially to operate to close its X" contacts comprising the contact 322 and the associated contact on the armature 32I. These contacts comprise means for completing the secondary energizing circuit of the relay 320,

this circuit extending from ground at the contact 322 by way of the armature 32I, the lower winding of the relay 320, the conductor 3| 8, the conductor 3I9, the armature 343 and through the winding of the relay 400 to battery. When the secondary circuit of the relay 320 is completed in the above-described manner, the relay 320 completes its operation and, at its armatures 323 and 325, connects the conductors 31 and 38, comprising the line 34 to the conductors 40 and M, respectively, comprising the link line 39 Included in the trunk line I8. At its armature 325 and back contact 326 the relay 320 interrupts its primary circuit, the relay now being held operated by virtue of the energized condition of its secondary circuit.

As noted previously, the relay 400 comprises means responsive to the operation of the relay 320 for interrupting the primary circuits of all the line relays such as the relays 3I0, 320, 330, and 340, for initiating the operation of the tone relay 0, and for initiating the operation or the timing means comprising the thermal relay 4I3. Thus, the relay 400 energizes in series with the lower winding of the relay 320 when the secondary energizing circuit of the latter relay is completed and in turn completes, at its armature 40I, an obvious circuit for energizing the upper winding of the tone relay 0. At its armature 405 and associated contact 406, the relay 400 also completes an energizing circuit for the thermal relay 4| 3, which circuit extends from ground at the armature 43I of the relay 430, by way of the contact 432, the armature 405 and associated contact 406, and through the resistor 439 of the thermal relay M3 to battery. The signal means comprising the tone relay 4I0, when energized in the above-described manner, operates in the manner of a buzzer by virtue of its self-interrupting contacts 4H and H2 and induces in its lower winding an alternating voltage which is applied across the conductors 26 and 21 through the condenser 449. This voltage causes current to flow back over the loop extending to the subscribers substation B and generates a. tone in the receiver at this substation to indicate to the calling party that the trunk line I8 is idle and has been seized. The calling party upon receiving this indication again actuates the hand generator at the substation B to project ringing current over the lines 34, 39, 28 and I8, and thus energize the drop 466. The operator is thus informed that an incoming call awaits attention.

The primary circuits of the various subscribers line relays are interrupted through the operation of the common cut-off relays 350 and 360 which respond, in the order named, to operation of the relay 400. Thus, when the relay 400 operates, it completes, at its armature 403 and associated contact 404, a circuit extending by way of the conductor 499 for energizing the relay 350, and the latter relay completes, at its armature 35I an operating circuit for the relay 360. Both cutoff relays are now operated so that the primary circuits of the subscribers line relays 3I0, 320, etc., are interrupted at the armatures 36I, 363369 and associated contacts of the relay 360, and the primary circuits of the line relays 330 and 340 are interrupted at the armatures 353 and 356 and associated contacts 354 and 351, respectively, of the relay 350. With the respective primary circuits of the various line relays interrupted in the manner described, these relays are not responsive to calls initiated on their respective associated lines. Also, and

326 and the relay 466 in series.

amour? as was pointed out above, the operation of the cut-oil relay 356 causes the sequential operation of the relays 296, 286, 216, I36 and I66 in the subofiice ll, so that the subscribers substations on lines terminating at the subofllce II are prevented from seizing the trunk line l4 leading to the tandem oilice. Similarly, the apparatus in the subofflce 12 operates to prevent the seizure of the trunk line l5 by a suboflice subscriber when the central exchange trunk line 16 is busied in the manner described above.

When the thermal relay 3 is energized over the above-traced circuit, it starts to operate and, unless its operation is interrupted within a predetermined time interval, closes its bimetallic element 481 to the associated contact to complete an obvious circuit for energizing the relay 426. This latter relay, at its armature 423 and associated contact 424, in turn completes an obvious energizing circuit for the slow-to-release relay 436. When the relay 436 operates, it completes, at its armature 43l and associated contact 433, an obvious energizing circuit for the relay 446. The relay 446, upon operating, opens, at its armature 443, the original secondary energizing circuit for the relay 326. Before this occurs, how-- ever, a shunt is connected around the armature 443 at the armature 436 of the relay 436 so that the secondary circuit of the line relay 326 remains closed. The relay 436, upon operating, also interrupts at its armature 43!, the energizing circuit for the thermal relay 4| 3. After a short interval required for cooling the element 481, this element moves away from its associated contact to interrupt the energizing circuit for the relay 426, permitting this relay to restore and break at its armature 423 the operating circuit iorthe relay 436. restores, opening the energizing circuit for the relay 446 and the shunt comprising the armature 436 around the armature 443. Due to the slow release characteristic of the relay 446, the shunt around the armature 443 is opened before this relay restores, thereby interrupting the previously-traced circuit for energizing the line relay The relay 326 thereupon restores,- opening its contacts 321 and 322 to further interrupt its secondary circuit and to disconnect the line conductors 31 and 38 from the link line conductors 46 and 4|. When the relays 466 and 446 restore, the operating circuit for the cut-off relay 356 is interrupted, thereby to cause the sequential restoration of this relay and the cut-off relay 366.

The above-described operation for the timing means comprising therelay4l3 is based on the assumption that the connection as established by way of the trunk line 18 to the operators station is not answered within a predetermined time interval. If the operator answers the call within the time interval required for operation of the thermal relay M3 by inserting the plug terminating the operators telephone in the jack 465, the drop 466 is restored to its normal position and a circuit is completed for energizing the relay 426, which relay operates to cause the energization of the relay 436, resulting in the interruption of the energizing circuit for the thermal relay M3 at the armature 43l to arrest the operation of the timing means. The a ovementioned energizing circuit for the relay 426 extends from battery at the jack spring 464 through the interrupting springs 418' and 419 of the impulsing device .461, the lower winding 448 of the repeater 446, the'lower conductor of This latter relay in turn 1 rupted three times.

the trunk line It, the lower winding 23' or the repeater 26 and through the winding of the relay 426 to ground. The relay 426 not only operates to complete an energizing circuit for the relay 436- at its armature 423 but, in addition, closes its armature 42l to the contact 422 and thereby prepares a circuit for applying battery to the respective lower conductors of the suboflice trunk lines l4 and I6. As will be pointed out hereinafter, the application of battery to the line con'- ductor 66, associated with the trunk line M, by

way of the resistor 566, constitutes the final step in the operations leading to the energization of the line relay 296 associated with the trunk line 14 on a call to a subscriber's line terminating at the subofflce II. I

When the relay 436 operates following the operation of the relay 426, it completes, at its armature 43l, an energizing circuit for the relay 446 and closes its armature 434 to the associated contact 435 to prepare a circuit for energizing the slow-to-release relay 456 and the rotary magnet 466 of the rotary stepping or automatic switch 461. In addition, the relay 436 closes, at its armature 436, the previously-mentioned shunt around the armature 443 and further prepares,

applying battery to the conductors of the subofiice trunk lines I4 and I5.

When the relay 446 operates, in response to the completion of its energizing circuit as described. above, it interrupts, at its armature 4, the energizing circuit for the tone relay 6 and, at this same armature, connects multiple ground to the conductor 499 included in the operating circuit of the common cut-oil? relay 356. At its armature 442, the relay 446 prepares a holding circuit for the line relays such, for example, as the relay 296 associated with the suboflice trunk line l4 and, at its armature 443, it interrupts the original secondary circuit for the line relay 326. The relay 446, upon operation, also prepares, at its armature 444, a holding circuit for the relay 416 and, at its armature 445, an'energizing circuit for the line relay associated with the called line terminating at the tandem oflice.

When the tone relay 6 is de-energized in the above-described manner, the resulting interruption of the signal indicates to the calling party that the operator has-answered and this party may, accordingly, transmit to the operator the information concerning the name or telephone number of the called party. It is pointed out that the control equipment associated with the trunk line I8, and more particularly the control apparatus for the rotary switch 461, is now conditioned to be responsive to impulses transmitted from the impulsing device 461.

Completion of the call to another tandem ofllcc l subscribers line the position corresponding to the called tandem.

ofiice subscriber's line. Thus, if the substation A is being called, the digit 3 is dialed at'the impulsing device 461, causing the previously-traced energizing circuit for the relay 426 to be inter- During each interruption,

this relay restores, opening, at its armature 423 and associated contact 424, the energizing circuit for the relay 436 and completing the previously prepared and obvious energizing circuit for the slow-to-release relay 458 and the rotary magnet 488. Due to the slow release characteristic of the relays 438 and 458, these relays remain operated during the impulsing. The first 01' these relays is held operated at conclusion of the impulsing by virtue of the closure of the interrupting springs 418' and 419' included in the im-,- pulsing device 481. Each time the energizing circuit of the magnet 458 is energized, the wipers 428 and 429 of the rotary switch 481 are stepped one step so that, at the end of the third impulse, they rest, respectively, on the third contact of each of the contact sets 418 and 419.

At the beginning of the first impulse the slowto-release relay 458 operates to prepare, at its armature 453 and associated contact 454, a circuit for energizing the relay 485 and to interrupt, at its armature 451, a point in the circuit extending from ground at the oil-normal springs 488, 489 for energizing the relay 418. Since the relay 458 remains operated during the impulses following the first impulse, the lastmentioned circuit is maintained open during the remaining impulses oi the first digit. At the end of the first'impulse, the off- normal springs 488, 488 of the rotary switch 481 are closed to prepare the above-noted circuit for energizing the relay 410, this circuit being completed when the relay 458 restores at the end of the first digit and extending from ground at the spring 488 by way of the elements 488, 451, 452, and the winding of the relay 418 to battery. Restoration of the relay 458 also opens, as at armature 453, the prepared point in the circuit for energizing the relay 485. When the relay 4'18 operates, it completes, at its armature 412, the previously prepared locking circuit for itself and, at its armature 411, prepares a circuit for energizing the relay 485. At its armature 411, the relay 418 interrupts the energizing circuit for the rotary magnet 468 and, at its armature 416, prepares an obvious energizing circuit for the release magnet 462. The relay 418 also completes the secondary circuit for the line relay 318 associated with the subscriber's line 33, this circuit extending from ground at the armature 445 by way of the armature 414, the wiper 429, the third contact of the contact set 419, the conductor 416, through the lower winding of the relay 318, over the conductors 318 and 319 and through the winding of the relay 488 to battery.

The relay 318 operates in response to the completion of its secondary circuit in the abovedescribed manner and, at its armatures 313 and 315, connects the conductors 35 and 36 comprising the line 33 to the conductors 48 and 4| comprising the link line 39. This relay also completes, at its armature 311 and associated contact 312, a. holding circuit for itself and opens, at its armature 315, a further point in its primary circuit. With the system in this condition, talking loops are completed between the calling and called subscribers lines and the central exchange operator's telephone, the latter loop including the trunk line 18. The operator may now indicate that such a connection has been established by applying ringing current in a Well-known manner between the secondary terminals of the repeater 446, which current is transmitted through the repeater 446 over the trunk line 18, through the repeater 28, and over the two link lines 28 and 39 and the two subscribers lines 34 and 33 to the signal devices at 7 the substations of the calling and called lines.

Since only one substation is associated with the line 33, code ringing is not required. If, however, this line were a party line, selective code ringing could be employed to inform the proper party on the line that his substation was being called. Following the operation of the signal devices at the calling and called substations, the calling and called parties may answer the call and converse.

The operator may maintain the operator's telephone connected to the established talking loop to monitor the connection if desired. In any case, it is necessary that the plug associated with the operator's telephone be retained in the Jack 485 in order to hold the previously-traced energizing circuit for the relay 428 completed and thus. prevent the sequential restoration oi the relays 438 and 448, in the manner noted above, to interrupt the holding circuit lor the operated line relays 318 and 328. It is pointed out that transmission battery is supplied to the telephones of the calling and called parties by local batteries located at each of these substations.

Release of the established connection When the conversation between the calling and called parties over the connection as established above is terminated, either of these two parties may inform the operator by operating his hand generator to transmit current over the central exchange talking loop comprising the trunk line 18, thereby to cause the reoperation of the signal device comprising the ,drop 466. The operator then removes the plug associated with the operator's telephone from the Jack 465 to interrupt the previously-traced energizing circuit for the relay 428. This relay restores, causing the sequential restoration of the relays 438 and 448 in the order named, thereby momentarily interrupting, in the previously-described manner, the secondary energizing circuits for the line relays 318 and 328.. The latter relays in turn restore, further to open, at their respective armatures 311 and 321, the respective secondary circuits therefor. These relays also disconnect, in an obvious manner, their associated subscribers lines from the link line 39.

When the secondary circuits for the relays 318 and 328 are interrupted, the relay 488 restores, to open, at its armature 485, a point in the circuit for energizing the thermal relay 413. The relay 488 also opens, at its armature 483, the previouslytraced holding circuit for the common cut-oft relay 358. .The latter relay in turn restores, opening the circuit holding the common cut-oi! relay 388 operated. The two cut-oil relays restore to recomplete the primary circuits for all of the line relays individually associated with individual ones of the subscribers lines and subofflce trunk lines terminating at the tandem ofllce. When the relay 358 falls back, it interrupts at its armature 358 and associated contact 358, the circuit, traced hereinafter, holding the line relay 288 in the suboflice 1 1 energized, thereby to initiate the sequential restoration of this relay and the relays 288, 218, 138 and 168. When the two last-named relays restore, the primary circuits for the line relays associated with the subscribers lines terminating at the subofllce 11 are completed, thereby to condition these relays to be responsive to calls initiated on the respective associated lines. In a similar manner the primary circuits of the line relays associated with the subscribers lines extending to the subofice 12 are recompleted.

When the relay 420 restores, it recompletes the circuit-,for energizing the slow-to-release relay 450, causing this relay to operate and interrupt at its armature 45I the original circuit for energizing the relay 410. The relay 450 also completes, at its armature 453, a circuit for energizing the relay 485, causing this relay to operate, but without eflect at this time. The relays 430 and 440 both restore before the relay 450 falls back and the relay 440 completes, at its armature 445 and associated lower contact, a circuit for energizing the release magnet 462, causing this magnet to operate its armature and permit the switch 401 to restore its wipers to their normal or home positions and to open its oil-normal springs 488,

480. At its armature 444, the relay 440 interrupts the holding circuit for the relay 410 so that shortlyafter the release magnet 462 is energized, the relay 410 falls back to interrupt at its armature 418 the energizing circuit for this magnet. The arrangement is such that the relay 450 restores shortly after the relay 430 falls back, thereby to reprepare, at its armature 45I, the originalv circuit for energizing the relay 410, this circuit being maintained open, when the switch 401 restores, at the off-normal springs 488, 489. When the relay 410 falls back, the circuit for energizing the relay 485 is broken, permitting this latter relay to restore. Thus, all of the relays illustrated in Figs. 4 and 5 are restored to normal, and the system is in its normal idle condition.

Reverting calls to tandemsubscribers substations In the event the call initiated on the line 34 from the subscriber's substation B is to be extended to a substation on the same line such, for example, as the substation C, the call is initiated to cause the sequential operation of the line relay 320 and the relays 400, M0 and M3 in the manner described above. When the line relay 320 operates, it connects the associated subscriber's line 34 by way of the link lines 39 and 28 to the trunk line extending-to the operators station in the central exchange, so that further operation of the calling subscriber's hand generator causes operation of the drop 466. After the operator has answered the call and received the information that the substation C is desired, the party at the substation B hangs up and the operator at the central exchange transmits coded ringing current back over the established loop including the line 34 to signal the party at the substation C that this substation is being called, following which the calling and called parties may converse over the connection consisting solely of the line 34.

It is pointed out that the trunk line I8 and its associated equipment need not be tied up on reverting calls. Indeed, if all of the parties on a particular line and the operator are familiar with the coded calls corresponding tothe substations associated with such lines, there is no necessity for the operators taking any part in establishing the connection since operation of the hand generator at the substation B, for example, causes operation of the signal device or bell at the substation C. Although such operation of the hand generator at the substation B causes the energization, in the previously described manner, of the line relay 320, which relay initiates the operation of the relays 400, M0 and M3, the latter relay operates in the previously described manner to cause, after a predetermined time interval, the restoration pf all of -these relays and the disconnection of the calling subscribers line from the trunk line I8. 'It is thus apparent that reverting calls or calls between substations'common to a. party line need not tie up the equipment associated withthe central exchange trunk line I8.

If desired, busy signal means of any desired form may be associated with such lines to signal the central exchange operator that a particular line is busy in. connection with a reverting call of the type noted, thereby to prevent the operator from connecting another subscriber's line to the busy party line.

A call from a tandem oflice subscribers line to a line terminating at the central exchange Inthe event a connection is to be established between a substation associated with one of the tandem subscribers lines and a line terminating at the central exchange I0, the operations necessary .to signal the central exchange operator and to establish a talking connection from the calling subscriber's substationto the operator's telephone are exactly the same as those described above. When the operator answers and learns from the calling party the name or number of Call from one subojfice subscriber's line to another line terminating at the same suboflice .scriber operating his hand generator to energize the primary circuit for the line relay I20. Assuming that the trunk lines I4 and I8 are idle, the primary circuit of the relay I20 is energized, this circuit extending from the hand generator at the calling substation by way of the subscriber's line conductor I92, the armature I22, the armature I3I of the common cut-oflf relay I30, the lower winding of the line relay I20,

and over the subscriber's line conductor I93 to the hand generator. The line relay I20 operates, in response to its energization over the abovetraced circuit, and, at the X contacts associated with its armature I23, completes its secondary circuit, this latter circuit including the winding of the relay 200 and extending from ground by way of the armature I23, the upper winding of the relay I20, the conductor I04, the armature 2H and thewinding of the relay 200 to battery. At its armature I22, the line relay I20 opens its primary circuit only after the, above-traced looking circuit is completed and, at its armatures I2I and I22, connects the subscribers line conductors I92 and I93 to the link line conductors I03 and I02, respectively. 4;

When the relay 2-00 operates, in response to its energization in series with the upper winding of the relay I20, it completes at its armature 20I an obvious circuitfor energizing the cut-off relay I30. At its armature 203, the relay 200 completes a circuit for energizing the tone relay 206. The last-mentioned relay, by virtue of the self-interrupting contacts associated with its armature 206, operates buzzer fashion to induce in its upper winding waiting tone current which is transmitted over the lines I I6 and 42 to the receiver at the calling subscriber's substation. At its armature 202, the relay 200 completes an ob vious circuit extending from ground at the ar'- mature 213 for energizing the heating resistor embodied in the thermal timing relay 294. The lastmentioned relay, in cooperation with the relays 290, 280 and 210, operates in a manner identical with that described above, for the corresponding elements 3, 420, 430 and 440, respectively, of the tandem oflice, to release the trunk line I4 and the control apparatus associated therewith in the event the central exchange operator does not answer the call within the time interval required for the operation of the relay 294. At its armature 204, the relay 200 interrupts a point in the charging circuit for the subofflce battery.

When the cut-off relay I30 operates in response to its energization, as described above, it completes, at its armature I34 an obvious circuit for energizing the cut-off relay I60. With the two relays I30 and I60 operated the primary circuits for the line relays IIO, I20, I40, etc., are interrupted at the armatures I3I, I32, I33, etc., and the armatures I6I, I62, I63, etc., thereby to guard the line I4 from seizure by another party during the time it is occupied with the call being described.

From the foregoing description, it will be seen that in response to the operation of the hand generator at the station D, the line relay I20 is energized and locked to connect the subscriber's line 42' to the trunk line I4. In order more fully to describe the circuit operations, it will now be assumed that the central exchange trunk line I8 is busy and the subofiice trunk line I4 is idle at the time the calling party at the station D operates his hand generator. If this condition prevails, the common cut-off relay 350 is in its operated position by virtue of the energized condition of the relay 440. As a consequence, the line relay 290 is energized over a circuit extending from battery at the contact 358 by way of the armature 356, the contact 385, the arma ture 386, the trunk line conductor 30, the repeater winding 2| 8 and the winding of the relay 290 to ground. With the relay 290 operated the relays 280, 210, I30 and I60 are also necessarily energized over more or less obvious circuits traced in detail hereinafter. With the common cut-off relays I30 and I60 operated the primary circuits for the line relays individually associated with the respective subscribers lines are open and, consequently, the ringing operation of the party at the substation D, or any other substation, is without effect. The calling party failing to get waiting tone under these conditions must necessarily repeat the ringing operation until waiting tone is returned to him when he is informed that the central exchange operator has been signalled.

Returning now to the point in the operation when the line relay I20 is operated to connect the subscribers line to the trunk line I4, the continued operation of the hand generator at the calling substation transmits ringing current through the repeater 209 and over the trunk line conductors 29 and 30 to cause the energization of the primary circuit for the line relay 340. More specifically, this circuit extends over the calling subscriber's line 42', the link line II 5 and the trunk line I4 to the bridge comprising the condenser 346, the lower winding of the relay 340, the armature 345 and associated contact 341 of the relay 340, and the armature 356 and associated contact 351 of the relay 350. In response to such energization, the relay 340 partially operates to complete, at its armature 3 and contact 342, its secondary energizing circuit including the winding of the-relay 400, this circuit extending from ground at the contact 342, through the upper winding of the relay 340, over the conductors 3I8 and 3l9 and through the winding of the relay 400 to battery. The relay 340 now completes its operation to open, at its armature 345 and associated contact 341, its previously-traced primary circuit and to close, at its armature 343, an obvious circuit for energizing the line relay 380. The latter relay in turn operates to connect, at its armatures 38I and 384, the trunk line conductors 29 and 30 to the link line conductors 26 and 21, thereby to complete a connection between the calling subscriber's substation and the central exchange operator's station. Operation of the armature 38I also disconnects charging battery from the negative trunk line conductor 29 at the contact 382 and operation of the armature 384 disconnects the armature 386 from its associated contact 385 to open a further point in the primary circuit for the relay 340 and to prevent battery from the resistor 336 from being applied to the conductor 30, thereby to energize the relay 290, when the cut-off relay 350 operates.

Continuing now with the operation of the apparatus in the tandem oflice I3, the relay 400 operates simultaneously with the complete operation of the relay 340 to initiate the operation of the timing means comprising the relay M3, to complete the energizing circuit for the tone relay M and to complete the circuit for ener-- gizing the connnon cut-off relay 350, all in the manner described in connection with calls from one tandem subscribers line to another tandem subscribers line. The relay 350, in addition to completing a circuit for energizing the relay 360, operates its armatures 353 and 356 into engagement with the contacts 355 and 358, respectively Since the apparatus included in the suboffice I2 is identical with that embodied in the subofilce II, it will be understood, from the preceding description, that the operation of the relay 350 to apply, at the armature 353, battery to the trunk conductor 32, causes the apparatus in the suboffice I2 to operate to interrupt the primary circuits of all of the line relays individually associated with the subscribers lines 45, 46, 41, etc., extending to this suboflice. Thus, the apparatus included in the suboilice I2 is conditioned so that the trunk line I cannot be seized by any of the subscribers lines terminating at this office. The relay 360, upon operating, interrupts the primary energizing circuits of the line relays associated with the tandem subscribers lines, such, for example, as the lines 33 and 34.

Continued operation of the hand generator at the calling subscriber's substation causes ringing current to be transmitted over the loop as established in the above-described manner to the central exchange operators station, thereby to cause the operation of the drop 465 and to signal the central exchange operator that a call on the trunk line I8 awaits attention.

The operator may thereupon insert the plug associated with the operator's telephone in the jack 465 to establish a talking connection with the calling subscriber and to initiate, through the resulting sequential operation of the relays 420, 430 and 440, in the order-named, the conditioning of the rotary stepping switch 401 to be responsive to impulses transmitted from the impulsing device 461. 'The manner in which the enumerated relays operate is described in a previous portion of the specification and need not be repeated. Following receipt of the information concerning the party. desired by the calling subscriber, the calling subscriber hangs up and the. central exchange operator actuates' the impulsing device 461 to cause the automatic switching equipment associated with the trunk lines l4 and i8 to connect the-called subscribers line to the first of these trunk lines. Thus, the digit 1 is the first digitdialed, causing one impulse to be transmittedv to interrupt only once the previously-traced circuit for energizing the relay 420. When this relay restores, at the beginning of the impulse, it completes the previously prepared energizing circuit for the rotary magnet.

460 and'the slow-to-release relay 450. The relay 450, at its armature 45l and associated contact 452, interrupts the circuit for energizing the relay 410 and, at its armature 453, prepares an obvious circuit for energizing the relay 485. At the beginning of the impulse, the rotary magnet 460 steps the wipers 428 and 429 of the switch 401 to a position corresponding to the trunk line I4, or into engagement with the respective first contacts of the two contact sets 418 and 419. The off-normal springs 488 and 489 are also closed during this stepping operation, so that, when the relay 450 restores after an interval following the single impulse, an obvious circuit is completed at the armature 451 for energizing the relay 410. Restoration of the relay 450 also interrupts the previously prepared circuit for causing operation of the relay 485.

When the relay 410 operates .in response to its "energization in the manner described above, it

closes, at its armature 412, a locking circuit for itself extending to ground at the operated armature 444 of the relay 440 and, at its armature 41l, prepares the circuit for energizing the relay 485, this latter circuit being held open at the restored armature 453 of the relay 450. At its armature 416, the relay 410, upon operating, prepares the circuit for energizing the release magnet 462, this circuit being held open at the operated armature 445, of the relay 440. At its armature 411, the relay 410 interrupts a point in the operating circuit for the rotary magnet 460 thereby to prevent the switch 401 from responding to further impulses dialed at the impulsing device 461. In addition, the relay 410, at its armatures 413 and 414, completes, respectively, an energizing circuit for the relay 490 and the second branch of the secondary circuit for the line relay 340. The first of these two circuits extends from ground at the armature 444 by way of the armatures 413 and 403, the wiper 428 and the associated first contact of the contact level 418, over the conductor M8 and through the winding of the relay 490 to battery. The second branch of the'secondary circuit for the line relay 340 extends from ground at the operated armature 445 by way of the armature 414, the wiper 429 and the first contact of the contact level 419, and the conductor 414 to the upper terminal of the upper winding of relay 340. The closure of the lastmentioned circuit is of no efiect at this time, since a multiple, circuit to ground is already tact 342 of the relayj j340.

Inresponse to the completion of the abovetraced'energizing circuit, the relay 490 operates and, at its armature '49l,'connects battery to the conductor 50, which conductor is connected by way of the trunk line conductor 30 and the lower repeater winding 2"! to the ungrounded terminal of the line relay 290. Battery is extended to the conductor 50 over a path comprising the resistor 500, the armature 438 and associated contact 439 of the operated relay 430, the armature 42! and associated contact 422 of the operated relay 420, and the armature 4! and its associated armature 492. Operation of the relay 490 also disconnectsthe line conductor 50 from the link line conductor 21 at the armature 492. Thus, an impulsing 011': t is completed for the line relay 290 included ihe subofllce II.

The equiprn] 't associated with the trunk line I8 is now in condition for transmitting further digits of impulses to the automatic switching equipment located in the .suboflice H and associated with the subofiice trunk line l4. Moreover, the completion of the above-=traced ener- V gizing circuitv for the line relay 290 causes this relay to operate and initiate the conditioning of the automatic switching equipment associated with the trunk line I4 to be responsive to additional transmitted impulses. Thus, when the line relay 290 is energized over the above-traced circuit, it operates and, at its upper contact 2!,

completes the circuit for energizing the slow-torelease relay 280. The latter relay operates and, at its armature 28l, closes a shunt path around the armature 21l, at its armature 282, completes the circuit for the slow-to-release holding. relay 210, and at its armature 283 prepares a circuit for energizing the relays 250 and 230 in parallel.

When the hold relay 210 operates, it opens, at its armature 21l, the original operating circuit for the relay 200 and the secondary circuit or the line relay I20, this operation occurring only after the armature 28! has placed a shunt around the armature 211. The relay 210 also opens, at its armature 213, the previously completed energizing circuit for the timing means comprising the thermal relay 2 94, thereby arresting the operation of this relay. In addition, the relay 210 interrupts, at its armature 214 and the lower associated contact, the previously completed energizing circuit for the tine relay 205 and, at this same armature and the associated upper contact, applies multiple ground to the conductor I05. At its armature 215, the hold relay 210 also prepares a path for energizing the secondary circuit of the line relay associated with the called subscribers line. With the system in this condition. the automatic equipment associated with the trunk line i4 is in condition to respond to additional series of impulses transmitted from the impulsing device 461 at the central exchange operators station.

The central exchange operator now actuates this device in accordance with the digits in the number corresponding to the called telephone or,

in the present instance, in accordance with theclosed at the armature 3 and associated condigits 1 and 2, since the line 43' is the second '1 line in the first group of ten lines and, consef quently, the telephone number of the called subscriber is No. 112. In response to the operation-r of the dial of the impulse device 461 in accordance with the second digit 1 and on the returns of the dial to normal, the impulse springs 418' and 419' are momentarily opened once to inter rupt the energizing circuit of the line relay 420. At its armature 423, this relay closes the energizing circuit for the slow-to-release relay 450, the circuit to the rotary magnet 460 now being interrupted at the armature 411 of the relay 410. The relay 450 operates and, at its armature 453. completes the previously prepared energizing circuit for the relay 485, causing the latter relay to operate and, at its armature 483, to short-circuit, in an obvious manner, the winding of the relay 480.

In response to the restoration of the relay 420 during the dialing of the digit 1, battery is removed, at the armature 42l, from the conductor 50 connected to the trunk line conductor 30 and thus the previously-traced energizing circuit for the line relay 290 is interrupted. When this relay falls back, it completes a circuit for energizing th' relays 230 and 250 in multiple, this circuit extending from ground by way of the armature Hi, the contact 293, the armature 283, the armature 242 and associated contact 244, where the circuit divides, one path going through the winding of the relay 230 to battery and the other path extending by way of the armature 24l and through the winding of the relay 250 to battery. The relay 230, upon operating, at its armature 232, opens a point in the circuit for energizing the operating magnet H2 and, at its armature 23l, prepares a new operating circuit for itself in case the digit dialed comprises more than one impulse. The relay 250, upon operating, at its armature 25I, short-circuits the relay 240 and prepares a circuit for energizing itself and the relay 240 in series. The short-circuiting path noted extends from ground by way of the armature 213 and its associated upper contact, the armature 25l, the winding of relay 240, the armature 24l and by way of the armature 242 or the armature 23l, the armature 283 and the armature 29i to ground.

When the second digit comprising one transmitted impulse is terminated, the contacts 418' and 419' of the impulsing device 461 again close to cause the reenergization and operation of the relay 420. This relay, at its armature 423, interrupts the circuit for energizing the slow-torelease relay 450 and again completes the circuit for the relay 430. It will be understood that the latter relay does not restore during impulsing due to its slow-to-release characteristic. After an interval, the relay 450 restores to open, at its armature 453, the original energizing circuit for the relay 485 and remove the shunt from around the winding of the relay 480. Thus, the relay 4B0 energizes in series with the relay 485 to prepare, at its armature MM and associated contact 484, a circuit for energizing the relay 485', this circuit being held open at the restored armature 453 of the relay 450.

While the above-described operations are taking place, the armature 42l is closed to its associated contact 422, immediately upon the reoperation of the relay 420, thus connecting battery by way of the resistor 500 and the armature 49| to the conductor 50 to complete the previously-traced energizing circuit for the relay 290. When the relay 290 reoperates, in response to the completion of its energizing circuit in the above-described manner, it removes, at its armature 29l, the short circuit from around the relay 240. The latter relay is now energized in series with the relay 250 over a circuit extending from ground at the armature 213 by way of the armature 25l and through the windings of the relays 240 and 250 in series to battery. At its armature 242 and associated contact 243, the relay 240 prepares a point in the circuit for energizing the relay 260. At its armature 241, it opens a point in the original circuit for energizing the relay 250 and, at its armature 245, it prepares a point in the circuit for energizing the operating magnet 212 of the minor switch 225 and the slow-to-release relay 2l0 in parallel. In case the called subscriber's line were included in the second group of lines associated with the contact set 221, so that the second digit would necessarily comprise two impulses, the slow-to-release relay 230 would be maintained in its operated position during the second impulse to complete a circuit for the relay 260 by way oi the armature 23! upon a second de-energization of the line relay 290. In the present case, however, since the second digit dialed is 1 and the line relay 290 is not de-energized a second time, the relay 260 is not at this time energized, and the relay 230 restores after an interval. The latter relay, upon restoring, at its armature 232, prepares a further point in the circuit for energizing the operating magnet 2I2. At its armature 23l the relay 230 opens a point in the circuit for energizing the relay 250 so that the latter relay will not be affected by the impulses oi the third digit dialed at the operator's station. The automatic switching equipment associated respectively with the trunk line i8 and the trunk line i4 is now in condition to respond to the dialing of the third digit, which digit, in the present instance, is 2.

In response to the dialing of this digit, the relay 420 is again de-energized during each impulse and completes, at its armature 423, the en ergizing circuit for the relay 450, which relay again operates to complete, at its armature 453, a circuit for energizing the relay 485', this circuit extending from ground at the armature 453 by way of the armatures 48| and 48! and through the winding of the relay 485' to battery. When the relay 485 operates, it completes, at its armature 486, a path for short-circuiting the winding of the relay 480, this path extending from ground at the armature 453 by way of the armatures 48l and MW, the winding of the relay 480' and the armature 486 back to ground at the armature 444 of the energized relay 440.

Before proceeding with the description of the operation of the automatic switching equipment associated with the trunk line l4 in response to the de-energization of the line relay 290 during the impulses of the third digit, it is pointed out that the relay 456, due to its slow-to-release characteristic, remains operated during the transmission of impulses comprising digits greater than 1 and holds, at its armature 453, the shunt across the winding of the relay 480 so that the relay 4% is retained in its operated position. Hence, the conductor 50 is connected by way of the armature 49E to battery for a period during each succeeding impulse and corresponding to the energized condition of the relay 420 when the armature 42l is closed to its associated contact 422. In this way, the energizing circuit for the line relay 290 is alternately interrupted and completed during each impulse of any third digit greater than 1.

Returning now to the operation of the apparatus associated with the trunk line i4, when the third digit is dialed, and upon the first restoration of the line relay 290 in the above-described manner, there is completed, at the armature 28i energizing circuit for the operating magnet I2,-this circuit extending from ground by way of the armature ZSI, the contact 293, the armature 283, the armature 245, the armature 232 and through the winding of the operating'magnet 2 I2 to battery. A branch from this circuit extends through the winding of the slowto-release relay 2l 0, which relay operates and, atits armature 2H, disconnects the switch wipers 2I3 and 2I4 from ground at the armature 215.

In response to the energization of its operating magnet 2I2, the minor switch 225 steps its wipers 2 I3 and 2 I5 into a position corresponding to the first subscriber's line of the first and second groups or onto the respective first contacts of the two contact sets 226 and 221'. Simultaneously with such stepping operation, the off-normal contacts 2I6 are closed to prepare a circuit for energizingthe release magnet 2I5. At/the conclusion of the first impulse of the third digit when the relay 290 restores to interrupt the circuit for the magnet 2 I2, this magnet de-energizes to condition the switch 225 to take a second step. The wipers 2 I 3 and 2 I4 are thus stepped during each succeeding impulse of the third digit at the rate of one step for each impulse. In the present case wherein the called line is the second line of the first group and the final digit comprises two impulses, the wipers 2I3 and 2I4 will be stepped to their respective second off-normal positions or into engagement with the respective associated second contacts of the contact sets 226 and 221.

At the end of the third digit, when the interrupting springs 418' and419 of the impulse device 461 are again closed to complete the energizing circuit for the relay 420, this relay reoperates to interrupt, at its armature 423, the circuit holding the relay 450 operated. When the latter relay falls back, in response to its de-energization, it opens, at its armature 453, the shunt from around the winding of the relay 480', permitting this relay to operate in series with the relay 485' to interrupt, at its armature 483, the energizing circuit for the relay 490. The latter relay restores r to connect the line conductor 50 to the line conductor 21 and thereby substitute battery from the impedance element 499 for battery from the re sistor 500. Before the last-described sequence of operations is completed and immediately upon the reenergization of the relay 420, the energizing circuit for the line relay 290 is completed at the armature 42I so that this relay is in its operated condition when holding battery through the impedance 499' is substituted for operating battery through the resistor 500.

The line relay 290, followingits reenergization, reoperates to open the previously-traced energizing circuit for the relay 2i!) and the operating magnet 2I2 of the minor switch 225. At its armature 2| I, the relay 2 I completes the secondary circuit for the line relay IIO associated with the called line 43', this circuit extending from ground by way of the armature 215, the armature 2i I, the armature 222, the wiper 2I3 in engagement with its second bank contact, the conductor I06, the upper winding of the line relay H0, the conductor I04, the armature RI and through the winding of the relay 200 to battery.

' In response to the completion of its secondary circuit, as above described, the relay IIO operates and completes, at its armature II3, a locking circuit for itself, which circuit comprises this armature, the upper winding of the relay I I0, the conductor I04, the armature 28I, the winding of the relay 200 and battery. When the line relay H0 operates it connects, at its armatures I I I and I I2, the subscriber's line conductors I82 and I83 of the line 43' to the link line conductors I02 and 'I03, respectively. It will now be seen that the through the jack 465 and the repeaters 446 and 20, to the link line conductors 26 and 21 to transmit such current by way of the trunk line I4, the repeater 209, the link line H and the two sub- 15 scribers lines 42' and 43', to the respective bells or signal devices at the calling and called substations. In case more than one substation is connected to the called line 43, code ringing may be used to signal the desired substation. The operation of the signal devices indicates to the calling and called parties thata connection is established, following which they may remove their receivers and converse as desired.

Before describing the release of the connection V and in order to complete the description of the operation, it will be assumed that the called line is included in the second group of ten lines, or the group of lines having line relays comprising secondary energizing circuits including the respective contacts of the contact set 221. Thus,

i assume that it is desired to call the substation F on the line 44, which line has associated therewith the line relay I40 whose secondary circuit includes a branch extending from battery on the conductor I04 by way of the first contact of the contact set 221 and ultimately to ground at the armature 215. To complete this circuit it is necessary that the armature 222 of the relay 220 be operated. Energization of the relay 220 is obtained by the operators dialing a second digit of two impulses instead of one impulse as was the case for the selection of the lines in the first group of ten lines. It will be remembered from the foregoing description that at the end of the first impulse of the second digit the two relays 250 and 240 are energized in series from ground at the operated armature 213 and that the relay 230, due to its slow-to-release characteristic, is maintained operated. With the three relays noted in their energized condition, a circuit is prepared for energizing the relay 260, which circuit extends from the contact 293 by way of the operated armatures 283, 23I and 242, the contact 243, the restored armature 22I and 5 through the winding of the relay 260 to battery.

It will be observed that the branch of this circuit extending to the common terminals of the relays 250 and 240 is interrupted at the operated armature MI and, hence, these relays are not afiected by the second impulse of the second digits At the beginning of the second impulse of the second digit whenthe line relay 290 again restores, the above-traced circuit for energizing the relay 260 is completed at the armature 25. The relay 260 operates, the short circuit for the winding of the relay 220 is opened at the armature 253i and the two relays 260 and 220 are energized in series in a circuit extending from ground 'at the operated armature 213 by way of the operated armature and the windings of the two relays noted to battery. The relay 220 upon operating interrupts, at its armature 22I, the original operating circuit for the relay 260 and, at its armature 222,- prepares a circuit for energizing the secondary circuit of the line relay associated with the selected subscriber's line included in the second group of ten lines. Shortly following the end of the second digit the relay 230 restores to prepare, at its armature 232, the above-mentioned circuit for energizing the rotary magnet 2I2 and the slow-to-release relay Zill in parallel. The operations which occur in response to the impulses comprising the third digit dialed at the central exchange opera or's station are exactly the same as are set forth above. In the present assumed case wherein the called line 44 corresponds to the first ofi-normal position of the switch 225, this third digit will comprise a single impulse so that at the conclusion thereof the wiper 2I4 will stand in engagement with the first contact of the contact set 221. Thereafer, and when the slowto--release relay 2 I0 restores shortly following the end of the third digit, the secondary circuit for the line relay I40 is completed at the armature ZII. This circuit extends from ground at the armature 215 by way of the armatures 2H and 222, the wiper 2I4 and its associated first contact, the upper winding of the relay I40, the conductor I04, the armature 28I and the winding of the relay 200 to battery. The relay I40 operates to complete, at its armature I43, an obvious locking circuit for itself and to connect, at its armatures MI and I42, the conductors of the called line 44 to the conductors of the link line II5. Thus, a connection is established between the calling and called parties. From the foregoing description 1t will be apparent that in the event a connection is desired to a line in the first group of ten subscribers lines terminating at the subofiice II, the second digit dialed at the central exchange operators telephone will necessarily comprise a single impulse, whereas if the called line is included in the second group of ten lines the second digit will necessarily comprise two impulses.

Release of the connection As pointed out above, the release of the connection established in the manner described above, as well as the setting up of the connection, is und r the control of the operator in the central exchaure. Thus, when the conversation is terminated, either the calling or the called party may signal the operator that the connection is no longer desired by ringing off to transmit ringing current over the trunk line I4 and the trunk line I8 to the drop 466 at the central exchange operators station. causing the operation of this drop. The operator then initiates the release of the connection by removing the plug associated with the operators telephone from the jack 465, thereby interrupting at the contact 464 the previouslytraced circuit for energizing the relay 420. This relay restores and interrupts, at its armature 423. the circuit holding the relay 430 operated and closes, at the contact 425, a circuit for energizing the relay 450; When the relay 420 restores, it also opens, at its armature 42I, a point in the original energizing circuit for the line relay 230. The latter relay is at this time, however, held operated from battery at the impedance element 409'. The relay 450, upon being energized, again establishes the short circuit around the winding of the relay 480', permitting this relay to restore to cause the operation of the relay 490, which latter relay operates to disconnect, at its armature 49I, the line conductor 50 from the line conductor 21 and thereby interrupt the holding circuit for the line relay 290. The operation of the relay 450 in response to restoration of the relay 420 is, however, only momentary, since the relay 430 restores shortly after the relay 420 falls back and opens, at its armature 434, the circuit for energizing the relay 450, thereby to initiate the reoperation of the relay 480 and the interruption of the energizing circuit for the relay 490. When the latter relay falls back, the line relay 290 is again energized from battery at the impedance element 499'.

When the relay 430 restores, it also interrupts, at its armature 43! and associated contact 433, the circuit holding the relay 440 operated and, at its armature 436 and associated c ntact 431, opens the shunt around the armature 4 3, thereby to interrupt the previously-traced secondary circuit holding the line relay 340 and the relay 400 operated. At its armature 438, the relay 430 also opens a further point in the original energizing circuit for the line relay 290. When the relay 400 falls back, it interrupts, at its armature 403, the multiple circuit holding the common cut-ofi relay 350 operated, and opens, at its armatures MI and 405, respectively, a point in the circuit for energizing the tone relay M0 and the momentarily recompleted energizing circuit for the thermal relay 3.

When the relay 440 restores, it opens, at its armature 442, the circuit including the impedance element 499' holding the line relay 290 energized. At its armature I. and associated lower contact, the relay 440 opens the circuit for the cut-off relay 350, permitting this relay to restore, and interrupt, at its armature 35I, the circuit holding the cut-off relay 360 operated. It will be understood in view of the previous description that the restoration of the relay 350 to remove, at the armature 353 and its associated contact 355, battery from the lower conductor 32 of the trunk line l5, leading to the subofiice I2, initiates the restoration of the cut-off relays, corresponding to the relays I30 and I in the suboflice II, thereby to recomplete the primary circuits of the line relays associated with the subscribers lines terminating at the ofllce I2. The relay 360 upon restoring completes, at its associated armatures, the individual primary circuits for the line relays respectively associated with the subscribers lines such, for example, as the lines 33 and 34. Shortly before the restoration of the cut-off relay 350, the line relay 340 restores to open, at its armature 34I, a further point in its secondary circuit, to complete, at its armature 345, a point in its primary circuit and to interrupt, at its armature 343, the circuit holding the line relay 380 operated.' The relay 38B restores and, at its armature 38I, disconnects the trunk line conductor 29 from the link line conductor 26 and reconnects charging battery at the contact 382 to the trunk line conductor 29. The relay 380, at its armature 384, also disconnects the trunk line conductor 30 from the link line conductor 50 and prepares a point in the primary circuit for the line relay 340, this latter circuit, as well as the corresponding circuit of the relay 330 being completed upon the restoration of the relay 350 to disconnect its armatures 353 and 356 from battery at the respective associated contacts 355 and 358, and to reconnect these armatures to their respective associated contacts 354 and 351. Since the relay 380 restores before the cut-0d relay 350 falls back, a holding circuit extending from battery at the resistor 336 and by way of the armature springs 356, 385 and 386 is momen-. tarily completed for the line relay 290 included in equipment of the subofilce II. This holding cir-' cult is interrupted upon the sequential restoration of the relays 440 and 350, permitting the line relay 290 to restore to initiate the restoration of the switching equipment associated with the trunk line I4 in the suboflice II. At this point, all of the line relay equipment associated with the lines illustrated in Figure 4 is restored to normal.

Returning now to the operations which occur following the interruption of the circuit holding the relay 440 energized, it will be seen that, after an interval, this relay restores to disconnect, at its armature 442, holding battery for the line relay 290 and to prepare, at its armature 44 I the circuit for energizing the tone relay 4I0, this latter-circuit being held open at the armature 40I of the restored relay 4001* The relay 440, upon restoring, also prepares, at its armature 443, a point in the common portion of the secondary energizing circuits for the-line relays associated with the lines accessible to the link line 28, namely, the relays 3I0, 320, 330, 340, etc. It is pointed out, however, that before the armature 443 falls back, the armature 445 is moved away from its associated upper contact, so that the latter armature interrupts the previously-traced branch of the secondary circuit for the relay 340 comprising the multiple path shunting the armature 34I and extending from ground at the'armature 445 by way of the wiper 429 and the conductor 4I4. Thus, both paths extending to the upper terminal of the upper winding of the relay 340 are open at the time the relay 440 completely restores its armature 443 to complete the path extending from battery at the relay 400 to the lower terminal of this winding.

Restoration of the armature 445 completes, at its associated lower contact, the previously prepared energizing circuit for the release magnet 462, causing this magnet to operate-and permit the switch 401 to restore its wipers 428 and 429 to their respective normal positions and to open the off- normal springs 488 and 480.

At its armature 444, the hold relay 440, upon restoring, interrupts the holding circuits for the relays 410, 480, 485 and 485', permitting these four relays to restore. When the relay 410 falls back, it opens, at its armature 416, the circuit for energizing the release magnet 462. It will be apparent from the foregoing description that the automatic switching equipment associated with the trunk line I8 and the line relay equip-- ment associated with the respective subscribers and suboifice lines illustrated in Figure 4 are now restored to the condition which prevailed at the outset when all of these lines were idle;

Turning now to the operations which occur upon the restoration of the line relay 290 associated with the trunk line I4, this relay initiates therstoration to normal of the automatic switch 225 and the control equipment associated therewith. Ihus, at its armatureZQI, the relay 290, upon" restoring, interrupts the circuit holding the series relay 280 operated. After an interval, the slow-.to-release relay 280 restores and, at its armature 28!, opens the circuit holding the relays 200, H0 and I20 operated. At its armature 202, the relay 200opens the circuit of the hold relay, 210 and, at its armature 283, opens a opens a point in the circuit of the tone relay 205 and, at its armature 204, prepares a point in the charging circuit for the common battery of the subofiice II. The line relays H0 and I restore simultaneously with the relay 200, to disconnect, i

at their armatures III, H2 and I2I, I22, respectively, the subscribers lines 42 and 43' from the trunk line I4. At their respective armatures H2 and I22 and the respective associated lower contacts, the line relays H0 and I20 prepare points in their primary circuits which circuits are, however, still maintained open due to the energized condition of the common cut-01f relay I30. From the foregoing description, it will be seen that the line relays H0 and I20 are tie-energized in response to the restoration of the relay 420. It will further be observed that the subscribers at the substations D and E can not energize the line relays individually associated with their respective lines to initiate a call until such time as the apparatus associated with the trunk line I4 is fully released.

Shortly after the restoration of the relay 280, the hold relay 210 fallsback and, at its armature -21I, prepares-the secondary circuit for the subscribers line relays, which circuit includes the winding of the relay 200. "At its armature 214, the hold relay 210 removes ground from the conductor I05 to interrupt the circuit holding the commoncut-ofi relay I30 operated. [At its armature 213, the relay 210 prepares a point in the circuit for energizing thethermal relay 294, and, at its armature 213 and associated upper contact, the relay 210 opens a point in the common branch of the holding circuits for the relays 220, 240, 250 and 260 causing their de-energization, if energized. At its armature 212, the relay 210 completes a path including the upper winding of the tone relay 205 for transmitting waiting tone current to a calling subscriber. At its armature '214, the relay. 210 prepares a point in the circuit to the tone relay 205 and, at its armahim 215, this relay disconnects ground from the minor switch wiper 2I3 and completes the circuit for energizing the release magnet 2I5 of the minor switch 225. The switch 225 responds by restoring its wipers 2I3 and 2I4 to their respective normal positions and opening the off-normal springs 2I6. The off-normal springs open, in turn, the circuit for energizing the release magnet 2I5. It is pointed out that the secondary circuits for the restored line relays, I I0 and I20 and including the winding of the relay 200 are opened at the armature 215 of the relay 210 before the armature 21I engages its associated contact. Thus, these relays are prevented from being momentarily reoperated.

The cut-off relay I30, upon de-energizing, at its respective armatures I3I, I 32, I33, etc., coinpletes the primary circuits for the line relays IIO, I20, etc., individually associated with the respective subscribers lines of the first group,

thereby to condition these relays to be responsive to calls initiated on their respective associated lines. At its armature I34, the relay I30 interrupts the operating circuit for the cut-off relay I00 permitting this relay to restore and complete at its armatures IBI, I62, I63, etc., the primary circuits of the relays I40, I50, etc., in-

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