US1895113A - Automatic telegraph switching system - Google Patents

Description

' Jan. 24, 1933. G. s. VERNAM AUTOMATIC TELEGRAPH SWITCHIbiG SYSTEM Filed July 23, 1930 5 Sheets-Sheet 1 EMPZEQ EukEwE mun-2E EMPZEQ INVENTOR' GILBERT s. VERNAM SEE. mmn

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muhzam m mm muFzEl Nn ATTORNEY Jan. 24, 1933. s, VERNAM 1,895,113

AUTOMATIC TELEGRAPH SWITCHING SYSTEM Filed July 23. 1950 5 sheer s sheet 2 INVENTOR GlLBERT 5 VERNAM BY g ORNEY Jan. 24, 1933.

G. s. VERN-AM AUTOMATIC TELEGRAPH SWITCHING SYSTEM File y 25. 1930 5 Sheets-Sheet 5 m OC lNVENTOR GILBERT S. VERNAM ATTORNEY Jan. 24, 1933. G, s, VERNA 1,895,113

AUTOMATIC TELEGRAPH SWITCHING SYSTEM Filed July 23, 1930 5 Sheets-Sheet 4 INVENTOR GILBERT S. VERNAM Patented Jan. 24, 1933 GILBERT S. VERNAM, OF RIVER. EDGE,

COMMUNICATIONS LABORATORIES, IN 0.,

NEW YORK Application filed July 23,

This invention relates in general to a telegraph exchange system andparticularly to an automatic printing telegraph exchange system for facilitating telegraph communication, in either direction, between a plurality of customers stations and a central tele-- graph station.

The objects of this invention are to provide means by which a customer can select one of a number of classes of telegraphic service furnished by a central telegraph station; to provide means by which the calls for any particular class of service will be confined to the first idle printer in a group furnishing that class of service to provide means under control of a central station operator alone for releasing an established connection between a customers station and the central station, and to provide means for controlling the printer motor at a calling or called subscribers station.

The preferred embodiment of the present invention is shown in the accompanying drawings in which,

Figure. 1 shows the system schematically.

Figs. 2 and 3 show the outward circuit, or the circuit from the calling central station to the called customers station.

Fig. 4 shows the primary line finders of the inward circuit, or the circuit from the calling customers station to the called central station operator.

Fig. 5 shows the selecting circuits, the secondary line finders and the central station receiving operators set associated with the inward circuit.

Fig. 6 shows the wiring arrangement for starting the first idle secondary line finder.

The complete inward circuit is shown when a subscribers station as 52A, Fig. 2, is associated with line 51, Fig. 4, and Fig. 5 is placed to the right of Fig. 4 so that the leads 551 and 541 of the former are respectively opposite the leads 651 and 641 of the latter.

Referring to Fig. 1, the customers stations 52A to 52G are shown connected by lines 51A to 51G to a central telegraph station X. At the central station X, as is shown by lines 24 and 25, each of the lines PATENT em-C NEW JERSEY, ASSIGNOR 'ro INTERNATIONAL or NEW YORK, 1v. Y., A coarona'rron or AUTOMATIC TELEGRAPH SWITOHING SYSTEM 1930. Serial No. 470,007.

51A to 51G is multipled to the central station inward circuit or concentration sys-, tem" Y and to the central station outward circuit or switching system Z. More specifically, a group of customers stations is associated with 'a group of primary line finders 26, and a group of connectors 43'; and the lines 51A, 51B, etc., connecting each customers station in the group withthe central station are multipled to each primary line finder in the associated group of such finders 26, andtoeach connector in the associated group of connectors 43. The number of primary line finders 26 and the number of connectors 43 to be provided depends respectively upon the expected amount of busy hour inward and outward trafiic, and this number may be varied as is found necessary to handle the traflic in an economical manner. As an example of a suitable arrangement, we may assume that each roup of 200 customers station lines is muFtipled to a group of twenty primary line finders and each group of 100 lines is multipled to a group of 10 connectors.

The concentration system Y comprises a group of primary finders 26; a group of trunks 27 leading from the primary finders 26 to a group of selecting circuits 28, which provide access to trunks 29, 30, 31, 32 and 33, etc.; groups of secondary line finders 34, 37 40 associated with these trunks; and groups of printers 36, 39, 42, etc., associated by trunks 35, 38 and 41, etc. with the secondary finders. A selecting circuit is individual to each primary finder. ary finders 34, 37, 40, etc. each contain a plu'-' rality of secondary finders the number of which is determined, as in the case'of the primary finders, by the amount of traific to the particular printer group 36, 39, 42, etc. Each trunk 29, 30, 31, 32 and 33 of the selecting circuits is multiplied to a different group of secondary finders 34, 37 40, etc., so that whenever, for example, a customer dials to The groups of second select trunk 29, his line is invariably connectgrams; (2) A connection to a cable recording.

operator for sending cablegrams; (3) A connection to a chief equipment man; (4) A connection to an operating room traflic manager.

It will probably be found advantageous in practice to'have one group of central station operators handle inward calls and another group handle outward calls. The group of receiving operators mav be further sub-divided so that each sub-group handles separate classes of inward calls; one group handling land line telegrams, another group cablegrams, etc. and if so desired, separate subgroups of sending operators may likewise andle separate classes of. outward service. The switching system Z includes groups of connectors 43; groups of trunks 44; grou s of second selectors 45 associated'by the trun s 44 with the connector groups 43; trunks 46; groups of first selectors 47 associated by trunks 46 with the second selector groups 45; trunks 48; and groups of printers 49 associated by these trunks 48, with the first selector group 47. The selector group 47 contains a plurality of first selectors, each individual to a central station sending operators printer in group 49. Each first selector is multipled to the second selectors in selector group 45 in such a way that the first selector has access to sub-groups of second selectors, each capable of extending a connection to any one of a particular group of 1000 customers stations. The number of second selectors in any such sub-group is determined by the amount of traflic between the central station and the particular group of 1000 customers lines to tion to any one of a which the sub-group of second selectors has access. Each second selector in a particular sub-group 1s multipled to a particular suboup of connectors, in connectorgroup 43,

in such a way that any second selector in a sub-group has accessto a sub-groupof connectors each capable of extending a connecparticular group of 100 customers stations. I

A description of the operations which take place in establishing the circuits in either direction between the central station and the subscribers station will disclose the methods and means used in carrying'out the invention as well as its novel features.

A general idea of the operation ofthe system may be obtained from a description of the incoming and outgoing operations respectlvely which take place when customers station 52A, for example, desires to establish connection with, say, a printer in printer individual to the actuated primary line nection, for example, with customers station- The sequence of operations in establishing said inward circuit will be described first. On customer 52A operating a ke to calling position, an idle primary line nder 26 at the central station finds his line 61A, connecting it to a selector switch in groupigg, er. When connected to the selecting switclf, the customer then selects a type of service, as for example, that furnished by printer group 36 in the manner hereinafter described. After the customer has selected the type of service given by printer group 36 the first idle secondary line finder in the group of finders 34 selects the trunk 29 thereby connecting the calling station 52A to the first idle receiving operators set in the printer group 36. Upon the establishment of connection between the calling subscribers station and the called central station operators set, the printer motor at the subscribers station is alone started. As the central station oper ators printer motor runs continuously, communication between the two stations can then be carried on. The release of the connection between the two stations at the end of a message is under the control of the central station operator, as will be described later, though the calling subscriber can stop his own printer motor.

The sequence of operations in establishing the outward circuit hereinbefore mentioned is as follows: when a central station operator in chargeof a printer in printer group 49 desires to establish connection-with customers station 52A, he dials the number correindividual to his printer, to choose one of the trunks 46 leading to an idle second selector in the proper thousands group of the second selector groups 45. The second digit dialed operates the second selector, causing it to select one of the trunks 44 leading to an idle connector in the proper hundreds group of the'connector groups 43. The third and fourth digits dialed operate the selected connector to establish. a connection over lines 25 and line 51A to the called customers station 52A. Assuming that the central station 01)- erator receives no indication that the called subscribers line is busy, he then operates a hey to cut through position, thereby starting the printer motor at the subscribers station. As thecentral station operators motor is running continuously, communication can then take place between the two stations. As in the case of the inward circuit, the release of-the established connection is under the control of the central station operator,

though the called subscriber can stop his own printer motor.

Referring now to Figs. 2 and 3, which illustrate the outward circuit in detail, there is shown a calling operators set 100; a first selector 200 which is individual to operators set 100; a second selector 300 which is the first idle selector in the selected thousands group which has access to the customers line;

a connector switch 400 which is the first idle connector in the selected hundreds group, a line relay 436 and a cut-off relay 438 which are individual to the called station and are common to both the inward and outward circuits, and a subscribers station 52A. It is apparent from the previous description of the system as a whole that the second selector 300 223, 224 and 251 to a number of first selectors similar to 200, which likewise have access to it; the connector 400 is multiplied by trunks 323, 324 and 351 to a number of second selectors similar to 300, which also have access to it; and that the relay 438 is multiplied by wires431 and 432 to a number of connectors similar to 400 which have access to relay 438 and the called customers station, and conductors 441 and 442 are multiplied to the primary line finder banks in the group associated with the called subscribers station while 440 is connected to the group stations of which 52A is one.

As the customers station is common to both the outward and inward circuits, to avoid repetition it will be described first.

At the customers station 52A a line 'circuit 51 extends from ground 50, throughthe sending contacts 52 of a printer, a line magnet 53, contact 55, a three position calling key 24, lower winding 59 and upper winding 60 o the central station. When contact 55 is closed, or when the calling key 54 is in its unoperated position, both the lower or high I resistance winding 59 and the'upper or low resistance winding 60 of are in the line circuit. When the calling key 54 is operated to the right however, and contact 56 closed, the lower or high resistance winding 59 is shunted. The line circuit then extends from ground at 50, sending contacts of the printer 52, line relay 53, pulsing contacts 63 of the dial 64, contact 46, re sistance 71 and lamp in parallel, upper the polar relay 58 winding 60 of polar relay 58, line 51 to the lamp 70, whose op central station. The dial eration will be described later, is shunted by resistance 71, which is of such a value that the dial lamp will not be lighted until the circuit is ready for the operation of the subscribers dial64. The dial 64 is of usual type, with pulsing contacts 63 and off-nor: mal contacts 65. The polar relay 58 has a tongue which, in the normal idle condition of the circuit is held away from its back .relay will restore the polar relay relay associated with the group of a polar relay 58, and over line 51 to contact A by a small current through both windings 59 and 60 in series, or through winding 60 alone. Upon a reversalof current through the polar tongue closes against its back contact A and is held there by a biasing spring 66. Another reversal of current through the polar tongue to normal and open contact A. The relay tongue controls a circuit for operating a control relay 67, which in its preferred form is capable of operating nating current. lVhen the polar relay tongue is in its normal position away from contact A, the control relay 67 is deenergized, butwhen the tongue moves against contact A, the control relay is energized over'a circuit extending from source of current 74, resistance 68, contact Aof polar relay 58, contact- A of release relay 72, ofi-normal con relay 58, however',-this.

upon direct or alteris against contact 55, removes the dial lamp 70 from the line circuit.

The release relay 72, which is adapted when operated to deenergize the control relay 67 and open the shunt around the high resistance 59 of polar relay 58, is controlled both by thekey 54 when operated to the clearout position so that contact 61 is momentarily closed, and by the tongue of polarrelay 58. When the polar relay tongue is against its back contact A and the control relay 67 is operated, the momentary closing of contact 61 b N the calling key 54 establishes a circuit fier operating the release relay 72 from source of current 74,'resistance 68, contact A of polar relay 58, contact 61 of key 54, winding of release relay 72, resistance69, back to source of power 74. In operating, the release relay locks itself over an obvious circuit through contact 62 of key 54. The operation of deenergizes the control turn opens the motor circuit and removes the short circuit from the high resistance Winding 59 of polar relay 58, reducing the line current. The release relay 72 is deenergized by the retraction of key54 which closes contact 56. This opens contact 62 breaking the locking circuit of the release relay. If the release relay is operated by the subscriber before the desired to disconnect, the operation by the latter of a recall key in the case of a receiving operator, or the operation of a key to dial position in the case of tor, tobe described later, reconnects negative battery to the line circuit opening contact A of polar relay 58, thus deenergizing the rethe release relay 72 relay 67, which in lease relay 72. Upon restoration of the recentral station operator a sending operacall key or the operation of a key to cut through position by the central station operator, positive current is reconnected to the line circuit, andthe subscribers printer motor 73 is started as described above.

To initiate a call the customer operates the calling key 54 to the calling position, closing contact 56; thereby short-circuiting the high resistance winding 59 of the polar relay 58. The line circuit now extends through the upper winding 60 of the polar relay 58, the dial lamp 70 which is shunted by resistance 71 and is not lighted by the line current even though thus increased, contact 56 and operating spring of the calling key 54, the pulsing contacts (33 of the. dial 64, the printer line mag net 53, sending contacts 52 to ground at 50. The short-circuiting of the high resistance winding 59 increases the line current with the result that the line relay 436 at the central telegraph station is operated. The opera tion of line relay 436 starts an idle primary line finder 26 (Fig. 1) of the group associated with the calling line, to connect customers station to a selecting circuit 28 (Fig. 1). The further operation of the circuit for handling inward calls will be described in more detail later.

It will suffice for the present to observe that after a connection is finally established between the calling customers station and a central office receiving printer, such as printer 36, 39, 42, etc., positive potential is applied to the line. This results in the operation of the polar relay 58 of the'customers station in a direction to close its contact A which energizes the control relay 67. The control relay closes its contact A and starts the printer motor 7 3. 'It also closes its contact B and establishes a shunt around the dial lamp 70 which having been lighted when the customers line was extended to the selecting circuit is now extinguished. Calling key 54 should preferably be restored to its original unoperated position against contact 55 at this time. The line circuit may now be traced from ground at 50 through printer sending contacts 52, line magnet 53, contact 55 of calling key 54, contact B of control relay 67, upper winding 60 of polar relay 58, line 51 to the central telegraph station and through the concentration system A (-Fig. *1), at that station to a receiving operators set 36, 39, 42, etc. As will be described in more detail later, the printer motor associated with each receiving operators set at the central station is continuously running while the receiving operator is in attendance. Consequently it is unnecessary, and no means are provided, for starting his printer motor.

When the desired messages have been transmitted, the central station operator releases the line circuit 51 from battery 433 associated with line relay 436. The change in the direction of the current passing through the polar relay 58 causes contact A of polar relay 58 to open. This releases control relay 67 which stops the motor 73 and restores the customers station circuit to normal. Should the calling subscriber operate the calling key 54 to the release position, thereby closing contact 61 before the central station operator desires to release the connection, the latter may operate a recall key, which deenergizes the release relay 72, and then restart the subscribers motor 73 as described above.

To initiate an outgoing call from the central station, the sending operator dials the number assigned to the customers station- 'line, operating the proper selector switches in groups 47 and 45 (Fig. 1), and the proper connector switch in group 43 in a way that will be explained in more detail later. The result of the operation of these intermediate switches is thatthe central station operator establishes a direct connection to the customers station. After this connection is established, by operating a key the central station operator applies positive potential to the line from the the case of the inward circuitpreviously described, this positive current causes the polar relay 58 to close its contact A thereby operating the control relay 67. The controlrelay by closing its A contact starts the motor 73 and by closing its B contact shunts out the high resistance winding 59 of th polar relay 58. As the calling key 54 is in its normal position, the station line circuit for outward service is now the same asfor inward service after the customer has released the calling key and has established connection with the printer at the central station.

The breaking of the established connection by the central station operator is followed by the same effects at the customerls station in this case as in thecase of the inward circuit. In this case also the central station operator can deenergize the released relay 72 at the subscribers station, if it is operated before the former desires to disconnect.

Referring now to Fig. 3, central station sending operators set 100 comprises apparatus for jdialing, for transmitting and receiving printer signals, and a three position circuit-controlllng key. A printer motor, notshown, is also located at this set and is left running continuously while the sending operator is in attendance. This key 121 is adapted to be moved into three positions, namely, to release,- dial and cutthrough positions. Normally it is in release position, at which time contacts 128 and 129 are closed; while contact 130 is open, so that the dial lead 123 to the selector 200 is open. The line circuit of the sending 'operators set now extends from positive battery 101,

attery 101 (Fig. a). As in through resistance 102, sending contacts 103 of a printer, relay 104, resistance 131, contact 129 to ground at 132. The operators printer set line circuit is thus held. closed. The differentially wound line relay 104 has an upper winding 105 and a lower winding 107. ne. end of the lower winding is grounded at 106, while its other end is extended through resistance 108 to the positive pole of grounded battery 101. The current through this lower winding is normally about half that through the upper winding. The

. line magnet 113 of the printer is in a local circuit extending from ground 114 through winding of line magnet 113', contact'A of relay 104 which is normally closed, resistance 109; or when contact A is open, through condenser 115 and resistances 116 and 109, to the positive pole of battery 101. When printer signals pass through the winding'105 of line relay 104, the circuit; from battery 101, winding 107 of relay 104'to ground at 106, cooperates with the line circuit causing contact Aof relay 104 to open and close, thus operating printer magnet 1131" The line circuit for the selector switch, which .is normally open, extends from grounded negative battery 133, resistance 134, contact 128, to an open contact F of relay 201 of the first selector 200. a

When the key 121 is operated to dial position closing contact 130, the dial lead 123 is closed, thereby establishing a circuit for operating relay 205 of first selector 200, from ground 132,- through contact 130, dial 127, resistance 135 and busy lamp 126 in parallel contact A of relay 201, windings 208 and 207 of relay 205 in series, to grounded bat-- tery 206. Relay 205 thereupon energizes, closing its A contact. An operating circuit for slow releasing relay 210 is thereby completed from grounded batte 209 winding of relay 210, the A contact 0 relay 205, the E contact of relay 2 01 to ground at 202. The operation of relay 210 closes its A contact, thereby placing ground at 211 on release lead 224.

The sending 0 digit of the ca ing signal allotted to the desired customers station. In response to the impulses corresponding to this first digit, relay 205 is energized and deenergized so that it alternately closes its A and B contacts. When relay 205 opens its A contact the slow releasing relay 210 is not'deenergized, but remains energized throu bout the entire series of impulses. When re ay 205 closes its B contact, relay 212 and vertical magnet 213 are operated. Since relay 212 is slow releasing, it likewise remains ener 'zed, during the entire series of impulses. e vertical magnet 213, on the contrary, responds tothe dialed impulses. The 0 rating circuit for vertical magnet 213 and relay 212 may be traced from grounded battery 214 through erator now dials the first the winding of vertical magnet 213, winding ofrelay 212, contact B of relay 210, contact B of relay 205, contact E of relay 201 to ground at 202. The operation of the vertical magnet steps the wiper shaft (not shown) up to the bank level corresponding to the dialed digit. At the first upward movement of the wiper shaft'the off-normal contacts 219 and 220 close.

Upon the operation of relay 212 and the off-normal contacts 219 and 220, relay 216 is energized over a circuit from grounded battery 215, winding of relay 216, off-normal contact 219, contact A of relay 212, contact A of .relay 210 to ground at 211. Relay 216 looks itself over a circuit from off-normal contacts 219, through contact A of rotary magnet 217, contact B of relay 216.and contact E of relay 201 to ground at 202.

The wipers 225, 227 and 229 have now been stepped up to the level of the bank terminals 226. 228, 230, etc. having access to the group of 1000 lines which includes the called line. Although only the above positioned bank terminals are shown leading to the first idle second selector 300, other bank terminals (not shown) but connected by trunk conductors similar to 223, 224- and 251 to other second selectors, are capable of being tested by test wiper 225. When some of the trunks are busy, the bank terminals corresponding to terminal 226 having access to the b trunks will be grounded at a second selector 300 if the second selector has not yet found a connector,,or at a connector such as 400 when the selector is fully operated, in a way which will be described later, while those having access to the idle trunks will be ungrounded. a

At the endof the series of impulses corresponding to the first digit dialed, rela 205 remains energized with Relay 210 alsoremains energized, grounding the release lead 224 at 211. Relay 212 however, releases as its circuit is opened at contact B of relay 205. Upon the release of relay.212, an operating circuit is closed for rotary magnet 217 from contact A of relay 216, (relay 216 having been operated upon closing of oif-n'ormal contacts), contact B of relay 212 and contact A ofrelay 210 to ground at 211., The rotary magnet operates and rotates the wipers 225,

227 and 229 so that each wipernow contacts with the first corresponding bank terminal ofits contact A c osed.

grounded battery 218, through winding of rotary magnet 217,

is connected to an idle bank terminal 226, a circuit may be traced from grounded battery 215 through winding of relay 216, offnormal contact 219, contact A of rotary magnet 217, winding of;relay 201, contact 203,

release lead 224, contact A of release relay 210 to ground at 211. When the rotary mag net releases and the wiper 225 is connected to a busy bank terminal 226, a circuit may be traced from grounded battery 215, through winding of relay 216, cit-normal contact 219,

contact A of rotary magnet 217, contact C of relay 201, conductor 224, wiper 225 to ground on terminal 226 which is connected to the grounded release lead of asecond selector or a connector.

From the circuits traced it is seen that when the bank terminal 226, connected to wiper 225, is bus and grounded, the operating circuit for re ay 216 is grounded at bank terminal 226 without passing through relay 201. Relay 201 consequently remains unoperated. The operation of relay 216 closes a circuit for operating the rotary magnet 217. The rotary magnet 217 then operates, rotating the wipers one step and opening at its contact A the operating and locking circuits for relay' 216. This interaction between relay 216 and the rotary magnet 217 continues in this manner until the rotating wiper reaches an idle trunk. 1

When this occurs, as described above, relay 201 is connected in series with relay 216. Relay 216 is marginal and does not operate in series with relay 201, the winding of. which is of comparatively high resistance. The failure of relay 216 to operate when the wiper 225 is rotated to an idle trunk leaves the rotary magnet circuit lay 216, preventing rther rotation of the wiper 225 on that level.

Upon operating, relay 201 connects test bank contact 226 to ground at 211 over a circuit from test bank contact 226, wiper 225, contact D of relay 201, release lead 224 contact A of relay 210 to ground at 211. This makes the trunk busy and prevents other first selectors from establishing a connection with the same trunk.

A digression is now. necessary to explain that the second selector 300 and the first selector 200 are identical, and the details of relay selector 300 have therefore been omitted.

ofplen at contact A of retor; the dial lead 223 to battery 206A through both windings 208A and 207A of relay 205A; and the release lead 224 to open contact A of relay 210A. I

The first selector 200 is multipled by means of conductors 223, 251 and 224-to the bank contact-s of'first selectors (not shown),

but as lead 224 is now grounded and there-.

fore bank contacts 226 of these other first selectors are also grounded, none of these -first selectors can become connected to the particular second selector, in this case selector 300, that'is now connected to the selector 200 upon the operation of relay 201.

The release lead 224 is connected-to release lead 224A of the second selector, which as yet is not grounded at 211A. As the dial lead now extends from battery 206A through windings 207A and 208A of relay 205A of the second selector, contact A of relay 201A,

bank contact 228 and wiper 227 of the first selector, conductor 223, contact B of relay 201, lead 123, resistance 135 and lamp 126 in parallel, dial 127 and contact 130 of calling key 121 to ground at 132, the circuit for relay 205A of the second selector is completed and it is accordingly energized. When this relay is energized, a circult for operating relay 210A of the second selector is completed. The operation of relay 210A applies ground at 211A of the second selector to release lead 224A. The release lead now extends back from ground at 211A of the second selector through conductor 224A, test bank contacts 226, wiper 225, conductor 224,

contact D of relay 201, contacts 203, wind- I ing of relay 201, contact A of rotary magnet 217', off-normal contact 219 and winding of relay 216 to grounded battery 215. Belay 210 .of the first selector is released by the operation of relay 201 since its operating circuit is open at contact E of that relay. The operation of relay 201 also by openingits A contact opens the operating circuit for relay 205 which also releases. As relay 210 of the first selector is of the slow releasing type, however, it does not release until res lay 210A of the second selector is operated,

grounding the release leads 224 at 211A of the second selector. Relay 201 of the first selector is, therefore, held operated over the circuit previously traced, extending from ground at 211A. Relay 201 of the first selector by-opening its E contact also prevents the operation of release magnet 221 when relays 205 and 210 of the first selectorare released.

When all the trunks on the selected level are busy the first selector will rotate beyond the last or tenth contact. The eleventh rotary operation of the switch opens contact 203 and closescontact 204 which respectively open the circuit of relay 201 and short circuit the upper or high resistance winding 208 of relay 205. The current in the dial lead 123 is accordingly increased-and a busy lamp 126 at the central station operators set is lighted. on observing this indication of a busy trunlt the operator moves the calling key 121 to release position removing ground at 132 from relay 205. Relay 205 is lease magnet 221, off-normal contact220, con- 404. As the dial tact C of relay 210, contact B of relay 205, contact E of relay 201 to ground at 202.

When the outward circuit has been extended to the second selector 300, the second or hundreds digitdialed by the sending operator operates this selector in the same way that the first selector was operated by the first digit dialed. The 0nd selector 300 extends the outward circuit over conductors 351, 323 and 324 to the first idle connector switch 400 (see Fig. 2) associated with the group of 100 lines containing the called customers station.

If all the trunks on the selected level of, the second selector are busy, the previously described operations lamp 126 will be lighted and the sending operator informed that a busy trunk condition ex sts. The operator can then move key 121 to release position, as described above. restoring both the first and the second selectors to normal.

If there is an idle trunk on the selected level the printing line will be extended by the operation of relay 201A through the first and second selectors to open contact D of relay 421 of the connector switch 400. The dial lead will be extended through the first and second selectors to the connector switch 400 and through both windings 402 and 403 of relay 401 in series to grounded battery circuit is complete from battery 404 associated with relay 401 to ground 132 at the central station. relay 401 will operate. The operation of relay 401 energizes relay 406 which is slow releasing. The circuit for operating relay 406 extends from grounded battery 407 through winding of relay 406. contact A of relay 401 to ground 405. Relay 406 on clos ng its contact B applies ground at 408 to the release lead 424 which extends back from the connector switch to hold operated relay 201 of the first and relay 201A of the second selector switches. As in the case of relay 210 of selector 200,2relay 210A of selector 300 is not released until relay 406 of the connector applies ground at 408 to release trunk 424.

The connector switch 400 is now operated by the third or tens digit dialed by the sending operator. Relay 401 alternately closes operation of this sec-- will result, the busy its A and B contacts in response to the-impulses corresponding to this digit in the same manner as did relays 205 and 205A of the two selectors. Relay 406 being slow releasing remains energized with its contacts closed throughout the entire series of impulses corresponding to this digit. When contact B of relay 401 is closed, a circuit is established for operating the slow release relay 412 and the vertical magnet 413 in series. This circuit may be traced from grounded battery 414, winding of vertical magnet 413, winding of relay 412, off-normal contact 410, contact C of relay 406, contact B of relay 401 to ground at 405. As relay 412 is slow releasing, it likewise remains energized throughout the entire series of impulses. The vertical magnet 413 on the other hand operates in response to the impulses and steps the Wipers 427 and 429 up to the level corresponding to the dialed digit.

The first vertical movement of the wiper shaft (not contacts closing contacts 409 and 411 and opening contact 410. The closing of these contacts has two results. First, it prepares a circuit for the release magnet 426, though this magnet cannot operate until relays 401 and 406 are deenergized. Secondly, it changes the pulsing circuit through the vertical magnet 413. This circuit now extends from ground 405, contact B of relay 401, contact C of relay 406, contact 411, contact A of relay 412, winding of relay 412, winding of relay 413 to grounded battery 414.

At the end of this group of impulses corresponding to the tens digit. relay 401 comes to rest energized, with its A contact closed. Belay 406 is thus held energized while relay 412'wl1ose circuit is open at contact B of relay 401 is released.

The units digit is then dialed by the sending operator causing relay 401 to energize and deenergize. Since the pulsing circuit is now changed, this closes parallel operating circuits for the rotary magnet 424 and the relay 417. Relay 417 operates at the first impulse and, as it is slow releasing, remains energized throughout the series of impulses. The rotary magnet 424, on the contrary, operates in response to each impulse and steps the wipers 4 27 and 429 around to the terminals of the called line. The operating circuit for the rotary magnet may be traced from grounded battery 423, winding of rotary magnet 424, contact E of relay 42l,'contact D of relay 416, contact B of relay 412, off-normal contact 411, contact C of relay 406. contact B of relay 401 to ground at 405.

The circuit for operating relay 417 may be traced from grounded battery 418, winding of relay 417, contact D of relay 416, contact B of relay 412, off-normal contact .411, contact C of relay 406, contact B of relay 401 to ground at 405 The operation of relay 417 shown) releases the off-normal a lished for relay 416. This possible operating circuit may be traced from grounded battery 415, winding of relay 416, contact A of relay 421, contact B of relay 417, wiper 427 to the grounded bank terminal 428. If relay 416 should operate in such acase, the shunt path previously mentioned prevents its operation from opening the pulsing circuit at its D contact. a

If the called line is busy, the test bank contact 428 now connected with Wiper 427 will be grounded through the wiper of some other connector or line finder switch. In this-case relay 416 will operate. Relay417, being of the slow releasing type, remains energized for a short period after the wipers 427 and 429 reach the terminals of the called line. But since the circuit for relay 417 is open at contact B of relay 401,.due to the closing of the pulsing contact 125 of thedial 127, it releases shortly afterwards. If relay 416 oper- 'aiing winding 422 of relay 421 so that the reates during this interval, that is, while the wiper 427 is in contact with terminal 428 of the called line and relay 417 is operated, relay 416 will be locked when relay 417 releases. The locking circuit for relay 416 in this case. may be traced from battery 415, winding of relay 416, contact of relay 421, contact C of relay 417, (relay 417 now being released) contact B of relay 416, conductor 424, contact B of relay 406 to ground 408. Relay 416 at its D contact opens the pulsing circuit so that any further operation of the sending operators dial can have no effect on the connector switch. Relay 416 at its C contact also opens the circuit ofthe lower operlay cannot operate.

The operation of relay 416 likewise establis'hes a shunt around the upper or high re sistance winding 402 of relay 401, thus 'increasing the current on the dial lead 323 which extends to ground 132 at the sending operators calling key 121, and lighting the operators busy lamp 126. This circuit may be traced from grounded battery 404, winding 403 of,relay 401, contact A of relay 416', contact E of relay 417, dial lead 423 through the first and second selectors, busy lamp 126, contact 130 to ground at 132.

Upon this indication of a busy customers line the operator moves the calling key 121 to release position, removing ground from dial lead 423 and releasing relay 401 which in turn releases relay 406. The releaseof relays 406 and 401 closes the previously prepared circuit for the release magnet 426 of the connector switch and this magnet restores the connector to normal. The operating circuit for the release magnet may be traced fromgrounded battery 425, through winding of magnet 426, contact F of relay 421, oli-normal contact 409, contact D of relay 406, contact B' of relay 401, to ground at 405. The release of relay'406 also removes ground at 408 from release trunk 424, thus opening the operating circuit of relay 201 of the first selector, relay 201A of-the second selector, and relay 416. Therelease of relay 201 of selector 200, by closing its E-contact, results in the operation of the release magnet 221'which restores selector 200 to normal. In a similar manner the release of relay 201A causes selector 300 to restore to normal.

If the called station is not busy, test bank contact 428 will not be grounded but .willbe connected to battery437 through cut-oil relay 438. In this case relay 416 does not operate,v since the batteries associated with relays 416 and 438 are of the samepolarity and' poteptial. Relay 421, however, does operate. Thefv sequence of operations of the connector switch when the called line 'is busy,a'nd when it is not busy, are theysame up -to'the' pointf I when the wipers 427 and 429Iha v'e connected.- with the called line. Beyondflthisi fioint thet' zi operations of theconnectorare d'ifl' each case. Whentlie called gstationwis 1101;

busy. relay 417 releases at the end'foffthe} series of units digit impulsessince is opened at contact B of relay401; relav 417 releases a circuit is'closed o; a crating relay 421. This circuit be trac from battery 437 associated with cut-ofi re- 1 0 circuit; L

When

lay 438 through the test bank terminal 428, v wiper 427, contact A of relav 417, winding. 422 of relay'421, contact C of relay 416, re-

lease trunk 424, contact B of relay 406 to ground at 408. Relay 421 operates to close its locking contact C first, locking the relay through contact A of relay 406 to ground at 408. Contact B of relay 421 then operates connecting ground at 419 directly through wiper 427 to the test bank contacts 428, making this trunk busy and operating cut-off relay 438. At its contacts-E and A relay 421 also opens the rotary magnet circuit and the operating circuit for relay 416 respectively tact B of relay 438, to ground 50 at the called customers station. a

When the customers line has been selected in the manner above described, the central station operator moves the cut-through position opening contact 128 to remove negative battery 133 from the line circuit and closing contact 136 to con- The closing of this contact energizes the' control relay '67 which closes its.A and B contacts. The closing of the former starts the station printer motor 73. The closing of the latter shunts the winding 59 of the polar relay 58. i

The line circuit may be traced from ground at 50, the sending contacts 52 of the printer, line magnet 53, contact 55 of calling key 54, contact B vof control relay 67 winding 60 of relay 58, line 51, contact B of cut-ofi relay 438, connector 400, selector 300, selector 200, line 151, to battery 101.

As the printer motor at the central station set is running continuously and the customers printer motor has been started, the sendi ng operator may now send to the customers station. When the message has'been transmitted and acknowledged the sending oper-- ator restores calling key 121 to release position removing ground from dial lead 123; thus opening the operating circuit for relay 401. Relay406 is released when relay 401 releases, removing ground from the locking circuit of relay 421 and from the release lead 424. The removal of ground from the release lead 424 opens the operating circuits of relay 4%1, relay 201 of selector 200, and relay 201A 0 201A and ;201 closes an operating circuit for the release magnets 221 and 221A of both of these selectors, and the release magnets re store the selectors to normal. othe release magnet of the connector switch e ends through contact F of relay 421. This arrangement of the release circuit prevents the release magnet from restoring the connector to normal until after relay 421 has been released, so that the wipers of the connector switch will be open circuited when they restore and thus avoid any possible interference with other lines on the same level when traversing the bank terminals of such lines while restoring to normal. When relay 421 releases, however, the connector-switch restores to normal. The release of relay 421 also removes ground at 419 from the test bank terminal 428,.so that the cut-off relay 438 releases and applies negative potential from battery 433,- resista-nce 434 winding of the key 121 to selector 300. The release of the relays The v circuit 7 line relay 436 and contact C of cut-01f relay 438 to station'line 51, opening contact A of polar relay 58 which releases control relay 67 stopping the motor and, restoring the station to normal as previously described.

As an alternative method of stopping the customers printer motor, the customer may operate the key 54 to the release position,

thereby closing contact 61. The release relay 72 is thus operated over a circuit previously described, and, locks itself over an obvious circuit through contact 62 of key 54. The energization of the release relay opens the circuit ofthe control relay 6 at contact A of the release relay, thus stopping the sub:

scribers motor .73. In this case, however, the

connector and selector switches are not released, but the line current is reduced by the opening ofthe shunt around the lower high resistance winding of the polarv relay 58. This reduced line current makes the central station printer spin without printing,'thus informing the sending operator that the customers printer motor has been stopped. The sending operator may now release the connection as previously described or if desired may start the customers motor again by.

momentarily operating the key 121 to dial position, and then restoring it to the cutthrough position. When in the dial position, the key connects negative batterX to the line circuit, which opens contact of polar relay 58 thus opening the circuit of the release relay 72 and releasing it. Upon moving the key 121 back to cut-through.

position, the centralstation operator reconnects positive batter 101 to the line circuit,- closing contact A o polar relay '58 and're-' starting thecustomers printer motor in the manner described above.

:The complete circuit for inward service is shownby connecting the customers station, comprising the parts shown in Fig. to line 51. leading to contact of C the cutoff relay 438 and the line relay436 shown in Fig. 4 and by lacing line 551 and line 541 of the primary nder 500 end to end with line 651 and line 641 respectively of the selector circuitas shown in Fig. 5.

Referring to Fig. 4, the line and cut-ofi. relays 436 and 438 are individual to each customers line and are used both in the inward circuit and the outward circuit as previously described. The line 51 extending from the customers station is multipled after passing through these relays to associated groups of connectors and primary line find- 51, and the bank terminals'545 and 549 con- I nected to another customers station are alone shown in the finderswitch 500. It 1 s obvious, however, from the general'd'escrip'tion of the 40 i mina1'543. Thecircuit for energizing the system previously given, that 198 other cuscarries the line wire terminals 547, 549 I for two hundred lines while the upper tomers stations are connected to finder switch 500 and that the 200 customers stations connected to the switch are multipled by means of conductors such as 550 and 552 to a plurality of other finder switches, the number of which is determined by traffic conditions. y I

The line finder switch 500 is in general similar in. mechanical construction to the selector and connector switches used for out- 1 ward service. Each switch, however, has two hundred point banks having ten-levels and twenty terminals per level instead of the one hundred point bank terminals possessed by the connector switches. The lower bank etc. bank carries the private or test terminals 543 and 545 for the same two hundred lines. Unlike the connector and selectorv switches, the primary line finder hunts both in the vertical and rotary directions and also operates automatically instead of in response to dial im: pulses as do the connector and selector switches. R

When the customer operates a key 54 (see Fig. 2) to calling position to initiate a .call, the high resistance winding 59 of polar rela 58 at the customers stationis shunted in t e manner previously described, and an increased line current results which operates line relay 436 at the central oflice. This relay closes a circuit to connect the battery 437 associated with relay 438 to the test bank terminal 543. It also operates group relay 554. The circuit for placing battery on the test bankterminal 543 may be traced from battery 437, winding of relay 438, contact B of relay 436, conductor 442 to test bank ter- I group relay 554 may be traced from grounded ttery 555, winding of relay 554, contactAof relay 436 to ground at 535. Ten ofthese relays 554 are provided for each group of two hundred lines or one relay for each twenty lines on the same level. The relay- 554 grounds the proper vertical commutator terminal of each line finder switch, that is, it grounds the first contact 508 on the home switch and also, for use in case the home switch is busyygrounds successive contacts 509, etc. on successive switches.

The-home switch is a device for reducing the huntin time of the vertical commutators. As t ere are ten levels of bank terminal in each primary line finder, ifa particular line were invariably associated in each of the finders with thetenth level ofbank terminals, it is plain it would always 'be necessary to step the vertical commutator of any duced into the bank multiple,

finder ten levels upward in order to find that line. To obviate the necessity of stepping the commutator up in this way, a slip is introthe first idle switch) that is, each 1 group of twenty lines terminates on diii'erent levels in each of the primary finders in a particular group. For example, if there are twenty line finder switches for a group of 200 the first level, is known as the home or first preference switch for that group. The relays 554 are arranged so that each line will normally start a home switch but if that switch is busy it will start the second home switch, and if both are busy it will start a switch in which the lines containing the calling line are on the second terminal bank level or if these are busy it will start a switch having the calling lines on the third level, etc. As a result of this arrangement, the switches are usually required to step up only one level and it is only when most of the switches are busy that they are required to step up to the higher levels. It is apparent that the contacts 508, 509, etc., of the vertical "commutators must be wired with a multiple slip in a manner similar to contacts 543 and 547 which are shown multipled by leads 550 and 552 respectively to other primary finder switches.

The circuits which cause the-initial energization of the home-switch and then of successive switches if the busy, will be described later. I

Relay 554 at its A contact also grounds the start lead 553 to energize relay 512 of the home switch or, if that switch is busy, of following. The circuit for relay-512 may battery 513 through winding-of relay 512, contact E of relay 536A, start lead 553A, contact A of relay 554, contact A of relay 558 which is normally energized to ground 562..

'Relay512 operates stepping relay 525. The grounded circuit for 525 may be traced from home switch is e traced from grounded battery 540,13ontact H of relay 536A, winding 563 of relay 525, contact A of rotary magnet 523', contact A of vertical magnet 522, contact Aef relay 512 to ground 514. Relay 525 closes a circuit for operating the vertical magnet 522 from grounded battery 540, through contact H of relay 536A, winding of the vertical magnet 522, contact F of slow-operating relay 515, contact A of relay 525, contact A of relay 512 to ground at 514. Upon the completion of this circuit, the vertical magnet 522 operates, raising the switch shaft (not shown) inj eluding commutator wiper 507. The move ment of this shaft closes the vertical offnormal contact 530 and opens contact 529. The release magnet 527 does not operate at this time as its circuit is open at contact D of relay512. The vertical commutator seg ments 508, 509, etc.,are open. except the top segment 510 which is permanently grounded at 511 and the segment corresponding to the level of the calling line which is grounded at 556 through contact B of relay 554. The tenth or top segment 510 is permanently grounded so that the vertical commutator will invariably stop on the tenth level, should the start lead 553A be accidently grounded. Relay 525 and vertical magnet 522 are so arranged that they will mutually operate and release one another so long as the wiper 507 is not in contact with a segment WhlCll'lS grounded at 556. In other words, the vertical commutator shaft will he stepped vertically until it reaches the level-in which the calling line appears or until it reaches the tenth level.

The operation of vertical magnet 522 opens its A contact and the original operating circuit for relay 525. If the vertical commutator segment 508, 509, etc., which is then in contact with the brush 507, is not grounded at 556, relay 525 will release. The release of relay 525, releases the vertical magnet 522-as its circuit isthen opened at contact A of relay 525. The release of vertical magnet 522 closes its A'contact which in turn causes the operation of relay 525. Relay 525 then closes A contact and operates vertical magnet 522 again, causing the switch to take a second vertical step. Y

The mutual interaction between relay 525 and vertical magnet 522 continues until the brush 507 reaches the grounded commutator segment 508, 509, etc., which is on the first level in the home switch and on higher levels for other switches. When this occurs, relay 515 operates in series with the right hand winding 563 of relay 525; This operating circuit maybe traced from battery 540-, through contact H of relay 536A, winding 563 of relay 525, contact A of rotary magnet 523, winding 517 of relay 515, brush 507, vertical commutator segment,

' contact B of relay 554 to ground at 556. The

closing of this circuitv holdsrelay 525 energized and prevents any further opening of the vertical magnet circuit at contact A of the former relay, thus preventin further vertical stepping of the brush Relay 515 looks itself through its upper winding 516 in series with the winding of the vertical magnet 522, from battery 540, contact Hof relay 536A, verticalmagnet 522, upper winding 516 of. relay 515, contact D of relay 515, contact A of relay 512 to ground 514. The resistance of the winding 516 of relay 515 which, is now in series with the vertical mag- ,net 522 is such that the current from battery 540 is now insuflicient to operate vertical magnet 522 and it releases. Relay 515 also prepares a locking circuit for relay 501, transferring that circuit from a circuitextending from ground 531 at the OE-normal contacts, contact C of relay 515, contact E of relay 501 to grounded battery 504, to a calling line.

The operation of relay 515 in opening its A contact also opens the release magnet circuit. This circuit when closed may be traced from grounded battery 528, winding of release magnet 527, off-normal contact 530, contact A of relay 515, contact B of relay 532, contact D of relay 512to ground at 531 at the off-normal contacts. It is apparent from this circuit that the release magnet can operate only when relays 515, 532 and 512 are released.

The operation of relay 515 transfers the stepping circuit from vertical magnet to the rotary magnet 523. The operating circuit rotary for the magnet may be traced from grounded battery 524, winding of rotary magnet 523, contact E of relay 515, contact A of relay 525, contact A of relay 512 to ground at 514. Relay 515 is designed to be slow in operating in order to allow a short time between the last vertical step of the commutator shaft and the first rotary step which might result from their vertical vibration.

The operation of the rotary magnet523 over the circuit previously traced opens its contact A and the operating circuit for relay 525, and relay 525 is released. The rotary magnet circuit is in turn opened at contact A of relay 525 'and accordingly releases. This interaction between relay 525 and the rotary magnet 523 continues, stepping the wipers around until one 'of the test wipers 542 or 544, reaches the bank terminal of the This calling line is connected to battery 437 through winding of cut-ofi relay 438 as has been previously described.

It willbe understood that during the totary stepping of the switch, locking circuits of relays 501 and 532 are opened each time the 'rotary magnet releases opening its B contact. This is for the purpose of preventing false operation of these relays when the wipers step over terminals of busy lines, the test Eontacts of which are grounded. In such cases a circuit is closed from ground to the per winding 502 of relay 501, contact D of relay 532, contact D of relay 501, left hand winding 526 of relay 525, contact A of relay bank terminal 545, through wiper 544.'up-

or F of relay 532 might be induced in the left hand winding 526 of relay 525. To prevent the operating and locking of relay 501 or relay 532 by this induced current, their locking circuits are opened by the rotary magnet 523. The locking circuit for relay 501 may be traced from grounded battery 504, through winding 503 of relay 501, contacts E of relay 501, B of relay 515, B of rotary magnet 523 and contact B of relay 512, to ground at 514. The locking circuit for relay 532 may be traced from grounded battery 535, through winding 534 of relay 532, contact F of relay 532, contact B of rotary magnet 523, contact 15 B ofrelay 512, to ground at 514. Both of these circuits. are opened at contact B of rotary magnet 523when it releases, thus preventing the locking of relays 501 or 532 should. these relays be operated by induced current. If wiper 542 reaches a bank terminal 543 connected to battery 437, that is to say, if it reaches a bank terminal associated with a calling line, relay 532 will be operated sufliciently to close its locking contact F. The operating circuit for relay 532 may be traced from battery 437 through winding of cutoff relay 438, contact B of line relay 436, test bank terminal 543, wiper 542, winding 533 of relay 532, contact B of relay 536A, left hand winding 526 of relay 525, contact A of relay 512 to ground at 514. When the looking contact F of relay 532 is closed, the lower winding 534 of that relay is energized and the relay then fully operates. The closure of the above circuit prevents relay 525 from releasing. This prevents further interaction between relay 525 and rotary magnet 523 which prevents further stepping of the latter. Cut-off relay 438 establishes a holding circuit for itself, independent of line relay 436, which extends directly to the test bank contact 543 and to ground at 51 4 in the manner previously traced. The operation of relay 438 also opens the circuit of line relay 436 at contact C of the former relay and connects'the station line 51 directly to wiper .546. When relay 436 releases, it in turn releases relay 554 unless another station in the same group of twenty line's iscalling at this time. In this case relay 554 remains energized since it is common to each one of the twenty lines on the same level.

Relay 532 also opens a circuit to relay 501' 55 so that its circuit as previously described is now opened at contact 1) of relay 532. A call from the station associated with 545 is thus prevented from interfering with the busy primary finder.

Relay 532 also establishes a circuit for operating relay 536A. This circuit may be traced from grounded battery 539 through winding 537 of relay 536A, contact C of relay 532, to ground 531 at off-normal contacts.

Relay 536A operates and closes a locking circuit for relay 532 which prevents relay 532 from releasing when the rotary magnet releases. This circuit may be traced from bat tery grounded 535, winding 534 of relay 532, contact F of relay 532, contactsGr and C of relay 536A, winding 526 of relay525, contact A of relay 512 to ground at 514. Then contact C of relay 608 (Fig. 5) closes, as described later, this circuit is grounded at 610, instead of at 514, thus holding the release lead 541 grounded when relay 512 releases.

Relay 536A also removes grounded battery 540 from relays 525 and 515 by opening its H contact and therefore releases these relays. It also removes ground from relay 512 by opening contact E, and switches start lead 553A from relay 512 through to the start lead 55313 and the next finder switch.

Any further calls from this group of twenty customers stations associated with the same relay 554 will be handled by the next idle primary finder. The circuit for starting the next idle finder a sociated with this groupof twenty lines may be traced from ground 562, contact A of relay 558, contact A of re- I .lay 554, contact F of relay 536A, contact B of relay 536D to start lead of the next idle finder.

lVhen a primary commutator of the later switch, but on 'some' finder is started by the I group relay acting through the starting-'cirhigher contact. Which contact is grounded depends on the place of the later switch in the .series which lies between the home switch having the calling line on its first bank level and the last switch having the calling line on its tenth bank level.

The operation of relay 532 extends the line circuit 551 through to the selecting circuit 600 (Fig. 5). The line circuit 551 now extends (see Fig. 2) from ground 50 at the cfistomefs station through the printer set, as previously traced to bank terminal 547, (Fig. 4), and

thence through ,wiper 546, contact A'of relay 501, contact A of relay 532, line 551, contact A of relay 601, (Fig. 5) winding of relay 603 contact A of relay 604, resistance 607' to grounded negative battery 606. Relay 603 is thereupon energized and operates slow re-' lease relay 608 which places ground at 610 on release lead 641, an extension of release lead 541 of the primary line finder. The operating circuit for relay 608 maybe traced from grounded battery 609, windingof relay 608, contact B of relay 603, contact D of relay 601 to ground at 632.

Relay 536A also establishes a direct 'con tact from ground at 610 of relay 608 of they selector circuit to wiper 542 of the primary finder, which keeps relay 438 operated when ground at 514 is removed from 541. by release of relay 512. This circuit may be traced from wiper 542 through contact E of Relay 532 then operates, causing relay 532, contact D of relay 501, contact C of relay 536A, release trunk 541, release trunk 641, contact C of relay 608 to ground at 610. At the end of this sequence of operations relays 532 and 536A are held operated the other relays of the primary finder are released.

If the calling line has been associated with the test bank contact 545 connected to wiper 544, relay 501 would have operated instead of relay The operation of this relay causes it to close its locking contact E and to establish a locking circuit which has been previ ously traced. The operation of relay 501 also switches the line circuit 551 from wiper 546 to wiper 548 and connects wiper 544 directly to contact B of relay 536A. Relay 536A upon operating connects the wiper 544 through its C contact to the release trunk ground at 610 of the selecting circuit 600. Relay 501 also closes a circuit foroperating relay 532 through its lower wi'nding 534. This circuit may be traced from grounded battery 535 through winding 534 of relay 532, contact F of-relay 501, contac C of relay 512, to ground at 531 of the-oflenormal contacts.

the operation of relay 536A the functions o which have been previously described. The interaction, between the starting circuits of the various primary finders in a particular group remains to be described. These circuits are so arranged that the home switch of any calling line, if idle, will first be operated by an associated group relay 554 and also arranged so that no antecedent primary finder will take a call away from a subsequent finder by releasing when the latter has been operated but before it has found the calling line. 1

Each group of twenty customers lines is associated with the relay 554. When a call is made by a customer, that relay starts the primary finder having on its first terminal bank level the group of twenty lines containing the calling line, provided this switchis idle. In

other words, any call from a customers station invariably starts the home switch, it idle, but if that switch is busy, the relay 5'54 starts an idle one of the primary finders in the group to which the customers line is multipled; As between the idle primary finders in the group, that finder will be started which has the group of twenty lines, containing the calling line. on the lowest banklevel.

. The start leads 553A, 553B, etc., lead to the group relays 554, which invariably when actuated start the home switch? corresponding to the calling line, if the home switch is not busy. If the home switch is busy, the next idle switch is started over a circuitpreviously traced. If this next primary finder is also busy, the starting circuit willbe extended in a similar manner to successive primary finders until an idle one is started.

536A is relay 536A, to ground at 562 or Relay 536A has a locking winding 538 and similar locking windings are providedon relays 536B,-536C, etc., of the other line finders. If group relay 554 is operated at a time when line finder 500 is busy and therefore relay closed for relay 536A, extending from grounded battery 561, through-contact A of relay 560, winding 538 and contact D of relay 536A, contact A of relay 554 and contact circuit prevents relay 536A from releasing as long as group relay 554 is held energized by an incoming call not yet switched through the primary line finder Similar locking circuits are provided for all ofthe primary line finders and serve to prevent any primary line finder that has been held operated by a prior call from releasing and then taking awa a call from any other primary'finder that as been started by a subsequent call before the latter has found the calling line.

Relay 536A has a contact A, which is connected in parallel with similar contactsD of the relays 536D, 536C, etc., of all the'primary line finders serving the same group of two hundred lines. If any of the relays 536A, 536B, etc., of a particular group of line finders is not operated, the chain circuit through the contacts of these relays will be closed; while, if all of these relays are operated, this chain circuit will be broken. When the chain circuit is closed, relay 558 is energized over a circuit from grounded battery 559 through winding of relay 558, contact A of from battery 559, Winding of relay 558, contacts D of relays 536 B, C, D, etc., whichever is closed, to

operated, a locking circuit will be A of relay 558 to ground 562. This locking ground at .562. When all of relays 536 A, B,

C, etc., are operated, or in other words, when all of the primary finders associated with a particular group of two hundred customers lines are busy, the circuits previously traced are opened at the contacts previously mentioned, and relay 558 is released.

The release of relay 558 removes ground at 562 from the grouprelay A contacts. associated with start'leads 553A, 553B, etc., of

the primary start lead.. Consequently the locking circuits, for the relays 536A, etc., are opened,

and where any'finder in this group, of which a part, becomes idle,

a relay 536A, B, etc., is that relay will release. 'When it releases the chain circuit will again be closed through its D contact, and relay- 558 again operates.

line finders corresponding to a group of two hundred lines, since these group of relay 558 permits the idle switch to respond to another call from a customers station.

' If any part of the start leads 553A, 553B,

etc., becomes grounded as a result of trouble in thecircuit, the idle finders associated with the group of two hundred lines will start one at a time and if no lines are calling they will step up to the 10th level which is permanently grounded, and then rotate to the eleventh step, closing contact 505 which operates relays 532 and 536A. The operating circuit, for relay 532 'maybe traced from grounded'battery 535, winding 534 of that relay, contact 505, contact C of relay 512 to ground 531 atthe oil-normal contacts. As there is no bank terminal such as 547 connected to wiper 546 however, and therefore the line circuit 551 is not grounded at 50 at a customers station, relays 603 and 608 of the selecting circuit 600 are not operated. Moreover, since relay 608 does not operate there will be no ground on the release trunk 541, or 641, when relay 512 releases. Relay 536A remains looked through its lower wind ing 538 and the circuit previously'traced. All other relays of the line finder release,

however, and; the release magnet 527 opcrates over a circuit previously traced to restore the switch to its normal position. When every one of the relays 536A, B, C etc.,

- are operated, and relay 558 is consequently released, relay 560 will operate over a circuit from grounded battery 561, winding of relay 560, contact B of relay 558, to the grounded start lead. The operation of relay 560 by opening its contact A, removes battery 561 from the locking windings of the relays 536A, etc., permitting the relays of all idle finders to release. Whenthe relays 536A,

.B, etc., are released, the trouble ground in the start lead will again operate each idle finder insuccession. If any station is attempting to make a call at thistime, the first finder to operate after the station calls will find the calling line. By means of relays 558 and 560 then, the primary lin finders are accessible even when a start lead is improperly grounded.

Referring now to Fig. 5, when relays 438 and 532 (see Fig. 4) operate as previously .of relay 436 so that the dial lamp. at the customers station is brightly lighted. This indicates to thecustomer. that he may now dial to select the desired type of service.

When he dials, relay 603 operates and'sends impulses through its B contact to hold slow relay release relay 608 energized and throughits A contact, contact B of relay 608 and offnormal. contact 611 to operate relay 617 and the rotary magnet 616 in-series. .This

rotary magnet is part of a simple ten point switch known as a minor switch. 1.,This

switch has two wipers 618 and 619 capable of rotating over the banks 633 and 634 respectively. As the" rotate they are held by a holding pawl {not shown), but if the release magnet 614 is operated to release this pawl, the wipers may be returned to their normal positions by a spring (likewise not shown).

In response to the first impulses dialed,

617 and the rotary magnet 616 operate, the latter" advancing the wipers 618 and 619 one step. This circuit may be traced from grounded battery 615, winding of rotary magnet 616, winding of. rela 617, off-normal contact 611, contact of relay 608, contact 'A of relay 603, contact D of relay 601 toground at 632. The off-normal contacts operate, contact 611 opening and contacts 612 and 613 closing, on the first step, of the wipers. The latter contacts remain closed until the wipers return to normal.

On the closure of the off normal contacts 613, the relay 604 is operated over a circuit extending from grounded battery 615, offnormal contact 613, winding of relay 604 to ground. The operation of this relay places resistance 605 in, the line circuit, dimming lamp 70 of the customers station, informing the customer that his line has not been extended through the secondary line finder. When the line circuit has been extended through the secondary finder the relay 601 operates, as will be later described, opening its A contact, and removing resistance 605 from the line circuit.

The opening of the OE-normal contact 611 changes the impulse circuit. It now extends from groundat 632, contact D of relay 601, contact A of relay 603, contact B of relay 608, contact B of relay 617, windings of relay 617 and rotary magnet 616 to grounded battery 615. Relay 617 holds the circuit to both wipers open. After a group of impulses have been dialed and the wipers 618 and 619 have been rotated to the-desired contact, relay 603 comes to rest energized. Relay 603 holds 608 energized and releases relay 617 and the rotary magnet 616. .Relay 617 upon releasing closes its contacts A and C and thereby closes the circuits to both wipers. The upper wiper 618 now establishes, a circuit from theitest bank terminals 625 of an idle finder 700B in the selected group of secondary line finders to groundedbattery.

at 602. This circuit'may be traced from test bank terminals 625, conductor 620F,:.

wiper 618, contactA of relay- 617, winding of relay 601 to grounded battery 602. The

relay 601 will operate. The operation of re lay 601 opens its A contact, cutting resistance 605 from the line circuit. and extending the line circuit through to the bank terminal of the secondary line finder.

The secondary line finder circuits are the same as those of the primary line finder except for a change in the wiring of the start leads which is shown in Fig. 6. Parts of the secondary line finder similar to those of the primary finder, exceptwhere specifically numbered on the accompanying drawings, will be designated in the description by the same reference characters. Each of 'these secondary line finders 700A, 700B, etc., serves to connect a receiving operators printer set 800, etc., to any one of not more than two hundred trunks leading to the selecting circuits as typified by 651. Each secondary line finder has four wipers and two two hun-' dred point banks as in the case of the primary line finder (although only one pair of w pers is shown in the drawings). The selectlng circuit which has been previously described determines which group of secondary line finders, corresponding to a particular class to telegraphic service, is to start to find the trunk associated with the calling line. As in the case of the primary line finders, ten relays 701B, etc., are provided, one for each group of twenty lines. These serve to ground the proper terminal associated with the vertical commutator wiper and to ground the start'lead for, operating the relay 512 of the secondary line finder. Conductor 704 extends to the vertical commutator bank 506. and conductor 705 extends to the start lead 707, shown in Fig. 6.

The starting circuits for the secondary line finders are arranged as shown in Fig. 6. keys or switches 726, 727, and 728. are provided for each secondary line finder. With these keys in their normal position, that is, against their A and C contacts the confinon start lead 707 isadapted to start the first. secondary finder in the selected group over start lead 753A. When this finder is busy, the common start lead 707 is extended to successive finders until an idle one is found and started. As all of the group relays 701B, etc., are 'connected'to this common start" lead 707. instead of starting the home switch as do the group relays associatedwith the primary finders 500, these operated under these conditions.

pleted to ground 51 4 at group rela s invariably start the first idle secondary fihder in the selected group. With this arrangement, the first incoming call will operator always come to the first receiving associated with key 726' and with relay 736A. If the first operators printer isbusy the relay 7 36A will be energized and the start lead! 767 will then be connected through to the secondary line finder associated with the second operator and so on until an idle operator is connected to the calling line.

Assuming'that the first finder is busy and its relay 736A is operated, the circuit for reaching the next idle operator may be traced from the common start lead .707 which is connected to the ten relays 701A, 01B, etc., corresponding to a group of two hundred customers lines. contact A ofkey 726, contact A of relay 736A, contact A of key 727, contact B of relay 736B to start lead 706B of the second associated finder. Assuming that the second finder is not busy it will therefore'be When a group of printers is provided, the incoming tratfic will be concentrated on the first printer of the group. during the least busy hours of the day. During the busy hour the first printers will be busy almost continuously and the subsequent printers will receive occasional calls as the traflic varies. This method of connection provides a convenient means for regulating the number of operators needed for handling the incoming traflic at different hours during the day.

If any operators position is vacant the corresponding make-busy key 726, 727. 728 etc., will be operated. For example, if the key 726 is operated and its B contact is closed the common start lead 707 is connected directly through to contact A of key 727 of the "next secondary finder so that if this next finder is' idle, it will be started in response I v to anincoming call. The C contact is also broken by this makebusy key 726, which has the efi'ect of opening the branch of the chain circuit with Fi circuit t at relay 736A, if operated,-'would previously described in connection have. It will be apparent thatwhen contact C of key 726, therefore, is open and all of the other secondary finders corresponding to this group of two hundred trunks are busy, the relay 558 of the secondary finder start circuit will be released and ground removed from the contacts A of the group relays 701A, 701B, etc., associated with start lead 707 permitting these relays to release when their associated switch becomes idle. v

To repeat, when the secondary line finder 700B has found the callingselecting circuit, an operating circuit for relay 601-is com: the secondary line finder. The completion of this circuit causes relay 601 to operate, thereby extending the line circuit 551 through-the selecting circuit 4, and has the same effect on this I

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