US1979020A - Telephone exchange system - Google Patents

Description

Oct. 30, 193%Q w. WHITNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed oct. 12, 1952 1o Sheets-sheet 1 Y ull :Qu QG u @t HHH HHH m E IIILAIL, nlu mw s .o S uw b uw mm m T W .|..TL .nl n ..m @s msi@ um W m u/H wQN I. I n V W \u W M w 6. w W mmm. www h y \m.N B hmmm. mmm mmm d mmm h. P

ATTORNEY Oct. 30, 1934.

W. WHITNEY TELEPHONE EXCHANGE SYSTEM -Filed Oct. l2, 1932 10 Sheets-Sheet 2 INVENTOR W. WH/ TNEY B @gmw A TTOR/VEV Oct. 30, 1934. w. wHlTNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed Oct. l2, 1932 10 Sheets-Sheet 5 /NVENTR W WH/ TNE y ATTORNEY Oct. 30, 1934. w. WHITNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed Oct. 12, 1932 10 Sheets-Sheet 4 //V VEN TOR W. WHITNEY ATTORNEY OCt. 30, 1934. w WHlTNEY Y 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed Oct. 12. 1932 10 Sheets-Sheet 5 /NVENTOR W. WHITNEY ATToR/vey ct. 30, 1934. w, WHlTNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed oct. l12. 1932 1o Sheets-sheet e /N VEN TOR W. WHITNEY B md A TTORNE V Oct. 30, 1934. w, wHlTNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed Oct. 12. 1932 10 Sheets-Sheet 7 ATTORNEY Oct. 30, 1934. w. WHITNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed 0G12. 12, 1932 .10 Sheets-Sheet 8 /A/VE/VTOR W. WH/TNEV ATTORNEY Oct. 30, 1934. w. WHITNEY TELEPHONE EXCHANGE SYSTEM Filed Oct. l2, 1932 10 Sheets-Sheet 9 /NVENTOR W. WH/ TNEY BV ATTORNEY oct. 3o, 1934. w, WAITNEY 1,979,020

TELEPHONE EXCHANGE SYSTEM Filed Oct. .12, 1952 10 Sheets-Sheet 10 /NVENTOR W. WHITNEY By ATTORNEY Patented Oct. 30, 1934 rEELEPHONE EXCHANGE SYSTEM Wiley Whitney, Bloomfield, N. J., assignor to Bell'` Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 12,

23 Claims.

This invention relates to telephone exchange systems and more particularly to systems in which connections are established by dial switching equipment and in which an operator is enabled lto intercept calls which have been extended to certain terminals of selector switches. It is desirable to enable calls tobe intercepted when a connection has been extended to linal selector terminals which are Vacant or not in use, to terminals of lines on which the number has been changed, to terminals of lines which have been denied service for non-payment, to terminals of lines on which an error has been made in the directory listing, to terminals of lines which have been disconnected or when the nal selector has been set upon a particular terminal for the purpose of obtaining veriiication request service. Also when a selector switch preceding the nal .selectorV or connector has been set upon a trunk 2o. terminal which is Vacant or not connected to a iinal selector, it is desirable to enable the at tempted call to be intercepted in order that the subscriber may be apprised of his dialing error and an attempt made to complete the desired lil .25V connection. In addition, when a call has been calls are incoming to lines which are temporarily` out of service. This procedure requires that intercepting positions must be provided local to each oiiice cfthe exchange area. It is, of course, ap-

each oiiice anda centralized A switchboard provided forV serving all oflices of the exchange area. If, however, the A switchboard is centralized it is most economical to also centr-alize intercepting operators positions on the centralized A switch-` board. Since it is highly desirable to provide facilities for enabling the intercepting operators to complete as many intercepted calls as possible,

whereby when an. intercepted call has then trunked to the centralized intercepting operators position from any cnice of the exchange area,v

the operatormay readily have accessto complet- A ing` equipment in the originating office for comparent that considerable economy could be real-A ized ifthe A switchboard could be removed fromv it therefore becomes necessary to providemeans 1932, Serial No. 637,426'

character whereby the completion of intercepting calls ltrunked to a centralized intercepting operators position may if the desired line terminates in the originating ofce, be controlled over the same circuit employed to trunk the call to the operators position.

Although the present invention, for purposes of illustration, has been disclosed in an embodiment directed to the trunking of intercepted calls from offices of a dial switching system of the power driven or so-called panel type, it will be apparent that it is equally applicable to systems employing step-by-step type switches. In accordance with the invention the intercepting trunks from the final selector banks, incoming selector banks, or from plugged up subscribers lines of each office are terminated in the banks of trunk finders at that cnice. As many trunk iinders are provided at each ofce as are necessary to handle the intercepting tranic, an idle trunk finder being always allotted for use. When a call is initiated which becomes extended to an intercepting trunk appearing in the bank of an allotted trunk nder, the trunk iinder is started tohunt for and connect with the intercepting` trunk thereby extending the connection over an interoflice. trunk in which the trunk nder terminates to a trunk jack at the centralized intercepting operators position. The intercepting operator answers the call with the answering plug of a cord circuit of her position and obtains from the calling subscriber the designation of the connection which the calling subscriber has attempted. to complete. If the connection can be completed in the originating cnice the intercepting operator then plugs the calling plug of her cord circuit into a calling jack of the interofce trunk thereby causing the incoming end of the interoice trunk circuit to become automatically associated with an operators position on a B switchboard and then passes information for completing the connection tothe B operator.

The B operator upon receiving the information, sets up on her keyboard the necessary record of the correct designation and the sender at her position is then controlled from the keyboard to control selector switches at the originating officey overl a. control circuit extending over the interoce trunk to extend a connection. to the line to which the calling subscriber 'eli fil

desires connection. As soon as the connection has thus been established, a talking connection is completed from the calling line over the selector switches initially set by the calling subscriber, the intercepting trunk, trunk finder and the selector switches of the originating office set by the distant B operator to the correct called line. Thereupon the end of the interoice trunk incoming to the centralized intercepting operators position is cut oif and the intercepting operators position and the B operators position equipment is freed for other service.

The trunk finders are arranged for access to a maximum of eight hundred trunks and since the terminal capacity of the well yknown panel type finder switch is four hundred, the finders are arranged for allotment in pairs, the brushes on the shaft of one finder of each pair having access to four hundred trunks appearing in the left half of the frame and the brushes of the shaft of the other nderof the pair having access to four hundred trunks appearing in the right half of the frame. Two groups of relays are provided in the trip circuits, one group being assigned to groups of intercepting trunks appearing in the right half of the frame and the other group being assigned to groups of intercepting trunks appearing in the left half of the frame, andfdependent upon the operation of a relay in either group, the brush shaft of that one of a pair of allotted trunk finders will be started to hunt for the intercepting trunk upon which there is a call. The trunk finders are also divided into two groups and two allotters are provided which alternately allot an idle pair of trunk finders in each group for the purpose of equalizing the Wear on the trunk iinders.

For a more complete understanding of the invention, reference may be had to the following detailed description taken in connection with the attached drawings in which: v

Fig. 1 is a diagram showing the manner in which the remaining figures should be arranged to completely disclose the invention;

Fig. 2 shows in the upper portion thereof a calling line, the diagrammatic disclosure of portions of a line finder, district selector, incoming selector andthe sender of an originating office and in the lower portion thereof a second calling line which it will be assumed has been plugged out of service for inspection vor repair and the plugging-up line and trouble'intercepting trunk to which the line is connected. Fig.

. 2 also shows in the lower right portion thereof the diagrammatic representation of a called'subscribers line in the originating oiiice to which the intercepting operator may extend intercepting calls and the diagrammatic representation of a final selector;

' Fig. 3 shows in the upper portion thereof the diagrammatic representation of a final selector to which the incoming selector of Fig. 2 has access, which in turn has access to an intercepting trunk and a verification intercepting trunk terminating in the bank of the trunk finder of Fig. 4 and in the lower portion thereof an intercepting trunk extending from the lbank of the incoming selector of Fig. 2 and terminating in a bank of the trunk finder of Fig. 6;

Figs. 4 and 6 show two trunk finders having access to the intercepting trunks of Figs.- 2 and 3 and connected to the outgoing end of an interoflice intercepting trunk extending to ,a centralizedv intercepting operators position;

Fig. 5 shows an incoming selector associable with the outgoing end of the inter-office intercepting trunk of Fig. 6 for extending intercepting calls over the final selector diagrammatically shown in Fig. 2 to called lines in the originating office;

Fig. '7 shows the incoming end of the interoioe intercepting trunk terminating at the centralized intercepting operators position and the diagrammatic representation of a B operators equipment associable therewith for controlling the incoming selector of Fig. 5 and the nal selector of Fig. 2;

Fig. 8 shows a cord circuit of the intercepting operators position;

Figs. 9 and 10 taken together show a trip, start and allotter circuit for allotting and starting trunk finders such as are shown in Figs. 4 and 6;

Fig. 9 shows the trip circuit and Fig. 10 shows the start and allotter circuit; and

Fig. 11 shows the intercepting operators telephone and key set circuits.y

The line finder 201, district selector 202, incoming selector 203, final selector 204, shown diagrammatically in Fig. 2, the final selector 300, shown diagrammatically in Fig. 3, the trunk finders 400 and 600, illustrated in Figs. 4 and 6 and the incoming selector 500, shown in Fig. 5 are all of the well known panel type. For a complete disclosure of the circuits of line finder 201 and district selector 202, reference may be had to Patent No.

1,862,549, granted June 14, 1932 to R. Raymond and W. J. Scully. For a complete disclosure of the circuits of incoming selector 203 and final selectors 204 and 300, reference may be had to Patent No. 1,658,829, granted February 14, 1928 to Un C. H. Berry. The sender indicated by the rectangle 205 of Fig. 2 may be of the type disclosed in the patent to Raymond and Scully above referred to. The allotter switches 1000 and 1010 shown in Fig. l0 are of the well known non-restoring step-by-step type. The trip, start and link circuit and B switchboard sender indicated by the rectangle in the lower portion of Fig. 7 may be of the general type disclosed in Patent No. 1,753,348, granted April 8, 1930 Newsom.

The trunk finders are divided into two groups on the trunk finder frame, the finders of one group in which finder 400 is included being located on one-half of the frame and the finders of the other group of which finder 600 is one, being located on the other half of the frame. All finders of the first group have access to the terminals of 400 trunks and all finders of the second group have access to the terminals of 400 other trunks f so that a total of 800 trunks may be served. The trunk terminals of each group of 400 are further subdivided into ten banks of forty terminals each, each trunk finder having access thereto being provided with ten sets of brushes cooperating respectively with the ten banks. brush set of any one of the finders of the rst group, ten triprods, one for each brush set extend before all nders of the group. The magnet 402, for example, serves when energized tok-,1.

For tripping any 603 of finder 600 or the corresponding brush set 15E two groups of trunk finders.

Ythe pair of nders 400 and 600.

of any other iinder of the same group. Corresponding trip magnets such as 402 and 602 are connected in parallel for simultaneous operation.

vTen trip circuits of which one is shown in Fig. 9 are provided, each trip circuit serving the two corresponding subgroups of trunks appearing in the corresponding terminal banks of the For example, the trip circuit of Fig. 9 serves the subgroup of forty trunks to which the brush set 403 of finder 400 has access, and the subgroup of forty trunks to which the brush set 603 of finder 600 has access. When any trunk of the first subgroup is calling, relay 905 is operated and when any trunk of the other subgroup is calling, relay 904 is operated. Either relay when operated prevents the operation of the'other relay and causes the trip magnets 402 and 602 to be operated for tripping the brush set of a started trunk finder which has access to the subgroup of trunks in which the calling trunk is located. The operation of relay 904 or 905 causes the start circuit shown in Fig. l0, there being a single start circuit common to the ten trip circuits, to start an allotted trunk finder in f the group of iinders having access to the calling trunk.

The trunk nders of the two groups are arranged to be allotted in pairs, each pair comprising a trunk nder in each group, as for example, For allotting the trunk finders two allotter circuits 1000 and 1010 are provided as shown at the left of Fig. 10, each allotter serving to allot one half of the pairs of trunk finders and the other allotter serving to allot the other half of the pairs of trunk finders. The two allotters are arranged to operate in conjunction with the start circuit shown at the right of Fig. 10 so that upon successive calls one of a pair of iinders allotted by one allotter and then one of a pair of finders allotted by the other allotter and so on will be started. The particular finder of the pair to be started is determined in accordance with which relay 904 or 905 of the Y operated trip circuit is operated at the time. For

example, if the allotter 1010 has allotted the pair of trunk finders 400 and 600 then if subgroup relay 905 is operated, the start circuit will cause the trunk finder 400 to be started, or if the subgroup relay 904 is operated, the start circuit will cause the trunk finder 600 to be started.

Completion of an intercepted call from a final selector terminal 300 corresponding to the directory number dialed.

It will also be assumed that that particular called line has been disconnected from the terminal bank of the final selector, either because the called line has been given a new number, or service of the called subscriber has been discontinued or a mistake in directory listing has been made, and that such terminals have been connected to an intercepting trunk 307 over which the calling subscriber may have access to a centralized intercepting operators position. `When therefore the 3 brushes of final selector 300 have been positioned upon the terminals of its bank corresponding to the numerical designation dialed, which terminals are indicated as 301, 302 and 303, a circuit is established from ground at the iinal selector over brush 304, terminal 303, upper back contact of relay 305, upper operating winding and lower non-inductive winding of relay 306 in parallel to battery.

Relay 806 operates and locks ovei its upper front Contact to ground on terminal 303 and connects battery in parallel through resistance 900 at the lower winding of relay 901, over ccnductor 902, inner lower back contact of relay 305, inner upper front contact of relay 306, conductor 308, to the test terminal 401 of the intercepting trunk 307, appearing in the terminal bank of trunk nder 400, thus marking the intercepting trunk 307 as calling. Relay 306 also closes a circuit extending from ground at its lower front contact, lower normal contacts of relay 305, conductor 903, lower back contact of subgroup relay 904 to battery through the upper winding of subgroup relay 905 of the trip circuit of Fig. 9. Relay 905 operates, at its upper back contact opens the operating path of subgroup relay 904 to prevent a call in the other subgroup of trunks served by the same trip circuit from being served at this time and closes a circuit for operating relay 1001, extending from ground at its lowermost front contact, over the lower back contact of relay 901, inner lower back Contact of relay 906, conductor winding of relay 1001 to battery. At its lower front contacts, relay 905 also closes a circuit extending from ground, upper back contact of relay 901, lower back contact of relay 906, lower winding of relay 908, conductor 909, to battery over the upper back contact of relay 1002.

Relay 908 upon operating closes the operating circuit of trip magnets 402 and 602, extending from battery through the windings of these mag-- nets in parallel, conductor 910 to ground at the upper front Contact of relay 908, the contacts of relay 908 being protected by a parallel circuit to ground through condenser 911 and resistance 912. The operation of trip magnets 402 and 602 rotate trip rods (not shown) preparatory to tripping the corresponding brush sets of the allotted pair of trunk iinders. Relay 908 also closes a locking circuit for itself extending from ground at the lowermost contact of relay 905, lower back contact of relay 901, upper winding and inner upper front Contact of relay 908, back contacts of relays similar to relay 90S of succeeding trip circuits, conductor 914 to battery in parallel through the lower winding of start relay 1002 and resistance 1003. By thus wiring the locking circuit through contacts of relays 908 of other trip circuits only relay 908 of one trip circuit of the frame may be held operated at one time.

Start relay 1002 operates in the locking circuit of relay 908 and at its inner upper front contact closes a circuit from ground over conductor 915, lower contact of relay 908, to battery through the winding of relay 913. Relay 913 operates and connects ground from the intermediate lower front contact of relay 905, upper front contact of relay 913 to conductor 916 as an indication that a trunk finder of the group in which finder 400 is located should be started to hunt for the b calling trunk. Had subgroup relay 904 been operated instead, then the operation oi relay 913 would connect ground from the intermediate lower front contact of relay 904 over the lower front contact of relay 913 .to conductor ,917 as an indication that a trunk iinder of the group in which finder 600 is located should be started to hunt for the calling trunk. Relay 913 also closes an obvious circuit for relay 918 and closes a locking circuit for relay 905 extending from battery over the lower winding and inner lower iront contact of relay 905, tor ground at the inner lower front Contact o relay 913. Relay 918 locks over its upper contact and the upper back contact of relay 901 to ground at the lower front contact of relay 905 and closes an operating circuit for relay 906 extending from ground at the lower front contact of relay 918, lower winding of relay 906 to battery through the upper winding of relay 901. Relay 901 does not receive sufcient current to operate at this time, but relay 906 operates. Relay 918 also closes a circuit extending from ground at its lower contact, over the inner lower front contact of relay 908, conductor 919 to battery through the winding of relay 1004 and in parallel therewith either over the upper back contact oi relay 1005, lower back contact of relay 1006, winding of relay 1007, lower winding of relay 1008 to battery over the inner lower normal contacts oi relay 1009 or over the upper front contact of relay 1005, upper normal contacts of relay 1016, winding of relay 1017, upper winding of relay 1018 to battery over the upper normal contacts of relay 1019 dependent upon whether relay 1005 is or is not operated at this time. It will be assumed that relay 1005 is not operated and that consequently relay 1007 operates in parallel with relay 1004, relay 1008 not receiving sufficient current to cause its operation,

l because of the high resistance of the winding of relay 1007.

Relay 1007 upon operating locks itself and relay 1004 to ground i ground over its upper alternate contacts and winding through resistance 1012 to battery and prepares an operating circuit for relay 1005 extending from battery through resistance 1013, winding of relay 1005 to ground at the upper g alternate contacts of relay 1011, but relay 1005 being shunted by ground from the contact of relay 1004 over the lower back contact of relay 1005, does not operate until relay 1004 releases. Relay 1011, at its inner upper front contact closes a circuit for relay 1014 extending from battery,

winding of relay 1014, inner upper back contact of relay 1015, inner lower normal contacts of relay 1008, inner upper front contact of relay 1011, to ground at the front contact of relay 1007. Relay 1014 closes an obvious circuit for operating relay 1028 which locks over its upper winding, and the upper back contact of relay 1027 to ground at its own inner lower front contact.

Assuming that allotter 1010 is standing in a position to allot the pair of trunk nders 400, 600, relay 1014 upon operating closes ay start circuit extending from ground at its lower front contact, brush 1030 of allotter 1010, conductor 604,`upper back contact of relay 605, winding of relay 606 to battery. Relay 606 operates and closes an obvious circuit for relay 607 which in turn extends conductor 916 over the lower back contact of relay 608, middle upper front contact of relay 607,"to battery through the winding of relay 609, and extends conductor 917 over the upper back contact of relay 608, inner upper front contact of relay 607, to battery through the winding of relay 610. If subgroup relay 905 has been operated, ground will have been connected to conductor 916, and relay 609 will therefore operate. However, if subgroup relay 904 has connected ground to conductor 917, relay 610 will operate. Relays 609 and 610 determine Whether the shaft of trunk finder 400 or the shaft of trunk finder 600 will be started to hunt for a calling trunk. Since it has been assumed that relay 905 was operated, relay 609 will operate and lock over its inner lower iront contact to ground at the middle lower front contact of relay 606. With relay 609 operated, relay 606 now locks from battery over its winding and inner lower front contact, back contact of relay 611, middle lower front contact of relay 609, conductor 612, commutator segment 414 and brush 415 of nder 400 to ground. Relay 609 also extends its locking ground through the winding of relay 608 to battery, thus operating relay 608 which opens the initial operating circuits of relays 609 and 610 and closes an obvious operating circuit for relay 605 and a circuit for relay 613 extending from battery through the winding of relay 613, upper front contact of relay 607 to ground at the inner lower front contact of relay 608. Relay 608 also closes at its inner upper front Contact one point in a chain circuit through the contacts of similar relays of all trunk nders of the group normally allotted by allotter 1010 to conductor 930 for causing the start circuit of Fig. 10 to direct all calls to the other group of finders normally allotted by allotter 1000 as will be hereinafter described.

Relay 605 upon operating opens the initial operating circuit of relay 606, removes battery through resistance 617 over the lower back contact of relay 613, the lower back contact of relay 605 and conductor 618 from the terminal on which brush 1031 of allotter 1010 is sending to mark the trunk iinder as busy to the allotter and closes the circuit of updrive magnet 416 of trunk finder 400 extending from battery through the winding of magnet 416, conductor l406, inner upper contact of relay 609, inner upper front contact of relay 605, to ground at the upper front contact of relay 606. With magnet 416 operated the shaft of trunk nder 400 is started upward to hunt for the terminals of the calling trunk. At the time relay 613 operated, a circuit .was closed from ground at its inner lower front contact over conductor 1029, brush 1033, middle upper back contact of relay 1026. to battery through the lower winding of relay 1028 orholding relay 1028 operated. W ith relays 605 and 606 operated, a circuit is closed from ground over the inner upper front contacts of relay 606 and 605, lower iront contact of relay 607, conductor 1039, brush 1032 of allotter 1010, upper back contact of relay 1015, upper front contact of relay 1028, upper winding of relay 1008 to battery over the inner lower normal contacts of relay 1009. Relay 1008 now operates closing a short circuit around the winding of relay 1007 extending from the upper terminal of the winding of relay 1007, inner lower alternate contacts of relay 1008, inner upper front contact of relay 1011 to the lower terminal of the winding of relay 1007. Relay 1007 releases. Relay 1008 upon operating releases relay 1014 and locks in a circuit from battery through its lower winding and inner lower alternate contacts, inner upper. front iso .nemaoeo contact of relay 1011, lower back contact of .relay 1006, upper back contact of relay 1005.conductor 919, inner lower front contact of relay 908 to ground at the lower contact of relay 918. Relay 1008 at its inner upper `front contact establishes a holding circuit through the upper winding of start relay 1002 for preventing another call 4from being served -until the present call is safely handled and lprepares an alarm circuit as will be described ater.

Relay 1-014 upon releasing removes ground from trunk iinder start `conductor 604 and closes a circuit from ground at its back contact over the vlower front contact of relay 1028 :to battery through the winding of relay 1015. Relay 1015 upon operating Vconnects the winding of relay 1027 over its lower front contact to brush 1031 of allotter 1010 and closes a circuit from battery through the winding of stepping relay 1040 and back contact of stepping magnet 1041 of allotter 1010, upper back contact of relay 1026, inner lower front contact of relay 1015, lower back contact of relay 1027, to ground at the inner lower front contact of relay 1028. Relay 1040 operates and connects its operating ground to the winding of magnet 1041 which operates in turn opening the operating circuit of relay 1040. Relay 1040 now releases opening the circuit of magnet 1041 which releases to advance the brushes of allotter 1010 one step and to restore the operating circuit of relay 1040. In this manner allotter 1010 is advanced step-by-step until brush 1031 engages a terminal of its bank to which battery is connected through a resistance such as 617 of an idle pair of trunk iinders in the allotter group. When wiper 1031 engages such a terminal, relay 1027 operates opening the circuit of stepping relay 1040 to arrest furtherstepping of the allotter and opens the holding circuitiof relay 1028. Since the holding path previously traced for relay 1028 is also opened as soon as allotter brush 1033 moves off of the terminal connected to conductor 1029, relay 1028 releases in turn releasing relay 1015. With relay 1015 released, the circuit of relay 1014 is prepared sothat it may operate on the next call directed to allotter 1010. The allotter 1010 has now preallotted another pair of trunk nders.

As soon as the shaft of trunk finder 400 has advanced through the tripping zone to trip the brush set 403, since trip magnet 402 has been operated, the commutator brush 419 engages commutator segment 420 closing a circuit from ground over brush 419 and segment v420, conductor 407, inner lower front contact of relay 607, conductor 1034, lower normalv contacts of key 1042,.lower front contact of relay 1002, conductor 914, to the upper winding of relay 908, thus short-circuiting this winding and causing relay 908 to release. Relay 908 upon releasing releases trip magnets 402 and 602 and releases relays 913 and 1004. Relay 1008 also releases provided that at this time the operating circuit through the upper winding of relay 1008 has been opened through the operation of relay 1015 as previously described. Relay 913 upon releasing removes ground from conductor 916 which initially caused the operation of relay 609 and opens the operating circuit of relay 918.

Relay 1004 upon releasing removes the short circuit previously traced around the winding of relay 1005 and relay 1005 now operates. As soon as brush 419 leaves the commutator segment 420, relay 1002 releases again connecting operating battery over its upper back contact for relays such as 908 of the trip circuits so that other calls may be handled in other vtrip circuits. Onthe next incoming call from one of the trip circuits having access to the start circuit of Fig. 10, relay 1004 will bereoperated to close a shunt around the winding of relay 1011 extending from ground, contact of relay 1004, lower front contact of relay 1005, winding of relay 1011, to ground at the upper alternate contacts of relay 1011 and relay 1011 releases. With relay 1005 operated a circuit is established from ground on conductor 919, upper front contact of relay 1005, upper normal contacts of relay 1016, winding of relay 1017, upper winding of relay 1018 -to battery over the upper normal contacts of relay 1019. Relay 1017 operates in this circuit closing at its contact a holding circuit for itself and for relay 1004, but relay 1018 does not -receive sufficient current to operate. With relay 1011 released and relay 1017 operated, a circuit is closed from ground at the contact of relay 1017, lower back contact of relay 1011, upper normal contact of relay 1018, upper back contact of relay 1025, to battery through the winding of relay 1024. Relay 1024 closes an obvious circuit through the upper winding of relay 1038, which relay operates and locks over its lower winding, lower back contact of relay 1037 to ground at the upper front contact of relay 1038. Relay 1024 `also closes a start circuit over brush 1020 of allotter 1000 for starting one of the pair of trunk finders which the allotter 1000 has preallotted. Following the starting of one of the pair of trunk finders as determined by the operated condition of subgroup relay 904 or 905 of the trip circuit, relays 1018, 1025, 1027, 1050 and stepping magnet 1051 function in the same manner as relays 1008, 1015, 1037, 1040 and magnet 1041, previously described to advance allotter 1000 to preallot another pair of trunk finders in its allotter group.

As soon as the started trunk finder has advanced its brush shaft through the tripping zone, ground is placed on conductor 1035, establishing a circuit over the lower normal contacts of key 1052 and the lower contact of relay 1002, which in the manner previously described, causes the release of relay 1004 and the release of relay 1018 if it has not at the time been released through the operation of relay 1025. Relay 1004 upon releasing opens the holding circuit of relay 1005 which'wfollowing the release of relay 1011 was held operated in a circuit from ground at the contact of relay 1004, upper normal contacts of relay 1011, winding of relay 1005, resistance 1013 to battery. With both relays 1005 and 1011 released, the next incoming call is directed to a trunk finder in the group allotted by allotter 1010 in the manner previously described.

It will be recalled that the trunk nder 400 has been started and that the brush set 403 thereof has been tripped through the operation of trip magnet 402. As soon as the nder leaves normal, a holding circuit is established from ground over commutator brush 421 and segment 422, conductor 408 to battery through the winding of relay 609 and through the inner lower front contact of relay 609 through the winding of relay 608 for holding these relays operated as long as the trunk finder is orf-normal. The finder shaft moves the tripped brush set 403 over the terminals of its associated bank until the test brush 409 engages terminal 401 of the calling trunk upon which terminal it will be recalled battery potential has been connected through the winding of relay 901 of the trip circuit. A circuit is thereupon completed over brush 409, upper back contact of relay 410, lower rback contact of relay'411, conductor 412 to ground through the Awindingof relay 611'. Relays 611 and 901 operate. Relay 611 opens the holdingcircuit of relay 606, but relay 606 remains operated over another holding circuit extending from battery through its winding and inner lower front contact, conductor 413, centering commutator segment 467, and brush 423` to ground until the brush set 403 is fully centered on the terminals of the calling trunk 307. Relay 606 then releases opening the circuit of updrive magnet 416 to arrest further movement of the shaft of trunk nder 400. Relay 606 also releases relay 607 and opensone holding circuit for relay 609, but relay 609 is locked operated as previously described as long as nder 400 remains oir-normal. With relay 607 released a circuit is closed from ground at the inner upper back contact of relay 410, conductor 417, the lower back contact of relay 607, conductor 418, brush 424, terminal 425, conductor 309, winding oi relay 305 of the trunk 307 to battery. Relay 305 operates, locks over its lower alternate contacts and the inner lower front contact of relay 306 to ground, connects ground to trunk terminal 401, over conductor 308, the inner upper front contact of relay 306, inner lower and lowermost alternate contacts of relay 305 to ground at the lower front contact of relay 306 thereby releasing relay 611, and opens conductors 902 and 903 extending to the trip circuit of Fig. 9. Relay 305 also at its inner upper front contact connects battery to the upper back contact of sleeve relay 306 so that should the calling subscriber restore rst, the sleeve terminal 303 of the intercepting trunk 307 will be marked with busy potential. Relay 305 also opens at its upper back contact the initial operating circuit of sleeve relay 306.

At the trip circuit, relay 901 operated at the time relay 611 of the trunk iinder operated, opening the locking circuits of subgroup relay 905 and relay 918. Relay 901 upon operating locks over its upper winding through the lower winding of relay 906 to ground at the lower contact of relay 918 until relay 918 releases. Relay 918 releases slowly to prevent the startingA of another trunk lnder in case relay 901 is operated'and released momentarily on the overrunning of the trunk nder before its brushes have settled back on the terminals of the calling trunk andhas operated relay 305 of the trunk to open the operating circuit of relay 901 extending over conductor 902. When relay 305 of the trunk circuit operates and opens conductors 902 and 903, the operating circuit of relay 905 is opened and relay 905 releases, and the operating circuit of relay 901 is opened and this relay releases as soon as relay 918 vreleases to open its locking circuit. With relays 901 and 918 both released, if no other call is awaiting attention, relay 906 releases and prepares the trip circuit to handle another call. If other calls are waiting on other banks, relay 1001 of the start circuit will be operated and will hold relay 906 locked over its upper winding preventing other calls in the bank served by the trip circuit of Fig. 9 from being served until waiting trunks in all other banks have been found. The operation of relay 901 also opens the locking circuit of relay 908 which relay releases at this time in case the trunk finder has failed to close the shunt path for relay 908 by the engagement of brush 419 with commutator segment 420.

At the trunk nder the release of relay 611 also closes a circuit extending from battery, winding of relay 411, lower back contact of relay 410,

conductor 427, lower back contact of relay 428,

lower front contact of relay 411, upper back contact of relay 410, brush 409 and terminal 401 to ground as tracedv at the lower front contact of relay 306. Relay 411v also closes the talking conductor 310 of trunk 307 over brush 429, the l inner upper front contact of relay 411, the inner upper back contact of relay 428 to ground through the winding of relay 431, and conductor 311 of trunk 307 over brush 430,*the inner lower front contact of relay 411, middle lower normal contacts of relay 428, to ground through winding of relay 432. Relay 411 at itsupper front contact also closes a shunt around the upper high resistance windings of relays 433 and 434 extending from the left terminals of the windings of f relay 433, upper contact of relay 411, upper back contact of relay 435 to the left terminal of the upper winding of relay 434.

Following the seizure of the intercepting trunk 307 by the final selector 300, the sequence switch 207 of the incoming selector will have advanced into the ringing position 12 as described in Patent No. 1,658,829 granted to C. H. Berry above referred to, and ringingy current will be co-nnected from the source 208 over the lower'contacts o f cam 209, winding of vringing current cut-off relay 210, right back contact of relay 211, right contacts of cam 212, brush 213 and the terminal upon which it is resting, brush 312 of the final selector, terminal 302 to trunk conductor 311. In position 12 of sequence switch 207, a circuit is also closed over the lower contact of interrupter 214, contacts of cam 215 to battery through the right winding of relay 211 in which circuit relay 211 operates closing a'circuit from battery, winding of sequence switch magnet 207, contacts of cam 216, front contact of relay 211, to ground at the upper contacts of cam 217 for advancing the sequence switch intoV position 13. Relay 211 releases after the sequence switch leaves position 12. In position 13 a circuit is prepared for relay A211 through itsl left winding and the lower left and right contacts of cam 217 but relay 211 is prevented fromv operating by a shunt around its left winding, extending through resistance 218,

contacts of cam 219, Vhack contact of relay 210, left back contact of relay V211, to ground at the upper contacts of-carn 217. The subsequent closure of the upper contact of interrupter 214 establishes a circuit over the contacts of cam 220, contacts of cam 216 to battery through the winding of sequence switch magnet 207 for advancing the sequence switch into position 14. In position 14 ringing current is connected from source` 208 through interrupter 221, the left contacts of cam 209 and thence as traced to trunk conductor 311. As soon as the trunk finder 400 has connected with the trunk 307 and relay 411 has operated theringing current connected to trunk conductor 311 ilows through the winding of relay 432 caus- 3' back contact of relay 437, contact of relay 432,

upper normal contacts of relay 43,8, conductor 439., toground at the lower front contact of relay 605. Relay 436 upon operating locks over its upper front contact, the upper normal contacts of relay 438, to ground on conductor 439 and establishes a circuit extending from battery through the upper winding of marginal relay 438, lower iront contact of relay 436, lower right winding oi repeating coil 440, conductor 441, lower back contact ci relay 625, trunk conductor 626, lower back Contact of relay 700, lower left winding of repeating coil 701, inner lower back contact of relay 702, winding of polarized relay 703, upper back Contact of relay 702, upper left winding of repeating coil 701, inner upper back contact of relay 700, trunk conductor 627, upper back contact of relay 625, conductor 442, upper right winding of repeating coil 440, upper front contact oi relay 436, to ground through the lower winding of relay 438. Relay 703 which is polarized receives current and in the proper direction to operate, but marginal relay 438 does not receive suicient current because of the high resistance of the winding of relay 703 and does not therefore operate. Relay 703 closes an obvious circuit for relay 704 which in turn closes a circuit for lighting trunk lanip 706 which extends from battery over the upper contact of relay 704, back contact of relay 705 to ground through lamp 706. The lighting of lamp 706 is a signal to the intercepting operator that a call is incorning to her position. Relay 704 also closes a circuit extending from` ground at its lower contact through the winding of relay 708 and resistance 709 to battery for operating relay 708. Relay 708 connects the windings of relay 710 through the right windings of repeating coil 701 to the tip and ring contacts of trunk jack 707.

Had the calling subscriber initiated a call to the tip party of a called party line formerly connected to the terminals 301, 302 and 303 of final selector 300 then ringing current from the source 208 would have been connected in the well known manner to trunk conductor 310 instead of to trunk conductor 311 and relay 431 in the trunk finder would be operated instead of relay 432. With relay 431 operated, an obvious circuit is closed for relay 437 which operates, locks over its inner lower front contact and conductor 430 to ground at the lower front contact of relay 605, closes the circuit of relay 436 over its upper front contact and also closes an obvious circuit for relay 448. Relay 436 causes the lighting of the trunk lamp 706 in the manner previously described. Relay 448 reverses the talking conductors at the outgoing end of the inter-office intercepting trunk so as to prevent false supervision to the incoming selector 203 from the intercepting operators position or from the completing incoming selector 500.

The intercepting operator upon seeing the lighted lamp 706 inserts the answering plug 800 of her cord circuit into jack 707 of the trunk thereby establishing a circuit from ground through the winding ci sleeve relay 705 of the trunk, sleeves of jack 707 and plug 800, windings of relays 801 and 802 in series to battery and in parallel therewith through resistance 803 to battery. Relay 705 and 801 operate but relay 802 being marginal does not operate because of the high resistance of relay 705. Relay 705 opens the circuit of lamp 706 to extinguish it. At the operators cord circuit, relay 801 upon operatingr closes a circuit for lamp 805 extending from battery, inner contact of relay 801, resistance 806,

back contact of relay 807, back contact of supervisory relay 808, to ground through lamp 805. A circuit is also established in parallel with lamp 805, over the inner lower back contact of relay 809, inner normal contacts and winding of relay 810 to ground at the right normal contact of listening key 811. Relay 810 locks in a circuit from battery at the inner contact of relay 801, inner upper alternate contacts and winding of relay 810 to ground at key 811. A circuit is nov1 closed from ground through the upper winding of marginal relay 710, inner upper front contact of relay 708, upper right winding of repeating coil 701, tips of jack 707 and plug 800, upper normal contact of key 814, upper left winding of repeating coil 813, upper back contact of relay 802, upper winding of relay 808, lower baci: contact of relay 800, upper back contact of relay 837, resistance 838 to battery, and from 48 volt battery through the lower winding of relay 710, inner lower front contact of relay 708, lower right winding of repeating coil 701, rings of jack 707 and plug 800, lower normal contact of key 814, lower left winding of repeating coil 813, inner lower back contact of relay 802, middle lower back con7 tact of relay 809, resistance 839 to ground at the inner upper back contact of relay 837. Super- Visory relay 808 operates, but relay 710 being marginal does not` receive sufficient current to operate at this time. guishes cord supervisory lamp 805.

When the operator throws her listening key 811, to the right or talking position, relay 810 releases and a circuit is established from ground at the upper alternate contact of key 811 for relay 1 817 which operates and establishes a circuit from battery at the inner contact of relay 801, inner lower contact of relay 817, conductor 815, winding of relay 1100 to ground. Relay 1100 operates and establishes a circuit from ground at its outer contact through the Winding oi relay 1101, resistance 1102, back contact of relay 1103, conductor 1104, next to the lower front contact of relay 817, middle lower back contact oi' relay 800.

thence as traced to battery through the lower winding of relay 710. Relay 1101 operates closing a. circuit from ground at its contact through the contacts of interrupter 1105, back contact of relay 1106, winding of relay 1107 to battery. Relay 1107 operates and locks through its winding and the winding of relay 1106, the outer contact of relay 1107 to ground at the contact of relay 1101, but relay 1106 being shunted does not operate until interrupter 1105 opens its contact. Relay 1107 at its inner contact closes an obvious circuit for holding relay 1101 and connects 24-volt battery through resistance 1102 over the circuit previously traced through the lower winding of relay 710, thereby causing the operation of relay 710. As soon as interrupter 1105 opens its contact, relay 1106 operates and on the next closure of the interrupter contacts, relay 1103 operates, locks to the inner contact oi relay 1100, opens the operating circuit of relay 710 and closes a circuit extending from ground at its front contact through the upper winding of relay 1108 for connecting the operators headset 1109 to the cord circuit.

Relay 1108 upon operating establishes a talking path from the upper right winding of repe'ating coil 813, inner upper right contact oi key 811, conductor 819, upper contact of relay .1108, right winding of repeating coil 1110, condenser 1111, lower contact of relay 1108, conductor 820,

inner lower right contact of key 811, to the lower Lil right winding of coil 813. Assuming that the operators telephone set 1109 is plugged up, the

talking path just traced is inductively associated with the operators transmitter through the left winding of repeating coil 1110 and is connected. with her receiver over the back contacts of relay 1112.

When relay 710 in the incoming end of the inter-ofce trunk operates momentarily, it closes an obvious circuit for reversing relay 711 which in turn completes the circuit o relay 702 extending from battery at the front contact of relay 705, lower front contact of relay 711, winding of relay 702 to ground at the inner upper `back contact of relay 712. Relay 702 upon operating disconnects the winding of relay 703 from the trunk circuit thereby releasing relay 703 and with relay '711 operated, it establishes a circuit from battery through the upper winding of relay 713, inner upper front contacts of relays 711 and 702, upper left winding of repeating coil 701, upper back contact of relay 700, thence as traced to ground through the lower winding of relay 438 'and establishes a second circuit from ground through the lower winding of relay 713, lower front-contacts of relays 711 and 702, lower left winding of repeating coil 701, lower back contact of relay '700, thence as traced to battery through the upper winding of relay 438. Relays 438 and 713 operate, relay 713 closing a holding circuit for relay '708 to hold relay 708 operated following the release of relay 704 which releases when relay 703 releases. In order to insure that relay 708 will not release following the release of relay 704 and before relay 713 closes its holding circuit, it is made slightly slow to release. Relay 702 upon operating also closes a circuit extending from battery at the lower Contact of relay 705, through the winding of relay 714 to ground at the upper contact of relay 702, thus operating relay 714 which locks over its inner upper front Icontact under the control of relay 705 and at its lower contact makes the contacts of completing jack 715 effective as will be later described. When relay 710 releases at the end of the tripping cycle as previously described, it opens `the circuit of reversing relay 711 which reverses the connec tion of battery and ground to trunk conductors 626 and 627.

Relay 438 upon operating as previously described locks over its upper winding and upper alternate contacts to ground over conductor 439 and opens the locking circuit of relay 436 which relay releases, disconnects the windings of relay 438 from the circuit previously traced over trunk conductors 627 through the windings of relays 713, and connects a low resistance holding bridge across the trunk conductors, extending from trunk conductor 627, upper back contact of relay 625, conductor 442, upper right winding of repeating coil 440, upper back cont-act of relay 436, conductor 443, upper back contact of relay 628, conductor 629, low resistance windings of relays 434 and 433, upper front contact of relay 411, upper back contact of relay 435, conductor 630, lower lback contact of relay 628, conductor 444, lower back contact of relay 436, lower right winding of repeating coil 440, conductor 441, lower back contact of relay 625, to trunk conductor 626,thus providing a holding circuit for supervisory relay 713 at the incoming end of the inter-cnice intern 'cepting trunk circuit. Relay 433 operates in this circuit and relay 434 may operate, but without function at this time. Relay 433 upon operating closes a circuit from Lground at its contact over conductor 445 to battery through the winding of relay 631which operates and provides another holding circuit for relay 613.

Relay 438 upon operating also closes a circuit from ground at its lower Contact as soon as interrupter 446 closes its lower Contact through the winding of relay 428 which operates, locks over its inner lower iront contact to ground at the lower contact of relay 438, opens at its lower back contact one holding circuit of relay 613, opens the circuits previously traced through the windings of relays 431 and 432, and closes a circuit from battery through resistance 447, lower back contact of relay 435, conductor 632, inner upper back contact of relay 633, conductor 634, lower back contact of relay 448, lower alternate contacts of relay 428, middle lower front contact of relay 411, brush 430, trunk conductor 311, terminal 302, brush 312, brush 213, right contacts of cam 212, right back contact of relay 211, winding of relay 210, contacts of cam 209 to ringing generator 208. Relay 210 in the incoming selector operates, removing the shunt from the left winding of relay 211 which operates to open the ringing circuit at its right Contact and to close a circuit from ground at the upper contacts of cam 217, left front Contact of relay 211, contacts of cam 216, to battery through the magnet winding of sequence switch 207 thereby advancing the sequence switch out of the ringing position 14 into the talking position.

At its inner upper front contact, relay 428 also closes a circuit extending from ground at the contacts of cam 222 in the incoming selector over brush 223, brush 313, terminal 301, conductor 310, trunk nder brush 429, innerl upper contact of relay 411, inner upper front contact of relay 423, upper back contact of relay 448, conductor 635, upper back contact of relay 633, conductor 636, upper left winding of repeating coil 440, winding of relay 449, lower back contact ci relay 450 to 411, upper back contact of relay 410, brush 409,

terminal 401, conductor 308, inner upper iront contact of relay 306, lower front contacts of relay 305 to ground at the lower front contact of relay 306, and opens the initial operating circuit of relay 449.

At is upper front contact relay 428 prepares a circuit for relay 435 which is closed as soon as interrupter 446 makes its upper contact extending from battery, winding of relay 435, upper contact of relay 428, upper contact of interrupter 446, to ground at the lower front contact of relay 438. Relay 435 upon operating locks over its upper front contact to ground at thelower contact of relay 438, disconnects tripping battery through resistance 447 at its lower contact, connects the left windings or" repeating coil. 440 through to the repeating coil 224 in the incoming selector 203, l, :I

operator may receive information concerning the call which the subscriber desires to make.

- v It 4will be assumed that the call is one which the operator can complete and is for a line 225 which terminates in the same oiilce in which the calling line terminates. The operator will therefore insert the calling plug 821 of the cord circuit which she has used to answer the call, into the completing-ntercepting jack 715 of the interoiiice intercepting trunk circuit thereby establishing a circuit from battery', windings of relay 827 and 826 in series and in `parallel therewith through resistance 828, thence over the sleeves of plug 821 and jack 715, lower back contact of relay '716, resistance 717 to ground at the upper front contact of relay 714. Relays 826 and 827 will both operate, relay 826 closing a circuit from battery over its lower front contact, upper back contact of relay 830 to ground through lamp 829 for lighting the lamp and also closing a circuit from battery over its lower front contact, normal contact of key 824 to ground through the winding of relay 823. With relays 823 and 827 both opt. @rated a circuit is now established from battery 25` right vwinding of retard coil 325, winding of supervisory relay 831, lower front Contact of relay 827, lower right winding of repeating coil 813, inner lower front contact of relay 823, lower normal contacts of relay 822, rings of plug 821 and jack 715, lower front contact of relay 714, upper backcontact of relay `718, lower winding of retard coil 719, both windings of relay 720 in series, upper winding of retard coil 719, lower back contact of relay 713, tips of jack v715 and plug 821, upper normal contacts of relay 822, inner upper front contact of relay 823, upper right winding of repeating coil 813, inner upper front Contact of relay 827 to .ground through the `lefttwindin'g of retard coil 325. Since relay 714 is operated, relay '720 .operates in this circuit, but due to the high resistance of relay '720, the cord supervisory relay 831 does not operate. Relay 714 is provided so that 'the relay 720 will not operate in case the operator plugs into the completing jack 715 in errorinstead of answer jack 707 `when answering a call. Relay 720 upon operating closes an obvious circuit through the upper winding of relay '713 Vand this relay operates locking from ground over its inner lower front contact and lower winding to battery over the sleeve of jack 715 and short-circuiting resistance 717. Relay 716 also establishes another holding circuit for relay 714 extending from `battery at its upper front contact and the winding and inner upper front contact of relay '714 Vto ground, short-circuits the lower high resistance windings of relays 721 and 722 at its ,inner upper front contact and `at its lower front Contact establishes a `circuit for relay 723 extending from ground at the lower front contact of relay '716, lower normal contacts of relay 724i, inner lower back contacts of relay 725, upper iront contact of relay .708, winding of relay 723, lower back contact of relay '7.18, resistance 726, to battery.

Relay 723 operates and 4locks ina circuit from battery as traced through its winding and inner lower front contact, lower normal `contacts ci relay '724 to ground at the lower frontcontact of relay 7,15 so that yit is held operated after 725 front contact and the upper back contact of relay 725 to conductor 730, connects battery through the winding of relay 731 over its upper `front contact and the upper back contact of relay 732, to hunting conductor 733, establishes at its inner upper front contact a new holding path for relay '738` andA at its lower front contact prepares a future operating path for relay 724.

rIhe connection of ground to the start conductor 727 causes the trip, start and link circuit 728 to start hunting for the trunk circuit of Fig. '7. When the terminals of the trunk circuit are connected with, battery on conductor 730 causes the trip, start and link circuit to cease hunting and the circuit over conductor 733 is then closed, thereby 90 operating relay 731. Relay 731 connects battery and ground through the windings of retard coil 734 to the tip conductor 735 and ring conductor 736, respectively and closes an obvious circuit for operating relay 725. The trip, start and link circuit 728 proceeds to associate the central B operators position circuit therewith and, with battery and ground on conductors 735 and 736 causes the associated operators position circuit to function to transmit a double order tone to the intercepting operator over conductors 735 and 736, front contacts of relay 731, condensers 737 and 738, thence over the talking connection pre- Viously traced to the intercepting operators cord circuit thence over the inner contacts of talking key 311 which is still operated to the right, `to the intercepting operators headset 1109. The intercepting operator hearing the order tone passes the required number for completing the desired connection to the B operator.

The operation of relay 725 as previously described disconnects battery from conductor 730 and connects ground thereto over its upper front contact through the winding of relay 739, removes ground over its lower back contact from 115 start conductor 727, opens at its inner lower back contact the operating circuit of relay 723, which reiay is now held operated under the control of relays '724 and '716 and, with relay 739 now Operated closes a holding circuit for itself extending 120 from ground at the front contact of relay '739, inner upper front contact of relay 725, winding of relay 732 to battery through the winding of relay 725. Relay 732 does not operate in this holding circuit since its winding is shunted by 125 ground Vapplied over the lower front contact of relay 731.

After the B operator has completely registered the number passed to her by the vintercepting operator on the registers of the sender indicated in the rectangle 728, high resistance battery` is connected at the sender to conductor 733 in place of ground, thus causing relay 731 to release. -Relay 731 upon releasing opens the talking circuit from the B" operators position to the intercepting operators position, disconnects battery and ground through the windings of retard coil 734 .from talking conductor 7,35 and '736, and opens the short-circuit from the winding of relay 732 which now operates in theholding circuit of 14C. relay 725. With relay 732 operated a new holding path is established from ground at its inner upper front contact for holding relay '708 operated after relay 723 releases as `later described, and conductor 733 is disconnectedfrpm the wind- 145 ing of relay ,731 and is connected over the upper front Contact of relay 732 to ground ,through the winding of relay 712 and over the upper back contact of relay '700 to ground through the upper winding of relay '718. Relay 712 operates pro- Aconductor '735, upper front contact of relay '700,

viding over its upper front Contact a new holding ground for relays 725 and 732 for holding these relays operated after relay '739 releases. At its upper back contact relay '712 opensthe circuit of relay 702 which now releases and at its lower contact closes a circuit extending from ground at the inner upper front contact of relay '723, lower contact of relay '712, lower back contact of relay '702, winding of relay 700, lower back contact of relay '718, resistance '726 to battery, relay '718 not having operated at the time the circuit previously traced through its upper winding was closed because of its marginal characteristic. Y

Relay '700 which is slow to operate, operates in the circuit just traced after a sufcient interval to allow the capacity on trunk conductors 626 and 627 to be discharged in a circuit extending from conductor 626 over the lower back contact of relay '700, the lower left winding of repeating coil '701, the inner lower back contact of relay '702, winding of relay '703, upper back contact of relay '702, upper left winding of repeating coil '701, upper back contact of relay '700 to conductor 62'7 before the trunk conductors are connected over the inner front contacts of relay '700 and conductors r735 and '736 through the trip, start and link circuit to the stepping relay of the as-V sociated sender. Relay r100 locks over its lower front contact, lower front contact of relay '708 to ground at the lower front contact of relay 716 and at its Lipper back contact opens the operating circuit previously traced for relay 748. Relay 702 upon releasing also disconnects battery and ground through the windings of relay '713,

vbut relay .'713 upon releasing performs no useful function at this time since relay '708 which was formerly held operated over the contacts of re lay '713 is now held operated over the inner upper front contact of relay '723.

When relay '702 releases disconnecting battery and ground through the windings of relay '713 from trunk conductors 626 and 62'7, the circuit previously traced through the winding of relay -433 is opened and relay 433 releases in turn releasing relay 631.

.501 at the completing incoming selector 500. Relay 625 upon operating disconnects trunk conductors 626 and 62'7 from the windings of relays 433 and 434 and with relay '700 operated establishes a fundamental circuit extending from ground over the right contacts of cam 502, conductor 503, lower back contact of relay 639, inner lower front contact of relay 625, conductor 626, inner lower front contact of relay '700, conductor '736 through the winding of the stepping relay (not shown) of the sender '728 returning over conductor 62'7, inner upper front contact of relay 625, upper back contact of relay 639, conductor 504, lower right contact of cam 505, upper right contact of cam 506 to battery through the winding of relay 50'7.

The stepping relay of the sender and relay 50'7 operate, relay 507 closing a circuit from battery through the lower winding of relay 508, upper right contact of cam 509, upper right contact of 513. Relay 508 operates and locks through its lower winding, upper right contact of cams 509 and 510, front contact of relay 50'7, lower right contactof cam 511, upper right contact of cam 512, upper front contact of relay 508 to ground until the sequence switch 520 leaves position 2. Relay 508 also closes a circuit extending from battery,v winding of relay 514, lower contacts of cam 515, lower front contact of relay 508 to ground over the left contacts of cam 501, relay 514 locking over the upper contacts of cam 516 to ground at its inner upper front contact and closing a circuit from ground at its lower front contact and the upper contact of cam 51'7, conductor 513 to battery through the winding of relay 613 of the trunk finder to hold the trunk finder and outgoing trunk circuit. Relay 514 also closes a circuit for advancing sequence switch 520 of the incoming selector into position 2 which circuit extends from battery, winding of the sequence switch magnet, lower contacts of cam 519, upper front contacts of relay 514, left contact of cam 521 to ground. As soon as the sequence switch reaches position 2 holding ground is connected to conductor 518 over the left contact of cam' 51'7 as long as the incoming selector circuit is offnorrnal.

With the sequence switch in position 2, the circuit of the updrive magnet 522 is closed from battery through the winding of magnet 522, lower left and upper right contacts of cam 512, to ground at the upper front contact of relay 508. During the upward travel of the brush shaft, ground is intermittently connected from the left contacts of cam 501, over the lower front contact of relay 508, left contacts of cam 523, brush 524 and commutator segment 525, lower left and upper right contacts of cam 50G to battery through the winding of relay 50'7 holding relay 50'7 operated and intermittently shunting down the stepping relay (not shown) of the sender. When the sender has received suicient shunting impulses to satisfy it with respect to the incoming brush registration', the fundamental circuit is opened atthe sender and relay 50'7 releases as soon thereafter as brush 524 engages the next insulating portion of the commutator segment 525, in turn releasing relay 508. Relay 508 opens the circuit of updrive magnet 522 t0 stop the further upward movement of the switch shaft. At its upper back contact relay 508 closes a circuit extending from ground over the lower left contact of cam 526 to the magnet winding of sequence switch520 for advancing the sequence switch into position 3. When the sequence switch leaves position 2 relay 514 releases.

With the sequence switch in position 3 a circuit is closed from battery through the winding of trip magnet52'7 to ground at the lower left contact of cam 513 and magnet 52'7 operates in order to be ready to trip the selected brush set of selector 500 on the next upward movement of the brush shaft. The fundamental circuit is again closed in the sender and relay 50'7 reopern ates operating relay 508 in a circuit from battery through the lower winding of relay 508, upper right contacts of camsv 509 and 510, front contact of relay 50'7, upper left contact of cam 528, upper left contact of cam 523, to ground at the upper right contact of cam 513 and locksin the circuit just traced through its lower winding to the front contact of relay 507 thence over the upper left

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