US1542977A - Telephone-exchange system - Google Patents

Description

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Patented June 23, 1925.

UNITED STATES PATENT OFFICE.

SAMUEL B. WILLIAldS, OF BROOKLYN, AND EDWARD E. HINRICHSEN, OF NEW YORK, N. Y., ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed April 30, 1923.

ratus for the establishment of connections.

The object of this invention is to enable an increase in the capacity of groups of lines or trunks, such as those leading to branch exchanges, without disturbing existing equipment and to otherwise improve the service provided for said exchanges.

A feature of the invention relates to a system wherein, when a connection is built up to a particular group of lines, the established connection is partially released and is automatically reestablished to a given one of the lines in the group.

Another feature relates to means, in a system having the lines of a group appearing in one or more switches with provision for building a connection through to one of said switches, whereby when the connection is intended for said group it is temporarily released and automatically reestablished to an idle one of said lines in whatever switch it may appear.

Other features and advantages contemplated by the invention will be taken up in detail hereinafter and pointed out in the appended claims.

Considering the drawing, Figs. 1 to 13, inclusive, taken in the order illustrated in Fig. 14 disclose the details of a telephone system incorporating the features of the present invention.

Fig. 1 illustrates a line switch of the coordinate type in which the subscribers lines terminate and also two of a number of trunks outgoing to a district selector switch.

Fig. 2 shows the controlling elements associated with one of the outgoing trunks.

Fig. 3 discloses a district selector switch of the coordinate type.

Fig. 4 illustrates a group selector switch of the coordinate type in which terminate Serial No. 635,421.

trunks incoming from the district selectors.

Fig. 5 shows one of a numberof coordinate connector switches for completing connections to called lines and P. B. X. trunks.

Fig. 6 represents a sender selector switch also of the coordinate type.

Figs. 7 and 8 illustrate one of a number of common register senders.

Fig. 9 shows at the left of the sheet a sender connector device for connecting any of the senders with the common marker or selection controlling device.

The remainder of Fig. 9 together with Fig. 10 disclose the common marker for controlling the district switches.

Fig. 11 shows a sender connector device for connecting the line marker with any of the several register senders. This figure also shows testing relays for testing the trunks interconnecting the group selector and connector switches together with certain control elements of the line marker.

Fig. 12 discloses the remainder of the line marker.

Fig. 13 illustrates a second coordinate group selector switch similar to the switch shown in Fig. 5 and belonging to the same group for establishing connections to called lines and P. B. X. trunks.

General description of system and appalrows.

The line switch 100, selector switches 300 and 4100, connector switches 500 and 1300 and the sender selector switch 600 employed in this system are of the coordinate type such as shown and described in the patent to S. B. Williams, No. 1,517 .331, issued December 2, 1924. The subscribers lines enter the exchange and appear in the coordinate line switches 100 in Vertical rows 110 and 111. each linehaving access to a group of horizontal links such as the groups represented by links 106 and 107 and links 108 and 109. Line 101, for instance, has access to the group of links containing the links 106 and 107. Each of the outgoing trunks 114, 115, etc, occupies a full vertical row of contacts 112, 113 and leads to the district switches.

Trunk 114 which is shown in full, appears in the district switch 300 in the vertical row of contacts 308. Another trunk 115 is shown occupying the vertical row of contacts 309. The district selector switch 300 also has a plurality of groups of outgoing trunks appearing in rows 311, 312, 313, etc. Each outgoing trunk is shown as hav ing an appearance before a single horizontal link such as the links 303, 30 1, 305, 306 and 307. These trunks are multiplied to appear before corresponding horizontal links in a number of district switches belonging to the same group. These other district switches also receive trunks incoming from other line switches similar to the switch 100 serving other calling lines in the exchange.

The subscribers lines are divided into a number of groups as called lines known as terminal line groups. For convenience, there may be live of these terminal line groups accommodating an exchange of 10,- 000 lines in capacity, each such group serving 2,000 lines. As will be explained hereinafter, each terminal line group is made up of a number of group selectors and a number of connector switches. The trunks outgoing from the district switches are, therefore, arranged to have access to any of the five terminal line groups of switching apparatus.

The group of trunks appearing in the upper section 302 of the vertical row 311 in the district switch 300 lead to the group selector switches of a particular terminal line group. One of these trunks 350 is shown extending to the group selector switch e00. The group of trunks occupying the lower section 301 of the same vertical row may lead to the group selectors of the same or of a different terminal line group as desired. Other groups outgoing from the district switches are distributed to other terl'ninal line groups. In addition to these groups of trunks, the district switches may have access to trunks extending in other directions.

As above observed each terminal line group of switching apparatus is equipped with a plurality of group selectors and a plurality of connector switches. There will be as many connector switches as are necessary to accommodate the 2,000 called subscribers lines together with provision for as many P. B. X. trunks as may be required. There will be as many group selector switches as is necessary to extend the trunks incoming from the district switches to the connectors. If there are 2,000 lines in the group having directory numbers together with a number of groups of P. B. X. trunks, these may be distributed in any suit able manner among as many connector switches as the total number of lines and trunks utilize.

Each of the several district subscribers lines is provided with a directory number and occupies a given position in one of the connector switches. Moreover, for each group of private branch exchange trunks there is a single call-line which has a directory number identifying the P. B. X. and which is located in the connector switches along with the regular subscribers lines. The several trunks belonging to each private branch exchange group represented. by a call-mmiber line are, however, independent of directory numbers. In other words, for each P. B. X. call-line there may be as many trunks outgoing to the district P. B. X. represented as necessary and these may be located in one or in'a number of connectorswitches in any arbitrary manner. In ort er to call a group of P. B. X. trunks, the subscriber dials a number indentitying that particular P. B. X. group. The apparatus in the exchange establishes a connection through the district switch into the group selector of the proper terminal line group and thence from the group selector to the particular connector switch in which appears the corresponding call-line. Immediately that the call-line is selected the connection through the group selector and connector switches is released and is automatically reestablished through the group selector and the proper connector to the first idle P. B. X. trunk of the required group. If this first idle trunk is located in the same connector switch with the call-line, then the connection is reestablished to the connector switch first used. However, the first idle trunk may appear in a ditterent connector switch, in which case, the reestablished connection leads to such other connector switch and thence to the selected idle P. B. X trunk.

Considering the terminal line switching apparatus shown in the drawing there are illustrated a number of direct subscribers lines 53st, 535, and 1322 appearing in the connector switches 500 and 1300. There is also illustrated a P. B. X. call-line 538 appearing in the switch 500 and a number of P. B. X trunks 536, 537, 530, 1323 and 1324. connprising the group represented by the call-line 538. It will be noted that a portion of these P. B. X. trunks are located in the switch 500 with the call-line 538, while the remainder of the trunks of this group are situated in a second and difl'erentconnector switch 1300., It will be um'lerstood, as previously explained, that all of these trunks may be located on a single connector switch or that they may be distributed among still other connector switches in the group (not shown).

All numbered lines including both direct subscribers lines and P. B. X. call-lines appear in the connector switches in groups or vertical rows according to their numbers. For instance, the vertical row of contacts 532 in the connector switch 500 represents a group of ten lines. Only three of these lines are illustrated in the drawing, the two subscribers lines 534 and 535 and the. P. B. X. call-line 538. In the second switch 1300 shown, the vertical row 1320 represents another group of ten numbered lines. In like manner, there will be as many of these vertical ten-line groups in these and other connector switches as is neces sary to accommodate the full 2,000 numbered lines. In addition to the numbered lines the P. B. X. groups also appear in vertical rows. The particular group shown occupies either all or a portion of the vertical row 533 in the switch 500 and also either all or a portion of the vertical row 1321 in the switch 1300 according to the number of trunks necessary for this particular group.

The connector switches are also provided with a number of groups of horizontal links, each group having access to all numbered lines of a particular units designation together with P. B. X. trunks. For example, the group of links comprising the links 501 and 502 have access to the call-line 538 in the row 532, to the trunk 536 in the row 533 and also to other lines or trunks in other rows (not shown). The horizontal test link 503 is associated with this group of horizontal links and serves for test purposes as hereinafter described. For each of the remaining nine units designations, there is a group of these horizontal links having access to lines andtrunks. Two of these groups, one including the horizontal links 504, 505 and 506 and the other includii'ig links 507, 508 and 509, are illustrated. In a similar manner the switch 1300 has a number of groups of horizontal links of which the links 1301 to 1306 are a portion.

The district marker shown in Figs. 9 and 10 includes two sets of testing relays 1000 and 1003. The set 1000 serves to test the horizontal links of the section 302 in any district selector switch with which it is associated and also to test the outgoing trunks which have access to these links. The connecting device 1002 which comprises a number of multi-contact relays 1015, 1016, etc., serves to connect the set of relays 1000 with the proper group of outgoing trunks, the multi-contact relays each being individual to a different group. Likewise, the other set of test relays 1003 serves to test the setof horizontal links 301 in all switches and the outgoing trunks to which these links have access. Also a connecting device 1001 consisting of multi-contact relays 1022, 1023, 1019, 1020, 1025 and 1026 serves to connect the marker testing relays with the individual switches. Relays 1023. 1020 and 1026, for instance, are individual to the particular switch 300 shown in the drawing.

The line marker shown in Figs. 11 and 12 includes a plurality of registers 1200, 1201. and 1202 which receive numerical records from the controlling sender. It also includes the multi-contact relay translating device 1204 which is operated according to the settings of the registers to select the vertical operating magnets 515, 1308, etc.,

individual to the different vertical rows of numerical lines in the connector switches. Moreover, the line marker includes a multicontact relay translating device 1203 which serves to associate the register 1201 with the connecting devices 510 and 1316 individual to the connector switches 500 and 1300, respectively. The device 510 consisting of relays 511, 512, 513, etc., serves to associate certain test relays in the marker with the horizontal links of the group having access to the called lines of the desired units designation in the connector switch 500. The device 1316 similarly comprising a number of multi-contact relays 1317, 1318, etc., serves to connect the same testing relays in the marker with the horizontal links of the group having access to the called lines of the desired units designation in the connector switch 1300. In Fig. 11 the set of testing relays of the marker are associable through the multi-contact relay connecting devices 4-01 and 102 with the groups of trunks outgoing from the selector switch and other switches and with the horizon tal links of these group selectors.

Detailed description of estabiislwnent 0/" a connection.

inner contact of cut-off relay 120, conductor 1 104:, through the substation loop, conductor 103 to ground through the outer contact of relay 120. Relay 121 operates and a circuit is closed from battery through the winding of relay 129, right back contact Of 1 relay 128, left contact of relay 121, conductor 156 to ground.

Relays 128, 129 and 130 enclosed within the broken rectangle pertain to the vertical group of lines in the row of the switch 100. These relays are brought into action whenever one of the lines of the corresponding group initiates a call.

Relay 129 completes a circuit from battery through the winding of relay 131, inner front contact of relay 129 to the grounded conductor 156. Relay 129 also closes a circuit from battery through the left hand winding of relay 130. outer "front contact of relay 129, left back contact of relay 135, outer right contact of relay 137, conductors 158 and 156 to ground. Relay 130 operates and closes a circuit for relay 128. Relay 128 looks through its left contact and the contacts of relays 1.31 and 132 to ground. Relay 130, in operating, completes a circuit from battery through its right hand winding and inner right contact, winding of relay 135, outer right contact of relay 137, conductor 158 to ground. Relay 135 operates and closes a circuit from battery through the winding of slow-to-release relay 136, inner right contact of relay 135, inner right back contact of relay 137, conductor 158 to ground. Relay 136 closes a substitute holding circuit for relays 130 and 135.

With relay 135 operated, a circuit is closed from battery through the winding of the vertical operating magnet 116, outer right front contact of relay 130. left front contact of relay 1355, contact of relay 136, conductor 158 to ground. The magnet 116 operates and prepares the contacts in the vertical row .110. Magnet 116 also closes a circuit from ground through its contact, conductor 159, innor contact of relay 131, outer left contact of relay 130, right contact of relay 121, left hand winding of the horizontal group relay 122 to battery. Relay 122 is a group relay individual to the group of horizontal links including the links 106 and 107. Similarly, relay 123 is a group relay individual to the other group of horizontal links illustrated.

Relay 122 operates and closes a circuit from battery through its right hand winding and right contact. right back contact of re lay 123, winding of relay 13 1, conductor 159 to ground. Relay 134 operates in this circuit. Another circuit is closed from battery through the winding of the vertical operating magnet 118, brush 1 141 of allotter switch 143. contact of slow release relay 139, left contact of relay 137, outer right contact of relay 135, conductor 158 to ground. It is assumed that the first one of the outgoing trunks 114 is idle and that the allotter switch 143 is standing in a. position to allot this trunk as shown in the drawing. The allotter switch 143 has a position for each of the several trunks which lead out of the line switch to the succeeding district selectors. Consequently. the vertical magnet 118 relative to the idle trunk 1141 operates and prepares the contacts in the vertical row 112. hilagnet 118. in operating. completes a circuit from battery through its winding and inner contact. conductor 160. winding of relay 137, outer right contact of relay 135, conductor 158 to ground. Relay 137, however. being shunted by the circuit above traced does not operate this time. Magnet 118. furthermore, closes a circuit from ground through its outer contact, conductor 151,

winding of trunk relay 14:6 to battery. l l ith relay 1416 operated a circuit is completed from battery through the winding of relay 139, winding and contact of stepping magnet 13S, brush 1&5, contact of relay 14:6 to ground over conductor 151. The magnet 138 operates, interrupts its own circuit and advances the brushes 14A and 1415 to the next set of terminals. If the following trunk is idle then the allotter switch comes to rest,

but if it is busy, the switch continues until an idle trunk is found. hen the switch leaves the position shown it opens the shunt around relay 137 and this relay operates in series with magnet 118. Relay 137 opens the circuit of relay 136 which commences to deenergize. Relay 136 being slow, holds its armatures for an interval after the release of relay 137 which is sufficient for certain operations to take place.

During the interval mentioned a circuit is closed from ground over conductor 158, inner right front contact of relay 137, outer contact of relay 134, left back contact of relay 123, left front contact of relay 122, back contact of relay 127, assuming the first link 107' is idle, winding of magnet to battery. Magnet 125 operates and effects aconnection between the link 107 and the incoming line and also between the link and the outgoing trunk 11 1. Immediately that this connection is established, a circuit is closed from battery through the winding of magnet 125, winding of relay 127, cont-acts of the switch 100, over the sleeve conductor to ground at the outer contact of magnet 118. The switch is temporarily held by means of this circuit but relay 127 being shunted does not operate at this time. An other circuit is closed from battery through the winding of cut-01f relay 120 over the sleeve conductor to ground at the contact of magnet 118. Relay 120 opens the circuit of relay 121, which in turn, opens the original energizing circuit of relay 129.

Should another line in the same vertical group attempt simultaneously to make a call while a subscriber in a succeeding vertical group is calling, his attempt to make such a call will be unsuccessful. When the line relay 121 releases following the opening of its circuit by relay 120, it opens the holding circuit of relay 131, but since the second subscriber in the same group is calling relay 131 is held energized over a parallel circuit through the left contact of the line relay similar to relay 121. Relay 131 in remaining energized preserves the locking circuit of relay 12 which prevents the reenergization of relay 129. A second subscriber in the first group Who has removed his receiver while the line relay of the first calling subscriber is energized, therefore, cannot succeed in making a call until a simultaneous call in subsequent groups have been handled or until a call has been made in each of said succeeding groups. In this latter event a series circuit is closed for relay 132 through the back contacts of all relays similar to relay 129 and relay 132 operates to unlock relay 128.

At the instant relay 146 energizes, the ground potential on conductor 151 is extended through the contact of this relay over conductor 150, through the back contact of relay 204, conductor 206, thence through the winding of relay 613. Relay 613 operates and locks through its winding and inner left contact, conductor 207, outer left back contact of relay 201 to ground. Relay 613 completes a circuit from ground through its outer right contact, conductor 209, winding of slow-to-release relay 204 to battery. Relay 204 operates and applies holding ground to the conductor 150, whereby magnet 125 and relays 120 and 146 are held energized when magnet 118 becomes deenergized. Relay 613 operates similarly to the relay 120 of the line switch and brings the group relays 614. 615 and 616 and the control relays 619, 620, 621, 617, 622 and 623 into play to cause the extension of a connection through the sender selector switch 600 to the allotted idle register sender.

With relays 616 and 617 operated a circuit is closed from battery through the winding of vertical magnet 629, contacts of relays 616 and 617, outer right contact of relay 623 to ground. Magnet 629 operates and brings about the energization of relay 612, which in turn, locks in a circuit including the re lay 621. Relay 617 also closes a circuit from battery through the winding of vertical magnet 631, brush 627 of allotter 626, contact of slow relay 625, left contact of relay 623, contact of relay 617 to ground. The magnet 631 operates and closes a locking circuit through its winding and contact and the winding of relay 623, the latter relay, however, remaining deenergized due to the shunt around its winding. Magnet 631 also closes a circuit from ground through its outer contact, conductor 638, through the brush 628, contact and winding of magnet 624, winding of slow relay 625 to battery. Magnet 624 steps the switch 626 forward to the set of terminals representing the next idle sender and in so doing removes the shunt from the winding of relay 623. Re-

lay 623 opens the circuit of slow-to-release relay 622 which commences to deenergize. During the interval that relay 622 is deenergizing'a circuit is closed from ground through the inner right front contact of relay 623. rightcontact of relay 621, left front contact of relay 612, front contact of relay 611. assuming the link 608 to be busy, hack contact of relay 609, winding of the iorizontal magnet 610 to battery. Magnet 4 610 operates the switch and connects the incoming trunk conductors through the link 607 to the group of conductors 632 leading to the selected idle sender.

Immediately that the connection is es tablished a circuit is closed from battery through the winding of relay 201, conductor 210, contacts of switch 600, conductor 638 to ground at the contact of magnet 631. Relay 201 operates and opens the circuit of relay 613 which causes the deenergization of relays 612 and 619 provided no other sender is being sought through the same vertical group in the switch 600. Relay 201 also closes a holding circuit for the relay 204 which maintains a holding ground potential on the conductor 150. Furthermore, relay 201 connects the tip and ring conductors of the trunk through the sender selector switch to the impulse relay 700 and balancing coil 701 of the sender. This results in the closure of a circuit from battery through the resistance 718, winding of relay 700, outer left contact of relay 703, conductor 640, through contacts of the switch 600, conductor 641, outer right contact of relay 201, conduct-or 149, thence through the line switch 100 and the subscribers substation loop and returning over the other side of the line to conductor 148 to the inner right contact of relay 201, conductor 642, through the switch 600, conductor 643, inner left contact of relay 703, right hand winding of the balancing coil 701 to ground. Relay 700 operates and closes a circuit for slow-to-release relay 702. Relay 702 places ground on the holding conductor 720. This ground potential is transmitted by way of conductor 638 and results in a holding circuit for the magnet 610 and relays 609 and 201 in substitution of the circuit temporarily maintained by the vertical. operating magnet 631.

Following the series of operations just related slow relays 136 and 622 become deenergized. Relay 136 opens the circuits of relays 130 and 135. Relay 130 opens the circuit of magnet 116 and relay 135 opens the holding circuit of magnet 119 and relay 137. Magnet 116 causes the release of relays 134 and 122. YVith the vertical magnets deenergized the connection is now held through the line switch 100 due to the maintained energization of magnet 125 which, as above mentioned, is held in a circuit closed to ground over the sleeve conductor 150. Relay 127 now operates in series with magnet 125 and extends the horizontal start circuit to the next link. Relay 622, in releasing, similarly brings about a release of the corresponding elements in the sender selector switch 600 and the connection through this switch is now held by the magnet 610, the circuit of which is controlled by the slow relay 702 in the sender. Relay 609 now operates in series with magnet 610.

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or u- The apparatus is now in condition for receiving the first series of impulses. The calling subscriber, consequently, manipulates his impulse transmitter 163 to send a single impulse representing the first digit of the wanted number. At the time relay 702 operates it closes a circuit from battery through the winding of slow release relay 706, left back contact of relay 704, left back contact of relay 705, conductor 720, to ground at the left contact of relay 702. Relay 702 also closes a circuit from battery through the resistance 739, left hand winding of relay 707 to ground at the right contact of relay 702. Relay 707, however, does not oper ate since its winding is shunted by the following path: battery, through the resistance 739, contact of relay 700 to ground at the right contact of relay 702.

In response to the first opening of the line by the calling subscriber, relay 700 rcleases and opens the shunt aroun: the winding of relay 707 and this latter relay operates. Relay 707 closes a circuit from battery through the winding of relay st, outer left contact of relay 707 to the grounded conductor 720. Relay 70et operates and locks in a circuit through its left front contact, left contact of relay 705 to ground on conductor 720. Relay 70% opens the original circuit of relay 706, but this latter relay remains energized in a circuit traceable through the outer right front contact of relay 707 to the grounded conductor 720. .K-elay 707 closes a circuit through the left hand winding of relay 708 and relay 708 operates and closes a circuit from battery through its right hand winding and inner right contact to the grounded conductor 720.

Relay 708, in operating completes a circuit from battery through its left hand winding and left contact, conductor 72%, outer right back contacts of counting relays 715, 714L, 713 and 712 in series, winding of relay 712, outer left back contact of relay 713, conductors 725 and 726, outer right contact of relay 705, left front contact of relay 704i, left contact of relay 705 to the grounded conductor 720. So long as relay 707 remains operated relay 712 is shunted and does not receive suflicient current in the circuit traced to energize. At the end of the impulse relay 700 operates and shunts relay 707 and this relay releases, opening the original circuit through the left hand winding of relay 708. Relay 712 now operates in series with the left hand winding of relay 708. Relay 712 locks in a circuit from battery over conductor 727, inner right contact and winding of relay 712, outer left back contact of relay 713 to ground over conductor 7 It should be noted at this point that the armatures of the counting relay 712, which is also true of the remaining counting relays, are so arranged that the inner right contact is closed slightly in advance of the opening of the outer right back contacts. 3y this arrangement the locking of the relay is certain to occur before the energizing circuit is opened.

Immediately that the relay 712 opens its back contact the circuit through the left hand winding of relay 708 is opened. Relay 708 is wound differentially and when the left hand winding is opened, the effect of the right hand winding is to cause a quick release.

After the usual interval has elapsed following this impulse, slow-to-release relay 706 becomes deenergized and a circuit is completed from ground over conductor 720, contact of relay 706, right contact of relay 70st, inner right contact of relay 705, conductor 722, right back contact of relay 808, winding of relay 807 to battery. Relay 807 operates and closes a circuit from battery through its winding and inner upper cont-act, thence over conductor 830 winding of relay 705, through contacts of relays 70 i, and 706 to ground. Relay 705, however, being shunted by the above circuit does not operate at this time. Relay 807 serves to connect the counting relays to the register relays of the register 800. With relay 807 operated and relay 712 energized a circuit is closed from the grounded conductor 725, outer left front contact of relay 712, conductor 728, outer right back contact of relay 717,-conductor 729, conductor 831, contact of relay 807, thence in parallel one branch leading through the winding of relay 804 and the winding of relay 832 to battery and the other branch leading through the winding of relay 823 to battery. Relays 804, 832 and 823 operate and lock through the inner left front contact of relay 804, conductor 825 to the grounded conductor 720. Relay closes an obvious circuit for relay 808 which operates and locks to the grounded conductor 825. Relay 808 opens the shunt around the winding of relay 705, which energizes in series with relay 807. Relay 705 opens the circuit of relay 704, which in turn, opens the circuits of relays 705 and 807. Relay 807 disconnects the counting relay from the register 800. Vith relays 7 04 and 705 deenergized relay 706 again operates in the cirucit abo e traced. Relay 705 also releases relay 712.

The subscriber operates his dial to trans mit the second series consisting of two inipulses and in the manner already fully explained relays 712 and 713 are operated. Relay 713, in operating, opens the holding circuit of relay 712 which thereupon releases. After the proper interval has elapsed follow ing the series. slow relay 700 releases and a circuit is closed from ground. over conductor 722 as above traced, through the right front: contact of relay 808, right back contact of relay 812, winding of relay 811 to battery. Relay 811 operates, connects the counting relays to the second register 801 and closes a locking circuit through its winding and inner upper contact, over conductor 830 as previously traced, through the winding of relay 705. Relay 705 being shunted does not operate at this time.

Since the counting relay 713 is operated a circuit is traceable from the grounded conductor 725, through the outer left front contact of relay 713, conductor 730, conductor 837, through contact of relay 811 winding of register relay 810 to battery. Relay 810 locks through its inner left contact to the grounded conductor 825. Relay 810 at its outer left contact closes a circuit for relay 812 which operates and locks to the conductor 825. Relay 812 opens the shunt around relay 7 05 which operates and in the manner explained brings about the release of relay 704, relay 718 and relay 811 and also releases itself.

The subscriber next transmits the third series consisting of three impulses. In response to this series relays 712, 713 and. 714 are operated and relays 712 and 713 successively release. After an interval relay 706 releases and closes a circuit as traced over conductor 722, through the right front contacts of relays 808 and 812, right back contact of relay 816, winding of relay 815 to battery. Relay 815 operates, connects the counting relays to the register 802 and closes a locking circuit for itself over conductor 880 through the winding of relay 705.

With relay 815 operated and the counting relay 714 energized, circuits are closed from ground over conductor 7 25, through the left front contacts of relay 714, conductors 729 and 780, thence over conductors 881 and 887, through contacts of relay 815, windings of relays 818 and 814 to battery. Relays 813 and 814 lock through their inner left contacts to the grounded conductors 825. These relays also close a circuit for the relay 816 which operates and locks through its left contact to the conductor 825. Relay 816 opens the shunt around relay 705, which in turn. operates in series with relay 815. In a similar manner to that already explained relay 705 brings about its own release and the release of relays 704 and 815.

The subscriber now transmits the final series consisting of four impulses. In response to this series counting relays 712, 713, 71.4 and 715 are operated in succession and relays 712, 713 and 714 are released in succession. After an interval relay 706 releases and a circuit is closed by way of conductor 722, through the right front con tacts of relays 808, 812 and 816, right contactof relay 820, winding of relay 819 to battery. Relay 819 connects the counting relays to the register 803 and closes a. locking circuit for itself over conductor 830, through the winding of relay 705. Vith relay 819 operated and relay 715 operated a circuit may be traced from ground over con.-

ductor 725. outer left back contact of relay 712, inner left contact of relay 715, conductor 731, conductor 838, through contact of relay 819, relay 833 to battery. Relay 833 locks through its inner left contact to the grounded conductor 825. Relay 833 closes a circuit for relay 820 which looks through its inner left contact to conductor 825. Relay 820 opens the shunt around relay 705 which brings about its own release and the release of relays 704 and 819.

As soon as the thousand digit is recorded on the register 800, the sender is connected to the district marker in order that the record may be transferred thereto for detern'iining the group selective operation of the district switch 300. hen relay 808 operates a circuit is established from the grounded conductor 825, through the outer left contact of relay 808, conductor 839. winding of relay 709 to battery. Relay 709 operates and locks through its outer contact to the grounded conductor 720. Relay 709 closes a circuit from the grounded conductor 720, through the outer left contact of relay 711, inner contact of relay 709, conductor 7 32, winding of relay 904 to battery. Relay 904 closes a circuit from ground through its right contact, right contact of relay 907. winding of relay 908 to battery. Belay 908 operates and locks through its inner contact, middle back contact of relay 909, conductor 914, contact of slow relay 912 to ground. Relay 908 closes a circuit from battery through the right winding of relay 903, left contact of relay 904, left back contact of relay 906, outer contact: of relay 908, middle back contact of relay 909, conductor 914 to ground. Relay 903 closes a circuit for relay 907. Relay 907, in turn, closes a circuit from battery through the left winding and contact of relay 903, left back contact of relay 905, left contact of relay 907, winding of relay 909 to ground over conductor 914. Relay 903 is locked and relay 909 operates in this circuit. Relay 908 now becomes released. Relay 909 causes a. circuit to be closed for the multi-contact relay 901, which is individual to the particular sender shown and serves to connect that sender with the district marker. Another multi-contact relay 902 is individual to another sender and serves for a similar purpose. The circuit of relay 901 leads from battery through the winding thereof, inner right contact of relay 903, inner contact of relay 909 to the grounded conductor 914. Relay 901, in operating, closes a circuit from ground through its contact, outermost contact of relay 909, inner left back contact of relay 911, Winding of relay 910

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