US1501033A - Telephone-exchange system - Google Patents

Description

July 15 .1924.

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Patented July 15, 1924.

UNITED STATES PATENT OFFICE.

WALTER P. ALBERT, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF YORK.

' 1 TELEPHONE-EXCHANGE SYSTEM.

Application filed May 19,

To all whom it may concern:

Be it known that I, WALTER P. ALBERT, a citizen-of the United States of America, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description. 7

This invention relates to telephone exchange'systems and particularly to systems in which machine switches are employed for the extension of connections.

here a central office in an exchange system is designed to extend calls, which either originate locally or in distant calling offices, both to local called lines in the central office and to outlying called offices, the proper apparatus is provided in the central ofiice for selectively routing the calls to their destination. *This apparatus may consist of automatic switches and selecting devices. Moreover, the distant called offices may be provided with selective switches, indicators or other selective apparatus for completing incoming connections or assisting in the completion of such connections to the calledlines.

In general, the number of switches in the train needed for the completion 'of a call will depend upon the capacity of the ofiice containing the called line. This is true where the called line is located in the same office with the switches used to make the selection. Another factor that has a bearing on the number of switches is the capacity of the exchange system or the number of offices in the are-a to which calls must be made from the central ofiice. The standard practice is to adjust the capacity of all offices such that a given number of switches, say two, an incoming and a final selector, are sufficient. To enable the se lection of the desired office, two additional switches are usually provided in the central office, namely, a district and an office selector. 7

An initiated call, which may originate locally in the central office 'or, as shown in the present disclosure, may originate in a distant manual office served by'an operator, is first extended to the district selector in operators in calling offices. limited number of such lines in comparison 1921 Serial No. 470,767.

the central oflice. The majority of calls thus originated are destined for lines vin distantofiices and accordingly the complete designation, consisting of a standard number. of digits, is registered on a-central office register sender. .The sender controls however, a limited number of ,lines which lead to supervisors desks, complain-t operators, information operators and other similar positions. These lines should, of course, be accessible to the subscribers and Due to the to the capacity of a regular ofiice a single switch, such as a final selector is adequate to make all selections for calls of this nature. The incoming switch is omitted and connections are extended through the district and office selectors directly to the special final switches. This means that the two selections which usually occur at the incoming switch are unnecessary and consequently the corresponding registration in the sender must be taken care of otherwise.

With the foregoing explanation in mind, thepresent invent-ion has as its object to provide, in a system of'this charactenmeans associated with a train of switches for rendering ineffective a portion of the registration on the sender which determines the operation of said switchesand which means serves to operate a signal when the switches 'extend connections to busy lines.

A feature ofthe invention relates to the provision, in a system where connections are arranged to be extended over a train of switches under the control of a register sender, and where certain connections require only a portion of the switches, of a device associable with the extended connection 'for rendering ineffective that port-ion of the designation on the sender pertaining to the eliminated switches and operating a signal when the called line is found busy.

Another feature relates to a device arranged in common to a plurality of final switches for rendering ineffective a portion of the designation registered in the sender when the switches normally controlled by such portion of the registration are omitted from the connection.

Other features and advantages of the invention will be more clearly understood from a consideration of the following detailed description and from the appended claims.

Referring to the drawing, Figs. 1 to 8 inclusive, when arranged in the order illustrated in Fig. .9, disclose so much of a telephone exchange system as is necessary for a thorough comprehension of the invention.

Fig. 1 shows a subscribers line terminating before an answering opera-tors position in an originating oiiice, the operators cord circuit and a portion of the associated equipment and the outgoing end of a trunk line leading to a distant central switching ofiice. Fig. 2 shows a district selector switch in the central switching office in which the incoming trunk from the originating manual office terminates.

Fig.3 illustratesan ofiice selector switch in the central switching office which together with the district selector serves to select trunk lines outgoing to any of the distant offices in the outlying area and also to select trunks leading toloeal switches in the same oflice.

Fig. 4 shows a final selector switch in the central switching office where the district andoflice selectors are located and has access to lines of special character such as those leading to operators positions. This figure further discloses a switching device arranged in common to all of the final selectors, the function of which will be taken up hereinafter.

Above the broken line in Fig. 5, there is shown in schematic form, the incoming and final selector switches in a distant full mechanical office which is accessible byv trunk lines leading from the office selector switches in Fig. 3. Below the horizontal broken line, there is illustrated one of the special lines in the central switching office which leads from the terminal bank of the final selector switch and appears at an operators position. n

Fig. 6 shows the trunk finder switch of a register sender unit which has access to the incoming trunks shown in Fig. 2 for the purpose of associating with any desired one thereof the register sender to which this trunk finder is individual.

Fig. 7 illustrates the counting relay set and controlling sequence switch of the sender.

Fig. 8 shows parts of an operators keyboard which is common to all of the register senders at her position and also the several registers of the register sending unit shown,

which are arranged to take up their positions in accordance with designations registered on the keyboard.

Description of apparatus.

The automatic selector switches shown in Figs. 2, 3 and 1 are of the well known power driven type in which a plurality of sets of brushes are mounted on a vertical brush shaft arranged to be selectively tripped into engagement with their individual section of the panel terminal bank. The brush shafts are propelled in a vertical direction by means of constantly rotating power drums and which in their upward or setting movement revert impulses to the sender to measure off the distance traversed. In general construction and operation, these switches are all of the same character as the one shown and described in detail in the patent to Craft and Reynolds N 0. 1,128, 696, issued January 5, 1915. The trunk finder switch 600 illustrated in Fig. 6 is also a panel type power driven switch and differs only from the switches above mentioned as regards certain of its details. For example, only a single set of brushes is mounted on the shaft and is in constant engagement with the terminals of the bank with which they cooperate.

The sequence switches 210, 310, 110, 120, 610 and 710 and also the register sequence switches 800, 810, 820, 880, 8 10, 850, 860 and 870 are substantially similar in principle and construction to the one described in the patent to Reynolds and Baldwin No. 1,127;

808, issued February 9, 1915. As regards the sequence switches 210, 310, 610 and 710, each of which occurs on a separate sheet of the drawing, it may be noted that all con tacts located on the several sheets are controlled by the sequence switches correspondingly situated. In Fig. 4:, where two sequence switches appear, the contacts belonging to sequenceswitch 120 are confined within the area of the small rectangle at the bottom of the sheet, while all remaining contacts on the sheet are a part of sequence switch 110. In Fig. 8, the contacts of the several register sequence switches are segregated by means of the vertical broken lines.

The operators keyboard which is common to all of the register sender units at her position comprises a plurality of rows of keys upon which she records the oflice and numerical designation of called lines. The first four registers 800, 810, 820 and 830 are used respectively for controlling the districtbrush, district group, oftic e brush and oflice group selections to select trunks leading to the desired office or to local switches and consequently receive that portion of the entire designation which pertains to the called oflice or the called group of lines. These registers may be set respectively-by means of four different rowsofkeys, the several keys of each row determining a different setting position for its'register. 'As an alternative, a single row of keys may be provided, each of which when actuated causes all of the four ofiice registers to take up settings characteristic of the particular key. In the drawing, this latteraplan is illustrated and twoof the office keys 819 and 821only are shown.

The remaining four registers 840, 850, 860 and 870' correspond to thefourdigits of the numerical designation and 'are set respectively by the thousands, hundreds, tens and units keys on the operators keyiboard. These numerical registers in their set position control the sender to determine the incoming brush, incoming group, final brush, tens and units selective movements of the incoming and final switches on calls extended to offices or groups of lines having a capacity necessary to require the use of these twoswitches.

General description of the system.

In the system disclosed, it is assumed that the call to be extended over the district selector and ofiice selector 250 and 350 and thence in the proper direction is one which originates in adistant calling office such as the manual ofiice shown in F i-g. 1. So far as the invention is concerned, however, it matters not where the call originates whether in a distant officeor locally as will be seen hereinafter. The answering operator in the originating office, after being notified by thecalling subscriber of the number desired, communicates with the operator in the central switching oflice by means of an order wire, which is not shown, and re quests her to assign .an idle trunk for use. The latter operator, who may be termed a cordless operator, assigns the trunk and orally receives from the originating operator the name of the desired oilice and the number of the called line therein. The cordless operator at the time of assigning the trunk depresses an assigning key 209 which initiates the movement of the trunk finder of an idle register sender unit to asone belonging 'to a distant full mechanical oflice, such as the line 510, the ofiice record on the register sender determines the selec-' tive movement of the district selector switch 2-50 and the oflice selector switch 350 which choose atru'nk line 330-831 outgoing from the central switching oflice and'terminating as well as in an incoming selector switch at the called office. Thereafter the register sender controls the incoming selector switch 500 and final selector switch 501 in accordance with the designation registered on the numerical registers to complete the connection to the terminals of the called line.

On the other hand, it may be that the de sired line is one which leads to an operators position in the central switching oiiice, such as the position indicated in the lower section of Fig. 5. A call of this character might be one where the calling party wishes to communicate with an information "operator, a complaint operator, the supervisor, the trouble man or with the operators at any of the special positions. the office record on the registers of the sender determines the setting of the district and ofiice switches to route the connection over a trunk leading directly to the final selector switch 460. In order not t necessitate the use of designations having a reduced number of digits for special calls and to avoid confusion on the part of the operator in knowing how many keys on her keyboard to depress the universal number scheme is preserved for these special lines for ordinary lines. Consequently, the register sender when set in ac In this case, I

cordance with the designation of a line leading to an operators position has re 'ceived a full record and is prepared to control both incoming and a final selector, but as the number of the special lines is comparatively small, the incoming switch has been omitted and that part of the designation recorded on the sender which ordinarily determines the incoming brush and incoming group selections 1S unnecessary.

nection is extended to one of these final switches to satisfy the lncoming registrations. After these registrations have been disposed of the final brush, tens and units selections take place under the control of the sender and the called line is selected. If the called line is found to be busy, the se quence switch 4L20 again becomes effective and'causes' the transmission of a busy signal current back to the operator in the originating oflice to advise her that the connection should be released.

7 Detailed description of operation.

in considering the detailed operation of the system, it will be first assumed that the subscriber of line wishes-to converse with the subscriber of line 510 which belongs to the'full mechanical oiiice illustrated in the upper part of Fig. 5. The operator,

lBO

. assi nin ke' 209.

and the number of the called line.

in response to the call initiated on the line 100, inserts the plug 101 of the cord circuit 103 in the jack 102 of the calling line and communicates with the subscriber. On learning the designation of the desired line, she converses over the order wire, not shown, with the cordless operator in the central switching ofiice and requests the assignment of an idle trunk for the extension of the connection and also communicates to the cordless operator the name of the oiiice The cordless operator, observing that the trunk line 200201 is not in use at the time, notifies the originating operator of its identity and at the same time depresses her The actuation of key 209 completes a circuit from battery through the winding of sequence switch 210, the right-hand contact of sequence switch spring 208 (1), contacts of key 209 to ground. Sequence switch 210 energizes and moves out of its normal position and into vposition 3; In position 3 of sequence switch 210, a circuit is established from ground through the lower right-hand contact of sequence switch spring 220 (1+12).upper lefthand contact of said spring (2+17), left-- hand armature and back contact of relay 205, right-hand contacts of sequence switch spring 211 (3), conductor 2412, right-hand contactof sequence switch spring 634 (1), winding of sequence switch magnet 610 to battery. The sequence switch 610 advances out of position land into position 2.

hen sequence switch 610 is in position 2, the trunk finder switch 600 is started in operation to hunt for and find the set of ter minals in its bank identifying the assigned trunk 200201 in order to associate the register sender therewith. The circuit for the up-drive power magnet 615 of the trunk finder switch may be traced from battery through the winding of said magnet, contact of sequence switch spring 60& (2), back contact and left-handarmature of relay 601 to ground. As soon as the brushes 619, 620, 621, 622, and 623 encounter the terminals 62 1, 625, 626, 627 and 628 individual to the assigned trunk, a circuit is established from battery through the winding of relay 601, lefthand contact of sequence switch spring 603 (2), brush 621, terminal 626, conductor 631, contacts of sequence switch spring 21 1, closed in position 3, back contact and outer right-hand armature of relay 205, upper left-hand contactof sequence siitch spring 222 (2+11), lower left-hand contact of said spring (2+4) to "ground. Belay 601 becomes energized, opens the circuit of magnet 615, and completes a holding circuit for itself from battery through the winding of said relay, righthand contact of sequence switch spring 603 (2+17), right-hand armature and contact of relay 601, brush 619,

terminal 621, conductor 629, lower left-hand contact of sequence switch spring 213 (2f{+16), upper right-hand contact of said spring (2+1-2-,};) to ground. Relay. 601 in operating completes a circuit from ground, left-hand armature, front contact, righthand contact of sequence switch spring 605 (2), winding of sequence switch magnet 610 to battery, driving said sequence switch out of position 2 and into position 6. In position 6 of sequence switch 610, a circuit is closed as follows: ground, through the contact of sequence switch spring 602 (6), brush 620, terminal 625, conductor 630, lefthand contact of sequence switch spring 212 (3), right-hand winding of relay 205 to battery. Relay 205 operates and completes a circuit from battery through the winding of sequence switch magnet 210, lower left hand contact of sequence switch spring 215 (1+3), upper right-hand contact of said spring (2+12), front contact and left-hand armature of relay 205, upper left-hand contact of sequence switch spring 220 (2+17), lower right-hand contact of said spring (1+12) to ground. Sequence switch 210 moves out of position 3 and into position 5. The cordless operator in the central switching ofiice having received the name of the called oflice and the number of the desired line proceeds at once to set up this designation on her keyboard. Assume that the name of the called oliice is represented by the office key 821 and that the number of the called line 510 is 4 7 3 2. Accordingly, she actuates the office key 821, the No. 1- thousands key 822, the No. 7 hundreds key 823, the No. 3 tens key 824 and the No. 2 units key 825. At the time the sequence switch 610 moves into position 6, a circuit is established for each of the oflice and numeri cal registers and these registers commence to rotate. This circuit may be traced from ground through the contact of sequence switch swings 609 (5+6) to conductor 635 thence in parallel through the right-hand armatures and back contacts of relays 801, 302, 803, 80-11:, 805, 806, S07, and 808 respectively through the winnings of registers e00, e10, e20, 830, sic, e50, 860 and 870 to battery and ground. brush register 800 reaches position 1, a circuit is closed from battery through the winding of relay 801, contact of sequence switch spring 626 (1), left-hand contact of key 82 1 to ground. Relay 801 operates and opens the circuit of register 800 causing this register to come to rest in position 1. )Vhen the district group register 810 reaches position 2, a circuit is closed from battery through the winding of relay 802, contact of sequence switch spring 827 (2), lefthand contacts of oflice key 821 to ground. Relay 802 operates and opening the circuit of register 810 causes this register to stop When the district 830 advances to. position 4, a circuit is closed from battery throughthe winding of relay 804, right-hand contact of sequence, switch spring 829(4), right-hand contacts of key 821 to ground. Relay 804 becomes energized and arrests the. register 830 in position 4. In a similar manner when registers 840., 850, 860, and 870 reach positions 4, 7, 3. and 2 respectively, circuits are closed for the relays 805, 806., 807, and 808 through thecontacts of sequence switch springs 831, 832,

833, and 834 and the. respective keys 822, 823., 824 and 825 to ground. Relays 805, 806, 807 and 808 become energized and the corresponding registers stop in positions 4 and 7, 3 and 2. 7

After all the registers have taken their settings and the relays801, 802, 803', etc. are

energized, a circuit is closed from ground through the contacts and left-hand armatures of-all these relays in series, conductor 846,. upper contact of sequence switch spring 606 (6), winding of sequence switch magnet 610 to battery. Sequence switch 610 leavesposition 6' and moves into position 10. In posit- ions 7 and 8 of sequence switch 610, a temporary circuit is estab-' lished fro-m ground through the contact of sequence switch spring 611 (7+8), conduc-v tor 636, through the windings of magnets 809,811, 812,813, 814, 8,1 5, 816 and 817m parallel to battery. The magnets 809, 811, 812, etc. are key release magnets and when energized operate to release all depressed keys on the operators board.

In position 10 of sequence switch 610,:a circuit is established as follows fordriving the sender sequence switch 710 out of position 1 to place the sender in. conditiontocontrol brush selection at the district switch: battery, through the winding of the magnet of sequence switch 710,.contact of spring 706. (1), contact of spring 607 (10) to ground.-

With the district sequence switch 210 in position 5, and the sender sequence switch 710 in position 2, the fundamental circuit "is closed for district brush selection. This circuit may be followed," from battery,

through the right-hand windingof relay 205, lower left-hand contact of spring 223 lay 712, right-hand contact of-spring701 (2), contact of spring 702 (2+4) to ground; Relay 205 becomes energized'in circuit from battery through the winding if sequence switch magnet 210, lower lefthand contact of sequence switch spring215 (5), upper right-hand contact of said spring (2-1-12), front contact and left-hand armature of relay 205 to ground through the contacts of sequence switch spring 220.

Sequence switch 210 is driven interposition 6 where a circuit is established for the updrive power magnet 224 to cause the upward movement of the brush shaft 227 for the purpose o-fselecting the proper setof brushes to be tripped. The circuit of the power magnet 224 may be traced from battery through the windingof said magnet, lower right-hand contact of spring 215 (6), upper right-hand contact of said spring '(2-1-12), front contact and left-hand armature of relay 205., through the contacts of. sequence switch spring 220 to ground The stepping relay 700 which also operates in the fundamental circuit in series with relay 205, closes, a circuit from ground through, its armature and contact, lower contact of spring 711 (2), conductor 721,

contact of spring 847 (1), conductor 835 and thence to the conductor 719, Fig. 7, armature. and back contact of counting relay 714, winding of, counting relay 715 to battery. Y

It may be well to explain at this point that the conductors leading from the contacts of the several register sequence switch springs in Fig. 8, such as the conductor 835, which are shown as terminating in .small circles including thedifferent ordinals from 0 to 9,, are, in actual practice, connected to the conductors terminating in the similarly labeled circles at the armatures of the counting relays.

Relay 715 becomes energized in the cir cuit above traced and closes a holding cir-. cuit from battery through the winding of relay 715, winding of relay 714, contact and armature of relay 715, contact of spring 705 (2) to ground. Relay 714, however,

cannot energize at this time since its Winding is shunted by the direct path to ground closed at the armature and contact of stepping relay 700.

As the brush shaft 227 approaches the first brush tripping position, brush 234 encounters a metallic segment of commutator 236 and the following circuit is closed for relay 205: battery to the right-hand'winding and contact and inner right-hand armature of said relay, upper left-hand contact 236, brush 234 to ground. This direct cirthe counting relay 712. shunted by the stepping'relay 7 00 does not cuit to ground shunts the stepping relay 700 in the fundamental circuit. Relay 7 00 on deenergization opens the shunt around the winding of counting relay 714 and this relay operates in series with relay 715. Upon the next energization of relay 700 which occurs when the brush 234 engages with the next insulating segment of commutator 236, the stepping circuit is extended by way of conductor 719, armature and front contact of relay 714, right-hand armature and contact of relay 712, winding of relay 713 to battery. Relay 713 becomes operated and closes a circuit for itself and the winding of Relay 712 being operate. As the brush shaft 227 reaches the second brush tripping position, brush 234 engages a metallic circuit of commutator 236, the stepping relay 700 is shunted and releases its armature topermit the operation of the 0 counting relay 712. Relay 712 at its outer left-hand armature opens the fundamental circuit and at its inner lefthand armature closes a circuit including the upper contact of spring 7 03 (2),windin-g of sequence switch 710 to battery. Sequence switch 710 is driven out of position 2 and into position 4. On leaving position 2, se-' quence switch 720 opens at the contact of spring 705 the holding circuits of the energized counting relays. As soon, following the opening of the fundamental circuit at the sender, as the brush 234 engages the next insulating segment of commutator 236, relay 205 becomes deenergized and opens the circuit of power magnet 224. The brush shaft 227 comes to rest. Relay 205 also completes the circuit from battery through winding of sequence switch 210, upper contacts of spring 211 (6), back contact and left-hand armature of relay 205, contacts of sequence switch spring 220 to ground. Sequence switch 210 moves out of position 6 and into position 7.

)Vith the district sequence switch 220 in position 7 and sender sequence switch 710 in position 4, the fundamental circuit is again established over the path previously traced and relay 205 becomes operative. Relay 205 locks in the fundamental circuit as before and also closes a circuit from battery through the winding of sequence switch magnet 210, lower. left-hand contact of spring 215 (7 upper right-hand contact of said spring (2+12), front contact and left hand armature of relay 205 to ground through the contacts of sequence switch spring 220. Sequence switch 210 moves out of position 7 and into position 8 and the circuit of the updrive power magnet 224 is again closed through the right-hand contacts of sequence switch spring 215, front contact and left-hand armature of relay 205 and contacts of sequence switch spring 220. A circuit is also closed from battery through the winding of trip magnet 226 upper righthand contact of spring 220 (7 lower righthand contact of said spring (1-1-12) to ground. Trip magnet 226 becomes energized and on the first upward movement of the brush shaft 227 in the group selecting operation, the selected set of brushes 228, 229 and 230 are tripped into engagement with the terminals of the bank.

The stepping relay 700 which also operates in the fundamental circuit establishes a circuit from ground through its armature and contact, upper contact of spring 711 (4), conductor 722, contact of sequence switch spring 848 (2), conductor 836 and thence to conductor 720 (Figure 7), armature and back contact of No. 2 counting relay 716, winding of relay 717 to battery. Relay 717 operates but due to the shunt around the winding of relay 716 this counting relay remains inert. In the upward movement of the brush shaft 227, the brush 234 engages a metallic segment or commutator 237 for each group of terminals passed over by the brushes 228, 229 and 230 and a circuit is closed as follows for the relay 205: battery through the right-hand winding and contact and inner right-hand armature of said relay, upper left-hand contact of spring 223 (2+12) upper right-hand con tact of spring 238 (7 {}|8) commutator 237, brush 234 to ground. For each closure and opening of this circuit the stepping relay 7 00 is deenergized and energized permitting a pair of counting relays to be energized and locked. When finally the 0 relay 0perates,.it opens the fundamental circuit and at its inner left-hand armature and contact closes the circuit including the upper contact of spring 703 (4) for driving the sequence switch 710 out of position 4 and into position 6. The sender sequence switch 710 on leaving position 4 opens the holding circuits of the energized counting relays. As soon after the opening of the fundamental circuit by the relay 712 as brush 234 engages an insulating segment of commutator 237, the holding circuit of relay 205 is opened and this relay becomes deenergized. Relay 205 opens the circuit of power magnet 224 causing brush shaft 227 to cease its upward movement. Relay 205 also establishes a circuit from battery through the winding of sequence switch magnet 210, upper contacts of spring 211, (8), back contact and left-hand armature of relay 205 through the contacts of sequence switch spring 220 to ground. Sequence switch 210 advances out of position 8 and into position 9.

In the position 9 of sequence switch 210, a circuit is immediately closed from battery to search for an idle trunk,

205, lower left-hand contact of spring 223,

'(9+9-. upper left-hand contact-of spring 238 (9+9 to ground. Relay 205 becomes operative and locks in a holding circuit, provided the first trunk in the group, upon the terminals 231, 232 and 233 of which thebrushes 228, 229 and 230 are now standing, is busy. This holding circuit may betraced from battery through the lefthand windingof relay 205, contact of spring 221 (9+10), front contact and outer righthand armature of relay 205, upper left-hand contact-of spring 222 (2+11), upper righthand contact of said spring (9+16i) test brush 230, and thence to ground over the busy test terminal 233. As will be explained hereinafter, the busy condition of the trunk is indicated by the presence of a ground potential on the test terminal and an idle trunk is characterized by the absence of potential on the test terminal. Relay 205 on operating, closes a circuit from battery through the winding of sequence switch magnet 210, lower left-hand contact of spring 215 (9), upper right-hand contact of said spring (2+12), front contact and left-hand armature 205 through the contacts of sequence switch spring 220 to ground, advancing sequence switch210 out of'position 9 and into position 10. The brush shaft 227 is again moved upwardly to drive the brushes 228, 229 and 230 over the terminals to the bank The circuit of the power magnet'224 leads from battery.

through the wlnding of sald'magnet, righthand contacts of sequence switch spring 215,

front contact and left-hand armature of re -la'y 205 and thence to ground through the contacts of sequence switch springs 220. On

reaching the test terminal 233 of the first idle trunk, the test brush 230 finds no ground potential thereon andconsequently the relay 205 releases its armatures to open the circuit of the power magnet 224. The switch comes to rest and a circuit is closed at the same time from battery through the winding of sequence switch magnet 210, upper contacts of sequence switch spring 211 (10), back contact and left-hand armature of relay 205 through the contacts of sequence switch spring 220 to ground. Sequence switch 210 moves into position 11.

The circuits are now prepared selection and the fundamental circuit is established to control the brush selective movement of the oflice selector 350. This circuit may be traced from battery through the right-handwinding of relay 300 lower left hand contact of spring 303 (1), left-hand.

for the next tact of spring 613 (10), through the winding of the stepping relay 700, contact and outer left-hand armature of relay 712, contacts of spring 701, (6), contact of sequence switch spring 612 (10), brush 632, terminal 627, conductor 632, lower contact of sequence switch spring 219, brush 229, terminal 232, conductor 240, contact of spring 302 (1+4) to ground. Relay 300 becomes energized and locks in a circult from battery through its front contact and inner right-hand armature, through its outer right-hand armature and contact, lower right-hand contactof spring 303 (1+4) upper left-hand contact of spring 301 (1+4) and thence as above traced over the fundamental circuit to ground. Relay 300 closes a circuit from battery through the winding of sequenceswitc'h magnet 310, lower left-hand contact of spring 307 (1), front contact and left-hand armature of relay 300 to ground driving sequence switch 310 out of position 1 and into position 2; In position 2 of the sequence switch, a circuit isclosed for the updrive powermagnet 311, traceable from battery through the winding of said magnet, righthand contacts of spring 308 (2), front contact and left-hand armature of relay 300 to ground. The magnet 311, causes the upward movement of brush shaft 314 to select the proper set of brushes.

The stepping relay 700, which also energizes in the fundamental circuit, completes a circuit from ground through its armature and contact, lower contact of spring 709 (6), conductor 723, upper contact ofspring 849 (2) conductor 837 and thence to conductor 720 (Figure-7) armature and; back metallic segment ofcommutator 321 and a circuit is closed as follows for relay 300: Battery through the right-hand winding and front contact and inner right-hand armature, and through the outer right-hand armature and contact of said relay, lower righthand contact of spring 303 (1+4), upper right-hand contact of said spring, (1%+2), commutator 321, brush 318 to ground. This circuit holds the relay 300 energized and shuts out the stepping relay 700 in the fundamental circuit. The relay 700 deenergizes removing the shunt from around the winding of relay 716, permitting this latter relay to operate in series with relay For each brush tripping position passed over a pair of countingrelays are similarly operated until finally the 0 count ing relay 712 becomes energized The relay 712 opens the fundamental circuit and also closes the above traced circuit for advancing the sender sequence switch 710 out of position 6 and into position '8.

As soon, following the opening of the fundamental circuit at the sender, as, the brush 318 moves on to the next insulating segment of commutator 321 the circuit of relay 300 is opened and this-relay retracts its armatures to open thecircuit of power magnet 311. The relay 300 also establishes a circuit from battery through the winding of Sequence switch magnet 310, lower righthand contact of spring 307 (2) back contact and left-hand armatures of relay 300 to ground, driving said sequence switch out of position 2 and into position 3.

In position 3 of sequence switch 310 and position 8 of sender sequence switch 710, the fundamental circuit is closed as previously traced for controlling group selection at the ofiice switch. Relay 300 operates and locks as above explained and also closes the circuit from battery through the winding of sequenceswitch magnet 310, lower left-hand contact of spring 307 (3), front contact and left-hand armature of relay 300 to ground. Sequence switch 310 moves out of position 3 and' into position 4. The tripping magnet 313 is energized in a circuit from battery through the winding of said magnet, lower left-hand contact of spring 306 (3+7) to ground. The magnet 313 positions the trip rod so as to trip the selected set of brushes 011 the next upward movement of the shaft 314. In position 4 of sequence switch spring 310, the power magnet 311 is again energized in a circuit from battery through the winding of said magnet, righthand contacts of sequence switch spring 308, front contact and left-hand armature of relay 300 to ground. The brush shaft 314 is driven upwardly, tripping the selecting brushes 315, 316 and 317 andmoving them over the bank in the group selecting operation.

The stepping relay 700 upon energizing in the fundamental circuit establishes a circuit to ground through, its armature and contact, upper contact of spring 709 (8), conductor 7241, left-hand contact of spring 851 (41), conductor 838 and thence to conductor 730 Figure 7, armature and back contact of relay 731, winding of relay 732 to battery. In the manner already explained relay 732 operates and prepares a circuit for itself and relay 731 but the latter relay being shunted cannot operate at this time. As the brush shaft 314'moves from one group selecting position to another, it closes and opens the following circuit for relay 300 causing the 8110088811 6 deenergization of the stepping relay 700 in the fundamental circuitzbat-tery, through the right-hand winding, front contact and inner right-hand armature and outer right-hand armature and contact of relay 300, lower right-hand contact of spring 303 (1+4), upper left-hand contact of said spring (351+a) commutator 322, brushv 318 to ground. For each shunting of the stepping relay 700, an additional pair of counting relays are energized until finally the zero relays 712 and 713 become energized. The relay 712 on operating, opens the fundamental circuit and also completes the above traced circuit for driving sequence switch 710 out of position 8 and into position 10. In leaving position 8, the sequence switch 710 opens the holding circuits of the energized counting relays. At the time the last or 0 counting relay 712 operates the brushes 315, 316, and 317 have been driven to the desired group of terminals, namely the group in which appear trunks leading to the desired office.

As: soon, following the opening of the fundamental circuit by the counting relay 712, as the brush 318 engages the next insulating segment of commutator 322 the holding circuit of relay 300 is opened and this relay becomes deenergized to sever the circuit of power magnet 311, causing the brush shaft 314 to cease its upward movement. Relay 300 at the same time closes a circuit from battery through the winding of sequence switch magnet 310, lower righthand contact of spring 307 (4:) back contact and left-hand armature. of relay 300 to ground. Sequence switch 310 advances out of position 1 and into position 5.

Upon reaching position 5, the sequence switch 310 clloses a circuit from battery through the left-hand winding of relay 300, left-hand contacts of spring 309 (5+7) to ground. Relay 300 actuates and closes a holding circuit for itself, provided the first trunk in the selected group outgoing to the distant office, upon. the terminals of which the brushes 315, 316 and 317 are positioned, is busy. The holding circuit of relay 300 may be traced from battery through the right-hand winding and front contact and inner right-hand armature of said relay, outer right-hand armature and contact of said relay, upper left-hand contact of spring 305, (5+18), upper right-hand contact of said spring (5-l-6i), test brush 317 to ground through the test terminal 326 of the first busy. trunk. Relay 300 on operating closes a circuit from battery through the winding of sequence switch magnet 310, lower left-hand contact of spring 307, (5) front contact and left-hand armature of relay 300 to ground, driving said sequence switch into position 6. The circuit for the updrive power magnet 311 is now closed as previously traced and the brushes 315, 316 and 317 are driven over the terminals of the group to search for an idle trunk.

When the first idle trunk in the group is reached, there being no ground potential on the test terminal 326, the energizing circuit of relay 300 is opened. This relay remains energized for an instant, y means of the following holding circuit: Battery through the left-hand winding of relay 300, upper left-hand contact of spring 309 (5+7), upper righthand contact of said spring, +6), commutator 323, brush 319 to ground. lVith' the brushes 315, 316 and 317 accurately centered on the terminals 324, 325 and 326 of the idle trunk, the brush 319 engages. an insulating segment of commutator 323 and the holding circuit of relay 300 is opened. Relay 300 releases its armatures, the opening circuit of the power magnet 311 and causing the brush shaft to come to rest. Relay 300 also establishes a circuit from battery through the winding of sequence switch magnet 310, lower right hand contact of spring 307 (6) back contact and lefthand armature of relay 300 to ground, driving the sequence switch out of position 6 and into position 7. In this position a circuit is closed from battery through the left-hand winding of relay 300 upper left-hand contact of spring 309 (5+7) lower left-hand contact of said. spring (7) to ground. Helay 300 actuates and closes a circuit from battery through its right-hand winding and front contact and inner right-hand armature, outer right-hand armature and contact of said relay, upper left-hand contact of spring 305 tact of said spring (7+18) conductor 241, terminal 233, brush 230, upper right-hand contact of spring 222 (9+1G4), lower lefthand armature and said spring (10-ij5+18) to ground. Relay 300 remains energized in this circuit during the conversation period. It will be noted that when sequence switch 210 reached position 10%, the circuit from ground just traced was closed through test brush 230 to the test terminal 233. The application of ground potential to the test terminal and its multiples renders the trunk 23-9, 240 and 241 busy to all other district selector switches. Relay 300, upon operating, closes the circuit from battery through the winding of sequence switch magnet 310, lower leftehand contact of spring 307 (7) front contact and left-hand armature of relay 300 to ground, driving sequence switch 310 into position 8. As sequence switch 310 moved into position 6%}, a circuit is closed as follows and is maintained until the sequence switch leaves position 84;: ground through the upper righthand contact of spring 306 ('6; +3-l brush 317 to the test terminal 326 and its multiples before other switches. This groundpotentia-l on the multiples 326 identifies-the trunk 330, 331 as being busy. The district and ofiice selective switches have thus been posi- 5+18)', lower left-hand con-.

tioned to extend the incoming connection to trunk 330, 331, outgoing from the central switching office to the distant full mechanicalofiice to which the called line 510 belongs.

Since a detailed description of the operation of the incoming and final selective switches 500 and 501 is not essential to an understanding of the invention, these switches have been indicated in diagrammatic form. They may be of the power driven full mechanical type, being similar in general construction to the other switches shown in this case and more particularly to the character of the incoming and final selective switches disclosed in detail in the application of F. A. Stearn, filed June 3, 1921, Serial No. 474,702.

In the well known manner, the fundamental circuit for controlling the brush selection at the incoming selector switch is established and the brush shaft carrying the brushes 502 and 503 is driven upwardly. At the same time the stepping relay 700 in the fundamental circuit operates and closes a circuit from ground though its armature and contact, upper contact of spring 708 (10), conductor 726, upper contact of spring 852 (4) lower contact of springs 853 (5+9) conductor 842 and thence to conductor 719, Fig.

7, armature and back contact of relay 714,

winding of relay 715 to battery. The counting relays are operated and when relay 712 finally becomes energized the fundamental circuit is opened and" sequence switch 710 is driven into position 12.

The fundamental circuit is again closed and the incoming selector 500 operates in its group selecting movement. The stepping relay 700 energizes in the fundamental circuit and closes the circuit from ground through its armature and contact, lower contact of spring 708 (12) conductor 725, upper contact of spring 854 (4), conductor 841 and thence to conductor 720, Figure 7, armature and back contact of relay 716, winding of relay 717 to battery. A pair of counting relays are energized for each group of terminals passedover by the incoming selector switch and when finally the relay 712 attracts its armatures, the fundamental circuit is opened and sequence switch 710 moves into position 14.

Trunk hunting next occurs at the incoming switch and an idle trunk is chosen leading to the final selector switch 501. A fundamental circuit isestablished and the final selector switch is operated in its brush selecting movement; The stepping relay 700 which energizes in the fundamental circuit closes a circuit from ground through its armature and contact, lower left-hand contact of spring 707 (14), conductor'729, right-hand contact of spring 855, (7), conductor 843 and thence to conductor 720,

Figure 7, armature and back contact of relay 716, winding of relay 717 to battery. When the proper brush selecting position is reached the 0 counting relay 712 operates and the sender sequence switch 710 advances out of position 14 and into position 15.

The selection of the proper group of ten lines, next takes place and the relay 700 energizing in the fundamental circuit establishes a circuit from ground through its armature and contact, lower right-hand contact of spring 707 (15),; conductor 728, left-hand contact of sequence switch spring 856 (3) conductor 844, thence to conductor 733, Figure 7, armature and back contact of relay 734, winding of relay 735 to battery. At the end of the tens selection, the 0 counting relay 712 is operated and sequence switch 710 moves into position 16. The fundamental circuit is closed for units selection and relay 700, closes a circuit from ground through its armature and contact, upper contact of spring 707, (16) conductor 727, right-hand contact of spring 857 (2), conductor 845 and thence through conductor 720, Figure 7, armature and back contact of relay 716, winding of relay 717 to battery. WVhen the brushes 506 and 507 of the final selector switch reach the terminals 508 and 509 of the called line the 0 relay 712 is operated to open the fundamental circuit and to advance the sender sequence switch 710 out of position 16 and into position 17. In the well known manner, the called subscribers line is tested and if found idle, ringing current is applied to operate the bell at the substation;

Restoration of sender.

All selections having been completed, the register sender is no longer needed and may be restored to its normal condition. The initiation of restoration is effected when the sender sequence switch 710 reaches the position 17. In this position a circuit is closed from battery through the winding of sequence switch magnet 610, lowercontact of spring 606 (10) contact of spring 704 (17) to ground. Sequence switch 610 advances out of position 10 and into position 13. A circuit is now established from ground through the contact of spring 602 (13) brush 620, terminal 625, conductor 630, lefthand contact of spring 212, (11), righthand winding of relay 205 to battery. Re lay 205 operates and closes a circuit from battery through the winding of sequence switch magnet 210, lower left-hand contact of spring 215 (11), upper right-hand contact of said spring (2+12), front contact and left-hand armature of relay 205 through the contacts of spring 220 to ground. Sequence switch 210 thereupon advances out of position 11 and into position 12, and re lay 205 becomes deenergized.

If, at this time the operator in the originating oflice has inserted plug 104 of her cord circuit in the jack 105 of the assigned trunk 200, 201, or, as soon she does make the insertion, a circuit is established from battery through the winding of relay 106, sleeve of plug 104, sleeve of jack 105, lefthand low-resistance winding of relay 112, right-hand high-resistance winding of said relay to ground. Due to the high-resistance of the right-hand winding of relay 112, the flow of current is insuflicient to operate relay 106. Consequently the lamp 109 is li hted in a circuit from battery through said lamp resistance 108 and thence to ground as traced through the windings of relay 112. Relay 112 also operates and a circuit is established from battery through the contact of spring 216 (18-1-12), righthand winding of relay 202, conductor 200,

upper right-hand winding of repeating coil windings of the polarized relay 111, lower right-hand winding of repeating coil 110, contact and armature of relay 112, conductor 201, left-hand winding of relay 202, contact of spring 217, (18+12) to ground. The current flowing in this circuit operates relay 202 but is not in the proper direction to cause the energization of the polarized relay 111. Relay 202 in turn closes a circuit of relay 203 which latter relay establishes a circuit from ground through its armature and front contact, right-hand contact of spring 212 (12) right-hand win ding of relay 205 to battery. Relay 205 operates and closes a. circuit from battery through the winding of sequence switch magnet 210, lower left-hand contact of spring 215 (12), upper right-hand contact of said spring (2+12), front contact and left-hand arma ture of relay 205 through the contacts of sequence switch spring 220 to ground. The sequence switch 210 moves from position 12 into position 13, which is the talking position.

Sequence switch 210 on leaving position 12 opens at the upper right-hand contact of spring 213, the holding circuit of relay 601. Relay 601. becomes deenergized and closes a circuit from ground through its left-hand armature and back contact, lefthand contact of spring 605 (3+17), winding of sequence switch magnet 610 to ground. Sequence switch 610 advances into position 18 where a circuit is closed for restoring the J brush shaft 617 of the trunk selector switch 600. This circuit may be traced from battery through the winding of down-drive magnet 616, contact of spring 614 (18) to ground. In the normal position of the.

brush shaft 617, a circuit is closed from battery through the winding of sequence switch magnet 610, left-hand contact of spring 634 18), spring 618 and its normally closed contact to ground. Sequence switch 610 vwith subsequent calls,

Response of the called subscriber and 0e lease of the established connection.

hen the called subscriber at substation 510 responds,areversal of current is caused over the talking circuit in the well known manner to permit the energization of the polarized relay 111 in the outgoing end of the trunk circuit 200211 at the originating oifice. Relay 111' modifies the circuit of relay 106 by excluding the high resistance right-hand winding of relay 112. The removal of this high resistance increases the current flow sutliciently to cause the energization of the marginal relay 106. Relay 106 in, operating closes a, shunt circuit as follows around the lamp 109: battery, through the armature and contact of relay 106, resistance 107 i and. thence through the low resistance, left-hand winding of relay 112 to ground through the contact and armature of relay 111. Thisshunt circuit causes the extinguishment of lamp 109 and the operator is advised thereby that the called operator has answered.

At the end of the conversation when the called subscribed places his receiver on the switchhook, current over the talking circuit is again reversed, relay llldeenergized, relay 106 also deenergizes and the supervisory lamp 109 is illuminated. The originating operator removes the plug 104 of her cord circuit from the jack 105 of the outgoing trunk causing the deenergization of relay 112. 'Relay'112 at its armature and con tact opens the circuit of relay 202 which in turn releases the relay 203. Relay 203 closes a circuit from ground through its armature and back contact of spring 243 (13), lamp 206, to battery. The lamp 206 is lighted and notifies the cordless operator at the'machine switching office that the connection is no longer required and should be released. She thereupon actuates herdisconnect key 24 1- closing a circuit from ground through the contacts of said key, contacts of spring 245 (12+17), winding of relay 204 tobat tery. Relay 204 completes a. circuit from battery through the winding of sequence switch magnet 210, contact of spring 246 (12+17), contact and, armature of relay 204 through the contacts of sequence switch spring 207 to ground. Sequenceswitch 210 leaves'position 13. and moves intoposition 18 where a circuit is established for releasing the brush shaft. 227 of the district selector switch 250. This circuit may be traced from battery through the winding of the down-drive power magnet 225, lower right-hand contact of spring 222 (18), lower left-hand contact of said spring (Mi-+18) to ground. After the brush shaft has been fully restored to its normal position, a circuit is closed from battery through the winding of sequence switch magnet 210, lefthand contact of spring 208 (7+17), normal Sequence switch 210 by means of this circuit is advanced into position 1.

At the time sequence switch 210 leaves position 16;}- itopens, at the upper right-hand contact of spring 222, the holding circuit of relay 300. Relay 300 retracts its armatures and a circuit is closed from battery through the winding of sequence switch magnet 310, lower right-hand contact of spring 30. (8+17) back contact and left-hand armature of relay 300 to ground. Sequence switch, 310 is driven from position 8 into position 18 where a circuit is established for restoring the brush shaft 314 of the ollice selector 350. This circuit may be traced from battery through the winding of the downd-rive power magnet 312, lower contacts of spring 309 (18) to ground. In the fully restored position oi the brush shaft 314, a circuit is closed from battery through the winding of sequence switch magnet 310, upper right-hand contact of spring 307 (3+18), normal position segment 320, brush 319 to ground. By means of this circuit the sequence switch 310 is moved into its posi tion 1 and the circuit of the power magnet 312 is opened.

The opening of the talking circuit serves in the well known manner to bring about a release of the incoming and final selector switches 500 and 501.

E stahlishmcnt 0 a connection to a local. line in the central switching ofitce.

.which leads directly to the final selector switch 460 which has access to all of the special lines. There will be as many of these final selector switches as is necessary to handle calls made. into the group of special lines.

The initiation ofthe call, the responseby the originating operator, the assignment of position segment 235, brush 234; to ground.

' 330331 outgoing to the distant mechanical office, appear, it is necessary to perform a different combination of selections at the district and office selectors 250 and 350. Assume that the designation which governs the settings of the district and oflice switches to select a trunk having access to the group of special lines is represented by the key 819 on the operators key board and that the identity of the particular called line 444445 in the group is represented by the N0. 4 7 3 2. Accordingly the operator depresses key 819, the No. 4 thousands key 822, the No. 7 hundreds key 823, the No. 3 tens key 824 and the No. 2 units key 825. By inspecting the connections of the contacts of key 819 with the contacts of the registers 800, 810, 820 and 830, it will be noted that this key causes the district brush register 800, district group register 810 and the office brush register 820 to take exactly the same settings as key 821 which was used for the call previously considered. The office group register 830, however, is set in position 3 instead of in position 4 as in the former case. This different combination of settings of the district and oflice registers will determine that a trunk leading to one of the final selector switches 460 will be chosen. For simplicity it has further been assumed that the number identifying the called line 444445 is the same as the number taken for the called subscribers line 510 in the distant mechanical office and accordingly the numerical register 840, 850, 860 and 870 take the same settings as before.

After all the registers have been positioned in the manner hereinbefore explained, the sequence switch 610 moves from position 6 into position 10 where the previously traced circuit is closed for driving the sender sequence switch 710 into position 2 under the control of the registers and counting relays, district brush selection, district group selection and office brush selection take place precisely as hereinbefore described. At the end of this time, the se-.

quence switch 210 is in position 11, the office selector switch 310 is in position 3 and the sender sequence switch 701 is in position 8. The fundamental circuit is again established for controlling group selection of the office switch 350. Relay 300 operates, locks in the fundamental circuit and completes a circuit for driving sequence switch 310 into position 4 where the brush shaft 314 is moved upwardly under the control of the up-drive magnet 311. The stepping relay 700, energizing in the fundamental circuit, closes a circuit from ground through its armature and contact, upper contact of sequence switch spring 708, conductor 724, lower contact of sequence switch spring 858 (3), conductor 839, thence to conductor 733, Figure 7, armature and back contact of relay 734, winding of relay 735 to battery. Relay 735 operates and prepares a circuit for itself and relay 734.

hen the brushes 315, 316 and 317 have been driven to the group of terminals containing the terminals of the trunks leading to the final selector switch 460, the 0 counting relay 712 is operated to open the fundamental circuit and also to complete a circuit for driving the sender sequence switch 710 out of position 8 and into position 10. Following the group select-ing operation the sequence switch 310 is advanced into position 6, where trunk hunting ensues. The brushes 315, 316 and 317 are driven into engagement with the terminals 327, 328 and 329 of the first idle trunk in the group which leads to the idle final selector switch 460. Thereafter the sequence switch 310 advances into position 8.

Immediately that the trunk 332, 333 and 334 is selected and the sequence switch 310 has reached position 8, a circuit is estab-- lished as follows: battery, through the winding of relay 400, lower left-hand contact of spring 416 (1+14), upper left-hand contact of said spring,. upper left-hand contact of spring 406 (14-10), lower right-hand contact of spring 405 (14-15) resistance 430, conductor 332, terminal 327, brush 215, and thence as previously traced over the fundamental circuit through the winding of the stepping relay 700 and returning to brush 316, terminal 328, conductor 333, resistance 432, upper left-hand contact of spring 417 (16+10), upper right-hand contact of said spring (1+15) to ground. Relay 400 becomes energized and closes a holding circuit for itself from battery through the winding and front contact and lefthand armature of said relay, upper left-hand contact of spring 406 (1+10) and thence over the fundamental circuit as traced to ground. Relay 400 in operating completes a circuit from battery through the winding of sequence switch magnet 410, upper right-hand contact of spring 412 (1), front contact and right-hand armature of relay 400 to ground driving sequence switch 410 out of position 1 into position 2. Immediately that seway to position 2, a circuit is closed from

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