US1244571A - Telephone-exchange system. - Google Patents

Description

J. h. WRIGHT.

TELEPHONE EXCHANGE SYSTEM Patented Oct. 30, 1917.

' APPLICATION FILED PEI. 26. ISIZ; 1,244,571 l4 HEETSSHEET L s m W W WEB ' iv-palm J. L. WRIGHT.

TELEPHONE EXCHANGE SYSTEM. APPLICATION man FEB. 26. m2,

Patented Oct. 30, 1917.

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1.1. WRIGHT. [A TELEPHONE EXCHANGE SYSTEM.

AFPLICATION FILED FEBJEJISIZ I V 1,244,571. Patented 00t.30,1917.

J. L. WRIGHT.

TELEPHONE EXCHANGE SYSTEM. APPLICATION HLED FEB. 2a. 1912.

Patented Oct. 30, 1917.

H SHEETS-SHE ET'L 1 L. wmHTQ TELEPHQNEEXCHANGE SYSTEM.

'Arrupmpu FILED ran, 25. m2.

Patented Oct. 30, 1917.

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wirtweooeo l. L. WRIGHT.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION HLED FEB. 25. \912.

Patented Oct. 30,1917.

3. L. WRIGHT.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION HL'ED FEB. 26" !9l2- Patented Oct. 30, 1917.

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AEPPLICATIOER FILED FEE. 26. 1-912- Patented Oct. 30,1917.

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Patented Oct. 30,1917.

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APPLICATION E!L:D FEB. 26. [M2- l. L- WRIGHT.

TELEPHONE EXCHANGE SYSTEM.

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' Patented Oct 30,1917.

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A. L. WRIGHT.

TELEPHONE EXCHANGE SYSTEM.

Patented Oct. 30,1911.

APPLICA T|0N FILED FEB- 26 I912.

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I. LIWRIGHT.

TEEEPHONE EXCHANGE SYSTEM,

APPLICATION FILED rmza. I9I-2.

1,244,571. Patented Oct. 30,1917.

' 14 SHEETS--SHEET :4

UNITED STAITES PATENT OFFICE.

JOSEPH L. WRIGHT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASBIGNOK, BY MESNE ASSIGNMENTS, TO JAME R. GARFIELD, TRUSTEE, OF OLEVIELAND, OHIO.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Oct. 30, 1917.

Application filed February 26, 1912. Serial No. 680,015.

To all whom it may concern:

Be it known that 1, Josnrk L. Wmon'r, a citizen of the United States, and resident of lVashington, District of Columbia, have inwented certain new and useful Improvements in Telephone-Exchange Systems, of which theifollowing is a specification.

My invention relates to telephone ex change systems, and especially to semi-auto matic. systems -whieh employ switching mechanism controlled by operators for efli'cctin; connections between subscribers.

The general object of this invention is the improvement of the systems mentioned.

Some of the improvements may be stated as follows:

To simplify the operators impulse or sending device, so that the impulses instead of passing through the various cam springs and contacts of the key-board are sent directly through the operators circuit to the automatic switches.

To regulate the impulses from the sending device when transmitted to the driving magnets oi the various switches, and to re move the static charge from the impulse conductors:

To insure positive release between the various automatic switches:

' matic exchange with doublc supervision and able means.

control by the manual operator To prov de special switclnng means which can be common to more than one op orator for originating calls and supervising connections: and

To form .the various primarytrunks into grou'ps-aiul-to provide each group with an independent cont-rolling means for pickingout .idle key-sets.

'lo dispense with the operators transmitter so that it will not be necessary for her to ask the number of the wanted party,

as thisfunction is controlled automatically by a phonograph attachment or other suit- My invention is illustrated in the accom- .panymg drawings, wherein:

Figure 1. shows a subscribers line equiptogether with a time element controlling device or kiclcotf switch.

Fig. T'shows the circuit of the operators key-setswitch and its associated Shifting switch.

Fig. 8 shows an operators keyboard and sending" device.

Figs. 8? and 8 show the circuits whereby the operators transmitter is replaced by either a phonograph or suitable tone test signal.

Fig. 1" shows a portion of an operators cord circuit and trunk terminating in a manual exchange.

Fig. 2* shows a trunk from the manual exchange terminating in the semiautomatic exchange in a first selector switch.

F ig. 6 shows the circuit used for control for distributing the trunks from the manual exchange .to operatoifs key-set switches.

F ig. 2 shows the circuits and method of controlling reverting calls.

Fig. 9 shows the arrangement of the various figures for a call from the subscriber in the semi-automatic exchange to another subscriber in the same exchange.

Fig. 10 shows the arrangement of the rariousfigurcs where a call is from a subscriber in a manual exchange to a subscriber in the semiautomutic exchange.

Fig. 11 shows the arrangement of the figures for a reverting call.

Referring to Fig. 1. the subscribers staiion at A is equipped with apparatus usual in common battery exchanges aud'the line wires from this station terminate at the central ofiice in a line relay 2. The line relays are divided into groups, there being ten groups to each one hundred lines. Each group of ten line relaysis common to one switch busy, while the line relay when ac' tuated makes the individual contact in the primary selector switch busy.

The switch W starts to rotatewhenever the group relay is energized, and continues to rotate until an idle primary switch is picked cut.

Referring now to Fig. 2, the primary switch 0 is shown, which picks out the calling line. This switch first starts to rotate until the row wiper 64 picks out the busy row contact and after reaching this contact it ceases to rotate and steps vertically until the individual busy test contact, leading to the line relay 2, is found.

The first selector switch is shown at D, and responds to impulses from the sending device to pick out an idle trunk leadingto a second selector switch in the proper row.

The wipers 63 ofthe primary switch C and wipers 56 of the first selector switch D are joined, as indicated by the heavy lines,

for conversational purposes. The tip and sleeve conductors are separated by the con densers 4.3 and 4:4. Through-relay 23 and the retardation coil 26 talking current is furnished to the calling subscriber. Relay 21 is the starting relay of the primary switch,

. and corresponds to the line relay 2 (Fig. 1), as it controls the action of the operators key-set switch (Fig. 7). Relay 22 is the row test relay, while 2% is the individual test relay. Relay 25 is operated when the key-set switch picks out the trunk, and re mains energized while the impulses are being transmitted, thereby opening the trunk con" duo-tors. Relay 27 is the test relay of the first selector switch, and remains energized while the. test wipers 57 are passing over busy contacts. Belay 28 is energized whenever'either the rotary or vertical magnets of the primary switch are operated and also when the vertical magnet of the first selector switch is operated. The circuits of these magnets are normally completed-through the back contactsof this relay-28, and so, there fore, when it is actuated, the ma gnct circuits 5e are opened. The action thus set up between the relay and the magnets causes the latter to vibrate and to continue to do so until their-energizing circuits are opened. The resistance coil i2 is placed in series ith the rotary relay 29. This relay. rec ves impulses from the operators sending de'yice and operates magnet 34, causing the switch D to rotate. operaixes, it closes its associated contact sprin 'sand places ground between the coil and t e Winding ofthe relay 29. This action of the ma et '34 serves to regulate the action of he repeating relay 29 and the magnet 34. This arrangement does away with the. necessity for line adjustment becalled subscriber answers.

lVhen the magnet 34 tween the repeating relay and the magnet which it operates and also serves to take up any irregularity ofthe impulses transmitted by the operators sending device.

In case the conductors leading to the repeating relays have any static charge, it is dissipated bythe ground being placed between the coil and the relay at the end of every impulse received from the sending device.

Referring now to Fig. 3, the second selector switch at E is operated first in a rotary direction, to pick out the row and then in a. vertical direction, to pick out the idle contact in the row, and is similar to the firstselector switch shown at D. 81 is the repeating relay, and is in series with the regulating coil 86. 82 is the interrupter relay corresponding to relay 28 (Fig. 2). 83 is the test relay used in picking out an idle connector switch.

' Referring'now to, Fig. 4, the connector switch G is provided with a set of wipers 390, leading to talking conductors of the called line, and also with wipers 391 leading to thccut-ofl' relay 108 (Fig. 5). 305 and 310 are the repeating relays and respond to impulses from the operatorssending device. 315 is a control relay and re-' moves the relay and retardation coil 335 from the wipers, while the switchG is pass ing over busy contacts. 320 is the tip battery supply relay, and responds when the called subscriber answers. 340 is the ringing relay, operated. by the commutator 370. This relay is cut off by the action of the relay 330 controlled by relay 320 when the 345 is the busytest relay, and upon acting when a busy line is found, locks itself through the test wire 306. This relay connects a suitable busy tone test, which is connected to the wire 341,

'to the trunk conductor 301, si naling thecalling subscriber when the cal ed for line is bus". '-'Tl 1e action of this relay also operates 'tlie release magnet 365, restoring the switch Gr. A controlling or party line distucts and wiper oi": the portion J cut on the generators 2356, 357, or 359 to either thev tip or sleeve contact of the ringing relay 340. The contacts and wiper of the portion 1 serve to restore the distrilniting switch to its normal or idle position. The contacts and wiper of the portion H serveto connect ground to either the tip or sleeve contacts of the ringing relay 3&0. When theportion tributing switch is shown at F. The con- I J cuts on generator to the tipcontact, the

portion H cuts-on ground .to the sleeve. contact, and when the portion J cuts on generator to the sleeve contact, the portion H cuts on g, M11311 to the tip contact. With this arrangement, it is possible to ring subscrib: ers bells connected to either tip or sleeve side of the line to ground, as Well as to'ring .thei'n over a. metallic circuit. Portion H of the switch also serves to release the connector switch G after the called subscriber hangs up his receiver, or when the calling subscriber hangs up in case the called subscriber does not answer.

lVhen the. switch F is. in its normal position, the wiper of H. rests on the. contact 334-. the wiper of Tom the contact 336, while the wiper of J rests upon the contact A suitable tone test is connected to the wire 392, and is connected to the. contact of the ringing relay 340 through the condenser 370 and retardation coil 605, so that whenever this relay operates, the calling subscrl or is aware that the called subscriber is being rung.

The two repealing relaysf-SOS and 310 each have windings connnon to the resistance coil 370. In this connector circuit. the impulses are regulated by both the rotary and vertical magnets 350 and 355 respectively, and also by the action of the magnet 360. controlling the switch 1*.

Figj 5 shows a subscriber's station at AA connected to the regular lineequipment.-

Connected to this line is a polarized relay 120. This relay is commie-ted to the line through the terminals 116 and 117, and also connected to the'jack 110, which is located before a special or information operator. This jack has an associated lamp 109. which i lighted-by the armature 114 engaging the Contacts 115. This polarized relay is tuned or responds to the same current as the sub scribers bell formerly located at Theregular o|- erator receiving a call for this line. not knowing that the telephone has been removed. puts the call through ill the regular manner, thereby causing the generator current to be placed on the called line. which would ordinarily have operated the subscribefis bell at A. instead of. however. operating this bell, the relay 120 is operated. causing the lamp 100 to light. The special operator thereupon places the. plug into the jack 110. and connects hcr telephone set across the conductors 105 aml 1043. This action energizes the tip rclau-in the connector circuit (Fig. l) preventing any further 'action of the ringing relay. lhc special operator informs the calling sub- Soriber that the number of the party he has called for has been changed, and gives him the new number. The jack 110 is provided Wvith designating strips. in which are pla ed -both the old and the new number of the party whose telephone has been changed.

"-lho calling subscriber thereupon hangs up his receiver, calls again. and gives the regular operator the new number.

The special operator. .-\vithdrawing the plug from the jack 110. releases the connector in the same manner as would a called subscriber.

Referring now to Fig. (l. the witch shown at Y corresponds to the switch \V (Fig. l) and picks out an idle opcrators key-set switch.

The switch X is the time. element control switch and comes into action when the relay 1550 and the relay 132 have been held energized beyond thc maximum time limit. The relay 132 is energized as soon as an idle keyset switch is picked out. and should only remain energized long enough for the keyset switch (Fig. 7) to pick out the tenth contact in the tenth row. The magnet, 77 causes the switch X to rotate when the contact springs 30 are closed by'a suitable cam on the sending device. These contacts are closed once at each rotation.

\Vewillassumc that the relays 132 and 130 have been held energized beyond the maximum time and the switch X is rotating. When the wiper .1 reaches one of the contacts connected to the wire 13!), the circuit of relay 78 is closed to ground through the contacts of relay 13-32. The switch X continues to step at ea h rotation of the sending dc vice. 'and when the wiper :1 reaches one of the contacts to which the relay T6 is collnccted. this relay operates and performs the following functions: (lround is placed on the wire 14!) through the wiper and con tacts of the. lower bank of the switch \V (Fig. 1) to wire (30 operating relay Zl lherc by causing the. switch I) to take one step. Ground is also placed on wire l'll. H2 to the release magnet ltiU of the switch M. thereby restoring it. The wires 18 and HR are also opened. thereby disconnecting relay 5 and relay 21. The falling back of this lattcr rclay. disconnects relay li-ill (Fig. (5) unlocl ing relay TH. and no further action takes place.

if a calling subscriber is (Ulllltt'tttl to the primary switch t. and a faulty connection takes place. as just described. he can hang up his receiver and as the switch l) has taken one step. the. circuitof the release magnet 132 is closed and the switch will restore, after which the switch l) drops back. .H'tcr hanging up. the subscriber can mak' a recall. and becoimconnected to another trunk.

'lhc switch X performs no functions with regular connections. unless the key-set switch aml trunk should become tied up. whereupon it comes into play aml releases the tied-up apparatus.

Referring now to Figs. T and h. the keyset switch and operatouskev-hoard and. 'sendil'ig device are shown. -carr1es the wipers 161 It; and 11M d The switch M fact, this switch operates in the same manner as the switch (3 (Fig. 2). "l-he wipers 167 connect to the tip and sleeve sides ol the trunk shown in 2. over which the.

operator converses with the calling subscriber, and over which the impulses are transmitted. 168 is the row wiper and picks' out the group of ten, in which the calling trunk is located. Relay .154 is connected to the individual test wiper which picks out the particular trunk in the group calling. Relay 156 is the signal relay, and pulls' up in series with relay 25 (Fig. 2) when the trunk is picked out, and when energized closes the circuits of the two lamps 243 and 244, (Fig. 8), notifying-the. operator of a call. Relay 152 is the starting relay and corresponds to relay 21 (Fig. 2), while 153 is the row test relay. Relay 155 responds when the operator presses the answering button 248, thereby connecting her telephone set across the tip and sleeve conductors of the trunk. 157 is actuated when the operator presses the starting button 247. The action of this relay discon' nects-relay 155, and connects the starting wire controlled by the cam 231 to the stepping magnet 161, thereby causing the switch arms tmstep over the banks N, O, P. This stepping magnet is operated once at each rotation of the sending device and cuts on the impiilses from the keyboard in regular order. The order inwhich these impulses are transmitted, is as follows: At the first rotation of the sending device, impulses cor responding to the thousands are sent over the tip side of thetrunk. At the second rotation, a singletest impulse is sent over the sleeve side of the. trunk. At the third rota tion, ".Lnpulses corresponding to the hundreds are sent over the tip side of the trunk, and at the fourth rotation, a single test impulse is sent over the sleeve side of the trunk. At the fifth. rotation, the selective ringing impulses are sent over the tip side of the trunk, and at the sixth rotation the hundreds impulses. are sent over the sleeve side of the trunk. At the seventh rotation, the tens impulses are sent over the tip side of the trunk, and at the eighth rotation, the

single test impulse is sent over the sleeve side of the trunk.

At the next rotation of the sending de vice, the wiper passing over the bank of contacts P, closes the circuit of the relay 158, causing the switch to rapidly rotate until it reaches itsnormal position. Just beforereaching its normal position, however, the circuit of'the release magnet 166, of the key-set switch M is energized, there .by restoring it to its normal position and preventing the operator listening in or in- I te'rfering with the connection.

, Relay163 corresponds to relay 2S 2), and causes the magnets 1.64, 105 and 161 to vibrate-until their energizing circuits are opened.. Thoperators keyboard, shown in Fig. 8, consists offive rows of buttons, each row having ten buttons. Number 1 button of each row is connected to a contact operated by the earn 232. Number 2 button of each row is connected to a contact oper ated by the cam 233'. Corresponding buttons in' each row are connected to the same contact. The contact controlled by the cam 232 is closed just long enough to keep the the impulses are connected to either the tip or sleeve side of the trunk, depending upon the position of the arm in regard to the contacts of the bank N. The buttons or keys shown in these five rows, in Fig. 8, are of the usual locking and indicating type. When any one button of a certain row is de pressed, it will release the button formerly depressed. The buttons 246, 247 and 248 are of the noirlocking type, and the contacts controlled by them are only closed while the operator is pressing the button.

Referring now to Fig. l the operators cord circuit terminates in .a plug P The answering end of the cord circuit is not shown, but the talking conductors are separated. by condensers in the usual manner. The sleeve relay 415 is energized in series with relay 425 when the plug is placed in the jack J The action of the relay 415 lights the lamp 411. tip supervisory relay and is actuated when the called partyanswers.

The portion of the trunk shown terminates at the manual exchange in the jack J through the contacts of relay 430. The jack J hasassociated with it a signal lamp 414, and a button 416. The lamp lights when the operator at the semi-automatic exchange answers. When the operator at the manual exchange presses the button 416, the relay 430 is operated, severing the trunk circuit and connecting her telephone set across the out-going end, thuspreventing the calling subscriber from hearing her repeat the number to the operator at the semiautomatic exchange.

Referringnow to Fig. 2, the trunk con-- doctors 412, and 413 from the manual exchange are connected for conversational purposes to the wipers 447 of the first selector The relay 410 is thev Th e and will respond when the trunk plug P is inserted in the jackJ The coil"495,"

however, is of such a high resistance that the relay 410 (Fig I) will not pull up or even hold up through it. Relay M5 is actuated when the keyset switch picks out the a trunk and in turn closes the circuit of relay H0. This. latter relay disconnects relay 435. which is the starting relay and cor- Relay 4'50 is of a high resistance, and is actuated when the called subscriber answers. The action of this relay shunts \out the resistance coil 495,. thereby actuating relay 410 (Fig. 1), notifying the operator atthe manual exchange that the subscriber at the semi-automatic exchange has answered his telephone.

Referring now to Fig. 6, the circuit shoWn is similar to that of Fig. 6. In fact, the main diii'erence is that the time element switch, instead of releasing the various switches after a predetermined time, simply removes ground from the winding of relay 130. All of the connections of the switch Y remain the same. \Vhen the relay 76, belonging to the time element switch, is operated, the relay 130 is disconnected. This controlling circuit provides against tying up the trunks from the manual eX- changein case several operators plug into trunk jacks at the same instant, thereby holding the relay 130 energized by parallel paths, as the wire 79 is multipled to a grmip of trunks. In case such a condition should arise, the control switch acts after a suitable time, operating relay 76, thereby unlocking relay 130, thus preventing any tie-up.

Referring now to Fig. 2", thespecial first selector switch shown as DD is the same as that at D (Fig. 2) The relay 740 is the test relay, while 7 50 is the rotary repeating relay; Relay 735 responds when the opcratorls key-set switch (Fig. 7) picks out the trunk. The keys or buttons 726, 7 27 and 741 are placed before the operator and associated with a key-set switch such as shown in Fig. 7.

By pressing button 726, ground is connected to wire 1'40, thereby energizing relay 152 of Fig. 7, causing the switch M. to rotate until the last or tenth row contact is found. This tenth contact is connected permanently to ground, and therefore, the switch after reaching this contact will step up vertically until the tenth contact in therow is found. This last or tenth contact connected permanently to battery B. Therefore, the switch M will come to rest when this contact is picked out. Other contacts belon ing to this set lead to wires 59, 60, .61 and 62 of the special reverting call switch (Figffl T e special first selector switch and can call any subscriber in the exchange. ltclay 730 acts when the called party answers, and lights the lamps 724. One of the lamps is individual to each operator, that is. where the samespecial switch ckinmmu'to a group ofoperators. ln case'the switch wasindividual to a special operator such as the chief or information operator, only one lam p" 724 would be needed. answers, the operator, pressing button. 741 connects her telephoneset across the trunk wires, allowing her to converse with the called party. To release the switch or switches, the operator presses button-727, thereby connecting an impulse from the'cam a 728 to relay/T25. The action ofthisrelay places a momentary battery impulse to the release magnet 270 and also to the-test wiper 7418, thereby releasing both the first selector and second selector switches.

Other features in connection with the various figures will be brought out 'inthe de- 'tailed description of operation.

In descril 'n'g the operation of my system,

lay 4, which in turn .connectsground' to one terminal of the relay 5, and also closesthe circuit of the stepping magnet 7. The stepping magnet 7 operating closes the circuit of relay 6, which in turn opens the circuit of the magnet, causing it to vibrate and step around the wipers of the switch This switch will continue to rotate untilan idle n'imary switch, such as shownat C (Fig. 2) isyfound. As soon as such an idle switch is found, relay 5 is placed in series with relay 21 (Fig. 2), by the fi'illowing path: ground. contact of relay 4'. 5, 18, contacts of relay 76 (Fig. (3), 148, upper bank of switch W, 14, 21, 70, contact of relay 24 to batery B. The relay 5 becoming energized opens the circuit of the stepping magnet 7, bringing the switch \V to rest. Relay 21 operating closes the circuit of the rotary stepping magnet 31 by the following path: -batteryB, l80,bac-k contact of relay 24, 71, contact of relay [28, back contact of relay 22, 31 to ground. The operation of magnet 31 causes the primary switch C to rotate until the wiper 64 reaches the busy contact, to which is connected wire 13, leading to the contacts of relay 3.

The wiper 64 is carried on the same spindle with Wipers 63 and 65, and while the switch is.=mtating, the wiper 64 passes over \Vhcn the called party.

I contacts rendered busy-by the action of re lay 22,

' tery .lay 3. As there are ten of these group relays to each one hundred lines, it follows that the wiper 64, to reach its-extreme position, passes over ten contacts.

There are ten sets of individual contacts arranged in vertical rows, associated with each row contact, and which the wipers 63 and 65 respectii rly engage. It therefore follows thatafter the switch picks out the group in which a line is calling, it will after: ward step vertically until the wipers engage the contacts of the calling line. I

As soon as the row contact is found, the circuit of relay 22 is closed as follows: bat- B, 80, contacts of relay 24, 71, 22, 64, 13, contact of relay 3 to ground. The relay 22 operating disconnects the rotary magnet 31, and in its place connects thevertical magnet 30,thereby causingthe switch to step vertically until the busy individual test As soon" as suchsa contact is found, the circuit'of relay 24 is closed by the following path: battery B, 24, ,68, 67, 11, contacts of relay 2 to ground through the. contacts of relay 1. The. relay 24 operating opens the wire 71, disconnecting re which in falling back disconnects relay 24 from wire 67 and connects it instead to wire 66. The relay 24 is now placed in contact is found.

series with relay 1 and the operating of this a latter relay disconnects line relay 2 and the connects battery to .connects ground to the retardation coil 26,

, key-set switch (Fig. 7).

' 136 to relay -group relay 3.

23 and 25, and the falling back of relay 22- and battery is thereby supplied to the calling subscriber for talking purposes.

The relay 21 remains-ener wed until the primary switch finds the ca ling 'line, and until the key-set switch finds the calling trunk. The relay 21 when first actuated places battery on the wire 79 to relay 130 to ground, and also places battery towire 362 leading to the individual test contact of the The relay 130 operatingcloses the circuits of the stepping magnet of the switch Y through the normally closed contacts of relays 131 and 132. The switch magnet 133. in operating closes the circuit of the interrupter relay 134, which causes a vibrating efl'ect between the magnet and the relay, and the switch will continue to rotate until an .idle key-set switch is found. Whensuch a switch is found, as shown in Fig. 7, relay 131is placed in series with relay 152 Fig. 7 by the following path: ground, contacts of relay 130, 131, 138, through the ban! contacts of Y, 140, 152,195, 196,197, to batt'ry through the operators jack 400.

Relay 131 operating places battery on wire 132, causing it to operate. As

soon as thislatter relay operates, it places.

' keyset switch to The operating of relay 24 the windings of relays lamps 243 and 244 (Fig. 8).

tinue to rotate until'the row contact is found,

.whereup'on the circuit of the relay 153 is closed by the following path". battery contacts of relay 152,176, 153,

139, contacts of relay 132 to ground.

The action of the key-set switch M is identical with that of the primary selector switch C (Fig. 2). I i The operating of relay 153 disconnects the rotary magnet 165 and in its place connects the vertical magnet 164, thereby causing the step vertically until the busy individual test soon as tl1 r'lay 154 is closed astfollows: ground, 62, 80, contacts of relay 21 to battery' B.

tical magnet causing the key-set switch M to rest on contacts leading to the calling contact is found. Asthis contact is found, the. circuit of The operating of relay 154 discon-- nects relay152, thereby cutting off the ver-.

primary trunk (Fig. 2). Relay 152 becoming disconnected opens the circuit of relay 153, and'this latter relay in falling back laces relays 156 and 25 in, series by the folowing path: ground,- backcontact of relay 153, 175',"back contact of: relay 157, 202,.

contacts of relay 155, 156,493, contacts of .relay- 158, 176, 1.69, 59, 25 tobattery B through the contacts .era'ting of relay '25 of relay 24. The opdisconnects relay 21- and relay 5 (Fig. 1).

The releasing of relay 5.

frees the'switch W, allowing it to pick out 3 other primary switches.

Belay 156 operating places battery on wires 181 and 183, thereby lighting'the two As soon as relay 21, in Fig. 2, became dis- 7 connected, battery was removed from the individual test contact of the key-set switch, thereby allowing the relay 154 to-fall back. The action of relay 21 also opens the circuit of relay 130, which inturn opens the circuit of relay132, and allows the switch Y to be used by other trunks in picking out key-set switches. V

In the present system, I have provided ten primary switches such as shown in Fig. 2, for each one hundred lines. Each group of ten primary switches, as shown in Fig. 2, is provided, with one Y switch for picking out idle key-set switches."

The wire 141, leading fromthe Y switch to the row contact of the key-set switch, is

Images