US1606019A - Telephone system - Google Patents

Description

Nov. 9, 192a. 1,06,019

' H. D. CURMER ET'AL TELEPHONE SYSTEM Nov. 9, 1926. --l,60"6,0l9

H. D. CURRIER ET AL TELEPHONE SYSTEM EramZZZzzrrzler 55017952755757? Nov. 9, 1926. 1,606,019

H. D. CURRIER ET AL TELEPHONE SYSTEM Filed March 23. 1921 4 Sheets-$heet 4 Patented Nov. 9, 15926.

nears stars were PATENT HIRAM D. CURRIER, OF CHICAGO, AND GEORGE E. EATON, OF OAK PARK, ILLINOIS, ASSIGNORS TO KELLOGG S'WITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE SYSTEM.

Application filed March 23, 1921.

Our invention relates to multi-oiiice systems, that is, systems in which two or more exchanges are interconnected by means of trunk lines and trunking calls between exchanges are handled over these wires by operators in the originating exchange who pass the calls to operators in the distant exchanges, which latter complete the connections to the called subscribers lines.

In the system of our invention we have abandoned the former practice which involved A operators cutting in on the B operators head telephone over an order wire, passing the wanted number, the A operator then receiving the designation of the trunk to be used, and plugging into that trunk with her calling cord, while the B operator plugged into the called line. In the system embodying our invention, the A operator reaches the B operator by plugging in with the calling cord into a trunk jacket, and automatic selectingswitch mechanism then extends the call to an operator in the distant exchange, and namely to an idle operator there, and connects directly into her head telephone. This permits us to do away with B operators in the sense of operators who handle trunk calls only and all operators in the system put up local calls which are completed in their own exchanges, and also serve as B operators in the sense that they receive calls transferred from distant exchanges and complete the connections required for such calls.

A particular feature of the present invention consists in this that when a trunking call has been completed from a calling subscriber in one exchange to a line of a called subscriber'in a distant exchange, the interofiice trunk is released and rendered available for further use instantly upon the conclusion of conversation as a consequence of acts performed at the connected substations. A considerably greater number of trunking calls can thus be passed over each inter-office trunk than in the previous systems in which the trunks are freed only by the operators themselves, as it would frequently happen that an operator would be busy with other work and could not promptly take down a cord circuit whose use was finished.

Other features of the invention will be found in an improved system of signals for Serial No. 454,978.

the operators, and these and other particular items of novelty will be explained in the description and pointed out in the claims.

e have illustrated our invention in a circuit diagram consisting of Figure 1, which comprises parts 1, 2 and 8, while Figure 2 illustrates a modification of the invention.

Referring first to Figure 1, in part 1, We have illustrated a subscribers telephone line circuit and a cord circuit suitable for interconnecting local subscribers lines within one exchange, which we have designated B. The said cord circuit may also be used for trunking calls to distant exchanges, and when its calling plug CP is inserted in a trunk switch jack 67, (referring now to part 2) the automatic selecting switches C and D are set into operation to extend the call over the interoliice trunk wires :0 and 3 and land it at the distant exchange E (part 3) in the ear of some operator there who is not busy at the time, that is, one who has not her head telephone cut in on some other local cord or trunk, for it will be understood that at exchange E the operator will be provided with local cord circuits identical in character with the one shown in Figure 1, part 1.

The system as a whole, therefore, may consist of two exchanges B and E, at which the operators will have identical equipment, that is, a suitable number of local cord circuits, such as shown in Figure 1, part 1, and also a suitable number of trunking cord circuits, such as shown in Figure 1, part 3. Furthermore, before each operator will be suitable trunk jackets 67 connected with switch pairs, such as O and D, so that any operator at any exchange can in addition to establishing local connections pass trunk calls to distant exchanges as well as receive trunk calls from such distant exchanges.

To describe the various instrumentalities in a general way, at A we have shown a common battery subscribers local substation connected atv the exchange with a usual form of line circuit comprising line relay LR and cut-off relay CO, together with multiple line lamps LL. The operators cord circuit shown in Figure 1, part 1, comprises an an swering plug AP and a calling plug GP, connected by talking wires which are indicated by the heavily marked lines. It is provided with answering and calling super visorysignals and the necessary relays for controlling them and with suitable relay apparatus for providing the various features now considered necessary to a modern manually operated telephone switchboard, such as secret service, automatic ringing, instantaneous disconnect, line lamp recall, etc.

The apparatus for transferring trunking calls from one exchange to another includes a number of spring jacks 67 at each operators position which terminate in multiple contacts located in a number of finder switches as C, and one of these will automatically select a jack 67 in which an operator has inserted a plug, such insertion serving to initiate the travel of an idle switch C. When the switch C has completed its operation, the switch 1) at the distant exchange will be set in motion, and it comprises suitable magnets, relays and oftnormal springs to effect theautomatic selection of an idle trunk cord of the kind shown at E in part 3. y y

he latter has but a single plug 167 to which extend the talking conductors indicated by the heavily marked line and suitable relayinstrumentalities and circuits for testingg ringin and supervising at the exchange E, an also for extending the required signals back over the trunk line to the originating exchange B.

A more complete understanding of the -precise arrangement of the parts and their operation, one with the other, will be ob tained from the following description of operation. i

\Ve will first assume that a subscriber at A desires to converse with a called subscriber at F, the latters line ter'1ninating in an exchange distant from exchange B to which the calling subscriber belongs. The removal of the receiver at A energizes relay LR lighting lamps LL, which lamps are distributed at various positions in the switchboard. An operator seeing the lamp at her position displayed, will insert the answering plug AP in a. jack of the calling line and re1ay16 instantly energizes by current through its two windings, normal contact 4, thesleeve plug and jack contact and through cutoil relay CO, the latter also energizing and clearing the line for talking, as well as putting out the lamps LL by tie-energizing the linerelay. The energizing relay 16 by its contact 18 shunts out its high resistance upper winding so that if another operator has plugged into another jack of the line of A, such other operators relay 16 will fail to energize because of the shunt established by the low resistance winding at the first operators relay 16, and the second operatorgwill get no response when she asks for the number and will withdraw her plug. The operating relay 16 of the first cord by its contact 19 energizes listening relay 7 b current flowing to ground at 35, with the result that contacts 9 and 10 connect the operators telephone set to the calling line and she inquires and learns the. number of the wanted subscriber. Furthermore, by the operation of relay 16, the supervisory relay 12 has been cut across the calling line, supplying talking current thereto, and by its armature 14 preventing the premature display of supervisory signal 15, while its contact 13 actuates counter relay 53, resulting in the actuation of magnet 54 to count a call as answered by the o erator. The operator at B learning that t e line of the wanted subscriber terminates at the exchange IE, will now insert calling plug GP into spring jack 67, such spring ack being assigned for calls to be extended to E, and she will first have actuated her cutout key OK to close itscontacts 46 and 47. The inserting ot plug OP has established an energizing circuit for the relay. 36 extending through contact 5 of relay 1, the sleeve plu and jack contact, and to battery throng relay 68 at C, as well as an energizing circuit for relay 34 in parallel with the one just described. As a result the relay 68 energizes and sets in travel the switch at C by closing its contact 69 which grounds. starting wire SlV (which extends from switch C as a common wire to all relays 68 connected with spring 'acks 67 adapted to be selected by the switch C). Current will now flow from battery through the resistance r, motor magnet MM, normal contact 83 and the ground through contact 69, and. magnet MM will energize and (ole-energize, stepping the switch wipers 75, 76, 77, and 78 a first step from normal in search of terminals of the spring jack in which the plug has been inserted. On the first step the springs ON are shifted to their alternate positions and successive actuations of magnet MM are produced by its armature over a circuit through alternate contact ON, to ground throu i contact 82 and 87. Such actuations will continue, each causing astep of the. wipers 75, 76, etc., until they engage multiplejacks in their banks connected to a jack 67 in which a plug has been placed, and which has not been already selected. As soon as this occurs the motor magnet MM will be shunted preventing its further actuation, and this shunt may be traced from battery through the resistance *1", the low resistance upper winding of relay 84, through wiper contact 75, its engaged bank contact and through normal contact 74 and alternate contact of relay 68 associated with the spring jack 67. The relay 84 attracts its armature contact 87 opening the circuit for magnet: MM, and energizing relay 79, while contact 86 connects the relays high resist ance lower winding in series with its upper winding and the relay locks to ground at 71, the circuit being traced through wiper 76. The relay 72 energizes and opens its contact 74 so that no other switch whose wiper 75 engages a multiple of the seized contact will stop, while the opening of contact 73 keeps ground ofi' the starting wire SW, so that when relay 79, which is now energized, closed alternate contact 83 and thus extends starting wire SW to starting wire SLV which extends to another finder switch in the usual manner, the latter will not be started. The relay 79 having energized as above described, locks itself to an off-normal ground by its contact 81 and by 82 opens another contact in the circuit of magnet MM.

By the closure of contacts 85 and 88 of relay 84, the relay 9% in the distant exchange has had its windings connected across the trunk wires 00 and y, and current flows from battery through the upper winding of 94, normal contact 90, over the heavily marked talking conductor via the tip contact of 67, UP, the alternate contact at 16, over the common wire to ground through the winding of the relay 55, while another circuit is established from battery through the other winding of relay 55, the alternate contact 17, to the right through the ring contacts GP, 67, over the talking conductor, and through normal contact 93 and the lower winding of relay 9% to ground, it being remembered that at the time the operator at B inserted the calling plug she threw over the levers 46 and 47 of her cut-out key. As a result, the relays 95 and both energized, and it is to be understood that the relay 55 is common to all cords of a position. When the operator first threw over the levers of her cut-out key, the closure of contact at 18 energized the relay 57, with the result that a tone from the constantly operating interrupter mechanism 61 was transmitted via contact 56 into the operators head telephone through the winding of her induc tion coil, and she thus had an audible indication which was terminated when the relay 55 was energized as just described, because the opening of contact 56 interrupted the tone circuit. By the cutting ofi of this signal she knows that the switch C has properly performed its function and has extended the call over the wires 50 and g to the distant exchange and that the switch D is starting its travel.

The starting of D is effected by the energization of relay 94: which by closing contact 95 energizes motor magnet Mlil by current via normal contact ON, and said magnet by a suitable pawl and ratchet mechanism steps the wipers 10 1, 105 and 106 one step from normal to engage the first set of contacts leading to a trunk circuit, such as that shown at E. Upon this first step, the contacts ON are shifted and if the first contact engaged by wiper 104 is a busy contact, it will be grounded, the man ner of such grounding to be later explained. The result is that in case of such grounded contact a circuit will be established from battery through relay 102, the armature contact of magnet MM, contact 97, contact 91, the relay 101, and over wiper 104 to the engaged busy contact and to ground. Consequently, relays 102 and 101 energize and the latter is of slow release construction so that rapid interruptions of its circuit as the switch travels are not effective to cause its armature contact to restore. The opening of contact 103 tie-energizes magnet MM whose retracted armature in turn de-energizes relay 102, whereupon magnet MM instantly is again energized by current through the now closed contact 103, the alternate contact at ON, the contact 97 and 91, the relay 101 and to ground, through the wiper 10 i and the engaged grounded contact, whereupon magnet MM steps the wipers another step, and by the closure of its armature contact will again energize the relay 102 over the previously described circuit to wiper 104: and now to ground to the next engaged contact if it is busy. Thus a see-saw action between relay 102 and magnet MM is produced, the slow relay 101 being in the circuit of which ever one of the other two is energized, and this see-saw action will continue until the wiper 104 engages a contact in its bank which leads to a trunk line in the exchange E which terminates before an operator who is not busy, that is, who has not her head telephone in use, then the see-saw action terminates because the engaged contact of such a trunk line will be characterized by a freedom from ground. When this occurs the circuit will remain open through the slow relay 101 whose armature will retract and energize the slow release relay 89 by current through contact 98 and to ground through the shifted offnormal contact. By the shifting of contacts 90 and 93 to engage their alternate contacts a circuit is closed from battery through relay 55 at B over the lower heavily marked talking conductor to the right through wiper 106 and its engaged idle contact, through winding 0 of the induction coil at E in series through the two windings of relay 107, through winding a of the induc tion coil, to the left over the heavily marked talking conductor, and through the lefthand winding of relay 55 to ground. This energizes relay 107 and its armature 108 operates relay 110 which closes contact 114 and grounds the contact engaged by the wiper 104: of the switch B, the result being that relay 89 at D by its armature Contact 91 locks to ground via relay 101 at contact 11 1. lVhen relay 89 first operated the shifting of its contact 92 energized the relay 96 which was immediately locked to ground to the off-normal contact via its armature Switch 99, and said relay 96 by opening contact 98 opens the initial energizing circuit of relay 89, but the latters slow release construction causes it to hold its armature in operated position until the substitute circuit oye'r wiper 104 was established, as just described. The relay 96 by means of switch contact 97 which has now opened, has effectively prevented any reoperation of motor magnet MM until the relay 96 is de-energized, which can only happen after the switch D is restored to normal, and the con- I tacts ON are consequently shifted to their original position.

Referring now to the apparatus at E, the relay 110 (which energized as the result of the closure of contact 108) energized relay 1'09 and also relay 116, which latter, by its contacts 117 and 121, connects the operators relay 158 across the talking conductors, and said relay 158 energized by current through the windings of relay at B over a path which is obvious from the preceding description. As a consequence, the operators talking set at 168 is connected into circuit with that of the operator at B through the contacts 59 and at B. he operator at B now tells the operator atE the number of the subscriber wanted, and the latter plugs into a spring jack of the line, having first tested it in the usual way and found it idle.

It will be observed that upon the energization of relay 110, the signal lamp 152 was lighted by current flowing through alternate contact 112 so that the operator at E knew which of her trunk circuits was to be used in establishing the connection. The relay 116 (there being a relay 116 for each cord circuit at the operators position) in addition to cutting the operators telephone relay 158 into circuit closed its armature contacts 118, 119, 120 to ground, and it is to be understood that the short wires indicated at its armature contacts are connected to the private terminals of all trunks belonging to the operators position whose nead telephone is now out into use, so that as long as the relay 116 remains energized no other switch D can connect effectively with any trunk assigned to the said operator.

Furthermore, we have illustrated at H a relay 116 which is common to a group of trunk circuits E and the relay 116 in con- 'unctio'n with relays 116 of the trunk circuits l5 and the operators listening relays 7 of the local cords shows clearly the exact wiring of this part of the system. It has al ready been stated that the operator at B is provided with incoming trunks like that illustrated at E and the operator at E has not only incoming trunks E but is also provided with local cord circuits B and it is to be understood that the wiring and interrelation of the local cord circuits and the trunk circuits at the various operators positions in both exchanges are alike. The relay 7 shown at H is the listening relay 7 of a local cord circuit B located at E and the connections from the armature contacts 8, 9, 10 and 11 are omitted for convenience but it is to be understood from this diagram at H that whenever the listening relay 7 of any local cord circuit B is energized the operators head set is cut in and its alternate contact 166 is closed to connect ground thereto.

The alternate contacts 166 of the operators listening relays 7 of cord circuits B of each operators position are multipled to a common conductor CW which conductor CW extends to the winding of the relay 116 which is common to a group of trunk circuits at E at this particular operators position, it being understood that there is a relay 116 common to each operators position and its group of trunk circuits E. Now when the operators telephone set is cut in on a calling line by means of any relay 7 of any of her local co'r'ds the closure of its alternate contact 166 will place ground on the common conductor ClV which leads to the relay 116, and this ground will close an energizing circuit for relay 116 common to the trunk circuits E associated with this operators position. The relay 116 upon energization will close its alternate contacts 161, 162, 163 and 164 and assuming that each operat'oi"s position isequipped with four trunk circuits such as E the closure of these four alternate contacts will ground the private contacts of the four trunks at the switches D and prevent any of the trunks from being selected so that it is impossible for the operators telephone set to be con nected in on two different calls at the same time and from the above description it is also seen that a trunk call will only land at an operators position whose telephone set is idle at the time the switch engages the trunk.

\Ve left the operator. at E just having received the number of the called subscriber I from the operator at B. The latter now restores her out out key with the result that the windings of the calling supervisory relay CSR are substituted in the circuit of the windings ot' the relay 55. and the relay 57 7 her out out key CK, closes its contacts 46 and 47, and a circuit is closed for relay CSR which may be traced from battery, through its lower winding and over the heavily marked talking conductor to E, through winding 0 of the repeating coil to the right, to connect to the armature 129 of relay 127, through normal contact 180, thence through the lower winding of relay 107 through winding a of the induction coil to the left, over the talking wire and through the upper winding of the relay CSR to ground at 38. Thus it will be seen that the upper or high resistance winding of the relay 107 is short-circuited, and consequently, relay CSR at B receives enough current to energize it to actuate its armature, and contact 32 is opened, thereby preventing the display of signal 28 so that we have the dark key shelf feature.

The operator then having found the called line idle inserts her plug 167 in a multiple jack of that line, the immediate result being the energization of relay 122 in. the trunk circuit and of cutoff relay CO of the called line circuit, which latter relay clears the line. Relay 122 by contact 126 de-energizes relay 116, whose retracted armature contacts 117 and 121 disconnect the operators head telephone, while its other armatures unground the terminals of the other idle trunks at the position rendering them selectable by switches D. The master ground contact MG at 122 is now closed operating the relay 133 by current traversing the. contact 113 at relay 110, and the armature 136 puts out the signal at 152 and locks the relay 133 to ground at contact 112 of relay 110, while contact 135 establishes another locking circuit for the relay 133 extending to the master ground MG. The contact 137 operates the counter magnet 157 to count a completed trunk call for the operator at E and relay 138 immediately thereafter opens contact 139 to prevent any possible reoperation of the counter magnet.

Assuming that the substation F has a harmonic bell, the operator will now actuate her ringing key button to close one of the contacts 155 of her ringing key, and will select the one connected to the generator of proper frequency, and in so doing will momentarily close the end spring 154, which latter spring will close a circuit to energize relay 140 by current through said relay and said spring, and contact 132 over ground wire GW to ground at MG, said relay 140 by its contact 142 locking itself to ground at MG via the normal contact at 150. The result of the closing of contact 141 of relay 140 is that the relay 144 is connected in circuit with the constantly rotating interrupter 159, and said relay 144 will alternately energize and deenergize, attracting and releasing its contacts 146 and 147 to connect and disconnect generator from the called line to periodically ring the bell at the substation, the path of the ringing current being traced through a contact 155 (the contact remaining closed after being once operated, although the end contact 154 restores as soon as the operator removes her hand from the button), the winding of the relay 149, alternate contact 147, tip plug and jack at 167, through condenser and call bell at the substation, back through the ring contact at 167 and to battery at alternate contact 146. If during a ringing interval, the called subscriber removes his receiver at the substation, the slow release relay 149 will receive enough current to actuate its armature to open contact at 150 and this will de-energize relay 140 by opening its locking circuit and the relay 144 will have its connection with interrupter 159 opened at contact 141, and will remain de-energized so that no longer can ringing current be applied to the called line. As soon as contacts 146 and 147 are closed after the subscriber removes his receiver, or if they are closed at the time he does so, the relay 127 is energized by current from battery through its lower winding, through winding (Z of the induction coil, over the ring plug and jack contact at 167, the switch hook contact at F, back through the tip plug and jack contact at 167, normal contact 147, alternate contact 123, winding 6, the upper winding of said relay 127- to ground. Contact 128 of relay 127 now closes a circuit which energizes relay 130 by current over the ground wire GVV, and said relay 130 by its contact 131 locks itself to said ground, and by opening contact 132 cuts off all the ringing key apparatus and relays definitely from the ground wire. lVhen on the response of the called subscriber the relays 127 and 130 operate as just described, the relay 130 opens the short circuit about the upper winding of the relay 107, but before it does so, the relay 127 by its contact 129 has provided another shunt about the upper winding so that the lamp 28 remains dark while the subscribers are talking.

The subscribers at A and F are now in conversation, the talking circuit being traced from A to F over the heavily marked conductors, the transmitter of the substation at A receiving its current through the wind ings of relay 12, while the transmitter at F receives its current through the windings of relay 127.

hen the subscribers have finished conversation they replace their receivers, and we will assume that the subscriber at A does so first. He consequently opens the circuit of his answering supervisory relay 12 and the lamp 15 is displayed by current through normal contact 14, alternate contact 20, to ground through alternate contact 35. Furthermore, the bust relay 1 is, operated by [ill cuia ent through it and traced to ground through the same contacts 20 and 35, and said relay 1 by its armatures 2 and 6 opens up the talking conductors of the cord strands; by its contact 4, it places the sleeve contact of the plug on open circuit, thus removing the busy test from the multiple jacksof the line of A, and in so doing deenergizes cut-ofi' relay G which now places the line relay LR under substation control. The closure of alternate contact at 4. maintains the relay 16 operated, however, a substitute locking circuit for said relay being traced through contacts 20 and 35 to ground. The opening of contact of relay 1 would deenergize the sleeve relay 36 at the calling end of the cord were it not for the fact that relay CSR is still energized, because the called subscriber is assumed not to have replaced his receiver as yet, and the closed contact 33 keeps the winding of relay 36 operatively connected to the sleeve strand of the cord extending to plug Cl Now when the called subscriber at F at the end, of conversation replaces his receiver before the subscriber at A, the resulting de-energization of relay 127 by the opening of its circuit at the substation switch hook, will serve to open the contact 129, and since the relay 130 will remain energized by current through its locking armature 131, the only path for current through the winding of relay CSR at B will be through the two windings of the relay 107 at E, and this current will be so slight that relay ,CSR will retract its armature to light the lamp 28. The relay 36 is thus wholly disconnected from the Sleeve strand of the cord, and consequently de-energized opening the talking conductor of the cord circuit at contacts 37 and 40.

It will be. seen that as soon as the relay 36 is cut oil from the sleeve strand of the cord, the only battery connection to said cord strand is through the winding oi rc lay 34, which relay is of very substantial resistance, for instance, 7000 to 7500 oluus. Current continues flowing through said lay and through, the sleeve contact at C1 67, to ground, through relay 68 at C, and this current is sullicient to maintain the relay 34 operated but the relay 68 owlng [0 its relatively ineliicient construction and the adjustment'of its armature, aliows its armature contacts ,to be opened, and this results in the restoration of the switches C and D as follows: The opening of contact 71 opens the locking circuit of relay 84, which (le -energizes and in so doing opens the talking .i'vires extending to wipers 77 and 78 at contact 85 and 88, and by closing normal. contact 87 energizes release magnet RM by current through alternate contact 82 of relay .79, and said release magnet RM withdraws the retaining pawl of the switch and the wipers are Spring-restored to normal. The

opening of contact 71, of course, has deen ergized relay 72, while the restoration to zero of the switch has placed contacts ON in their normal position, and all the mechanism at C is now at normal.

On the opening of contacts 85 and 88, the. relay 107 at i") has its circuit opened, and consequently is (lo-energized. The rctrao tion of its armature de-energizes relay 110. the latter by restoring armature 115 de-cn ergizing the relay 109. The opening of contact 114 removes ground from wiper at E, and as the relay 109 is relatively sluggish to restore, it will keep its armature attracted long enough to insure that the relay St) at D will allow its armature to tall back, whereby contacts 90 and 93 place the tall:- iug wipers 105 and 106 on open circuit, while- 92 falling back energizes release magnet RM by current from battery through said magnet, cont-act 100, normal contact 92, to ground through the shifted contact ON, and said magnet Rivl withdraws the retaining pawl of the switch 1) which r'springrestored to its zero point, at which time the contacts ON open tie-energizing relays 96 and magnet RM, and the apparatus oi the switch is at normal.

It is thus seen that when the two subscribers have replaced their receivers, the 95 two switches C and D are released and fully restored, and this is very important inasmuch as it trees the trunk wires m, 3 which extend from one exchange to another, (usually involving a very substantial investment in capital) so that the freeing of them and the rendering of them promptly available for another connection is an item of the greatest importance in the economical operation of a telephone system.

The operator at B seeing the signal lamps and 28 displayed, withdraws the plugs AP and GP which (lo-energizes the relay 3-4;, which in turn tie-energizes relay 1, and the apparatus and cord circuit are at normal.

It is (it course obvious that the relay 1 when it first energizer gave the calling subscriber the advantages of instantaneous d3" connect and line lamp recall, irrespective of the Withdrawal of the plug AP.

The dc-encrgization, of relay 110 at E as above described results in the l ghting of the SllpGlVlSOl'y lamp S, and theoperatcr at E observing the s gnal withdraws the plug 167 to dc-energize relay 1.222 of the cord, and by the shifting of its contacts including that of master ground MG, the up paratus oi. the trunk cord is placed at nor-- .mal, while the withdrawal of the plug 167 has restored the line circuit at F by de-energizing line relay CO.

Lamp 1.53 in the trim}: circuit E increly a guard lamp which is lighted as soon as master ground MG is connected up, the said lamp being lighted indicating to the oper" ator that she has not actuated her ringing key lever to ring the called subscriber. As soon as she does so closing contact 154, the relay 140 energizes and locks puts out the lamp 153.

Let it be asunned that although the called substation bell was rung, the called subscriber did not answer the call. In such case the calling subscriber will replace his receiver and de-euergize relay 12 to energize relay 1. Relay 36 is then cut oil from the cord strand and it is plain from the preceding that switch G will restore.

Circuit being opened thereby at wipers 7'l78, relay 107 at E deenergizes, and as a consequence relay 110. The supervisory lamp S at E will now be lighted and the operator will pull out plug 167.

Let it be assumed now that a calling subscriber at A removes his receiver to initiate a call for a subscriber in his own exchange. The operation of the line circuit and cord circuit of Figure 1, part 1, would be the same as that already described until after the operator has received the number 01" the called subscriber. In this case, she would test a multiple spring jack of the called subscribers line whose line circuit and substation would have exactly the same arrangement as that of the subscriber A. To make the test the operator touches the tip or" the plug GP to the sleeve of a jack of the called line, and if this spring jack is busy because a plug of another cord circuit has already been 3 placed in a multiple of the jack tested (pro vided always that the subscribers have not effected the automatic disconnect), there will be apotential above ground at the tested sleeve contact and an impulse of current will flow through the tip of plug GP, normal contacts 46-42 the closed contact 8 of relay 7, and to ground through the test relay 62 which is common to an operators position, and said relay will actuate its armature 63 to close battery through the tertiary winding of the operators induction coil, giving her the customary busy click.

Moreover, the test arrangement provides means for giving the operator a revertive tone test, it she tests a spring jack of the line in which she has already inserted the answering plug of the cord, that is, if the calling subscriber want-s another subscriber on his own line, the system thus providing for the case in which there are a number of substations connected to a single line. In making such a revertive test the operator will receive the click as usual, but in addition the closure or" contact 64 will connect the revertive tone test apparatus to the operators head telephone, the circuit being traced through contact 64, contact 11, normal contact 4, through the sleeve contact or plug AP to the sleeve of the jack in which that plug is inserted, thence to the sleeve of calling plug GP and ring in the usual man-,

ner.

But assuming now that the substation called for is on an idle line entirely independent of that of the subscriber at A, the operator receiving no click upon her test, inserts the calling plug GP in the tested jack, thus placing the relays 36 and 34 oi her cord circuit in connection with ground through the winding of cut-oft relay GO of the called line, and said relays 36 and 34 are both operated with results to the switching instrumentalities of the calling end of the cord circuit as previously described herein, and the cut-oil relay GO of the called line will o1 course energize to clear the line circuit for talking and ringing, the line relay LR being disconnected. The operator at B now actuates whichever ringing key lever 49 will impress current to the proper frequencyto ring the bell of the called substation, the lever staying in its shifted position, while the end springs 51 and 52 of the ringing key are shifted to close their contacts but only as long as the operator holds the ringing button down. By the closing of contact 52, the relay 22 energizes over a circuit which may be traced through said contact, through contacts 3, 30, 82, and alternate contact 35 to ground and said relay 22 by its contact 26 locks itself to ground at By the closure of contact 51 the upper winding of the ringing relay 41 receives current which goes to ground of contact 25 of relay 22 so that the called substation is instantly rung and will continue to be rung as long as the operator keeps the levers 51 and 52 shifted. When she releases the button said levers restore to normal, and the upper winding of relay 41 is disconnected, but the lower winding of said relay by the closing of contact 24 of relay has been connected with the constantly operating interrupter I and will alternately be energized and de-energized, cutting in and out the selected ringing generator. The flow of ringing current is to be traced from ground through the generator sel cted, the shifted lever 49, lower winding of relay 29, alternate contact 42, when relay 41 is energized, contact 46, the tip plug and jack contact, through the called subscriber and its bell, back to the ring plug and jack contacts and to battery at alternate contact 45. If the subscriber answers in a ringing interval the reduced resistance at his substation caused by the removal of his receiver will now open.

allow sufficient current to flow through the lower windin of relav 29 to ener ize it it D u b having previously remained inert because of the high resistance call bell circuit at the substation), and the said relay 29 by opening its contact at 30, tie-energizes the relay 22 by opening its locking circuit extending to ground at 85 and the said relay 22 restores not to reoperate because the contact 52 is Its retracted armature contacts 23 and 27 reestablish the talking circuit at these points and the opening of contact 24: prevents any further operation of ringing relay 41, which relay deenergizes, and the contacts 42 and 45 complete the talking circuit between the subscribers. The closing of contacts 42 and also connects the two windings of calling supervisory relay CSR to the called for line and it energizes, since the substation receiver has been removed.

If the called subscriber had removed his receiver during a silent interval, the contacts 42 and would then have been closed and relay CSR would instantly have energized over called for line, and by opening its contact 32, would have tie-energized the relay 22 with results as before.

The calling and called subscribers are now in conversation, and, when they have finished they replace their receivers. It will. be assumed that the called for subscriber does so first. The opening of the transmitter circuit through the substation tie-energizes relay CSR and its retracted armature, contact 32 will cause the lamp 28 to be lighted by closing the circuit of said lamp to ground at alternate contact Nothing further results at this time, but when the calling subscriber A replaces his receiver, the resulting de-energization of relay 12 by the restoring of contact 14 energizes the relay 1 by current flowing to ground at alternate contact 35, and by its armatures 2, 4, and 6 all three contacts of plug AP are placed on open circuit so that the line of the calling subscriber is restored to its normal condition as far as signaling and testing purposes go. It will be observed that the closing of alternate contact 4 of relay 1 establishes a substitute locking circuit for the relay 16 before said relays arinatures have time to retract, said substitute circuit being traceable through alternate contact 20 and to ground at alternate contact One circuit through the sleeve relay 36 has already been opened at contact 33 of relay CSR, and the opening of contact 5 at relay 1 opens the other circuit through said relay 36 so that the said relay now deenergizes. The only instrumentality now in circuit with the cut-off relay of the called for line is the relay 34 which is of so high resistance, say between 7000 and 7500 ohms, that'sufficient current does not flow therethrough and through the called cut-off relay CO to enable the latter to retain its armature attracted, although due to its greater efiiciency, the relay 34 continues to hold alternate contact closed. The result is that the restoration of the contacts of relay ()0 of the called for line places the line circuit of the said line under control of the substation switch hook so that the substation is provided with line lamp recall service at this time, and the said line will furthermore test idle at this time because of the high resistance of the relay 34 which results in a potent-ial so slight upon the multiple jacks of the called line as to make the operators test ineffective if some operator tests that line.

Both lines are now free and the lamps 28 and 15 are both displayed and the operator withdraws the two plugs, and restores all apparatus of the cord circuit to its normal condition.

if the calling subscriber had replaced his receiver before the called for subscriber did so, relay 12 would be tie-energized and the calling line would, by the resulting operation of relay 1, instantly have been given disconnection and recall as before. The called for line, however, would not be free until the called for subscriber replaced his receiver for the reason that the relay CSR would remain operated until that time, and by its contact 33 would hold the relay 36 in circuit with the cut-off relay C0 of the called for line. hen, however, the called for subscriber did replace his receiver, his line would be freed in the described obvious way.

It will be noted that the circuit of the calling supervisory lamp 28 is led through the back contact 26 of relay 22, and as the said relay is energized when the operator depresses her ringing button, the lamp is at that time put out and remains out until the called for subscriber replaces his receiver when the lamp is lighted, either through its original energizing circuit, namely, via the back contact at 26, or if the calling subscriber has already replaeed his receiver, the said lamp 28 will be energized by current through alternate contact 3 of relay 1. We thus have what is known as the dark key shelf method of operation.

Referring now to Figure 2, we have illustrated a cord circuit which may be substituted throughout the operation of the system as hereinbefore described, for that shown in Figure 1, part 1. Corresponding relays have been given corresponding reference characters, and it is not considered that a detailed description of this circuit is at all required in view of what has already been said in connection with the cord circuits illustrated in Figure 1, part 1.

Particular attention is however called to the relation in Figure 2 established between the relays 36 and 3-1. It will be noted that relay 36 is here connected permanently in series between the winding of the relay 34 and the live side of the central source of current. In addition to this connection which results in the relay 36 being permanently connected to the sleeve strand of the cord circuit, the winding of said relay is connected to two branch Wires, one controlled by the lower contact of the calling supervisoryrelay CSR, while the other is controlled by the lower contact of the relay 1. In accordance with this arrangement, when the relay CSR de-energizes at the end of conversation, it will open one circuit through the relay 36, and when the relay 1 is energized it will open another circuit through the relay 36, the points controlled by these two relays CSR and 1 being intermediate between the winding of the said relay and the sleeve strand of the cord circuit. In accordance with the arrangement of Figure 2, however, this will not result in depriving the relay 36 fully of current because it is permanently connected to the sleeve strand of the cord circuit through the winding of the relay 84. Owing, however, to the very high resistance of the latter relay, which we have already mentioned as being desirably between 7000 and 7500 ohms resistance,-

the flow of current through the relay 36 at this time will be so very slight that the said relay will not maintain its armature in its attracted position, but on the contrary will allow it to restore. The relay 34 will remain energized with the same result as heretofore explained, and the cut-oil relay of the line will also de-energize as before.

lVhile we have illustrated and described aparticular embodiment of our invention, it is to be understood that it is of considerable scope, and we do not intend to be limited to the particular devices and connections herein shown and described, but intend to include all such modifications as will suggest themselves to those skilled in the art, and to claim the invention in its general aspects.

Having described our invention what we claim as new and desire to secure by United States Letters Patent is:

1. In a telephone system a pair of connected telephone lines, link and trunk, circuits having terminals applied to the calling and called lines respectively and rendering them busy, an automatic n-on-preselecting switch interconnecting said first circuits by means 01. a third link circuit, means controlled by the subscribers to restore said switch while said link and trunk circuits remain connected to said lines and a signal for said link circuit inert during the extension of a connection to a called line and controllable by said called line only upon termination of conversation.

2. In a telephone system a pair or" connected telephone lines, link circuits having terminals applied to the calling and called lines respectively and rendering them busy, disconnect means associated with the terminal applied to the calling line, an automatic selecting switch interconnecting said first circuits by means of a third link circuit, means controlled by the subscribers to restore said switch without restoring said terminals, said disconnect means operated by said calling subscriber to free his line from said terminal applied thereto prior to disconnection of said terminal.

3. A telephone system comprising a calling line, a link circuit having an automatic selecting switch provided with bank contacts and wipers, said switch operable to cause its wipers to engage certain contacts in said bank contacts to extend the circuit of the calling line, means including a manually operated terminal to extend said line to said circuit, a called line and switching contacts at the substations of said lines effective to restore said selecting switch while said manually operated terminal is connected with said line and a signal for said means inert during the extension of a connection to said called line and controllable by said called line only upon the termination of conversation.

i. A telephone system including a pair of connected telephone lines and a link circuit having an automatic traveling switch provided with bank contacts and spring restored wipers for engaging said bank contacts through which bank contacts and wipers the connection extends, plug and jack connections one for each line and connecting its respective line to said circuit switching means operated from the substations and including circuits through said plug and jack connections for restoring said circuit switch and a signal associated with the plug and jack connection of the calling line controlled by said called line to indicate the condition of said called line.

5. A telephone system including a pair of connected lines, the connection including non-preselecting traveling switch mechanism and plug connections one on each side of such mechanism, means controlled from the calling station to automatically restore said mechanism and a signal associated with one of said plug connections inert during the extension of a connection to said called line and controllable by said called line only upon the termination of conversation.

6. A telephone system including a pair of connected lines, the connection including non-preselecting traveling switch mechanism and plug connections one on-each side of such mechanism, means cooperatively controlled from the calling and called stations to automatically rest-ore said mechanism and a signal associated with the plug and jack connection of the callingstation inert during the extension of a connection to said called line and controllable by said called line only upon the termination of conversation.

7. A telephone system including a pair of connected lines, the connection including rotary traveling switch mechanism having individual driving means and plug connections one on each side of such mechanism, and means controlled from the calling station to automatically restore said mechanism, said means including a device for changing the test condition of the calling line while the associated plug connection remains.

8. A telephone system including a pair of connected lines, the connection including non-numerical switch mechanism having individual driving-means and plug connections one on each side of such mechanism, and

means cooperatively controlled from the calling and called stations to auton'iatically restore said mechanism, said means including a device for changing the test condition of the calling line while the associated plug connection remains.

9. A telephone system including a pair of connected lines, the connection including a link circuit having an automatically selecting switch at each end, said switches having stationary bank contacts and traveling contact mechanism adapted to engage said stationary contacts and said switches operative to establish the connection through their respective bank contacts and contact mechanism, plug connections one between each switch and the associated line, means controlled from a calling or called station over a plug connection for restoring said switches to their respective zero points and a signal associated with the plug connection of the calling line inert during the extension of a connection to said called line and controllable by said called line only upon the termination of conversation.

1 0. A telephone system including a pair of connected lines, the connection including a link circuit having an automatically selecting switch at each end, said switches having traveling contact mechanism operative in establishing the connection, plug connections one between each switch and the associated line, a signal associated with the plug connect-ion of'the calling line controlled by said called line for indicating the condition of saidcalled line, and means controlled over the calling line only for restoring said switches to their respective zero points prior to the response of the called nection, plug connections one between each switch and the associated line, and a signal associated with the plug connection of the calling line controlled by said called line for indicating the condition of said called line, and means controlled over a plug con nection for restoring said switches to their respective zero points, said telephonesystem including also devices operative by the response of the called station to change the control of said means.

12. A telephone system including a pair of connected lines, the connection including a link circuit having an automatically selecting switch at each end, said switches having traveling contact mechanism operative in establishing the connection, plug connections one between each switch and the associated line, and means controlled over the calling line only for restoring said switches to their respective zero points prior to the response of the called for subscriber, said telephone system including also devices operative by the response of the called station to change the control of said means.

13. A telephone system including a pair of lines teri'ninating in multiple line jacks and line signals before a number of operators and connected by a link circuit having an automatic selecting switchat each end, plug connections one between each switch and the associated line, one switch operated when connection is made by a plug connection "from a calling line to select said line said other switch operating automatically to select said other plug connection, a supervisory signal associated with the lug connection of the calling line opera le from the called station when the receiver is replaced to change its indication, and connections preventing any changes in the indication of said signal when the subscriber answers the call.

14. A telephone system including a calling telephone line terminating in line jacks and line signals before a plurality of operators, a manual link circuit connected therewith via one of said multiple line jacks and having a manually operated terminal, a calling and a called signal for said link circuit, means including automatic-selecting switch mechanism for extending connection from saidcircuit to a called line, means for preventing display of said called signal when connection is made to the called line and prior to response at the substation, and a switchhook effective on replacement of the receiver to display said signal.

15. A telephone system including a-called line terminating in multiple line jacks and signals and a calling line terminating in multiple line jacks and signals, a manually operated link circuit for connectin said line in circuit via one of said multip e line jacks, automatic selecting and connecting switch mechanism included in such connection, an operators position on said connection having a calling and a called supervisory signal therefor, switching devices preventing a change in the indication of said called signal when the called subscriber answers, and apparatus effective to change its indication when said subscriber replaces his receiver.

16. A telephone system including a calling telephone line terminating in multiple line jacks and line signals, an operators cord terminal in connection with said line via one of said multiple line jacks, a distant operators position and means including automatic selecting mechanism for connecting from said cord terminal to an operator controlled switchat said position, a signal for said cordterminal, means for preventing itsdisplay when connection is extended to said distant position and a switch controlled at a connected called station effective to display said signal when the subscriber replaces his receiver.

17 In a telephone system a telephone line, a link circuit having a terminal in connection with said line, an automatic selecting switch for selecting said link circuit to extend the circuit of said terminal, means at the substation of said line to change resistance at said terminal to restore said switch and a supervisory signal associated with said link circuit inert during the extension of a connection to a called line and .line, said switch and its associated link circuit extending the circuit of said terminal, a predetermined flow of current through a contact of said terminal while connection exists, and relay means operable under substation control to create a lesser flow of current through said contact to restore said switch.

19. In a telephone system a telephone line terminating in multiple line jacks and line signals, a link circuit temporarily applied with said line Via one of said multiple line jacks, a second link circuit connected to said first link circuit, and an automatic traveling switch operable to select and to interconnect said circuits when said first link circuit is applied to said telephone line, and a signal for said link circuit inert during the extension of a connection to a called line and controllable by said called line only upon termination of conversation.

Signed by'us at Chicago, in the county of Cook and State of Illinois, this 18 day of March, 1921.

I-IIRAM D. CURRIER. GEORGE R. EATON.

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