US2298489A - Group-call telephone system - Google Patents

Description

Oct. 13, 1942. 'GQKINER GROUP-CALL TELEPHONE SYSTEM Filed Sept. 10, 1941 2 Sheets-Sheet 2 Patented Oct. 13, 1942 UNITED STATES PATENT OFFICE GROUP-CALL TELEPHONE SYSTEM Glenn Kiner, Markham,

11]., assignor to Kellogg Switchboard and Supply Company, Chicag 111., a corporation of Illinois Application September 10, 1941, Serial No. 410,238

Claims.

General description The system of the invention may be used, for example, in calling volunteer firemen over regular subscriber lines to inform them of the locaoperator is provided with an individual supervisory signal for each branch of the group-call circuit to indicate which of the transferred lines (if any) are in use. The group-call operator may converse with any subscribers thus telephonically connected to the group-call circuit and request any who are not the desired subscribersto replace the receiver.

Individual supervisory signals also keep the tion of a fir l0 operator informed at all times of the answered A group-call line is provided with branches or unanswered on each corresponding respectively to the separate tele- Aicordmg to t f feature the phone lines constituting the group to be called. l l F mm 18 so assoclated with Each branch is provided with ringing equipment the group'can clrcult that the group-can 9 t and Supervisory equipment. Means is provided 15 tor must first call the supervisor over 1115 line controlled over the group cau line for trans and obtain a response thereover before she is ferring each of the subscriber lines of the pre- W cau the Subscnb'ers over the selected group from its regular switchboard terflea/Cure a t the Supervlsor to minals to its corresponding branch of the groupuse dlscretlon m detertmmng Whether or not can mm 20 the group-call operator is to call the preselected A feature of the invention is that each of the group idle lines of the group is transferred from the An assocm'ted feature m an emergency group-call line into its ringing circuit when the the group'cau operatpr t .able to slmllla'te operator Starts the ringing operation and response on the supervisors line when the groupcomes automatically disconnected from the ringcan operator knqws g the need for q ing circuit and connected back to the group-call grou? of Subscribers. 15 urgent and lmmedlate line when the call is answered on such line. As 1 1s ltnable topbtam a response on the supera consequence, the group-call operator may con- Vlsor s verse with the Subscribers one by one as they m A further feature is that the supervisor hlmrespond, the ringing continuing on the other self may slgnal p' f m by relines while the group-call operator is conversmoving the recelver on i mm to .mstmct her ing with those who have already responded an to call the group of subscribers. This latter feaof the lines finally becoming connected back to ture 1S Valuable e p example some an the gmumcau circuit when a response has been fire reports are made dlrectly to the supervisor rather than to the group-call operator.

obtained on all lines.

A further feature is that a line over which a response has been obtained may be automatically disconnected from the group-call circuit and transferred back to the regular switchboard terminals upon the receiver being replaced at the responding substation. This arrangement enables any desired one of the lines of the group to be immediately transferred back to normal telephone service to enable a regular call to be made from or received at such line. This feature is particularly advantageous for the line of a fire chief or other person who occupies a supervisory position.

According to a further feature, arrangements are provided whereby any desired line of the group may be recalled after a response has been obtained and the receiver has been replaced. This feature enables the subscriber to be recalled to receive additional or change instructions. 7

According to a further feature, the group-call Other objects and features of the invention will become more apparent as the description progresses.

The drawings Referring now to the accompanying drawings, comprising Figs. 1 and 2, they show by means of the usual circuit diagrams a sufiicient amount of the apparatus involved in a group-call telephone system embodying the features of the invention to enable the invention to be understood.

Fig. 1 shows the system especially adapted for use when the group-call operator is expected to exercise the desired discretion as to when to call and when not to call the lines constituting the group. 7

Fig. 2 is a desirable modification especially adapted for use when a remote supervisor exercises the discretion as to when to call and when not to call the group.

In Fig. l, the group-call line G0! is shown connected in common to the left-hand portion of each of the line circuits LCI to LC3, indi- Vidual respectively to the lines I5I to I53.

Being regular subscriber lines, the lines I5I to I53 normally extend (through the indicated transfer-relay contacts) respectively to the switchboard jacks JI to J3 and their multiples, whereby incoming and outgoing telephone service may normally be obtained.

The group-call operator, whose telephone is indicated at I08, may make connection (through the group-call line GCI) with all of the circuits LCI to LC3 by means of the talking key K2.

The group-call operator is provided with a ringing key KI, through which she can bring about the operation of a ringing relay in each of the circuit LCI to LC--3 to cause ringing current to be projected over the lines I5I to I53.

Referring particularly to the line circuit LCI relay IIlI is the line relay arranged to supply talking current to the line I5I and to exercise control over the other relays of the line circuit; relay I02 is the answer-test relay arranged to bring about the termination of the ringing operation when an answer is secured on the line I5I; relay I03 is the ringing relay arranged to transfer the associated called line from the group-call line to the ringing circuit when the key KI is operated: relay I M is the call supervisory relay, being operated when the ringing operation is started in the line circuit LCI; relay I05 is the answer supervisory relay arranged to be operated through contacts of relay I04 to give answered supervision; relay IE6 is a transfer relay, which transfers the line I5I from the jack J I and its multiples to the group-call circuits GCI LI and L2 are the call and answer-supervisory lamps; and the key K4 is a recall key which may be actuated by unlock and restore answer-supervisory relay I05 to enable a new ringing operation to be initiated.

Referring now particularly to the line circuit LC2, relays I II to II 5 correspond respectively in function to relays IIlI to I 05 of the line circuit LCI. Similarly, the key K5 and lamps L3 and L4 correspond respectively to the key K4 and lamps LI and L2 of the line circuit LCI. Transfer relay H6 is associated in common with line circuits LC-2 and LC3.

The line circuit LC-3, indicated as a broken line rectangle, may be similar to the line circuit LC2.

It is to be noted that the conductors Ill and I14 of the group-call circuit GCI are broken between the line circuits LC2 and LC3. This break is to indicate that as many additional line circuits as desired may be inserted between line circuits LC-2 and LC-3.

It is to be observed that the line I5I is an individual line, having substation I5I thereon, while lines I52 and I53 are party lines, each having a number of substations thereon. The invention has been illustrated in connection with a party-line system of the so-called harmonic ringing type, each of the substations on the line being run by a different frequency of ringing current, such as for example 30-cycle, IZ-cycle, 54- cycle, and 66-cycle ringing current. On line I52, the subscriber at the 42-cycle substation I63 is the one to be called over the group-call line GCI As a result, 42-cycle ringing current is arranged to be sent out through the line circuit LC2, as indicated. Similarly, the line circuit LC3 is provided with 66-cycle ringing current, as indicated, to adapt it for calling the subscriber at the 66-cycle substation I59 on the associated line I53.

The line circuit LCI is arranged to supply the usual 16-cycle ringing current to the associated individual line I5I.

Referring now particularly to Fig. 2, the arrangement disclosed therein is generally similar to that shown in Fig. 1, differing principally in that the arrangement of Fig. 2 includes the supervisors line 253 and associated circuit arrange ments.

The line circuits LC4 and LC5 are connected in multiple to the group-call line G02, as shown, and are assigned respectively to the subscriber lines 25I and 252. Relays 20I to 206 of the line circuit LC4 correspond respectively to relays IIJI to I96 of the line circuit LCI. Similarly, key K9 and lamps L9 and LID correspond respectively to the key K4 and lamps LI and L2. The line circuit LC5, indicated only as a broken-line rectangle, may be similar to the line circuit LC4. The conductors 2' to 214 of the group-call line GC2 are shown broken between the line circuits LC-4 and LC5 to indicate that as many other line circuits as desired may be interposed between the two shown.

The switchboard jacks J4 and J5 represent the normal switchboard terminals of the lines 25I and 252 respectively.

Line circuit LC6 is individual to the supervisors line 253, which latter line may be a special line, used only in connection with the group calls.

The line circuit LCG includes line relay 22I, answer-test relay 222, ringing relay 223, and retard coil 224.

It is to be observed that the talking key K6 connects the conductors of the operators telephone 250 to the talking conductors 215 and 216 extending to the line circuit LCS, and that a tandem connection to the talking conductors 2' and 22 2 of the group-call line G02 may be made through contacts of the connect key K'I. The arrangement is such that the ringing key KI 0 cannot become connected with the ringing concluctor 213 of the group-call line (even though keys K1 and K8 are operated) until a response on the supervisors line 253 results in the operation of line relay 22I; neither can ground potential be applied to the conductor 274 in the common group-call line G02 to actuate the transfer relays such as 296 until line relay 2II of the supervisors line 253 has been operated. The emergency key KI I, however, is provided in line circuit LCB to simulate a response on the line 253 to enable line relay 2 to be operated in an emergency to condition the group-call circuits when no response can be obtained over the supervisors line.

The invention having been described generally, a detailed description of the operation of the apparatus shown will now be given. The system as illustrated in Fig. 1 will be considered first.

Making common connection with the group of lines Let it be assumed that the system of Fig. 1 is installed as illustrated to enable a group of volunteer firemen to be called when needed. When the group-call operator receives a report of a fire warranting the calling of the volunteer firemen reached over the group of lines including lines I5I to I53 to Fig. l, the operator actuates the talking key K2, thereby connecting the conductors of the operators telephone I00 respectively with the conductors HI and I72 of the group-call line GCI. A ringing circuit is preidle.

conductors Ill and I12 of the group-call line GCI. At the same time, transfer relay IIG operates to disconnect each of the party lines of the called group from its associated regular switchboard terminals and to transfer it to the talking conductors of the group-call line G I by way of contacts 01 the associated ringing relay and the associated talking condensers.

By the described operation of relays I06 and H6, the operators telephone I00 and the group lines, including I5I to I53, are placed in common telephonic communication, through operated key K2.

Call supervisory lamps, such as LI, L3, and L5, become lighted as a result of the application of ground potential to conductor I74. Lamps LI and L3, for example, may become lighted through contacts of line relays MI and I II respectively. The lighting of a call lamp individual to a line indicates to the operator that the associated line is idle. If all the group lines are idle at the moment, all of the lamps such as LI, L3, and L5 become lighted to indicate that fact to the groupcall operator.

One or more lines, however, may be in use at the time the above transfer is accomplished by the described operation of relays I06 and II 6. Assume, for example, that party line I52 is in use, all of the other lines of the group being The busy condition of party line I53 is indicated to the group-call operator by the failure of the call lamp L3 to light, which failure of the lamp L3 to light is occasioned by the immediate operation of line relay I I I over the busy line I52.

Upon noting the unlighted condition of the call lamp L3, the group-call operator may converse with the subscriber whose receiver (not shown) is removed online I52. If the subscriber whose receiver is removed is the subscriber at the 42-cycle substation I53, the substation of the desired fireman, the operator may request that the desired fireman at that substation be called to the telephone, unless he himself is speaking, in which event she may immediately give the desired instructions.

On the other hand, if line I52 is in use because the receiver is removed at some other substation thereon (the -cycle substation I32 for example), the group-call operator may explain that an emergency fire call is being made over the line and request the subscriber to replace his receiver to allow the emergency call to be made.

When the receiver has been replaced on line I 52, line relay III restores, closing a lighting circuit for call lamp L3 over conductor I14. Lamp L3 thereupon becomes lighted to indicate that the line has become idle.

The ringing operation After having actuated the key K2, the operator may operate the key KI to cause ringing current to be projected over each of the lines of the group. She may operate the key KI and leave it operated to apply continuous ringing current, or she may operate the key KI intermittently to cause the ringing on the lines to occur intermittently.

When the key KI is operated, ground potential is applied, through contacts of the operated talk key K2, to conductor I I3 of the group-call line GCI. The ringing relays of the several line circuits are thereupon operated. Ringing relay I03 of the line circuit LCI is operated through contacts of line relay IOI, answer-test relay I02, and answer-supervisory relay I05. Upon operating, relay I03 applies ground potential to the upper or tip talking conductor of the called line, and applies ringing current from the 16-cycle source IN to the lower or ring conductor of the called line. The complete ringing circuit for substation l'ol on individual line I5I is from the indicated free negative pole of the grounded exchange battery, through the secondary winding of ringing transformer I01, the common 16-cycle ringing lead, the two windings of answer-test relay I02 in series, contacts of ringing relay I03, contacts of transfer relay I06, the lower or ring conductor of line I5I, through the usual ringer and condenser (not shown) at substation I6I, the upper or tip conductor of line NH, and thence to ground, through contacts of operated relays I06 and IE3. The previously mentioned usual condenser in the ringing circuit prevents direct current from flowing until a response has been obtained and relay I02 is prevented from operating responsive to alternating current, such as by being provided with the indicated copper sleeve and copper collar.

In the line circuit LC2, the operation of ringing relay I I3 results in ringing current being applied from the illustrated 42-cycle ringing lead and through the upper winding of answer-test relay II2 to the called line I52, a return path to ground being provided through the upper contacts of relay II3. The 42-cycle ringer (not shown) at the desired substation IE3 is thereby operated. At the same time, 66-cycle ringing current is similarly transmitted through the line circuit LC3 to actuate the ringer at the 66-cyc1e substation I59 on party line I53.

It is to be noted that the answer-test relays I02 and II2 are similar, each being illustrated as a double-wound differential relay. This arrangement is customary when the comparatively high frequency harmonic ringing current of from 30-cycles to 66-cycles, for example, is to be transmitted through the same type of relay that may be used also for the passage of the comparatively low frequency 16-cycle ringing current used for signaling individual-line substations. The upper winding of the relay is customarily arranged with the correct number of turns for operation when any frequency of ringing current from 30- cycles to 66-cycles is used. The differentially wound lower winding of the relay is included also in the circuit (as is illustrated in connection with the line circuit LCI) when the 16-cycle ringing current is used. The lower winding of the relay partially neutralizes the effect of the upper Winding of the relay, lowering the tendency of the relay to respond during the longer half-cycles of the 16-cycle ringing current.

In the line circuit LCI, as a further result of the operation of ringing relay I03, call supervisory relay I04 operates in a circuit including grounded conductor I14, lower contacts of line relay ISI, and the lower contacts of relay I63. At its inner contacts, relay I84 locks itself by shunting the lower contacts of relay IE3. At its lower contacts, relay m4 prepares an operating circuit for answer-supervisory relay I05.

In the line circuit LC2, call-supervisory relay I I4 is operated in a similar circuit, locking itself at its inner contacts, and preparing a circuit for relay H5 at its lower contacts.

The above operation of the calLsupervisory relay in each of the line circuits responsive to the starting of the ringing operation prepares for the subsequent operation of an answer-supervisory relay in each line circuit when a response occurs on the associated line.

Response When the subscriber at substation It! removes his receiver, the application of ringing current to his line is terminated. If the receiver is removed in the silent period between successive operations of ringing key KI and between the consequent successive operations of ringing relay I03, line relay IIII operates directly and immediately over the called line to open the ringing circuit at its upper contacts. On the other hand, if the response occurs during an application of ringing current, the closure of the usual directcurrent bridge across the conductors of the called line permits direct current to flow in the abovetraced ringing circuit, whereupon answer-test relay IB2 operates. Upon operating, relay I02 open-circuits and restores ringing relay I03, whereby the application of ringing current is terminated and line relay IfiI is again connected to line I5I. Relay I02, being slow-acting, remains operated for a slight interval after relay I03 restores. During this interval the operation of line relay IIlI occurs. At its upper contacts, relay Ii'II opens the circuit of relay I33 to thereby prevent resumption of the ringing operation when relay I 92 restores.

At its lower contacts, line relay Ifil open-circuits and extinguishes the call lamp LI, at the same time open-circuiting the slow-restoring call-supervisory relay I9 5. At the front contact of the lower armature of the line relay Iill, ground potential on conductor I14 is extended, through contacts of call-supervisory relay I94, and contacts of recall key K5, to answer-supervisory relay I05. Relay I95 thereupon operates. At its upper contacts, relay I85 disconnects ringing relay I 83 at an additional point to prevent resumption of ringing when the receiver is replaced and relay I OI restores; at its lower contacts relay I85 closes a self-locking circuit to conductor I'M; and at its inner lower armature it disconnects transfer relay I65 from conductor I14 and connects it to a new circuit which includes conductor I15 and the front contact of the lower armature of line relay IcI. Transfer relay I 85 is maintained operated over this new circuit, and answering supervisory relay I85 remains operated in its locking circuit including its lower contacts.

Answer lamp L2 becomes lighted in parallel with answer-supervisory relay H35, whereby the operator is given positive answered supervision with respect to line I5I.

The group-call operator may now converse with the subscriber at substation I6I and give him any desired information or instructions.

When the subscriber at the called 42-cyole substation I63 on line I52 responds, answer-test relay II2 operates momentarily (assuming that the response occurs during a ringing period). Ringing relay H3 is consequently restored, whereupon line relay I I I operates over the called line. The operation of line relay III results in the operation of answer supervisory relay II5, through the front contact of the lower armature of line relay III, and through contacts of the slow-restoring call supervisory relay H4. Relay II5 opens a further point in the circuit of ringing relay H3 at its upper contacts, while at its lower contacts it looks itself directly to conductor I14. Call supervisory lamp L3 becomes extinguished when disconnected at the lower contacts of line relay III, and call supervisory relay II4 restores. Lamp L4 becomes lighted in parallel with relay H5 to give the operator answered supervision with respect to line I52.

In a similar way, the call lamp L5 of the line circuit LC3 becomes extinguished and the answer lamp L6 becomes lighted when the subscriber at the called 66-cycle substation I 69 on party line I53 responds.

Disconnect When the subscriber at substation IGI on individual line I 5| replaces his receiver, following his receipt of information or instructions from the group-call operator, the consequent restoration of line relay Ifll results in the relighting of call lamp LI. Answer lamp L2 remains lighted under this condition in parallel with answersupervisory relay I615 (locked up at the lower contacts thereof) as a reminder that the call over line I5I has been answered. The relighting of lamp LI along with lamp L2 indicates to the group-call operator that the sub-scriber on line I5I has replaced his receiver.

As a further result of the restoration of line relay IiH, transfer relay I95 restores (answersupervisory relay I being in operated condition) Upon restoring, transfer relay I96 transfers the conductors of line I 5| back to its regular switchboard terminals, including the jack J I and its multiples, enabling the subscriber at substation IBI to make immediate use of his telephone line in the regular manner. If the subscriber at substation IGI is the fire chief, O1 someone else in a supervisory capacity, he may immediately make an outgoing call in the usual manner, to the fire station, for example.

When the subscriber at the called 42-cycle substation I63 on party line I52 replaces his receiver, the consequent restoration of line relay III results in call lamp L3 becoming relighted as a disconnect signal, answer lamp L4 remaining lighted. Similarly, call lamp L5 of line circuit LC3 becomes relighted as a disconnect signal when the receiver is replaced at the called 66- cycle substation I69.v The lines I52 and I53, however, remain connected respectively with line circuits LC2 and LC3, as the common transfer relay I I6 is not affected by the restoration of the line relay in either of the latter line circuits.

Recall Any one of the substations may be recalled after the receiver has been replaced, which is particularly desirable if, for example, the subscriber replaces the receiver before the groupcall operator has given complete instructions. or if the group-call operator receives additional or chan ed instructions for one or more of the firemen.

To recall the individual line I5I, the groupcall operator need only momentarily operate recall key K4 of the line circuit LCI, followed by an operation of the ringing key KI. When key K4 is momentarily operated, answer supervisory relay I restores and opens a further point in its previously existing locking circuit at its lower contacts. Transfer relay I86 is again connected to the grounded conductor I14, with the result that it is again operated to transfer line I5I back from its regular switchboard terminals to the line circuit LCI. At the upper contacts of relay I05, the circuit of ringing relay IE3 is again prepared, with the result that this relay may be operated under the control of ringing key KI to again operate the ringer at substation IEI.

Answer lamp L2 becomes extinguished when lower contacts of relay I65 are opened. Lamp L2 remains extinguished, and relay I05 remains restored, after the momentary operation of key K4 because the lower contacts of relay I05 have opened.

Call supervisory relay W4 is again operated (re sponsive to the reoperation of ringing relay I03) to lock itself operated at its inner contacts and to prepare a reoperating circuit at its lower contacts for answer-supervisory relay I05. As a result, the circuit conditions in line circuit LCI are identical with those existing during the initial ringing operation on the line I5! previously described.

When the recalled subscriber responds, line relay IUI is again operated to open-circuit ringing relay I03; to restore call supervisory relay I04; and to reoperate answer-supervisory relay I05. The call lamp LI is again extinguished, and the answer lamp L2 becomes lighted again. The operator may now give the additional or changed instructions to the answering subscriber.

A momentary operation of therecall key K5 similarly enables the selected substation I63 on line I52 to be recalled. Relay H5 restores and lamp L4 becomes extinguished when the key K5 is momentarily operated. The circuit of ringing relay I I3 is again prepared at the upper contacts of relay I I5.

Clearing out When a satisfactory response has been obtained on all lines of the called group, the operator may restore the talking key K2. When this occurs the ringing key KI is disconnected from the line circuits, along with the conductors of the operators telephone I08. At the lower contacts of key K2, ground potential is removed from conductor II4. By this operation any operated ones of the relays of the line circuits (such as I04, I05, and I06 of the line circuit LCI) are restored, and any lighted ones of the supervisory lamps (such as LI and L2) are extinguished. Transfer relay IIB also restores. The circuits are thus returned to their illustrated normal condition.

Operation of the system of Fig. 2

Referring now particularly to Fig. 2, let it be assumed that the system as illustrated therein is used to call firemen, for example. The operator is preferably instructed to communicate immediately with the supervisor at substation 263 upon receipt of a report of a fire. For this purpose, the operator may actuate the talking key K'I, followed by actuation of the ringing key K6.

Calling the supervisor Actuation of key K'I connects the conductors of the operators telephone 200 to the talking conductors 215 and 216, extending through line circuit LCB to the supervisors line 253. The call buzzer B is disconnected by the key K1, and at the lower contacts of the key a lighting circuit for supervisory lamp L8 is established through contacts of line relay 2I I of the line circuit LC--6.

When the ringing key K6 is operated a circuit is thereby closed, through contacts of the key KI, contacts of line and answer-test relays 2H and 222, for ringing relay 223. Upon operating, ringing relay .223 applies ringing current to line 253 from the 16-cycle ringing source 201.

When the supervisor responds, by removing the usual receiver (not shown) at substation 263, the resultant closure of a direct-current bridge across the conductors of line 253 permits answer-test relay 222 to respond. The circuit of ringing relay 223 is thereby temporarily interrupted. Relay 223 thereupon restores and reconnects line relay 2I I. Relay 2II energizes over line 253 and interrupts the circuit of ringing relay 223 at an additional point, thereby preventing resumption of the ringing operation.

At its upper contacts, line relay 2 disconnects ground potential from conductor 279, thereby extinguishing supervisory lamp L8 to give the operator answered supervision. The group-call operator and the supervisor may now converse over the established connection, through contacts of the talk key Kl, over conductors 215 and 216, and line 253.

Upon being informed of the report, the supervisor may or may not instruct the group-call operator to call the volunteer firemen over the firemen lines, such as 25I and 252.

Making the group connection Assuming that the supervisor instructs th group-call operator to call the firemen, the operator operates connect key K8, thereby extending connection to conductors 2II to 214'constituting the group-call line GC2. The operators telephone 260 and the supervisors substation set 263 are both thereby telephonically connected with the conductors 2' and 212 of the groupcall circuit.

With line relay 2II in operated condition, ground potential on conductor 211 is now extended, through contacts of the connect key K8, to conductor 2'54 of group-call line G02.

In the line circuit LC4, the placing of ground potential on conductor 274 by the described operation of connect key K8 results in call lamp L9 becoming lighted, and in the operation of transfer relay 206 through contacts of answer-supervisory relay 2B5. Relay 266 transfers lin 25I from its normal switchboard terminals through contacts of ringing relay 2%, and through the illustrated individual talking condensers to talking conductors 2' and 212, now telephonically connected to operators telephone 2% and substation 263, as pointed out.

Similar operations occur at the line circuit LC5, including the lighting of call lamp LII, as well as at the other line circuits which may be interposed between line circuits LC4 and LC5 at the broken portion of conductors 2' and 214. It will be understood, of course, that the line relay is immediately operated at any line circuit to extinguish the call lamp in the event that the associated line is busy when transferred thereto as above described.

Ringing When ringing key K6 is operated to signal the lines of the group, ground potential is extended through contact of the key K1, and thence through the inner contacts of the operated line relay 2| I, contacts of th key K8, to the common ringing conductor 273. From thence a circuit path extends to the ringing relay of each of the idle line circuits. The circuit of ringing relay 203 includes contacts of line relay 23!, of answertest relay 202, and of answer-supervisory relay 203. Responsiv to the operation of relay 203, ringing current is applied to the associated line 25L Call-supervisory relay 2% responds to the operation of relay 283 by closing a locking circuit for itself in parallel with the lower contacts of relay 203. At its lower contacts relay 2G4 prepares a circuit for answer-supervisory relay 295.

Similar operations occur in the other line circuits, such as LC5.

Response .supervisory relay 205 through contacts of the slow-restoring call supervisory relay 284. Relay 205 closes a locking circuit for itself at its lower contacts; disconnects ringing relay 263 at its upper contacts; and, at its inner lower armature, it transfers relay 205 into a new circuit including the front contact of the lower armature of line relay 20l, enabling the line 25l to become disconnected from the group call circuit when the receiver is subsequently replaced thereon. Answer-supervisory lamp LID becomes lighted in parallel with the winding of relay 205.

As the called firemen respond, they may receive their instructions from the supervisor at substation 263 or from the operator at telephone 200, or jointly from both. The operator may keep the supervisor informed of the condition of the lines as disclosed by the supervisory lamps, such as L9 to L12.

Recall When a satisfactory response has been obi tained from all the firemen, the supervisor at substation 263 may replace his receiver (not shown), whereupon line relay 2!! restores. At its inner contacts line relay 2| l disconnects ringing key K6 from key K8 and ringing conductor 213 of the group-call line G02, again preparing a ringing circuit in the line circuit LCB over which the supervisor at substation 263- may be recalled in the discretion of the operator at telephone 200. At its upper armature, line relay 2 removes ground potential from conductor 21! and replaces it on conductor 2'16. As a result of the removal of ground potential from conductor 211, conductor 214 is deprived of ground potential, clearing out the line circuits such as LC--4 and LC5. The placing of ground potential on conductor 218 by line relay 2 closes a lighting circuit for supervisory lamp L8, through contacts of the actuated key Kl. Lamp L8 thereupon becomes lighted as a disconnect signal. The operator at telephone 200 is then expected to restore the keys K1 and K8.

Restoration of connect key K8 extinguishes hold lamp L1, while the restoration of key K1 extinguishes the supervisory lamp L8.

The supervisor calls When the supervisor at station 263 removes his receiver (not shown) to originate a call, the resultant energization of line relay 2! l, in addition to preparing a ringing circuit over conductor 219 for the group-call line G02, applies ground potential to conductor 21?, thereby lighting supervisory lamp L8 as a call lamp and operating the call buzzer B, through contacts of the key K1 in normal condition. The operator at telephone 200 responds by actuating the key K1, thereby completing a talkin circuit between telephone 200 and substation 263; preparing a ringing circuit from the ringing key KB to the group-call circuit; disconnecting the call buzzer B; and extinguishing the supervisory lamp L8.

The supervisor may now instruct the operator at telephone 200 to call the firemen, which she may do by actuating the key K8, followed by desired actuation of the ringing key K6 as hereinbefore described.

I claim:

1. In a telephone system, subscriber lines each having its own terminals through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, the group-call operator having a ringing key common to all said branches, means in each branch responsive to an actuation of said key for projecting ringing current over the associated transferred line, and means in each branch for preventing, the said projection of ringing current so long as a receiver is oil the hook at a substation on the associated subscriber line.

2. In a telephone system, subscriber line each having its own terminals through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, the group-call operator having a ringing key common to all said branches, means in each branch responsive to an actuation of said key'for projecting. ringing current over the associated transferred line, and means in each branch circuit responsive to the call over the associated subscriber line being answered for disabling the means therein for applying ringing current and for maintaining it disabled after the receiver has been replaced on the called line.

3. In a telephone system, subscriber lines each having. its. own terminals through. which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, the group-call operator having a ringing key common to all said branches, means. in each branch responsive toan actuation of said key for projecting ringing current over the associated transferred line, means in each branch circuit responsive to the call over the associated subscriber line being answered for disabling the means therein for applying ringing current andfor maintaining it disabled after thereceiver has been replaced on the called line, and recall means ineachbranch for enabling. the group-call 0perator to recall the associated subscriber line after the called subscriber thereon has answered and again replaced his receiver.

4. In a telephone system, subscriber lines each having its own terminals through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, each of the transferred lines being connected telephonically with the group-call line when transferred to its associated branch thereof, the group-call operator having a telephone connected with the group-call circuit enabling her to converse with any subscriber who has the receiver removed when his line is transferred, and supervisory means including signals individual respectively to said branches for informing the operator of the busy or idle condition of each of the transferred lines.

5. In a telephone system, subscriber lines each having its own terminals through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, means for transmitting a call signal over each of said subscriber lines, means responsive to the removal of the receiver on one of said subscriber lines for terminating the signaling operation thereover, and means responsive to the subsequent replacement of the receiver for transferring the concerned subscriber line back to its own said terminals.

6. In a telephone system, subscriber lines each having its own terminals through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, means for transmitting a call signal over each of said subscriber lines, means responsive to the removal of the receiver on one of said subscriber lines for terminating the signaling operation thereover, means responsive to the subsequent replacement of the receiver for transferring the concerned subscriber line back to its own said terminals, and recall means in the branch associated with the last-named line circuit for causing said line to be transferred again thereto and for again enabling said signaling means to signal thereover.

7. In a telephone system, subscriber lines each having its own terminals through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, means controlled at will by a group-call operator for transferring each of said lines from its associated switchboard terminals to its associated branch of the group-call line, means for signaling on each of said subscriber lines, and means responsive to the replacement of the receiver after it has been re- 7 moved on one of said lines in answer to said signaling for transferring such subscriber line back to its own said terminals.

8. In a line circuit for use between a group-call line and a subscriber line, a transfer relay for transferring the subscriber line from its regular switchboard terminals to the line circuit, a line relay operable over the transferred line when response occurs thereon, a supervisory relay responsive to the operation of said line relay, and circuit connections controlled jointly by said line and supervisory relays for causing said transfer relay to transfer said line back to its regular switchboard terminals when the line relay is restored at the end of the condition of response on the subscriber line.

9. In a line circuit for use between a group-call line and a subscriber line, means responsive to a call on said group-call line for transferring said subscriber line from its regular switchboard terminals to the group-call line by way of said line circuit, a pair of supervisory signals assigned to said line circuit, means for energizing the first of said signals dependent upon the transferred line being or becoming idle, means for calling over the transferred line when idle, and means dependent upon said call being answered for energizing the second of said signals.

10. In a group-call telephone system, normally separate subscriber lines, switchboard means comprising separate terminals for each of said lines through which regular telephone service may be rendered, a group-call line having branches corresponding respectively to said subscriber lines, a switching device, and means responsive to actuation of said device for disconnecting each of said subscriber lines from its associated switchboard terminals and transferring it to its associated branch of the group-cal] circuit.

' GLENN KINER.

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