US2165579A - Telephone system - Google Patents

Description

July 11, 193 N. H. SAUNDERS TELEPHONE SYSTEM Filed Jan. 14, 1937 3 Sheets-Sheet l bmt x283 Elli MA N x m L INVENTOR. RMAN H. SAUNDERS ATTORNEY;

July 11, 1939. N. HfsAuNDERs TELEPHONE SYSTEM Filed Jan. 14, 1937 HOUMS HOLOEI'IHS o1 3 Sheets-Sheet 2 omN ORMAN H. SAUNDERS M ATTORNEY.

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TELEPHONE SYSTEM v Filed Jan. 14, 1937 3 Sheets-Sheet 3 T0 DISTANT EXCHANGE RLSE i o E F I Q C) 5- l Lu 9 E m r m WW 1 m 1 M m *5 I\ O m INVENTOR; N RMAN H. SAUNDERS Y Patented July 11, 1939 urrso STATES TELEPHONE SYSTEM Norman H. Saunders, Homewood, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application January 14, 1937, Serial No. 120,507

2-2 Claims.

The present invention relates in general to improvements in telephone systems, but is particularly concerned with means for handling long distance or toll calls in connection with an automatic telephone system.

When a toll call is received at an automatic exchange, it usually comes in on a manual switchboard. An operator thereat, upon learning the number of the wanted subscriber, sets up the connection by means of a suitable cord circuit and the automatic switches in the usual manner.

It is desirable that a toll call be given preference over a local call so that the toll trunk lines between cities will not be tied up for a single call any longer than is absolutely necessary. The operator that receives a toll call frequently finds that the wanted subscribers line is busy. For instance, if two automatic subscribers are talking over a local connection and either of these subscribers is wanted for a toll connection, it is desirable that the operator be able to inform the desired subscriber that he is wanted for a toll call. In order to accomplish this purpose, a new and improved connector switch has been provided by means of which the operator can establish a connection with a busy line and inform the wanted subscriber thereon of the waiting toll call.

The object of the invention is to provide a toll oiiering connector switch that is accessible both to local subscribers and to the toll operator in order that connections may be extended to wanted subscribers in an automatic system. Since all the connector switches in the telephone system are capable of seizing either idle lines or busy lines, special arrangements must be provided whereby the'seizure of a switch by a regular subscriber prevents that switch from cutting in on a busy line; and whereby the seizure of a switch by the toll operator permits the operator to control that switch, when a busy line is encountered, to cut in on the busy line and offer the toll connection to the wanted subscriber. Heretofore, the operator has been provided with a key to ground the conductors of the trunk line to unbalance a differentially wound relay in the connector. This caused the operation of the differential relay and permitted the connector to cut in on a busy line. With this type of toll oiiering connector, the regular local subscribers soon found out that they could control the connector to cut in on busy lines by merely grounding one of their line conductors momentarily and thus eavesdrop on private conversations. In fact, a discharged telephone employee has sold an apparatus that would perform this operation, to regular subscribers in a telephone system.

In this present invention, toll offering by the operator is controlled by the momentary application of positive booster battery to the conductors of the trunk line to control the connector to cut in on a busy line. This practically eliminates the possibility of a local subscriber controlling a connector to cut in on a busy line, since the connector will only cut in on a busy line when positive booster battery is applied to the trunk conductors.

Another object of the invention is to provide a trunk repeater over which connections are extended to subscribers in a distant automatic exchange. The trunk repeaters are accessible to local automatic subscribers and to the toll operator to extend connections th-ereover. Furtherirore, the operator can control the trunk repeater to connect positive booster battery to the trunk line conductors and thereby control the connectors in the distant automatic exchange to cut in on busy lines.

The foregoing objects, together with others not specifically pointed out, will be described hereinafter with reference to the accompanying drawings comprising Figs. 1, 2, and 3. The drawings show by means of the usual circuit diagram sufficient of the apparatus involved to permit the same to be readily understood.

Fig. 1 shows the calling end of a toll operators dialling cord 0, terminating in a plug P, and equipped with a dialling key K. The dial CD may be associated with the cord circuit by operating the key K to the right. The cord circuit 0 may be of any suitable type and is therefore not shown in full; only those elements which concern the invention are shown. The

line switch LS, accessible to the operator at the jack J, is one of a plurality of line switches accessible to the operator over a like number of jacks, such as jack J. The regular telephone I subscribers lines also terminate in line switches and are accessible in the banks of the connectors. The line switch LS may be of the same construction as the line switch LS-i shown in Fig. 2, which is of the well-known rotary type having no normal position and moves its wipers in one direction only. The line switch LS, together will all other line switches in the system, have access to selector switches, such as selector switch S. The selector S is of the well-known vertical and rotary type of Strowger switch and has access to outgoing trunk repeaters, such as outgoing trunk repeater OTR, and to connector switches, such as connector switch C.

In Fig. 2 there is shown a connector switch C. which is of the well-known vertical and rotary type of Strowger switch, that has been modified by additional relays, the function of which is part of this invention and will be described in de- 7 tail subsequently in connection with the operation of the connector switch shown. The connector switch C has access to automatic subscribers lines, such as the line of substation A. The substation A is of the type usually found in all automatic telephone systems, and is shown with its line conductors terminating at the exchange in the individual line switch LS-l, which has access to selector switches, such as selector switch S shown in Fig. 1. The line switch LS| is a standard rotary line switch of the type disclosed in Patent No. 1,693,037, granted to John Erickson, November 27, 1928. This switch is of the step-by-step type in which the wipers move in a forward direction only, and in which the wipers are advanced when the stepping magnet retracts its armature rather than when it attracts its armature.

In Fig. 3 is shown an outgoing trunk repeater OTR, which is one of a plurality of trunk repeaters accessible, for example, from the level of the selector switch, such as selector switch S, and is used to extend calls over the trunk line comprising conductors 30 and 3| to a distant automatic exchange.

Throughout the drawings numerous types of relays, well known in the automatic telephone art, are shown. Slow-to-operate relays are shown having a solid black upper section. Slowto-release relays are shown either with a crosshatched lower section or with double lines representing a copper sleeve on the cores of the relays. The shunt field relay in Fig. 3, is shown by representing the two windings of the relay on separate cores included in a shunted magnet circuit. A number of three-pole relays of the type covered by Pye Patent No. 1,673,884, issued June 19, 1928, are also employed and are shown with their cores equipped with a bar magnetically separating the two windings of the relays. This type of relay only operates when the circuit through both its windings assist each other when they are energized, or when the energizing circuit is completed through its upper or operating winding alone, and will not operate when the energizing circuits through both its windings oppose each other.

In order to make the invention clear, it is believed advisable to describe the manner of operation by explaining how a connection is established between two local automatic telephone subscribers and then by explaining the operation when the toll operator extends a connection to a busy line.

For this purpose, it will be assumed that a local automatic telephone subscriber, whose substation equipment is similar to that of the subscrib er at substation A, has removed his receiver from the switch-hook and has dialled the directory number of the subscriber at substation A. Responsive to the removal of the receiver at the calling subscribers substation, a line switch similar to line switch LS| shown in Fig. 2, operates in the usual manner and extends the connection to an idle selector switch, such as selector S, over the trunk conductor l0, H and I2. The calling subscriber receives the usual dial tone signal to indicate that the selector is in a position to receive the first digit of the called number. He-

sponsive to the dialling of the first digit of the called number, selector S operates to raise its wipers |3-|5, inclusive, opposite the level of the bank contacts corresponding to the digit dialled, and then the wipers are automatically rotated to select an idle trunk line accessible in that level.

It will be assumed that the first idle line encountered by the wipers |3|5, inclusive, is the trunk line comprising conductors Ni -l8, in elusive, extending to connector C, shown in Fig. 2. When the connection is extended to connector C, line relay 203.energizes and prepares the connector for operation. The energizing circuit for line relay 203 may be traced over the following path: ground, upper winding of line relay 203, upper or operating winding of the three-pole electro-polar relay 202, normally closed contacts controlled by armature 2M, conductor l8, wiper l5 of the selector S, conductor l2, over the calling subscribers line switch and subscribers line and return, conductor I0, through the selector S, wiper l3 of the selector, conductor it, normally closed contacts controlled by armature 2 |5, lower or polarizing winding of the three-pole electropolar relay 202, lower winding of line relay 203, to battery. Line relay 203 operates and completes an obvious energizing circuit for slow-torelease relay 204 at armature 2|9. Release relay 204, upon operating, at armature 2H5 grounds the release conductor I! to maintain the preceding switches operated, opens a point in the circuit for the release magnet 2|3 at armature 2|8 and its back contact, and at its front contact closes a point in the operating circuit of vertical series relay 205 and the vertical magnet 2| I. The closing of the contacts at armature 2|'| prepares a holding circuit for ring-cut-oif relay 206 and switching relay 2|0 that will be ex-,

plained subsequently.

The connector switch C is now in readiness to receive the second series of impulses corresponding in number to the second digit of the called number. Responsive to the second operation of the calling device at the calling subscribers station, the circuit of line relay 203 is interrupted a number of times. Attention is called to the fact that the flux generated by the current flow through the upper winding of the threepole electro-polar relay 202 is in opposition to the flux generated by the current flow through the lower winding, therefore, the relay does not operate. The first time the line relay 203 falls back, a circuit is completed from ground, armature 2|9 and its resting contacts, armature 2E8 and its front contact, contacts 220 of the off-normal springs ON, winding of vertical series relay 205, winding of the vertical magnet 2| to battery. Vertical magnet 2| operates over this circuit and raises the shaft and wipers of the switch in the well-known manner, one step. Vertical series relay 205 operates in series with the vertical magnet 2||. The contacts 220 of the off-normal springs ON are open and contacts 22| are closed in response to the raising of the shaft and wipers of the switch. Each succeeding time the circuit of line relay 203 is interrupted, a circuit is completed from ground, armature 2!!! and its resting contacts, armature 2|0 and its front contact, contacts 22| of the oiT-normal springs ON, armature 222 and its front contact, winding of the vertical series relay 205, winding of the vertical magnet 2| I, to battery. Due to their slowrelease characteristics, relay 204 and relay 205 remain energized throughout the series of impulses. vertical magnet 2|| operates in the wellknown manner to raisethe wipers 223-225, inclusive, opposite the level of bank contacts corresponding to the number of impulses transmitted by the calling subscriber. At the end of the vertical movement, vertical series relay 205 falls back and by closing the resting contacts of armature 222 prepares the circuit for operating rotary magnet 2|2 in parallel with relay 209,

Responsive to the dialling of the last digit by the calling subscriber, the rotary magnet 2 l 2 and relay 209 are operated over the following circuit: ground, armature 219 and its resting contact, armature 218 and its front contact, contacts 22| of the off-normal springs ON, armature 222 and its resting contact, armature 22B and its resting contact, over one path including the winding of relay 269, to battery, and over the other path including armature 228 and its resting contact, winding of the rotary magnet M2, to battery. Each time the line relay 2G3 falls back, in response to the impulses transmitted from the calling subscribers dial, the rotary magnet 2E2 operates in the well-known manner to advance the wipers 223225, inclusive, into engagement with the contacts of the called line. It should be noted that at armature 229 and its restingcontact, relay 2B9 opens a point in the operating circuit of the switching relay 2H) and at the front contact of this armature connects the test wiper 224 to the winding of the busy test relay 288. Relay 259 also, at its armature 221, completes a circuit around armature 225 and its resting contact in order to guard against the rotary magnet circuit being interrupted by the operation of busy test relay 208 as a result of wiper 224 passing over busy test contact.

It will be assumed that the wipers 223-225, inclusive, have been rotated, in response to the dialling of the last digit, into engagement with the bank contacts to which conductors rec-232, inclusive, of substation A are connected. Relay 209, due to its slow release characteristics, remains energized a short period of time after the last impulse has been received. If the subscriber at substation A is engaged in a conversation, ground is encountered on test conductor 231, by the test wiper 224 of the connector switch C, and a circuit is accordingly completed by way of ar mature 229 and its front contact, armature 238 and its resting contact, winding of the busy test relay 208, to battery. Busy test relay 2% operates over this circuit and at armature 23s and its front contact prepares a locking circuit for itself and at armature 242 connects the busy tone to conductor 18 to give the calling subscriber the busy signal. Relay 289 subsequently falls back and at the normally closed contact controlled by the front contact of armature 229 completes the locking circuit for busy relay 208 from ground at armature MS of the operated release relay 204. At armature 24! and its front contact, busy test relay 208 prepares a circuit for the toll offering relay 231, but since the calling subscriber has no facilities for initiating the operation of the threepole electro-polar relay 202, the toll offering relay 20] cannot be operated at this time.

When the calling subscriber hears the busytone transmitted back over his line, he hangs up his receiver and accordingly opens the circuit for the line relay 293. Upon falling back, line relay 2G3 opens the circuit of release relay 2%. Relay 264 restores and at armature 2 i 6 removes ground from the release trunk conductor ll to permit the preceding switches to release. At armature 2E8, relay 2G4 completes a circuit from ground at the resting contact of armature 219, armature M8 and its resting contact, lower armature and resting contact of back-bridge relay 2611, contact 245 of the operated off-normal springs ON, winding of the release magnet 2|3, to battery. Release magnet 2H3 operates, causing the shaft and wipers of the switch to restore to normal. The operated busy relay 208 falls back when the holding ground is removed at armature 2I6.

It should be noted that when the subscriber at substation A is busy that the test wiper 22d, of the connector switch C, encounters a ground potential on the bank contact to which test conductor 2: is connected. Ground is applied to conductor 23| either from the upper armature and front contact of the line relay 234 of the line switch LSl, or from the test conductor of the selector switch to which test Wiper 341 of the line switch LS-l is connected by way of armature 23d and its front contact. Furthermore, it should be understood that the selector switch to which the line switch LS-l is in engagement with is similar to selector S shown in Fig. 1, and that the connector switch used to complete the connection with the wanted subscriber, is similar to the connector switch C shown in Fig. 2.

Having explained the operations that take place when a local subscriber endeavors to establish a connection with a busy subscriber at station A, a description will now be given of the operation of'the circuit when the wanted subscribers line is idle. the line of the wanted subscriber at substation A is idle when the calling subscriber has operated the connector C to his line. Such being the case, when the test wiper 224, of the connector switch C, comes to rest in engagement with the test contact to which conductor 23! is connected, it will find no ground potential and the busy test relay 2&8 will not be energized. Instead, when the slow acting relay 2% falls back, shortly after the last impulse has been received for operating the rotary magnet 2H2, a circuit is closed through the lower winding of the switching relay 210 as follows: from ground by way of armature 2E6, armature 249 and its resting contacts, lower winding of switching relay 2H], armature 229 and its resting contacts, test wiper 224, conductor 23 l, winding of cut-off relay 233 of the line switch LS-i, self-interrupting contacts of the operating magnet 249, winding of the operating magnet 249, to battery. When the above traced circuit is completed, the cut-off relay 233 of the line switch LS-i, is operated to clear the line of the substation A of its normal battery and ground connections in the line switch LSI. It should be noted that relay 233 is not fully operated at this time, due to a mechanical interlocking arrangement between the armature of this relay and the armature of the line relay 234, and the wipers of the line switch LS-l are not connected up. The

switching relay 2m, of the connector C, also opture 252 connects a ring-back tone circuit to the calling line.

The connection to the desired line has now been completed and the ringing current from the generator, INT. GEN, is intermittently transmitted out over the line to operate the ringer at substation A. The ringing circuit may be traced as follows: from interrupted generator INT, GEN, winding of ring-cut-off relay 296, armature 255,

It will now be assumed that armature 25L wiper 223, conductor 230, condenser and ringer at substation A, conductor 232, wiper 225, armature 253, armature 251, to ground. A portion of the generator current passes through small capacity condenser 258, armature 252, and conductor l6, to the telephone at the calling station for transmitting the well-known ring-back tone to the calling subscriber each time the called partys bell is rung. The ringing current is intermittently transmitted over this circuit until the called subscriber lifts his receiver, thereby short-circuiting the bell and condenser at his station and completing a direct current path over the above traced circuit for the lower winding of ring-cut-ofi relay 206. Ring-cut-oii relay 2B6 operates and at armature 253 completes a locking circuit for its upper winding from ground at armature 211. At armatures 255 and 257 and their resting contacts relay 2% opens the ringing circuit and at the front contacts of these armatures it completes the talking circuit to the subscriber at substation A.

Responsive to the completion of the talking cir cuit, back bridge relay 28! operates over the called subscribers loop as follows: ground, lower winding of back bridge relay 2M, armature 239 and its resting contact, armature 2'5? and its front contact, armature 252 and its front contact, wiper 225, conductor 232, over the called subscribers line, and back over conductor 230, wiper 223, armature 25! and its front contact, armature 255 and its front contact, armature 259 and its resting contact, upper winding of back bridge relay 20l, to battery. At armature 2M and its front contact, relay Zill closes another point in the circuit for grounding release trunk conductor l 7 and at armature 262 completes an additional locking circuitv for thering-cut-off relay 206 and the switching relay 2 is. The grounding of release trunk conductor IT at armature 26I and armature 2M, and the two locking circuits for maintaining the ring-cut-ofi relay 2% and switching relay 2l0 at armatures 252 and 21?, is for the purpose of maintaining the connector in its operated position until the last party of the connected subscribers hangs up his receiver. Relay 20l maintains the connector in an operated position as long as the called subscriber does not hang up his receiver and, the release relay 2% maintains the connector in an operated position as long as the calling subscriber has his receiver off the switch-hook. As a further result of the operation of the back bridge relay 20 l, the connections between the windings of the line relay 283 and trunk conductors l6 .and i2 are transposed, thereby reversing the direction of current flow in the calling lines. This reversal of current, as is well known in the telephone art, is for the purpose of operating the calling subscribers meter or to operate his coin-collect mechanism as the case may be.

The connection now having been completed, the calling and called subscriber may converse with each other as desired. After the conversation is completed both subscribers hang up their receivers. Since the connector switch C is of the well know last-party-release-type switch, the connection is not released until both subscribers have replaced their receivers. If the calling subscriber hangs up first, the loop circuit of line relay 203 is open. The line relay 23 restores to normal and upon falling back opens the circuit of the release relay 204. Release relay 262 subsequently falls back and at the resting contact of armature 218 prepares a circuitfor the release magnet 213. This circuit however is not completed until the back bridge relay 20l restores to normal and closes its lower armature and resting contact. The removal of ground at armatures 2H5 and 2|! has no effect at this time because relay 20! is still operated. When the called subscriber hangs up his receiver the loop circuit for back bridge relay 2D! is open and the relay is accordingly restored to normal. Relay 20! removes ground from the release conductor I? at armature 26! thereby causing the selector switch S and the calling subscribers line switch LS to be released in the well known manner. Relay 2!]! opens the locking circuit for the ringcut-ofi relay 206 and the switching relay 2H3 at armature 262 and they accordingly restore to normal. At the lower armature of back bridge relay 20I, the following circuit is completed for the release magnet 2l3: ground, armature 2m and its resting contact, armature H8 and its resting contact, lower armature and resting contact of the back bridge relay 20!, contacts 245 of the operated offnormal springs ON, winding of release magnet 2l3, to battery. The operation of release magnet 2l3 causes the shaft of the connector to restore to normal and it accordingly opens the circuit to the release magnet 2H3 by opening contacts 225 of the off normal springs ON. All the apparatus used in establishing the above described connection is now in its normal position and may be used for extending other calls. It may be well to mention at this time however, that if the called subscriber replaces his receiver first the back bridge relay 20! restores to normal and again transposes the connection between conductor l6 and I8 and the battery and ground through the windings of the line relay 203, and at armatures 26l and 262 opens a point in the circuit which is now maintained from armatures 2E6 and 2 i I on the release relay 2M. tact, back bridge relay 205 also prepares a point in the circuit for operating the release magnet 2|3. This circuit is not completed because the line relay 203 has not been deenergized. When the calling subscriber hangs up his receiver, the i line relay 23 and release relay 2% restores to normal and the circuit for the release magnet 2 I3 is now completed. The holding ground potential is removed from release trunk conductor IT at armature 246 and the locking circuit for ringcut-oif relay 2% and switching relay 2 I is opened at armature 2 I1 and the relays restore to normal. From the foregoing description of the release of the connector switch C, it will be understood that the connection will not be restored to normal until the last party hangs up his receiver.

The foregoing description was for the purpose of describing the operation of the connector switch C when local subscribers of the telephone exchange establish connections. A detailed description will now be given of the operation that takes place when the toll operator at the manual switchboard has received a toll call, from a distant city, for a subscriber in the automatic exchange. It will be assumed for this purpose, that the subscriber at substation A is the subscriber wanted to complete the toll call.

The toll operator, upon receiving a call from a distant manual exchange, answers this call by inserting the answering end of the plug of her cord circuit into the answering jack and receives the number of thewanted subscriber in the automatic exchange from the calling manual subscriber. It will be assumed thatthe subscriber desired is the subscriber at substation A which is accessible to the operator over the trunk terminating in jack J. The operator, upon observing the idle condition of the busy visual l, seizes the associated trunk by inserting the plug P into jack J, and by then operating her key K. Upon insertion of the plug P' into jack J, busy visual signal I is operated from ground supplied by spring 2 and its grounded working contact, The operation of the busy visual signal indicates to other operators, at whose position this trunk is multiplied, that the trunk is taken into use. Responsive to the operation of key K, a circuit is closed for sleeve relay 3 of the cord, by way of spring 20 and the sleeve of plug P, which has been grounded by spring 2 of jack J. Relay 3, upon operating, at armature 5 completes a locking circuit for itself independent of the spring 4 controlled by key K and at armature 6 prepares a circuit for polarized relay 1.

The operation of key K also connects the calling device CD to the tip and ring conductor of cord This completes a loop circuit by way of plug P, jack J and conductors 8 and 9 to the line relay of the line switch LS, which is similar to line switch LS-l shown in Fig. 2. Responsive to the operation of the line relay in the line switch LS, the rotary magnet is operated in the well-known manner and seizes a trunk line extending to an idle selector switch, such as selector switch S. The selector S is one of a plurality of such selectors which are accessible to the toll operator by way of line switch LS. The selector S is prepared for operation in response to its seizure over the loop circuit, which now includes wipers I9 and 2| of the line switch LS, and ground is returned over the test conductor and test wiper 20 of the line switch to maintain the line switch in its operated position. The operator now operates her calling device CD in accordance with the first digit of the wanted subscribers number, thereby controlling the selector to raise its wipers l3-l5, inclusive, to the group of bank contacts in which the trunk to the desired hundred group of connectors is terminated, The vertical magnet of the selector switch S is then automatically operated in the well known manner to rotate the wipers 8345, inclusive, to find an idle trunk line extending to a connector switch. It will be assumed that the wipers 13-55, inclusive, seize the trunk conductors 56-! 8, inclusive, extending to an idle connector switch C. The selector switch S switches through in the well known manner and extends the loop circuit over wipers l3 and i5, conductor l6 and I8, normally closed contact controlled by armatures 2l5 and 2M, lower and upper windings of three-pole electro-polar relay i292, lower and upper windings of line relay 203, to battery and ground respectively.

The operation of the connector switch C under control of the toll operator at the manual switchboard, is exactly the same as has previously been described in connection with a local call. It will therefore be assumed, that the operator has dialed the second digit, and has accordingly operated the vertical magnet 2 of the connector to raise the wipers 223-225, inclusive, of the switch to the level in which the wanted subscribers line is terminated, and that in response to the last digit of the wanted subscribers number the rotary magnet 2l2 has rotated the wipers 223-225, inelusive, into engagement with the set of bank contacts associated with substation A. If the wanted subscribers line is idle, the connector operates in the well known manner, which has previously been described in detail, seizes the called line, transmits the ringing current, and when the wanted subscriber answers, the connection is completed between the operator at the manual switchboard and the wanted subscriber at substation A.

In order to describe the toll offering feature of the present invention, it will be assumed for the present that the subscriber at substation A is busy when the wipers of the connector are positioned into engagement with his line. Therefore, the cut-off relay 233 of line switch LS-l, which is individual to the wanted subscribers line, is operated and test conductor 23! is grounded by the connector and selector switch over which his connection is extended by way of Wiper 341, and armature 236 and itsfront contact. The ground returned over this path also extends by way of the winding of relay 233, self-interrupting contacts of the operating magnet 249, and winding of the operating magnet 249, to battery to maintain relay 233 operated.

After the last impulse of the last digit has been transmitted to the rotary magnet and relay 209, as has been previously described, slow to release relay 209 remains operated for a short period of time. The ground potential encountered by the test wipers 224 on conductor 23! completes a circuit for the busy test relay 208 over the following path: wiper 224, armature 229 and its front contact, armature 228 and its resting contact, windingof busy test relay 208, to battery.

At armature 239 and its front contact, relay 268 prepares a locking circuit for itself from groundat armature 216. This circuit is completed subsequently at the normally closed contact controlled by armature 229 and its front contact,

when relay 209 falls back.

Immediately after the operator has transmitted the last digit of the wanted subscribers number, she restores her key K to normal. This extends the loop circuit to the right-hand winding of the repeat coil R, in series with the polarized relay 1 and the armature 0 of the operated. sleeve relay 3. The loop circuit for the line relay 203 of the connector circuit may now be traced over the following path: ground, uppers.

winding of line relay 203, upper or operating winding of the three-pole electro-polar relay 202,

normally closed contacts controlled by armature 2l4, conductor l8, wiper I5 of the selector S, wiper 2| of the line switch LS, conductor 9, jack J, plug P, normally closed contacts of the lower spring combination of the key K, lower righthand winding of the repeating coil R, armature 6, both windings of polarized relay 1, upper righthand winding of the repeating coil R, normally closed contacts of the upper spring combination of the key K, plug P, jack J, conductor 8, wiper IQ, of the line switch LS, wiper l3 of the selector S, conductor I6, normally closed contacts controlled by armature 2|5, lower or polarizing winding of the electro-polar relay 202, lower winding of line relay 203, to battery. The line relay 203 remains operated when the key K is restored to normal, however, the polarized relay 1, which is now included in the loop circuit of line relay 203, operates and thereby lights the supervisory lamp L at the operators position.

Referring again to the operation of the busy test relay 208, it will be noted that at armature 242 and its front contact, the busy tone from the busy machine is connected by way of armature 26l and its resting contact to the trunk conductor l8. When the toll operator hears the depresses the toll ofiering key K2 thereby connecting positive booster battery to the loop circuit for the line relay 203. When positive booster battery is connected to the loop circuit, two separate circuits may be traced. One circuit is as follows: from positive booster battery (negative terminal grounded), resistance: 21, key K2, plug P, jack J, conductor 9, wiper 2| of the line switch LS, wiper iii of the selector S,,conductor l8, armature 2l4 and its normally closed contacts, operating winding of the three-pole electro-polar relay 202, upper winding of line relay 203, to ground. This circuit reverses the direction of normal current flow in the operating winding of relay 202 and the upper winding of line relay 203. The other circuit, closed simultaneously with the above traced circuit is as follows: from positive booster battery, resistance 21, key K2, lower key K, lower right hand winding of repeating coil R, armature 6, windings of polarized relay 1, upper right hand winding of repeating coil R, upper key K, plug P, jack J, conductor 8, wiper 19 of line switch LS, wiper l3 of the selector S, conductor l6, armature 2|5 and its normally closed contacts, lower or polarizing winding of relay 202, lower winding of line relay 203, to negative exchange battery. In this circuit the normal flow of current is increased considerably due to the fact that the two batteries are in series. Considering these two circuits together, it will be noted that by reversing the direction of current flow in the operating winding of relay 202, the current flow through the two windings of the relay assist each other and the relay operates. Although the direction of current flow in the upper'winding of relay 203 has been reversed, the relay does not fall back because the current flow .through its lower winding has been increased by the application of booster battery in series with the regular exchange battery. Therefore line relays 203 of the connector and polarized relay 1 of the operators cord 0 remain energized and relay 202 is operated. In response to the momentary operation of relay 202 a circuit is completed for the toll offering relay 201 over the following path: ground at the lower armature of relay 209, armature 24!, armature 244, winding of toll offering relay 201, to battery. Relay 20'! operates and at armature 262, completes a locking circuit for itself independent of the circuit including armature 244. When the toll ofiering key K2 restores to normal, the normal loop circuit including the line relay 203, electro-polar relay 202, and the polarized relay 1 in the operators cord circuit, is again completed. The line relay 203 and the polarized relay 1 remain operated as before, and the three-pole electro-polar relay 202 restores to normal. Referring again to the operation of the toll oiTering relay 207, it will be noted that at armature 261 the busy tone transmitted to the operator is disconnected from the lower trunk conductor. At armature 243, relay 20'! transfers the holding circuit for the busy test relay 208 from the grounded release conductor I! to the grounded test wiper 224. Due

relay 20'! disconnects the back bridge relay 20! from the talking conductors of the trunk and at the front contacts of these armatures connects the talking conductors of the trunk through to the busy subscribers line.

It will be noted from the above description .that even if the subscriber at substation A is busy in the conversation with another local subscriber and the line is marked busy, the operator, by means of the toll offering key K2, can control the connector switch C to cut in on the busy line.

The toll operator may now inform the called subscriber that he is desired for a toll call. If the subscriber at substation A does not wish to take the toll call at the present time, the operator removes her plug P from the jack J and the entire connection is released in the Well known manner. In the event that the subscriber A wishes to take the toll call, he informs the subscriber with whom he has been conversing and they both hang up their receivers. When the subscribers engaged in the local connection hang up their receivers, the switches used in establishing the connection, restore to normal and the ground potential is removed from the test conductor 23L When this occurs, the busy relay 203, which was held in it's energized position from the grounded conductor 23l, restores to normal. In response to the restoration of relay 208, the following operations take place. The locking circuit for the toll offering relay 201 is opened at armature 24! and the relay accordingly restores to normal. At armature 239, the original locking circuit for the busy test relay 208 is opened, and at armature 240 the circuit for the lower winding of the switching relay 2! is again closed. When the toll oifering relay 201 restores to normal the windings of the back bridge relay 20! are again connected to the talking conductors of the trunk at armatures 259 and 260 and their respective resting contacts. The circuit for energizing the switch-through relay 2") is completed from ground at armature ZIB, armature 240, lower Winding of switching relay 2| 0, armature 229 and its resting contacts, wiper 224, conductor 23!, winding of the cut-ofi relay 233, self-interrupting contacts of the operating magnet 249, winding of the operating magnet 249, to battery. The operating magnet 249 does not respond over this circuit. However, the cu -off relay 233 and the switching relay 2H) both energize. As has been described hereinbefore, the line switch is of the Well known interlocking mechanism type and it will suffice to state that the cut-off relay clears the called line of attachments. Switching relay 2E0, upon operating, completes a locking circuit by way of its upper winding and armature 250 to ground at armature 2H, and at armature 254 places an additional holding ground for the cutoff relay 233, which is independent of the circuit just traced in series of the lower winding of switching relay 210. The lower winding of the switching relay 210 is now shunted by ground at armature 2| 6 and at armature 254. Relay 2| 0 opens a point in the circuit for the rotary magnet 2l2 at armature 228, and at armature 252 pre pares the ring-back tone circuit to indicate to the operator that the ringing has been started. At armature 25| and 253 and their respective front contacts, switching relay 2) connects interrupted generator to the called line. The ringing current from the generator INT. GEN. is intermittently projected over the called line to operate the ringer at substation A. The ringing circuit is the Same as has been described as hereinbefore,

and it should be understood that when the ringing current is transmitted, the ring-back tone circuit which is completed at armature 252 is heard by the operator at the toll switchboard and indicates to her that the signalling has begun. When the called partly answers the call by removing his receiver from the switchhook, the ring-cut-ofi 285 operates and locks itself at armature 256, to ground at armature 2H. At armatures 255 and 251, relay 2G6 opens the ringing circuit and at the front contacts of these armatures connects the talking conductors of the called line straight through to the calling line thereby connecting the windings of the back bridge relayZUl to the called line. Theback bridge relay 28.5 energizes over the loop circuit including the called line and at armatures H5 and 2M and their respective front contacts reverses the direction of current fiow over trunk conductors l6 and IE to the polarized relay in the operators cord circuit 0. Due to the reversal in the direction of current flow through the windings of the polarized relay 1, the relay restores to normal and causes the lamp L to be extinguished, thereby notifying the operator that the called subscriber has answered. Transmission battery is supplied to the calling line or operators trunk line by line relay 2133 and is supplied to the called line by back bridge relay 294. The operator at the toll board now restores her listening key to disconnect her head set from the trunk and the calling subscriber in the distant manual exchange may now converse with the automatic telephone subscriber at substation A. Transmission battery is supplied to the calling manual subscriber from the windings of relay 23. After the conversation has been completed, both subscribers hang up their receivers.

When the distant manual exchange subscriber hangs up his receiver, the supervisory lamp L2 is lighted at the toll board and indicates to the operator that the calling subscriber has released the connection. The operator removes the answering end of the cord circuit from the answering jack (not shown) thereby releasing the distant exchange trunk for other calls. When the subscriber at substation A hangs up his receiver, the back bridge relay 20! is restored to normal and again reverses the direction of current flow through the polarized relay l at the operators cord circuit 0. The direction of current flow through the relay is in the proper direction and the relay energizes, lighting the supervisory lamp L, thereby indicating to the operator that the called subscriber has released the connection. The operator now removes the plug P, of the circuit 0, from the jack J and sleeve relay 3 and polarized relay 1 both restore to normal. When the plug P is removed from the jack J, ground is removed from spring 2 of the jack and the busy visual i and all other busy visuals operated over the multipled conductor are restored to normal. The loop circuit, over which line relay 203 of the connector C was operated, is opened by the removal of the plug P and the connector switch restores to normal. Ground is subsequently removed from the release trunk conductor I? and results in the restoration of the selector switch S and the line switch LS. The switches are now in a position to be seized for another call.

The operation of the connector has been described when it is used as a regular local connector by regular subscribers in the automatic system, and a description has also been given of the operation of the connector when it is used as a toll offering connector under control of the toll operator. The connector functions in the same manner in both connections with the exception that when the operator extends the call to a busy line, she may, at her discretion, cut in on the busy subscribers line and offer the toll call tothe subscriber thereon or she can release the connection. In order for her to offer the connection to the busy subscriber, she must operate her toll offering key K2 to connect positive booster battery to the trunk conductors. The three-pole electro-polar relay will then respond to initiate the operation required for the connector to cut in on the busy line and also to prevent the ringing current from being connected thereto. If a local subscriber should attempt to operate the connector to cut in on a busy line by grounding either of the line conductors, the three-pole electro-polar'relay 292 will not respond because if one of the conductors is grounded, the circuit for the operating winding of the electro-polar relay is short circuited and if ground is applied to the other trunk conductor, a circuit will be completed for the polarizing winding but no amount of current flow though the polarizing winding will energize the electro-polar relay when the operating winding has no current flow.

A description will now be given of the operation of the equipment when the operator at the toll board receives a toll call from the distant manual exchange and desires to extend the call to an automatic subscriber in a distant automatic exchange.

It will be assumed that the operator at the toll switchboard has received such a call and has inserted the plug P, of the cord circuit 0, into jack J and that the line switch LS has seized an idle selector switch such as selector switch S. Furthermore, it will be assumed that the first digit of the wanted subscribers number has been dialled and that the selector S, under control of the vertical and rotary magnets, has raised the wipers i345, inclusive, to the proper level and that the wipers have been rotated over the bank contacts and have engaged an idle trunk line extending to an outgoing trunk repeater, such as outgoing trunk repeater OTB. Therefore, the trunk comprising conductors E i-2G, inclusive, extending to the outgoing trunk repeater OTR, is the trunk engaged by the selector switch S.

In response to the seizure of the outgoing trunk repeater OTB, by the selector S, the line relay 3% is operated over the following path: ground, upper winding of line relay 39 upper or operatin" winding-of the three-pole electro-polar relay upper left-hand winding-of repeater coil RI, normally closed contacts controlled by armature 399, conductor 26, wiper E5 of the selector switch S, wiper 25 of the line switch LS, conductor 9, jack J, plug P, operated contacts of the lower springs of key K, calling device CD, operated contacts of the upper springs of key K, plug P, jack J, conductor 8, wiper I9 of the line switch LS, wiper 53 of the selector S, conductor 2:1, normally closed contacts controlled by armature 3B5, lower left-hand winding of repeating coil Rt, bottom or polarizing winding of relay 334, to battery. Relay 3% completes an obvious circuit for the slow-torelease relay 355 which energizes and at its upper armature places a ground potential on the release conductor 25 to maintain the selector S and line switch LS in an operated position, and at the same time completes a circuit for the ri ht-hand winding of the shunt-field 3&2. Relay 3%? is not operatively energized at this time, owing to the fact that the flux that is generated in the righthand core is shunted away from the armature and heelpiece by the left-hand core. It will be noted that when relay 304 energized that a circuit was closed at armature 3" to complete a loop circuit by way of the trunk conductors 3t and 3| to the automatic switches in the distant automatic exchange. When this loop circuit is closed the switches in the distant automatic oiiice are seized in the usual manner and are prepared to receive the impulses transmitted by the operator at the toll board. The line relay 304, of the outgoing trunk repeater CTR, repeats the im pulses over the trunk line by momentarily opening and closing the loop circuit at armature 350 in accordance with the impulses transmitted from the operators calling device CD. Release relay 305, due to its slow release characteristics, remains energized during the impulse series. The loop circuit including conductors 30 and 3 l which is closed by armature 3 I 0, also includes the righthand windings of the repeating coil Rl in series with the left-hand winding of the shunt field relay 302. The shunt field relay 302, however, is not energized at this time, because the flux generated in the left-hand winding coincides in direction with the flux normally shunted from the armature by the core associated with said winding. Each core now acts as a magnetic short circuit for the flux generated in the other core. The toll operator 'dials the number of the wanted subscriber in the distant automatic exchange and the line relay 304- of the outgoing trunk repeater responds, thereby repeating impulses, by way of armature 310, over the trunk conductors 38 and 3|. The operator then restores her key K to normal to disconnect the calling device CD from the line. The switches in the distant automatic office are controlled by the impulses transmitted over the trunk line and extend the connection to the wanted subscribers line.

It will be assumed that the final digits of the wanted subscribers number operates a connector switch, similar to the connector switch C shown in Fig. 2, and that the line of the Wanted subscriber is similar to the line of substation A in Fig. 2. It will therefore be understood from the previous description of the connector switch C, that if the wanted line is idle the switching relay of the connector is operated, ringing current is transmitted over the wanted subscribers line, and the wanted subscriber is signalled in the usual manner.

It will be assumed, for the purpose of this description, that the wanted subscribers line is busy when the connection is extended to his line and that the busy tone is received, in the usual manner, by the operator at the toll board. Since the connectors in the distant automatic office are of the toll oifering type, the operator can, by operating her toll offering key K2, control the connector at the distant oflice to cut in on the busy subscribers line so that the operator may offer the toll call to the subscriber connected thereto.

Therefore, it will be assumed that when the operator at the toll board receives the busy tone indicative of the fact that the caled subscriber is engaged in a conversation, that the operator desires to offer the call to the busy subscriber.

When the operator momentarily depresses her toll offering key K2, positive booster battery is applied to the tip and ring conductors of the plug P, jack J, conductors 8 and 9 extending to the line switch LS, wipers l9 and 20, wipers l3 and i5 of the selector S, to conductors 24 and 26, respectively, extending to the outgoing trunk repeater OTR. It will be noted that the booster battery extending over the tip conductor of the operators cord circuit is in series with the polarized relay l in the operators cord. Referring now to Fig. 3, it will be noted that the booster battery applied to conductor 26 is extended by way of the normally closed contacts controlled by armature 359, upper winding of the repeating coil RA upper or operating winding of the threepole electro-polar relay 3G3, upper winding of line relay 3% to ground. The booster battery applied to conductor 2% is extended by way of the normally closed contacts controlled by armature 30B, lower left-hand winding of the repeating coil Rl, lower or polarizing winding of the three-pole electro-polar relay 303, lower winding of line relay 384, to battery. Therefore, the normal current flow in the circuit for the lower windings of relays 303 and 304 is increased considerably when booster battery is applied to conductor 24 due to the fact that the two batteries are in series. The booster battery applied to conductor 26 reverses the direction of current flow in the upper or operating winding of relay 303 and the upper winding of line relay 3%. Considering these two circuits together, it will be noted that by reversing the direction of current flow in the operating winding of relay 202, the current flow through the two windings of the relay assist each other and the relay operates. Although the direction of current flow in the upper winding of line relay 3% has been reversed, the relay does not fall back because the current flow through its lower winding has been increased by the application of booster battery in series with the regular exchange battery. Therefore, line relay 3% of the outgoing trunk repeater OTR, and polarized relay 1 of the operators cord 0 remain energized and three-pole electro-polar relay 303, of the outgoing trunk repeater OTR, operates. In response to the momentary operation of the electro-polar relay 333, booster battery is applied, at the upper and lower armatures, to the trunk conductors 3D and 3! extending to the distant exchange.

As has been mentioned, hereinbefore, the connector switch at the distant automatic exchange is the same as the connector switch C shown in Fig. 2. Therefore, it will be understood, that the operation of three-pole electro-polar relay of the connector of the distant exchange intiates the operation for controlling the switch to cut in on the busy subscribers line. key K2 in the operators cord circuit 0, which is only momentarily operated, disconnects the booster battery potential from the trunk conductors 24 and 26, extending to the outgoing trunk repeater OTR, and the three-pole electro-polar relay 3B3 restores to normal and in doing so removes the booster battery potential from the trunk conductors 30 and 3i extending to the polar relay of the connector switch in the distant exchange. Since the connector switch of the distant exchange has cut in on the busy line, the busy tone is removed from the trunk conductors and the operator may offer the toll call to the busy subscriber.

The toll offering 5 If the subscriber does not desire to take the scriber with whom he is engaged in conversation, and they both hang up their receivers.

As soon as the subscribers hang up their receivers, the ring-cut-off relay, of the distant exchange connector, connects the ringing current to the wanted subscribers line and he is signalled in the same manner as has been hereinbefore described. 7

Responsive to the called subscriber answering, the back bridge relay of the connector operates and in doing so reverses the direction of current flow over conductors and 3!. The reversal in the direction of current how in conductors 3B and 3| obviously reverses the direction of current how in the left-hand winding of the shunt field relay 302. Heretofore the magnet flux set up by lefthand winding of relay302 has been in such a direction as to coincide with that set up by the right-hand winding of said relay and accordingly the flux was short-circuited, so to speak, as none of it was forced to flow out through the heel piece and armature of the relay but rather flowed through the two cores and associated yoke in series. Due to the reversal of current in the lefthand winding, however, the flux produced thereby opposes that produced by the right-hand winding, thus forcing it to pass out through the heel piece and armature and return through the two cores in parallel. The armature of the relay is now attracted and closes a circuit for the reversing relay 30| At armatures 306 and 309 andtheir associated front contacts, reversing relay Sfii reverses the direction of current flow in the loop circuit of the operators cord circuit 0. Due to this reversal of current, the polarized relay "6 of the operators cord circuit 0 falls back, thereby extinguishing the supervisory lamp L. This notifies the operator that the called'subscriber has answered. Reversing relay 30! of the outgoing trunk repeater, at armatures 30'l1and 308, places a short circuit around the upper and lower wind.- ing of the three-pole electro-polar relay 303 to remove their impedance from the transmission circuit. A

The connection is now completed between the subscriber at the distant manual exchange and the wanted subscriber at the distant automatic exchange. When the conversation is completed and the subscribers hang up their receivers, the operator at the manual switchboard receives the usual disconnect signal by the lighting of lamp L2 when the distant manual subscriber hangs up his receiver and by the lighting of lamp L' when the distant automatic exchange subscriber hangs up his receiver. -Briefly, when the distant automatic exchange subscriber hangs up his receiver, the connector again reverses the direction of current flow in the trunk conductors 30 and 3| and the shunt field relay 302 restores to norto indicate to the operator that the distant automatic exchange subscriber has replaced his receiver on the switchhook. The operator now removes the plug-P from the -jack- J thereby At its lower opening the loop circuitfor maintaining line relay 304 of the outgoing trunk repeater energized. Line relay 304 falls back and at armature 310 opens. the loop circuit for holding line relay of the connector at the distant exchange in its operated position. The line relay of the connector at the distant exchange falls back, opens the circuit for the release relay which also falls back and completes the circuit for operating the release magnet and at the same time removes ground from the release trunk to release all other switches used in establishing the connection. Responsive to the operation of the release magnet the switch restores to normal. Due to the falling back of line relay 304 of the outgoing trunk repeater OTR, release relay 305 falls back and at its upper armature removes the holding ground from relay 302 and the release trunk conductor 25. The selector and line switch used in completing the connection both restore to normal in the well known manner.

The operator now removes the plug P from the jack J and the circuit for the busy visual l, and all busy visuals multipled thereto, is opened at spring 2 of jack J. In the operators cord, the circuit for. the sleeve relay 3 is accordingly opened when the plug P is removed from the jack J and at armature 6 the circuit for the polarized relay 1 is opened. Polarized relay 1 restores to normal and the lamp L is extinguished. The cord circuit is now available for completing other connections.

It should be clearly understood, from the foregoing description, that the invention covers new and improved circuits for completing toll oiTering connections in an economical and efficient manner, and that the local telephone subscribers cannot control the circuits to cut in on busy lines.

.erators switchboard, automatic switches, operator controlled means for operating said switches to extend a connection to one of said busy lines, a booster battery, operator controlled means for connecting'said booster battery to said connection, and means at one of the switches responsive to the connection of said booster battery for completing a talking connection with said busy line.

means for, making said line busy, automatic switches, an operators position and means thereat forv operating said switches to extend a connection to said busy line, means at said position for momentarily applying a battery potential augmenting the exchange battery potential to the talking conductors of said connection to operate one of said switches to establish a talking connection with said busy line, and means responsive to the establishment of said talking connection for preparing said one switch to signal the subscriber on said line when said line becomes idle.

3. In a telephone'system, calling lines of two classes, called lines, automatic switches, means for operating said switches to establish a connection from a calling line of either class to a called'line; means for preventing one of said switches from completing a talking connection when a connection is extended to a busy called line, means controlled by a calling subscriber of one class when connected to a busy called line for connecting an abnormal direct current po- 2. In a telephone system, a subscribers line,"

tential to the connection, and means responsive to said potential for controlling said one switch to establish a talking connection between the calling line of said one class and said busy called line.

4.- In a telephone system, a called station, an operators position, automatic switches including a connector switch, an exchange battery, means at said operators position included in a circuit with said exchange battery for operating said switches and said connector to establish a connection with said called line, a booster battery, means at said position for connecting said booster battery to said circuit, and means responsive only to the application of said booster battery for operating said connector to extend a talking connection to said called line when it is busy.

5. In a telephone system, an operators switchboard, a trunk line, a repeater for extending connections over said trunk line to a distant automatic exchange, switches at said distant exchange for extending connections to busy or idle subscribers lines, means at said operators switchboard for establishing a connection via said repeater and trunk line to said automatic exchange switches, means for operating the switches at said exchange to select a wanted subscribers line, means at said operators switchboard for controlling said repeater to send current of an increased potential over the conductors of said trunk line, and means at one of said switches responsive to said current of an increased potential for enabling said operator to establish said connection when said line is busy.

6. In a telephone system, calling stations of two classes, an automatic switch common to both classes, said switch having access to called stations, means at said calling stations for operating said switch to establish a connection with 21, called line, means for preventing the completion or" a connection with a busy called line when a station of one class extends said connection, a booster battery, means at the station of the other class for momentarily applying said booster battery to the talking conductors when a busy line is encountered, and means in said switch responsive only to the application of said battery for completing a talking connection with a busy line.

'7. In a telephone system, a first'class calling station, a second class calling station, automatic switches common to both classes, a called station, means at said calling stations for operating said switches to extend a connection to 2, called station over two paths, one of said paths automatically predetermined to establish a talking connection between a calling and a called station when said called station is idle, the other of said paths selectable only by said first class calling station to extend a talking connection to said 7 called station during the time said called station is busy, means at said first class calling station for momentarily increasing the current flow in one of the talking conductors and simultane-' tion of the busy condition of said called station, a relay in said switch for transmitting ringing current to signal a called station only when it is idle, a source of direct current at said calling station, means for connecting said current to the line conductors of said calling station, means in said switch operated in response to said current for controlling said switch to complete a temporary talking connection between said calling station and said busy called station, and means operated responsive to said busy called station becoming an idle called station for disconnecting said temporary talking connection and for operating said relay.

9. In a telephone system, a calling station, a

called station, an automatic switch operated rom said calling station to extend a call to said called station, a switching relay in said switch for closing a circuit to apply ringing current to the line of said called station, means for preventing the operation of said switching relay when said called station is busy, a toll offering relay for extending a talking connection to a busy line, means for operating said toll offering relay controlled by the momentary application of battery potential to the talking conductors at said calling station, and means responsive when said busy line becomes idle for automatically disconnecting said toll offering relay and for operating said switching relay.

10. In an automatic telephone system, a busy exchange to said second exchange, an operators position, a busy called station at said second exchange, automatic switches at both of said exchanges, an outgoing trunk repeater at said first exchange connected to said trunk line, means at said operators position for extending a connection to said automatic switches in said first ex-,

change and for transmitting impulses to said switches to extend said connection to said repeater and trunk line to select switches in said second exchange, means in said repeater for repeating subsequent impulses from said operators position over said trunk line to control said switches at said second exchange to extend said connection to said busy called station, means at said operators position for further controlling the operation of said repeater to transmit a pulse,

of current of positive potential over said trunk line, and means at one of said second exchange switches responsive. only to said pulse of current of a positive potential for controlling said one switch to complete a talking connection with said busy called station. I

12. In a telephone system, a manual exchange, an automatic exchange and switches thereat, a trunk line extending from said manual exchange to said automatic exchange, means responsive to the seizure of said trunk line by the operator at said manual exchange for preparing said switches in said automatic exchange for operation, means for transmitting impulses over said trunk line to operate said switches into engagement with a desired line, means for signalling the operator at said manual exchange when the desired line is busy, a key at said manual exchange for connecting a battery potential to said trunk line, means at said automatic exchange responsive only to a momentary application of said battery potential over said trunk line for establishing a talking connection with the busy called line.

13. In a telephone system, subscribers lines, means for making any of said lines busy, an operators position, automatic switches, means at said operators position for operating said switches to extend a connection to one of said busy lines, a normal current flow in said connection, a booster battery, means at said operators position for connecting said booster battery to said connection, and means at one of said switches non-responsive to said normal current flow and responsive to the current flow from said booster battery for completing a talking connection between said operators position and said busy line.

14. In a telephone system, a calling station, a busy called station, an automatic switch, a dialling circuit from said calling station to said switch, means in said switch controlled over said circuit for extending a connection from said calling station to said busy called station, a booster battery at said calling station, means for connecting said booster battery to said dialling circuit, means in said circuit responsive to the current from said booster battery for controlling said switch to complete a talking connection between said calling station and said busy called station.

15. In a relay controller, a line relay, a threepole electro-polar relay, a battery having its positive terminal grounded, an energizing circuit for said line relay including the negative terminal of said battery, one winding of said line relay, polarizing winding of said polar relay, the operating winding of said polar relay, the other winding of said line relay and the positive terminal of said battery, a booster battery having its negative terminal grounded, means for connecting said booster battery to said energizing circuit in such a manner that the current flow in the operating winding of said polar relay is reversed, said polar relay operated responsive to the reversal in'the direction of current flow in its operating winding only.

16. In a relay controller, a line relay, a threepole electro-polar relay, a battery having its positive terminal grounded, an energizing circuit for said line relay including the negative terminal of said battery, one winding of said line relay,

polarizing winding of said polar relay, the operating winding of said polar relay, the other winding of said line relay and the positive terminal of said battery, a booster battery having its negative terminal grounded, means for connecting said booster battery to said energizing'circuit in such a manner that the current flow in the operating winding of said polar relay and one winding of said line relay is reversed and the current flow in the polarizing winding of said polar relay and one winding of said line relay is increased, said polar relay operated responsive to the reversal of said current flow and said line relay maintained energized responsive to the increased current flow in one of its windings.

17. In a telephone system, calling and called lines, means including an automatic switch controlled from a calling subscriber for, operating said switch to extend a connection to a called line, means for preventing the completion of said connection when the called line is busy, a loop circuit over which said switch was controlled, a relay in said circuit normally inoperative during the extension of said connection, an auxiliary battery, and means for connecting said battery to said loop circuit to operate said relay to complete said connection.

18. In a telephonesystem, calling and called lines, means including an automatic switch con trolled from a calling subscriber for operating said switch to extend a connection to a called line, means for preventing the completion of said connection when the called line is busy, a loop circuit over which said switch was controlled, a two winding relay in said circuit normally inoperative during the extension of said connection, an auxiliary battery, means for connecting said battery to said loop circuit in such a manner that the current flow in one winding of said relay is reversed and the current flow in the other winding is increased, said relay operated responsive to said reversal of current in one winding to complete said connection. 7

1.9. In a telephone system, an automatic switch having access to busy and idle subscribers lines, means in said switch when associated with a busy subscribers line for completing a connection to said line, means for reversing the direction of current flow in one of the conductors incoming to said switch and simultaneously increasing the current in another conductor incoming to said switch, said first means responsive only to said reversal and increase of current in said conductors.

20. In a telephone system, a calling station, a busy called station, an automatic switch, means for causing said switch to extend a connection from the calling station to the busy called station, a source of special direct current potential at the calling station, means at said calling station for connecting said source to the talking conductors of the connection, a relay in said switch responsive to the current from said source for causing the completion, in said switch, of the connection to the busy station.

21. In a telephone system, a repeater, lines incoming to said repeater conductively isolated from lines outgoing from said repeater, a means for reversing the direction of current flow in one of the incoming conductors to said repeater and simultaneously increasing the current in another conductor incoming to said repeater, means, responsive only to said reversal and increase of current in said incoming conductors, for reversing the direction of current flow in one of the conductors outgoing from said repeater and increasing the current in another conductor outgoing from said repeater.

22. In, a relay controller, a series circuit including the windings of a line relay, another relay and an exchange battery of ordinary potential, means for producing an extraordinary potential at a point in said circuit thereby reversing, in each of said relays, the direction of current fiow in at least one but not all of said windings, said means effective only to operate said second relay, said second relay operative responsive only to said means.

NORMAN H. SAUNDERS.

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