US2914618A - 3-wire connector - Google Patents

Description

Nov. 24, 1959 A. H. FAULKNER 3-WIRE CONNECTOR 2 Sheets-Sheet 1 Filed May 16, 1957 fig 2w: l M l 1 /7 \l I r W} Local 5m 7/.

Y 4o I INVENTOR.

Alfred H F llrner BY fi Nov. 24, 1959 A. H. FAULKNER 2,914,618

3-WIRE CONNECTOR 2 Sheets-Sheet 2 Filed May 16, 1957 Fig 2 L/O/V. 1

INVENTOR. A/fred H Faulkner BY 1? W 49' Ebination toll and local connector.

United States Patent 3-WIRE CONNECTOR Application May 16, 1957, Serial No. 659,623

18 Claims. c1.179 1s The present invention relates in general to telephone systems and is more particularly-concerned with combination toll and local connector switches in such systems.

The main object of this invention is an improved com bination toll and local connector switch which requires only three incoming leads from the preceding selector switches rather than the usual four leads which are required for present toll switches of like kind.

In the local switch train, only three leads are required between the selector and the connector. These are the and leads or talking conductors, and the C or control lead. The purpose of the C lead is to hold all .of the switches in the switch train operated during any given conversation. When a connector is seized on a local call, ground potential at the connector is applied .to the C lead. This ground potential is sent back over the C lead and holds all of the preceding switches op- .erated until the call is terminated.

In the toll switch train, four leads are presently required between the toll selector and the toll connector. Three of these leads are the same as those used in the local switch train while the fourth lead, called the EC or extra control lead, is provided in order that an operator at a toll board can control the start of ringing on a toll call. By means of the EC lead, the toll operator may also re-ring the called party. This is accomplished by means of the ring key at the toll' board which either applies ground potential to the EC lead or removes said potential depending on whether ringing is to be started or stopped. Generally, on toll calls, ground is applied to the EC lead at the toll first selector and is directed forward through the succeeding switches to the ring cut-01f relay in the toll connector. By operating the Ring Key at the toll board, the ground at the toll first selector is removed and the ring cut-off relay in the connector releases and ringing is begun in the usual manner.

Since four leads are necessary in a toll switch train, the bank contacts of all the toll switches except the connector must be wired for four leads. The present invention obviates the need for four leads and thereby lessens :the cost of the toll switches.

In the present disclosure, a transistor is used in the com- The transistor used is of the well-known P-N-P junction type. The emitter :of the transistor is connected to the C lead of the connector in parallel with the C lead ground, and the collector of the transistor serves as the EC lead and is part of the operating circuit for the ring cut-off relay. A

small resistance is placed in series with the C lead ground in order that the voltage at the transistor emitter can be "varied by the toll operator when direct ground is applied 2 release from the switch train. The voltage at the emitter of the transistor is insufficient to cause the transistor to be conductive on local calls and the transistor is thereby rendered non-conductive on such calls.

When the connector is seized for a toll call, direct ground is applied to the C lead from the toll first selector. At this time, the voltage atthe'emitter of the transistor in the connector is sufiicient to make the transistor conductive, thereby extending ground potential to the ring cut-off relay and causing it to operate. As long as the ring cut-oif relay remains operated, ringing will nottake place. When the connector switches through to the called party, the toll operator can start the ringing by throwing the Ring Key at the toll board. This causes additional resistance to be placed in parallel with the C lead and thus varies the voltage at the emitter of the transistor in the connector. This change in voltage is such that the transistor becomes non-conductive, thereby removing ground potential'from the'circuit through the ring cut-0E relay so that that relay will release. Ringing of the called party will take place immediately upon the release of the ring cut-off relay and further operation of the connector continues in the normal manner. 7 V c Having been given a brief description of the basic operation of the invention, the reader should be sufiiciently prepared at this time to understand the more detailed description which follows. I

Figures 1 and 2,'taken'together' show the combination toll and local connector switch with the interconnecting resistances in the preceding switches also being shown to more clearly illustrate the manner in which the transistor is made conductive or non-conductive as the case may be.

' Loc al calls A description of the operation of the combination toll and local connector shown in Figs. 1 and 2 on local calls willfirstbesetout. i

Reference will hereafter be made to a standard local selector switch, the circuit of which is not shown. Since any mention of that selector'will only be mad e in order to bring out several details of-the operation of the circuit shown in Figs. l and 2 and sinc'ethosedetails are only incidental to the'present invention, reference may be made to the H.'N. Newstedt- Patent No. 2,529,409 which discloses'the circuit of the standard local selector.

Whenconnector H is seized by a local selector such as that referred to above, relay 50 in the connector will become energized from ground in the selector, over the incoming C-conductor 7; through unoperated armature 17, resistance R12, VONl and through the upper winding of relay 50 to battery. The switch-through relay in the selector (not shown) is in series with relay 50 and-will also become energized. The operation of the switchthrough relay will extendthe talkingconductors in the selector through to thetalking conductors 5 and 6 of connector H. This will complete a loop circuit through line relay 30 in the usual manner and relay 30will operate.

The operation of relay 30-closes the operatingtcircuit to relay 40 at armature 31. At armature 43, ground is extended rearwardly through resistance 12, and armature 17, over the control conductor 7 to the preceding selector. The-purpose of this ground "is' to "hold the switch-through r ay in the selector operated during conversation.- It should also be noted that relay 50 is also held operated from the ground at armature ,43 through VONl. i V

At armature 41, a point in the release magnet circuit is opened toprevent the release of the switch upon the first vertical step due to theclosingj of VON2.- Armature 42 completes a circuit through resistances R10 and R11 in series to battery. The purpose will be fully explained hereafter.

Patented Nov. 24, 1959 of this circuit 4 At armature 44, the circuit to the vertical magnet and the lower winding of relay 50 in parallel is prepared.

As was before mentioned, relay 50 first operated from ground in the preceding selector and is held operatcdfrom ground at armature 43 ripen the operation of relay 40. I i

At armature '51 the operating circuit for relay 60 through its lower winding is partially completed. At armature '52 the circuit to the vertical magnet and relay 50 through its lower winding in parallel is further prepared. This circuit will be completed when relay 30 restores at armature 31 during pulsing. I

Relays 30, 40 and 50 will "remain operated until the calling subscriber dials the last ave digits of the called number.

At this point, it. would be well to describe the role of the transistor T, in this feir'cuit. It will be noted "that this transistor is in the P-N P fun ction type having an emitter, a collector and a base circuit. The emitter of T is connected in parallel the C conduetor 7. The collector forms a part of'theoperating circuitsffor relays and '60.- The base errant consists of resistances R10 and R11 and this circuit is completed from ground at armature 42 as was before described. -In order to clarify the explanation of the operation of T it would be convenient to assign values to'the various resistances which control its operation."

Resistances R1 and R2 represent the relays which are to be held operated inthe local switch train frorn ground at armature 43. It is assumed that each {of these relays are 1000 ohms or a net resistance of 500 ohms since they are in parallel. R12 is a part of 'the same circuit and is 30 ohms. R10 is 1150 ohms and R11 is 50 ohms. If it be assumedthat a 48 volt exchange battery is used, the voltage at the base of T will be 2.0 v

volts. No current will flow through the transistor unless the voltage at the emitter of T becomes positive with respect to the base. i.e. less negative than -2.0 volts. It can also be seen that'since the emitter of T is connected between 500 ohms and 30 ohms, the voltage at the emitter will be about 2.7 volts. This voltage is not positive with respect to the base andtherefore the transistor will be non-eonductive.

As has been pointed out before, relay 50 operates upon seizure from ground potential in the preceding selector. This direct ground which is applied to the C conductor will cause the transistor to be momentarily conductive because the voltage at the emitter will be less negative than -2.0 volts. As a. result, relay '60 will operate momentarily oven-its lower winding when relay 50 closes armature 51 Since the ground potential in the preceding selector is removed almost-immediately, and is replaced by battery potential, the transistor will become non-conductive and relay 60 will restore. 'I'ltls, the momentary operation of relay 60 is without e ect.

When the calling party dials the first digit into the connector H, relay 30 will follow the dial pulses in the usual manner and at armature 31, the operating circuit to the vertical magnet andthe holding circuit through the lower windingof relay 50 will be completed, fRelay 40 is a slow-to-release relay and will not release during'pulsing. I

In response to the operation of the vertical magnet the switch wipers of connector H;will--be;jstepped vertically, one step for each pulse received. When the wipers take the first vertical -st ep,j the vertical-ofi-normal springs VONl and VO N2 will operate. At VONl, a holding circuit through the upper winding of relay 50 is opened and at VONZ, thecircuit-to-the release magnet is 'partially prepared,

At the termination of' the-'first series'of pulses relay 30 remains energized over the -previously;described loop circuit and at armature 31 the holding circuit for relay 40 is completed. Atarmature 31, ground is also removed from the holding circuit to the lower winding of relay 50 and relay 50 will restore. At armature 52 the operating circuit to the rotary magnet and relay in parallel is prepared.

On the receipt of the next series of pulses, relay 30 will restore and operate in accordance with the pulses received and at armature 31 the operating circuit to the rotary magnet and relay 90 in parallel is completed and the operation of the rotary magnet will cause the switch wipers to rotate across the contacts of the previously selected level. Relay 90 is held operated in parallel with the rotary magnet, and being a slow-torelease relay it will hold operated throughout the entire series of pulses received. At armature 91 the busy tone circuit through condenser C1 and unoperated armature 11 is opened so that busy tone will not be returned to the calling party in case the switch wipers step across busy contacts in its rotary movement. At armature 92, a point in the operating circuit to the upper winding of relay 10 is opened, but this is without effect on local calls and will be described later in the description of toll calls. At armature 93 lt he Crwiper of the connector H is connected through to the busy test relay 70. At armature an alternate holding circuit is completed to relay 90. Thisiholding'circuit will insure the operation of relay 90 in case relay 70 becomes operated when-the C wiper of the connector engages grounded busy contacts as it rotates across the connector bank. I

At the termination of this last series 'of impulses relay 30 will remain operated and at armature 31 the holding ground for relay fli will be removed and relay 90 will restore. Prior to the restoration of relay 90the C wiper of the connector is resting on the contact asso ciated with the called'party. lithe called line is busy, ground potential will be present onthe C contact and will be extended by way of armature 93 and armature 89a to the busy test relay 70. Relay 70 will operate over this path. At armature 71 of relay 70 the busy tone circuit is prepared and will completed at armature 91 when relay 9i) releases. The operation ofarmature 72 is without effect on loca'l calls and will subsequently be described under the heading of toll calls. At armature '73 a holding circuit-forbusy test relay 70 is prepared, to ground at armature 43. This holding circuit will be completedfby way'of armature '94'when relay 9% releases. At armature 74 the operating circuit for relay is opened to prevent the operation of relay 90 in case the calling subscriber should open the circuit to relay 30 by hitting thehook switch. When relay W restores armature 91 will close ;and complete the busytone circuit through-condenser O1 and armature be found on the bank contact associated with .his line.

In this case, relay "ill will not operate and when-relay90 restores, the battery potential found at the'C wiper of the connector will be transferred through to the lower winding of relay '80 and unoperated armature 73 to ground at armature ,43. Relay "80 is a top step relay and will operate only its contacts at armature 88 when energized over its lower windingonly. The operation of armature 88 completes a circuit from battery through the rotary magnet and the upper winding of relay 80 to ground at armature 42. and relay 80 will operate completely over this circuit. It should 'be pointed out that v the rotary magnet will not operate in series with the upper At armature 81 the ring back tone circuit is partially completed and will be operative when armatures 82 and 84 operate. At armatures 82 and 84 the ringing circuit is completed through the upper winding of relay 60, through the called subscribers handset, and back to ground at armature 63 of relay 60. At armature 83a point in the operating circuit to the release magnet is opened. The operation of armature 85 is without eflect on local calls and will hereafter be described in connection with toll calls. At armature 86 the operating circuit to the lower winding of relay 60 is partially prepared and at armature 87 ground potential is applied to the C wiper of the connector in order to mark the called sub scribers line busy to other calls. additional holding ground is prepared for the circuit to the upper winding of relay 80 and will be effective when relays 60 and 20 operate. At armature 89a the operating circuit to relay 70 is opened and at armature 8% the operating circuit to the rotary magnet is opened to prevent any further operation of the rotary magnet from ground at armature 31. At this time automatic ringing will take place until the called subscriber answers the call by lifting his handset.

When the called party lifts his handset a direct current circuit is completed to the upper winding ofrelay 60 and back to ground at armature 63 of relay 60 over the previously described circuit. Relay 60 will then operate its X contacts at armature 64 and the operating circuit to the lower winding of relay 60 will be completed by way of operated armature 86, unoperated armature 18 toground at armature42 of relay 40. Relay 60 will then operate completely and at armatures 61 and 63 a loop circuit will be completed through the called subscribers telephone to back bridge relay 20. Relay 20 will operate over this loop circuit and at armatures 21 and 24 the battery and ground potential through relay 30 will be reversed over the talking conductors back through the local switch train for supervisory purposes.

Conversation may now take place between'the parties and at the termination thereof, the switch will release in the usual manner.

Toll calls The operation of connector H will now be described upon seizure by a toll operator for a toll callt;

The connector H is seized by the preceding toll selector (not shown) and relay 50 will operate in the manner hereinbefore described. Relays 30 and 40 will also operate as described and prepare the switch for dialling.

It will be noticed that in this case, however, ground is applied to the C conductor .by way of the operators ring key. Resistances R4 and R5 are representative of the relays in the-toll switch train which are being held operated from that ground. This circuit difiers from that of the local switch train in that the ground at the ring key is not removed until the operator operates the ringing key to remove the direct ground from the C conductor 4.

It will be remembered that in the local switch train ground is applied to the C lead at armature 43 back through resistance R12 and over the C conductor 7 to the preceding switches. As was true in the local switch train, resistances R4 and R5 are each 1000 ohms and offer a net resistance of 500 ohms in the circuit. R6 represents the interconnecting lead resistance between the switches in the toll switch train, this resistance being about 15 ohms.

Upon the operation of relay 40 in the connector armature 42 closes the base circuit to the transistor T. As before, the voltage at the base of T will be approximately 2.0 volts. The operation of relay 50 closes armature 51 and completes the operating circuit through the lower winding of relay 60 through transistor T. In the description of the local switch train it was pointed out that the operation of armature 51 was without effect because the transistor T was non-conductive at that time. On

At armature 89 "an 7 the emitter of T will be positive with respect to the volta 6 a toll calls however, since direct ground is applied at the ring key, the voltage at the emitter of the transistor will be less than -2.0 volts. Because of this, the voltage at age at the base and therefore the transistor will be conductive and relay 60 will operate completely over its lower winding by way of armature 51, C conductor '4,

and resistance'R6 to ground. Relay 60 will now holdoperated until the direct ground at the ring key is removed. It will be noted that the operation of relay 60 closes the X contacts of that relay at armature 64,'thns completing a holding circuit through the lower winding of 'relay 60, through unoperated armature 86 and the lower winding of relay '10, through transistor T, to ground at the ringing key. Relay 10 will not operate over this circuit however because it is short-circuited by way of the previously traced circuit through operated armature 51'of relay 50.

Upon receipt of the first series of impulses to the connector H relay 30 will follow each pulse and the switch wipers will step vertically in the usual manner. At the termination of the vertical movement of the switch wipers relay 50 will restore and at armature 51 the operating circuit for relay 60 is opened. The short circuit of the lower winding of relay 10 is thereby removed and relay 10 will operate only its X contacts at armature 17.

Upon receipt of the next series of impulses the switch wipers of cori'riectorH will step across each contact of the selected level of the connector bank.

If the called partys line is busy, test relay will operate as before described and at contact 72 the operating circuit to the upper winding of relay 10 is prepared and relay 10 will operate completely upon the restoration of relay 90 at armature 92. The operation of relay 10 at armatures 12 and 15 shunts the condensers C2 and C3 and opens the calling line at conductors 2 and 3. At armature 14 a circuit is completed to the upper winding of relay 20 through resistance R9 and the lower winding of relay 30 to ground. At armature 11 the busy tone circuit is completed through resistance R8 and will flash the busy signal to the operator at the toll board. The operation of armature 18 is of no effect when a busy line has been dialled.

If the called party's line is idle, relay 70 will not operate. Upon the restoration of relay 90, relay will operate its contacts over its lower winding as before described. Relay-80 will then operate completely from ground at armature 42 through its upper winding, and at armatures 82 and 84 the ringing circuit is prepared. It should be here noted that ringing will not automatically begin as in the case of a local call because relay 60 is operated and at armatures 61 and 63 the ringing circuit is opened. At armature 85 the operating circuit through the upper winding of relay 10 is completed by way of armature 17 to ground at the ringing key and relay 10 will operate completely over this circuit. The operation of relay 10 has thesame effect as before described. At armature 86 the holding circuit for relay 60 is transferred from the lower winding of relay 10 directly to the collector of the transistor by way of operated armature 18. Relay 60, being a slow-to-release relay, will not release while all this transfer takes place.

It will be remembered that in the description of local calls, ringing automatically began upon the operation of relay 80 at armatures 82 and 84. In the present case however, since the transistor is conductive, the ground at the operators ring key will hold relay 60 operated and at armatures 61 and 63 the ringing circuit is opened and, ringing cannot now take place.

When the operator desires to ring the called party she may do 'so by operating the ringing key. This will remove the direct ground from the emitter of the transistor T and the voltage at the emitter of the transistor T will decrease to about 4.0 volts. The transistor will immediately becomenon-conductive, thereby allowing relay 60 to release. At armatures 61 and 63 the ringing circuit will be closed and automatic ringing will begin as in the normal case.

It will be noted that upon the operation of the ringing key direct ground is removed from the C conductor 4, and battery, through resistance R7, is substituted therefor. The resistance of R7 is about 300 ohms and is necessary in order to obtain the proper voltage at the emitter of the transistor so as to make the same nonconductive. It will further be noted that when ground is removed upon the operation of the ring key, the toll switchtrain will not release because ground is still present on the C lead through resistance R3 which is approximately 30 ohms.

When the called party removes his handset a direct current circuit will be completed to the upper winding of relay 60 as was described in the operation of local calls. The energization of relay 60 over its upper winding will operate only its X contacts at armature 64. By this time the operator has released the ringing'key so that direct ground is again placed on the C conductor and the transistor is made conductive once more. Relay 60 will then operate completely over its lower winding through its X contacts at armature 64, operated armature 86, operated armature 18, and through the transistor T, to the direct ground at the ringing key. Relay 60 will remain operated over this circuit and at armatures 61 and 63 the talking conductors are extended through the connector and conversation may take place.

At the termination of conversation when the called party restores his handset the connector will not release. Because of this fact a toll operator may re-ring the called party if necessary by again operating her ringing key'and removing direct ground from the C conductor and substituting therefor, resistance battery. When the called party is re-rung the same operation is repeated.

If the toll operator wishes, she may release the entire switch train by removing the ground potential from the C conductor 4. The connector 1-1 will then restore in the usual manner.

What is claimed is: V I

1. In a telephone system, a called line, a combination toll and local connector switch, incoming conductors comprising a pair of talking conductors and a holding conductor terminating in said connector switch, means including a local switch train for seizing and operating said connector switch over said conductors to extend a local call to said called line, means including a source of potential in said connector switch for holding said connector and said local switchtrain, automatic ringing equipment in said connector switch connected to said called line in response to the completion of said local call to said called line, means including a toll switch train for seizing and operating said connector switch over said conductors to extend a toll call to said called line, means including another source of potential extending from said toll train over said holding conductor for holding said connector switch and said toll switch train, and control means in said connector switch connected to said holding conductor and controlled by the application of said other source to said holding conductor during the establishment of said toll connection for disabling the connection of said automatic ringing equipment to said called line to prevent automatic ringing of said called line on toll calls in response to the completion of said toll connection to said called line.

2. In a telephone system as claimed in claim 1 including means for varying the potential of said other potential feed from said toll train during the establishment of a toll connection to disable said control means to permit automatic connection of said automatic ringing equipment to the called line in response to the completion of said toll call to said called line.

3. In a telephone system comprising a local trunking system for use by local subscribers and a toll trunking system for use in toll calls, a final connector switch common to both trunking systems, means for operating said switch to complete a local connection or a toll connection to a called line, a holding conductor terminating in said 7 switch, local switches included in said local connections and toll switches included in said toll connections to said called line, means in said connector switch for connecting a holding potential to said conductor to hold the local switches included in a local connection to said called line, toll, means for connecting another holding potential to said holding conductor to hold said connector switch and the toll switches included in a toll connection to said called line, automatic ringing equipment normally connected for automatically ringing the called line connected with either type of connection, means for starting said automatic ringing at once in response to the establishment of a local connection to a called line, ring cut-oil means for automatically disconnecting said ringing equipment in response to a subscriber at said called line answering, and control means for operating said ring cut-oil means during the establishment of a toll connection to a called line in response to the connection of said other potential to said holding conductor by said toll means to prevent the starting of said automatic ringing means.

4. In a telephone system comprising a local switch train for use by local subscribers and a toll switch train for use on toll calls, a final connector switch common to both switch trains, means for seizing said switch in either a local or a toll call to a called line, a local holding circuit in said switch including a hold conductor for holding said switch and said local switch train, means in said switch for grounding said hold conductor to complete said local holding circuit in response to said seizure, toll means for, holding said toll switch train, said toll means grounding said hold conductor in response to the seizure of'said switch over said toll switch train, a toll relay in said switch, control means in said switch, controlled by said toll means grounding said hold conductor, for operating said relay, circuit means controlled by the operation of said relay for opening said local holding circuit and for holding said relay operated over said hold conductor, and means controlled by said toll relay for maintaining said switch operated.

5. In a combination toll and-local connector switch wherein means is normally effective to immediately and automatically ring a called line in response to the completion of a local call to a called line and wherein ring cut-oft means is operative after seizure of said switch by a toll train on a toll call to a called line for disabling the application of said automatic ring to a called line, including a hold conductor and means in said switch for feeding ground back over said hold conductor to hold said local connection, toll means for feeding ground forward through said toll train over said hold conductor to hold said toll train and said switch, and control means in said switch controlled by said ground feed forward over said hold conductor for controlling the operation of said ring cut-oil means to disable the immediate application of said automatic ring on a completed toll call to a called line.

6. In a final switch used on both local and toll telephone connections to a called line, a combined hold and ring control conductor, means for feeding ground potential back over said conductor to hold the local connection on local calls, toll means for feeding ground forward over said conductor to hold said toll connection and said switch on toll calls, ringing means for automatically ringing the called line in response to the completion of a local connection to said called line, and control means connected in parallel with said conductor and controlled by said toll means feeding ground forward over said vconductor, for disabling said ringing means to prevent ringing of said called line on completed toll connections to said called line.

7. In a final switch used in both local and toll connections extended to a called line, a hold conductor, means in said switch for connecting a predetermined potentialto said hold conductor to hold said local connections, a source of "ringing current for automatically ringing said line on completed connections to said line, a ring cut-ofi relay for disabling the application of said source to said line, toll means for connecting an im creased potential to said-hold conductor to .hold said switch during the establishment of a toll connection to said line, and control means connected in parallel with said hold conductor, and operative in response to said increased potential, for operating said ring cut-E relay to prevent the connection of said source to said line uponthe completion of a toll connection to said line.

8. In a telephone system, a switch, a hold conductor terminating in said switch, means in said switch for connecting a predetermined holding potential to said conductor and for holding said switch in an established connection to a called line, a source of ringing current in said switch for automatically ringing said line on completed connections to said line, ring cut-oil means in said switch for disabling the application of said source to said line, other means for connecting an increased potential to said hold conductor during the establishment of another connection to said called line, and control means in said switch operative in response to said increased potential connected to said hold conductor during the establishment of said other connection for operating said ring cut-off means to prevent the application of said source to said line.

9. In a telephone system, a switch, means for operating said switch to establish connections to called lines, a ring cut-oif relay in said switch for controlling the application of ringing current to a called line, a normally non-conducting device in said switch, means for connecting said relay to said device during the operation of said switch, means for connecting a predetermined potential to said device during the operation of said switch to enable said device to conduct and operate said relay over said relay connection to prevent the application of ringing current to said line, and means for connecting a decreased potential to said device before or after completion of a connection to said line for causing said device to become non-conducting to enable said relay to apply ringing current to said line.

10. In a telephone system, a switch, means for seizing and operating said switch in first and second operations to establish a connection to a called line, a ring cut-off relay in said switch for controlling the application of ringing current to a called line, a normally non-conducting device in said switch, means for connecting said ring cutoff relay to said device during said first operation of said switch, means for connecting a predetermined potential to said device during said operations of said switch to enable said device to conduct and operate said ring cut-off relay over said relay connection to prevent the application of ringing current to said line, a toll relay in said switch connected to said device, a short circuit for said toll relay completed during said first switch operation and opened subsequent to said first switch operation, a circuit for partially operating said toll relay (in series with said ring cut-off relay) in case said device is con- 10 the seizure of said switch for applying? a local potential to said device, said local potential being of insufficient potential to overcome said biasing potential and enable said device to become conductive-external means for applying an external potential to said device, said external potential being of suflicient potential to overcome said biasing potential-to enable said device tobecome con-- ductive, a ring cut-01f relay in said switch for controlling the application of ringing current to said line, means'for connecting said relay to said device and for operating said relay responsive to said device becoming conductive, and] means controlled by the operation of said relay for pre-' venting the application of ringing current to said line.

12. In a telephone system as claimed in claim 11, including a toll relay in said switch, means for operating said toll relay after an initial operation of said switch in case said device is conducting after said initial'opeF ation, and means controlled by the operation of said toll relay for disconnecting said local potential.

13. In a final switch used in both local and toll connections extended to a called line, a hold conductor, means in said switch for connecting a predetermined potential to said hold conductor to hold said local connections, a source of ringing current for automatically ringing said line on completed connections to said line, a ring cut-ofi relay for disabling the application of said source to said line, toll means for connecting an increased potential to said hold conductor to hold said switch during the establishment of a toll connection to said line, and operator-controlled means for reducing said increased potential to said predetermined potential to disable said control means to cause said ring cut-ofi relay to restore to connect said source to said line.

14. In a telephone system, a switch train including a group of automatic switches, a control conductor common to all of said switches, means for holding all of said switches operated over said control conductor, a normally non-conductive transistor connected in parallel 1 with said control conductor, automatic ringing equipment ducting at the time said short circuit is opened, circuit means (independent of said device) for fully operating said toll relay in response to said second switch operation completing a connection to the called line, and other circuit means completed by the complete operation of said toll relay for holding said ring cut-off relay operated as long as said device is conductive.

11. In a telephone system, a called line, a switch, means for seizing and operating said switch to establish connections to said line, a normally non-conducting device in said switch, means responsive to the seizure of said switch for biasing said device with a predetermined biasing potential, local means in said switch responsive to including a ring cut-off relay in one of said switches, the operating circuit of said relay including said transistor, means responsive to the operation of said relay for preventing the operation of said ringing equipment, and means for rendering said transistor conductive over said control conductor to thereby cause said relay to operate to prevent the operation of said ringing equipment, said last mentioned means maintaining the normal holding function of said control conductor.

15. In a telephone system, a switch train terminating with a combination toll and local connector switch, said connector switch being accessible over a trunk comprising two talking conductors and a control conductor, means for applying holding potential to said control conductor from said connector switch in local connections and from the toll train in toll connections, automatic ringing equipment in said connector, said equipment being automatically operative upon the completion of a local connection, a transistor in said connector, said transistor connected in parallel with said control conductor, means responsive to the application of holding potential to said control conductor from said toll train for causing said transistor to be conductive, and means responsive to the operation of said last mentioned means for preventing the ringing operation upon the completion of the connection.

16. In a telephone system, a switch train, a final connector switch in said train including automatic ringing equipment, a control conductor extending through said switch train, means for applying holding potential to said control conductor to hold said switch train operated, means for changing the value of said holding potential, and means in said connector for utilizing said changed value of said holding potential in order to control the ringing operation and maintain the normal holding function of said control conductor.

17. In a telephone system, a combination local and toll connector, switches preceding said connector, the connection between said preceding switches and said connector including a control conductor, means in said connector for backwardly holding said preceding switches from said connector in the case of a local call by maintaining on said conductor a first potential different from ground, a solid-state switching means connected to said conductor in said connector, said switching means being held non-conductive, in a local call, by said first potential means connected to said preceding switches for establishing on said conductor in the case of a toll call a second potential diiferent from said first potential to render said solid-state switching means conductive, and means in said connector connected to said switching means and controlled by the conductive state thereof for converting said connector to toll operation.

18. In a telephone system, the combination as claimed in claim 17 in which said connector includes ringing control means connected to said solid-state switching means and in which said preceding switches also have connected thereto manual control means forlchanging said second potential in a toll call so as to render said solid-state switching means non-conductive at will, said ringing control means being responsive to the last-mentioned change of conduction to initiate ringing in said connector under the-control of said manual means.

References Cited in the file of this patent UNITED STATES PATENTS

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