US2154786A - Telephone system - Google Patents

Description

April 18, 1939. R, TAYLOR 2,154,786

TELEPHONE SYSTEM Filed Dec. 11, 1936 2 Sheets-Sheet l lc rem- 4 T A V 0 00-1 I I v w B L v T c 1c uwp f/vv/v'ro/?- Patented Apr. 18, 1939 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application December 11, 1936, Serial No. 115,323 In Great Britain January 11, 1936 8 Claims.

The present invention relates to telephone systerns and is more particularly concerned with two-party line systems in which separate meters are provided for the two parties and no special operations are required of the subscriber for either incoming or outgoing calls. The chief object of the invention is to provide for correct operation in the case of re-ringing over a party line from a trunk operators position.

According to one feature of the invention in a telephone system including two-party lines arranged for individual signalling of the parties, a relay group in the outgoing circuit responsive to ringing current permits the two subscribers to be signalled individually over thepath over which an outgoing call has been set up.

According to another feature of the invention in a telephone system including two-party lines arranged for individual signalling of the parties, a relay group is provided whereby if a connection has been set up to an operator a re-ringing operation performed by the operator after the calling party has replaced his receiver effects the signalling of the original calling party only.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. 1 and 2. Fig. 1 shows the circuit connections of the telephone instruments of the two party-line subscribers X and Y who share a single pair of conductors extending to the main exchange, while Fig. 2 shows the equipment at the main exchange which is interposed between the party line and the exchange line relay equipment.

Referring to Fig. 1, it will be appreciated that the instruments of the two subscribers are identical except for one slight wiring difference and that they are connected diflferently to the exchange line. Thus under normal conditions the bell B of the X subscriber is connected from earth to the B leg while that of the Y subscriber is connected to the A leg. When the X subscriber removes his receiver to originate a call, the 5 switchhook springs SH are operated and a loop is extended over the A and B legs to the main exchange whilst during dialling earth pulses are transmitted over the B leg. Upon removal of the Y subscribers receiver, a loop is extended to the main exchange whilst during dialling loop impulses are transmitted. It will be seen that the instrument circuits of the two parties are substantially identical, discrimination between them being effected as regards incoming calls by a reversal of the A and B leads and as regards outgoing calls by a change of strapping on the terminal block provided.

It will be understood that relay P in Fig. 2 may be connected either to the P lead as indicated by the chain-dotted line or to the meter lead M as =5 indicated by the circle and dot line. The former connection will allow the party line set to work into an existing exchange in which upon the operation of the line relay earth is applied to the P contact in the final selector multiple to busy the 10' line. If however as will be assumed in the following description the main exchange employs line finders arranged to busy the final selector P contact by disconnection of the cut-off relay battery as soon as the line relay operates and to connect II earth to the M lead immediately the calling line is found, the later connection is employed.

It will first be assumed that the X subscriber initiates a call by removing his receiver from the switchhook whereupon a loop is complete over Q the line as follows:--Earth in the line relay set (not shown), positive lead, armature x12, lower winding of relay X, armature acyZ, B leg of the line, impulse springs IS, transmitter T, switchhook springs SH, induction coil IC, A leg, arma- Q5 ture .rzjl, windings of relays A and X, armature 1T3, negative lead to battery by way of the main exchange line relay which is also not shown. Relay A and the line relay operate in this circuit but not relay X which is differentially wound. Armature at operates relay B which connects relay P to the meter lead M while the energisation of the line relay initiates the operation of the line finder to hunt for the calling line. When it is found the X subscriber is connected through 85 to a first selector and receives dial tone and at the same time earth is returned over the M lead to operate relay P which at armature p5 prepares a circuit for relay XY.

The subscriber now dials the first digit of the it) wanted number and as soon as his dial is moved off-normal, direct earth is applied by way of the shunt springs SS to the B leg, and over transmitter T to the A leg. Relay A and the selector line relay are maintained operated but relay X is now 15 unbalanced and at armature .rl operates relay XR. Relay XR completes a circuit for relay XY at armature x1! and at armature m2 disconnects the positive lead to the first selector and applies a local earth to hold the selector line relay over 50 its battery-connected winding when the subscribers dial returns to normal and replaces the earth conditions by a loop. A further function of armature M2 is to prevent the earth which is applied to the A leg during dialling from shunting the ii earthed winding of the selector line relay and causing this relay to be so sluggish as to fail to respond to the impulses transmitted by the subscriber. On the operation of relay XY the leads extending to the first selector are reversed at armatures xyl and $112 while armature x144 extends the M lead through to the X subscribers meter. While the dial is returning to normal, earth pulses are transmitted over the B leg and armatures :tyZ and p3 to impulse the selector line relay over one winding. Subsequent digits dialled result in further automatic switches being set up to establish connection with the called subscriber who will then be rung in the usual manner. Upon his reply a metering potential will be applied to the M lead to energise the X meter over armature r114. Relays A and X in the party line relay set may chatter during dialling but relay B will hold operated during each pulse train due to its slug and relays P and XY are already locked up. On the completion of dialling each train when the loop conditions are restored,-relay X will release and in turn release relay XR.

Should the X subscriber desire to make a trunk call, the digits required to route the call 'to a manual board are dialled. Assuming now that the call cannot be completed on demand the operator tells the subscriber to hang up and relays A and B in the party line set release. The operator however maintains the earth on the M lead and relays P and KY accordingly remain operated while armature bl connects the re-ring relay RR to the outgoing negative lead by Way of condenser QB. Hence when the operator operates her ringing key to re-call the X subscriber thereby connecting the earthed ringing generator to the negative lead, relay RR will operate, its operation being rendered steady by the rectifier MRC which is connected in parallel. Armatures M2 and W3 short-circuit condenser QA and relays A and X and the ringing current is thus transmitted over armatures p3 and $112 to the B leg to actuate the bell of the X subscriber only. Armature 113 also removes the short-circuit from the ring-trip relay F which is thus included in series with the line but does not operate on alternating current only. When the X subscriber answers, the high impedance bell B and condenser C will be replaced by a direct current loop and relay F immediately operates over its upper winding in series with the ringing return battery. Thereupon at armature fl it renders its lower winding effective and at armature f2 opens the ringing circuit to the X subscriber. This relay serves toprevent the ringing current passing through the X subscribers transmitter to the A leg and ringing the Y subscribers bell. Relay RR remains operated and maintains relay F energised until the operator restores her ringing key whereupon relays RR and F release. Armature rr3 now transfers the short-circuit from relay A to relay F and relay A re-operates over the X subscribers loop in series with the battery feed relay and also relay X which does not now operate. The energisation of relay A operates relay B which at armature b'l opens the circuit of relay RR. The operator completes the trunk connection and conversation may now proceed.

Considering now the case of a call by the Y subscriber, when he removes his receiver a loop is completed to: operate relay A and the line relay as before. Relay A operates relay B and when the line finder finds the calling line, relay P is operated and dial. tone is returned to the subscriber exactly as in the case of a call by the X subscriber.

The Y subscriber now dials, and loop impulses are transmitted over the A and B wires to actuate the selector impulse relays. Relay X however remains unresponsive and hence relays XR and XY do not operate and the meter lead is connected over the back contact of armature $114 to the Y subscribers meter and thus when the called subscriber answers this meter will be energised.

Under operator re-ring conditions since relay XY is unoperated, the ringing current will be extended over the A leg to ring the Y subscribers bell only, and when he removes his receiver, relay F will trip the ringing as previously described and will be released when the operator restores her ringing key.

It will be appreciated that if while one party is awaiting recall by the operator the other party removes his receiver to initiate a call, this latte-r party will understand from the absence of dial tone that the line is not available for his use. This condition is not greatly different from that which arises if one party attempts to initiate a call while the line is in use by the other party and is not likely to cause difliculty in practice.

At the completion of conversation when the calling Y subscribe-r hangs up the calling loop is disconnected and relay A and the battery feed relay releases. After a short period relay B releases and also earth is removed from the M lead to release relay P whereupon the circuit is ready to deal with another call. When the X subscriber hangs up at the end of a connection, in addition to the relays mentioned above relay XY has also torelease before the party line set is restored to normal. The armatures xyl and $1112 and p3 and p4 which together constitute a means of reversing the A and B legs serve to prevent a loop being momentarily extended forward again and complicating the release of the switch when a calling X subscriber concludes conversation and restores his receive-r as would occur if armatures. of relay XY only were used.

Considering now incoming calls to the party line subscribers, it will be noticed that the positive and negative leads extending from the final selector multiple are reversed as regards the two sets of contacts allotted to the subscribers in this multiple. Ringing current is applied from the final selector over the negative lead and it will therefore be seen that when the X subscribers number is dialled ringing current will be connected to the B leg and when the Y subscribers number is dialled ringing current will be connected to the A leg.

The rectifiers MIRA and MRB serve to prevent the re-operation of relay X should an X subscriber accidentally actuate his dial after a connection has been completed. When the called subscriber answers, the battery feed from the final switch in the train is reversed as is well known, and will therefore connect the earthed winding of the battery feed relay to the negative lead and the battery-connected winding of this relay to the positive lead. Should the calling dial be moved off normal for any reason, earth will be extended over the A and. B wires and over armatures :vyl and p4, lower winding of relay X, positive'lead, to the battery-connected winding of the feed relay. Any tendency for relay X to operate is prevented by rectifier MRB which is now in a conductive direction and effectively short-circuits thelower winding of relay 1 X while the upper winding of relay X is shortcircuited by the rectifier MRA. It is important that relay X should not operate since the resultant operation of relay XR would open the holding circuit for the battery feed relay in the final switch at armature m2 and the connection would be broken down.

In order to minimise transmission loss by transformer action of the winding of X during speech, nickel iron sleeves are fitted on relay A to increase its impedance.

I claim:

1. In a telephone system, a two-party line, an outgoing circuit for said line for setting up outgoing calls from both parties on said line, a relay group in said outgoing circuit operated in accordance with the party making an outgoing call, and means in said relay group responsive to signalling current connected to said outgoing circuit for signalling either party dependent upon the operated condition of said relay group.

2. In a telephone system, a two-party line, an outgoing circuit for said line for setting up outgoing calls from both parties on said line, a relay group in said outgoing circuit operated in accordance with the party making an outgoing call, an operators poistion connected with in response to said outgoing call, and means in said relay group responsive to a re-ringing operation performed by the operator after the calling party has replaced his receiver for signalling only the original calling party.

3. In a telephone system as claimed in claim 1 wherein said party line comprises only two conductors and said signalling current is connected to either one of said conductors dependent upon the operated condition of said relay group.

4. In a telephone system wherein battery feed is reversed to the calling line on the reply of the called party in an established telephone connection, a calling line, a discriminating relay having two windings associated with said line, a circuit for operating said relay, a dial on said line efiective to complete said circuit and energize said relay during the establishment of a connection to a called line, and a rectifier connected in shunt of each winding to prevent energization of said relay in case said dial is operated after the battery feed in an established connection has been reversed on the reply of the called party.

5. In a telephone system as claimed in claim 1 including a discriminating relay in said relay group, means for operating said relay only in case a certain one party on said line makes an outgoing call, and means controlled by the operation of said relay for reversing the connections to the line conductors of said party line.

6. A telephone system as claimed in claim 2 including a ring-cut-off relay in said relay group operated in said re-ring operations in response to the calling party replying, and means controlled by said ring-cut-ofi relay for cutting off said ringing current to prevent signalling the other party on said party line.

'7. In a telephone system, an exchange, a party line comprising two conductors terminating in said exchange, a first and a second substation on said line, a dial at each substation, a set of outgoing terminals for said line over which outgoing calls are extended, a relay group'individual to said line connecting said line conductors to said outgoing terminals, a discriminating relay in said relay group only operated in case the dial at a particular one of said substations is operated during an outgoing call, and means in said relay group controlled by the operation of said relay for reversing the connection of said line conductors to said outgoing terminals.

8. In a telephone system, an exchange, a party line comprising two conductors terminating in said exchange, a first and a second substation on said line, a signalling circuit for the first substation including the first line conductor and a signalling circuit for the second substation including the second line conductor, means for operating the ringers at each substation over their respective signalling circuits on incoming calls, and a relay group individual to said line operated in accordance with the particular substation making an outgoing call to prepare a ringing circuit to signal said particular substation over its signalling circuit in case ringing current is connected to said relay group after said calling substation receiver is replaced.

REGINALD TAYLOR.

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