US2142661A - Telephone system - Google Patents

Description

Jan, 3, 1939.

R, TAYLOR lEVAL 2,142,661

TELEPHONE SYSTEM Filed March 7, 1935 1o' sheets-sheet 1 INVENTOR REG l NALD TA LOR ATTY:

GEORGE THOMAS ,BAKER Jan. 3, 1939. R. TAYLOR ET AL 2,142,661 1 TELEPHONE SYSTEM l Filed March 7, 1955 l0 Sheets-Sheet 2 i-Nvl-:NroRs REmNALD TAYLOR ATTYI Jan. 3, 1939. R, TAYLOR ET AL 2,142,661

' TELEPHONE SYSTEM FiledTMaroh 7, '1935 losheets-sheet 5 4INVEN'IRS REGI NALD TAYLO y GEORGE THOMAS BAKy R ATTY:`

Jan. 3, 1939. R, TAYLOR ET AL 2,142,661

' TELEPHONE SYSTEM Filed March 7, 1935 l0 Sheets-Sheetl 4 Z6 INVENTORS REGINALD TAYLOR.

GRGE THOMAS BAKER Jan- 3, 1939- l R, TAYLOR Er AL 2,142,661

TELEPHONE SYSTEM Filed March 7, 1955 lO Sheets-Sheet 5 TI l INVENTURS REGlNALD TAYLOR GEORGE THOMAS BAKER ATTY.'

Jan. 3, 1939. R. TAYLOR Er AL 2,142,661

TELEPHONE SYSTEM FiledMarGh 7, 1955 .O Sheets-Sheet 6 INVENToRs REGmALD TAYLOR GEORGE THOMAS BAKER ATTY.'

3, 1939. R. TAYLoR'x-:r AL E l 2,142,661

TELEPHONE SYSTEM Filed March 7, 1935 10 Sheets-Sheet '7 l N5 Ta :I: U N- "'f cal@ VENTORS REGIINALD 4TAYLOR GEORGE THOMAS BAKER ATTY.'

Jan. 3, 1939.

R. TAYLOR m- AL TELEPHONE SYSTEM Fi1ed Ma'rch 7, 1935 lO Sheets-Sheet 8 INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER Jan. -3, 1939. R. TAYLOR n AL I 2,142,663

. TELEPHON SYSTEM Filed Maron 7, 1935 1o sheets-sheet@ INVENTORS v REGINALD TAYLOR SEORGE THOMAS BAKER jam. 3, 1939. v v R TAYLORET AL l 2fl42661 TELPONE' SYSTEM Filed March 7; 19:55' 1o sheets-sheet 1o INVENToRs REGINA@ TAYLOR GEORGE THOMAS BAKER Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE Thomas Baker,

Glamorganshire, Wales, as-

signors to Associated Telephone and Telegraph Company, Chicago, aware Application March. 7,

Ill., a corporation of Del- 1935, Serial No. 9,716

In Great Britain March 15, 1934 9 Claims.

.The present invention relates to telephone systems and has as its object the provision of a new and improved automatic or semi-automatic telephone system which will be reliable in operation 5 and will present advantages as regards initial cost and/or cost of maintenance over existing systems.

According to one feature of the invention, a telephone system is arranged so that connections V0 are extended over two-directional switches which are arranged to operate with interrupter drive. By this means the number of relays required is reduced and the speed of operation of the switches is considerably increased.

According to another feature of the invention, a final selector switch is arranged so that number unobtainable tone is connected up in the switch circuit instead of being fed back over the switch wipers from the main distributing frame.

According to another feature of the invention, circuit arrangements are provided for a group selector and a final selector so that although battery feed for conversational purposes is fed from the group selector the battery feeding bridge is disconnected during the setting up of the connection and is re-connected when the connection has been completed.

According to a further feature of the invention, a group selector is arranged to feed forward ringing current to the called line and to connect up ringing current immediately when taken into use on one class of call and to connect it up dependent upon a subsequent operation when taken into use on another class of call.

In the new system it is proposed to make use of two-directional switches of the type having a so-called rectangular movement in which no release magnet is provided but the restoration of the switch to normal is effected by stepping the switch wipers forward to the end of the level and then allowing them to complete their restoration by a vertical and rotary movement. A switch of this type is described in United States Patent No. 2,028,689, granted Jan. 21, 1936, to

' R. N. Saxby, The present embodiment of the invention relates to an improved switching layout and switch circuits using the type of switch above referred to, in a satellite exchange. It will be understood, however, that it may be readily adapted for use in other circumstances, such as main exchanges, rural exchanges and networks employing register controllers.

The circuit arrangement of two-directional finder switches having access to subscribers lines L, has been described in United States application Serial No. 754,250, led Nov. 22, 1934, by R. Taylor and G. T. Baker, while further details and modifications of the non-numerical switching apparatus including discriminating arrangements have been described in BritishPatent No. 432,281, accepted July 24, 1935.

A detailed description of 'arrangements embodying the invention will now be given by way ci example with reference to the accompanying drawings comprising Figs. 1 to 10. These drawings show the circuits of the numerical switches employed for completing connections at the satellite exchange and in conjunction with the circuits of said British patent enable the setting n up c-f complete connections at the satellite exchange to be traced together with incoming connections from other exchanges.

Figs. l and 2 show a hundred outlet group selector for use in local connections, which is connected to a group finder GF shown at the lefthand side of the drawings and referred to in more detail in said British patent.

Figs. 3 and 4 show a hundred outlet group selector for use in connections extended from the main exchange and other exchanges which dial directly into the satellite exchange.

Figs. 5 and 6 show a hundred outlet group selector for use in extending trunk calls and calls from the manual board at the main exchange.

Figs. '7 and 8 show a hundred outlet nal selector, whilst Figs. 9 and 10 show a hundred outlet final selector similar to that shown in Figs. l and 8, but provided with P. B. X. facilities for 2 to 10 lines.

All the numerical switches are of the twodirectional type provided with rectangular motion such as that described in said United States Patent No. 2,028,689.

One important feature of the circuits shown in the drawings is that of arranging the group selectors to perform as many functions as possible so that the nal selectors may be made very simple and have only a few relays each. The three types of group selector circuit are also arranged to be fundamentally the same with suiti able modications as required for their different functions; thus, the circuit of Figures 1 and 2 is modiiied to provide for metering which is controlled by relays B and C, the circuit of Figs. 3 and 4 is arranged to transmit back busy flash, whilst the circuit of Figs. 5 and 6 is arranged to give either immediate ringing or operator-controlled ringing according as it is taken into use from the manual board at the main exchange or over trunk switches at the main exchange.

In the case of larger exchanges involving a further rank of switches the battery feed is preferably maintained in the penultimate stage. The group selectors similar to those illustrated could be used as second group selectors and considerably simpler switches would be employed as rst group selectors.

The circuit of Figs. 9 and 10 is arranged so that the switch can hunt over P. B. X. groups of from 2 to 10 lines and in this arrangement the miniature bank arc with screws previously used has been dispensed with, the control of P. B. X. hunting being effected over Wipers P and PI under the control of relay LK.

. Referring now to the detailed circuit operations of Figs. 1 and 2, it will be understood that this switch is intended to function with common discriminating equipment as described in said British patent and accordingly the bracketed conductors shown in the lower part of Fig. l may be assumed to connect with the banks of the hunting switch JB of the said British patent. The group finder switch GF performs a similar function to the group finder switch described in the said British patent in that as soon as the associated group selector switch in question is selected by the discriminating equipment the group nder is set in operation to connect this switch direct to the line nder which has selected the calling subscribers line. The idle condition oi the group selector switch is indicated to the discriminating equipment by the connection of marking battery by way of resistance YC to conductor P and further when the switch is selected the discriminating equipment then extends the calling subscribers line over the negative and positive leads to relay A. Relay A operates and in turn operates relay B (Fig. 2) which at armature bl connects direct earth to conductor P for guarding and holding purposes and also at armature b2 operates relay C. Relay C at armature cI disconnects earth lfrom the common conductor II which extends to the discriminating equipment and also to all other selectors in same group, the arrangement being that absence of earth on this conductor indicates to thediscriminating equipment that all the selectors are busy. The discriminating equipment also extends earth over conductor DM thereupon completing a self-interrupter driving circuit to the magnet of the group iinder GF which rotates its wipers in search of the calling line nder as determined by a battery potential connected to the appropriate contact in the bank GFI by the discriminating equipment.

When the group finder arrives at this contact the battery potential is extended over conductor T to bring about the operation of a fast operating relay in the discriminating equipment which disconnects earth from conductor DM and so holds the wipers of the group iinder on to the selected Contact. The disconnection of earth from the conductor DM also removes a shortcircuit from the switching relay SK which thereupon proceeds to operate over a circuit which may be traced as follows: earth, at armature bi, winding of SK, armature ski, conductor SW, discriminating equipment, conductor DM to battery in series with the driving magnet GPM. The magnet GPM is not operated in this circuit owing to the comparatively high resistance of relay SK which locks by way of its armature SICI; at armatures slc3, Skil and S765 extends the negative, positive and meter leads over the wipers of the group finder direct to the line nder, and at armature nating equipment. It is therefore unnecessary to wait for the group nder to iinish hunting and accordingly the switching operation of relay SK may take place independently of the operation of the group selector, possibly while impulsing is in progress. Relay A at its armature aI (Fig. 2) repeats the impulses to the vertical magnet VM of the group selector in a circuit which includes the low resistance left-hand winding of relay C and accordingly the shaft and wipers are raised to the desired level in the usual manner. As soon as the shaft moves from its normal position, offnormal springs NI-NBare operated. Springs NI open the initial energizing circuit of relay C but it will be appreciated that this relay remains held during the impulsing period owing to the intermittent energization of its low resistance winding in series with the vertical magnet and also by reason of the copper slug which delays its release. Relay B which is also intermittently energized during the impulsing period remains held continuously by reason of its copper slug. I

At the end of impulse series, relay A holds operated and after a short period relay C releases thereby completing the following circuit for the self-interruption of the rotary magnet RM: earth at armature Zkl (Fig. 2), armatures b5, f6, c3, interrupter springs rm, off-normal springs N2, winding of the rotary magnet RM to battery. 'I'he wipers are therefore automatically rotated over the level selected in search of a free outlet which is marked by low resistance battery connected to the bank contacts associated with test Wiper P. As soon as the wipers move from their normal rotary position, normal rotary springs NRI to NR3 are operated but their operation is without immediate eiect. If the rst outlet of the level selected is busy or disconnected the test wiper P will encounter earth or a disconnection so that the test relay LK is unable to operate and accordingly automatic rotation continues. When a free outlet is found the test wiper P encounters idle marking battery, and relay LK then operates over both its windings in series to earth by way of the resistance Il! in parallel with the winding of relay H. Relay LK opens the circuit to the rotary magnet at the break contact of its armature ZlcI, while at the make contact of this armature a circuit is completed for its right-hand holding winding which is suiiiciently low in resistance to mark the selected outlet as busy in the bank multiple. The operation of armature UCI 4also removes a short-circuit from the switching relay I-I which thereupon proceeds to operate in series with the left-hand winding of relay LK shunted by the resistance I0 to battery in series with the rotary magnet RM. It will be understood that the resistance IU is of low value as compared with relay I-I. Owing to the reversal of current ilow in the left-hand winding of relay LK the two windings of this relay are now in opposition so that the left-hand winding partly neutralizes the flux produced by the right-hand winding although the resultant linx is, under `the conditions described, su'icient to hold the relay operated.

In the event of two selector switches encountering the same outlet simultaneously, both re- 75 lays LK in the respective selectors will operate although one may operate somewhat before the other due to slight differences which are always present, even between similar relays. Consequently, with two selectors testing on to the marking battery of the same outlet the current in the holding winding of each LK relay will be approximately half the normal holding current and itis arranged that under these conditions the opposing right-hand winding almost completely neutralizes the effect ofthe left-hand winding and the relays will start to release. Again, due to inherent differences in the relays, one will start to release first and immediately it opens its make contacts it will restore almost full holding current to the other relay which then alone remains operated. n

If it is assumed that no other selector is testing on to the same Contact at this instant, relay LK will hold in spite of the opposition of its lefthand winding and relay H also operates. Relay H locks by way of its armature hl to battery by way of the resistance YB, at armatures h2 and h3 extends the negative and positive lines direct over the wipers of the selector to the outlet selected which may extend to a final selector, for example, that shown in Figs. 7 and 8, at armature h4 completes a holding circuit for relay B since relay A will now commence to release, and at armature h5 re-operates relay C which thereupon locks over its right-hand winding by way of its armature cl, the normal rotary springs N Ri which have operated meanwhile and armatures di and b2.

impulses corresponding to further digits dialled are now extended direct to the iinal selector taken into use, and serve to set the wipers into engagement with the desired Subscribers line.

If the subscriber is free battery is extended back by the nal selector over the SW bank and wiper to operate relay SD in the group selector (Fig. 2) which thereupon locks over armature sd I, and at armature 8d2 connects direct earth to the P wiper and bank contact for busying purposes, at the same time short-circuiting the holding winding of relay LK. Relay LK therefore releases and at armature llcl shunts relay H which also releases thereby at armatures h2 and h3 transferring negative and positive lines back -to relay A which immediately re-operates. Relay H also at armature h1 completes a circuitv prepared by relay SD at armature sdd for the extension of ringing current via the upper winding of relay F to ring the bell of the called subscribers instrument, the return circuit being made by way of armatures sd5 and f3 and resistance YA. During the ringing period a ringing tone is provided for the calling subscriber to assure him that the called subscriber is being signalled, and this is derived as a tapping from the main ringing circuit by way of the low capacity condenser I2 over armatures sd, c6, f4, condenser QB and armature h3 to the positive line.

When the called subscriber replies by removing his receiver from the switchhook, a direct current circuit is provided for relay F which operates from the battery superimposed on the ringing current, and at armature fl removes the short-circuit from its lower winding over which the relay locks for the remainder of the connection. Relay F at armatures f2, f3 and f4 opens the ringing and tone circuits and completes a circuit for operating relay D in yseries `with the called subscribers loop. Relay D at armature dl opens the locking circuit for the slow releasing relays C and B. Relay C which is only slightly slow releases iirst, and at armature c3 (Fig. 1) connects battery by way of the rotary magnet RM to the metering lead M to operate the calling subscribers meter if he is an ordinary subscriber. Upon the release of relay B this battery connection is replaced by earth which serves to operate the calling subscribers meter in cases where the call was originated from a coin box or barred trunk service line.

Release is controlled by the calling subscriber and is effected by replacing the receiver on the switchhook whereupon relay A releases owing to the opening of the line circuit and at the resting springs oi its armature di earth is extended by way of the operated springs NR3, test link TI and armature h to short-circuit relay SD. Relay SD thereupon releases and the iinal selector which has been holding in series therewith also releases. Relay SD also at armatures Sdi and sd?, opens the holding circuits of relays SK and F and upon the release of the latter the selfinterrupter driving circuit is again completed at armature fis to the rotary magnet RM from earth derived over the common conductor I3 from common equipment (not shown) arranged to give signal in the case of faulty release. The wipers are rotated forwards clear of the bankl after which they fall by gravity and restore backwards below the bank to their normal position. In this position the off-normal springs release; spring N opens the circuit to the rotary magnet while at springs N3 low resistance battery is again connected to conductor P to mark the selector as free to the discriminating equipment. It will be understood that although the driving action of the rotary magnet persists throughout the full release period the mechanism is arranged so that its action becomes ineffective as soon as the wipers are advanced out of engagement with the bank contacts. Should the calling subscriber hold the connection after the called subscriber has cleared, an alarm is provided in the form of an individual supervisory lamp LP which is lighted in circuit with conductor il extending to other supervisory apparatus (not shown) common to the exchange.

If the required subscribers line is found to be engaged, the iinal selector connects back earth to the contact engaged by wiper P which causes relay LK to release which in turn releases relay H, whereupon busy tone is extended from the busy tone common BT by way of the condenser QC, springs NR2 and armatures SdB and c5 to the positive line to inform the calling subscriber of the busy condition of the desired party. The nal selector is also released owing to the opening of the calling loop at armatures h2 and h3 when relay I-I restores.

If all the outlets in the selected level are engaged the wipers are rotated to the 11th position where wiper P encounters a low resistance battery I4 which is common to a group of switches. Relay LK thereupon operates as in the case of a successful call and in turn permits the operation of relay H. Owing to the operation of cam springs SI in the 11th position relay LK when it operates does not provide a circuit for its low resistance holding winding so that the resistance I4 is not short-circuited, and is therefore available for initiating the switching condition in other group selectors. Relay H in operating closes a circuit at armatures h5 for operating relay C and under these cnditioris relay C at armature c5 releases relay LK which in turn releases relay H to extend busy tone to the calling subscriber over the circuit previously traced. Relay C at armature cl connects earth via springs NRI and operated cam springs S2 to wiper SW for operating an overow' meter (not shown, but assumed to be connected to conductor I6).

It will be appreciated from reference to the said prior British patent that the group selector in addition to its normal function as described is also taken into use under other circumstances, namely, when all the busy and number unobtainable tone relay sets associated with the discriminating equipment are engaged. In this event, the discriminating equipment selects a disengaged group selector in the manner described, but on the operation of relay SK relay D is prematurely operated from an earth connected to the lead SW in the discriminating equipment. Relay D thereupon locks over its left-hand winding by way of armature slcZ, resistance YE, armature d6, springs NR and armature cl; and at armature dl causes busy tone to be extended over the positive lines to the calling subscriber. Further, at armature d5 battery is extended from the resistance YC over the common conductor l 5 to metering equipment adapted to register the overflow condition, and at armature d4 the circuit is opened to the Vertical magnet VM to prevent the switch responding to dialled impulses. Should the switch be held unduly on a busy connection attention is called by the continued glowing of the lamp LP which is lighted over` armatures f1 and cl3.

Referring now to the group selector shown in Figs. 3 and 4, it will be remembered from the introduction that this is arranged to deal with calls incoming from the main exchange and also from dialling-in exchanges.

When the switch is taken into use over the negative and positive conductors, relay A is operated over the calling circuit and in turn operates relay B which at armature bl (Fig. 3) operates relay C and at armature b3 (Fig. 4) lights the individual supervisory lamp LP in circuit with the exchange supervisory apparatus connected to the common conductor 26. The operation of relay C is without function at this stage. Relay A responds to the dialled impulses and at the resting springs of its armaturen! repeats these impulses to the vertical magnet VM in circuit with the low resistance right-hand winding of relay C and accordingly the shaft and wipers are raised to the desired level in the usual manner. The condenser QC and associated resistance are intended to prevent arcing taking place at the contacts of armature al during impulsing. Off-normal springs Nl-N3 are operated as soon as the shaft leaves its normal position, springs Nl open the initial energizing circuit of relay C and springs N3 disconnect the supervisory lamp LP. Relay C remains held during the impulsing period owing to the intermittent energization of its low resistance winding in series with the vertical magnet and also by reason of the copper slug which delays its release. Similarly relay B which is also intermittently energized during impulsing remains heli continuously by reason of its copper slug. At the end of the vertical impulse period relay A holds operated and after a short interval relay C releases thereby completing a self-interrupter circuit for the rotary magnet RM. Earth for this circuit is derived from the resting armature Zlcl of the test relay LK and self-interruption is controlled` by the springs rml mechanically associated with the rotary magnet. The wipers of the switch are therefore automatically rotated over the selected level in search of a free outlet which is marked by low resistance battery connected to the bank contacts associated with the test wiper P'. The condenser QC and associated resistance again prevent arcing, this time at the interrupter springs rml.

Normal rotary springs NRI-NR3 are operated when the wipers move from their normal rotary position; at springs NRI connect earth to the common conductor 2l to start up the ringing machine if it is not already in position, while springs NRZ open the impulsing circuit to the vertical magnet.

If the rst outlet of the selected level is busy or disconnected the test wiper P will encounter earth or a disconnection so that test relay LK is unable to operate and accordingly automatic rotation continues.

When a free outlet is found the test wiper P encounters idle marking battery and relay LK then operates over both its windings in series to earth by way of the resistance 22 in parallel with the winding of relay H. Relay LK opens the circuit to the rotary magnet at the break contacts of its armature llcl, while at the make contacts a circuit is completed ior its` holding winding which is suiiiciently low in resistance to mark the selected outlet as busy in the bank multiple. The operation of armature Zki also removes the shunt from the winding of the switching relay H which then operates in .series with the left-hand winding of relay LK shunted by the resistance 22. It will be understood that relay LK is similar in function to reiay LK described in connection with Figs. l and 2 in that it guards against dual switching of selectors on the same outlet.

If it is assumed that no other selector is testing on to the same contacts at this instant, relay LK will hold in spite of the opposition of its left-hand winding and relay H also operates. Relay ii locks by way of its armature hl, at larmatures h2 and h3 extends the negative and positive leads directly over the wipers of the selector to the outlet selected which may extend to a nal selector for example that shown in Figs. '7 and 8, at armature h4 completes a holding circuit for relay B since relay A will now commence to release, at armature h5 re-operates relay C over its left-hand winding to earth connected over armature bl and normal rotary springs NH3. Relay C thereupon locks by Way of its armature c2 and springs NR3. Impulses corresponding to further digits di-alled are now extended direct to the final selector taken into use and serve to set the wipers of this switch into engagement with the desired subscribers line.

If the subscriber is free, battery is extended back by the nal selector over the bank and wiper SW to operate relay SD which locks over armature cdi, and at armature S612 connects dir-ect earth to the wiper P for busying purposes, at the same time short-circuiting the holding winding cf relay LK. Relay LK therefore releases and at armature Zltl short-circuits relay H which also releases to transfer the negative and positive lines back to relay A which immediately recperates. Relay H also at armature h6 completes a circuit prepared by relay SD at armature 8d3 for the extension of ringing current via the upper winding of relay F to ring the bell of the called subscribers instrument, the return circuit being made by Way of armatures 8d4 and f3 and resistance YA. During the ringing period a ringing tone is provided for the calling subscriber to assure him that the called subscriber is being signalled and this is derived as a tapping from the main ringing circuit by way of the low capacity condenser 23 and armatures sd? and f4.

When the called subscriber replies and removes his receiver from the switchhook a direct current circuit is provided for relay F which operates from the battery superimposed on the ringing current and at armature fl removes the shortcircuit from its lower winding over which it locks for the remainder of the connection. Relay F at armature f2, f3 and f4 opens the ringing and tone circuits and completes a circuit for operating relay D in series with the called subscribers instrument. Relay D at armature d! opens the circuit of the supervisory lamp LP and it will be appreciated that this relay could if necessary be arranged to reverse the battery connections of relay A to the calling circuit for metering or supervisory purposes.

Release is controlled by the calling subscriber and is eiected by replacing the receiver on the switchhook whereupon relays A and B release in turn, and at armature b3 relay SD is short-cirv cuited. Relay SD therefore releases, and the `circuit at springs N2.

nal selector which has been holding in series therewith also releases. Relay B at armature hl releases relays Fand C and a self-interrupter driving circuit is then completed to the rotary magnet RM from earth derived over the cornmon conductor 25 extending to common supervisory equipment (not shown). The wipers are rotated forwards clear of the banks after which they fall by gravity and restore backwards below the banks to their normal position where the off-normal springs release and open the homing If the calling subscriber delays to release after the called subscriber has cleared, a supervisory lamp LP is lighted over armatures b3, f1, sd and dl and an alarm is provided after an interval by common equipment connected to conductor 25.

If the required subscriber is engaged when his line is connected with the nal selector connects earth to the bank and wiper P which causes relaylLK to release and in turn releases relay H which at armature h5 provides a circuit for eX- tending from earth over armature hl, springs NRS and armature C2 for operating relay F over its lower winding since relay SD is not operated at this stage. Relay F in operating under these conditions -at armature f5 extends busy flash and tone from the cam assembly BF via the righthand winding of relay A to the positive line to inform the calling subscriber or alternatively the operator of the busy condition of the desired party. During the ash period relay A is released but relay B is held over its lower winding from battery supplied trom the cam assembly BH.

If all the outlets in the selected level are engaged the wipers are rotated to the 11th position where wiper P encounters low resistance battery 24 which is common to a group of switches. Re-

lay LK therefore operates as in the case of a successful call and permits the operation of relay H. Owing to the operation of cam springs Si in the 11th position, relay LK when it operates does not provide a circuit for its low resistance holding winding so that the resistance 24 is not short-circuited and is therefore available for initiating the switching condition in other group selectors. Relay l-l re-operates relay C` which locks at armature c2 and at armature c3 releases rel-ay LK. Relay LK in turn causes relay H to release and relay F is now operated over its lower winding to extend busy flash and tone to the calling party in the manner described with reference to Figs. 1 and 2. Relay C at armature 04 in conjunction with the operated cam springs S2 connects earth to wiper SW for operating an overflow meter (not shown but assumed to be connected to conductor 2B).`

Referring now to the group selector shown in Figs. 5 and 6, it will be remembered that this is arranged to deal with trunk calls and calls from the manual board at the main exchange, discrimination being effected by means of sign-als extended from the distant exchange in accordance with the route over which the selector is taken into use. v

When the selector is taken into use for a trunk call, earth is connected to the positive line and operates relays A and OC in series over their lower windings. Relay OC, it should be explained, is differentially wound and does not operate when both its windings are energized simultaneously. Relay A operates relay B which in turn at armature bl completes par-allel circuits for operating relays C and TO over their lefthand and upper windings respectively. The latter relay is energized over its upper high resistance winding in circuit with the rotary magnet RM and locks for the remainder of the connection over its lower winding. Relay TO performs no immediate function but relay C in operating at armature 0| lights the supervisory lamp LP in circuit with the exchange supervisory apparatus connected to the common conductor 3U.

Before the receipt of the rst train o-f impulses, earth on the positive line is replaced by a loop so that relays A and OC become energized over both their windings and the latter accordingly releases for the reason explained. When the impulses are received, relay A responds and at the resting springs of its armature al repeats these impulses tothe vertical magnet VM in series with the low resistance right-hand winding of relay C so that the shaft and wipersy are raised to the desired level. Off-normal springs NI and N2 are operated as soon as the shaft leaves its normal position; springs N! opening the initial energizing' circuit to relay C which, however, remains held during the impulsing period and springs N2 prepare a circuit to the rotary magnet RM. At the end of the train of impulses relay A holds operated and after a short interval relay C releases thereby at armature c2 completing a self-interrupter driving circuit for the rotary magnet RM. Earth for this circuit is derived from the resting armature of the test relay LK and the self -interruption is controlled by the interrupter springs rml of the rotary magnet. rIhe wipers of the switch are therefore automatically rotated over the selected level in search of a free outlet which is marked by low resistance battery connected to the bank contacts associated With testy wiper P. Normal rotary springs NRI and NR2 are operated when the wipers take the first rotary step thereby at springs NRI disconnecting the impulsing circuit to the vertical magnet.

If the first outlet of the selected level is busy or disconnected, the test wiper P will encounter earth or a disconnection so that test relay LK is unable to operate and accordingly automatic rotation continues.

When a free outlet is found the test wiper P encounters idle marking battery and relay LK then. operates over both its windings in series to earth by way of the resistance 3l in parallel with the winding of relay H. Relay LK opens the circuit to the rotary magnet at the break contacts of its armature llcl to prevent further rotation, while at the make contacts a circuit' is completed for its holding winding which is suciently low in resistance to mark the selected outlet as busy in the bank multiple. The operation of relay LK also removes the short-circuit from the winding of the switching relay H which then operates in series with the left-hand winding of relay LK shunted by resistance 3|. Relay LK is similar in function to relay LK described with reference to Figs. 1 and 2 and guards against dual switching of selectors on to the same outlet.

It it is assumed that no other selector is testing on to the same contact at this instant, relay LK holds in spite of the opposition of its lefthand winding and relay H also operates. Relay H locks by way of its armature hl, at armatures h2 and h3 extends the negative and positive leads direct over the wipers of the selector to the outlet selected which may extend to a final selector for example that shown in Figs. '7 and 8, at armature h4 completes the holding circuit for relays B since relay A will now commence to release, and at armature h5 completes circuits for operating relays C and F over their left-hand and lower windings respectively. The operation of relay F is without immediate function but relay C immediately locks over armature cl and the normal rotary springs NR2 and at armature c4 connects relay SD to the wiper SW. Impulses corresponding to further digits dialled are no-w extended direct to the final selector taken into use and serve to set the wipers of this switch into engagement with the desired subscribers line.

If the desired subscribers line is free, battery is extended back by the final selector over the bank and wiper SW to operate relay SD which locks over its armature soll, and at armature Sdi? connects direct earth to the P wiper for busying purposes, at the same time short-circuiting the holding winding of relay LK. Relay LK therefore releases and at armature Zkl short-circuits relay H which also releases to transfer the negative and positive lines back to relay A which immediately re-operates. Relay H also at armature hl operates relay CN which at armature cnl connects an additional earth toits lower terminal, at armatures cu2 and cm3 prepares the ringing circuit and at armature (m4 provides an earth for holding relay A.

Application of ringing current to the selected subscribers line is controlled by the operator and is eifected by the operation of the ringing key in her cord circuit which unbalances the negative and positive lines for example by connecting an earth to one of the conductors. The differential relay OC therefore again operates and under these circumstances at armature oc2 completes a shortcircuit over armature to3, to2 and sdS tothe lower winding of relay F which releases to complete the ringing circuit to the called subscriber from its upper winding over armatures f2 and cu2, at the same time at its resting armature fl maintaining a short-circuit to its lower winding over armatures SdB, fl, cnl and to3 after the release of relay OC when the ringing key is restored. Ringing current is no-w extended via the upper winding of relay F to ring the bell of the called subscribers instrument the return circuit being made by way of armatures C123 and f3 and resistance YA. During the ringing period ringing tone is provided for the operator to assure her that the called subscriber is being signalled, and this is derived as a tapping from the main ringing circuit by way of the low capacity condenser 32. When the called subscriber replies, relays F and D are operated in a similar manner to that described with reference to Figs. 3 and 4. Relay D at armatures dl and d2 reverses the battery and earth connections to the calling circuit, thereby causing a signal to be given to the operator that the called subscriber has replied.

Release is controlled by the operator who receives a clearing signal when the called subscriber replaces his receiver owing to the release of relay D which restores normal battery and earth connections to the calling circuit. The operator then releases the connection and owing to the opening of the line circuit, relay A releases and in turn opens the circuit to relay B. Relay B releases after its slow period and at armatures bl and b4 opens the circuits of relays TO, C, CN and F, and at armature bl extends earth to short-circuit relay SD. Relay SD therefore releases and the nal selector which has been holding in series therewith also releases. A selfinterrupter driving circuit is now completed to the rotary magnet RM from earth on the common conductor 33 extending to supervisory equipment (not shown). 'Ihe wipers are therefore rotated forwards clear of the banks after which they fall by gravity and restore backwards below the bank to their normal position where the offnormal springs release and open the homing circuit at springs N2.

If the required subscriber is engaged when his line is connected with, the final selector connects earth back over the bank and wiper P which causes relays LK and H to release in turn. Since relay CN is normal at this time, busy ash and tone from the cam assembly BT is extended through the upper winding of relay A to the negative line to inform the operator that the desired party is busy. During the flash period relay A is released but relay B is held over its upper winding to holding battery supplied from the cam assembly. Simultaneously with the release of relay H to extend the busy signal, earth is connected to wiper SW to bring about the operation of the switching relay in the nal selector preparatory to trunk offering; the circuit for this may be traced as follows: earth at the resting armature 8d2, armatures h6, to5, c4, wiper and bank SW.

The operator on receiving the busy signal proceeds to offer the call and to do this she first operates the trunk oifering key in her cord circuit which has the effect of unbalancing the line circuit and results in the operation of the differential relay OC. Since relay SD is normal the operation of relay OC under this condition completes a circuit for operating relay CN over armatures S125, to2, co2, springs NR2 and armatures cl and b4. Relay CN locks over armatures cnl, at armature ont disconnects the busy flash signal from the line, and at armatures cu2 and cn3 extends the operators speaking circuit by way of the final selector to the busy connection to enable her to offer the call to the wanted subscriber. Relay CN also at armature cn Operates relay D over both its windings in series for supervisory purposes, and at armature cit-5 connects the upper winding of relay SD in circuit with the test wiper P.

If the offered call is accepted the operator then requests both subscribers in the existing connection to hang up their receivers and when this is done the busy earth on Wiper P is replaced by battery fed through the desired subscribers cut-ofi relay so that relay SD immediately operates. Relay SD at armature sd2 connects direct earth to the P conductor to guard the connection and at the same time removes the shortfcircuit from its lower winding so that it then holds in series with switching relay H in the iinal selector. Further, at armature sda relay D is released thus restoring to normal the battery and earth connections to the calling circuit which influences supervisory apparatus in the operators cord circuit to inform her that the connection is now released. The operator now recalls the wanted subscriber by operating the ringing key in her cord circuit which again operates relay OC and as relay SD is now operated the lower winding oi relay F becomes shortcircuited over armatures sd, to2, 002 and i203. Relay F releases and connects ringing current to the line at armatures f2 and f3. From this point the circuit operations proceed as described previously with the exception that when the called subscriber replies, the operator then extends the connection to the subscriber who has originated the trunk call.

If all the outlets in the selected level are engaged the wipers are rotated to the 11th position where wiper P encounters low resistance battery 34 which is common to a group of switches. Relay LK therefore operates as in the case of a successful call and permits the operation of relay H. Owing to the operation of the cam springs SI in the 11th position, relay LK when it operates does not provide a holding circuit for its low resistance rightfhand winding so that resistance 34 is not shunted by a low-resistance and is therefore available for initiating similar switching operations in other group selectors. Relay H re-operates relays F and C as before and the latter locks and at armature c3 releases relay LK. Relay LK in turn releases relay H and toneless ash from the cam assembly BF is now extended by way of the upper winding of relay A to the negative line to inform the operator that the desired connection is unavailable owing to the all-outlets-busy condition of the group selector. Relay .C at armature c4 in conjunction with the operated cam springs S2 connects earth to wiper SW for operating an overflow meter (not shown but assumed to be connected to conductor 35).

0n calls incoming from the manual board there is no provision for unbalancing the line circuit and consequently relays OC and TO remain normal throughout the connection. On a successful connection, ringing current is not withheld but is connected up by the operation of relay CN immediately the required subscribers line is seized. If the required subscribers line is busy, busy flash and tone are connected up and as relay TO is not operated there is no earth connection to the wiper SW, so that the final selector releases. If all the outlets are engaged busy ilash and tone are provided in a similar manner to that already explained.

The outlet nal selector shown in Figs. 7 and 8 is adapted to be'taken into use from one or other of the group selectors described, and its idle condition is indicated by the presence of low resistance battery on the private conductor P derived by way of the resistance YA, off-normal springs N3 and armature h6.

When the switch is seized, relay A is operated over the negative and positive conductors from the calling circuit and in turn operates relay B which at armature 176 operates relay C, and at armature bl provides an alternative circuit for the marking battery to the P conductor. Relay A responds to the dialled impulses and at the resting springs of its armature al repeats these impulses to the vertical magnet VM in series with the low resistance lower winding of relay C over armatures b4 and el and normal rotary springs NR4, the shaft and wipers are accordingly raised to the desired level. The condenser QA and associated resistance are provided to prevent arcing at the contacts of relay A. Off-normal springs Ml--N3 are operated as soon as the shaft leaves its normal position; springs NI open the initial energizing circuit to relay C which, however, remains held during impulsing owing to the intermittent energization of its low resistance winding and by reason of the copper slug which delays its release. Similarly, relay B which is intermittently energized during impulsing remains held continuously by reason of its copper slug.

At the end of the impulse period relay A holds operated and after a short period relay C releases and at armature cl completes a circuit via armature b-S and springs NRZ and N! for operating relay E. Relay l at armature el transfers the impulsinlg circuit to the rotary magnet RM and at armature e5 re-operates relay C which thereupon at armature cl transfers the holding circuit for reiay E to the control of its own armature e3.

Upon the receipt of the next series of impulses corresponding to the final digit, relay A again responds and repeats these impulses to the rotary magnet RM in series with the low resist-v ance lower winding of relay C so that the wipers are rotated into engagement with the desired subscribers line. The condenser QA and associa-ted resistance again prevent arcing at armature al. Normal rotary springs NRl-NR4 are operated when the wipers move from their normal rotary position; springs NRI transfer the holding circuit of relay B to the control of its own armature b2, springs NRZ open the initial energizing circuit to. relay C and springs NR4 disconnect the vertical magnet VM. Relays B and C again hold during impulsing.

At the conclusion of rotary stepping, relay A is again held operated and upon the release of relay C and during the slow release period of relay E the following test circuit Ais completed to the switching relay H: earth at armature e3, upper winding of relay H, armature c2, test wiper P and bank contact.

lf the desired subscribers line is free, the test wiper P will encounter battery by way of the cutoff relay in the associated line circuit so that relay l-I operates in series therewith and at armature lei completes a locking circuit for itself from battery by way of the vertical magnet VM to earth fed over the SW lead in series with relay SD in the preceding selector. As already explained, this circuit provides thenecessary signal to the preceding selector to initiate the ringing condition. Relay H moreover at armatures h3, h5 and he prepares for the extension of the negative, positive and P wires to the desired subscribers line circuit and upon the release of relay E the cut-ofi relay is then held over the P wire to earth fed from the preceding group selector. Relay C is re-operated over armature e5 in its resting position but its operation is without eiect in these circumstances. Relays A and B are released by the operation of relay H to complete the circuit for the application of ringing current to the desired subscribers line under the control of the group selector in the manner previously explained.

If the desired subscriber is engaged when his line is connected with, the test wiper P will encounter earth in place of battery and consequently relay H does not operate. When relay E releases after its slow release period it extends earth at armature e3 over springs NR3 and armature h6 to the P conductor to short-circuit the holding relay in the preceding group selector. Busy tone is then provided from the preceding group selector and at the same time the loop circuit to the nal selector is opened.

` If, however, the call has ben extended by a trunk operator (by a group selector as shown in Figs. 5 and 6, with relay TO operated) the nal selector isnot released on busy but is caused to switch through to provide a trunk offering circuit. This is effected as follows: when relay E releases, relay C re-operates and remains operated until relays A and B restore When the calling circuit is disconnected at the group selector. During the slow release period of relay C a circuit is completed to relay H as follows: battery through the rotary magnet RM, armatures h2, e2, b5, springs rml and N2, armature c5, lower winding of relay H to earth on the SW lead from the group selector. Relay H locks over its light armature hl to battery via the vertical magnet VM as for an ordinary call and completes the transmission circuit to the busy connection. The trunk call is then offered to the desired subscriber and the circuit operations which ensue are as described for Figs. 5 and 6.

On a completed call, release of the connection is under control of the calling subscriber and is effected by replacing the receiver on the switchhook. This brings about the release of the preceding group selectos!` which in turn disconnects earth from the lead SW to release the switching relay H in the nal selector. A self-interrupter driving circuit is now completed for the rotary magnet RM over armatures h2, e2, h5, springs rml and N2, armature c5, test link T4 to earth derived over the common conductor from common supervisory equipment (not shown). The wipers are therefore rotated forwards clear of the bank after which they fall by gravity and restore to normal backwards below the banks to their normal position where the off-normal springs restore and at springs N2 open the homing circuit. Resistance battery by way of the resistance YA is again connected to the P conductor at the resting oir-normal springs N3 to indicate that the switch is again free.

On an incompleted call, that is, when the desired subscriber is engaged and is not being called by a trunk operator the release of relay A from the preceding selector causes relays B and C to release in turn and when all these relays are normal the homing circuit is completed to the rotary magnet.

Private conductors of spare or unallotted lines are connected to a low resistance switching battery while the positive lines are connected direct to earth. Consequently if the wipers of the final selector are set into engagement with one of these lines, relay VH operates as for a successful call and the subscriber disengaged signal is provided on the SW lead to the preceding selector which prepares for the connection of ringing current. Meanwhile relay E of the nal selector releases after a short interval, relays A and B release following the operation of relay H, and during the slow release period of relay B, relay C re-operates. When relay B releases, the circuit to relay C is again opened and during its slow release period earth on the positive line from the bank contact corresponding to the spare number is extended to the upper winding of relay A which thereupon re-operates. Relay A at armature al now holds relay C over springs NRI and the resting armature b2 and at armature a2 connects number unobtainable tone from conductor NU to the negative line. Battery connected to the transformer winding of the number unobtainable tone generator serves to operate the ringing trip relay F in the group selector and the number unobtainable tone is then extended through to the calling subscriber.

The 100 outlet nal selector shown in Figs. 9 and l0 is similar in operation to that shown in Figs. 7 and 8, but is provided with P. B. X. facilities on 2 to 10 lines, so that in addition to selecting an individual line it is enabled to select an idle one of a group of lines.

Final selections of this type have recently made use of a metal bank arc in which screws are inserted to mark the P. B. X. groups. In the present arrangement the metal bank arc has been dispensed with and the marking of the P. B. X. groups is effected by making suitable connections to contacts in an ordinary bank of contacts engaged by wiper Pl. The iirst line of each P. B. X. group in this bank is connected to earth, intermediate lines are left disconnected, and the last two lines of each P. B. X. group is connected to resistance battery. The contacts corresponding to individual lines are left disconnected.

When the switch is taken into use relay A is operated over the negative and positive conductors from the calling circuit and in turn operates relay B which at armature b operates relay C and at armature bl provides an alternative circuit for the marking battery to the P conductor. Relay A responds to the dialled impulses which are repeated to the vertical magnet VM in series with the low resistance lower winding of relay C over armatures b4 and el and springs NRG and accordingly the shaft and wipers are raised to the desired level. Oil-normal springs Nl-N4 are operated as soon as the shaft leaves its normal position; springs N I open the initial energizing circuit to relay C which, however, remains held during impulsing owing to the intermittent energization of its low resistance winding and by reason of the copper slug which delays its release. Similarly relay B which is intermittently energized during impulsing remains held continuously by reason of its copper slug.

At the end of the impulsing period, relay A holds operated and after a short interval relay C releases, and at armature c! completes a circuit for operating relay E over springs N4, armature cl, springs NRZ and armature h6. Relay E at armature el transfers the impulsing circuit to the rotary magnet RM and at armature e5 re-operates relay C. Relay C thereupon at armature cl completes a holding circuit for relay E in series with relay LK which also operates and at armature llcl completes a holding circuit for its righthand winding in series with the rotary magnet RM over springs N2 and rml and armatures h2 and e2. It will be understood that the resistance YC and YD in series with the right-hand winding of relay LK are of high value so that there is no possibility of the rotary magnet operating in this circuit. Upon the receipt of the next series of impulses corresponding to the final digit, relay A again responds and repeats these impulses to the rotary magnet RM in series with the low resistance lower winding of relay C so that the wipers are rotated into engagement with the desired subscribers line. Normal rotary springs NRI- NRS are operated when the wipers move from their normal rotary position; springs NRI transfer the holding circuit of relay B to the `control of its armature b2, springs NRZ open the initial energizing circuit to relay C and springs NR4 disconnect the vertical magnet. Relays B and C again hold during the impulsing period.

At the conclusion of the rotary stepping, relay A is again held operated and upon the release of relay C and during the slow release period of relay E the following test circuit is completed to the switching relay H: earth at armature e3, left-hand winding of relay LK, upper winding of relay H, armature c2, test wiper P and bank contact. It will be appreciated that upon the release of relay C relay LK holds in series with the rotary magnet.

It will rst be assumed that an individual line has been selected. If the desired subscribers line is free the test wiper P will encounter battery by way of the cut-oir relay in the associated line circuit so that relay H operates in series therewith, and at armature hl completes a locking circuit for itself from battery by way of the vertical magnet VM to earth on the SW lead in series with relay SD in, the preceding selector. As already explained this circuit provides the necessary signal to the preceding selector to initiate the ringing condition. Relay H moreover at armatures h3, h4, h5 and h6 prepares for the extension of the negative, positive and P wires to the desired subscribers line circuit and upon the release of armature e3 the cut-off relay is held over the P wire to earth in the preceding group selector. Relays A and B are released by the operation of relay H to complete the circuit for the application of ringing current to the desired subscribers line from the `group selector in the manner previously explained.

If the desired subscriber is engaged when his line is connected with, test wiper P will encounter earth in place of battery and consequently relay H does not operate. Relay E thereupon releases after its slow release period and at armature e3 extends earth to the P conductor to short-circuit the holding relay in the preceding group selector. In response to this signal, busy tone is provided from the group selector and at the same time the nal selector is released. If however the call has been eX- tended by a trunk operator the nal selector is not released on busy but is caused to switch through to provide a trunk oiering circuit. This is effected by the re-operation of relay C which in connection with Figs. 7 and 8 (as described) causes the switching relay H to operate and lock to provide the offering circuit.

If the call is for a P. B. X. subscriber, the operation is the same as described up to the setting of the wipers into engagement with the line corresponding to the digits dalled which in this case is the rst line of the P. B. X. group.

If this line is free the wiper P encounters battery fed through the cut-off relay so that relay H operates and switches the connection through as already described.

If the line is engaged the wiper P encounters earth so that relay H does not operate, and in addition, since this is the iirst line of the P. B. X. group the wiper PI encounters earth which serves to short-circuit the holding winding of relay LK. Relay LK releases before relay E and at armature Zlcl completes the following self-interrupter driving circuit to the rotary magnet: earth at armature b', springs NR?, low resistance left-hand winding of relay E, armatures Zlcl, e2 and h2, interrupter springs rmi, off-normal springs N2, winding of the rotary magnet RM to battery. The switch therefore commences to hunt for a free line in the group and relay E holds operated.

If an intermediate line or the last line of the group is disengaged the wiper P encounters battery from the cut-off relay and relay LK which is fast operating immediately operates over its left-hand winding and at armature Ik! opens the driving circuit to the rotary magnet and thus prevents further rotation. Relay H also operates over its upper winding in series with relay LK to connect the lines through as already explained.

If all the lines in the group are engaged, the wipers are rotated to the last line where wiper Pi encounters a low resistance battery which serves to operate relay LK over its right-hand winding to open the driving circuit. The hunting operation is thus stopped and when relay E releases, earth is extended to the P conductor over armature e3, springs NRS and armature h5 to set up a busy condition in the preceding group selector, after which the nal selector is released.

It will be appreciated that P. B. X. hunting can only take place if the first line of a P. B. X. group is dialled, since it is dependent upon the wiper PI encountering earth. Consequently, if any line other than the rst is dialled, the call proceeds as for an ordinary line. This facility is made use of for night service under which circumstances an intermediate line is allocated, such for example as the watchmans line and the P. B. X. hunting operation is automatically suspended.

On a completed call, release of the connection is under the control of the calling subscriber and is effected by replacing the receiver on the switchhook. This brings about the release oi the preceding group selector which in turn releases the switching relay H in the final selector. A self-interrupter driving circuit is now completed for the rotary magnet RM from earth over the common conductor SO extending to common supervisory equipment (not shown). The wipers are therefore rotated forward clear of the banks after which they fall by gravity and restore backwards below the banks to their normal position where the off-normal springs release and at springs N2 open the homing circuit. Resistance battery by way of resistance YA is again connected to the P conductor at the resting offnorrnal springs N3 to indicate that the switch is again free.

On an incompleted call, that is, when the desired subscriber is engaged, the release of relay A from the preceding selector causes the release of relays B and C in turn and when all these relays are normal the homing circuit is completed.

Private conductors of spare or unallotted lines are connected to low resistance switching battery, while the positive conductors are connected direct to earth. Consequently if the wipers of the final selector are set into engagement with one of these lines relay H operates as for a successful call and the subscriber disengaged signal is provided on the SW lead to the preceding selector which prepares for the connection of ringing. Meanwhile, relay E in the nal selector releases after a short interval and during the slow release period of relay B relay C re-operates over armature e5, springs NRZ and armature h6. When relay B releases, the circuit to C is again opened and during its slow release period earth on the positive line of the spare number is extended over armatures b3, h5 and c4 to the upper winding of relay A which re-operates. Relay A now at armature al holds relay C over the resting armature b2 and at armature a2 connects number unobtainable tone from conductor NU to the negative line. Battery connected to the transformer winding of the number unobtainable tone generator serves to operate the ringing trip relay F in the group selector and number unobtainable tone is then extended through to the calling subscriber.

The test links designated T throughout the drawings are provided for the purpose of producing busy and holding conditions while the apparatus is under the supervision of the maintenance staff.

We claim:-

1. An automatic selector switch having wipers, a plurality of lines accessible to said wipers, a primary and a secondary magnet for said switch, means for operating the primary magnet to step the wipers in one direction and a self-interrupted circuit for operating the secondary magnet to step the wipers in another direction, said lines divided into groups, a test relay, said test relay operated to stop the operation of the secondary magnet when an idle line is found and when all the lines in a group are busy, and means for again rendering said self-interrupted circuit operative for operating said secondary magnet intermittently when a release is initiated to step the wipers to a position from which they are automatically restored.

2. An automatic switch having wipers, means for moving the wipers in two directions including a primary and a secondary magnet,saidsecondary magnet having a self-interrupted circuit, means for controlling said circuit for operating said secondary magnet to connect with a line and to release the switch, said primary magnet operated by impulses, a quick acting relay energized when an idle line is found to stop the operation of the secondary magnet, and a second relay operated after the quick acting relay to complete a connection over the wipers to the idle line.

3. An automatic switch having wipers, a primary and a secondary magnet for moving the wipers, lines accessible to the wipers, means for operating the primary magnet by impulses to select a group of lines, a change-over relay for switching the circuit to cause operation of the secondary magnet after a first series of impulses, a relay operated when an idle line is found or when all the lines in a group are busy for stopping the operation of the secondary magnet,

means for operating said change-over relay when the last line of a group is busy, and means controlled by said change-over relay to give a busy signal to the calling subscriber.

4. An automatic selector switch having vertical and rotary magnets, lines accessible thereto, means for operating said magnets to select a line, a test relay, a line relay, a slow-acting relay controlled by the line relay, oir-normal contacts operated when the switch is operated, and a circuit for the rotary magnet including, normally closed contacts of the test relay, normally closed contacts of said slow-acting relay, said oi normal contacts, and a pair of contacts opened when the magnet is energized; said magnet operated over said circuit 'to operate and to release the switch.

5. In a telephone system, a group selector, a iinal selector accessible thereto, lines accessible to said inal selector, a relay in the group selector energized when the nal selector finds an idle line to complete a metallic circuit through said group selector, a battery feed bridge in the group selector, means for transmitting a signal from the final selector when a busy line is encountered, said relay deenergized in response to said signal to connect said battery feed bridge to the connection.

6. In an automatic circuit arrangement, a group selector, a final selector accessible thereto,

lines accessible to said final selector, a relay in the group selector operated to maintain a metallic circuit therethrough until the final selector nds a line, a battery feed bridge in the group selector, means for transmitting a-signal from the final selector when said line is encountered, said relay operated responsive to said signal to connect said battery feed bridge to the connection.

7. In an automatic circuit arrangement, groups of extending circuits, a control circuit in each group, an automatic switch associated with the circuits, means for transmitting impulses thereto, wipers therein having a two-directional path for establishing a connection with any one of said circuits, stepping circuits for controlling the wipers including a self-interrupted circuit, said two-directional path of the Wipers comprising movement in one direction controlled by a stepping circuit responsive to said impulses and movement in another direction controlled by the selfinterrupted circuit, means operative at one time responsive to termination of said impulses for rendering said self-interrupted circuit operative and operated at another time responsive to the encountering of an engaged one of said circuits or of a control circuit by said wipers to indicate that .a connection is unobtainable.

8. In an automatic circuit arrangement as claimed in claim 7, means for reoperating said last-named means to cause the wipers to return to normal by another path.

9. In an automatic circuit arrangement as claimed in claim 7, means for reoperating said last-named means to cause the wipers to resume movement in said other direction.

REGINALD TAYLOR. GEORGE THOMAS BAKER.

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