188,689. Baron, H., (Aldendorff, F.). May 17, 1921. Automatic exchange systems.-The bank contacts of a uni-motional switch are divided into groups, a group marking switch first causing the main switch to advance the wipers to the group in which a wanted line terminates, a second marking switch then marking the wanted set of terminals in this group and causing the main switch to advance its wipers to them. The invention is described as applied to a system of 100 subscribers in which a calling subscriber S, Fig. 1, is connected by a quick-acting line finder F and an associated trunk finder TF, to a unimotional connector WS, associated with which is a slow-acting line finder CS, which also sets itself upon the calling line. The tens impulses are repeated by the quick-acting line finder F and operate a group-making switch sg, associated with the connector WS, the contact sets of which are divided into ten groups, each group being provided with a marking contact-strip 65, 66, &c., the first strip 65 being connected to the second contact 61 of the switch sg, the second strip 66 to the third contact 62, and so on. Thus, if three tens impulses are sent, potential is applied by the arcuate wiper 60 to the contacts 61, 62 and strips 65, 66 and the driving magnet 68, which is energized over the wiper 69. advances the wipers 70 - - 73 to the first set of contacts in the third group. The units impulses are then sent and repeated by the line-finder F to an associated units marking switch S', the contacts of which are multipled in the tens groups of the connectors WS. The wanted set of contacts in the third group is thereby marked and the connector wipers are further advanced until this set is reached. The trunk finder TF then moves to the next idle trunk, and the quick-acting finder F and the units marking switch S' are restored for use in another connection. The group-marking switch sg is also restored to normal. A modification is described in which both group and units marking switches are associated with the trunk finder TF, reverting impulses being used to arrest the wipers of the connector first on a selected group and then on a desired line therein. According to another modification, not described in detail, a units marking switch is allotted to each connector. The first two arrangements are described below in greater detail. First arrangement, Fig. 1. Quick-acting line finder F. Response of line relay 4 on calling subscriber S removing his receiver, energizes the stepping magnets 25 of idle line finders and closes contact 9 to mark the test terminal of the calling line in the line finders selectable. When the wipers of a finder F engage the calling line, relays 6, 24 are energized, the former de-energizing the line relay 4, and the latter opening the circuit of the stepping magnet 25 and extending the calling line to the impulse relay 35, which completes a circuit for a release relay r. The release relay r closes a circuit for the stepping magnet 74 of a switch DS, common to a group of line finders F, which rotates its wipers 76, 77, 78 until the contacts 83, 80, 84 associated with the line-finder F in use, are reached, when a test relay 78 is energized and opens the circuit of the stepping magnet 74. Operation of group-marking switch sg and selection of a tens group in connector WS. The calling subscriber now dials the first digit, thereby de-energizing the impulse relay 35 a corresponding number of times and causing impulses to be transmitted to the stepping magnet of the switch sg over a circuit 22, 39, 55, 46, 58. The arcuate wiper 60 is thus moved round to apply potential to one or more of the strips 65, 66, &c. As soon as potential is applied to the first strip 65 a circuit 60, 61, 65, 69 is completed for the stepping magnet 68 which steps the wipers 69 - - 73 of the connector WS over all the contacts of the first group on to the first set of contacts in the second group. If the first digit is three the magnet 68 continues to be energized over the strip 66 and the wipers are further advanced to the first contact set in the third group, where they stop since the wiper 69 finds no potential on the strip 67. Operation of units marking switch S' and selection of the wanted line by connector WS. On the sending of the first tens impulse the slow-acting relay 55 is energized in series with the magnet 68 and energizes the stepping magnet 121, which moves the switch S' out of its normal position. On the cessation of the tens impulses, when the relay 55 relapses, the impulse circuit is transferred to the stepping magnet 121 over a slow acting relay 123', and when the units impulses are dialled the wiper 125 is advanced to engage a units marking contact, say 126. The relay 123' completes a circuit for a relay 128 which locks up over contact 130 and energizes the stepping magnet 280 of a switch DS', common to a group of marking switches S', which rotates its wipers 151, 270, 131' to engage contacts 150, 283, 132', associated with the switch S' in use, when a test relay 285 is energized and opens the circuit nf the stepping magnet 280. When the relav 123' relapses after the cessation of the units impulses, the stepping magnet 68 of the connector WS is again energized in a circuit 131', 130', 129, 48, 142, and the wipers 69 - - 73 advance until the wiper 70 engages contact 145 marked by the units marking switch S', when a test relay 143 is energized in series with relay 146 (over circuit 131'. 132', 125, 70, 47, 149, 151). Test relay 143 opens the circuit of stepping magnet 68, locks up over contact 152, and prepares a circuit for the busy test relay tr. Relay 146 opens the locking circuit of relay 128, which breaks circuit of relay 285 thereby rendering the switch DS' available for another connection. Engagement of calling line by slow-acting line finder CS. This occurs before the operations described in the previous paragraph, on the energization of the release relay r, which energizes the starting relay 51 in a circuit 40, 43, 45, 52. Relay 51 closes a circuit$6, 88, 91 for the stepping magnet 93, which moves the wipers 92 - - 95 onto the first set of contacts, where the magnet 93 is again energized over strip 94', and continues to advance the wipers until the calling line is engaged. The test relay 92' is then energized in a circuit 78, 82, 44, 98, 95, 100, 29, 76, the magnet 93 is de-energized at contact 91, and line relay 3 is energized over contacts 101, 102 and the subscriber's loop. Relay 82 also responds in series with test relay 92', locks up over contact 37, and opens the circuit of relay 79, thus making the switch DS available for another connection. Busy test, signal and release. If the wanted line is busy the test relay tr does not respond and busy tone from a source 183 is transmitted to the calling subscriber. When the calling party hangs up, the line relay 3 is de-energized and release is effected as described in a later paragraph. Supply of ringing current. If the wanted line is idle the busy test relay tr responds (over contacts 153, 155, wiper 71, test wire as 161, and cut-off relay as 6 of the called subscriber), ringing relay 171 is energized, and ringing current from a generator 291 is intermittently sent to the called subscriber over contacts 174, 175. When the called party answers, a ringing cut-off relay 170 is energized and opens the circuit of the ring- ing relay 171. The talking circuit is now completed over contacts 101, 102, 172, 173, and 180, 178. Restoration of group and units marking switches sg and S'. operation of trunk finder to move to an idle trunk, and release of quick-acting line finder F. On the response of test relay tr the circuit of relays 51, 43 is opened at contact 110, the holding circuit of relay 143 being transferred to the control of relay tr in a circuit 152, 155, 299, 103. The relapse of relay 51 closes a circuit 59, 300', 190, i for the stepping magnet of the group marking switch sg which is restored to normal, the circuit of the magnet 68 being kept open at contacts 299' controlled by relay tr during this operation. The de-energization of the relay 43 completes a restoring circuit i, 41, 200, 191 for the stepping magnet 121 of the units marking switch S', and also energizes a relay 197 which closes a stepping circuit for the driving magnet 194 of the trunk finder TF, the wipers of which are advanced to the next set of contacts. Relav 82 is thereupon de-energized and opens the circuit through the lower winding of relay 197, which, however, is held energized, during the operation of the magnet 194, by a current impulse sent over contacts 195, 196 through its upper winding. Tf the next trunk is engaged, the relay 197 is still held energized when this impulse ceases, by a current over the wiper 49 and its upper winding from a contact such as 280 or 185 of an engaged line finder CS or connector WS, or a contact 192 of another trunk finder TF. The stepping magnet 194 thus continues to receive impulses over the contact 193 until an idle trunk is engaged, when the relay 197 de-energizes and breaks the circuit of the stepping magnet 194. On the first energization of relay 197, release relay r responds, and a circuit 34, 20 is completed for a relay 30, which de-energizes relay 24, thereby disconnecting the subscriber's line at 17, 18 and reconnecting the stepping magnet 25. Release. On the calling subscriber hanging up, the relapse, of line relay 3 causes the de-energization of relays tr, 6, 92', 143. Relay tr completes a circuit over contacts 189, 184 for stepping magnet 68, which restores the connector WS to normal, whilst relapse of relay 92' disconnects the calling line at contacts 101, 102 and completes a circuit for stepping magnet 93, which moves its wipers to the normal position in which the circuit of the relay 93 is broken at contact 94'. Should the calling subscriber abandon a call when th