238,851. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Stehlik, R. F.). Aug. 22, 1924, [Convention date]. Addition to 234,059. Automatic exchange systems.-In a system in which two co-ordinate primary call-finders PF, Fig. 1, are set on to a calling line by numerical impulses, each group of 100 lines is provided with a common set of tens and units line relays 231 - - 240, 241 - - 250, Fig. 3, which act as counting relays to determine the number of impulses in each of the series. The circuits are such that, in order to prevent wrong connections due to two or more lines simultaneously calling, only a tens relay operates at first and in operating prevents the continued operation of any other tens relay to the left thereof, after which a transfer relay 253 connects up the units relays in place of the tens relays, the circuits of these also being such that not more than one can remain operated at the same time. The primary finders PF are connected over a distributing frame IDF to the banks of secondary finders SF, Fig. 2, of hunting type. the next idle secondary finder being assigned by an allotter SFA. whilst the primary finders PF are assigned by allotters PFA1, PFA2, Fig. 4, which act in synchronism but are so arranged that only one has its wipers engaging with their bank at the same time. The hunting operation of the secondary finders is controlled by common testing means arranged in the allotter SFA and also by the allotters PFA1, PFA2 which mark the primary finder PF employed in a particular call. After the number of a calling line has been registered upon the common relays, Fig. 3, the control of the release of the connection is removed from the calling subscriber until both primary and secondary finders have completed their operations and the call has been extended to a first group selector S. Special provision is made for releasing the operated apparatus in the case of a prematurely-abandoned call, or if a primary finder is not found by a secondary finder within a given time. A primary finder is marked non-selectable to the allotters PFA1, PFA2 if, even though idle itself, all the secondary finders which have access thereto are busy. Certain features of the system described form the subject-matter of a divided Specification 249,154. Initiation of call; operation of recording relays, Fig. 3. When subscriber A (No. 60 in the bank of finder PF) removes his receiver, the sixth tens relay 236 operates over the circuit 216, 7, A, 8, 206, locks up to conductor 288, thereby breaking the locking circuits of all tens relays to the left, earths conductor 281 at armature 258 to determine the number of tens impulses to be subsequently transmitted, closes an alternative earth connection to the sixth tens conductor 206, and completes a circuit for relay 251 which removes the normal earth connection from the tens conductors 201 - - 210 so that no other tens relay is able to operate. Relay 251 also completes a circuit for relay 253 which transfers the leads 7 &c. from the tens relays to the units relays. The tenth units relay 250 now operates over the circuit 230, 7, A, 8, 206, 259, connects earth to conductor 284 to determine the number of units impulses to be subsequently transmitted, operates relay 252 which disconnects all the units relays from the conductors 221 - - 230, and connects earth to the start conductor 285. Control and operation of primary finder PF. Relay 304, operating over conductor 285, (1) completes a circuit 317, 348, 46 for relay 23 which connects the allotted finder PF to the common controlling leads 41 - - 45, (2) connects the earthed conductor 281 to the upper winding of two-step relay 301 which operates only its armature 312 to prepare a locking circuit, and (3) connects conductor 281 over interrupter 339 to conductor 282. At the first closure of interrupter 339, relay 261 operates partially and at the succeeding opening of the circuit operates fully, connecting conductor 282 both to conductor 283 and to the upper winding of relay 262. At the next closure of the interrupter, therefore, an impulse is sent over conductors 283, 42 to the vertical magnet. 28 of the finder PF and at the end of the impulse, relay 262 operates fully and extends the connection from conductor 282 to the upper winding of the first tens relay 231. Further impulses are then transmitted to the magnet 26 in a similar manner, the tens relays 231 - - 235 acting as counting relays until, after six impulses, the complete operation of relay 235 removes the earth connection from conductor 281 and impulsing ceases. Relay 301 now operates fully and switches over the impulsing circuits from the tens relays to the units relays, so that the earth connection on conductor 284 causes the transmission of further impulses which this time pass from the interrupter 339 over the circuit 286, 287, 41 to the rotary magnet 27. After ten such impulses, relay 249 disconnects earth from conductor 284, impulsing ceases and relay 302 operates fully. Operation of secondary finder SF and allotter SFA, Fig. 2. The operation of starting relay 304 also connects earth to conductor 44 and thence over conductors 52, 58 to relay 148 in the allotter SFA. Relay 148 connects the common test relay 147 over wiper 142 to the test wiper 102 of the allotted finder and also connects the interrupter 150 to the stepping magnet 104 so that finder SF is rotated until the finder PF is reached when test relay 147 operates over the circuit 142, 102, 50, 45 in series with relay 305. Relay 147 connects earth over wiper 143 to switching relay 105 which in operating extends this earth over wiper 144 to relay 149 and stepping magnet 145 of allotter SFA. After an interval, relays 148, 147 release and the de-energization of magnet 145 steps forward wipers 141 - - 144 in search of the next idle finder. The earth connection for holding up relay 105 and for marking the finder SF busy is now supplied by relay 305 over the circuit 320, 325, 45, 50, relay 305 having been slightly slow to energize on account of the shunt resistance 331. Completion of connection to selector S; release of recording relays. When both switches PF, SF have completed their operations, relays 302, 305 complete a circuit 313, 323, 347, 47, 30, for switching relay 21 which switches the calling line through to the selector S at which relays 121, 122 operate and earth the test conductor 113, thus transferring the control of the release of the connection to the calling party. Relays 302, 305 also energize relay 303 which opens the circuit of all the operated relays, Fig. 3, except relays 252, 253. After an interval the relapse of relay 304 disconnects relays 303, 23, and relays 252, 253 de-energize and permit the registration of another calling number. Allotters PFA1, PFA2; maintaining synchronized. Relay 346, energized bv relays 302, 305 completes circuits for stepping magnets 349, 354 so that when relays 302, 305 release, both allotters advance their wipers and the one 347, say, which has its wipers on the bank selects the next idle primary finder. If the next terminal engaged by the wiper 347 is busy, relay 346 operates again over the circuit 355, 350, 372, 318, 347 and locks up over contacts 351, 356. Since the energizing circuit of relay 346 contains normal contacts 355, 350 in series, the relay is unable to energize until both magnets have completed their strokes, whilst the provision of contacts 351, 356 ensures relay 346 remaining energized until both magnets have fully energized. Prematurely-abandoned call. If a subscriber removes his receiver and immediately replaces it so that only a tens relay has time to operate, the permanent holding up of the recording relays is prevented by relays 308, 307 which energize slowly and after an interval remove the earth from the holding wire 288, thus unlocking the operated tens relay. Operation if the primary finder PF is not found by a secondary finder. Relay 251 operated by any tens relay causes the successive operation of relays 308, 307, 306, but the operation of relay 261 at the commencement of impulsing opens the circuit of relay 308 so that relays 308, 307, 306 de-energize slowly in succession. If the finder PF has not been found by a secondary finder by the time that relay 306 de-energizes, circuits are closed at armature 326 for relays 346, 303 which advance the allotters PFA1, PFA2 and disconnect the start relay 304. A new primary finder is then allotted and the number of the calling line set up afresh. All secondary finders busy. If all the secondary finders SF in the group having access to the primary finder PF are busy, relay 110 operating over a chain circuit removes earth from conductor 43 and connects earth to conductor 47, thus marking the finder PF busy to the allotter PFA1. Relay 110 also disconnects battery from magnet 145 to prevent useless hunting of the allotter SFA. All primary finders busy. A relay 371 is normally short-circuited by parallel earth connections to lead 43 in each idle finder PF. If, however, all the primary finders accessible to the allotters PFA1, PFA2 are busy or are associated with busy groups of secondary finders, relay 371 operates and disconnects relay 346 from the test wipers 347, 357 so as to prevent the automatic hunting of the allotters, whilst a circuit over whichever of these wipers is earthed is completed for relay 303 which prevents a call from starting until an idle primary finder is available.