Patent GB-172277-A (GB)
Abstract: 172,277. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Willis, B. D., and Ray, A. J.). Nov. 29, 1920, [Convention date]. Automatic exchange systems; party-line systems.-To prevent false signalling in a code-signalling arrangement for calling party-line stations, ringing current can only be cut off or the connection released in the intervals between complete code signals. The invention is shown applied to a connector H, Fig. 2, which establishes connection with a wanted line and subsequently effects the operation of the code-selecting switch F, Fig. 3, the wipers 234, 235 of which are adjusted by the last two digits so as to determine the connection of battery to certain contacts of the code switch E, and thereby control the application of the ringing generator G to line. The ringing cut-off relay 125 is adapted to energize only in a direct current circuit completed when the relay 231 is de-energized, which only occurs during code signal intervals. A holding circuit is , completed for the connector H over a grounded conductor 173 by a relay 205 which is only energized, to break this circuit and permit release, during the intervals between code signals. A set of relays I, common to the exchange or the group of connectors, serves to ground intermittently the lead 213 leading to the ringing relay 217 and the code switch stepping magnet 214. Operation of connector H to select wanted line. The vertical and rotary magnets 102, 110 are operated in known manner under control of the line relay 100, release relay 101, and series relay 103 to select the wanted line. If this is idle, the busy relay 118 is not energized, and relay 114, which was energized in parallel with the rotary magnet 110, completes a circuit over the upper winding of the relay 117 and the switching relay 160 of the called line switch C<1>. Relav 160 removes the line relay bridge at the line switch C<1>, whilst the relay 117 locks up over its lowerwinding and extends the impulse circuit over the conductor 176 to the code-selecting switch F. Operation of code-selecting switch F. The next series of impulses, representing the first of the two code-selecting digits, is repeated by the linerelay 100 over contacts 120, 122, 104, 105, 124, 111, 113, wire 176, contacts 211, 209, relay 202 to the vertical magnet 201, which raises the wipers 234, 235 to the desired level. When these impulses cease, relay 202 de-energizes, so that the final set of impulses passes from the conductor 176 over contact 211, 210, 238, relay 204, to the rotary magnet 203, which rotates the wipers 234, 235 to the contacts leading to the desired pair of terminals in the code switch E. Relay 204 energizes a relay 205 which locks up over wire 173 and by earthing the conductor 239 starts the interrupter I, which consists of a set of relays arranged to interrupt one another's circuit so asto intermittently ground the conductors 213, 212 &c. Assuming the code number called to be 22, the wipers 234, 235 are connected over the contacts 245, 246 to the 3rd, 6th, 15th, and 18th contacts in the path of arm 236, which, with arm 237, is rotated by stepping magnet 214. At the end of the last set of impulses, relay 204 closes a circuit from the grounded wire 213 for the magnet 214, which moves the arms 236, 237, on to their first set of terminals, thereby closing a circuit for relay 231 (over grounded terminal 228<1>, arms 237, 236 and contact 227), which connects up the ringing relay 217, so that succeeding impulses over the wire 213 energize the magnet 214 and the relay 217 in parallel. Ringing current is thus connected to the called line at each impulse over wire 213, until the arm 236 reaches the first contact, the 3rd, connected to wiper 234, when the relay 232 is energized to disconnect the ringing relay. On reaching the next contact, ringing is resumed at each impulse until the arm 236 reaches the contact (the 6th) connected to wiper 235, whereupon the relay 231 is short-circuited, and disconnects the ringing relay 217. The relay 231 remains de-energized until the arm 236 reaches the starting-contact in the second half of its travel, when the same cycle of operations is repeated. Preventing false calls. Subscribers on a party line are instructed to wait for the completion of a ringing code signal before removing their receiver. If, however, a subscriber answers during the transmission of a code-signal, the ring-cutoff relay 125 does not respond until a direct current circuit is completed for it (over resistance R<1>, contact 233 and wire 175), which only occurs during signal intervals when the relay 231 deenergizes. To prevent a false signal if the wanted party does not answer and the calling subscriber hangs up while a code signal is being transmitted, the connector H and the switch F are so arranged that they can only release during signal intervals, since at other times a holding circuit is completed for the relays 205, 117, 125 over the arm 237 and conductor 206. When the arms of the switch E, however. reach the 12th or 25th terminals, the relay 205 is de-energized, and the switches H and F release in the usual manner.