Patent GB-259391-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1925-10-23
Abstract: 259,391. Western Electric Co., Ltd., (Bell Telephone Laboratories, Inc.). Oct. 23, 1925. Automatic exchange systems ; coin-freed Systems.- A group selector having access over some Levels to prepayment lines and over another level or levels to free lines such as to a zero operator has means which, in the event of an attempt to call a prepayment line without the insertion of a coin, prevents the seizure of an outgoing trunk and causes the call to be routed to a special operator. The selector responds to the first digit in the usual manner but its further operation is controlled by a special relay which responds to the insertion of a coin or, in the case of a free call, to the operation of shaft-springs, and removes a normal earth connection from the testwiper, so permitting the usual trunk-hunting operation to take place. If, however, the relay is not operated, the test-wiper remains permanently earthed and the switch rotates to eleventh rotary terminals where further springs are operated which route the call to the special operator. Call to prepayment line. A calling line 1 is connected over a call-finder LF to a first group selector S-I at which relays 24, 25 energize, the latter causing the operation of relays 19, 18. Relay 18 earths conductor 53 through an impedance coil 17 to hold up the finder LF. The first digit is repeated by relay 24 to magnet 27 and at the first step the stepping relay 38 energizes over off-normal contacts 59 and locks up. At the end of the digit the relapse of series relay 26 completes a circuit for rotary magnet 36 in series with relay 37 which connects relay 23 to the upper talking conductor. If a coin has been inserted, relay 23 energizes over the substation earth 58 and removes a normal earth from the test-wiper 22 so that hunting takes place in the usual manner under the interaction of magnet 36 and relay 38. The call is completed in known manner over switches S-2, C and when the called subscriber 2 replies, the reversal of current in the talking leads operates polarized relay 13 which in turn operates relay 12. Relay 12 also reverses the talking leads and operates relay 16. Collection or refund of coin. When the calling subscriber hangs up, the removal of earth from the test conductor releases relay 19 which connects interrupter 9 to relay 11. At the first operation of relay 11, coin-collecting battery over lamp 43 and relay 15 is connected over the calling subscriber's leads to operate magnet 74 to collect the coin thereby opening the earth connection 58. If the coin has been correctly collected, the next operation of relay 11 causes the release of relay 18 since relay 15 is not again operated, and the release of finder LF follows. If the call has been unsuccessful, coinrefunding battery is applied in a similar manner over the back contact of relay 16. Operation if no coin inserted; preventing fraud. If no coin has been inserted, relay 23 remains de-energized and the test-wiper remains permanently earthed so that the switch rotates to eleventh rotary contacts at which springs 49 operate and complete a circuit for relay 73. Relay 45 now operates and switches the calling line through to the special operator's jack 54 and lights lamp 10. Relay 45 also energizes a common relay 47 to prevent the connection of any other calling line to the operator's position. If the calling subscriber, without inserting a coin, attempt to call a prepayment line by directly earthing one of his leads, marginal relay 68 operates in series with relay 23 and connects a fresh earth to wiper 22 so that the call is routed to the special operator as before. Call to zero operator's position. No charge is made for calls to this position which is reached over the tenth level of the selector, relay 23 being operated to permit hunting over a circuit including resistance 72 and tenth-level springs 46.